The Nano-Micro Interface: Bridging the Micro and Nano Worlds [1 & 2, 2 ed.] 3527336338, 9783527336333

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Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jorg ¨ Fecht The Nano-Micro Interface Volume 1

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Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jorg ¨ Fecht

The Nano-Micro Interface Bridging the Micro and Nano Worlds

Volume 1

Second Edition

Editors Prof. Marcel Van de Voorde

TU Delft Fac. Techn. Natuurwetenschappen Eeuwige Laan, 33 1861 CL Bergen he Netherlands

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Dr. Matthias Werner

NMTC Soorstr. 86 14050 Berlin Germany Prof. Hans-Jorg ¨ Fecht

University of Ulm Inst. Micro & Nanomaterials Albert-Einstein-Allee 47 89081 Ulm Germany

Library of Congress Card No.: applied for British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library. Bibliographic information published by the Deutsche Nationalbibliothek

he Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at . © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Print ISBN: 978-3-527-33633-3 ePDF ISBN: 978-3-527-67922-5 ePub ISBN: 978-3-527-67921-8 Mobi ISBN: 978-3-527-67920-1 oBook ISBN: 978-3-527-67919-5 Cover Design Adam Design, Weinheim,

Germany Typesetting Laserwords Private Limited,

Chennai, India Printing and Binding Markono Print Media Pte Ltd, Singapore

Printed on acid-free paper

V

Contents

Volume 1 Foreword XV Acknowledgment XVII List of Contributors XIX Introduction XXVII Part I Nanotechnology Research Funding and Commercialization Prospects – Political, Social and Economic Context for the Science and Application of Nanotechnology 1 1

A European Strategy for Micro- and Nanoelectronic Components and Systems 3 Neelie Kroes

1.1 1.2 1.2.1

Introduction 3 Why are Micro- and Nanoelectronics Essential for Europe? 4 An Important Industry with a Significant Potential for Growth and a Massive Economic Footprint 4 A Key Technology for Addressing the Societal Challenges 4 A Changing Industrial Landscape for Microand Nanoelectronics 5 Technology Progress Opens New Opportunities 5 Escalating R&D&I Costs and a More Competitive R&D&I Environment 5 New Business and Production Models 6 Equipment Manufacturers Own Key Elements of the Value Chain 7 Europe’s Strengths and Weaknesses 7 Industry Structured around Centers of Excellence and Wider Supply Chains Covering all Europe 7 Leading in Essential Vertical Markets, Almost Absent in Some Large Segments 8 Undisputed European Leadership in Materials and Equipment 8

1.2.2 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.4 1.4.1 1.4.2 1.4.3

VI

Contents

1.4.4 1.5 1.5.1 1.5.2 1.5.3 1.6 1.6.1 1.6.2 1.6.3 1.7 1.7.1 1.7.2 1.7.3 1.7.4 1.8

Investments of EU Companies Remain Relatively Modest 9 European Efforts So Far 9 Regional and National Efforts Reinforcing the Clusters of Excellence 9 A Growing and More Coordinated Investment in R&D&I at EU Level 9 Technology Breakthroughs but Gaps in the Innovation Chain 10 he Way Forward – A European Industrial Strategy 10 Objective: Reverse the Decline of EU’s Share of World’s Supply 10 Focus on Europe’s Strengths, Build on and Reinforce Europe’s Leading Clusters 11 Seize Opportunities Arising in Non-conventional Fields and Support SMEs Growth 11 he Actions 12 Towards a European Strategic Roadmap for Investment in the Field 12 he Joint Technology Initiative: A Tripartite Model for Large-Scale Projects 13 Building on and Supporting Horizontal Competitiveness Measures 15 International Dimension 15 Conclusions 16 Annex 1.A 16 References 17

2

Governmental Strategy for the Support of Nanotechnology in Germany 19 Gerd Bachmann and Leif Brand

2.1 2.2 2.3 2.4 2.5

Introduction 19 Future Options 20 From Basic Science Funding to the Nanotechnology Action Plan 21 Funding Situation 2011 24 Patent Applications in Nanotechnology: An International Comparison 24 Innovation Accompanying Measures 27 Outreach and Citizen Dialogues 27 Chances – Risks Communication 28 Database for Nanomaterials 28 Education 29 Involved Organizations 30 Cooperation of the Governmental Bodies 31 International Cooperation 32 Research Marketing 33 Activities within the Framework of the European Union 33

2.6 2.6.1 2.6.2 2.6.3 2.6.4 2.7 2.8 2.9 2.9.1 2.9.2

Contents

2.10

Activities within the Framework of the Organization for Economic Cooperation and Development (OECD) 34 References 34

3

Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region 37 Lerwen Liu

3.1 3.2 3.3 3.4 3.5 3.6

Introduction 37 Public Investments 40 Infrastructure 45 R&D and Commercialization 48 Nanosafety, Standardization, and Education Summary 52 Glossary 52 References 53

4

Near-Industrialization Nanotechnologies Developed in JST’s Nanomanufacturing Research Area in Japan 55 Yasuhiro Horiike

4.1 4.2

Introduction 55 Utilization of Ionic Liquids Under Vacuum Conditions for Nanoparticle Production and Electron Microscopic Studies 57 Introduction 57 Production of Metal Nanoparticles by Sputtering Instrument 57 Electron Microscopic Studies of Biopsy Specimens Using IL 58 Conclusion 59 Solution Plasma Process: An Emerging Technology for Nanoparticles Synthesis 60 Solution Plasma Process 60 Synthesis of Carbon Nanoparticles and Its Application in Electrochemistry 61 Conclusion 61 2D Inorganic Nanosheets 62 Background 62 Synthesis of Titanium Oxide Nanosheets 63 Production of TiO2 Particulates in Novel Shapes and heir Commercialization 64 Fabrication of Nanostructured Films and heir Applications 64 Conclusion 65 Ultimate Separation of SWCNT and Its Application to Novel Electonic Devices 66 Research Background 66 Production of 2G-SWCNT and Its Applications 66 Conclusion 69 Development of Liquid Crystalline Organic Semiconductors 69

4.2.1 4.2.2 4.2.3 4.2.4 4.3 4.3.1 4.3.2 4.3.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.5 4.5.1 4.5.2 4.5.3 4.6

51

VII

VIII

Contents

4.6.1 4.6.2 4.6.3 4.7 4.7.1 4.7.2 4.7.3 4.7.4 4.8 4.8.1 4.8.2 4.8.3 4.8.4 4.8.5

Historical Background 69 Research Project 69 Conclusion 72 Polymeric Micelles for Cancer herapy 72 Background and Present Status 72 Polymeric Micelles as Nanocarriers 72 Perspectives to Industrialization 73 Conclusions 74 Nanoparticulate Vaccine Adjuvants and Delivery Systems 75 Introduction 75 he Role of Nanotechnology in Vaccine Developments 75 Biodegradable Nanoparticles as Vaccine Adjuvants and Delivery Systems 76 Clinical Application of Particulate Vaccine Adjuvants 77 Conclusions 77 References 77

5

Quo Vadis Nanotechnology? 79 ́ Witold Łojkowski, Hans-Jörg Fecht, and Anna Swiderska Sroda

5.1 5.2 5.3 5.4 5.5

Introduction 79 What is Nanotechnology? 80 Quo Vadis Nanotechnology – In Academia? 82 Quo Vadis Nanotechnology – In Industry Eyes? 85 Quo Vadis Nanotechnology – In Governments’ and Funding Agencies’ Eyes? 86 Quo Vadis Nanotechnology – In the World of Regulations, Laws and Standards? 87 Quo Vadis Nanotechnology – In Society’s Eyes? 89 Effect of Education on Nanotechnology Development 90 Conclusions 91 Limitations of the Chapter 93 Acknowledgements 93 References 93

5.6 5.7 5.8 5.9 5.10

Part II Development of Micro and Nanotechnologies

95

6

Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces 97 Jared J. Victor, Uwe Erb, and Gino Palumbo

6.1 6.2 6.3 6.4 6.5 6.6

Introduction 97 Superhydrophobic Surfaces in Nature – he Lotus Effect 98 Basic Wetting Properties 99 Advanced Wetting Properties 100 Aspen Leaves as a Biological Blueprint 101 Template Design 103

Contents

6.7 6.8 6.9

Polymer Pressing 107 Process Scalability 109 Conclusions 111 Acknowledgments 112 References 112

7

Multisensor Metrology Bridging the Gap to the Nanometer – New Measurement Requirements and Solutions in Wafer-Based Production 115 Thomas Fries

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11

Unflexible Metrology Solutions are Inefficient 115 he Solution is Named Multisensor Metrology 116 Basic Setup of a Multisensor Metrology Tool 118 Different Measuring Technologies Available 118 Metrology on Wafers has Reached the hird Dimension Roughness Measurement 124 Geometrical Data – TTV, Bow, Warp, and So On 124 Nanotopography 128 TSV Measurement 130 Film hickness and Stack Layer hickness 132 Summary 133 References 134

8

Nanostructural Metallic Materials – Nanoengineering and Nanomanufacturing 135 Michael E. Fitzpatrick, Francisca G. Caballero, and Marcel H. Van de Voorde

8.1 8.2 8.2.1 8.2.2 8.3 8.3.1 8.3.2 8.3.3 8.3.4 8.3.5 8.3.6 8.4 8.4.1 8.4.2 8.4.3 8.4.4 8.5

Introduction 135 Nanometallics and Nanomaterials 136 Nanomaterials Science and Engineering 136 Nanocrystalline and Nanostructured Metals 137 Production and Manufacturing of Nanometallic Materials 139 Processing Routes for Nanometallic Materials 139 Primary Production 140 Secondary Processing 141 Nanoengineering in the Modern Steel Industry 142 Metal Matrix Nanocomposites 145 he Future of Nanometallic Materials 145 Nanomaterials Engineering – Issues and Properties 146 Mechanical Properties of Materials and Assemblies 147 Joining of Nanometallic Materials 147 Characterization of Properties under Operating Conditions 148 Design Principle for Nanotechnology Engineering 149 Analytical Techniques for the Study of Nanoand Micromechanics 149 Neutron and Synchroton X-Ray Techniques 151

8.5.1

123

IX

X

Contents

8.5.2 8.6

In situ and Environmental Testing of Materials and Components 154 Summary and Future Trends 154 Acknowledgments 155 References 156

9

Bulk Metallic Glass in Micro to Nano Length Scale Applications 159 Jan Schroers and Golden Kumar

9.1 9.2 9.2.1 9.3 9.3.1 9.3.2 9.3.3 9.4 9.5 9.6 9.7

Introduction 159 Bulk Metallic Glasses 159 Size-Dependent Properties of a BMG Processing of BMGs 162 Mold Materials 164 Micromolding Process 166 Mold Filling Kinetics 166 Surface Patterning 170 3D Microparts 175 Surface Finish 179 Conclusions and Outlook 181 Acknowledgments 182 References 183

10

From Oxide Particles to Nanoceramics: Processes and Applications 189 Jean-François Hochepied

10.1 10.2

Introduction 189 Solution Chemistry Processes for Oxide Nanoparticles Usable for Nanoceramics 189 Dense Nanoceramics 193 Monophased Nanoceramics 194 Processes 194 Properties 195 Multiphased Oxide Nanoceramics 197 Multiferroic Nanoceramics Composites 197 Porous Ceramics 199 Random Porosity 199 Fuel Cells 199 Ceramic Membranes for Water Treatment 201 Ordered and Hierarchical Porosity 201 Conclusion and Perspectives 202 References 202

10.3 10.3.1 10.3.1.1 10.3.1.2 10.3.2 10.3.2.1 10.4 10.4.1 10.4.1.1 10.4.1.2 10.4.1.3 10.5

160

Contents

Part III Nanoelectronics and System Integration

205

11

Creating Tomorrow’s Applications through Deeper Collaboration between Technology and Design 207 Jan Provoost, Diederik Verkest, and Gilbert Declerck

11.1 11.2 11.3

Introduction 207 A Holistic Approach – Imec’s INSITE Program 208 Bottom-Up – Designing Tomorrow’s Manufacturable Technology 210 Modelling the Cost of Future Technology with and without EUV Lithography 211 Developing PDKs and Test Chips for Advanced Nodes 212 Looking for Optimal SRAM Memory Cells 213 Designing Sophisticated 3D Test Chips 214 Optical Data Paths Between and on Chips 215 New Materials and Transistors for Next-Generation Chips 216 Top-Down – Designing Future Nanoelectronic Applications 217 Designing a New Toolbox for the Life Sciences 218 he Vision 218 A Tool to Detect Circulating Tumor Cells 218 Designing Next-Generation Wireless Radios 219 he Vision 219 SCALDIO: A Highly Reconfigurable Radio Transceiver 220 Designing a Microsized Hyperspectral Camera 221 he Vision 221 he Challenge: A Mass-Produced, Microsized HSI 221 Conclusion 222 References 223

11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.4 11.4.1 11.4.1.1 11.4.1.2 11.4.2 11.4.2.1 11.4.2.2 11.4.3 11.4.3.1 11.4.3.2 11.5

12

Multiwalled Carbon Nanotube Network-Based Sensors and Electronic Devices 225 Wolfgang R. Fahrner, Giovanni Landi, Raffaele Di Giacomo, and Heinz C. Neitzert

12.1 12.2 12.3

Introduction 225 CNN without Matrix 226 Crystalline Silicon/Polymer Heterojunctions with and without CNTs for Applications as Diodes, Solar Cells, and Electrical Memories 230 PEDOT:PSS with and without CNTs on Crystalline Silicon for Photovoltaic Applications 230 PMMA with MWCNTs on c-Si Heterodiodes 233 Polymerized Oxadiazole/Crystalline Silicon Heterojunction as Electrical Memory Element 234 Bio-Nanocomposites with CNTs and Fungal Cells with Sensing Capability 236

12.3.1 12.3.2 12.3.3 12.4

XI

XII

Contents

12.5

Conclusions 238 Acknowledgments References 239

239

13

Thin Film Piezomaterials for Bulk Acoustic Wave Technology 243 Jyrki Molarius, Tommi Riekkinen, Martin Kulawski, and Markku Ylilammi

13.1 13.2 13.3 13.3.1 13.4 13.5 13.6 13.7 13.8

Introduction 243 Zinc Oxide (ZnO) 244 Aluminum Nitride (AIN) 252 Layer Transfer Method 256 Scandium-Alloyed Aluminum Nitride (Sc:AIN) Lead Zirconate Titanate (PZT) 261 Lead-Free Piezoelectric Materials 262 Future Trends and Applications 263 Conclusions 264 Acknowledgments 265 References 265

14

Properties and Applications of Ferroelectrets 271 Xunlin Qiu, Dmitry Rychkov, and Werner Wirges

14.1 14.2

Introduction 271 Preparation of Polymer Foams or Void-Containing Polymer Systems 272 Polymer Foams 272 Void-Containing Polymer Systems 274 Charging Process 276 Dielectric Barrier Discharges in Cavities 276 Polarization versus Electric-Field Hysteresis 277 Piezoelectricity of Ferroelectrets and its Stability 278 Applications 280 Concept for Focusing Ultrasound 281 Ferroelectret Microphone 282 Control Panels and Keyboards 283 Conclusions 284 References 285

14.2.1 14.2.2 14.3 14.3.1 14.3.2 14.4 14.5 14.5.1 14.5.2 14.5.3 14.6

257

Contents

Volume 2 Foreword XVII Acknowledgment XIX List of Contributors XXI Introduction XXIX Part IV

Biomedical Technologies and Nanomedicine 289

15

Translational Medicine: Nanoscience and Nanotechnology to Improve Patient Care 291 Bert Müller, Andreas Zumbuehl, Martin A. Walter, Thomas Pfohl, Philippe C. Cattin, Jörg Huwyler, and Simone E. Hieber

16

Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine 311 Costas Kiparissides and Olga Kammona

17

Biofunctional Surfaces 341 Wolfgang Knoll, Amal Kasry, and Jakub Dostalek

18

Biomimetic Hierarchies in Diamond-Based Architectures Andrei P. Sommer, Matthias Wiora, and Hans-Jörg Fecht

363

Part V Energy and Mobility 381 19

Nanotechnology in Energy Technology 383 Baldev Raj, U. Kamachi Mudali, John Philip, and Sitaram Dash

20

The Impact of Nanoscience in Heterogeneous Catalysis 405 Sharifah Bee Abd Hamid and Robert Schlögl

21

Processing of Nanoporous and Dense Thin Film Ceramic Membranes 431 Tim Van Gestel and Hans Peter Buchkremer

22

Nanotechnology and Nanoelectronics for Automotive Applications 459 Matthias Werner, Vili Igel, and Wolfgang Wondrak Part VI Process Controls and Analytical Techniques 473

23

Characterization of Nanostructured Materials 475 Alison Crossley and Colin Johnston

XIII

XIV

Contents

24

Surface Chemical Analysis of Nanoparticles for Industrial Applications 499 Marie-Isabelle Baraton

25

Nanometer-Scale View of the Electrified Interface: A Scanning Probe Microscopy Study 537 ̈ Peter Muller, Laura Rossi, Santos F. Alvarado Part VII Creative Strategies Connecting Nanomaterials to the Macroscale World 551

26

Nanostructured Cement and Concrete 553 Henning Zoz, Reinhard Trettin, Birgit Funk, and Deniz Yigit

27

Hydrogen and Electromobility Agenda 567 Henning Zoz and Andreas Franz

28

Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials 583 Seok-Woo Lee and Julia R. Greer

29

Position and Vision of Small- and Medium-Sized Enterprises Boosting Commercialization 599 Torsten Schmidt, Nadine Teusler, and Andreas Baar

30

Optical Elements for EUV Lithography and X-ray Optics 613 Stefan Braun and Andreas Leson

31

Industrial Production of Nanomaterials with Grinding Technologies 629 Stefan Mende

32

Guidelines for Safe Operation with Nanomaterials 647 ́ ́ Iwona Malka, Marcin Jurewicz, Anna SwiderskaSroda, Joanna Sobczyk, Witold Łojkowski, Sonja Hartl, and Andreas Falk Part VIII Visions for the Future 677

33

Industrialization – Large-Scale Production of Nanomaterials/Components 679 Marcel Van deVoorde Index 685

XV

Foreword Curiosity-driven fundamental research is part of human culture, the benefit of which is improved knowledge and understanding of phenomena, behavior, processes, and organic and inorganic matter. An integral part of curiosity is raising the question on intelligent and sustainable use of the knowledge, for example, for improving the quality of life. Society not only tolerates but also favors and finances research work; not forever, as at a certain point, the proof of usefulness of new results and dedicated innovation becomes evident. Fantasy and imagination have to be followed by innovation with market potential, economic benefit, and creation of working places. he fascination of nanoscience has been based on curiosity. An unexploited body of phenomena, matter, and behavior offered almost unlimited development for fantasy and imagination. For most fields of human needs like housing, daily water and food, health, communication, mobility, and power providing comfort for life nanoscience principally offers great potential for advanced solutions. he potential is based on some of the main characteristics of nanoscience and nanotechnology: small mass and volume (a small number of atoms and molecules) per material unit with a high ratio of atoms/molecules of different behavior at surfaces, a very large number of material units to be built together with new architecture (“architectonics”*), potentially interface-dominated stringent space limitations for electric charges, and consequences on electric, magnetic, and optic behavior of building blocks. he great potential for innovation offered by nanoscience and nanotechnology is evident. As a matter of fact, for the last decades, nanoscience and nanotechnology has been a university and research center topic to a large extent. Nano-Industry is still in its infancy: nano-Electronics and nano-Chemistry are already on the way of industrialization, nano-Health and nano-Biotech made a good start, and nano-Structural materials have still to find their way and need to be promoted. Nano-Industrialization needs development of fabrication and manufacturing. Top-down approaches based on continuous tailoring and miniaturization from the microscale as well as bottom-up approaches based on assembling nanoscale units or new collective phenomena based on nanoscale effects need to be developed for the production of new sustainable and safe devices in industrial quantities.

XVI

Foreword

his book is an important and early contribution to the development of nanoManufacturing. It provides some directions for nano-Industry developments in the near future, especially for nano-Electronics and nano-IT, nano-Power and nano-Health, it describes examples with successful industrialization, and shows visions for the future in Europe, United States, and Asia. Tsukuba April 2014

Louis Schlapbach Prof. em. ETH/Empa, Scientist at NIMS Tsukuba

XVII

Acknowledgement he editors gratefully acknowledge the technical support of H. Faisst, C. Kotlowski and Dr. K. Bruehne of the ULM (D) University, Nanomaterials Institute, as well as various technical contributions and academic editing by Professor M. E. Fitzpatrick, Executive Dean of the Faculty of Engineering, Coventry University, UK. he generous support by the EUREKA programme through the research cluster Metallurgy Europe is gratefully acknowledged.

XIX

List of Contributors Sharifah Bee Abd Hamid

Marie-Isabelle Baraton

University of Malaysia Nanotechnology & Catalysis Research Centre (NANOCAT) Malaysia

University of Limoges and CNRS SPCTS Centre Europ. de la Céramique 12 rue Atlantis 87068 Limoges Cedex France

Santos F. Alvarado

ETH Zürich Magetism and Interphase Physics HPP N22 Hönggerbergring 64 8093 Zürich Switzerland Andreas Baar

Innos-Sperlich GmbH Bürgerstraße 44/42 D-37073 Göttingen Germany Gerd Bachmann

VDI Technologiezentrum GmbH Innovation Management and Consultancy VDI-Platz 1 40468 Düsseldorf Germany

Leif Brand

VDI Technologiezentrum GmbH Innovation Management and Consultancy VDI-Platz 1 40468 Düsseldorf Germany Stefan Braun

Fraunhofer Institut für Werkstoff- und Strahltechnik Winterbergstraße 28 01277 Dresden Germany

XX

List of Contributors

Hans Peter Buchkremer

Raffaele Di Giacomo

Forschungszentrum Jülich Institute for Energy and Climate Research (IEK) IEK-1: Materials Synthesis and Processing 52425 Jülich Germany

Salerno University Department of Industrial Engineering (DIIn) Via Giovanni Paolo II 132 84084 Fisciano (SA) Italy Jakub Dostalek

Francisca G. Caballero

National Center for Metallurgical Research (CENIM-CSIC) Physical Metallurgy Department Av. Gregorio del Amo, 8 E-28040 Madrid Spain Philippe C. Cattin

University of Basel Department Biomedical Engineering Spitalstrasse 21 4031 Basel Switzerland

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Uwe Erb

University of Toronto Department of Materials Science and Engineering Wallberg Building College Street 184 (Suite 140) Toronto, ON M5S 3E4 Canada Wolfgang R. Fahrner

Alison Crossley

University of Oxford Department of Materials Begbroke Science Park Begbroke Hill Oxford OX5 1PF UK

Faculty of Mathematics and Computer Science Fernuniversitaet Hagen Universitaetsstrasse 1 58084 Hagen Germany Andreas Falk

Sitaram Dash

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India Gilbert Declerck

imec Kapeldreef 75 3001 Leuven Belgium

BioNanoNet Forschungsgesellschaft mbH Graz Austria

List of Contributors

Hans-Jorg ¨ Fecht

Sonja Hartl

University of Ulm Institute of Micro and Nanomaterials Albert-Einstein-Allee 47 89081 Ulm Germany

BioNanoNet Forschungsgesellschaft mbH Graz Austria

Michael E. Fitzpatrick

Coventry University Faculty of Engineering and Computing Priory Street Coventry CV1 5FB UK Andreas Franz

Zoz Group Maltoz-Straße 57482 Wenden Germany

Simone E. Hieber

University of Basel Biomaterials Science Center c/o University Hospital Basel 4031 Basel Switzerland Jean-Franc¸ois Hochepied

MINES ParisTech PSL Research University Centre for Materials Sciences CNRS UMR 7633 BP 87 91003 Evry France and

Thomas Fries

Fries Research & Technology GmbH Friedrich-Ebert-Straße 51429 Bergisch Gladbach Germany

ENSTA ParisTech UCP, 828 Bd des Maréchaux 91762 Palaiseau cedex France Yasuhiro Horiike

Julia R. Greer

California Institute of Technology Division of Engineering and Applied Science MC 309-81 California Blvd. 1200 E. Pasadenam, CA 91125 USA

University of Tsukuba Department of Graduate School of Pure and Applied Science Tennodai 1-1-1 Tsukuba 3058571 Ibaraki Japan

XXI

XXII

List of Contributors

Jorg ¨ Huwyler

Olga Kammona

University of Basel Department of Pharmaceutical Sciences Division of Pharmaceutical Technology Klingelbergstrasse 50 4056 Basel Switzerland

Chemical Process & Energy Resources Institute Centre for Research and Technology Hellas P.O. Box 60361 57001 hessaloniki Greece Amal Kasry

Vili Igel

NMTC Nano & Micro Technology Consulting Soorstraße. 86 Reichsstr. 6 14052 Berlin Germany Colin Johnston

University of Oxford Department of Materials Begbroke Science Park Begbroke Hill Oxford OX5 1PF UK Marcin Jurewicz

Bialystok University of Technology Faculty of Management Bialystok Poland U. Kamachi Mudali

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Costas Kiparissides

Aristotle University of hessaloniki Department of Chemical Engineering P.O. Box 472 54124 hessaloniki Greece Wolfgang Knoll

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Neelie Kroes

European Commission Vice-President and Commissioner for the Digital Agenda Rue de la loi 200 B-1049 Bruxelles Belgium

List of Contributors

Martin Kulawski

Lerwen Liu

Oy Advaplan Inc. Alakartanontie 6 A 17 02360 Espoo Finland

NanoGlobe Pte Ltd Battery Road 4 Bank of China Building #25-01 049908 Singapore Singapore

Golden Kumar

Texas Tech University Texas USA Giovanni Landi

Faculty of Mathematics and Computer Science Fernuniversitaet Hagen Universitaetsstrasse 1 58084 Hagen Germany Seok-Woo Lee

California Institute of Technology Division of Engineering and Applied Science MC 309-81 California Blvd. 1200 E. Pasadenam, CA 91125 USA

Witold Lojkowski --

Bialystok university of Technology Faculty of management ojca tarasiuka 2 16-001 kleosin Poland Iwona Malka

Polish Academy of Sciences Institute of High Pressure Physics Warsaw Poland Stefan Mende

NETZSCH-Feinmahltechnik GmbH Sedanstraße 70 P.O. Box 14 60 95100 Selb Germany

Andreas Leson

Fraunhofer Institut für Werkstoff- und Strahltechnik Winterbergstraße 28 01277 Dresden Germany

Jyrki Molarius

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland

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List of Contributors

Bert Muller ¨

Jan Provoost

University of Basel Biomaterials Science Center c/o University Hospital Basel 4031 Basel Switzerland

imec Kapeldreef 75 3001 Leuven Belgium Xunlin Qiu

Peter Muller ¨

IBM Zurich Research Laboratory Säumerstrasse 4 8803 Rüschlikon Switzerland Heinz C. Neitzert

Salerno University Department of Industrial Engineering (DIIn) Via Giovanni Paolo II 132 84084 Fisciano (SA) Italy Gino Palumbo

Integran Technologies Inc. 6300 Northam Dr Mississauga ON L4V 1H7 Canada Thomas Pfohl

University of Basel Department of Chemistry Klingelbergstrasse 80 CH-4056 Basel Switzerland John Philip

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany Baldev Raj

National Institute of Advanced Studies (NIAS) Bengaluru 560012 Karnataka India Tommi Riekkinen

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland Laura Rossi

IBM Zurich Research Laboratory Säumerstrasse 4 8803 Rüschlikon Switzerland

List of Contributors

Dmitry Rychkov

Andrei P. Sommer

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany

Institute of Micro and Nanomaterials University of Ulm Albert-Einstein-Allee 47 89081 Ulm Germany

Robert Schlogl ¨

Abteilung Anorganische Chemie Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4-6 14195 Berlin Germany Torsten Schmidt

GXC Coatings GmbH Im Schleeke 27-31 D-38642 Goslar Germany Jan Schroers

Yale University Department of Mechanical Engineering and Materials Science Becton Center 217 Prospect Street 15 New Haven, CT 06520 USA Joanna Sobczyk

Institute of High Pressure Physics Polish Academy of Sciences Warsaw Poland

Anna S´widerska-S´roda

Institute of High Pressure Physics Polish Academy of Sciences Sokolowska 29/37, 01-142 Warsaw Poland Nadine Teusler

Innos-Sperlich GmbH Bürgerstraße 44/42 D-37073 Göttingen Germany Marcel H. Van de Voorde

University of Technology DELFT Faculty of Applied Science Materials and Engineering Department Eeuwigelaan, 33 1861 CL, Bergen he Netherlands Tim Van Gestel

Forschungszentrum Jülich Institute for Energy and Climate Research (IEK) IEK-1: Materials Synthesis and Processing 52425 Jülich Germany

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List of Contributors

Diederik Verkest

Werner Wirges

imec Kapeldreef 75 3001 Leuven Belgium

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany

Jared J. Victor

University of Toronto Department of Materials Science and Engineering Wallberg Building College Street 184 (Suite 140) Toronto, ON M5S 3E4 Canada Martin A. Walter

Institute of Nuclear Medicine University Hospital Bern Freiburgstrasse 4 3010 Bern Switzerland Matthias Werner

NMTC Reichsstr. 6 14052 Berlin Germany

Wolfgang Wondrak

Daimler AG Power Electronics Advanced Engineering Hanns-Klemm-Straße 45 71034 Böblingen Germany Markku Ylilammi

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland Henning Zoz

Matthias Wiora

Institute of Micro and Nanomaterials University of Ulm Albert-Einstein-Allee 47 89081 Ulm Germany

Zoz Group Maltoz-Straße 57482 Wenden Germany Andreas Zumbuehl

University of Fribourg Department of Chemistry Chemin du Musée 9 1700 Fribourg Switzerland

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds Marcel H. Van de Voorde, Matthias Werner, and Hans J. Fecht

1 Introduction

his book is about bridging the gap between nanoscience and technology, microsystem engineering, and the macroscale world. he interface between micro- and nanoscale technologies becomes a key field of endeavor. he first edition of this book, published in 2004, dated from an international workshop in 2003 in Berlin, Germany, and highlighted these emerging technology trends through contributions from 25 authors representing international research groups. he first edition was rather successful, but there have been many advances in the last 10 years that require an upgraded and extended second edition. In the new edition, featuring 6 parts and about 30 chapters, we have expanded the scope and coverage, as well as updated the book to cover recent developments and innovations. he book maintains the theme of addressing the interface between micro- and nanotechnology, with a strong focus on benefits that arise from exploiting synergy effects. he book’s contributions cover the entire range of basic technology aspects with special emphasis on industrial manufacturing of nanotechnology products and on potential applications. Moreover, business activities such as market expectations and market growth, transnational networking, and investment opportunities are highlighted and explained. Nanotechnology is gaining more and more interest also in the financial community. More than $US 3 billion is being spent around the globe on nanotechnology research this year alone. Recently published articles concerning possible future applications of nanotechnology predict a big commercial impact on nearly any industry branch. However, only very limited information is available on the market situation today as well as on the future prospects and the time-to-market span for nanotechnology products. How likely is the predicted huge impact on the global economy? What does that mean for established and start-up companies?

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds

2 Nanotechnology

“Nanotechnology” is a loosely applied term, often understood as a kind of ultimate miniaturization of high-tech devices. But in fact, it does not refer simply to objects whose dimensions are entirely in the nanometer range; rather, it can be applied generally to refer to

• functional objects where one of the dimensions, upon which the function relies, is less than 100 nm. Some dimensions of the objects may lie in the microscale or above; • any equipment used in the fabrication or measurement of nanoscale objects, including those where the function relies on a feature or features with dimension less than 100 nm. Most fundamental physical properties change if the geometric size in at least one dimension is reduced to a critical value below 100 nm, depending on the material. his allows tuning of the physical properties of a macroscopic material, if the material is fabricated from nanoscale building blocks with controlled size and composition. By altering the sizes of those building blocks, controlling their internal and surface chemistry, their atomic structure, and their assembly, it is possible to engineer properties and functionalities in completely new ways. Nanoparticles and nanomaterials exhibit radically different phenomena and behaviors compared to their macroscale counterparts. hese include quantum effects, statistical time variations (fluctuations) of properties, surface and interface interactions, and the consequences of the absence of defects in the nanocrystals observed in conventional crystalline materials. Nanoparticles and nanomaterials have unique mechanical, electronic, magnetic, optical, and chemical properties, opening the door to enormous new possibilities for engineered nanostructures and integrated nanodevice designs, with application opportunities in information and communications, biotechnology and medicine, photonics, and electronics. Examples include developments in ultrahigh-density data storage, molecular electronics, quantum dots, spintronics, and others. Atomic or molecular units, with their well-known subatomic structure, offer the ultimate building blocks for bottom-up, atom-by-atom synthesis and, in some cases, self-assembly manufacturing. Advanced nanostructured materials such as high-purity single-wall carbon nanotubes are being considered for microelectronics, sensors, and thermal management for micro- and optoelectronics, including flat panel displays. he latest developments in “nanobiotechnology” clear the way to revolutionary cancer diagnosis and treatment, bone repair, and tissue regeneration.

3 Nano-Industry is Arriving

he new nanotechnologies are driven by two approaches to their manufacture:

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

• “top-down” approaches based on continuous miniaturization from the microscale;

• “bottom-up” approaches based on nanoscale building blocks or nanoscale effects for the production of new devices. As nanotechnologies become increasingly embedded in products and processes, their integration with the microscale will be critically important. his has many challenges both in understanding the fundamental scientific principles that underlie the integration, and also in the industrial realization of components that exploit nanoscale phenomena. he extrapolation of engineering principles and mechanical and physical properties from the macroscale to the nanoscale is not straightforward: some scaling laws may reach their limit of validity, for instance in mechanical properties of ceramics due to the drastic change in properties during the transition from the macro to nano phases. Similarly, manufacturing techniques and methodologies for macromaterials and components cannot be simply extrapolated for the fabrication of nanocomponents. For example, nanofabrication requires to some extent expensive clean rooms, new expertise, and new techniques for quality control during manufacturing. As a consequence, companies will not be able to use their existing production lines for newly developed nanoscale technologies. New measurement techniques and newly developed standards for engineering processes will be needed, alongside novel methods for lifetime prediction and the assurance of reliability in use. Mass-production demands reliable and reproducible properties for materials and products. his means good control in manufacturing, with in situ measurements for quality control. Methods are needed for joining materials and components at the nanoscale, and the assessment of properties such as fatigue, creep, and corrosion in volumes that are minute compared to conventional testing requirements. here is a critical role for developments in nanomeasurement techniques for nanotechnology products and applications, underlined by the increasing involvement of metrological institutes in the new field of “nanometrology.” Standardization of nanotechnology from production to application is an important element in its fundamental engineering development, and these elements are covered within this book. In addition, standardization will be critical in tackling societal issues around nanotoxicology and other concerns frequently associated with rapidly growing new technologies. Nanotechnologies are subject to the same requirements as any of the systems that they integrate or replace, in terms of performance, safety, risk management, economy, and biocompatibility. Nanotechnology gives the potential for the creation of new products, but also the possibility to upgrade conventional technologies: an example presented in the book is the application of “nanoconcrete” in bridge construction. Because of the impacts on existing applications, there is the opportunity for industries in Europe and the United States to recapture global markets in well-established fields, such as steel and textiles, for example, by the development and application of advanced nanotechnologies.

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds

4 Applications and Markets

Many consumers are already unknowingly using products based on nanotechnology. A case in point is high-performance sun protection cream, based on nanocrystalline titanium dioxide that provides UV absorption but, because of the fine particle size, does not appear white on the skin. Another example is the Giant Magneto Resistive Effect (GMR), used in computer hard disk drives. he current high storage densities may only be obtained through the use of nanotechnologies. he breadth of applications, and the potential contribution of nanotechnologies, is shown in Figure 1.

5 Research and Development

European industry is a world leader in nanotechnology, alongside the United States and Japan, as it becomes evident by the number of patents and scientific publications. Although there are many advantages for industry in the development and application of nanomaterials and components, production costs are considerably high, particularly initially, and products often require more intensive quality control. As a consequence, the added value brought by nanotechnology must be very significant in terms of improved or new properties and functionalities. his book highlights the competitive advantages that will be available to companies that invest in nanotechnologies. he performance of microsystems depends on the understanding of the properties on both the nano- and microscales. In the words of the Review Committee of the National Nanotechnology Initiative in the United States: “Revolutionary Quantum dots Opto-electronics Improved reliability Enhanced eletrical properties

Hydrogen storage Batteries Solar cells

Improved transport kinetics

Enhanced properties

Catalysis High surfaceto-volume ratio

Enhanced reactivity

Reduced dimensions

Green tyres Tools Increased wear resistance

Smaller grain size

Coatings Increased hardness

Higher resistivity Electronics Sensors

Figure 1 An overview of the potential applications of nanotechnology.

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

change will come from integrating molecular and nanoscale components into high order structures … To achieve improvements over today’s systems, chemical and biologically assembled machines must combine the best features of the top-down and bottom-up approaches.” his requires extensive research, building upon current knowledge, and practice. he research needs to move from demonstration of nanoscale possibilities to the development of new ways of working in manufacturing. here is a particular challenge for small-to-medium enterprises (SMEs). hey can benefit greatly from new technologies, but often cannot afford the research and development costs. New models of partnership between SMEs and major industrial players, academic, and national laboratories are required. SMEs in the future will play a key role in the industrialization of nanotechnology because of their flexibility.

6 The Infinite Space at the Bottom and the Tremendous Opportunities to Climb Up

Figure 2a illustrates schematically the tremendous opportunities nanotechnology offers for engineering and improving the performance of materials, systems, and devices, as well as for scientists on fundamental grounds searching for unexpected effects. In Figure 2, materials engineering, with support of materials science, seeks to optimize materials properties by varying the materials’ chemical composition, phase structure, and microstructure (e.g., dislocations, grain boundaries, phase boundaries, point defects density, and arrangement). Figure 2b shows the great opportunities offered by new degrees of freedom in shaping properties of matter. Further, nanoarchitectures and nano-micro architectures combine the nano-micro building blocks into microsystem technologies. he new degrees of freedom produced through combining multiple effects at the nanoscale gives a vastly increased range of potential properties than was available before the nanotechnology era. When considering the further step of the combination of nano-sized pieces of material (nano-building blocks) and micro-sized materials into nano-micro systems (the art of doing this can be called nano-micro architecture) the new space for discoveries and applications becomes very large indeed. he new, virtually infinite space of parameters that can be tuned to control material properties opens up opportunities for new discoveries, particularly to solve key societal needs: supply of energy without irreparable damage to the environment, delivering clean water, radically improving the efficiency of medical treatments, supporting developing countries to improve quality of life, and accelerating economic growth in technologically advanced countries. hus an exponentially growing, new space for research and development is opening for humanity that holds great promise for all citizens of the globe.

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds

Devices

(a)

Chemical composition

Chemical composition

Joining

Optimising material properties

Optimising material properties

Microstructure

Microstructure

Nano-mocro systems with radically improved properties.

Micro-nano architecture

Microstructure

Optimising material properties

Microstructure

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tio n po si co m al ic

he m

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New properties

C

he Size and m ic al co m po si tio n

shape

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XXXII

Optimised properties

Microstructure

(b)

Figure 2 (a) Materials science and engineering optimize materials properties, by varying materials’ chemical composition, phase structure, microstructure (e.g., dislocations, grain boundaries, phase boundaries, point defects, etc.) density, and arrangement. (Image courtesy W. Lojkowski, Unipress, Poland.) (b) Nanotechnology exploits

in addition to microstructure and chemical composition the effect of size and shape of matter on its properties. Further, nanoarchitecture and nano-micro architecture combines the nano-micro building blocks into nano-micro systems. (Image courtesy W. Lojkowski, Unipress, Poland.)

7 The Second Edition, 2014

his second edition maintains the theme of addressing the interface between micro- and nanotechnology, with a strong focus on the benefits that arise from exploiting synergy effects. he book’s contributions cover the entire range of basic technology aspects with the goal of developing new and improved

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

1. A European Strategy for Micro- and Nanoelectronic Components and Systems

Part VIII: Visions for the future Part I: Nanotechnology Research Funding and Commercialization Prospects – Political, Social and Economic Context for the Science and Application of Nanotechnology

33. Industrialization – Large-Scale Production of Nanomaterials/Components Part VII: Creative Strategies Connecting Nanomaterials to the Macroscale World

XXXIII

26. Nanostructured Cement and Concrete

2. Governmental Strategy for the Support of Nanotechnology in Germany 3. Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region 4. Near-Industrialization Nanotechnologies Developed in JST’s Nanomanufacturing Research Area in Japan 5. Quo vadis Nanotechnology?

27. Hydrogen and Electromobility 28. Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials 29. Position and Vision of Smalland Medium-Sized Enterprises Boosting Commercialization 30. Optical Elements for EUV Lithography and X-ray Optics

Part II: Development of Micro and Nanotechnologies 6. Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces 7. Multisensor Metrology Bridging the Gap to the Nanometer – New Measurement Requirements and Solutions in Wafer-Based Production

The Nano-Micro Interface: Bridging the Micro and Nano Worlds

8. NanostructuralMetallic Materials – Nanoengineering and Nanomanufacturing

31. Industrial Production of Nanomaterials with Grinding Technologies

9. Bulk Metallic Glass in Micro to Nano Length Scale Applications 10. From Oxide Particles to Nanoceramics: Processes and Applications

32. Guidelines for Safe Operation with Nanomaterials Part VI: Process Controls and Analytical Techniques

Part III: Nanoelectronics and System Integration

23. Characterisation of Nanostructured Materials

11. Creating Tomorrow’s Applications through Deeper Collaboration between Technology and Design

24. Surface Chemical Analysis of Nanoparticles for Industrial Applications

12. Multiwalled Carbon Nanotube NetworkBased Sensors and Electronic Devices

25. Nanometer-Scale View of the Electrified Interface: A Scanning Probe Microscopy Study

13. Thin Film Piezomaterials for Bulk Acoustic Wave Technology 14. Properties and Applications of Ferroelectrets

Part V: Energy and Mobility 19. Nanotechnology in Energy Technology

Part IV: Biomedical Technologies and Nanomedicine

15. Translational Medicine: Nanoscience and Nanotechnology to Improve Patient Care

20. The Impact of Nanoscience in Heterogeneous Catalysis

16. Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine

21. Processing of Nanoporous and Dense Thin Film Ceramic Membranes

17. Biofunctional Surfaces

22. Nanotechnology and Nanoelectronics for Automotive Applications

18. Biomimetic Hierarchies in Diamond-Based Architectures

Figure 3 The 8 parts of the book and the subsequent 33 chapters.

applications. Moreover, business aspects such as potential markets, roadmaps, transnational networking, and investment opportunities are highlighted and explained. he book comprises eight parts and is subdivided into 33 chapters. PART I represents an overview of the state-of-the-art in commercializing nanotechnology, with particular case studies of the strategies being implemented in

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds

Germany and Japan. It highlights the global research efforts and gives a summary of the engineering and manufacturing developments, as well as the key markets. PART II features the main classes of materials – metals, ceramics, and polymers – and how nanotechnology can in each case have benefits for properties and applications. Novel materials such as bulk metallic glasses are also considered. Part III looks at the integration of nanoelectronics devices into larger systems, with examples of carbon nanotubes, piezomaterials, and ferroelectrets, and how there will need to be collaboration in the future between technology and design. Part IV looks at applications in biomedical technologies and nanomedicine. Bioactivation, biomimicry, and biofunctionality are all critical properties for the development of transformative applications in medicine, including diagnostics, drug delivery, and regenerative treatments. Part V covers energy and mobility applications. For transport applications, nanomaterials can have impact in areas as diverse as catalysis for exhaust treatments to nanoelectronics for vehicle sensing and improvements in fuel efficiency. Part VI covers process control and analytical techniques, specifically characterization techniques, surface chemical analysis, and interface studies, and gives guidelines for their application in industrial manufacturing. Part VII is devoted to creative strategies connecting nanomaterials to the macro world and gives insights into the engineering challenges of manufacturing at the nano- to macrolength scales, and shows cases in the development of production technologies for nanomaterials and components. he standardization of nanomaterials will be essential both for manufacturing and marketing purposes. he part gives examples of successful developments of large-scale production technologies for nanoproducts, including novel techniques such as grinding. PART VIII concludes the book with a vision for the future of nanomaterials, through industrialization and large-scale production of components.

References 1. Roco, M. et al. (2010) Nanotechnology

Research Directions for Societal Needs in 2020, Springer, Heidelberg.

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Part I Nanotechnology Research Funding and Commercialization Prospects – Political, Social and Economic Context for the Science and Application of Nanotechnology

he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

3

1 A European Strategy for Micro- and Nanoelectronic Components and Systems1) Neelie Kroes

1.1 Introduction

Micro- and nanoelectronic components and systems2) are not only essential to digital products and services, but they also underpin innovation and competitiveness of all major economic sectors. Today’s cars, planes, and trains are safer, more energy-efficient, and comfortable thanks to their electronic parts. he same holds for large sectors like medical and health equipment, home appliances, energy networks, and security systems. his is why micro- and nanoelectronics is a KeyEnabling Technology (KET) [1] and is essential for growth and jobs in the European Union (EU). his communication sets out a strategy to strengthen the competitiveness and growth capacity of the micro- and nanoelectronics industry in Europe. In line with the updated industrial policy [2], the aim is for Europe to stay at the forefront in the design and manufacturing of these technologies and to provide benefits across the economy. he strategy spans policy instruments at regional, national, and EU level including financial support for research, development, and innovation (R&D&I), access to capital investment (CAPEX) as well as the improvement and better use of relevant legislation. he strategy builds on Europe’s strengths3) and on regional clusters of excellence. It covers the whole value chain from material and equipment manufacturing to design and volume production of micro- and nanoelectronics components and systems. he importance of the area and the challenges faced by the stakeholders in the EU require urgent and bold actions in order to leave no weak link in Europe’s innovation and value chains. he focus is on: 1) European Commission (23 May 2013), COM(2013) 298, official publication at http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=COM:2013:0298:FIN:EN:PDF. 2) Referred to as micro- and nanoelectronics in this communication, it spans from nanoscale transistors to microscale systems integrating multiple functions on a chip. 3) For example, electronics for cars, energy, and manufacturing sectors. he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

• attracting and channelling investments in support of a European roadmap for industrial leadership in micro- and nanoelectronics;

• setting up an EU-level mechanism to combine and focus support to micro- and nanoelectronics R&D&I by member states, the EU, and the private sector;

• taking measures to strengthen Europe’s competitiveness towards a global-levelplaying field regarding state aid, to support business development and SMEs, and to address the skills gap.

1.2 Why are Micro- and Nanoelectronics Essential for Europe? 1.2.1 An Important Industry with a Significant Potential for Growth and a Massive Economic Footprint

Micro- and nanoelectronics underpin a significant part of the worldwide economy. heir role will continue to grow as future products and services will become more digital, as illustrated below.

• he global turnover of the sector alone was around €230 billion in 2012 [3].

•

•

• •

he value of products comprising micro- and nanoelectronic components represents around €1600 billion of value worldwide. Despite the recent financial and economic setbacks, the worldwide market for micro- and nanoelectronics has grown by 5% per year since 2000. Further growth of at least the same magnitude is predicted for the remaining part of the current decade. he pace of innovation in the field is one of the main drivers behind the high growth rates of the whole digital sector which today has a total value of around €3000 billion worldwide [4]. In Europe, micro- and nanoelectronics is responsible for 200 000 direct and more than 1 000 000 indirect jobs [5] and the demand for skills is unceasing. he impact of micro- and nanoelectronics on the whole economy is estimated at 10% of the worldwide GDP [6].

1.2.2 A Key Technology for Addressing the Societal Challenges

Micro- and nanoelectronics are not only the computing power in PCs and mobile devices. hey fulfill also the sensing and actuating functions4) found for example in smart meters and smart grids for lower energy consumption, or in implants and sophisticated medical equipment for better health care and for helping the 4) A sensor is any device, such as a thermometer, that detects a physical condition in the world. Actuators are devices, such as switches, that perform actions such as turning things on or off or making adjustments in an operational system.

1.3

A Changing Industrial Landscape for Micro- and Nanoelectronics

elderly population. hey are also the building blocks for better security, for the safety and efficiency of the whole transport systems, and for environmental monitoring. Today no societal challenge can be successfully met without electronics.

1.3 A Changing Industrial Landscape for Micro- and Nanoelectronics 1.3.1 Technology Progress Opens New Opportunities

Two main tracks characterize technology development and drive business transformation. A first track progresses the miniaturization of components at the nanoscale along an international roadmap for technology development established by industry [7]. his is the more Moore track aiming at higher performance, lower costs, and less energy consumption.5) A second track aims at diversifying the functions of a chip by integrating microscale elements such as power transistors and electromechanical switches. his is referred to as the more than Moore track. his track is at the basis of innovations in many important fields such as energy-efficient buildings, smart cities, and intelligent transport systems. In addition, totally new, disruptive technologies and architectures are being researched. his is often referred to as the beyond CMOS6) track. It requires multidisciplinary research, deep understanding of physics and chemistry and excellence in engineering. Furthermore, in order to lower production costs, industry increases also step by step the size of the material support7) for producing micro- and nanoelectronics. Massive investments in R&D&I and CAPEX are required for such transitions in manufacturing standards. 1.3.2 Escalating R&D&I Costs and a More Competitive R&D&I Environment

Further miniaturization implies escalating costs for R&D&I and CAPEX. he R&D&I intensity “of the micro- and nanoelectronics industry increased from 11% in 2000 to 17% in 2009” [8]. his trend appears to continue. Such high investments can only be sustained by volume production. 5) Moore’s Law: doubling performance to cost ratio every 18–24 months. 6) Complementary metal–oxide–semiconductor (CMOS) is the standard technology for integrated circuits in the ‘more Moore’ track. 7) Micro- and nanoelectronics chips are produced on round material supports called ‘wafers’. Successive technology generations are identified by the diameter size of the wafers on which they are produced. Today production is mainly done on 200 and 300 mm wafers. he next wafer size will be 450 mm.

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

Baseline CMOS: CPU, Memory, Logic (nm)

More than Moore: Diversification

Moore’s law: miniaturization

6

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Passives

130 Co m

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Information processing Digital content System-on-Chip (SoC)

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HV Power

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Moore’s law and more.

Consolidation in the industry is ongoing. his could lead to a situation where only a few actors are left worldwide and perhaps none in Europe. It is estimated that a 10% share of the worldwide market is needed for a semiconductor company to sustain the investment to keep up with technology development. As a result, global alliances between companies are formed, for example the New York-based IBM alliance on 300-mm wafer technology and the Global 450 Consortium focusing on the transition to 450-mm wafers. In Europe, the nextgeneration technology development is centered on leading research centers such as LETI,8) Fraunhofer,9) and imec10) working in close cooperation with industrial players. Research itself is increasingly becoming global with the emergence of Asia as the home of patent holders and a skilled workforce. 1.3.3 New Business and Production Models

he micro- and nanoelectronics industrial landscape is changing drastically with a significant shift of volume production to Asia in the last 15 years.11) Overall, 8) LETI is an institute of CEA, a French research-and-technology organization. It specializes in nanotechnologies and their applications, from wireless devices, to biology, health care, and photonics (http://www-leti.cea.fr). 9) he German Fraunhofer-Gesellschaft undertakes applied research of direct utility to private and public enterprise and of wide benefit to society. Several institutes are focusing on integrated circuits and systems (http://www.fraunhofer.de). 10) Belgian IMEC performs world-leading research in nanoelectronics, leveraging scientific knowledge with global partnerships in ICT, health care, and energy (http://www.imec.be). 11) For example, capital expenditure of Korean companies increased from 13% in 2005 to 27% in 2012.

1.4

Europe’s Strengths and Weaknesses

production in Europe has dropped to just less than 10% of world production in 2011. Despite the strengths of US companies in the field, only 16% of production is made in the US. With the increased cost of setting up production facilities (fabs), the granting by territorial authorities of financial incentives has become an important element in the decision where to build new capacity. Tax breaks, land, cheap energy, and other incentives play a major role as does the availability of skilled labor force [9]. Another important trend is the rise of the foundry model.12) Foundries developed strongly in Asia and represent already around 10% of the worldwide electronic component production. In conjunction, there are an increasing number of “fabless” companies13) that generate income from selling chip designs. Without production, these fabless companies have not the high financial overheads of the manufacturing companies. Secure access to production capacity may however become problematic in the future as foundries extend their offer to include design and prototyping which would give them an insight into the end products. To minimize the risk, some companies doing own designs keep limited production lines in-house (the socalled fab-lite model). 1.3.4 Equipment Manufacturers Own Key Elements of the Value Chain

Without progress in production equipment, advances in further miniaturization and increased functionality of chips are not possible. Equipment manufacturers have become a key part of the value chain which is reflected in their prominent role in the international technology alliances.

1.4 Europe’s Strengths and Weaknesses 1.4.1 Industry Structured around Centers of Excellence and Wider Supply Chains Covering all Europe

Similar to the rest of the world, Europe’s micro- and nanoelectronics industry is concentrated around major regional production and design sites. he regions around Dresden (DE), Grenoble (FR), and Eindhoven-Leuven (NL-BE) host three main research and production centers with increased specialization in one of the three areas of more Moore, more than Moore, and equipment and materials. In addition, the region of Dublin (IE) hosts a large European manufacturing site of 12) A foundry is a company owning factories and offering manufacturing services to ‘fables’ customers. 13) A fables company designs its own components but outsources their manufacturing to a service provider (the ‘foundry’).

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

microprocessors, and Cambridge (UK), for example, is home to the leading company in the design of low power consumption microprocessors that equip most of today’s mobile devices and tablets. his clustering and regional specialization is essential for the future development of the sector. However, it relies on a wide supply chain spread across Europe. his includes relatively smaller but highly innovative and specialized clusters such as the regions of Graz and Vienna (AT), Milan and Catania (IT), or Helsinki (FI). Europe counts three large indigenous micro- and nanoelectronics companies ranking 8th (STMicroelectronics), 10th (Infineon), and 12th (NXP) in worldwide sales in 2012. Europe also attracted some major overseas companies that invest in Europe (e.g., GlobalFoundries and Intel). Micro- and nanoelectronics manufacturing in Europe is further served by a very competitive and extended value chain and ecosystem of companies, including many SMEs. he main manufacturing sites are embedded in the regional clusters as mentioned above. 1.4.2 Leading in Essential Vertical Markets, Almost Absent in Some Large Segments

Europe is relatively absent in the production of computer and consumer-related components that represent a large part of the total market. It is leading though in electronics for automotive (∼50% of global production), for energy applications (∼40%) and industrial automation (∼35%). Europe is also still strong in designing electronics for mobile telecommunications. European companies, including a large number of SMEs, are world leaders in smart micro-systems like health implants and sensing technologies. Although these are currently niche markets, they are areas of high growth (typically more than 10% per year). Another key asset is the European leadership in the high growth market of low power consumption components. 1.4.3 Undisputed European Leadership in Materials and Equipment

Europe has some of the most important equipment and materials suppliers including, for example, ASML and SOITEC that hold significant shares of the relevant world market. hese companies rely on many suppliers established throughout Europe, many of them SMEs. hese European equipment and material suppliers uniquely master highly sophisticated technologies ranging from optics and lasers to precision mechanics and chemistry. heir role in progressing the micro- and nanoelectronics area is significant and well acknowledged as for example illustrated by the recent strategic investment of major semiconductor companies in ASML.14) 14) See http://www.asml.com/asml/show.do?ctx=5869&rid=46974 – ‘As part of the program, Intel, TSMC, and Samsung will each acquire ASML shares, equal to an aggregate 23% minority equity stake in ASML for EUR 3.85 billion in cash’.

1.5

European Efforts So Far

1.4.4 Investments of EU Companies Remain Relatively Modest

Although in absolute terms investments by European companies are high (in the order of billions of euros), they remain relatively modest compared to investments made elsewhere. Europe’s business attractiveness nevertheless remains high given the size of its consumption which is above 20% of the world market. But future investments in electronics manufacturing in Europe are not guaranteed. Competition with other regions in the world is stiff. Public investment in R&D&I and policies to attract private investment remains highly fragmented across the EU despite the progress made in the last 5 years. his sharply contrasts with the fact that European R&D&I in micro- and nanoelectronics is world-class and very attractive to international players.

1.5 European Efforts So Far 1.5.1 Regional and National Efforts Reinforcing the Clusters of Excellence

Important efforts, notably over the last 15 years, have been devoted at regional level to build industrial and technology clusters in the area. he most successful clusters are the result of long-term sustained strategies that combine policies such as tax incentives, investment in R&D&I in public labs, intensive industry–academia cooperation, world-class infrastructures, critical coverage of the value chain and a dynamic business environment. he availability of skills and knowledge is equally of major importance for the field. With the challenges ahead including the increasing costs of R&D&I, the fierce worldwide competition and the erosion of some key parts of the value chain in Europe (e.g., the stage of packaging components into systems), much closer collaboration along value chains and in innovation ecosystems at EU level is a must. 1.5.2 A Growing and More Coordinated Investment in R&D&I at EU Level

Investment in R&D&I in micro- and nanoelectronics is part of the EU programmes for research and development since their inception. he EUREKA programme also has a large research cluster on micro- and nanoelectronics [10]. After 10 years of stagnation of EU support to R&D&I in the field,15) a gradual increase of around 20% per year started in 2011 leading to a budget of more than €200 million in 2013. In order to focus the R&D&I efforts and build critical mass, the commission, member states, and private stakeholders together launched, in 15) At ∼€130 million per year.

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

2008, a public–private partnership in the form of a Joint Undertaking16) (ENIAC JU). By the end of 2013, the ENIAC JU will have invested both from the public and private sides more than €2 billion on R&D&I in addition to around €1 billion invested in micro- and nanoelectronics in the Seventh Framework Programme. 1.5.3 Technology Breakthroughs but Gaps in the Innovation Chain

he focus in the EU R&D&I support is on preparing for the next two generations of technologies [11]. hrough these programmes, industry kept pace with the state-of-the-art developments in further miniaturization. Also through these programmes, sophisticated smart systems were developed that today are deployed for example in cars or health systems. However, the EU R&D&I programmes so far supported the early phases of the innovation process, that is validating the technologies up to a laboratory level.17) he logic was to leave the next steps getting closer to the final product up to industry, given the high level of investment these require. his led to clear gaps in the innovation chain. To be effective and cross the so-called valley of death, support to research and innovation in the field needs increasingly to address the whole innovation chain spreading beyond any one company, region, or member state. he ENIAC JU called recently for manufacturing pilot lines addressing particularly these higher scales of technological maturity. he strong interest demonstrated by the private stakeholders and the public authorities to support these pilot lines shows their strategic importance.

1.6 The Way Forward – A European Industrial Strategy

he proposed strategy builds on the European initiative on KETs and on the HORIZON 2020 [12] proposal for R&D&I. It focuses though on the actions that are specific for the challenges faced in micro- and nanoelectronics. 1.6.1 Objective: Reverse the Decline of EU’s Share of World’s Supply

Europe cannot afford to lose the capacity to design and manufacture micro- and nanoelectronics. his would put large parts of the value chains of major industrial sectors at risk and deprive Europe of essential technologies needed to address its societal challenges. 16) Based on Article 187 TFEU. 17) Technology Readiness Levels (TRLs) are used to assess the maturity of evolving technologies. Levels 1–4 typically refer to early R&D while levels 5–8 indicate prototyping and actual system validation in an operational environment.

1.6

The Way Forward – A European Industrial Strategy

Given the wide range of opportunities ahead and the challenges industry is facing, it is now urgent to step up and coordinate all relevant public efforts across Europe. An industrial strategy should ensure return to growth and reach, in a decade, a level of production in the EU that is closer to its share of world GDP. In detail, the aims are to:

• Ensure the availability of micro- and nanoelectronics that are needed for the competitiveness of key industries in Europe.

• Attract higher investment in advanced manufacturing in Europe and reinforce industrial competitiveness across the value chain from design to manufacturing.

• Maintain leadership in equipment and material supply and in areas such as more than Moore and energy-efficient components.

• Build leadership in the design of chips in high growth markets, notably in the design of complex components. 1.6.2 Focus on Europe’s Strengths, Build on and Reinforce Europe’s Leading Clusters

As indicated above, Europe’s assets in micro- and nanoelectronics include an excellent academic research community and industrial leadership in vertical markets. Moreover, when considering Europe as a whole, there is an industrial and technology presence across the full value chain including equipment, material, manufacturing, design as well as strong end-user industry. Building on these strengths and mobilizing the resources needed should make Europe a major player in micro- and nanoelectronics. Mobilizing resources will need alignment of actions at regional, national, and European level. his will build confidence and stimulate the renewal and growth of manufacturing capability in Europe. Emphasis is on reinforcing and building on the excellence of research and technology organizations (RTOs) in terms of facilities and staff. hey should be the “places to be” for talented engineers and researchers in the field, at the center of ecosystems to attract private investments in manufacturing and design. In order to maximize return on investment and ensure excellence, further progress towards complementary specialization and stronger cooperation between the main RTOs will be a key for success in line with the smart specialization strategy [13] of the EU. To ensure the further uptake of electronics in all industrial sectors and seize the opportunities arising from cross-disciplinary work, closer cross-border and cross-sector collaborations including end-user industries should be reinforced. 1.6.3 Seize Opportunities Arising in Non-conventional Fields and Support SMEs Growth

SMEs play a key role in emerging areas like plastic and organic electronics, smart integrated systems, and in general in the field of design. An important goal therefore is to better integrate SMEs in value chains, and provide them with access to

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

state-of-the-art technologies and R&D&I facilities. Support to centers of excellence that help embed micro- and nanoelectronics in all types of products and services will be essential to spur innovation across the economy and mainly in non-technology SMEs. EU-wide partnerships between end-user industries, public authorities, and suppliers (large and small) of micro- and nanoelectronics will help open up new high growth areas like electric vehicles, energy-efficient buildings and smart cities, and all types of mobile web services.

1.7 The Actions 1.7.1 Towards a European Strategic Roadmap for Investment in the Field

he aim is to attract higher public and private investments and channel these to implement a roadmap for leadership to be established by industry. he level of public and private investment will match the size of the challenge. he intention is to bring the total public and private investment in R&D&I at EU, national, and regional level to more than [€1.5 billion] per year, that is, a total budget of more than [€10 billion] over 7 years. To this end the Commission will pursue the dialogue with stakeholders and set up an Electronics Leaders Group to elaborate and help implement a European Industrial Strategic Roadmap that will build on Europe’s strengths and cover three complementary lines:

• he development of the More than Moore technology track on wafer sizes of 200 and 300 mm. his will enable Europe to maintain and expand its leadership18) in a market that represents roughly €60 billion per year and has a 13% yearly growth. It will have a direct impact on high-value jobs creation including notably in SMEs. • he further progression of More Moore technologies for ultimate miniaturization on wafer sizes of 300 mm. he investment should enable Europe to gradually increase production in this market that represents more than €200 billion.19) • he development of new manufacturing technology on 450-mm wafers. he investment will initially benefit equipment and material manufacturers in Europe who are today world leaders on a market of around €40 billion per year and will provide a clear competitive edge to the whole industry, in a 5–10 years range. he roadmap will be established at the latest by the end of 2013 as a set of concrete actions reinforcing notably Europe’s clusters of excellence in manufacturing 18) Currently, production in Europe in this track is more than 30% of the world value. 19) Europe’s share of production is around 9%, but Europe is still at the leading edge of technology in the miniaturization race.

1.7

The Actions

and design (see Section 4.1) and ensuring openness to partnerships and alliances across the value chain. he actions of the public sector, European Commission, member states, and regional authorities will consist of:

• Supporting R&D&I through institutional funding or grants to actions driven by the roadmap. Focused and coordinated interventions20) generating critical mass and maximizing return on investment will be mobilized. • Developing, in partnership with industry and in support to innovation, an advanced manufacturing and piloting infrastructure to bridge the gap in the innovation chain and connect design with actual deployment. • Facilitating access to financing CAPEX through loans and equities, notably regional funds and the innovation schemes of the European Investment Bank (EIB). In this context, the European Commission signed in February 2013 a Memorandum of Understanding with the EIB signalling KETs as a priority for investments. he commission will prepare the ground for industry to team up along the value chain and to develop and regularly update the roadmap. Member states, regional authorities, and the European Commission will support the roadmap individually and/or collectively including through a Joint Technology Initiative (JTI) and the EUREKA initiative. It will ensure the best use of regional Structural Funds including through smart specialization between the target clusters and the use of financial instruments foreseen under European Structural Investment Funds (ESI Funds) [13] Industry will engage in maintaining and expanding design and manufacturing activities in Europe and will regularly update the roadmap with the help of RTOs and the academic community in order to keep it up to date with the dynamics of market and technology developments. 1.7.2 The Joint Technology Initiative: A Tripartite Model for Large-Scale Projects

he European Commission will propose a JTI21) based on Article 187 TFEU that combines resources at project level in support of cross-border industry–academia collaborative R&D&I. he proposal for a Council Regulation to establish a JU will replace the two existing JU on embedded computing systems (ARTEMIS) and nanoelectronics (ENIAC) that were set up under the Seventh Framework Programme. Within HORIZON 2020 under the “Leadership in Enabling and Industrial Technologies” challenge, the new JTI will cover three main interrelated areas:

• Design technologies, manufacturing processes and integration, equipment, and materials for micro- and nanoelectronics. 20) From regional-, national-, and EU-level programmes. 21) he impact of the proposal will be presented in the impact assessment. he budgetary impact will be included in the legislative and financial statement.

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

Intensity of investment

14

Implementation in JTI

Industrially driven R&D Pan-Eropean innovation: Take-up, Assessment, Infrastructure, Design services

Advanced R&D

TRL

Capital-intensive R&D&I, Pilot lines, demonstrators/ applications

1

2

Basic principles observed

3

Technology concept formulated

Experimental proof of concept

4 Technology validation in lab

Technological research pillar 1

Figure 1.2

5

Implementation in H2020 6

Tech valid. in relevant environment

7

8

Demonstration Demonstration System in relevant in operational complete and environment environment qualified

KET pilot line and demonstrator projects pillar 2

9 Successful mission operations

Manufacturing and KET deployment project pillar 3

Relation between the intensity of investment versus industrial implementation.

• Processes, methods, tools and platforms, reference designs, and architectures for embedded/cyber-physical systems.

• Multidisciplinary approaches for smart systems. he new JTI will build on lessons learned from the current JTIs [14] and provide a simplified funding structure. It will mainly support capital-intensive actions22) such as pilot lines or large-scale demonstrators at higher technology readiness level up to level 8 as shown above. hese will require a tripartite funding model involving the European Commission, member states, and industry and will help align relevant investment strategies across Europe. he implementation will follow the principles of HORIZON 2020 and will be consistent with the cross-cutting KETs work programme to strengthen cross-fertilization between the different KETs. Support to the JTI will be complemented with EU funding for technological R&D and for innovation actions targeting notably SMEs. his will cover R&D&I in new areas of micro- and nanoelectronics (see Section 6.3), including those requiring the combination of several KETs such as advanced materials, industrial biotechnology, photonics, nanotechnology, and advanced manufacturing systems [15]. Within the new JTI the commission will furthermore explore how to simplify and accelerate state aid approvals including through a Project of Common European Interest according to Article 107.3(b) of TFEU. 22) Currently, public support to pilot lines in ENIAC JU is between €50 and €120 million per action.

1.7

The Actions

1.7.3 Building on and Supporting Horizontal Competitiveness Measures

he access to a highly skilled workforce of engineers and technicians and to high quality graduates is essential for attracting private investments in electronics. Similar to the whole ICT sector, micro- and nanoelectronics is suffering from an increasing skills gap and a mismatch between supply and demand of skills. he commission will continue to promote digital competences for industry through the e-Skills initiative and has recently launched the “Grand Coalition for ICT skills and jobs.” For micro- and nanoelectronics the engagement of industry to attract the young generation early in its education is critical. In addition to industrial efforts and relevant initiatives at regional and national levels, the commission will continue to cofinance in HORIZON 2020 projects to develop and disseminate training and teaching materials on the latest technology in micro- and nanoelectronics as well as support awareness campaigns targeting young entrepreneurs. In addition, the European Commission is putting in place an EU Skills Panorama with updated forecasts of skills supply and labor market needs up to 2020, to improve transparency for Skills, Competences, and Occupations classification (ESCO), as a shared interface between the worlds of employment, education and training and to support mobility. Together with RTOs, universities and national and regional authorities, the commission will seek to make shared facilities and services for testing and early experimentation of micro- and nanoelectronics technologies available to start-ups, SME’s, and users across Europe. Furthermore through public procurement of innovations that are driven by micro- and nanoelectronics such as health or security equipment better conditions for market developments in these fields will be created. 1.7.4 International Dimension

he European Commission will promote international cooperation in micro- and nanoelectronics especially in areas of mutual benefit such as international technology road-mapping, benchmarking, standardization, health and safety issues linked to nanomaterials [16], and preparing the transition to 450-mm wafer size, or advanced research in beyond CMOS. he European Commission will continue its efforts to move towards a more transparent and global-level-playing field in international multi- and bilateral fora by limiting trade/market distortions and to support industry in sectorial trade negotiations and in relevant issues demanding an international debate such as the problem of nonpracticing entities (NPEs).

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1 A European Strategy for Micro- and Nanoelectronic Components and Systems

1.8 Conclusions

As it has done in strategic fields such as aeronautics or space, Europe has no other choice but to engage in an ambitious industrial strategy for micro- and nanoelectronics. his communication proposes such a strategy that is based on a European roadmap for the field. It supports smart regional specialization and promotes close cooperation along the value and innovation chains. he EU, national, and regional financial resources in this field have to be aligned in order to reach the critical mass needed to attract investments and the world best talents. Financial resources will be concentrated on Europe’s leading clusters. he further development of these will enable the whole European businesses, wherever located, to exploit the latest developments in micro- and nanoelectronics. he action plan in Annex 1.A summarizes what should be done.

Annex 1.A

1

2

Main actions:

By:

When:

Pursue the dialogue with stakeholders, set up an Electronics Leaders Group to elaborate and help implement a European Electronics Industrial Strategic Roadmap Promote smart specialization, use of financial instruments foreseen under European Structural Investment Funds (ESI Funds) and HORIZON 2020 Promote, under the Memorandum of Understanding signed with the EIB on KETs, the means to ensure capital investment in production in Europe Adopt Council Regulation and launch of the new tripartite JTI

European Commission, industry

The latest by end 2013

European Commission, member states

Ongoing – to be reinforced

European Investment Bank, Industry

1Q2014

European Commission, member states, industry European Commission, member states, industry

Early 2014

Within the JTI, explore how to simplify and accelerate state aid approvals including through a Project of Common European Interest according to Article 107.3(b) TFEU

3Q13

References

Annex 1.A (Continued)

3

4

Main actions:

By:

When:

Continuous dialogue with key RTOs, regions, and member states to strengthen the micro- and nanoelectronics ecosystem at a European level Within HORIZON 2020 make shared facilities for testing and early experimentation available to start-ups, SME’s, universities, and users Invest in building bricks (education, training); foster a favorable engineering environment in Europe Elaborate and implement a market-pull strategy focused on electronics-intensive products using diverse instruments such as public procurement Elaborate policy actions aimed at establishing a world-level-playing field by limiting trade/market distortions including within the Government and Authorities Meeting on Semiconductor (GAMS)

European Commission, member states, regions, RTOs

On-going – to be reinforced

RTOs, European Commission

1Q2014

Member states, academics

1Q14–4Q20

Industry, member states, regions, European Commission

By 2Q2014

European Commission, industry

Ongoing – to be reinforced

References 1. European Commision (2012)

2.

3.

4.

5.

(COM(2012) 341 final “A European Strategy for Key Enabling Technologies – A Bridge to Growth and Jobs”. European Commision (2012) COM(2012) 582 final ‘A Stronger European Industry for Growth and Economic Recovery’. World Semiconductor Trade Statistics (WSTS) (2012) http://www.wsts.org/ (accessed 22 May 2014). IDATE (2012) Digiworld Report, http://www.idate.org (accessed 22 May 2014). EC http://ec.europa.eu/enterprise/ sectors/ict/files/kets/hlg_report_final_en. pdf (accessed 22 May 2014).

6. ESIA See European Semiconductor

Industry Association (ESIA) Competitiveness Report, 2008 “Mastering Innovation Shaping the Future”, http://www.eeca.eu/images/static_website/ newsroom/publications/ESIA_Broch_ CompReport_Total.pdf 7. International Technology Roadmap for Semiconductors (ITRS) http://www.itrs.net (accessed 22 May 2014). 8. OECD Information Technology Outlook http://www.oecd.org/internet/ieconomy/ oecdinformationtechnologyoutlook2010. htm (accessed 22 May 2014). 9. See Semiconductor Industry Association (SIA) (2009) Maintaining America’s

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Competitive Edge: Government Policies Affecting Semiconductor Industry R&D and Manufacturing Activity, March 2009, http://www.semiconductors.org/ clientuploads/directory/DocumentSIA/ Research%20and%20Technology/ Competitiveness_White_Paper.pdf (accessed 22 May 2014). 10. CATRENE http://www.catrene.org/ (accessed 22 May 2014). 11. Along the International Technology Roadmap for Semiconductors (ITRS) http://www.itrs.net/ (accessed 22 May 2014). 12. European Commision (2011) COM(2011) 809 final “Proposal for a REGULATION OF THE EUROPEAN

13. 14.

15. 16.

PARLIAMENT AND OF THE COUNCIL establishing Horizon 2020 -he Framework Programme for Research and Innovation (2014–2020)”. EC http://s3platform.jrc.ec.europa.eu/ home (accessed 22 May 2014). EC First Interim Evaluation of the ARTEMIS and ENIAC Joint Technology Initiatives, 2010, http://ec.europa.eu/dgs/ information_society/evaluation/rtd/jti/ artemis_and_eniac_evaluation_report_ final.pdf (accessed 22 May 2014). European Commision (2012) See COM(2012) 582 final Section III.A.1.ii). European Commision (2012) COM(2012) 572 final: Second Regulatory Review on Nanomaterials.

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2 Governmental Strategy for the Support of Nanotechnology in Germany Gerd Bachmann and Leif Brand

2.1 Introduction

Nanotechnology is a term which encompasses highly interdisciplinary approaches of the sciences, for example in the field of electronics, optics, life sciences, and materials science, aiming to explore the possibilities of innovation for applications across industrial sectors. he most significant features of nanotechnology are the fabrication of nanoscale structures, following the ongoing trend of miniaturization of technical systems, the controlled assembly of atoms and molecules to create useful/valuable components, the increasing integration of biological diversity, and the elucidation and comprehension of physicochemical phenomena and materials properties by nanoanalytics. Nanotechnology has emerged as a technology focus at the end of the 1980s, using technological solutions that were already available in thin film deposition, ultraprecision engineering, nanoparticle synthesis, and supramolecular chemistry, which all had already reached high standards at that time. Today, nanotechnological R&D is targeted on the investigation, fabrication, and application of material structures smaller than 100 nm. In this size regime, materials show new functional properties that open totally new application perspectives to science and industry. Interdisciplinary approaches for a knowledge-based application of dimension, form, and geometry are necessary to use the nanoscalebased property changes for new products in an intelligent and demand-oriented manner. Further to the need and desire to comprehend the physical function of the single material components, it is strategically important to know the performance when they are assembled into larger systems. For the competitiveness of future-oriented industries, it is relevant to invest in research and applications that are based on the combination of chemical process development, structuredependent property changes, and knowledge-based material generation. R&D and value chain strategies aim at solutions to make energy supply secure, to design smart packaging and sensor technologies for the food sector, to provide care for a rapidly ageing population and medicine of the future, to improve mobility for the aged, and to address the changes in working and living conditions. Environment he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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2 Governmental Strategy for the Support of Nanotechnology in Germany

and climate protection will gain more and more importance as the world is facing global changes. In the future, we will be forced to use available resources with more responsibility and mindfulness. Also, the need to use energy in a more economical way will demand new concepts for the generation, conversion, storage, and use of energy. Nanotechnology as a crosscutting technology will enable mankind to cope with the present and future challenges.

2.2 Future Options

Nanotechnological applications already have an impact on a number of products and processes. A greatly enlarged surface area for the storage of charge carriers is created solely by reducing the size of particles built in battery or capacitor electrodes surfaces, which will enable future high-capacity energy storage systems for electric vehicles or for local energy storage possibilities for wind farms. It is also expected that by controlling the conductivity of battery systems through customized nanostructuring, significantly shorter loading times of batteries will be feasible. At the stage of construction, energy- and resource-saving applications are expected. In the future, multifunctional glass facades will be applied, with dirt-repellent surface structures, and which show a switchable transparency by incorporating nanometer-thin electrically controllable intermediate layers. Hence, the amount of light and heat passing through the panes can be controlled, and direct power generation by coating the glass with transparent photovoltaic layers will be feasible. he incorporated nanostructures are small compared with the visible light wavelength, so that the visible optical properties of the glass façade either are not influenced or can be changed intentionally. Energy savings are also possible by using lightweight components in cars and airplanes. Possible implementations are carbon nanotubes (CNTs). Uniformly dispersed in metals or plastics, entirely new composite materials can be produced that are much lighter than steel, while they show a significantly higher tensile strength. Applications with these composites show a lot of future potential, for example, for lightweight constructions, bridge cables or even for larger blades of wind turbines. Also the development of electronics into ever smaller everyday systems would not have been possible without nanotechnology. Only by the miniaturization of electronic structures energy losses can be minimized and switching speeds of processors can be increased. For example, today’s smartphones are far more powerful than PCs 10 years ago. Smartphones include a powerful camera chip with an aspherical ultraprecise lens in the front, they are a navigation system, and, in the near future, they will be able to monitor our health condition. In the health sector, the influence of nanobiotechnology will increase through the adjustment of surface structures to the usual sizes in biosystems and by the coupling of biological and technical units. hese R&D topics are affecting more and more tailor-made medicine towards personalized medicine, the increase of the efficacy of drugs

2.3

From Basic Science Funding to the Nanotechnology Action Plan

while avoiding unwanted side effects, the early diagnosis of diseases up to reliable point-of-care analysis, or the extension of the lifetime of implants. From a more general perspective, findings of nanotechnology are influencing more and more everyday life.

2.3 From Basic Science Funding to the Nanotechnology Action Plan

Global challenges such as climate change, demographic trends, the spread of common diseases, ensuring world food security, and the finiteness of fossil raw materials and energy sources require sustainable solutions that can be provided only by research, new technologies, and the diffusion of innovations. Nanotechnology as an “enabling technology” sets in at an early stage of the value-added chain. Its commercial relevance is mainly to be seen in its pacemaker function. Hence, the topics and strategies of the German funding activities for nanotechnology have remarkably changed in the last 20 years (Figure 2.1). First projects of the Federal Ministry of Education and Research (BMBF) at the end of the 1980s were mainly basic science oriented. In the mid-1990s, the BMBF changed its viewpoint from seeing nanotechnology not only as a bundle of single technologies but to realise that this discipline as an overlapping and crosscutting field has a broad innovation impetus on nearly all economically important branches and on many societal topics. Newer projects had a much higher application orientation and are performed today in joined industry–science cooperation, in nationally important innovation alliances or in excellence clusters with the main technological stakeholders. he actions related to nanotechnology (funding, public relations, regulation and legislation, topical and political dialogues, etc.) are performed as initiatives in existing BMBF research programs, like materials research, optical technologies, ICT, production research, or other diverse governmental ministry activities in economy, health, or environment. he BMBF project funds have increased more than tenfold since 1990. In 2011, the funding investments amounted to approximately 222 million euro, with a total of 26 departmental divisions involved. Besides supporting research topics, customized accompanying measures are of importance for a successful innovation policy. hese accompanying measures have been started already at the beginning of the 1990s in form of technology forecasting, innovation and technology analysis, and in recent times additionally as project-related risk research. And to build up technology transfer processes from scratch with all necessary actors, competence centers have been used, which rely on powerful networks with members from science and industry. One of these networks was the association of nanotechnology competence centers in Germany (AGeNT-D: Arbeitsgemeinschaft der Nanotechnologie-Kompetenzzentren Deutschlands). Germany is an export-oriented country, which is poor in natural resources and whose competitiveness is strongly dependent on industrial success in future

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2 Governmental Strategy for the Support of Nanotechnology in Germany

Development of Nanotechnology in Germany

BMBF research and funding

Pilot projects New materials, device development, surface technologies

250

Mio. € p.a.

Joint projects Interdisciplinary, for example, nanobiotechnology

Lead innovation

Innovation alliances

NanoMobil, NanoLux, NanoChem, NanoforLife, etc.

InnoCNT, LIB2015, OLED, Organic photovoltaics, etc.

Increasing relevance for applications

200 150 100 50 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

Accompanying measures

Technology scouting, for example fullerenes, magnetoelectronics, scanning probes, CNT, nanobiotechology, self-organisation, etc. Networking/cluster formation Innovation/technogy analysis Public relations Innovation accompanying measures Safety research

Nanotechnology competence centres

AGENT, national contact point

Potential analysis, ITA-prestudy, economic potential, risks of nanomaterials, converging technologies Brochures, nanoTruck, public dialogues Strategy development, market/innovation analysis, public relations, young talent/further education NanoCare, NanoCare2, NanoNature

Figure 2.1 Development of the BMBF funding volume and the related R&D and accompanying measures activities over the last 20 years.

markets. Hence, the government established the HighTech-Strategy in 2006, addressing goals in societal important areas like medicine, climate, energy, environment, mobility, and communication [1]. Germany should be enabled to compete on the future world markets via a coordinated innovation policy. his implies also a learning society and responsible acting. Nanotechnology is seen as an important field for the development of the HighTech-Strategy. Hence, due to its increasing economic and societal importance, to comprehensively use these potentials for Germany and to set up continuous value-added chains, the eight ministries Federal Ministry of Labour and Social Affairs (BMAS), Federal Ministry for Environment (BMUB), Nature Conservation and Nuclear Safety (BMU), Federal Ministry of Food and Agriculture (BMEL), Federal Ministry of Defense (BMVg), Federal Ministry of Health (BMG), Federal Ministry for Economic Affairs and Energy (BMWi), and Federal Ministry for Transportation and digital Infrastructure (BMVI) together with the BMBF have concentrated their activities in the frame of the “Nano-Initiative – Action Plan 2010”), and presented in 2006 a harmonized action framework across all departments, which pooled under one umbrella the different – sometimes even conflicting – approaches from small and medium-sized enterprises (SME) support, new lead innovations, over-enhanced risk research up to a comprehensive dialogue with the public regarding the chances and impacts of nanotechnology [2].

2.3

From Basic Science Funding to the Nanotechnology Action Plan

A responsible innovation policy, especially in nanotechnology as a young field, requires a good and fair cooperation of all stakeholders from research, education, economy, politics, and society. herefore, in order to continue to ensure, through a common platform, the opportunities of nanotechnology through a secure, sustainable, and successful use, the federal government submitted the “Nanotechnology Action Plan 2015” in early 2011 through a further coordinated activity of its interministerial steering group [3]. One of the federal government’s goals is to securely and sustainably boost nanotechnological innovations in order to strengthen the German economy and to provide benefits for the citizens. Hence, several fields of action have been addressed: • Securing of energy supply and protection of environment and climate. he use of nanoscale materials and effects opens up potentials for resourceand energy-efficient products and processes. his includes environmental technologies for the removal and avoidance of noxious substances, procedures of product-integrated environmental protection with optimized energy and material flows as well as efficient methods of conversion, storage, distribution, and use of energy. • Utilizing the possibilities of nanotechnology for health. New methods of prevention, diagnosis, and therapy need to be explored and methods of individualized medicine will gain importance. Nanoparticles provide new technical solutions which help to diagnose diseases earlier, to heal damaged tissue, to enhance the functionality of implants, and to more effectively transport drugs to where they are intended to take effect. • Enabling sustainable agriculture and food safety. Nanotechnological developments can contribute decisively to optimized electronic control methods in areas of intensive agriculture and forestry as well as in animal husbandry. In the field of plant protection, nano-encapsulated substances can be applied considerably more efficiently and in an environmentally friendly manner, preconditioning they fulfill the legal requirements. • Achieving environmental and energy-saving mobility. And it is the goal of the federal government to develop Germany into the lead market for electric mobility. For this purpose, modern electric drives and energy stores must be researched, as well as new materials for lightweight constructions. To reduce energy losses of buildings, nanomaterials for thermochromic house paints, passive and active micro-mirror arrays and switchable insulation materials or phase change materials as latent heat accumulator are necessary. • Optimizing communication technologies and printed electronics. For future communication systems, new quantum physical effects are observed, which provide completely new and inherently absolutely secure access to the transfer of information. Further, applications based on organic or printable electronics need a precise deposition of nanometer-thick multilayers and the printing of organic molecules or nanoparticles requires new concepts for tailor-made pastes, inks, and other printing formulations.

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2.4 Funding Situation 2011

Nanotechnology research and development is funded by the BMBF already for more than 20 years. At the beginning, the projects were mostly basic research related. But with increasing funding activities, a stronger application orientation could be observed. With the joint projects, the networking of the industry, especially SMEs, with the science community was launched. Later on, lead innovations were established as strategic research partnerships of politics, science, and industry in market areas important for Germany, like automotive, optics, chemistry, energy supply and medical devices, intended to secure existing market potentials and to develop new areas of growth. After that, innovation alliances have been created as a new funding instrument, which addresses areas of global market perspective and achieve a significant socioeconomic leverage through a strategically planned long-term perspective. Such innovation alliances were started for organic light-emitting diodes (OLEDs) [4], organic photovoltaics (OPV) [4], Inno.CNTs [5], lithium-ion batteries (LiB 2015) [6], and molecular imaging (MoBiTech) [7]. Further, leading-edge and excellence clusters are funded, which partially work on nanotechnology issues. In the area of institutional funding the research communities of Helmholtz, Leibniz, Max Planck, and Fraunhofer Society are supported. here are also crosscutting activities for targeted support to SMEs (KMUinnovativ, NanoChance) and the promotion of young scientists (NanoMatFutur, NanoFutur). Several accompanying measures are dealing with security issues of nanomaterials and public relations. So citizens can visit the nanoTruck or check the DaNa website www.nanopartikel.info for information about the opportunities and risks of nanotechnology. On behalf of the BMBF, the German nanotechnology National Contact Point (NCP) advises applicants in FP7 calls for proposals. he BMBF project funding accounted in 2011 for approximately 222 million euro, including the accompanying measures. About 18 million euro of these have been used for about 170 projects on prevention and supporting research in nanoCare, nanoNature and innovation accompanying measures. Together with the funding amounts of other governmental departments in height of about 45 million euro, of about 279 million euro spent in the field of institutional funding, of the VW foundation with 5 million euro and of about 80 million euro invested by the individual states, the overall nanotechnology public funding sum was approximately 630 million euro in 2011.

2.5 Patent Applications in Nanotechnology: An International Comparison

here is comprehensive research in Germany and in this context it is worthwhile to consider the transfer from nano-related R&D to commercial products, as research-to-market processes are a typical weakness of the German and more generally of European innovation systems compared to a number of other

2.5

Patent Applications in Nanotechnology: An International Comparison

countries. Statistical analyses of patent applications are acknowledged and valuable indicators for the assessment of scientific trends and developments in specific research areas. Moreover, patenting is basically driven by commercial aspects and thus mainly focuses on research items that are assumed to be economically promising. hey are typically launched to a large fraction by companies and private entities and are of general relevance considering the transfer from research to products and markets. Internationally leading patent authorities such as the United States Patent and Trademark Office (USPTO), the Japan Patent Office (JPO), and the European Patent Office (EPO) have introduced specific patent classification systems to cover nanotechnology-related applications For the current article, the “Worldwide Patent Statistical database” of the EPO and the free online patent service “esp@cenet” were selected for evaluation, giving access to the data of more than 90 patent authorities. Nanotechnology-related applications are recorded in class B82Y of the Cooperative Patent Classification system (CPC). Country assignments are achieved based on the first priority application. he global number of patent applications in nanotechnology has been increasing about tenfold over the past two decades. he EPO’s worldwide database meanwhile counts a total of around 150 000 patent documents since 1972. However, for the past 10 years, a level of saturation at about 12 000 per year has been reached. An international comparison of nano-related patents applied since 1972 shows the United States and Japan in leading positions with shares of 46% and 26%. Germany is following as the main European contributor with 8% followed by France (4%) and the United Kingdom (4%). he European Union (EU-27) as a whole contributes with a 20% share (Figure 2.2). he development since 2000 in Germany and some other countries is shown in Figures 2.3 and 2.4. Despite the fact that France is catching up on the per capita basis, Germany is by far the dominating European contributor, however, on the global scale ranging significantly behind the United States and Japan. Moreover, Korea in particular has shown considerably increasing application numbers since the middle of the last decade and meanwhile has caught up, displacing Germany Patent applications (countries); ~150 000 in total (since 1972) UK 4%

Korea 4%

Others 8%

France 4%

USA 46%

Germany 8% Japan 26%

Figure 2.2 Shares of nano-related patent applications for different countries since 1972.

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Nanotechnology patent applications: major contributors 7000 6000 USA

5000

Japan EU-27

4000

Korea

3000

China Germany

2000

France UK

1000 0 2000 Figure 2.3

25

2002

2004

2006

2008

2010

Temporal development of patent applications for selected countries since 2000.

Nanotechnology patent applications per 1 million inhabitants

20

USA

15

Japan EU-27 Korea China Germany

10

France

5 0 2000

UK

2002

2004

2006

2008

2010

Figure 2.4 Temporal development of patent applications per capita for selected countries since 2000.

from the third position. hat holds even more for the per capita view on the application numbers normalized to the countries’ population. However, the number of emerging countries considerably contributing to nano-related patenting is still quite low and even China has not yet reached a significant level (Figure 2.4). In conclusion, the performed patent analyses give hints to Germany’s nanotechnology scene ranging only in a stable midfield position with respect to the technology-to-market transfer process. he clear distance to the United States and Japan remains obvious. he situation is thus similar to numerous other technology areas with Germany and Europe having excellent positions in research but lagging behind their competitors in commercialization. In this context, it is a declared objective of the upcoming European Framework Programme “Horizon 2020” to improve this situation and tackle societal challenges even by bridging the gap between research and markets [8].

2.6

Innovation Accompanying Measures

2.6 Innovation Accompanying Measures 2.6.1 Outreach and Citizen Dialogues

he comprehensive information of the public about the pros and cons of nanotechnological materials is important in order to objectify the discussion on the application of nanotechnology. With regard to everyday products, it is important to make consumers more familiar with nanoproducts and to explain how and why nanoscale material is used. herefore, the properties of products with nanoscale components need to be properly imparted and the handling required for safe use needs to be clearly explained. his is a possible way to ensure an objective risk discussion, which avoids both global promises and the global rejection of synthetic nanomaterials. Surveys on the image of nanotechnology among the population as well as public discourses and offers regarding risk communication with the involvement of politics, science, economy and stakeholders help to facilitate future orientation and contribute to the responsible handling of nanotechnology. New insights are provided via trade media, internet portals, publications, brochures, and exhibitions. One focus of activity is on attracting potential young researchers. On www.nanoreisen.de the BMBF provides virtual online trips to the smallest known dimensions of our cosmos. Nanotechnology increasingly conquers even big technology museums, such as the “Deutsche Museum” (German Museum) in Munich with permanent exhibitions in the “New Technologies Center.” According to the motto “Hightech from the Nano-cosmos”, the nanoTruck initiative of the BMBF allows the direct experiencing of this future technology. On its tour through Germany, the nanoTruck reaches in particular young people and informs about chances, interesting career paths and exciting fields of work on nanotechnology as well as about new processes, products, risks, and application prospects. he aim of the nanoTruck initiative is to take nanotechnology out of the laboratories and to bring it to the people directly on the spot. he nanoTruck reaches over 100 000 visitors per year [9]. In interviews, there is also room for discussion about fears and constraints. Furthermore, brochures, internet portals, CDs, videos, stakeholder dialogues, consumer conferences, and educational supplements were used to explain the technological details to citizens, to give appropriate information to pupils, and to highlight qualification possibilities. In addition, on behalf of the BMBF and together with regional partners, dialogue events “citizens meet experts” are performed, where the citizens have the opportunity to discuss together with experts, to get answers on their open questions and to bring in their own wishes and suggestions for the future work in this field. Besides the classical project funding performed since some decades, an increase of technology transfer activities by initiating branch-related dialogues

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was started. hese branch-related dialogues are targeting mainly on SMEs in traditional fields, which have not really realized the new chances by using nanotechnological approaches. 2.6.2 Chances – Risks Communication

he related activities aim to contribute to the clarification of the possible impacts of nanomaterials on humans and environment, to research their potential risks and, if required, to establish the respective risk management. he main objective is always to carefully weigh the risks and impacts. he support measures aim at nanotechnologies that are safe and sustainable. Applications of nanotechnology should not endanger the environment and health. With the transfer of scientific knowledge into economic applications, aspects of the economic exploitation are combined with solution paths for the responsible use, necessary regulatory measures and with early involvement of the wider community through public discourses and other communication activities. As part of that, the BMBF has heavily increased its funding engagement for the investigation of (eco-) toxicological influences with the project-cluster NanoCare in the last years. But a responsible and secure use of nanotechnology globally will only be reachable by an international harmonization of product and security standards. herefore, the government supports activities targeting international coordination, like the nanotechnology action plan of the EU, the “international dialogue on responsible nanotechnology” or the activities of the Organization for Economic Cooperation and Development (OECD) with the Working Party on Nanotechnology (WPN) and Working Party on Manufactured Nanomaterials (WPMN). Already in 2006 within the framework of the “Nano-Initiative – Action Plan 2010,” the BMU has appointed the NanoCommission of the German Federal Government. he NanoCommission conducted the NanoDialogue, a stakeholder-dialogue, involving science, economy, politics, churches, and environmental and consumer associations [10]. he aim of the NanoCare dialogues was to impart current research results of BMBF projects on risk research in nanotechnology to citizens. Experts involved in the projects are available for the citizens for a direct exchange and for answering their questions. 2.6.3 Database for Nanomaterials

he BMBF support of nano-risk research started already in 2006. Priorities of these projects are comprehensive studies on the impact of synthetic nanomaterials on humans and the environment and the research for the responsible use of nanotechnology. Results of the NanoCare projects indicate that nanosize of materials alone is no basis for the risk assessment. In fact, nanomaterials can show different toxicological potentials depending on parameters like structure, morphology, chemical composition, and concentration. hus, potential risks

2.6

Innovation Accompanying Measures

must be studied on a case-to-case basis and the result must be verified by longterm studies. he joint project “Nanostructured Materials – health, exposure and material properties” (NanoGEM) investigated that “nano” does not automatically mean toxic. Besides, the size many other factors are responsible for whether a material has adverse health effects or not. herefore, it is important to understand that “risk” is defined via a combination of toxicology (toxicity) and exposure (i.e., the contact path). To support customers with reliable information on nanomaterials and nanotechnology, the BMBF started the DaNa project – acquisition, evaluation, and public-oriented presentation of society-relevant data and findings relating to nanomaterials. In an interdisciplinary approach of human toxicology, environmental toxicology, biology, physics, chemistry, and sociology, the DaNa project provides process results of research on nanomaterials and their influence on humans and the environment. For this purpose, results of completed and running projects are processed; scientific publications, reports, and latest news on human and environmental toxicology are evaluated; and the state of knowledge is wrapped-up in a knowledge database (www.nanopartikel.info). his portal also provides the layman understandable information and enables the exchange with scientists. 2.6.4 Education

he federal government supports also measure to secure the basis for well-trained specialist staff and an active, excellent research landscape, targeting on promoting young talents and creating competences and infrastructures. he innovative strength of nano-enterprises – in particular of SME – not only depends on the adequate availability of skilled staff, but to a great extent also on their targeted education and training. Educational offerings on nano are increasingly provided in the fields of physics, chemistry, materials sciences/materials, electrical engineering/informatics, and engineering sciences. An overview of nano-educational offerings provided by the BMBF is accessible via the internet portal www.nanobildungslandschaften.de. Currently, about every second person employed in nano-enterprises is a university graduate. Skilled workers account for 20% of the staff and the trend is rising. Small and medium-sized nanotechnology enterprises expect a demand of about 15 000 additional employees in the next 5 years. In future, the number of companies involved and the product diversity will further increase [11]. Already since 2002, young future scientists, qualified in nanotechnology and materials technology, have been funded by the BMBF through the competition “NanoFutur,” which is now continued as “NanoMatFutur.” Selected award winners get the opportunity to establish their own junior groups over a period of 6 years and to advance research works. With this, they qualify for a scientific career. And in their working groups, they train engineers and natural scientists both for industrial and academic careers.

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2.7 Involved Organizations

Germany is the leading nanotechnology nation in Europe and, comparing the commercial implementation worldwide, it is ranking third behind the United States and Japan. In Germany, more than 1000 enterprises are dealing with the development and marketing of nanotechnological products, procedures, and services on different stages of the value added chain – with tendency to rise. he percentage of innovative SME and start-ups is around 80%. More than 60 000 jobs in industry and around 10 000 jobs at universities and in research institutes in Germany depend on nanotechnology. In 2010, the turnover in nanotechnology generated by Germany-based enterprises worldwide can be estimated to around 13 billion euro. he annual research expenditure of the nano-related companies in Germany is over 1 billion euro, exceeding the sum of public funding significantly. he research based on the turnover is above average in nanotechnology, with around 10%, even for the limited area of nanomaterials, in which a great deal of attention is put into researching the possible effects on human health and the environment. German enterprises are manufacturers in the field of nanomaterials, nanotools, nanoanalytics, and equipment for the operation of nanotools (e.g., vacuum and clean room technology, plasma sources, etc.), manufacturers and users of nanooptimized components and systems as well as supplier of services in the field of consulting, contract coating, technology transfer, third-party analysis, and research. Here, almost all important branches of industries are represented: optics, electronics, structural engineering, medicine/pharmaceutics, chemical industry, textile, mechanical engineering, security technology, environmental technology, biotechnology, and consumer products. Usually, German enterprises are characterized by high export orientation [11]. In the field of basic research, the institutes of the Max-Planck Society and the Helmholtz Association belong to the world’s leading institutions in the fields of nanotechnology. In the field of key technologies, the activities of the Helmholtz Association aim at the integration of nano- and microsystems. Several Max-Planck Institutes have already been working for years in the fields of nanomaterials, supramolecular systems or characterization methods. Also the Fraunhofer Society and the scientific community Leibniz Association are well positioned and attentively monitor the application-relevant implementation activities. he Leibniz Gemeinschaft can rely on numerous institutes with excellent results in research into nanomaterials, surfaces, and opto- and nanoelectronic properties. And the Fraunhofer Nanotechnology Alliance comprises 20 institutes working on nano-related topics. Moreover, experts of nearly all German universities with technical–scientific focus are working on nanotechnological issues. Here, both applications of nanotechnology and their impact on humans and environment are surveyed. Within the framework of the excellence initiative of government and state, future concepts, so-called excellence clusters and postgraduate research programmes, are funded, which contribute to profound nanotechnology-relevant education and excellent research results.

2.8

Cooperation of the Governmental Bodies

Also departmental research is focused on nanotechnology. Safety research is particularly significant. For this reason, the Federal Institute for Occupational Safety and Health (BAuA) is working on projects in the field of nanotechnology and worker protection. he Federal Institute for Risk Assessment (BfR) deals with the evaluation of possible health impacts of the application of nanotechnology. he Federal Environment Office (UBA) works on environmental and health-related aspects of nanotechnology. his includes both the consideration and evaluation of the environmental compatibility of nanotechnological applications and the possible risks for environment and health. he Julius-Kühn-Institute (JKI) deals with the issue of supporting agricultural innovations in the nanotechnological field through risk assessments, and the Johann-Heinrich-von-hünen-Institute (vTI), inter alia, with nanostructured catalysts for the highly selective conversion of renewable raw materials into base and recyclable material for industrial purposes. he Max Rubner Institute (MRI) works on nanomaterials in the food sector. Nanoscale carrier systems for bioactive substances and their behavior during food processing and under gastrointestinal conditions are surveyed as well as the migration of nanoparticles from food contacting material, the influence of the particle size on the bioavailability and on the methods of acquisition as well as the characterization of nanoparticles in foodstuffs. he Federal Institute for Materials Research and Testing (BAM) makes decisive contributions by developing test methods and reference materials. With the development of measuring devices and procedures, the Federal Institute of Physics and Metrology (PTB), the national metrology institute, is responsible for the standardization of metrology in Germany and ensures the traceability of measuring results to the International System of Units (SI).

2.8 Cooperation of the Governmental Bodies

Successful innovation depends on good cooperation of all actors. Due to its versatile fields of application, nanotechnology is anchored in different departments of the federal government. his requires coordinated procedures, which take into consideration the different aspects of nanotechnology from research over commercial utilization up to the protection of the consumer, the environment, and the workplace, without resulting in doublings or unanswered questions being left. One focus of the coordinated cooperation is the regulation of nanomaterial-containing products. It is currently being examined to which extent the European and national legal frameworks need to be adapted to the use of nanomaterials in products in order to ensure consumer safety. Based on the results of the nano-risk research, the political challenge is to create appropriate regulatory frameworks to ensure safe and responsible use of nanomaterials, but without limiting innovation and the international competitiveness of the industry too much.

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To ensure the coordination within the federal government, an interministerial steering committee was established, which ensures coordination and cooperation. Information exchange, debate about the general strategy and the discussion about regulation and legislation is performed by regularly holding meetings with the responsible persons of the involved departments. he particular funding activities are managed by the individual working units of the governmental ministries independently. Most recently, another information exchange network formed with representatives of the ministries of the individual states, which inform each other about their activities, but also to explore, whether potential for joint activities exists, for example for coordinated showcasing at international trade fairs, or for joint funding strategies of the federal government and the individual states.

2.9 International Cooperation

Norms and standards can open up markets for innovative technologies and provide market transparency. hus, they contribute directly to an increase in competitiveness and to the innovative strength of the enterprises involved. he increasing research activities, product developments, and regulatory measures not only require standard definitions and terminology but also internationally agreed methods of measurement and processing methods. On the international level, the ISO (International Standardization Organization) and the IEC (International Electrotechnical Commission) are dealing with the standardization of nanotechnology with their committees ISO/TC 229 “Nanotechnologies” and IEC/TC 113 “Nanotechnology Standardization for Electrical and Electronic Products and Systems.” On the European level CEN (European Committee for Standardization) and/or CENELEC (European Committee for Electrotechnical Standardization) are carrying out work in their technical committee CEN/TC 352 “Nanotechnologies.” And on the national level DIN (German Institute for Standardization) and/or DKE (German Commission for Electrical, Electronic and Information Technologies of DIN) closely cooperate with the ISO/IECcommittees and introduce the respective European and German interest into the international committees. Germany has accepted to manage the IEC/TC 113 secretariat. For the industrial exploitation it is important to reach international agreements relating to the standardization, the safe handling, and use of nanotechnology in the regulatory bodies of the OECD, ISO, and EU. he federal government is involved in these international bodies by supporting the active involvement of German experts in the standardization committees. Topics in these standardization committees increasingly affect the measurement technology for various applications, whether in the determination of the particle size, the acquisition of toxicological effects, or for the chemical material specification.

2.9

International Cooperation

2.9.1 Research Marketing

Trade fairs with significantly international appeal contribute decisively to the increased visibility of German nanotechnology. he concentrated appearance on joint German exhibition booths (German Area of the BMBF, in particular for young enterprises and research groups, and the German Pavilion of the BMWi, for industrially oriented presentations) turned out to be successful. In the frame of the research marketing “Research in Germany – Land of Ideas,” R&D results are showcased to support SMEs on international markets, to support brain-gain effects by attracting good young people and to initiate international cooperation with the ability to strengthen existing bilateral complementary competences. 2.9.2 Activities within the Framework of the European Union

International collaborations are important future-oriented activities, both within the EU and beyond. Particular topics of importance, like standards, norms, or regulation cannot be solely addressed nationally. herefore, the BMBF is actively involved in the relevant processes and provides, for example, important facts on risk research and data for risk assessment. he integration into the European Research Area is intended to be further expanded by a strong German participation in the new EU research framework program Horizon 2020, which addresses nanotechnology as a key technology as well. Apart from the funding programmes of the federal government, the research framework programme of the EU is the most important source for publically financed research funding in the field of nanotechnology in Germany. he total funding amount of the 6th Research Framework Programme amounted to altogether almost 1.4 billion euro. Since 2007, more than 1.1 billion euro have been invested in the field of nanotechnology within the context of the 7th Research Framework Programme. A significant part of this amount went to enterprises and academic research institutions in Germany. In the field of industrial collaborative research, for example, the share of German partners in the funding amount was always about 20%. In 2014 the European Commission started the research programme “Horizon 2020”. he federal government will support the commission in the implementation of nanotechnology via networking in national activities for the joint research of chances and risks of nanotechnology, participation in transnational funding measures for nanotechnology, for example, ERA-NET EuroNanoMed and the ERA-NET SIINN (Safe Implementation of Innovative Nanoscience and Nanotechnology), cooperation in the identification of research topics of national and European relevance, and contributions for the improvement of societal framework conditions and the reduction of innovation barriers. he aim is the establishment of a responsible, integrated and economy-friendly innovation environment for nanotechnology in Europe.

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2.10 Activities within the Framework of the Organization for Economic Cooperation and Development (OECD)

In 2006, the WPMN of the Chemicals Committee and Working Party on Chemicals, Pesticides, and Biotechnology of the OECD was established. Aim of the Working Party is to deal with safety issues around nanomaterials within the framework of international cooperation. he Working Party consists of more than 100 experts of different stakeholders from OECD-member states, but also of nonmember states and experts of organizations like the UNEP, WHO, ISO, BIAC, TUAC, and environmental authorities. One of the topical fields of the WPMN is the “Sponsorship Programme.” Here, technical dossiers on representative nanomaterials are prepared under the responsibility of the states involved. Germany, together with France, is the responsible nation for the processing of titan oxide within the Sponsorship Programme and, in addition, contributes to the research on environmental risks caused by nanosilver. Moreover, data on zinc oxide, aluminum oxide, and cerium oxide as well as on CNTs are provided. In the WPMN, Germany is represented by the BMU. In 2007, the OECD established the WPN under the umbrella of the Committee for Scientific and Technological Policy (CSTP). Members are representatives from 26 nations, as well as from the EU, ISO, BRIC, and BIAC. he WPN acts as policy guidance committee on issues regarding the responsible global development of nanotechnology. In the WPN, topics such as scientific and economic indicators, analysis of national policies, identification of innovation barriers and challenges for the implementation of results, contributions of nanotechnology to cope with global problems, international cooperation, education, public dialogue, and politics forums are discussed with regard to internationally important political matters. In the WPN, Germany is represented by the BMBF.

References 1. BMBF – Federal Ministry of Educa-

tion and Research, Germany (2006) HighTech-Strategy for Germany. 2. BMBF – Federal Ministry of Education and Research, Germany (2006) Nano-Initiative – Action Plan 2010. 3. BMBF – Federal Ministry of Education and Research, Germany (2011) Action Plan Nanotechnology 2015. 4. Bundesministerium für Bildung und Forschung (2012) Organische Elektronik – Hightech aus Kunststoff, www.bmbf.de/de/16267.php (accessed 21 May 2014).

5. Inno.CNT www.inno-cnt.de (accessed 21

May 2014). 6. Bundesministerium für Bildung und

Forschung (2013) Innovationsallianz LIB, www.bmbf.de/de/11828.php (accessed 21 May 2014). 7. Bundesministerium für Bildung und Forschung (2007) Molekulare Bildgebung – Bilder für ein gesundes Leben, www.bmbf.de/de/11267.php (accessed 21 May 2014) 8. European Commission ec.europa.eu/research/horizon2020 (accessed 21 May 2014).

References 9. nano Truck www.nanotruck.de (accessed

21 May 2014). 10. Bundesministerium für Umwelt www.bmub.de/themen/ gesundheitchemikalien/nanotechnologie (accessed 21 May 2014).

11. BMBF – Federal Ministry of Educa-

tion and Research, Germany (2011) nanoDE-Report 2011.

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3 Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region Lerwen Liu

3.1 Introduction

he genesis of nanotechnology can be traced back to Richard Feynman’s famous lecture “here’s Plenty of Room at the Bottom” [1], which he delivered to the American Physical Society in 1959. his lecture has inspired scientists and engineers worldwide to develop technologies to image and manipulate atom and molecules, and to fabricate structures and devices atom by atom, molecule by molecule. Today nanotechnology is commonly defined as the understanding and control of matter at nanoscale dimensions between approximately 1 and 100 nm, where unique phenomena enable novel applications. Encompassing nanoscale science, engineering, and technology, nanotechnology involves imaging, measuring, modeling, manipulating, and fabricating matter at this scale. A nanometer is one-billionth of a meter. A DNA molecule is about 2.2 nm wide, the typical size of bacteria is in the order of 1 000 nm (1 μm), and the size of human hair is about 100 μm. Nanotechnology is revolutionizing how we make things, and it can change the way we live. It is able to transform multiple industries, including aerospace, agriculture, automotive, chemical, energy and environment, food, information and communication, medicine and health care, security, and transportation. Nanotechnology offers so many possibilities, such as providing cheap and clean energy; clean water; lighter and stronger materials; faster, more powerful, and energy-efficient computers; an exponential increase in information storage capacity and transmission speed; lotus-like self-cleaning surfaces; butterfly-wing structural colors; the reduction or elimination of pollution; and early detection and treatment for cancer and other diseases. he word “nano-technology” was coined in 1974 by Norio Taniguchi (a professor at the Tokyo Science University in Japan) where he defined the process that consists of the processing of separation, consolidation, and deformation of materials by one atom or one molecule. [2]. Manufacturing (in Japanese Monotsukuri, meaning making things) has been a focus of the Japanese industrial policy. It is known that nanotechnology enables the transformation of advanced manufacturing to make better, cheaper, and greener products. For the last two decades, Japan The Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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3 Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region

has committed itself to the use of nanotechnology in manufacturing to stay ahead of its competitors. Today, economies in Asia including South Korea, Taiwan, and mainland China are making significant progress in adopting nanotechnology in their manufacturing. And this contributes to the global dynamics of competitive manufacturing towards better, greener, and cheaper products. Since 1999, there have been significant changes in nanotechnology development worldwide. he announcement of the US National Nanotechnology Initiative (NNI) on 21 January 2000 created a strong response from the rest of the world, with a number of countries placing nanotechnology as a priority area in their science and technology (S&T) policy. Figure 3.1 shows the timeline of NNIs and programs in the 15 economies reviewed in this article with reference to the US NNI [3] and the European Commission’s (EC’s) 6th Framework Programme (FP6) where “Nanotechnologies and Nanosciences, Knowledge-based Multifunctional Materials, New Production Processes and Devices” was included as one of the seven priority thematic areas [4]. In 2001, Japan, China, and New Zealand began major programs focusing on nanomaterials (NMs). In the following year, South Korea, Taiwan, hailand, Australia, Hong Kong, and Vietnam launched national and regional nanotechnology initiatives. Subsequently, in 2006, Iran launched its national nanotech initiative program, followed by Malaysia and Indonesia. In 2013, countries such as Japan, Malaysia, and hailand received significant increase (up to 50%) in Nanotech R&D funding. As funding has experienced a significant increase over the past decade, nanotechnology is becoming mature for commercialization. he Russian government, with intentions to take a leadership position, launched a 10-year, USD 5 billion nanotechnology commercialization initiative in September 2007 managed by the Russian Corporation of Nanotechnologies (RUSNANO) [5]. China has built the Nanopolis Suzhou with USD 1.6 billion, an ecosystem to accelerate the commercialization and adoption of nanotechnology in China, and advance Chinese manufacturing and promote innovation. Asian nanotechnology initiatives have evolved towards becoming application and commercialization driven. To ensure the sustainable development of nanotechnology, nanosafety initiatives have been established in Taiwan, Australia, Japan, South Korea, Iran, and hailand; among them Taiwan and hailand allocated as much as 10% of their total nanotech funding to Nano EHS (Environment, Health and Safety) and standardization. his article does not intend to provide a review of technical capabilities. Instead, it provides an overview of those areas that ensure sustainable development of nanotechnology and industry leadership in 15 economies in the Asia-Pacific (AP) region, focusing on government policy and strategy, funding commitment and infrastructure, and R&D and commercialization. For detailed information of review in each economy in the AP region, including topics of education and outreach, standardization, and risk management, please refer to our book titled “Emerging Nanotechnology Power: Nanotechnology R&D and Business Trends in the Asia Pacific Rim” published by World Scientific. It can be ordered online at www.worldscibooks.com/nanosci/7224.html.

3.1

Introduction

39

Nanotechnology national initiatives timeline in Asia-Pacific region EU 6th Framework (2002–2006) EU 7th Framework (2007–2013) EU Nanotech action plan (2010–2014) Taiwan NNP Phase I (2003–2008) Phase II (2009–2014) Thailand NANOTEC established Hong Kong INMT NAMI (2006–2011) Vietnam NIIP Singapore A*STAR program Indonesia NNNDP started Nanotech fund (2009–) RUSNANO established (2007–2015)

Japan ATP USD 250 million/10Y

1992

2001

2002

2003

2004–5

2006

2007

2008–9

2010

2011

2012

2015

2020

Malaysia 9th plan (2006–2010)-NNIM NanoMalaysia (2012–) NND (2009–) INIC established NNI – 2006 10-year national plan (2005–2015) Australia nanoVic and ARC COE NNS (2007–2011) India Nano mission (2007) India NSTI Korea KNNI phase I (2001–2005) Phase III (2011–2020) Phase II first period (2006–2010) New Zealand MDIAMN Phase II (2007–2014) 11th five year plan (2006–2010) 12th five year plan (2011–2015) China 10th five year plan Japan 2nd basic plan NMP US NNI program setup

3rd basic plan (2006–2010)

Australia: NanoVic - Nanotechnology Victoria ARC COE - Australian Research Council Centre of Excellence European Commission: EU - European Union Hong Kong: INMT - Institute of NanoMaterials and NanoTechnology NAMI - Nano and Advanced Materials Institute India: NSTI - Nanoscience and Technology Initiative Indonesia: NNNDP - National Nanoscience and Nanotechnology Development Platform Iran: INIC - Iran Nanotechnology Initiative Council Japan: ATP - Atom Technology Program NMP - Nanotechnology and Materials Program Korea: KNNI - Korean National Nanotechnology Initiative

4th basic plan (2011–2015)

Malaysia: NNIM - National Nanotechnology Initiatives of NND – National Nanotech Directorate New Zealand: MDIAMN - Macdiarmid Institute for Advanced Materials and Nanotechnology Russia: RUSNANO - Russian Corporation of Nanotechnologies Singapore: A*STAR - Agency for Science, Technology and Research NNP - National Nanotechnology Program Taiwan: NNP - National Nanotechnology Program Thailand: NANOTEC - National Nanotechnology Center United States: NNI - National Nanotechnology Initiative Vietnam: NIIP - Nanotechnology Infrastructure Initiative and Programs

Figure 3.1 Major government nanotechnology initiatives timeline in the Asia-Pacific region. (The authors’ design and all the information is based on NanoGlobe research.)

3 Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region

3.2 Public Investments

here have been significant changes in the policy of S&T in AP economies since the announcement of the US NNI. Governments in the AP region started to place nanotechnology as one of the priority areas in their S&T policies and planned dedicated national nanotechnology programs (NNPs). he NNI was very timely announced as Japan and China were in the midst of planning their second S&T Basic Plan and 10th Five Year Plan, respectively. US government funding in nanotechnology has reached about USD 1.5 billion in 2009 [3] (it continues to rise), more than 10 times the amount in 1997 [6]. his order of magnitude of increase in government funding is typical in economies in Asia, Europe, and other parts of the world in the last 10 years. Japan was the first country in the world to start a major 10-year nanotechnology program (the Atom Technology Program) in 1992 with the amount of about USD 250 million, and was the largest government investor in nanotechnology R&D until 2003. Japan’s nanotechnology development is on par with other world leaders such as the United States and Germany. Figure 3.2 shows the nanotechnology government funding comparison for Japan, United States, and Germany during 2001–2008. Japan started the Nanotechnology and Materials Program (NMP) in 2001 when its second Basic S&T Plan began and nanotechnology was identified as one of the four priority areas (including life science, information technology, environment, and nanotechnology). here was a drop in funding in Japan from 2006 due to a new definition of nanotechnology which excluded some of the university programs [7]. he Japanese government has been investing heavily in nanotechnology and its funding per capita is the highest among the world’s top three nanotechnology players. Figure 3.3 shows the comparison in nanotechnology public investment per capita among Germany, Japan, and United States during the period 2001–2008. 1600 1400 1200 Million USD

40

1000

Germany

800

Japan

600

USA Japan (realistic)

400 200 0

2001 2002 2003 2004 2005 2006 2007 2008

Figure 3.2 Nanotechnology government funding comparison among the three largest economies during 2001–2008. (Emerging Nanotechnology Power: Nanotechnology R&D and Business Trends in the Asia Pacific Rim, World Scientific.)

3.2

Public Investments

10.0 9.0 8.0 7.0 6.0

Germany

5.0

Japan

4.0

USA

3.0

Japan (realistic)

2.0 1.0 0.0 2001 2002 2003 2004 2005 2006 2007 2008

Figure 3.3 Nanotechnology government funding per capita comparison among the three largest economies during 2001–2008. (Emerging Nanotechnology Power: Nanotechnology R&D and Business Trends in the Asia Pacific Rim, World Scientific.)

South Korea started its Korea National Nanotechnology Initiative (KNNI) in 2001 and committed 2.391 trillion won (USD 2 billion) over the period 2001–2010. After Phase I (2001–2005) of the KNNI, the South Korean government relaunched Phase II, which will continue until 2015. In 2010, the government set up the National Nanotechnology Policy Center to ensure South Korea’s global leadership in nanotechnology advancement. South Korea has entered Phase III (2011–2020) in its national nanotech program which is now market driven with clear strategic focused areas including information technology (IT) devices; nanobio; manufacturing, metrology and instruments; energy/environment; and NMs. he recent Nano-Convergence 2020 Initiative committed another almost half a billion USD over the next 9-year period to position South Korea to become a world leader in creating new products and new industries enabled by nanotechnology by 2020. South Korea aims to join the world’s top three nations in global nanotechnology competitiveness by 2015. Taiwan is another ambitious player. It launched its first phase of the Taiwanese NNP in 2003 with a total budget of about USD 550 million over 6 years. Taiwan is now in its Phase II (2009–2014) of NNI; different from Phase I, it has shifted the weight of different areas with the total funding of about USD 600 million, for example, a little more on industrialization, and emphasizing more on strategic projects and advanced research. he aggressive building of infrastructure has been reflected in the launch of major nanotechnology infrastructure building programs for South Korea and Taiwan in 2002 and 2003, respectively. he world’s most populated country China spent RMB 2–2.5 billion (USD 250–300 million) in the last Five Year Plan (2001–2005), which is a 10-fold increase from the 1990s. China’s R&D expenditure reached 2% GDP (gross domestic product) in the 11th Five Year Plan (2006–2010), which is double of that in the previous Five Year Plan and will increase further to 2.5% during the current 12th Five Year Plan (2011–2015). Nanotechnology is one of the four

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main basic science research areas, which include protein research, quantum manipulation research, and growth and reproduction research. Regional governments, such as Suzhou city, have identified that nanotechnology enables competitiveness of their manufacturing industries and creates new industries. Suzhou Industry Park (SIP, a joint venture between Singapore and Suzhou governments) launched the Nanopolis Suzhou initiative in 2010 and it completed Phase I in January 2013. By 2015, it will become the world’s biggest nanotech city with investment over USD 1.6 billion. As one of the fastest growing economies, India launched a special Nano Science and Technology Initiative (NSTI) in October 2001 by the Department of Science and Technology (DST) and subsequently the Mission on Nano S&T (Nano-Mission) was launched in mid-2007 with an allocation of USD 200 million for 5 years focusing on basic research, infrastructure development, commercialization, education, and international collaboration. Other funding agencies in India have launched nanotech R&D program, especially the Department of Information Technology launched a USD 25 million program in 2010. Iran launched its NNI in 2006, and has invested USD 100 million in nanotech R&D in the past 5 years. Iran aims to become the top 15 countries in the world in nanotech by 2020 in all rings of value chain including scientific publication, innovation, industry development, and wealth generation. New Zealand’s nanotechnology initiative is led by the MacDiarmid Institute for Advanced Materials and Nanotechnology, which was granted NZD 4.7 million per year over 6 years from 2001 plus a capital start-up grant of NZD 10 million. he institute is joined by the major research institutions in New Zealand and comprises over 40 principal investigators, 30 postdoctoral fellows, 80 PhD, and 20 Master students. In Australia, the Victoria State Government, with three major state universities including Monash University, Swinburne University of Technology, and RMIT University, launched an AUD 12 million Nanotechnology Victoria initiative (NanoVic) in 2002. he Australian National Nanotechnology Strategy (NNS) was announced in May 2007 with AUD 21.5 million over 4 years, aiming to focus on initiatives including health, safety and environment, public awareness and engagement, measurement, international engagement, and industry activities. he Australian Office of Nanotechnology (AON), based at the Department of Innovation, Industry, Science and Research (DIISR), coordinates the implementation of the NNS. he Hong Kong Innovation and Technology Commission (ITC) launched two strategic nanotechnology centers in 2003. One is the Institute of NanoMaterials and Nanotechnology (INMT) located at the Hong Kong University of Science and Technology (HKUST) and was funded with HKD 100 million for 4 years. he other is the Nanotechnology Center for Functional and Intelligent Textiles and Apparel (NTC) at the Hong Kong Polytechnic University (PolyU) with a total budget of HKD 14.7 million for 3 years. In December 2004, ITC further announced a more aggressive R&D initiative by setting up four strategic R&D

3.2

Public Investments

centers with nanotechnology selected as one of the focused areas. he Nanotechnology and Advanced Materials Institute (NAMI) was set up in 2006 with a total funding of HKD 400 million for 5 years. NAMI serves as an open R&D platform for Hong Kong in conducting coordinated, market-driven, and demand-led nanotechnology and advanced materials development. City-state Singapore’s nanotechnology strategy is led by the Economic Development Board (EDB) in coordination with other sister funding agencies such as the Agency for Science, Technology and Research (A*STAR) and universities. In 2002, the National University of Singapore (NUS) started its nanotechnology initiative called NUS Nanoscience and Nanotechnology Institute (NUSNNI) aimed at developing research, human capital, and long-term research capabilities. NUSNNI serves as a platform to coordinate interdisciplinary research activities and set research strategies. he Nanyang Technology University (NTU) started its nanotechnology initiative in 2005 called Nanocluster, which is a network of scientists and facilities to support nanofabrication, characterization, and exploitation of nanotechnology applications. A*STAR started in 2006 Polymer & Molecular Electronics program involving both NTU and NUS in addition to A*STAR research institutes. More aggressive programs launched in 2011 on Power Electronics and Printed Electronics (the size of about USD 15 million per program) to build up cutting edge capabilities for preparing the emerging industries. hailand leads the Association of Southeast Asia Nations (ASEAN) countries with the set-up of its National Nanotechnology Center (NANOTEC) in August 2003 committing USD 25 million over 2004–2008 from the National Science and Technology Development Agency (NSTDA). hailand’s most recent National Nanotechnology Policy 2012–2021 with the vision of building capabilities towards sustainable development to include agriculture, environmental conservation, energy, health care, and manufacturing. Vietnamese Ministry of Science and Technology (MOST) launched its NNP in December 2003, focusing on building world-class research institutions, education, and infrastructure, as well as strategic research areas. A new national Center of Excellence (COE) called Molecular and NanoArchitectures Center was set up in 2011 at Vietnam National University (Ho-Chi Minh City) to attract world’s top scientists for research in Vietnam. he Malaysian National Nanotechnology Initiative (NNIM) was officially launched in September 2006 by the then Deputy Prime Minister (who became the Prime Minister in April 2009), with a budget of MYR 20 million approved by the cabinet. Malaysia is in the process of setting up its National Nanotechnology Center (NNC). In October 2009, Malaysian Prime Minister announced that nanotechnology is included as one of the growth engine for the new economic policy for Malaysia. he Malaysia Nanotech Directorate (MNN) was set up in the Ministry of Science, Technology and Innovation (MOSTI). he MNN launched the NanoMalaysia Center in 2010 as a one-stop center for Malaysia nanotechnology development. It is seeking MYR 280 million (USD 90 million) funding from the government to kick off its operation at Senai Hi-Tech Park,

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Iskandar (Johor Malaysia, next to Singapore), in 2012. he NanoMalaysia initiative also serves as a commercialization platform for capability building and international collaboration to accelerate the adoption of nanotechnology in Malaysian industries. he world’s fourth most populated country, Indonesia, has spent the past few years in preparing its nanotechnology strategy. he Indonesia Society for Nanotechnology drafted the Indonesia nanotechnology recommendation and roadmap for the government in 2009. he Ministry of Research and Technology and the Ministry of Industry both launched research grant schemes of Development and Implementation of Nanotechnology for Support National Industry in 2009–2010. he Indonesia Institute of Science (LIPI) is forming a Nanotechnology Consortium consisting of nine research centers, four companies, and two professional organizations focusing on development advanced materials enabled by nanotechnology. Indonesia Agency for Agricultural Research and Development (IAARD) is in the process of setting up a Nanotechnology Laboratory in 2012 with a budget of about USD 5 million. Most recently, in April 2013, the national innovation council identified the need of formulating nanotechnology national policy to advance Indonesia’s S&T innovation. Figure 3.4 shows the comparison of government funding among 13 economies during the years 2006–2010. he sum of funding in the 13 economies amounts to USD 8586 million, exceeding that of the entire European Union (EU) (note that this may fluctuate with exchange rates). Figure 3.5 shows the comparison in government funding between the AP region, the EU, and the United States during the period 2006–2010.

Nanotechnology government funding in Asia pacific during 2006–2010 Million USD 10 000

5000 1200

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1000

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a d e n d ia m re or an an tna ys wa Ko ala eal gap Tai hail e Vi T M w Z Sin Ne

Figure 3.4 Comparison of nanotechnology government funding for 2006–2010 in logarithmic scale (in million USD) among AsiaPacific economies including Australia, China,

India, Indonesia, Iran, Japan, South Korea, Malaysia, New Zealand, Singapore, Taiwan, Thailand, and Vietnam.

3.3

Infrastructure

Public Nanotechnology Funding Comparision Among European Union, United States, and Asia Pacific during 2006–2010 in Million USD

8586

7936

7500

USA

EU

Asia

Figure 3.5 Government Nanotechnology Funding Comparison for the Asia-Pacific region, Europe, and United States during 2006–2010 (in million USD).

3.3 Infrastructure

Japan started to construct comprehensive R&D infrastructure, especially to facilitate collaboration between private and public sector in 1996 when the Japanese first S&T Basic Plan was launched. Dedicated R&D infrastructure for nanotechnology was set up during the second S&T Basic Plan started in 2001, where nanotechnology is identified as a priority area inspired by the US NNI. he Nanotechnology Researchers Network Center of Japan (Nanonet) was set up to provide coordinated facilities and information services and to promote collaboration between researchers domestically and internationally. In the third S&T Basic Plan started in 2006, the Nanonet was expanded, with stronger industry partnership focus, covering 13 COE consisting of 26 research institutions across Japan. Most recently, the Nanonet has evolved into Nanotechnology Platform, which serves as a user facilities network for the 10-year period of 2012–2021. he Japanese Ministry of Economy, Trade and Industry (METI) together with major industry conglomerates launched the Nanotechnology Business Creation Initiative (NBCI) in 2003 and currently has over 300 industry and research institution members. South Korea and Taiwan have similar structures and goals in their NNIs emulating the US NNI especially its interagency coordination. Phase I of both economies’ nanotechnology initiatives have the common focus of building infrastructure and strategic R&D, while Phase II will be focusing on accelerating commercialization and creating economic impact. In 2010, South Korea government set up the Nanotechnology Commercialization Platform Program committed USD 10 million over 5 years to accelerate the pace of commercialization development.

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During Phase I (2001–2005) of the KNNI, South Korea has built world-class integrated infrastructure for nanotechnology R&D and commercialization especially to promote collaboration among academia, national institutions, and industry domestically and internationally. he most notable world-class facilities are the National NanoFab Center (NNFC) and Korea Advanced NanoFab Center (KANC). South Korea has also established well-organized researchers and business network such as Korean Nanotechnology Researchers Society (KoNTRS) and Korean Nanotechnology Research Association (NTRA). Similarly, the first phase of Taiwan’s NNP has also built a major industrial common laboratory located at the Industrial Technology Research Institute (ITRI) and nine other academia core facilities centers across Taiwan. he Taiwan Nanotechnology Industry Development Association (TANIDA) was set up in 2007 to facilitate R&D cooperation between research institutions and industries with the aim of accelerating the commercialization of nanotechnology. ASEAN and other developing economies including China and India have been especially active in building R&D infrastructures. hailand government launched NANOTEC in August 2003. One of the key mandates for this center is to establish world-class infrastructures which include central core facilities in the NANOTEC Central Research Laboratory, National Network of COE in nanotechnology at eight universities, and a network of eight university-based centers with focus on textile and cosmeceuticals across hailand. Most recently, a new beam line was installed for nanotechnology R&D at the National Synchrotron Institute. Vietnam started its nanotechnology infrastructure upgrade program in 2003. Malaysia and Indonesia both have set up nanotechnology research COE. here are four main recognized nanotechnology research center in Malaysia focusing on zeolites and nanostructured materials, nanoelectronics, advanced materials, catalysts, and basic science research with state-of-the-art facilities for characterization, fabrication, and processing equipments. Indonesia has budgeted the building of a major nanotechnology infrastructure at Bandung Institute of Technology in 2009 with USD 20 million investments. In 2003, China launched the initiative of building major nanotechnology infrastructure including the National Center for Nanoscience and Technology (NCNST) located in Beijing and the National Engineering Research Center for Nanotechnology (NERCN) located in Shanghai. he NCNST is growing steadily, recruiting overseas Chinese scientists and now is with a total of 50 full-time faculties supervising 150 graduate students plus another 150 students from other research institutions who are conducting joint research projects with NCNST. he NCNST provides and manages the national characterization facility and also runs the Key Center for Biomedical Effects of Nanomaterials and Nanosafety for the Chinese Academy of Sciences (CAS). On the other hand, the NERCN based in Shanghai is currently not in operation. he Shanghai’s nanotechnology infrastructure is being coordinated by the Shanghai Nanotechnology Promotion Center (SNPC) [8], which provides not only information, networking, training platform, project funding but also NMs-testing facilities. he national nanotech centers building in 2003 was driven by the National Development and

3.3

Infrastructure

Reform Commission (NDRC) and managed by the CAS and MOST. he most aggressive and organized effort in China’s nanotech infrastructure building is the Nanopolis Suzhou which serves as an ecosystem of nanotechnology R&D and commercialization with USD 1.6 billion investment committed end of 2010. It has already been well known for its 24/7 operational world-class nanofabrication and characterization facilities and currently it is building a 6-inch Micro-Electro-Mechanical System (MEMS) pilot production line to serve domestic and international users from research organizations to industries. Details of Nanopolis Suzhou can be found at the Suzhou Nanotech Capability Report (free download at www.nano-globe.biz). Infrastructure development for nano S&T research is one of the four primary objectives of the India Nano-Mission launched in 2007.here are 11 centers with state-of-the-art R&D facilities across India plus the Center for Computational Materials Science in Bangalore. In 2010, three major strategic centers were set up including Institute of Nano S&T (Mohali, USD 28 million), National Center for Nano S&T (Bangalore, USD 23 million), and Center for Knowledge Management in Nanotechnology (Hyderabad, USD 2 million). Iran Nanotechnology Laboratory Network (INLN) shares more than 600 equipments with 45 research centers throughout country. he number of facility users shows an exponential growth reaching over 33 000 in 2011 compared with 740 in 2004. Iran is in the process of setting its national metrology center and is a very active member of ISO TC229 (Technical Committee – Nanotechnologies). Singapore, the smallest country in the region is well known for its world-class infrastructure for nanotechnology research and development. Singapore’s main government research institution A*STAR set up the Science Engineering Research Council (SERC) Nanofabrication and Characterization Facility (SNFC), which serves as a central facility and open to Singapore universities, research institutions, industry, as well as international collaborators. In addition, the Singapore University of Singapore (NUS) and NTU set up their own coordinated nanotech central facilities under the NUSNNI and NTU Nanocluster, respectively. Australia launched the National Collaborative Research Infrastructure Strategy (NCRIS) in 2005 and allocated AUD 550 million to major research infrastructure projects during 2005–2011. he total nanotech facilities investment is estimated to be over AUD 100 million. he MacDiarmid Institute in New Zealand received total of NZD 20 million in 2002 and 2007 as capital equipment investment from the government. For locations of the main nanotechnology facilities and key research centers of the 15 economies reviewed in our book, please refer to Figure 3.6. he map in pink indicates the Asia Nano Forum (ANF) network coverage as well. ANF is a network organization in nanotechnology covering 15 economies in the AP region and is headquartered in Singapore. ANF was established with the mission to promote responsible research and development of nanotechnology that educationally, socially, environmentally, and economically benefits each economy by fostering international network and collaboration. For details of ANF, please visit its website www.asia-anf.org.

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South Korea

China

Japan

Iran Taiwan

India

UAE

Hong Kong Thailand

Vietnam

Malaysia Singapore Indonesia

Australia

New Zealand

Figure 3.6 region.

Location of nanotechnology core facilities and R&D centers in Asia-Pacific

3.4 R&D and Commercialization

he AP region is advancing to becoming one of the most ambitious and dynamic regions of the world in nanotechnology research and development and commercialization. Japan has already been successful as a world leader in electronics, advanced materials, and precision machines manufacturing. Japan today is still ahead of all other economies in the region in nanotechnology R&D and especially in adopting nanotechnology in various industry sectors. Nanotechnology is considered as a key technology in the twenty-first century that innovates manufacturing and drives the growth of industries such as electronics, energy, environment, and biotechnology. Notably Japan nanotechnology is already in the market sectors including consumer electronics (Flat Panel Display (FPD), cell phone, digital camera, digital camcorder, and DVD recorder, DRAM (dynamic random access memory), flash memories); water/stain repellent and wrinkle- and shrinkage-free textile; water-resistant foundation cosmetics; DNA chip for analyzing genes; anticancer drug delivery; thin film solar cells; fuel cells; and device manufacturing with finer circuit width.

3.4

R&D and Commercialization

Since 2001, when South Korea started its KNNI, it has made quantum leap in its R&D and commercialization advancement. hree major strategic nanotechnology programs were set up, namely National Program for Tera-Level Nanodevices, the Center for Nanostructured Materials Project, and the Center for Nanoscale Mechatronics and Manufacturing. here had been more than three times increase in nanotechnology-related Science Citation Index (SCI) publication during 2001–2006 and nanotechnology-related patent application filed during 2001–2005 by South Korea. Major South Korean electronics conglomerates dominate the nanoelectronics product market. Samsung Electronics developed the world’s first 30 nm 64 Gb NAND flash memory. A number of innovative nanotech products are produced by South Korea Small and Mediumsized Enterprises (SMEs) and start-ups including conductive nanosilver ink; antibacterial powders; antiglare coating; color film with nanolayered structure; Carbon Nanotubes (CNTs) transparent conductive film; and pharmaceutical products for atopic dermatitis using nanohybrid technology. South Korea was ranked fourth in nanotechnology competitiveness in 2005. In KNNI Phase II, South Korea is aggressively pursuing commercialization of nanotechnology and international cooperation. Taiwan is another bright spot in terms of research and commercialization. Its R&D and commercialization activities in nanotechnology are mainly funded by the government NNP. Two-thirds of the NNP budget in both Phase I and II go to industrialization of nanotechnology projects. Two-thirds of Taiwan nanotechnology companies are in the traditional industry business [9]. Taiwan nanotechnology-related publication during 2003–2007 tripled. Nanotechnology innovative products developed by ITRI include light, thin, and flexible 7-inch active matrix thin film transistor-liquid crystal display (TFT-LCD) panel and electrets-based flexible speaker. China is known for its rapid rise in science publications including nanoscience. In 2007, China already climbed to be ranked #2 by number of papers published during 2007, second only to the United States [10]. Commercialization of nanotechnology in China is still in its infancy. he MEMS technology is relatively mature and there are over 50 MEMS companies in China today active in MEMS device design, fabrication, and foundry services. SIP is emerging as the China’s nanotechnology innovation and commercialization hub through its Nanopolis initiative (which aims to build an entire ecosystem for accommodating nanotech R&D and manufacturing within a 1 km2 world-class facility) [11]. Within the past 5 years, SIP has managed to attract increasing number of overseas Chinese technopreneurs to set up high-tech companies within SIP. By 2015, it targets to house over 200 nanotech-related companies within its Nanopolis doubling today’s number. Today, a number of innovative nanotech start-ups are already providing world-leading products enabled by nanotech innovation in Nanopolis Suzhou. Iran is racing forward to promoting sustainable development of nanotechnology with holistic approach with impressive achievements in science (ranked No.1 among Muslim countries in nanopublication). he number of nanoscience publication by Iranian scientists has been growing exponentially in the past 10

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years, exceeding 2000 in 2011 and ranked No. 14 (compared with 59 in 2000) in the world. Iran has made significant progress in nanotech commercialization, having a total of 130 nanotech manufacturing companies today and 68 start-ups (see [12]). Iran companies produce products ranging from NMs, functional materials (composites, construction materials, coating, textiles, membrane, and food packaging), fertilizers, instrumentation (CVD (chemical vapor deposition), STM (scanning tunneling microscope), AFM (atomic force microscopy)), and health-care products. Australia stands out in its world-class research especially in controlled fabrication of silicon-based transistor with nano- to atomic-scale precision. here are about 80 nanotechnology companies in Australia according to Australian NanoBusiness Forum (ANBF). Australia nanotechnology products include sunscreen lotion using nanoparticles (NPs), supercapacitor using nanostructured materials, bionic ear implants using biocompatible NMs, and drug delivery technology using nanostructured silicon. New Zealand is proud to excel in research areas such as nanofabrication and devices, electronics and optical materials, molecular materials, soft materials, inorganic hybrid materials, and fusion of nanoscience and biology. In terms of application and commercialization, the MacDiarmid Institute for Advanced Materials and Nanotechnology shows its strength in biochip for cell imaging; atomic-cluster-based sensors and interconnects; optoelectronic materials growth (producing world record ZnO diode); and NPs for diagnostics and drug delivery applications. Hong Kong nanotechnology places strong focus on commercialization especially in environment; energy; displays and electronic packaging; composites materials; advanced manufacturing; and textiles. Singapore intends to build a comprehensive nanotechnology ecosystem to promote nanotechnology application development and the growth of nanotechnology industries. Singapore EDB is the key driver for the nanotechnology strategy in Singapore. Singapore’s nanotechnology R&D and commercialization focuses on nano-enabled urban solution (such as cleantech), nanotoxicology, consumer care, and health care. Singapore is the most foreign-friendly economy in the region and the government is aggressively attracting multinational corporations and foreign start-ups to set up R&D and manufacturing centers in Singapore. Especially since 2008, funding agencies including the National Research Foundation and SPRING have launched new funding schemes to stimulate innovation, commercialization, and application R&D. he areas of focus in nanotechnology applications include biomedical, clean energy, environment and water, and electronics. Each of the areas involves world-class R&D infrastructure, researchers, multinationals, and start-ups. India Nano-Mission established seven strategic Centers for Nanotechnology focusing R&D on nanopowders/NPs, nanophosphor materials, drug delivery system (DDS), biosensors, and nanoeletronics. Nanotechnology application stresses on agriculture and food, drinking water, automobiles, energy, biomedical devices, and metrology.

3.5

Nanosafety, Standardization, and Education

hailand has its own priority in food, cosmeceuticals, textile, flexible polymer solar cells, DDS, and sensors for scents. Vietnam stands out its application R&D in CNT-based nanocomposites, CNTbased metallic coating, and electromagnetic shielding and conductive paint. Malaysia places its research focus on NPs, CNT, dendrimers, aerogel, Organic Light Emitting Diode (OLED), quantum dot, nanomagnetics, single electron transistor, and DDS. Malaysia nanotechnology companies are developing CNT nanocomposites, biosensors, nanocatalysts, and biofertilizers. Indonesia’s research institutions focus its R&D areas in nanostructures, nanoencapsulation, Ag NPs, nanocomposites, and nanocarbon. It envisions its nanotechnology commercialization priority should be NMs manufacturing, processing, and product development.

3.5 Nanosafety, Standardization, and Education

Nanosafe Australia (www.rmit.edu.au/nanosafe), which is a nationwide research network of toxicologists and risk assessors, is the most impressive initiative in Asia which integrates interdisciplinary expertise across Australia in fields directly related to nanotoxicology:

• • • • • • •

characterization of physicochemical properties; measurement of ultrafine particles in ambient air; toxicokinetics of particles; preclinical safety testing; immuno-, neuro-, and biochemical toxicology; occupational and food allergy; occupational hygiene, occupational safety and health (OHS), and workplace monitoring; • ecotoxicology and environmental toxicology; • ecological and human health-risk assessments. Nanosafe Australia supports government, industry, and non-government organizations (NGOs) in their efforts to understand the occupational and environmental health and safety issues surrounding nanotechnology products and their manufacturing processes; and to provide quality data for the appropriate risk assessment of NPs and NMs. Under the leadership of Professor Paul Wright (program director of Nanosafe Australia), ANF kicked off the Asia Nanosafety Initiative on 31 January 2013 during the Nanotech 2013 conference and exhibition in Tokyo. ANF is a very active member of the ISO TC229 Nanotechnologies represented by Dr Tsung-Tsan SU from ITRI, Taiwan. Japan is leading the JWG2 Measurement & Characterization and China is leading the WG4 Materials Specifications. Iran stands out not only for its centrally coordinated national nanotech initiative but also for its education and outreach efforts including

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• nano club For children; • nano-Olympia (reached 16 000 students in 2012, two orders of magnitude increase over 5-year period);

• student nanotech educational exhibitions; • 28 universities with MSc and 14 universities with PhD in nanotech; • industrialists’ knowledge promotion on nanotech (workshops, newsletters, leaflets, and industrial show). To a surprise for those who are not familiar with Iran, more than 50% of nanotech workforce in Iran is women.

3.6 Summary

Nanotechnology has experienced an exciting period of development as a result of (i) natural evolution of S&T with our increasing capability of imaging and manipulation at the nanoscale, (ii) strategic government funding with over an order of magnitude increase in the past 10 years worldwide, and (iii) maturity of commercialization and adoption especially starting 2010. Leading economies in Asia such as China, Japan, South Korea, Singapore, and Taiwan are racing in S&T innovation. Coherent strategic policy with focus on sustainability is especially apparent in South Korea and Taiwan where balanced development in R&D, infrastructure, education, and industrialization as well as EHS issues are considered and well executed. China, though still a development country and already the second largest economy in the world, is emerging as superpower in nanotechnology development in the next 5–10 years with the growth of innovation contributed by its overseas Chinese and domestic talents driven by its ambition to become world-class innovation hub and funded by its cash-rich governmental and private investors. In the practice of public private partnership (PPP), China stands out in government leadership in driving commercialization of nanotechnology. Asian nanotechnology development presents attractive opportunities for overseas governmental organizations, research institutions, and industries to form strategic alliance for innovation, manpower, commercialization, and market growth. Finally, we see increasing importance for establishing global alliance to ensure nanotechnology contributing to sustainable development. Visit our website www.nano-globe.biz to stay tuned with our initiatives for promoting global alliance for sustainable development.

Glossary

ANF ARC ASEAN CNT

Asia Nano Forum Australia Research Council (Australia) Association of Southeast Asia Nations Carbon Nanotubes

References

DDS FPD OLED MEMS METI NNI SME

Drug Delivery System Flat Panel Display Organic Light Emitting Diode Micro-Electro-Mechanical System Ministry of Economy, Trade and Industry (Japan) National Nanotechnology Initiative Small and Medium-sized Enterprise

References 1. Feynman, R.P. (1959) Plenty of Room

2.

3.

4.

5.

6.

at the Bottom, http://www.its.caltech. edu/∼feynman/plenty.html (accessed 19 December 2013). Taniguchi, N. (1974) On the basic concept of ‘nano-technology’, in Proceedings of the International Conference on Production Engineering, 1974, Tokyo, Japan, Japan Society of Precision Engineering, Tokio. National Nanotechnology Initiative www.nano.gov (accessed 19 December 2013). European Commission Nanotechnology http://cordis.europa.eu/nanotechnology (accessed 19 December 2013). Russian Corporation of Nanotechnologies www.rusnano.com (accessed 19 December 2013). Siegel, R.W., Wu, E., and Roco, M.C. (eds) (1999) Nanostructure Science and

7.

8. 9.

10.

11. 12.

Technology, Loyola College, Maryland, http://www.wtec.org/pdf/nano.pdf Japan Council for Science and Technology Policy (CSTP) www8.cao.go.jp/cstp/english/index.html (accessed 19 December 2013). SNPC www.snpc.org.cn/english/index.asp (accessed 19 December 2013). Taiwan Nanotechnology Industry Development Association www.tanida.org.tw (accessed 19 December 2013). “With Output and Impact Rising, China’s Science Surge Rolls On” by Christopher King at Science Watch http://archive.sciencewatch.com/ana/fea/ 08julaugFea/ NANO POLIS www.nanopolis-sz.cn (accessed 19 December 2013). ANF (2011) Asia Nano Forum Summit 2011 Presentations.

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4 Near-Industrialization Nanotechnologies Developed in JST’s Nanomanufacturing Research Area in Japan Yasuhiro Horiike

4.1 Introduction1)

his chapter describes nanotechnologies, which are set to be commercialized soon, being developed in one “Research Area” titled “Establishment of Innovative Manufacturing Technology Based on Nanoscience” (“Nanomanufacturing” for short) within the Core Research of Evolutional Science and Technology (CREST) Program administered by the Japan Science and Technology Agency (JST). JST is an independent public body under the Ministry of Education, Culture, Sports, Science, and Technology (MEXT). With the aim of promoting and encouraging the development of breakthrough technologies that contribute to the attainment of the country’s strategic goals, JST provides a variety of research funding programs for promising research projects. CREST is one of JST’s major undertakings for boosting fundamental scientific research. In addition, giving back the fruits of such research to society through innovations is another important mission of JST. he ongoing CREST program consists of Green Innovation (9), Life Innovation (8), Nanotechnology and Materials (10), Information and Communication Technology (9), and Research Acceleration (2), where a number in parentheses indicates the number of “Research Areas.” Each research area lasts for 8 years with solicitation for 5-year projects open for the first 3 years. Overall research fund that goes to a research area is 4.8 billion yen over the 8-year term. In 2006, 5 years after the US Government started the National Nanotechnology Initiatives (NNIs), JST launched the “Nanomanufacturing” research area (supervisor: Y. Horiike) to promote early industrialization of nanotechnologies. his area will terminate at the end of March 2014. he research projects pursued in the area are nanoparticles (NPs) (3), nanobiology (5), nanoelectronics (4), and others (4), where a number in parentheses indicates the number of research item. Out of these 16 projects, this chapter takes up the following seven as being near industrialization: 1) Yasuhiro Horiike, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, 305-8571 Japan. he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Section 4.2

Section 4.3 Section 4.4 Section 4.5 Section 4.6 Section 4.7 Section 4.8

Applications of ionic liquid (IL) to high-efficiency catalyst NPs and scanning electron microscope (SEM) observation of biomedical specimens High current density Li-air battery enabled by bimetallic NPs supported on carbon Versatile applications of two-dimensional (2D) nanosheets, in particular to high k capacitors and gate dielectrics Ultimate separation of single-wall carbon nanotube (SWCNT) and its application to a novel electronic devices Liquid crystalline organic semiconductors with high mobility and high thermal stability up to 200 ∘ C Polymeric micelles (PM) cancer therapy in progress in the late stages of clinical trial, and Clinical application of particulate vaccine adjuvants.

JST had settled upon a stratagem for the creation of innovations by nanosystems through development of various nanodevices based on fundamental technologies for nanotechnology and materials science area in Japan (http://www.jst. go.jp/crds/report/report05.html). According to the stratagem, a modified overview of R&D regions on nanotechnology and materials science, where the following Sections 4.2–4.8 are working out examples of some of these areas, is shown in Figure 4.1.

Nanosystems

Recovery/Regeneration

Green innovation

Life innovation

Systemization/Convergence Bionanotechnology

Nanodevice systems

Nanoelectronics

Green-nanotechnology

2: Observation of biomaterials in vacuum 7: DDS

2 , 3: Fuel battery

6: Organic transistor

6: Organic transistor

5: Thermoelectric element

6: Organic solar cell

5: CNT-CMOS

3: Li air battery

8: Vaccine adjuvants

4: High-k condenser

2, 3: Catalysis

Nanomanufacturing Fundamental and/or unique technologies, materials, etc.

3, 7, 6, 7, 8: Organic synthesis 2, 3, 4,5: Inorganic synthesis

2 : Ionic liquid

5: SWCNT

4 : Nanosheet

3 : Electrochemistry reaction direct observation

6: Liquid crystalline

5: Gel filtration

4: LB film

Figure 4.1 Modified overview of R&D regions on nanotechnology and materials science based on a report of Center for Research and Development Strategy (CRDS) of JST

3 : Solution plasma

(http://www.jst.go.jp/crds/report/report05.html). The following Sections 4.2–4.8 are working out examples of some of these areas, where numbers in the figure refer to section numbers.

4.2

Utilization of Ionic Liquids Under Vacuum Conditions

4.2 Utilization of Ionic Liquids Under Vacuum Conditions for Nanoparticle Production and Electron Microscopic Studies2) 4.2.1 Introduction

IL is a kind of organic salt, which can stay in liquid phase even at room temperature. One of fascinate features of IL is negligible vapor pressure that allows us to put IL in a vacuum chamber. Based on this fact, we are developing novel techniques for nanomaterial production and analyses by putting IL in sample chambers of several instruments that require vacuum conditions [1]. In this chapter, some utilitarian values developed by combining IL and vacuum techniques are shown. 4.2.2 Production of Metal Nanoparticles by Sputtering Instrument

he metal sputtering under reduced pressure is a widely used method to deposit a metal thin layer on surface of a solid substance. Our attempt was to subject IL to gold sputtering. Observation of the resulting IL by a transmission electron microscope (TEM) has revealed gold NPs suspended in the IL, as shown in Figure 4.2a [2]. Furthermore, this method was found to be applicable to preparation of many other NPs including alloy, metal oxide, and hollow NPs [3, 4]. he advanced features of this method are that NPs can be prepared without any chemical reaction and that amount of NPs is proportional to sputtering time without any variety of their mean diameter. It is, therefore, concluded that this sputtering method is quite an easy way to churn out pure NPs. Putting the prepared NP-suspended IL on a carbon substance and heating it were found to induce dense adsorption of the NPs onto the substance. his method is exploitable for preparation of Pt NPs- adsorbed carbon materials [5]. his method is also effective to adsorb Pt NPs on surfaces of carbon nanotubes (CNTs), as shown in Figure 4.2b [6]. he prepared Pt NPs-CNTs exhibit high catalytic activity against the four electron O2 reduction and this material is quite stable for long run, attracting several companies where practical fuel cells are developed. Alloy NPs can also be prepared by sputtering different metals onto IL at the same time. Chemical syntheses of these alloy particles are not easy because simultaneous reduction of different metal ions tends to produce core-shell-structure particles or mixture of different kinds of metal NPs. However, the simultaneous sputtering of different metals always produces homogeneous alloy NPs in IL and 2) Susumu Kuwabata, Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan and Tsukasa Torimoto, Department of Crystalline Materials Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 4648603, Japan.

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b

50 nm

2 mm

(b)

(a)

Figure 4.2 (a) TEM image of Au nanoparticles suspended in ionic liquid taken after subjecting the ionic liquid to Au sputtering. (b) TEM image of Pt nanoparticles-adsorbed carbon nanotube.

10

0.50

0.50 0.25 0 0.75

5

0.75 0.25 0 1

0 0 (a)

0.2 0.4 0.6 0.8

1

jpeak (mA cm–2)pd/Au

12 j (mAcm–2)pd/Au

58

Figure 4.3 (a) Cyclic voltammograms of AuPd nanoparticle-adsorbed carbon electrodes (solid lines: the positive potential scan, dotted lines: the negative potential scan) taken at 100 mV s−1 in N2 saturated 0.5 M ethanol/0.5 M KOH aqueous solution.

8 6 4 2 0

1.2 1.4

E/V vs. RHE

10

0

(b)

0.25

0.5

0.75

1

fAu.

The numbers given in this figure represent f Au values for preparation of AuPd particles. (b) Plots of peak current density observed in the positive potential scans as a function of f Au . The value for a bulk Pt electrode is shown by broken line.

the composition of NPs can be changed by changing the area ratio of the metal targets. he Au/Pd alloy NPs prepared by this method exhibit high electrocatalytic activities against ethanol oxidation, as shown in Figure 4.3a, which shows cyclic voltammograms taken by the Au/Pd NPs having different Au compositions (fAu ). As shown in Figure 4.3b, the alloy NPs having 0.5/0.5 of molar ratio were found to exhibit the highest catalytic activities [7]. Now collaborative projects using the alloy NPs prepared this way are arising between universities and industries. 4.2.3 Electron Microscopic Studies of Biopsy Specimens Using IL

Regarding the use of IL for electron microscopes, we have discovered a fascinating fact that IL can be observed by SEM without charging of the liquid [8]. In other words, IL behaves like a conducting material for SEM observation when the liquid is put on insulating samples. his fact became very useful to observe

4.2

Utilization of Ionic Liquids Under Vacuum Conditions

2 mm 50 μm (a)

(b)

30 μm 100 μm (c)

(d)

Figure 4.4 SEM images of yellow jacket (a), pulmonary adenocarcinoma cell (b), inside wall of colon (c), and fibrous blast cells (d) taken after IL treatments.

samples under wet conditions. In particular, since biological samples have quite complex surfaces, metal or carbon vapor deposition is not adequate to cover completely their surfaces. However, IL can easily spread on such complex surfaces, giving clear SEM images without any charging, as shown in Figure 4.4 [9]. his innovative treatment of the biological samples for SEM observation, which can be finished in quite short time without use of any sputtering or vacuum deposition instrument, is attracting many researchers and technicians who need SEM observation of the biopsy specimens. For such a purpose, synthesis of ILs, which are adapted to biomedical tissue, and development of the appropriate ways to apply the prepared ILs to many kinds of biopsy specimens are extensively studied. 4.2.4 Conclusion

IL possessing negligible vapor pressure enables us to introduce wet process in vacuum. Metal sputtering onto IL has been a unique way to mass produce NPs of pure metal and alloy. Interestingly, IL is not only a media for NP production but also functional material for immobilizing NPs onto carbon substrates. Based on these attractive features, the IL-sputtering method is now being improved by collaboration between universities and companies to industrialize this techniques aiming at quick production of electrocatalysts. Another attractive feature of IL is that it

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behaves as a conductive material for SEM observation. As a matter of fact, IL came into usage at some hospitals for clinical diagnosis with SEM observations. To support such practical usage, a new type of IL for SEM observation has been produced and come to market from an electron microscope company.

4.3 Solution Plasma Process: An Emerging Technology for Nanoparticles Synthesis3) 4.3.1 Solution Plasma Process

Liquid-phase electrical discharge processes have been recently studied in NP synthesis [10–12]. A special type of liquid plasma process, named solution plasma process (SPP), belongs to the nonequilibrium plasma process which occurred with a discharge voltage, current, and frequency, respectively, in the range of 1 kV, 1 A, and 103 Hz. he process offers a new reaction medium, where the active species and chemical reactions can be altered by varying the liquid media. he morphology and proposal model of SPP are shown in Figure 4.5. hese unique properties and novel reaction kinetics promote fast reaction and high density of radicals for the application of NP synthesis. he important merits of the Solution Plasma, as compared to other synthesis methods, consist in short processing time ranging from few minutes to several tens of minutes and operation in atmospheric pressure and room temperature with relatively low energy of plasma. It has been successful to synthesize the metal NPs and carbon materials. Plasma

(a) Figure 4.5

(b)

Gas

Liquid

Gas/Liquid Gas/Plasma interface

(a) Morphology and (b) model of solution plasma process.

3) O.L. Li and N. Saito, Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chigusa-ku, Nagoya, 464-8601, Japan.

4.3

Solution Plasma Process: An Emerging Technology for Nanoparticles Synthesis

4.3.2 Synthesis of Carbon Nanoparticles and Its Application in Electrochemistry

Carbon has been widely used as electrodes materials in electrochemical applications as it is a light material with good electrical and thermal conductivities. Taking appropriate starting material and selecting processing routes, various kinds of carbon materials including carbon fibers, spherical carbon, or carbon onions can be synthesized [13, 14]. Carbon precursor in solution plasma can be either graphite electrode or aromatic organic compound. he particle size and structure can be controlled by the type of precursor and input plasma energy, as shown in Figure 4.6a,b. he particle size and structure can be controlled by adjusting the input plasma energy. he as-prepared carbon material has shown outstanding performance in Li-air battery. Figure 4.7 showing the discharge capacity referred to as CNB reaches 3500 mAh g−1 with current density of 0.1 mA, which is 30% higher than that of commercial carbon electrode material referred to as KB. In addition, metal NP can be supported onto the as-prepared carbon material by a single process: by applying benzene as a carbon precursor, while gold (Au) and platinum (Pt) NP can be produced by electrode sputtering. he metal particles with size diameter of 1–2 nm are supported on 20–30 nm carbon porous material, as shown in Figure 4.6c. From X-ray Diffraction (XRD) pattern, the Au and Pt NPs formed were composed of purely crystalline structures. he bimetallic metal NPs exhibit extraordinary catalytic reactivity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). 4.3.3 Conclusion

New particles synthesis method was established by developing SPP and the reaction system (KURITA Seisakusho Co., Ltd.). his can provide us the size-regulated

2 nm

2 nm

(a)

(b)

2 nm (c)

Figure 4.6 Morphology of (a) carbon nanoparticle synthesized by graphite electrode as carbon precursor, (b) carbon nanoparticle synthesized by benzene as carbon precursor, and (c) gold with carbon nanoparticle synthesized by benzene and gold electrode as precursors.

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4 Near-Industrialization Nanotechnologies Developed

4.0 3.5

CNB 0.1 mA (3 times) KB 0.1 mA (3 times)

3.0 Voltage (V)

62

2.5 2.0 KB 0.5 mA 1.5 1.0

CNB 0.5 mA 0

500

1000

1500

2000

2500

3000

3500

Capacity (mAh g–1) Figure 4.7 Discharge curves of the Li−O2 battery. KB and CNB denotes Ketjenblack and Carbon Nanoball, respectively.

NPs with faster synthesis rate. We are developing the battery electrode and catalytic materials system for industrialization with Toyota Motor Corporation and Mejyo Nanocarobons Co., Ltd. Moreover, this process recently has been also utilized in the synthesis of catalyst in mesoporous silica (Taiyo Kagaku Co., Ltd.) and monodispersed carbon ink for light-weighting composite materials (TOYO JUSHI Co.). his process can encourage the industrialization of nanotechnology.

4.4 2D Inorganic Nanosheets4) 4.4.1 Background

Exfoliation of layered compounds yields molecularly thin 2D materials, which are an important class of nanoscale materials. In the mid-1990s, our group successfully delaminated a layered titanate into colloidal single layers via the intercalation of quaternary ammonium ions. We considered the obtained ultrathin oxide crystal as a nanosheet due to its unusual 2D morphology with a nanoscale thickness of ∼1 nm [15]. Since then, many layered compounds such as oxides, sulfides, hydroxides, and so forth have been exfoliated to produce a wide range of nanosheets in various compositions and structures [16]. Graphene, reported in 2004, is one of such nanosheets. Nanosheets often exhibit new or enhanced properties and reactivities 4) Takayoshi Sasaki, International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1, Namiki, Tsukuba, 305-0044 Japan.

4.4

2D Inorganic Nanosheets

Figure 4.8 Outline of synthesis and applications of 2D inorganic nanosheets.

due to their ultimate 2D structure, which is entirely composed of surface atoms. A range of applications can be developed based on these unique functionalities. As a typical example, here, we describe the production of titanium oxide nanosheets and the development of some practical applications. he outline is depicted in Figure 4.8. 4.4.2 Synthesis of Titanium Oxide Nanosheets

A starting layered titanate of Cs0.7 [Ti1.825 Υ0.175 ]O4 (Υ: vacancy) or K0.8 [Ti1.73 Li0.27 ]O4 is synthesized into a polycrystalline sample by firing a stoichiometric mixture of alkali metal salts and TiO2 at the high temperature of

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800–1000 ∘ C. he obtained powder sample composed of platy microcrystals is converted into a protonated form by acid leaching, and is subsequently shaken with an aqueous solution containing tetrabutylammonium (TBA) ions. he layered titanate undergoes total exfoliation into unilamellar nanosheets of Ti0.91 O2 0.36− or Ti0.87 O2 0.52− under optimized conditions to produce a colloidal suspension [15, 16], which shows strong light-scattering effects. he obtained nanosheet is extremely thin at ∼1.1 nm, which is inherent to the material. On the other hand, its lateral size ranges from 0.1 to 100 μm, which is dependent on the initial size of the layered titanate microcrystals and the mechanical shear applied in the delamination step. his production process has been transferred to industry. 4.4.3 Production of TiO2 Particulates in Novel Shapes and Their Commercialization

Because oxide nanosheets are obtained as a monodispersed colloidal species bearing negative charge, we can apply solution-based processing to organize them into various nanostructures, and can design a range of functional materials through this approach. Spray drying of the suspension of Ti0.91 O2 0.36− nanosheet produces hollow microspheres [17]. Sprayed droplets of the suspension swell like a balloon in a hot zone (∼240 ∘ C) and the nanosheets gather to form a shell in the evaporation process of water. Typically, the sphere diameter is ∼30 μm and the shell thickness is ∼50 nm, leading to an empty core of >99% of the volume. he microspheres can be converted via gentle mechanical crushing into flaky particulates. Subsequent heat treatment at >500 ∘ C promotes the phase transformation from the nanosheet structure into anatase, a polymorph of TiO2 . Due to the flaky shape, which has not been achieved by other routes, the obtained material has advantages such as high spreadability. he flaky particulates can be spread homogeneously on the skin, which gives efficient shielding from harmful UV light. his material has been applied to cosmetic products such as foundation makeup. 4.4.4 Fabrication of Nanostructured Films and Their Applications

Nanosheet films can be easily fabricated by conventional processes such as dip or spin coating. Due to the high 2D anisotropy, the nanosheets tend to be aligned parallel to the substrate surface to produce functional films with a smooth surface. For example, a self-cleaning coating has been attained by depositing Ti0.91 O2 0.36− nanosheet on glass substrate and subsequently heating at 400–500 ∘ C. he resulting glass is covered with a thin layer of anatase, which shows

4.4

2D Inorganic Nanosheets

photoinduced superhydrophilicity in high efficiency upon exposure to UV light [18]. Water droplets spread over the surface to wash out a stain. he coating film has additional advantages such as a smooth surface and a high hardness as a result of using the 2D nanosheets as a coating material. hese aspects give the coating film superior stain-resistant and anti-wearable properties, which are hardly attained with conventional photocatalytic films of anatase. he application of this technique using Nb3 O8 − nanosheet is undergoing verification testing for keeping windows of vehicles clean [19]. We have developed solution-based layer-by-layer assembly processes to construct multilayer films with a highly controlled nanostructure using the nanosheets as a building block. Interestingly, oxide nanosheets dispersed with TBA ions spontaneously float at the air–liquid interface due to the moderate amphiphilic property of TBA ions. Accordingly, the Langmuir–Blodgett procedure can be applied to transfer the floating nanosheets onto the substrate after packing them appropriately by compressing the surface with barriers. A monolayer film composed of neatly tiled nanosheets can be obtained, and repeating this procedure leads to the production of a highly ordered multilayer film [20]. Such films of Ti or Nb oxide nanosheets were found to exhibit very high dielectric and insulating properties despite their ultra-thinness [21]. For example, the films of Ti0.87 O2 0.52− and Ca2 Nb3 O10 − nanosheets show a relative dielectric constant, � r , of 120 and 210, respectively, even at a thickness of 5–30 nm. he leakage current density is very low, being J < 10−7 A cm−2 at 1 V. he performance is greatly superior to other well-known high-k materials such as (Ba, Sr)TiO3 . hese features strongly suggest that these oxide nanosheets are promising as high-k components indispensable in nanoelectronics. Research and developments are underway for their applications in future electronic devices such as capacitors and gate dielectrics.

4.4.5 Conclusion

It has been almost 20 years since we first reported the preparation of titanium oxide nanosheets. Along with fundamental investigations, various possible applications have been explored by utilizing their unique morphology and versatile functionalities. Production of thin flakes of TiO2 at industry has been attained, though still in a small scale, and some cosmetics combined with them are now on the market. he films fabricated with Ti or Nb oxide nanosheets are in a stage of the demonstration test at a railway company for their possible use as self-cleaning coating of train windows. Furthermore, based on their superior dielectric/insulating performance, development of high-k devices is under progress in collaboration with a major company.

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4.5 Ultimate Separation of SWCNT and Its Application to Novel Electonic Devices5) 4.5.1 Research Background

After the discovery of SWCNTs in 1993 [22], they have been attracting much attention for their potential use in electronic device applications due to the high carrier mobility. However, it is well known that there are two types of SWCNTs, metallic (m-) and semiconducting (s-) ones [23]. Mixed production has been one of the most challenging problems for the practical application of SWCNTs. Typically, one-third of raw SWCNTs should be metallic, and the rest semiconducting. In the early stages of SWCNT research, we did not have a method for preparing high-purity s-SWCNTs, and therefore, mixed m-SWCNTs fatally degraded the performance of thin film devices, typically thin film transistors (TFTs). In 2006, Hersam’s group reported a density gradient ultracentrifugation (DGU) method for the preparation of high-purity s-SWCNT ink, which substantially improved thin film device performances [24]. However, the high cost and the low throughput in DGU were unsolvable problems. herefore, we still needed a larger scale, low-cost separation method for industrial applications. In the JST-CREST project from 2007 to 2013, we have developed a new separation method that can be applied to industrial-scale production. 4.5.2 Production of 2G-SWCNT and Its Applications

he new separation method [25, 26] that we developed is an adsorption column chromatography based on the attractive interaction between an s-SWCNT wrapped with sodium dodecyl sulfate (SDS) and hydrogels, such as agarose or allyl dextran. First, the column was filled with hydrogel beads and was equilibrated with an SDS solution. Injection of an SWCNT/SDS solution after the SDS solution caused selective adsorption of s-SWCNTs in the column, while the m-SWCNTs flowed out through the column without interacting with the gel. his method exhibits two advantages over previous methods. he first one is the scalability. he column capacity can quite easily be increased with this method. For example, an 8 l column filled with hydrogel can separate 2 g of SWCNTs per day at a nearly 100 times lower cost than that of the DGU. he second advantage of the separation method is the precise structure sorting of s-SWCNTs. Not only meter per second separation of SWCNTs but also mono-structured s-SWCNTs can be sorted simply by injecting an excess amount of SWCNTs into the multicolumn system, where a tiny amount of the hydrogel was added to a series of columns. We obtained structure-sorted s-SWCNTs adsorbed in each column. 5) Hiromichi Kataura, Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Central 4, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562, Japan.

4.5

Ultimate Separation of SWCNT and Its Application to Novel Electonic Devices

Overloading SWCNTs

(7,3) (6,4)

s-SWCNT (6,5) s-SWCNT

s-SWCNT

(6,4) (6,5) (7,5) (8,3) (8,4)

(7,5)

(7,6) (8,6)

(8,3)

(10,3)

(9,4) (10,2) (8,7) (12,1)

s-SWCNT m-SWCNTs (a)

200 400 600 800 10001200 Wavelength (nm) (b)

Figure 4.9 Multicolumn system (a) and optical absorption of mono-structured s-SWCNTs (b).

his method is based on the diameter-dependent affinity between an s-SWCNT and the gel. Figure 4.9 shows the multicolumn system and the optical absorption spectra of 13 types of mono-structured s-SWCNTs [26] that were separated. he two integers in parentheses are the chiral index that defines the SWCNT structure [23]. Once we obtain the high-purity s-SWCNT ink, we can prepare TFTs by printing them on any surface. In addition, because an SWCNT has an inner space, we can introduce some molecules inside the SWCNTs and can control the sign and density of carrier of the s-SWCNTs by injecting charges from the inserted molecules. Figure 4.10 shows p- and n-type TFTs fabricated from pand n-type s-SWCNT ink. Here, we used tetrafluorotetracyanoquinodimethane (F4 TCNQ) for the p-type dopant molecule and cobaltocene for the n-type dopant. We propose that these carrier-controlled, high-purity s-SWCNT should be called second-generation (2G-) SWCNTs. By connecting p- and n-TFTs, complementary metal oxide semiconductor (CMOS)-type inverter logic circuits can be constructed. his demonstrated that p- and n-type s-SWCNT ink could produce conventional logic circuits by simply using a printing process without additional carrier doping. In addition, mono-structured s-SWCNTs can now be prepared on a large scale. hese mono-structured s-SWCNTs will substantially improve device performances because they all have the same band structure and are all switched on at the same gate voltage. Another promising application of s-SWCNTs is a thermoelectric device. We found a giant Seebeck coefficient (170 μV K−1 at 300K) in an s-SWCNT film, which

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4 Near-Industrialization Nanotechnologies Developed

0.5

14 Vdd = 12 V

12 P-TFT F4TCNQ@s-SWCNT Vin

Vout

10

0.4

8V

8 6

0.3 0.2

4V

4 n-TFT Cobaltocene@s-SWCNT

Idd (μA)

Vdd,Idd

Vout (V)

68

0.1

2 0 –12 –10 –8

0 –6

–4

–2

0

Vin (V) Figure 4.10 Output characteristics of inverter logic circuit constructed from a p-TFT (F4 TCNQ at s-SWCNT) and an n-TFT (cobaltocene at s-SWCNT).

Heating

Me ta Sem

Figure 4.11 Printed SWCNT thermoelectric device consisting of a series of six pairs of semiconducting and metallic SWCNT films. By placing a hand on one side of the device, 2.2 mV is generated.

4.6

Development of Liquid Crystalline Organic Semiconductors

is comparable to that of Bi2 Te3 alloys and 10 times higher than that of m-SWCNT film [27]. Carrier doping further improved the thermoelectric performance and estimated dimensionless thermoelectric figure of merit (ZT) at 350 K was 0.33. Figure 4.11 shows a trial manufacture of SWCNT thermoelectric device, which consists of a series of six pairs of s- and m-SWCNT films. A temperature difference of approximately 10 K generates 2.2 mV, meaning that each pair generates 0.36 mV. hese findings pave the way for emerging printed, all-carbon, flexible thermoelectric devices. 4.5.3 Conclusion

he new energy and industrial technology development organization (NEDO) of Japan created a project to industrialize SWCNT composite materials in 2010. In this project, m- and s-SWCNTs separated by the hydrogel column are provided to companies free of charge. Currently, some companies are developing practical devices that use s-SWCNT thin films or composite films for future products. 4.6 Development of Liquid Crystalline Organic Semiconductors6) 4.6.1 Historical Background

Organic semiconductors were practically applied to the photoreceptors for photocopiers in the 1970s, and to organic light emitting diodes (OLEDs) in the 1990s. In these applications, amorphous thin films of organic semiconductors are utilized because of technical requirements of the films used for these devices, for example, uniformity of the films in large areas, rather than high mobility. However, in order to extend device applications of organic semiconductors beyond these devices, for example, TFTs for display devices, which are limited by the mobility lower than 10−3 cm2 V−1 s−1 in the amorphous films, new materials exhibiting high mobility have to be developed because crystalline thin films including single crystals could not be the ones because of the difficulty in preparing uniform films in a large area and/or homogeneous gains for transistor arrays at that time when we started the research on liquid crystals. 4.6.2 Research Project

Since we discovered the electronic conduction in calamitic (rod-like) liquid crystals in 1995 [28], in which the electrical conduction had been thought to be ionic 6) Jun-ichi Hanna, Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.

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because of historical studies in 1970s, we have continued a basic research on liquid crystals as an organic semiconductor. Calamitic liquid crystalline molecules often form layered molecular aggregates called smectic mesophase in a certain temperature range. Because of an anisotropic molecular shape consisting of an extended π-conjugated system called a core and long hydrocarbon chains attached to it, the smectic mesophases exhibit a nano-scaled and microphase-separated structure of the ordered π-conjugated system where charge carriers can be transported. herefore, smectic liquid crystals can exhibit fast charge carrier transport and feasibility of fabricating uniform films thanks to molecularly ordered π-conjugated cores and soft nature of the mesophases formed in the self-organizing manner. For establishment of technical basis for device applications of liquid crystals in the future, a research project was proposed and was carried out from materials, understanding of basic electrical properties, and device applications points of view. And some goals for the research project were set for (i) establishment of a guiding principle to design a liquid crystalline molecule for high mobility, (ii) demonstration of new types of liquid crystalline organic semiconductors with multi-functionality, (iii) modeling of charge carrier transport properties of liquid crystals, (iv) understanding of electrical properties at the interface between electrode/liquid crystals, (v) total understanding of the carrier transport in organic materials from “amorphous materials” to “crystalline materials” in a framework of the molecular order, (vi) development of device fabrication processes utilizing liquid crystallinity, and (vii) demonstration of organic devices utilizing liquid crystals such as organic field effect transistors (OFETs) and OLEDs. As a result of 5 years research for the project, the following have been achieved: as for the materials, how the chemical structure of the core, the spacer, and the side chains affected charge carrier transport in liquid crystals was clarified, and a guiding principle of molecular design for liquid crystals exhibiting high charge carrier mobility was established; indeed, high mobility up to 0.5 cm2 V−1 s−1 for electron and hole was achieved; new functionality liquid crystals were explored, and new liquid crystals that show enhanced charge injection at the electrode interface and glassy smectic liquid crystals were synthesized and their unique properties were characterized; as for the understanding of charge carrier transport in liquid crystals, a new model for charge carrier transport in smectic mesophases, which includes a macroscopic view of not only a molecular aggregate described by the Gaussian disorder model but also charge transfer between neighboring molecules described by the Marcus rate, was proposed, and gave a good agreement with the experimental results; the effect of dipole on charge carrier transport in the smectic mesophases was clarified and formalized, which explains the temperature dependence of mobility in polar smectic liquid crystals at elevated temperatures; in addition, it was found that the electrical properties at the electrode interface were dominated by a Schottky type of energy barrier; as for the device applications utilizing liquid crystals, OFETs, OLEDs, and solar cells having an ordered bulk heterojunction were demonstrated.

4.6

Development of Liquid Crystalline Organic Semiconductors

Above all, OFET applications of highly ordered smectic liquid crystals were found to have high potential for immediate applications of liquid crystals because they could solve the problems remained in conventional soluble OFET materials, that is, poor surface morphology and poor uniformity in large areas and poor thermal stability in polycrystalline thin films. We have designed newly a smectic liquid crystal exhibiting highly ordered smectic phase of Smectic E (SmE), for which thermal stability of polycrystalline thin films was improved much because of a solid-like nature of the SmE phase, and synthesized for OFET applications. 2Phenyl-7-decylbenzothienobenzothiophene (Ph-BTBT-10) is a typical example. Polycrystalline thin films of Ph-BTBT-10 fabricated by a spin-coating technique at a temperature for the SmE phase, in which as-spin-coated liquid crystalline thin films were utilized as a precursor for polycrystalline thin films to fabricate OFETs, were molecularly flat and exhibited excellent film morphology in large areas as uniform and flat as those of the films fabricated by vacuum evaporation; in fact, the OFETs fabricated with the films of Ph-BTBT-10 exhibited high FET mobility of 4.6 cm2 V−1 s−1 , a high on–off ratio of >107 , and high thermal stability up to 200 ∘ C [29], as shown in Figure 4.12. 10–3 νs = −70 V 10–4 10–5 μFET = 4.6cm2/Vs, V th = –27V Ion/off = 4×107

Bottom gate and top contact of Au L = 100 μm, W/L=5

10–7 10–8

–0.14 –0.12

10–9

Drain current (mA)

Drain current (A)

10–6

Vg= –70V

Gate insulator SiO2 Bare (300nm) L =100 μm, W/L=5

–0.1

–60V

–0.08

10–10 10–11

–0.06

–50V

–0.04

–40V

–0.02 0 0

–30V –10

–20

–30

–40

–50

–60

–70

Source-drain voltage (V)

10–12 –70 –60 –50 –40 –30 –20

–10

0

10

Gate voltage (V) Figure 4.12 Typical field effect transistor (FET) performance of OFET fabricated with a polycrystalline thin film of Ph-BTBT-10.

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As described above briefly, another aspect of liquid crystals, that is, a selforganizing molecular semiconductor, has been well clarified through the present research, and it gives a good basis of device applications of liquid crystals in the future. We believe that liquid crystalline materials will be a key material for devices such as active matrices for e-papers and OLED displays and radio frequency integrated circuit (RF-IC) tags fabricated by printing techniques, in which high solubility of liquid crystals in organic solvents and self-organization of liquid crystalline molecules are made the best use of. 4.6.3 Conclusion

he present 5-years project for liquid crystals has established a good scientific and technical basis for device application of liquid crystals as an organic semiconductor. Above all, OFET applications of highly ordered smectic liquid crystals such as Ph-BTBT-10T are the most fruitful and promising for OFETs applications including TFT arrays in printed electronics. In fact, the high performance of OFETs fabricated with Ph-BTBT-10 have attracted high attention in the research community for industrial application of printed electronics including chemical companies and printing companies in Japan, resulting in collaboration researches for industrialization of Ph-BTBT-10 and its related materials and additional support from governmental organization of scientific research. 4.7 Polymeric Micelles for Cancer Therapy7) 4.7.1 Background and Present Status

Nanoscaled carriers can selectively deliver bioactive agents to solid tumors [30–32] based on the enhanced permeability retention (EPR) effect, which is characterized by leaky blood vessels and impaired lymphatic drainage in tumor tissues [33]. Preclinical and clinical data have identified the size, charge, surface chemistry, and stability and drug release of nanocarriers to affect their pharmacological efficacy [31, 32]. Producing safe nanocarriers with precise control of these properties has high potential for clinical translation. 4.7.2 Polymeric Micelles as Nanocarriers

PM, that is, self-assemblies of amphiphilic block copolymers consisting of a drug-loaded hydrophobic core and poly(ethylene glycol) (PEG) hydrophilic shell, 7) Horacio Cabral and Kazunori Kataoka, Department of Materials Engineering, Graduate School of Engineering, he University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan.

4.7

Polymeric Micelles for Cancer Therapy

73

Ligand-installed poly(ethylene glycol)-b-poly(amino acid) copolymer PEG-b-poly(L-Lysine) PEG-b-poly(α,β-aspartamide)s

PEG-b-poly(α,β-Aspartic acid) PEG-b-poly(α-Glutamic acid)

PEG-b-polyanion PEG-b-poly(α,β-Aspartic acid)

:Ca

2+

:PO4

3–

PEG-b-Poly(α,β-Aspartic acid) PEG-b-poly(α-Glutamic acid)

H3N

CI

siRNA

Polyion-complex formation Self-assembly

Small hydrophobic drugs (doxorubicin, paclitaxel, SN-38) Drug–polymer conjugates Physical drug incorporation Self-assembly

pDNA

H3N

CI N Platinum drugs H 2

Calcium phosphate crystal growth Organic-inorganic hybrid micelles formation Self-assembly

Ligand: Sensing Celluar and receptor specificity Extravasation by transcytosis Core: Loading of reporter and bioactive agents Protection of degradable biomolecules Controlled release ability

siRNA

NO3

Pt

Pt pDNA

H2 N

CI

Polymer-metal complex formation Self-assembly

PEG shell: Biocompatibility Reduced interaction with serum proteins Prolonged blood circulation

Tens of nanometers

Figure 4.13 Polymeric micelles self-assembled from PEG-b-poly(amino acid) copolymers incorporating drugs and genes by taking advantage of different driving forces.

are promising nanocarriers for tumor targeting (Figure 4.13) [32, 34]. While the PEG shell provides biocompatibility, the core allows incorporating a wide variety of bioactive agents. Poly(amino acid)s are advantageous backbones of block copolymers for constructing safe and biocompatible cores, as their side groups can be modified for proper assembly, loading, and release [32, 34]. PM present exceptional advantages as nanocarriers, including a relatively small size (10–100 nm), allowing deep penetration in tumor tissues, controlled drug release, prolonged blood circulation, reduced distribution to healthy tissues, and selective accumulation in solid tumors [32, 34]. heir surface can also be functionalized with ligands capable of recognition of cell-specific surface receptors, providing cellular selectivity [32, 34]. 4.7.3 Perspectives to Industrialization

Before PM are approved for clinical use, several specifications have to be satisfied, including components, fabrication process, adequate quality control, and finally, demonstration of safety and efficacy in clinical trials. Accordingly, several PM for chemotherapy have already progressed to clinical evaluation [35–38] (Table 4.1). While clinical testing of some PM is in the initial stage, paclitaxel-loaded PM (NK-105) and cisplatin-loaded PM (NC-6004) have advanced to their final clinical

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4 Near-Industrialization Nanotechnologies Developed

Table 4.1 Current status of polymeric micelles developed by Japanese companies. Name

Drug/Block copolymer

Company

Development phase

NK105

Paclitaxel/PEG-bpoly(modified aspartate)

Nippon Kayaku, Co.

Gastric cancer/ Phase II breast cancer (completed) Phase III (started July 2012; breast cancer) Phase II Triple negative breast cancer Phase II Various solid tumors

NK012

SN-38/PEG-b-poly(αglutamic acid) NK911 Doxorubicin/PEG-bpoly(α,β-aspartic acid) NC-6004 Cisplatin/PEG-b-poly(αglutamic acid) NC-4016 Dachplatin/PEG-b-poly(αglutamic acid) NC-6300 Doxorubicin/PEG-bpoly(aspartate-hydrazone) siRNA micelles siRNA/various polymers

Nippon Kayaku, Co. Nippon Kayaku, Co.

Nanocarrier, Co. Nanocarrier, Co. Nanocarrier, Co. Nanocarrier, Co.

Indication

Phase III (started Pancreatic cancer July 2013) Phase I Various solid tumors Phase I Various solid tumors Preclinical —

stage, that is, phase III, against breast cancer and pancreatic cancer, respectively, after showing superior efficacy in phase II trials, while improving the quality of life of patients by reducing the toxicity of incorporated drugs and eliminating prolonged hospitalization. Nanocarrier technologies already represent a several billion dollars market [30], which is expected to grow exponentially in the next years. In this situation, Japan has an internationally strong position, with a share of 5% of patents and >9% of publications [30]. While technology-driven startups and non-pharmaceutical industries lead the commercialization of PM in Japan (Table 4.1), big pharmaceutical companies will likely partner with them or license their technology, as PM progress into late stages of clinical development or ultimately complete clinical trials. 4.7.4 Conclusions

As described in Sections 4.7.2 and 4.7.3, different formulation of PM loaded with anticancer drugs have already been in clinical trial, and the most advanced one, that is, paclitaxel-loaded PM, is expected to be applied for the approval by the end of 2014. Also, block copolymers used for the preparation of PM loaded with gene and oligonucleotides have been listed in the products catalog of NOF Co., and are ready for the large-scale production in Good Manufacturing Practice (GMP)

4.8

Nanoparticulate Vaccine Adjuvants and Delivery Systems

grade. Accordingly, Japan has taken a leadership to prepare the reflection paper of PM, and it has just been released on the internet [39].

4.8 Nanoparticulate Vaccine Adjuvants and Delivery Systems8) 4.8.1 Introduction

Vaccination is a powerful method to induce humoral and cellular adaptive immune responses aiming to control viral and bacterial infections as well as tumor growth. To date, the majority of the vaccines have been developed using live attenuated organisms, inactivated whole organisms, or inactivated toxins. Recently, many vaccines under investigation were based on highly purified recombinant proteins, protein subunits, or synthetic peptides. New-generation vaccines utilizing immunogenic subunits derived from a particular pathogen are able to overcome safety problem. However, as compared with traditional vaccines, subunit vaccines are poorly immunogenic and thus require the use of adjuvants to induce optimal immune responses [40]. 4.8.2 The Role of Nanotechnology in Vaccine Developments

Adjuvants are compounds that enhance the immune response against coinoculated antigens. Until recently, aluminum-based compounds were the only adjuvants licensed for human use. Despite the subsequent discovery of many other considerably more potent adjuvants, such as complete Freund’s adjuvant (CFA) or lipolysaccharide (LPS), they are judged to be unsuitable for human use due to local and systemic toxicity [41]. In the past, many kinds of adjuvant have been developed, and they can be divided into two classes on the basis of their mechanism of action: vaccine delivery systems and immunostimulants. Nanotechnology provides multiple platforms that could be used as adjuvants in the next generation of vaccines. Among the various platforms, polymeric NPs, liposomes, and inorganic NPs have emerged as leading candidates. Among vaccine delivery systems, nanoparticulate materials are attractive because their particulate nature can control antigen release from the particles. In addition, 8) Takami Akagi and Mitsuru Akashi, Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan and Nanoparticle Adjuvant (Takeda Pharmaceutical Company Limited) Joint Research Chair, Graduate School of Engineering, Osaka University, 2-8 Yamadaoka, Suita, Osaka 565-0871, Japan; Tomohide Tatusmi, Department of Gastroenterology and Hepatology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan; and Masanori Baba, Center for Chronic Viral Diseases, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-0544, Japan.

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4 Near-Industrialization Nanotechnologies Developed

Antigen-loaded biodegradable nanoparticles

Induction of immune responses

Antigen-presenting cells Uptake of NPs

Degradation of NPs

Cellular

Humoral

Cytotoxic T Iymphocytes (CTL)

CTL

Virus 200 nm Antibody Protein, Peptide, DNA

Intracellular antigen release

Prevention

Therapy

Activation Figure 4.14 Immune induction by nanoparticle-based vaccine.

they can be passively or actively targeted to antigen presenting cells (APCs). Furthermore, particulate adjuvants are able to directly activate innate immune system (Figure 4.14). 4.8.3 Biodegradable Nanoparticles as Vaccine Adjuvants and Delivery Systems

In order to develop particulate adjuvants, we have designed a novel protein/peptide delivery system with self-assembled amphiphilic polymeric NPs. hey formulated amphiphilic NPs consisting of hydrophilic poly(γ-glutamic acid) (γ-PGA) and hydrophobic L-phenylalanine ethylester (Phe) side chain (Figure 4.15). he size of the γ-PGA-Phe NPs could be easily controlled from 30 to 200 nm by preparative conditions [42]. Dendritic cells (DCs) are professional APCs that play a central role in initiation and regulation of antigen-specific immune response. Targeted delivery of antigens to DCs and DC activation is an attractive strategy to enhance vaccine efficacy. Protein-encapsulated γ-PGA-Phe NPs could be successfully used to enhance the protein delivery to DCs. he NPs also had adjuvant activity via toll-like receptors (TLRs) for DC maturation [43]. hus, the NPs have significant potential as an antigen carrier and adjuvant for O

O

( NH-CH-CH2-CH2-C ) m ( NH-CH-CH2-CH2-C ) l C

COOH

O

NH CH-COOCH2CH3

γ-PGA-Phe NPs

CH2

500 nm

Figure 4.15 Chemical structure of γ-PGA-Phe and SEM image of NPs.

References

DCs. It has been demonstrated that the γ-PGA-Phe NPs are also effective for vaccines against viral infections such as influenza virus [44]. 4.8.4 Clinical Application of Particulate Vaccine Adjuvants

To apply the γ-PGA-Phe NPs as cancer vaccines, tumor-associated antigen (TAA)-derived peptide (EphA2, 9 mer) was surface-immobilized onto the NPs (Eph-NPs, 200 nm). Immunization of mice with Eph-NPs resulted in generation of EphA2-specific CD8+ T cells. Immunization with Eph-NPs tended to provide a degree of anti-MC38 liver tumor protection more than that observed for immunization with Eph + CFA [45]. Immunization with Eph + CFA induced liver damage as evidenced by elevation of serum alanine aminotransferase, while Eph-NPs vaccination did not exhibit any toxic damage to the liver. Moreover, the safety of the γ-PGA-Phe NPs was confirmed in a 14-day repeated dose toxicity study of NPs using rat. he NPs did not show any toxicity, and showed higher safety than alum. Based on these data, we are planning clinical trial (translational research) of cancer vaccine using TAA peptide-immobilized GMP-compliant γ-PGA-Phe NPs in Osaka University, Japan. 4.8.5 Conclusions

he particulate adjuvant will provide a novel immune therapy for cancers and infectious diseases. Joint Research Chair by Takeda Pharmaceutical Company and Osaka University was set up to develop a platform for the practical application and industrialization of vaccines using γ-PGA-Phe NPs as adjuvants. Next-generation vaccine adjuvants will be produced by the joint effort between academia and industry.

References 1. Kuwabata, S., Tsuda, T., and Torimoto, T.

(2010) J. Phys. Chem. Lett., 1, 3177–3188. 2. Torimoto, T., Okazaki, K.-I., Kiyama, T., Hirahara, K., Tanaka, N., and Kuwabata, S. (2006) Appl. Phys. Lett., 89, 243117/1–243117/3. 3. Okazaki, K.-I., Kiyama, T., Hirahara, K., Tanaka, N., Kuwabata, S., and Torimoto, T. (2008) Chem. Commun., 691–693. 4. Suzuki, T., Okazaki, K.-I., Suzuki, S., Shibayama, T., Kuwabata, S., and Torimoto, T. (2010) Chem. Mater., 22, 5209–5215.

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5 Quo Vadis Nanotechnology? ´ Witold Łojkowski, Hans-Jörg Fecht, and Anna Swiderska Sroda

5.1 Introduction

Nanotechnology attracts big attention in society, the academic world and industry. Exploiting its potential is a challenge for research institutions, universities, governments, research funding agencies, as well as investors. However, the present situation in the development of nanotechnology is quite different from the situation when the first “he Nano-Micro Interface” book [1] was published: nanotechnology is common practice in many areas of industry, has been, and is being developed in research centers all over the world. hus, nanotechnology is a matured research field. As such, new challenges arise as compared to the situation 10 years ago: How will nanotechnology address present-day important societal problems? Is it already time to select within nanotechnology the frontier research areas and the “robust research” needed by society in the phase of industrialization? Nanotechnology development, application, risk, and opportunities have become important issues not only for researchers, but also for industry, governments, funding and regulatory agencies, and society. In this introduction, we will briefly remind the definition of nanotechnology, and discuss the challenges nanotechnology creates for the above-mentioned stakeholders. he present review is largely based on the recent review by M. Roco et al. [2]. he reader may also refer to the nanotechnology roadmap published by the European Nanotechnology Platform [3] and the European Nanomedicine Platform [4]. A thorough nanotechnology roadmap can be found in the “GENNESYS White Paper” – a book devoted to enhance the impact of European synchrotron radiation and neutron facilities on nanotechnology and nanomaterials science [5]. he abbreviation GENNESYS stands for Grand European Initiative on Nanoscience and Nanotechnology using NEutron and SYnchrotron radiation Sources. he present chapter is also based on authors’ personal experiences and problems encountered in everyday work. Let us quote two recent situations from our professional life. Recently, one of us was discussing a nanoparticles coating technology of polymers with a PhD student, to make the surface biocompatible. he PhD student he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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5 Quo Vadis Nanotechnology?

said “But this layer is very thick, it has 100 nm thickness!” However, 100 nm, in reality, is a rather thin layer. hus, in the nanotechnology era, for a PhD student, it is a thick layer. he student was digging in the details of the structure with ambition to control its thickness at the level of 10 nm or less. his situation shows that for the present young generation, nanotechnology is something obvious. In another situation, at a high-level meeting on future research directions of a large consortium of universities and institutes, one of the directors attending the meeting opposed to define the new consortium in terms of nanotechnology. His words were more or less like “But now nanotechnology is everything. It is ridiculous to define it as a research area for our consortium.” hus, after 20–30 years of research and development in nanotechnology, it seems that it is time to rethink the meaning of this term for society, to assess whether it is one of practical significance or not, and to look forward, where nanotechnology is going.

5.2 What is Nanotechnology?

Materials engineering is transforming matter into useful materials, and nanotechnology permits to engineer the shape, size, and structure of materials on the nanoscale. According to the usual definition of nanotechnology, it is engineering materials in the scale from 1 to 100 nm. A second component of the nanotechnology definition is that it exploits new phenomena occurring when a characteristic dimension of matter is in the range 1–100 nm [6]. Nanotechnology is perhaps the most dynamic field of materials engineering. Expanding the range of dimensions available to materials engineering to the nanometer range is a megatrend. Man continuously has increased the precision with which materials are shaped and measured. In past ages, the precision with which materials could be shaped and manipulated was in the range of 1–0.1 mm (e.g., various constructions, ships, tools). In the microtechnology era, the precision was 1000 times higher: 0.001 mm. At the beginning of the twentieth century, the concept of microstructure emerged, which means that it became possible to observe the internal structure of defects in materials (e.g., grain boundaries, interfaces, precipitations) once micrometer resolution was available. At the same time, the precision of machining various mechanical parts was in the 1 μm range. Furthermore, already in ancient times and during the Middle Ages, nanoparticles of gold were used to change the color of glass [7]. However, the reason for the change of color and the fact that gold can form nanoprecipitates were not known, of course. Nowadays, engineers can routinely produce and observe structures (layers, particles, atomic clusters, precipitates, inclusions, tubes, cavities, etc.) with a precision of 1 nm, or even less. However, the real reason nanotechnology attracts particular attention is because – for such small structures – the properties of matter become size-dependent. We are used to the concept of material as such, but a material whose properties depend on its size and shape is conceptually quite

5.2

What is Nanotechnology?

new. he size and shape dependence of properties of matter opened a way to a number of important discoveries, many of which have found practical applications. It can be expected that we are at the beginning of the exploration of the fascinating opportunities nanotechnology offers. In the same way as materials science explains or attempts to predict the properties of materials from the point of view of their applications, nanoscience attempts to predict the properties of nano-structured materials. he new, frequently unexpected, properties of nano-structured materials are observed when the size of the structure becomes smaller than a characteristic dimension, which is usually between 100 nm (although this is not an absolute limit, since size-dependent properties can be observed also in the submicron range, e.g., mechanical and optical properties) and 1 nm. In fact, occurrence of such size-dependent phenomena is not surprising. Properties of atoms and matter are different. In the intermediate stage, when the size of matter approaches that of an atom, the properties are neither that of conventional matter nor of single atoms, and they are size-dependent. Nanotechnology opened the way for close interaction of the traditional fields of materials engineering, physics, and materials chemistry with biochemistry, biophysics, and biology. he simple reason is that the size of the nano-engineered structures is similar to that of biological structures: proteins, viruses, molecules. hus, it is possible to exploit various steric effects resulting from similar sizes of the nano- and biostructures, interaction of organic and inorganic nano-sized structures, formation of hetero: nano-bio structures and mutual exchange of methods of biochemistry, biophysics, and nanotechnology, leading to the dynamically growing field of bionanotechnology. In a way, arranging nanostructures on the nanoscale, and achieving structures whose properties depend not only on the chemical composition but also on shape and mutual arrangement of the nano- or bio-building blocks is another dimension of nanotechnology, further to the above-mentioned size effects. In short, nanotechnology is part of materials engineering, where the effect of matter size and shape on its property is exploited. However, nanotechnology also exploits novel properties of structures made by arranging nano-sized building blocks into engineered higher rank structures. Shifting the research interests in this direction is also called in [2] a “Nano1 => Nano2 transition” (Figure 5.1). his kind of technology is similar to the composites technology, by which various materials are combined into functional or construction materials; however, the structure is shaped on the nanoscale. Also organic–inorganic composites are well known; however, the world of structures made by joining nanomatter with nano-sized proteins and other molecules, like DNA or RNA, or their interactions, is a fascinating field of nanobiotechnology, where the new properties expected will result from the shape and arrangement of the building blocks, not only size. Examples are targeted drugs for cancer therapy. he above definition of nanotechnology is used in the “academia,” by scientists and researchers. However, when asking where nanotechnology is going, “Quo vadis nanotechnology?”, it might be interesting to first analyze in which space the movement is, and this depends on the different meanings nanotechnology has

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Market incorporating nanotechnology ($B)

82

10 000

1000

2020 World~$3 T US~$1.2 T Nano-systems

Nano 2 100

Nano 1

2009 World~$254 B US~$92 B Nanocomponents

10

2000 R&D definition long-term vision 1

2000

2005

2010

2015

2020

Year

Figure 5.1 Market of final products incorporating nanotechnology. The R&D focus evolves from fundamental discoveries in 2000–2010 (Nano1) to applications-driven fundamental and system research in 2010–2020 (Nano2). Based on [2].

for various stakeholders: beyond academia, there are industry, governments, and society.

5.3 Quo Vadis Nanotechnology – In Academia?

In the world of universities, research centers, and so on, nanotechnology is everyday practice. Nanotechnology research centers are now being created in every country of the globe that has a sufficient research capacity, also in the “developing world” [8], as well as at small universities in technologically well-advanced countries. Besides the well-established players, new important players in the field are, for example, Iran [9] and Turkey [10]; nano-research is developing in countries with relatively low gross domestic products (GDPs) (Vietnam [11], Egypt [12], Nigeria [13]). A strong R&D nanotechnology program was implemented by Russia [14]. Nano-research centers are being created even in universities that are far down in the ranking lists. It does not mean that all research in materials is focused on nanotechnology. However, once tools are available to investigate the structure of matter in the scale of 1 nm, a natural trend is to explain the properties of materials by studying nanoscale phenomena. For instance, when a precipitation process starts to grow new particles that are nanometer in size, the interfaces are 1 nm thick, thin film growing is from 1 nm thickness, and cracks have 1 nm diameter at their tip. Polymers have, in a natural way, their structure measured in nanometers.

5.3

Quo Vadis Nanotechnology – In Academia?

83

Tools for production of nanostructures are also becoming standard equipment in laboratories. Bionanotechnology centers have been popping up in many countries and regions. In summary, nanotechnology is, nowadays, everyday life in scientific laboratories all over the world. According to the report [2], the overall growth of interest in nanotechnology is 25% average per year. his situation makes a prediction of nanotechnology future quite a challenge. Is this a bubble that will burst and interest in nanotechnology will break down when the term will have become too much a commonplace? he answer may be found in the recent description of nanotechnology situation as a transition called “Nano1 => Nano2” [2]. For relatively simple nanostructures (e.g., nanoparticles, nano-coatings, nano-fibers, etc.), it means a transition from scientific challenges to innovation challenges: scale up of production, nanometrology, safety, and related research subjects, carried out in many applied research institutions. Furthermore, a broad field of nano-architectonics, as well as complex hierarchical nano-micro and nano-bio structures, nano-systems opens (Figures 5.2 and 5.3). In fact, we discussed above the changes of properties of matter if they are intermediate between the “classical” properties of materials, and the properties

(a) Classical materials Material (1) with engineered micro/nano structure and phase compostion Material (2) with engineered micro/nano structure and phase compostion

(b) Composites Different materials are organized in form of a compostite. The properties depend on the architecture of the composite, interfaces between materials, and the properties of the component materials.

Shape, joining technology

Composite

Tool Tool

(d) Nanotechnology: still materials engineering, but a new world

(c) Nanomaterials Are like classical materials, but emphasis is on engineering the structure in the nanoscale Nano2 transition.” [2]. he term nanotechnology has different meanings to different stakeholders. For the academia, it is one of the everyday technologies. It might thus be needed to define some specializations when new nano-research centers will be created. For industry, it will gradually become a technology that does not request a special mention, unless it is useful from a marketing or public perception point of view. For governments and regulatory bodies, the issue will be to determine how to take advantage of nanotechnology for economy growth and, at the same time, ensure social acceptance. Nations under pressure caused be ecological or political forces may look at nanotechnology as a key technology to solve their problems, probably in a very justified way, since the already available knowledge gives good grounds to think about radical improvements in health care, energy and resources, Information Technologies (IT), transport, and others. he field for new discoveries is immense, and the nano-bubble will not burst although the nano-label will not be always used to describe a nano-enabled technology. Although nanotechnology as pivotal enabling technology will influence our lives in any aspect that depends on technology, we may mention a few expected

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breakthroughs, which illustrate that it is of key importance for the future of our civilization. In respect to health, it may lead to a radical change in the treatment of cancer: the surgeon’s intervention will be rare, and if there is needed any at all, it will be at the end of the treatment. Most of cancer forms will be removed using targeted nanostructured drugs. Furthermore, timely diagnosis will be possible using nanotechnology-based sensors with a degree of sensitivity that is many orders higher than presently available. Nanotechnology-enhanced diagnostics will enable to early select the proper drugs. Time to market and the costs of new drugs development will be significantly shortened [21] (B. Loubaton, Chairman 2012 of the European Nanomedicine Platform, private communication). In regenerative medicine, recovery of lost tissue (nerves, bone, skin, etc.) will be possible by use of intelligent nanomaterials-based tissue re-growth scaffolds [4]. Convergence of nanoelectronics, nanobiotechnology, and biomedicine will lead to replacement of lost senses, or enhancement of the existing ones, or perhaps, like in scientific fiction books, acquiring new senses (magnetic field, acceleration, infrared light, ultrasound, etc.). he issue raises many scientific, ethical, political, and social questions [22] related to the emerging CONVERGING TECHNOLOGIES where nano, bio, info technologies and cognitive sciences merge for new solutions-enhancing human capacities [23]. In respect to environment and energy, low-cost filters to purify water or remove salt will be available for both technologically advanced countries as well as the developing countries, eliminating the water supply problem. Solar energy will be abundant and available at costs lower than the present gird electricity prices (TED Talk [19]). Furthermore, storage of energy using nanotechnology-based capacitors, supercapacitors or batteries will be competitive in terms of energy stored per kilogram or liter of equipment against the present energy density in conventional fuels, paving the way to very low-cost transportation since electricity will be generated from solar energy. Information technology is already based on nanotechnology. However, intelligent systems – so to speak systems that solve problems and learn – will be created based on extremely complex random networks made from nanostructured building blocks packed with extreme density in a unit of volume or surface [24]. In the materials field, continuous progress will lead to improved coatings, corrosion resistance, combined properties like strength and ductility, and so on, and new alloys or nano-composites with unexpected properties. Nanophotonics will enable new methods to control and exploit photons for information transmission and encrypting, as well as efficient solar energy at low costs [25, 26]. he potential of nanofluids is largely unexplored [3]. Nano-architectonics, nano-bio architecture, which is, building higher-order structures from nano building blocks made of materials and/or biomolecules, will lead to structures with unforeseen properties, or intelligent structures. Progress towards the sub-nanometer scale for the characterization of structures and their engineering in a scale less than 1 nm is sometimes called picotechnology [27]. It may include experimental techniques for picoscale studies of atoms,

References

molecules, structures less than 1 nm in diameter, picoelectronic devices, such as single-atom switches, single-photon gating systems, and others. Nano-metrology, methods of production cost reduction, reducing regulatory risks; LCA for environment impact will be leading subjects for industry involved in large-scale nanomaterials production. As usual in human activity, action is most important. Nature will bring us surprises and force to revise the foresights or theories. However, the surprises inherent to nanotechnology are much more surely to be encountered than in traditional research fields.

5.10 Limitations of the Chapter

he content of this chapter is not based on a rigid scientific study, and the opinions expressed reflect the personal views of the authors, reflecting their experience. he experience results from work in the Organization for Economic Co-operation and Development (OECD) Working Party in Nanotechnology, European Nanomedicine Platform, several European research projects connected with nanotechnology roadmapping and commercialization, as well as from interactions with industry.

Acknowledgements

his work was supported by the Interregional European Union project “NANOFORCE”, co-finansed by the ERDE.

References 1. Fecht, H.-J. and Werner, M. (eds) (2004)

he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Wiley-VCH Verlag GmbH, Weinheim, doi: 10.1002/ 3527604111, published online 2005. 2. Roco, M.C., Mirkin, C.A., and Hersam, M.C. (eds) (2011) Nanotechnology Research Directions for Societal Needs in 2020: Retrospective and Outlook, Springer, Berlin and Boston, MA, http://www.wtec.org/nano2/ (accessed 18 November 2013). 3. NANOfutures (2012) Integrated Research and Industrial Roadmap for European Nanotechnology. Report Coordination and Support Action (Grant

agreement no 266789), DL AS 24812012, http://www.nanofutures.info/sites/ default/files/NANOfutures_Roadmap% 20july%202012_0.pdf (accessed 21 May 2014). 4. European Commission, European Technology Platform on NanoMedicine, Nanotechnology for Health (2005) Vision Paper and Basis for a Strategic Research Agenda for NanoMedicine, Office for Official Publications of the European Communities, Luxembourg, http://www.etp-nanomedicine.eu/public/ press-documents/publications/etpnpublications/etp-nanomedicinevisionpaper (accessed 18 November 2013).

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6.

7.

8.

9.

10.

11.

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13.

14. 15.

16.

17.

(eds) (2009) GENNESYS White Paper – A New European Partnership between Nanomaterials Science & Nanotechnology and Synchrotron Radiation and Neutron Facilities, Max Planck Institute for Metals Research, Stuttgart, pp. 241–245, ISBN: 978-3-00-027338-4, www.mpi-stuttgard-mpg.de (accessed 18 November 2013). Definition proposed in Siegel, R., Hu, E., and Roco, M.C. (eds) (1999) Nanostructure Science and Technology, National Science and Technology Council, Washington, DC. Horikoshi, S. and Sapone, N. (2013) Microwaves in Nanoparticle Synthesis, Fundamentals and Applications, Wiley-VCH Verlag GmbH, pp. 1–23. Sci Dev Net http://www.scidev.net/ global/water/feature/nanotechnologyfor-clean-water-facts-and-figures.html (accessed 18 November 2013). Iran Nanotechnology Initiative Council http://irannano.org/nano/index.php? lang=2 (accessed 18 November 2013). (0000) 7th Nanoscience and Nanotechnology Conference – 2011, Sabanci University, Istanbul, Turkey, http://nanotr7.sabanciuniv.edu/en (accessed 18 November 2013). Asia NanoForum http://www.asiaanf.org/CountryHome.php?CN=12 (accessed 18 November 2013). Egypt Nano Technologies Co. http:// www.egyptnanotech.com/site/index2.php (accessed 18 November 2013). University World News http://www.universityworldnews.com/ article.php?story=20110305084259893 (accessed 18 November 2013). RUSNANO http://en.rusnano.com/ (accessed 18 November 2013). Trading Economics www.tradingeconomics.com/unitedstates/gdp (accessed 18 November 2013). Nano Business Alliance www.nanobusiness.org (accessed 18 November 2013). NanoMedicine European Technology Platform on NanoMedicine,

18.

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27.

http://www.etp-nanomedicine.eu (accessed 18 November 2013). NANOfutures European Initiative for Sustainable Development by Nanotechnologies, www.nanofutures.info (accessed 18 November 2013). Diamantis, P. (2012) Abundance is Our Future, TED Talk http://www.ted.com/ talks/peter_diamandis_abundance_is_ our_future.html?source=email#. T1KWa9Qbabx.email (accessed 18 November 2013). KNO Faculty of Physics, Astronomy and Applied Computer Science of the Jagiellonian University in Cracow, Poland, http://www.fais.uj.edu.pl/en_GB/ advanced-materials-and-nanotechnology (accessed 16 November 2013). Loubaton, B. (2012) Exploring the quantitative dimensions of the quantitative impact of nanomedicine. presentation on OECD and US NNI International Workshop on Assessing the Economic Impact of Nanotechnology, Washington, DC, March, 27–28, 2012, http://nano.gov/ sites/default/files/medicine_-_loubaton. pdf (accessed 18 November 2013). Bainbridge, W.S. and Rocco, M.C. (eds) (2010) Managing Nano-Bio-Info-Cogno Innovations, Springer, Berlin. Nanotechnology in the context of Technology convergence. Working party on Nanotechnology Document DSTI/STP/Nano (2013) CO Published by OECD. Gimzewski, J.K. (2012) here is no room at the bottom. Convergence, 12, newsletter of the International Center for Materials Nanoarchitectures (MANA), Japan. van Hulst, N. and Kennedy, S. (eds) (2011) Nanophotonics Foresight Report, D.L. B-26259-2011, http://outreach.icfo.eu/media/upload/ arxius/industry-reports/NanophotonicsForesight-Report.pdf (accessed 18 November 2013). Photonic Road SME http://www.photonicroad.eu/ (accessed 19 November 2013). Sattler, K.D. (ed.) (2013) Fundamentals of Picoscience, CRC Press.

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Part II Development of Micro and Nanotechnologies

he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces Jared J. Victor, Uwe Erb, and Gino Palumbo

6.1 Introduction

he idea of observing, understanding, and learning new concepts from nature for the duplication of attractive biological properties is called biomimetics and has recently been gaining a lot of interest with engineers at the forefront of advanced materials/device development [1]. In one particular example, these attractive biological properties are created through elegantly designed surfaces or interfaces containing structural features on the micro- and/or nanoscale. Since the 1990s superhydrophobic and self-cleaning leaf surfaces have been studied in great detail; the most popular and first to be thoroughly examined being the lotus leaf [2–6]. It has been shown that the extreme nonwetting properties of these leaves arise from a hierarchical dual-scale surface structure consisting of microscale papillae covered with nanoscale wax crystals [4, 7–11]. Superhydrophobic leaf structures, possessing these nonwetting surface features, have been used as a biological blueprint in the structuring of a variety of engineering materials, rendering their surfaces highly water-repellent [10, 12–18]. From a technological point of view such surfaces are of great interest for a number of applications including self-cleaning windows, glass, paints, and textiles; low-friction surfaces to minimize surface flow resistance; anti-adhesive surfaces to reduce contamination; and anti-icing surfaces. In the past, there have been many successful attempts at artificially reproducing the surface structures found on natural superhydrophobic surfaces. However, many of these approaches are time consuming, expensive, and/or have size restrictions that limit their use for practical applications. Common methods to create roughened dual-scale superhydrophobic surfaces are lithography [19], chemical vapor deposition (CVD) [20], chemical etching [21], plasma etching [22], selfassembly [23], and nanocasting [24]. All of these fabrication methods have one crucial commonality: they all create rough patterned or porous surfaces which have methyl or fluorine (chemically hydrophobic) terminal groups or to which a thin hydrophobic layer (low surface energy material) can be applied. Lithography and plasma-enhanced CVD are expensive methods that use nanomasks and costly he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

Table 6.1 Comparison of current and existing technologies for producing micro/nanoroughness polymer surfaces. Technique

Advantages

Disadvantages

Lithography

• •

High precision patterns Complex patterns

Deposition

• •

High precision patterns Complex patterns

Etching

•

Low costs

Self-assembly

•

High precision patterns

Current approach

• • • • •

Low costs Low precision patterns Easy to scale up Continuous process possible Can be incorporated in current process technologies

• • • • • • • • • • • • •

Difficult on polymers Difficult to scale up High costs Difficult on polymers Difficult to scale up High costs Low precision patterns Reproducibility concerns Difficult on complex shapes Adhesion problems Difficult to scale up High costs Low precision patterns

equipment to produce a highly structured surface. Etching procedures seem to be the most promising for a low-cost approach, but to date there have been very few publications indicating that large-scale production or structuring of complex geometries can easily be achieved using this method. he advantages and disadvantages of these fabrication methods are summarized in Table 6.1. his chapter describes the development of a template-based surface structuring technology that can be used to transfer the surface structure observed on the leaves of various aspen trees onto the surfaces of engineering polymers. he template design makes use of the unique microstructural features, strength, and chemical etching properties of nanocrystalline nickel electrodeposits. his technology (see current approach in Table 6.1) is relatively inexpensive, easy to scale up, and suitable for implementation in a number of polymer processing operations [16–18].

6.2 Superhydrophobic Surfaces in Nature – The Lotus Effect

here is a wide variety of superhydrophobic surfaces found in nature, most of these on the surfaces of plants or insects. Many plant surfaces display a similar type of extreme nonwetting behavior with the most well known being

6.3

Basic Wetting Properties

the extensively studied lotus leaf [2–5]. he origin of this property for plants is a combination of a dual-scale hierarchical surface structure coupled with low surface energy materials: for plants, these materials are their hydrophobic epicuticular waxes (waxes on top of the cuticle). hese waxes usually consist of a mixture of aliphatic hydrocarbons and/or their derivatives, with the main components being primary and secondary alcohols, ketones, fatty acids, and aldehydes [25]. Long chain carbon molecules containing one or two hydroxyl groups (nonacosanol – C29 H60 O or nonacosanediols – C29 H60 O2 ) account for the majority of the wax crystal chemistry. More often than not, epicuticular waxes show great morphological variability; however, they usually form three-dimensional structures having sizes within the nanoscale. Multiple different wax crystal configurations, such as 3D nanoplatelets, rods, tubules, and flakes, have been observed on many different plant leaf surfaces [5, 26]. In most cases, these hydrophobic nano-wax crystals are superimposed on top of an array of microscale protrusions (papillae) usually created by convex upper epidermal cells [6]. he combination of these papillae and hydrophobic 3D nanoscale wax crystals imparts the nonwetting property that certain plant leaf surfaces display [2, 27].

6.3 Basic Wetting Properties

he contact angle (� 0 ) is a quantitative measure of the wetting of a solid by a liquid. hermodynamically it can be thought of as a balance between the interfacial energies for the three phases present (solid, liquid, and vapor). Young’s equation relating this balance is shown in Eq. (6.1): �lv cos �0 = �sv − �sl

(6.1)

where � lv , � sv , and � sl refer to the interfacial energies of the liquid/vapor, solid/vapor, and solid/liquid interfaces [28]. Equation (6.1) accounts for the difference in chemical nature of the three phases present and assumes that the solid surface is microscopically smooth. When a liquid droplet encounters a solid surface it may wet the surface to varying degrees. For a hydrophilic solid surface, water droplets will spread out and wet the surface resulting in a contact angle (CA) less than 90∘ ; however, for hydrophobic surfaces a contact angle greater than 90∘ will be created which is characteristic of dewetting surfaces. he difference in contact angles for these two types of surfaces arises from differences in the chemical nature of solid surfaces and liquid droplets. For hydrophobic surfaces, the energy associated with the solid/vapor interface is lower than that for the solid/liquid interface. his results in a free energy driving force to create a small solid/liquid interfacial area, a large solid/vapor interfacial area, and, consequently, a contact angle above 90∘ . For hydrophilic surfaces, the free energies of these interfaces are reversed resulting in a contact angle below 90∘ .

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

Contact angles can range from 180∘ to 0∘ depending on the magnitude of the solid/vapor and solid/liquid interfaces. In the extreme limit, if a liquid creates a contact angle of 180∘ with a solid, a complete nonwetting condition is present and the droplet will only be in contact with the solid at one specific point. If the contact angle formed is above 150∘ , the surface is considered superhydrophobic. he majority of solid surfaces are classified as hydrophobic (150∘ > CA ≥ 90∘ ) or hydrophilic (CA < 90∘ ). In the other extreme, the case of complete wetting, liquid drops easily spread out over the entire surface forming a thin liquid layer on top of the solid. A contact angle of 0∘ is characteristic of this type of wetting condition. he spreading coefficient (S) is another useful way to describe the amount of wetting that will occur with a given solid surface and liquid drop. his coefficient is defined as the difference between the work of adhesion (W a = � lv + � sv − � sl ) for the solid/liquid interface and the work of cohesion (W c = 2� lv ) for the specific liquid [29]. It is known that a liquid will spread over a solid surface if the spreading coefficient (S = W a − W c ) is positive, and will not spread if this value is negative. Equation (6.2) [29] gives the simplified version of the spreading coefficient in terms of the three interfacial energies present when a liquid comes in contact with a solid: S = �sv –(�lv + �sl )

(6.2)

his equation indicates that spreading of a liquid on a solid surface will occur if � sv > (� lv + � sl ). his is why solid surfaces with very low interfacial energies (� sv ) such as many polymeric materials are much harder to wet by a given liquid than solids with larger � sv values.

6.4 Advanced Wetting Properties

When a liquid droplet encounters a rough solid surface, it may either form a homogeneous or a heterogeneous interface. A homogeneous interface is one where the liquid comes into complete contact with the solid and no air pockets are formed between the two phases. On the other hand, a heterogeneous interface has trapped air pockets between the liquid and solid making multiple areas where all three phases meet. In the case of a homogeneous interface, Wenzel [30] modified Young’s contact angle equation to incorporate the effect of surface roughness, as shown in Eq. (6.3): cos �W = Rf cos �o

(6.3)

where � W is the contact angle for a rough surface, � o is the contact angle for a smooth surface (Young’s contact angle), and Rf is a roughness factor equal to the actual contact area of the solid–liquid interface (Asl ) divided by its projection on a flat plane (Af ): Rf = Asl /Af . his equation indicates that if roughness is introduced into an inherently hydrophobic (or hydrophilic) flat surface, the contact angle will increase (or decrease) making the surface more hydrophobic (or hydrophilic).

6.5

Water

Water θo

θCB Polymer

(a)

Aspen Leaves as a Biological Blueprint

Smooth surface

Polymer (b)

Rough surface

Figure 6.1 Illustration demonstrating the contact angle. (b) A dual-scaled surface, effect of dual-scale surface roughening on showing trapped air pockets in red, exhibita hydrophobic polymer. (a) A smooth polying a superhydrophobic contact angle. mer surface exhibiting a slightly hydrophobic

Cassie and Baxter [31] further extended Wenzel’s equation for a homogeneous interface to include the effect of a heterogeneous interface (formation of trapped air pockets) on contact angles. In certain cases with extreme roughness within the appropriate size range, a droplet of water will rest on top of the “peaks” of the surface never coming into direct contact with the solid material found in the “valleys” of the surface. Within these valleys, air pockets are trapped between the solid and liquid phases, shown in Figure 6.1, which consequently alter the wetting and surface properties of the material. Cassie and Baxter’s [31] equation accounts for the liquid–air and the solid–air interfaces that are created underneath a water droplet when it is placed on such surfaces, as shown in Eq. (6.4): cos �CB = Rf fsl cos �o − fla

(6.4)

where f sl and f la are fractional geometrical areas of the liquid–solid and liquid–air interfaces under the droplet, respectively. From Eq. (6.4) it can be concluded that increasing the roughness factor (Rf ) and the fractional area of the liquid–air interface (f la ) of an already hydrophobic surface can drastically increase the contact angle. he creation of an effective superhydrophobic surface structure can be achieved by developing a stable composite interface which allows for air pocket trapping between the liquid and solid phases. It has been shown that a combination of nanostructure and microstructure features on the surface is well suited for this purpose [32]. In other words, a dual-scale hierarchical surface roughness is an effective way for developing superhydrophobic surfaces.

6.5 Aspen Leaves as a Biological Blueprint

he biological blueprint for the template development used in our technology was the hierarchical dual-scale surface structure found on quaking aspen and bigtooth

101

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

(a)

50 μm (c)

10 μm Figure 6.2 SEM micrographs of the adaxial side of a quaking aspen leaf: (a) low magnification overview, (b) and (c) microscale papillae, (d) nanoscale wax crystalloids [11].

(b)

20 μm (d)

5 μm Reproduced from [11], copyrights © 2013 with permission from American Journal of Plant sciences.

aspen leaves. Both leaves have surface structures similar to the lotus leaf; however, with a slightly simpler morphology which makes the surface reproduction of the template a little easier. Specifically, the microscale papillae on the aspen leaves are about twice as large at their base and only half the height of lotus leaf papillae, a width to height ratio which simplifies a template approach significantly. Respectively, Figures 6.2 and 6.3 are SEM and optical profilometer images of the adaxial side of a quaking aspen leaf. It can clearly be seen that this surface is covered by an array of microscale papillae (Figure 6.2b) with a finer layer of nanoscale surface roughness (3D wax crystalloids, Figure 6.2d) superimposed on top. he microscale papillae have average base diameter between 12 and 20 μm, average heights of 4–6 μm and average spacings between 8 and 10 μm. he average density of micropapillae was 2500 per mm2 . Superimposed on the micropapillae are nanoscale wax crystals with average thicknesses of 100–150 nm and lengths up to 1 μm. he contact angles of water droplets (5 μl volume) were 157∘ and 166∘ for bigtooth aspen and quaking aspen, respectively. his is close to the contact angle observed on the lotus leaf. It was also observed that water droplets easily rolled off the leaf surface at tilt angles of less than 5∘ . A schematic diagram of the surface structure of the leaves is shown in Figure 6.4. heir superhydrophobic properties are clearly visible in Figures 6.5 and 6.6. Note that the trapped air pockets can be seen in Figure 6.5.

6.6

μm

(a)

Template Design

4.73

3.50 10 μm (b)

2.50 1.50 0.50 –0.50 –1.50 –2.50

10 μm

–3.56

Figure 6.3 Optical profilometry images of the adaxial side of a quaking aspen leaf: 3D (a) and surface (b) views [10].

6.6 Template Design

he ultimate goal of the template technology to be developed was to create a surface structure similar to the one observed on aspen leaves (Figure 6.4) on the surfaces of inherently hydrophobic polymers. In other words, the template to be used to imprint the structure features on the polymer surfaces should be the negative of the surface structure shown in Figure 6.4. his was achieved by using the unique mechanical strength/chemical etching property combination observed for nanocrystalline nickel. A series of schematic diagrams illustrating the processing steps to structure softened polymer surfaces using a template-based approach are presented in Figure 6.7. he focus of this section is to describe the experimental Dual-scale hierarchical roughness Micrometer scale Nanometer scale

Figure 6.4 Schematic diagram of superhydrophobic leaf top surface in cross-section.

103

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

(a)

(b)

Figure 6.5 Photo illustrating the presence of air pockets (reflected light) trapped underneath water droplets on a bigtooth aspen leaf (b). (a) A red maple leaf with droplets is included to show the absence of air pockets on a nonsuperhydrophobic leaf surface.

1 mm Figure 6.6

Water drop (5 μl) on the adaxial side of quaking aspen leaf.

efforts used to obtain a suitably structured nickel surface (step 2 in Figure 6.7) possessing a dual-scale pitted structure, that is, the negative of the aspen leaves’ surfaces. Pressing polymers with templates containing this structure (step 4 in Figure 6.7) is expected to result in polymer surfaces displaying surface features similar to those present on the aspen leaves described in the preceding section. Nanocrystalline nickel sheets were electroplated onto titanium substrates. To fabricate these nickel deposits, pulsed current electrodeposition was used in a modified Watt’s type bath containing nickel sulphate, nickel chloride, boric acid, and saccharin. he main cathodic and anodic reactions for this process are Ni2+ + 2e− → Ni0 (as well as hydrogen evolution 2H+ + 2e− → H2 ) and Ni0 → Ni2+ + 2e− , respectively. Plating on a titanium substrate allowed for the easy separation of thick (1–2 mm) nickel plates following the deposition procedure, resulting in free-standing nickel sheets. A TEM micrograph of this electrodeposited material is shown in Figure 6.8.

6.6

(1)

As-deposited

(2)

(3)

Template

nNi Polymer

Polymer Reusable template

nNi

(4)

nNi

(5)

Roughened surface nNi

nNi

Template Design

(6)

Structured surface

nNi

Polymer

Polymer

Polymer

Figure 6.7 Schematic diagrams summarizing the surface structuring procedure. (Modified from Ref. [17].)

100 nm Figure 6.8 TEM micrograph of electrodeposited nanocrystalline nickel.

105

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

1 μm Figure 6.9 etched.

SEM image of a nanocrystalline nickel sample that was polished and chemically

Multiple 6′′ × 6′′ plates of nanocrystalline nickel (nNi, grain size: ∼25 nm) samples were fabricated. An SEM image of an nNi sheet that was chemically etched in 5% HNO3 for 30 min is given in Figure 6.9. Due to the very small grain size in nNi a unique etching pattern is observed. he surface is uniformly roughened on the nanoscale which could be used to reproduce the nanoscale roughness on the polymer surfaces. In order to create the required microscale roughness, the nNi was (a)

100 μm

(b)

10 μm (c)

5 μm

Figure 6.10 SEM micrographs of a structured nNi template: (a) low magnification image illustrating the array of microscale pits, (b) and (c) a single microscale pit and

(d)

500 nm

(d) high magnification image showing finer nanoscale roughness [10]. Reproduced from [10], copyrights © 2012, with permission from Trans Tech Publications.

6.7

Polymer Pressing

sandblasted prior to the chemical etching process to introduce localized deformation into the surface. Figure 6.10 gives SEM images of nNi sheets that were sandblasted using 180 grit Al2 O3 particles at 87 psi and then chemically etched in 5% HNO3 for 30 min. hese surfaces display a nanoscale surface roughness superimposed on an array of microscale pits, the type of surface that could produce structured superhydrophobic polymer surfaces using the described pressing procedure.

6.7 Polymer Pressing

Commercially available samples of polyethylene (PE), polypropylene (PP), and polytetrafluoroethylene (PTFE) were used to develop optimum pressing conditions that resulted in a complete surface structure transfer with minimal template–polymer adhesion. Once the appropriate pressing temperatures had been obtained for each polymer (150 ∘ C for PE, 160 ∘ C for PP, and 280 ∘ C for PTFE), 1′′ × 1′′ polymer coupons (∼4 mm thick) were pressed into structured nNi templates using a stainless steel compression press in a furnace. his results in the negative of the nNi surface structure being transferred to the softened polymer. hese process steps are also schematically summarized in Figure 6.7 [16]. he selection criterion for these polymers was that their Young’s contact angles (� o ) on flat surfaces are all above 90∘ . hese polymers are thermoplastics, allowing for their surfaces to be easily molded at elevated temperatures. Additionally, all three polymers were selected because of their relative low costs and widespread commercial use. Examples of SEM and optical images of polymer surfaces pressed with suitable nNi templates are given in Figures 6.11 and 6.12, respectively. Dimensions of all microscale features (measured from optical images) present on these pressed polymers and the nNi template surfaces are given in Table 6.2. All of the pressed polymer surfaces show similar surface structures as aspen leaves Figures 6.2 and 6.3, albeit on a slightly coarser scale. On these types of structured surfaces, microscale protrusions enable the formation of trapped air pockets between droplets and the solid surface, while the nanoscale features significantly increase the overall surface roughness. According to Cassie and Baxter’s [31] heterogeneous wetting case (Eq. (6.4)), for an inherently hydrophobic material (� o > 90∘ ), increasing the surface roughness (Rf ) and maximizing the amount of air trapped under a droplet (f la ) results in a superhydrophobic surface with a large contact angle (� CB ). Water contact angles using 5 μl droplets and roll-off tilt angles using 25 μl droplets for all pressed and unpressed polymers are given in Table 6.3. he data show that the pressing process indeed increased the contact angles for PE, PP, and PTFE from 96∘ to 151∘ , 104∘ to 153∘ , and 108∘ to 159∘ , respectively. In addition, the tilt angles for all polymers dropped from over 30∘ to below 5∘ . Clearly the presented structuring process drastically increased water contact angles and

107

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6 Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces

(a)

(b)

10 μm

100 μm

(d)

(c)

5 μm

500 nm

Figure 6.11 SEM micrographs of a pressed PE sample: (a) and (b) low magnification images illustrating the array of microscale protrusions, (c) a single microscale protrusion, and (d) high magnification image showing finer nanoscale roughness [10].

μm

(a)

29.9 25.0 20.0

100 μm

15.0 10.0

(b)

5.0 0.0 −5.0 −10.0 −15.0 −20.0 100 μm

−25.7

Figure 6.12 Optical profilometry images of a pressed PE sample: 3D (a) and surface (b) views [10]. Reproduced from [10], copyrights © 2012, with permission from Trans Tech Publications.

6.8

Process Scalability

Table 6.2 Average dimensions of microscale surface features on nNi templates and pressed polymers. Surface

Protrusion/pit size

Protrusion/pit spacing

Height/depth (�m)

Diameter (�m)

Interspacing (�m)

Density (mm−2 )

17.5 ± 8.5 15.4 ± 7.4 14.7 ± 6.3 16.7 ± 8.1

24.5 ± 10.4 24.0 ± 11.3 18.4 ± 8.8 26.5 ± 9.6

∼25.0 ∼22.6 ∼28.3 ∼23.8

697 805 676 729

nNi Template Pressed PE Pressed PP Pressed PTFE

Table 6.3 Aspen leaf and polymer contact and tilt angles. Surface

CA (∘ )

Quaking aspen leaf Bigtooth aspen leaf Unpressed PE Pressed PE Unpressed PP Pressed PP Unpressed PTFE Pressed PTFE

166 ± 3 157 ± 3 96 ± 5 151 ± 3 100 ± 5 153 ± 5 108 ± 3 159 ± 4

TA (∘ )

2 nm >1 μm

3–5 × 10−6

Fragile

13 × 10−6

Strong

>50 μm >50 μm >1 μm >10 nm >2 nm >2 Å

17 × 10−6 20 × 10−6 7 × 10−6 8 × 10−6 52 × 10−6 33 × 10−6

Strong Strong Strong Strong Soft Strong

that the pattern does not collapse during the forming process. An additional consideration influencing selection of the mold material is the difference in thermal expansion between mold and BMG [98]. Large thermal expansion mismatch may result in pattern distortion or stress buildup in the BMG, and thermal expansion mismatch is also important for the separation of the BMG from mold. For nano-scale patterning, wetting between mold and BMG has a crucial influence on the molding process [99]. Complete antiwetting conditions lead to enormously high molding pressures required for replicating features below 100 nm. In contrast, complete wetting could result in instantaneous filling of the mold by capillary action, rendering the molding process uncontrollable. Furthermore, it becomes increasingly difficult to release the BMG from the mold as wetting

165

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9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

between the two materials increases. Note, however, that wetting can be neglected for features larger than 5 μm. Chemical reactivity between the mold and the BMG is another decisive factor in selecting mold material. Chemical reaction between BMG and mold may result in the formation of an interface layer which prevents separation of molded parts. For example, Vit1 forms a strong interface layer with graphite, amorphous carbon, and Al2 O3 [100]. But often the formation of an oxide layer on the BMG’s surface facilitates separation. 9.3.2 Micromolding Process

Figure 9.3a illustrates the principle of TPF-based micromolding of BMGs. A mold is heated to the TPF temperature, after which the BMG is placed on the heated mold and equilibrated to attain the predetermined processing temperature. As a consequence, the BMG softens into a viscous liquid. A controlled pressure is applied to force the viscous BMG into the mold. TPF-based BMG processing requires precise temperature control. he viscosity of the BMG in its supercooled liquid state changes, as a rough approximation, by an order of magnitude in about every 20 ∘ C [101]. his reflects in activation energies for viscous flow of BMGs which are typically in the range of 80–230 kJ mol−1 [80, 102]. he forming system should be well insulated, because temperature fluctuations in the system are readily translated into temperature variations within the BMGs due to their relatively high thermal conductivity. Most severely, uncontrolled overshoot in temperature might result in crystallization, which severely hinders the flow of BMGs and degrades their mechanical properties drastically. he TPF processing temperature is selected on the basis of the temperature dependence of viscosity and crystallization time. A typical temperature used for TPF is chosen such that the viscosity decreases to 106 –108 Pa s while the crystallization time remains on the order of 3–5 min. As a general rule, in order to achieve maximum formability, the highest possible temperature where crystallization can still be avoided should be used [58, 103–105]. After micromolding, the process can continue in two different directions depending on the desired outcome. If patterning of the surfaces is the purpose, the BMG can be released from the mold as indicated in Figure 9.3b. Alternatively, the extra BMG layer can be removed (planarization) before releasing from the mold in order to fabricate 3D microparts (Figure 9.3c). Effective is a hot-cutting technique [71], where the molded BMG is reheated into the supercooled region and the BMG layer is separated from the miniature parts using a sharp scraper. 9.3.3 Mold Filling Kinetics

he flow of BMG former in their supercooled liquid state during TPF has been described assuming creeping flow characteristics [58]. As a consequence, under typical TPF conditions, the BMG exhibits laminar flow and thus can be described

9.3

Processing of BMGs

Temperature and pressure

BMG

Mold (a)

(b) Releasing

(c) Planarization

Patterned BMG Releasing

3D BMG microparts Figure 9.3 Illustration of TPF-based micromolding process to fabricate surface patterns and freestanding 3D components [10, 71]. (a) Mold and BMG assembly is heated to the TPF temperature, and upon applying pressure, the viscous BMG flows into the

mold pattern. (b) Separating the mold and BMG leaves the mold features imprinted on the BMG surface. (c) The extra BMG layer is removed by either hot cutting or polishing, and the BMG features can be subsequently released from the mold.

by the Hagen–Poiseuille law for cylindrical molds [106]. Figure 9.4a illustrates the filling of an infinite circular mold cavity of diameter, d, and length, L. As described by the velocity profile, the BMG in the center moves faster while the BMG touching the walls of the mold is stationary due to stick conditions. According to the Hagen–Poiseuille law, the flow rate (F = volume of fluid flowing per unit time) is proportional to the pressure difference (P) between beginning and end of the circular cavity and the fourth power of its diameter, d. F=

�Pd4 128�L

(9.1)

Here, � is the viscosity of the BMG supercooled liquid, which is defined by the TPF temperature. By substituting the flow rate (=�d2L/4t) and rearranging, Eq. (9.1) becomes P=

32�L2 td2

(9.2)

167

168

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications P

Tg< T < Tx

L Velocity profile d

100 μm

(b)

Pressure, P (MPa)

200 100 0 −100

η = 107 Pa s

θ = 90°

Anti-wetting θ < 90° Wetting θ < 90°

Y = 1−Nm−1

Desired molding region

−200 −300

(θ = 0°)

−400

T = 275 °C P = 13 MPa t = 120 s

200

t = 60 s

300

37.3 μm

Filling length, L (μm)

I/d = 3

400

(a)

−500 10

150

(a)

100

20

30 40 50 60 Diameter, d (nm)

70

80

90 100

50 0

(c)

(θ = 180°)

500

0

10

30 40 20 Diameter, d (μm)

50

Figure 9.4 Flow behavior and filling kinetics of a BMG in its supercooled liquid state obeying Newtonian flow. (a) A circular mold cavity filled with a BMG supercooled liquid obeys creeping flow. The velocity profile is parabolic due to stick conditions between the BMG and mold. (b) An SEM image of 10–50 μm diameter micro-pillars formed by molding Pt57.5 Cu14.7 Ni5.3 P22.5 BMG into

a silicon mold at 275 ∘ C under 13 MPa for 120 s. (c) The filling length plotted as a function of pillar diameter calculated from Figure 9.3b. The pillar length increases with diameter, but the ratio (L/d) remains constant around 4.4, suggesting that the flow of BMG supercooled liquid during micromolding can be accurately described by Hagen–Poiseuille law.

Equation (9.2) suggests a constant aspect ratio (L/d) for constant pressure, viscosity, and filling time. In order to test this prediction, Pt57.5 Cu14.7 Ni5.3 P22.5 BMG was formed by TPF into quasi-infinitely long cavities of varying diameter (5–50 μm) (Figure 9.4b). he length of the pillars increases with increasing diameter, but as predicted by Eq. (9.2), the ratio (L/d ≈ 4.4) remains constant. he validity of Eq. (9.2) can be further assessed by using the measured filling length as a function of mold diameter and then calculating the viscosity using Eq. (9.2). Figure 9.4c shows a plot of filling length versus mold diameter for Pt57.5 Cu14.7 Ni5.3 P22.5 . he L–d plot exhibits a linear relation with a slope of 4.5, confirming the relation P ∝ L/d. he viscosity value derived from this slope is 2.4 × 106 Pa s, which is in good agreement with the viscosity of Pt57.5 Cu14.7 Ni5.3 P22.5 calculated from

9.3

Processing of BMGs

the VFT (Vogel–Fulcher–Tammann) equation (� = 7.8 × 106 Pa s) [63]. hese observations provide quantitative evidence that the filling of cavities (d ≥ 5 μm) with BMG supercooled liquid can be accurately described by Eq. (9.2). However, Eq. (9.2) fails when the diameter d becomes smaller than 5 μm. his is demonstrated in Figure 9.5a, where Pt57.5 Cu14.7 Ni5.3 P22.5 BMG was molded into nanoporous alumina under the same TPF conditions used for Figure 9.4. A negligible filling depth is achieved in the nanoscale mold compared to the microscale mold (Figure 9.4b), where the filled aspect ratio is ∼4.4. his is because the capillary pressure required to fill nanoscale cavities becomes significant, and the applied pressure has to overcome the capillary pressure. herefore, in order to describe the flow of BMG on the nanoscale, Eq. (9.2) must be modified to consider capillary forces [99]: P=

32�L2 4� cos � − d td2

(9.3)

where � is the surface tension and � is the advancing contact angle between the BMG supercooled liquid and the mold. he second term in Eq. (9.3) arises from the capillary pressure, which becomes comparable to viscous pressure for d < 1 μm and becomes the controlling factor when d approaches 100 nm. For antiwetting (� > 90∘ ), the applied pressure must overcome the capillary pressure, which can be as high as 26 MPa for a channel of 150 nm diameter under complete antiwetting (� = 180∘ ) conditions. In the case of complete wetting (� = 0∘ ), the supercooled liquid spontaneously fills the mold cavity. However, such a condition leaves the molding process uncontrollable and also prevents separation of the BMG from the mold. he desired scenario for a controllable molding process combines partial wetting behavior with a molding pressure that is small yet large enough for the filling kinetics to be well controlled. he filling length during TPF of BMGs can be controlled by varying the experimental conditions and manipulating the contact angle (Eq. (9.3)). To demonstrate this, Pt57.5 Cu14.7 Ni5.3 P22.5 BMG was molded into 150 nm alumina pores under a pressure exceeding the capillary pressure of 20 MPa corresponding to wetting angle of 140∘ . he wetting angle between metallic glasses on various substrate materials has been measured [100, 107] and for Pt57.5 Cu14.7 Ni5.3 P22.5 on Al2 O3 an angle of 143∘ was determined [107]. he aspect ratio of the molded nanopillars is ∼6.7 (Figure 9.5b), and the uniformity of the nanorods suggests that TPFbased micromolding of BMGs is an eminently controllable process. Long BMG nanowires can also be molded by increasing the pressure, the temperature, and/or the molding time. Figure 9.5c shows Pt57.5 Cu14.7 Ni5.3 P22.5 BMG nanowires with an aspect ratio >200, molded by heating through the entire supercooled liquid region. hus, by changing the molding conditions, the filling depth of the features can be precisely controlled to yield shallow surface patterns or high-aspect ratio structures. High aspect ratio structures are particularly interesting for electrochemical and sensing applications [108–111].

169

170

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

(a)

(b)

500 nm

500 nm (c)

20 μm Figure 9.5 SEM images of Pt57.5 Cu14.7 Ni5.3 P22.5 molded into 150 nm alumina pores. (a) Filling length is insignificant under 13 MPa at 275 ∘ C for 120 s. Thus, the viscous term alone (Eq. (9.2)) cannot explain the difference between filling length at the microscale (Figure 9.3b) and the nanoscale (Figure 9.4a) under the same molding conditions. (b) By increasing the applied pressure to 38 MPa, 1 μm long

nanorods are formed. The filling of nanoscale pores can be described by taking capillary pressure into account, which is about 20 MPa for the combination of Pt57.5 Cu14.7 Ni5.3 P22.5 and 150 nm alumina pores (Eq. (9.3)). (c) Long BMG nanowires molded by heating Pt57.5 Cu14.7 Ni5.3 P22.5 through its entire supercooled liquid region from 230 to 300 ∘ C at a heating rate of 20 ∘ C min−1 under 50 MPa.

9.4 Surface Patterning

Chemistry is the most widely used surface engineering tool to modify the surface properties of a material. Surface topography, despite its vast utilization in nature as a toolbox for surface functionalization, has just begun to be explored in engineering materials. his is due to the limited availability of patterning techniques, particularly for metals. TPF of BMGs is an ideal technique for this application, enabling patterning of high-strength metals in a manner similar to plastics. Figure 9.6 shows scanning electron microscope (SEM) images of surface patterns with length scales from 250 μm to 100 nm transferred onto Pt57.5 Cu14.7 Ni5.3 P22.5 by TPF-based molding. his process can be extended to nonplanar surfaces by combining TPF-based molding and blow molding. BMGs exhibit high strength at room temperature, while above T g their flow stress becomes comparable to thermoplastic polymers and superplastic

9.4

500 μm (a)

Surface Patterning

200 μm (b)

100 μm (c)

1 μm (d)

1 μm (e) Figure 9.6 Pt57.5 Cu14.7 Ni5.3 P22.5 surface patterns prepared by molding at 270 ∘ C under 15 MPa for 90 s using different molds: (a) electroplated nickel, (b) silicon, (c) pyrolized SU-8, and (d) and (e) nanoporous alumina. The BMG perfectly

500 nm (f) replicates the mold features from 250 μm to 100 nm, and this process can be scaled down to 13 nm and applied to nonplanar surfaces. (f ) Hemispherical patterned surface prepared by combining TPF-based molding and blow molding.

alloys. Together with the absence of an intrinsic length scales in the amorphous structure, BMGs are ideally suited to serve as molds below their T g , yet can be thermoplastically patterned similar to plastics at elevated temperatures. he strong temperature-dependent strength of BMGs can even be exploited to use one BMG (with a higher T g ) as a mold for another BMG (with a lower T g ). Such a

171

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

Silicon, quartz, alumina 1000

100 Strength (MPa)

172

Nickel

10

Al–78Zn

1

0.1

Au-based

0.01

PMMA

100 (a)

200 300 Temperature (°C)

5 mm (b)

400

500

5 mm (c)

5 mm (d)

Zr-based Pt-based

5 mm (e)

9.4

Figure 9.7 (a) Temperature-dependent strength of various BMG formers with different T g [10, 99] compared to superplastic Al–78Zn [112], ultrafine grain nickel [113], and thermoplastic PMMA [114] at a strain rate of 10−2 s−1 . The strong temperaturedependent flow of BMGs can be utilized to prepare multiple BMG replicas which can be used as templates for polymers and other BMGs. (b) Hologram nickel master stamp used as a mold for Pt57.5 Cu14.7 Ni5.3 P22.5 . (c) Pt57.5 Cu14.7 Ni5.3 P22.5 hologram formed

Surface Patterning

by molding on nickel mold. A pattern resembling the nickel master mold is imprinted into Au49 Ag5.5 Pd2.3 Cu26.9 Si16.3 BMG (d) and gold-coated PMMA (e) using Pt57.5 Cu14.7 Ni5.3 P22.5 BMG as a mold. The dispersion of white light into different colors reflects the perfection of the replication of master mold pattern into the BMGs. Thus, multiple BMG replicas of an expensive master mold can be produced by simple TPFbased molding process.

←−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− temperature-dependent strength is the result of a crossover between the internal relaxation time scale set by the Maxwell relaxation time, �/G, (G: shear modulus) and the experimental time scale (given, e.g., by the inverse of strain rate). his offers a unique opportunity to replicate multiple molds/stamps which otherwise require expensive lithographic steps. Figure 9.7b–e show an example of such a process, where a nickel mold is replicated into BMG that is subsequently used as a mold for another BMG and polymer. Figure 9.7b is an image of a nickel master hologram stamp. Its inverted replica, fabricated by molding Pt57.5 Cu14.7 Ni5.3 P22.5 at 270 ∘ C, is shown in Figure 9.7c. he dispersion of white light into different colors indicates that the size and spacing of the gratings in the nickel master mold have been faithfully replicated onto the BMG. he pattern from Pt57.5 Cu14.7 Ni5.3 P22.5

Macro–micro–nano hierarchy

1 mm

10 μm

100 μm

500 nm

Micro–nano hierarchy

20 μm

10 μm

3 μm

Figure 9.8 Multiscale surface patterns prepared by TPF of BMGs. The nanopatterned micropillar was fabricated by stacking micro- and nanomolds together.

173

174

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

was then transferred onto Au49 Ag5.5 Pd2.3 Cu26.9 Si16.3 at 160 ∘ C (Figure 9.7d) and onto Poly(methyl methacrylate) (PMMA) at 130 ∘ C (Figure 9.7e). Pt-based BMG is suitable as a mold for both Au-based BMG and PMMA because at their respective processing temperatures, the strength of Pt-based BMG has decreased an insignificant amount compared to its room temperature strength. he patterned Au49 Ag5.5 Pd2.3 Cu26.9 Si16.3 and PMMA precisely duplicate the nickel master mold. Furthermore, the patterned Pt57.5 Cu14.7 Ni5.3 P22.5 , due to its high wear resistance, can be repeatedly used to imprint multiple samples of Au49 Ag5.5 Pd2.3 Cu26.9 Si16.3 and PMMA. his technology thus allows BMGs to be used as high-quality replicas of expensive and fragile master molds. he ability of BMGs to replicate a wide range of length scales can be used to generate multiscale patterns by combining molds with different patterns. Figure 9.8 shows examples of such multiscale pattern combining macro, micro, and nano length scales.

1 mm

1 mm

50 μm

100 μm

1 mm

100 μm

100 μm

Figure 9.9 BMG microparts fabricated by TPF-based micromolding and planarization techniques [10, 99].

9.5

3D Microparts

9.5 3D Microparts

By combining miniature molding with planarization methods (Figure 9.3), 3D microparts can be created. Such parts can have varying levels of complexity and shapes which span a wide range of length scales, as discussed in the following sections. Figure 9.9 gives examples of various generic shapes fabricated by BMG micromolding. Micromolding produces very accurate shapes without any burrs, unlike parts made by micromachining. hese parts can thus be directly used, for example, to build micromachines without additional treatments such as deburring or polishing. Figure 9.10 shows examples of complex gear and BMG microtools fabricated using the process described in Figure 9.3. he parts show excellent mold

200 μm (a)

100 μm (b)

200 μm

100 μm (c)

Figure 9.10 BMG micro-gears and microtools fabricated by micromolding and planarization techniques using silicon molds. (a) The precise replication of a complex gear indicates that the Zr35 Ti30 Cu8.25 Be26.75 BMG in its supercooled liquid state readily

(d)

flows into constricted areas of the mold. (b) A spiral-shaped Zr35 Ti30 Cu8.25 Be26.75 BMG spring with a thickness of 20 μm. (c) A BMG membrane consisting of 50 μm pores. (d) Sharp micro scalpels with a radius of curvature of about 1 μm.

175

176

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

replication and high accuracy. he precision and reproducibility of a microgear (Figure 9.10a) suggests a wide range of applications, including watches, microactuators, micromanipulators, and microharmonic drives. he use of microgears in microassembly offers numerous advantages such as zero backlash, high repeatability, extended longevity, and compact design. In addition, BMG microgears are mechanically superior and exhibit higher wear resistance [115, 116] compared to microgears fabricated from silicon and crystalline metals. he large elasticity of the BMG spiral spring shown in Figure 9.10b can be used to store substantial elastic energy. Figure 9.10c and 9.10d show an image of a BMG membrane with uniform pores and ultrasharp scalpels, respectively. Our method to create 3D BMG microparts can be extended to the nanometer scale. hree-dimensional nanostructures (nanowires, nanoparticles) have great potential for catalytic activity and fuel cell applications. Our process can readily produce metallic nanostructures in both amorphous and crystalline states. he nanostructures can be partially or completely crystallized during molding process by manipulating the molding temperature or time. Figure 9.11a shows an SEM image of Pt57.5 Cu14.7 Ni5.3 P22.5 BMG confined into 150 nm pores in alumina. he confinement dimensions can be currently decreased to 13 nm [99], limited only by mold availability; theoretical considerations suggest that even smaller dimensions are feasible. Alternatively, freestanding BMG nanorods for thermal

1 μm

1 μm (a)

(b)

(c)

100 nm

Figure 9.11 Pt57.5 Cu14.7 Ni5.3 P22.5 nanorods prepared by molding into porous alumina. (a) Top BMG layer is removed leaving BMG nanorods confined in 150 nm pores in

alumina. (b) Freestanding BMG nanorods produced by etching away the alumina. (c) A plastically deformed nanorod displaying shear bands.

9.5

3D Microparts

and mechanical characterization can be obtained by dissolving the alumina (Figure 9.11b). Using direct molding to create nanostructures is inexpensive and simple compared to currently used lithography and self-assembly approaches. he ability to precisely mold BMGs on length scales from 10 nm to a few centimeters can be utilized to create artificial microstructures to study the microstructure–property relationship. Fabrication methods that are used to create complex microstructures typically do not allow independent variation of size, shape, and fraction of second phase. As a consequence, the conclusions drawn from such experiments are often limited to qualitative trends. BMG micromolding is a novel approach to creating artificial microstructures which will allow microstructural features to be varied independently and their corresponding effect on the physical properties to be determined. As an example,

500 μm (a)

500 μm (c) Figure 9.12 Artificial BMG microstructures which allow carrying out mechanical characterization of BMGs on the small scale fabricated by micromolding and planarization techniques. (a) Pt57.5 Cu14.7 Ni5.3 P22.5 honeycomb structure with cell thickness of 15 μm and length of 470 μm (slenderness ratio ∼30). (b) The porosity of

500 μm (b)

5 mm (d) this honeycomb structure is about 95%, which results in elastic buckling (∼10%) prior to plastic deformation. (c) A flexible Zr35 Ti30 Cu8.25 Be26.75 hinge completely bends without plastic deformation. (d) A netshaped Zr35 Ti30 Cu8.25 Be26.75 tensile specimen whose gauge section contains microchannels of 50 μm diameter spaced at 30 μm.

177

178

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

50 μm

50 μm (a)

(b)

1 mm (c)

Figure 9.13 Pt57.5 Cu14.7 Ni5.3 P22.5 BMG MEMS components. (a) A linear comb-drive actuator. (b) Gyro comb-drive actuator. The comb teeth are 5 μm wide and 20 μm long. The combs move upon applying an AC voltage. (c) Bulk metallic glass hemispherical resonator fabricated through miniature blow

5 mm (d)

molding. Blow molding can be integrated into MEMS fabrication steps to fabricate read out and drive electrodes for the usage as a miniature gyroscope. (d) Accelerometer which encompasses length scales including 20 μm to several millimeters.

the size effects summarized in Table 9.1 and Figure 9.1 can be studied using the artificial microstructure approach (Figure 9.12). Micromolding of BMGs is not only limited to stationary parts but can also be combined with silicon lithography techniques to fabricate movable BMG parts [117]. Figure 9.13a shows the SEM image of a BMG linear comb-drive actuator where the silicon was selectively etched to free the BMG comb-drive while it still remained anchored to the silicon wafer at one end. Applying alternating voltage to the combs creates electrostatic forces between the combs, causing them to attract or repel depending on the polarity of voltage. he linear displacement due to electrostatic force can be converted into rotational or other motions by adding springs, levers, or cranks to the combs. Figure 9.13b shows a gyro-shaped BMG combdrive actuator which generates circular motion. he large elastic limit of BMGs

9.6

Surface Finish

can be utilized to obtain displacements in the BMG actuators which are significantly larger than those achieved with conventional MEMS materials. Figure 9.13c shows a BMG actuator which consists of several high-aspect ratio thin walls and precision springs. Figure 9.13d is an example of hollow BMG resonator fabricated by process described in the following section. BMG micromolding can also be integrated with other TPF-based techniques such as blow molding. his enables one to fabricate 3D microshells which remain firmly attached to a silicon wafer. Out-of-plane microshells are desirable geometries for various MEMS applications, especially resonators, yet they are challenging to fabricate. Figure 9.14a illustrates schematically the fabrication steps for BMG microshells. Silicon is patterned in such a way that large cavities are etched all the way through while small anchoring features are etched to a finite depth (step 1). A thin sheet of BMG is thermoplastically molded into the anchoring features and subsequently blown into hollow shells (steps 2–4). he scalloping roughness of the anchoring side walls and the difference in thermal expansion between silicon and BMGs can be utilized to strengthen the attachment. Figure 9.14b shows an example of a Pt57.5 Cu14.7 Ni5.3 P22.5 BMG microshell attached to silicon wafer fabricated by such a process. In addition to free expansion of diaphragms into hemispherical shapes, separate molds can be used to shape the blow-molded features, providing a versatile toolbox for complex 3D microshells. As an example, Figure 9.14c shows cubic microshells fabricated using this technique. Finally, the attachment of BMG and silicon wafer can be further utilized for packaging of MEMS devices (Figure 9.14d).

9.6 Surface Finish

Surface finishing is always a concern, owing to its nature as the most critical and least controllable aspect of micro- and nanomanufacturing. he disadvantage of planar polishing techniques is their limited access to recessed regions in nonplanar complex geometries. he surface finish of BMG parts fabricated by micromolding primarily depends on the mold surface. Silicon molds made by Reactiveion-etching (RIE) are typically rough due to side wall scalloping. As shown in Figure 9.15a, the side walls of BMG microgears perfectly replicate the scalloping roughness (≈300 nm) of the silicon mold. One way to improve the surface finish of molded BMG parts is to reduce the roughness in the mold, which dramatically increases the mold cost. Alternatively, the surface roughness of BMGs can be decreased by a self-smoothening process. Such a smoothening process is accomplished by surface tension-driven viscous flow in the supercooled liquid state (Figure 9.15b).

179

180

9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

3D BMG shell fabrication Step 1: Si mold with large through cavities and small anchoring sites Pressure and T > Tg Step 2: Molding BMG into anchoring sites

BMG

Step 3: Blowing through large cavities at T > Tg

Mold

Step 4: 3D BMG shells attached to Si wafer

(a)

Cubical 3D shells

3D shell

Si

(b)

(c)

Anchoring features

200 μm

MEMS packaging

Device

Step 1: Si wafer with devices surrounded by anchoring sites Pressure and T > Tg

Step 2: Molding BMG into anchoring sites

Step 3: Device cavities sealed by BMG layer (d)

BMG

9.7

Figure 9.14 (a)–(c) Schematic illustration of fabrication processes for 3D BMG shells attached to silicon wafer. (a) In step 1, a silicon mold containing large cavities surrounded by small anchoring features is prepared by etching. The large features are etched through the silicon while anchoring features are etched to a smaller depth. In step 2, a thin BMG layer is thermoplastically molded into the anchoring features by applying pressure only on the anchoring sites. In step 3, the BMG layer attached to the silicon wafer is thermoplastically blown through large cavities resulting in

Conclusions and Outlook

hemispherical BMG shells (b). Alternatively, the attached BMG layer can be blown into mold cavities and BMG shells with a desired shape can be fabricated (Figure 9.14a). This is illustrated in Figure 9.14c, which shows an example of a cubical Pt57.5 Cu14.7 Ni5.3 P22.5 BMG shell. (d) MEMS packaging using TPFbased micromolding of BMGs. In step 1, anchoring features are etched around MEMS devices in a silicon wafer. In step 2, a thin BMG layer is thermoplastically molded into anchoring features, sealing the devices underneath.

←−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

BMG’s ability to precisely replicate features and roughness suggests that TPF of BMGs on smooth substrates can be used to fabricate smooth metal surfaces. An Atomic force microscope (AFM) image and a height profile of Pt57.5 Cu14.7 Ni5.3 P22.5 BMG thermoplastically formed on cleaved mica are presented in Figure 9.15d. Remarkably, the surface of Pt57.5 Cu14.7 Ni5.3 P22.5 BMG formed on mica exhibits near atomic-scale smoothness over a large area, with a peak-to-valley roughness smaller than 2 Å. Atomically, smooth surfaces are of utmost importance in nanodevices, plasmonics, and data storage.

9.7 Conclusions and Outlook

Metallic glasses are an ideal material for many micron and nano length scale applications due to their superb strength and elasticity, low internal friction, and highly electrochemical activity. Applications can be realized through TPF of BMGs which is a highly versatile, robust, and economic process which allows parallel processing at highest precision and can be readily scaled up. Processing conditions such as temperature and pressure allow for implementation into established MEMS and Nano-electro-mechanical-systems (NEMS) fabrication methods and are CMOS compatible. In order to exploit the potential of TPF, the scientific community has to continue to develop BMGs with a combination of properties, enabling processing and improving applications. Furthermore, alternatives to the use of disposable silicon molds must be developed to reduce molding costs. As an engineering task, proof of concept methods have to be scaled up and implemented into large-scale fabrication processes.

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9 Bulk Metallic Glass in Micro to Nano Length Scale Applications

20 μm (a)

(b) 4

Z (Å)

3 2 1 0

0

1

(c)

2 X (μm)

3

4

2.0 1.5 Z (Å)

182

1.0 0.5 0.0 0

(d)

Figure 9.15 Surface finish of BMG parts fabricated by TPF-based micromolding [79]. (a) An SEM image of surface roughness on Pt57.5 Cu14.7 Ni5.3 P22.5 transferred from a silicon mold after TPF. (b) SEM image showing the surface smoothened by annealing at 270 ∘ C for 300 s. (c) An AFM image (5 μm × 5 μm) and the corresponding height profiles along

100 200 300 400 500 X (nm)

the indicated lines of Pt57.5 Cu14.7 N5.3 iP22.5 thermoplastically formed on silicon resulting in a surface that is as smooth as the silicon, with a maximum peak-to-valley roughness of 3.5 Å. (d) An atomically smooth surface is obtained after TPF of Pt57.5 Cu14.7 Ni5.3 P22.5 on cleaved mica. The peak-to-valley roughness in the 500 nm horizontal scan is about 2 Å.

Acknowledgments

he work was supported by the National Science Foundation (MPM #0826445 and CMMI#1266277).

References

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189

10 From Oxide Particles to Nanoceramics: Processes and Applications Jean-François Hochepied

10.1 Introduction

Applications of dense or porous nanoceramics require well-mastered elaboration processes and the refinement of the choice of precursors opens new ways towards improved functional materials. Nanoparticles are ideal bricks on condition that grain growth is prevented during sintering. Nowadays, many studies couple nanoparticle synthesis and their behavior during sintering. he interface between the worlds of solution chemistry and nanoceramics is the guideline of this chapter, but chemical or ceramic processes will not be described in detail here. he prefix “nano” has different meanings depending on whether you are (or speak to) a chemist or a ceramist. Chemists have been working hard for decades to produce nanoparticles or nanostructures with typical dimensions in the order of a few nanometers and are reluctant to name any objects with dimensions above 10–20 nm as “nano,” whereas ceramists sometimes call ceramics with grain size of several hundred nanometers as “nanoceramics.” Here, we will focus on nanograins with size inferior to 100 nm. In order to avoid a catalogue, the proposed selection of topics and examples is far from being exhaustive. he considered materials will be metallic oxides, mainly cerium/zirconium/titanium oxides and perovskites. Silica-based materials will be discarded.

10.2 Solution Chemistry Processes for Oxide Nanoparticles Usable for Nanoceramics

here are many processes to obtain oxide nanoparticles, but considering that a certain size distribution and agglomeration can generally be tolerated, it is usual to favor cheap processes able to produce large quantities of nanopowders. Nanoparticles in the range 5–20 nm with simple composition can generally be obtained by solution chemistry – if necessary, followed by thermal treatment in solution or in powder form. Depending on their nature, they may undergo only a moderate he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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From Oxide Particles to Nanoceramics: Processes and Applications

grain growth during sintering. Solution chemistry methods often allow particle shape tuning, which may be useful to make textured nanoceramics, dense or not. In addition to that, the selection of the exposed faces of the nanocrystals (correlated to shape control) may drastically change the particle surface energy and consequently their behavior during sintering. he optimal choice for the chemical system depends on several constraints: the chemical nature of the targeted materials, the desired particle size (and eventually shape), and last but not the least the production costs. Metallic salts can generally be co-precipitated by mixing with a base in aqueous solutions under the form of more or less hydrated oxides, especially when the reactivities of the co-precipitating cations are close. Conditions (pH, temperature, etc.) are generally chosen to ensure a high supersaturation favoring nucleation versus growth, which is easy when the oxides are poorly soluble. Amorphous or metastable phase can be precipitated and transformed into oxide nanoparticles by further treatments as solvothermal crystallization. With minimum care nanoparticles of mixed ferrites, mixed oxides such as Cex Zr1−x O2 [1], Snx Ti1−x O2 [2], and so on can be obtained by aqueous co-precipitation. Cationic doping is sometimes more difficult since the dopant may have a very different solubility as compared to the cation(s) of the host matrix. If some cations are highly soluble in water (mainly from columns 1 and 2 of the classification), different strategies should be used. A cheap and convenient way consists in co-precipitating poorly soluble species such as citrates, acetates, oxalates, and so on, if column 2 elements are involved (especially Ba2+ and Sr2+ ). his strategy is frequently used for perovskite synthesis, but size control is limited and annealing is necessary to get the oxide phase. A well-known variation of this strategy is the so-called Pechini’s method, patented in 1969 (USPO 3438723) for preparing ferrites: Pechini dissolved Fe3+ and divalent metallic cation M2+ in citric acid aqueous solution, added a polyol, and heated to form a resin, then calcined it to get MFe2 O4 ferrite particles. For column 1 elements, it is sometimes possible to get oxide nanoparticles in hydrothermal alkaline conditions (NaOH or KOH to introduce Na+ or K+ in the structure): for instance, potassium or sodium niobates can be obtained from niobium oxide in such conditions, but again size control at the nanolevel is quite poor. It is possible to lower the solubilities of the species by co-precipitating in water–ethanol mixtures: the optimization of the water/ethanol ratio may allow co-precipitation of pure mixed phases. Sol–gel method, consisting in hydrolyzing metallic alkoxides in water/alcohol mixture by acido-basic catalysis, is very efficient to copolymerize constitutive elements of a targeted composition and is frequently used for perovskites. Contrary to co-precipitation, the idea is not to generate a nucleation burst consuming quickly the soluble species but rather to control the balance between the relatively slow kinetics of precursors’ hydrolysis and condensation. his can be achieved by the choice of the ligand, the base concentration (catalyst), the choice of the alcohol, and the water/alcohol ratio. In such systems, the alkoxides of cations difficult to co-precipitate in water very often have close reactivity and copolymerize. If necessary, some precursors can even be synthesized with the right cation ratio at the molecular level, which

10.2

Solution Chemistry Processes for Oxide Nanoparticles Usable for Nanoceramics

seems highly favorable to get a homogeneous composition after hydrolysis. For instance, S. O’Brien et al. [3] hydrolyzed commercial barium titanium ethyl hexano isopropoxide at 100 ∘ C in diphenyl ether with oleic acid and obtained well-crystallized and monodispersed BaTiO3 nanoparticles. Interestingly, M. Kakihana et al. [4] evidenced that Pechini’s method also seems to involve the formation of heterobimetallic complexes as BaTi(C6 H6 O7 )3 in the case of BaTiO3 syntheses. Heterobimetallic alkoxide complexes can also be a powerful tool to get doped mixed oxides: S. Mishra et al. [5] prepared [(Pri OH)2 (OPri )2 Ti(μOEt)2 SnCl4 ] and [(Pri OH)(OPri )3 Ta(μ-OEt)2 SnCl4 ] complex precursors and co-hydrolyzed them to get Ta5+ -doped Ti0,5 Sn0,5 O2 nanoparticles as small as 3 nm in diameter with homogeneous Ti:Sn = 1 : 1 ratio according to energy dispersive X-ray spectroscopy (EDX) on isolated particles. Besides nanoparticles, classical sol–gel methods lead also to more or less crystallized nano-oxide particles with a few nanometer diameter, and connected by necks. Depending on the way in which solvent is removed, one can get xerogels or aerogels. Aerogels are obtained by CO2 supercritical drying, keeping the nanostructure built in solution, whereas xerogels are much denser and result from classical drying where capillary forces make the nano-architecture collapse. Nonaqueous systems work well for small and crystallized nanoparticles. As an example, M. Niederberger et al. [6] obtained well-crystallized and nonagglomerated 5–10 nm perovskite particles of (Ba,Sr)TiO3 : they dissolved Ba or Sr (metallic state) in benzyl alcohol, added titanium isopropoxide, and heated to 200 ∘ C in an autoclave for 48 h. hus, solution chemistry offers many possibilities to get oxide nanoparticles, the choice of the system being a compromise between specifications about size, crystallinity, homogeneity, possible defects, and costs. Besides nanoparticles, three-dimensional (3D) nanostructured microparticles, two-dimensional (2D) nanoplates, or one-dimensional (1D) objects as nanowires can also be interesting as ceramics precursors, for instance, with ideas of texturing dense ceramics or of creating new architectures for porous ceramics. 2D or 1D morphologies may be a natural growth shape for nanoparticles according to their crystal habit. he favored growth of ZnO along the polar axis leads to nanorods or nanowires. Sometimes, the mechanism forming 1D objects is more complex; for instance, sodium titanate nanotubes discovered by T. Kasuga et al. [7] result from rolling nanosheets. he fact that they can be transformed into titania nanotubes or nanorods by protonation in acidic media and calcination was the origin of many fundamental and applied research works. Such 1D titanates were tried as possible precursors for 1D BaTiO3 particles, but it is not easy to keep 1D particles in a quantitative manner after calcination. Reliable syntheses of perovskite single-crystalline nanowires have been a serious challenge for chemists, but some convincing recipes were discovered. J.J. Urban et al. [8] prepared a bimetallic alkoxide precursor (barium titanium isopropoxide or strontium titanium isopropoxide) and decomposed it at 280 ∘ C in heptadecane/30% H2 O2 solution/oleic acid mixture (inverse micelle system). Single-crystalline BaTiO3 or SrTiO3 nanorods were obtained, with diameters in

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the range 5–60 nm and length up to tens of microns. In the case of BaTiO3 , we should mention that some authors proposed a route avoiding solution chemistry: Y. Mao et al. [9] simply mixed and ground barium oxalate, titania, NaCl, and a nonionic surfactant. After annealing at 820 ∘ C, they obtained single-crystalline BaTiO3 nanowires 50–80 nm in diameter and >1 μm long. his system was found to be very sensitive to temperature and chloride ion. 2D oxide particle often originates from hydroxide with lamellar structure (brucite Mg(OH)2 or Ni(OH)2 , layered double hydroxides, for instance). Nanostructured microparticles may spontaneously result from homogeneous (co)precipitation in aqueous solutions, where supersaturation is generated relatively slowly (as compared to mixing) in the whole volume of a solution. Generally, the precipitation is triggered by heating (using conventional or microwave sources), with different possible effects such as lowering the solubility of cations in acidic conditions (forced hydrolysis), generating a base by in situ decomposition (urea as main example), and removing ligands that stabilized the cations (ammonia for instance). Forced acidic hydrolysis is relevant to poorly soluble cations (Ti4+ , Fe3+ , etc.), ammonia removal to divalent transition elements (Ni2+ ), urea decomposition to cations that can be solubilized in the initial weakly acidic conditions (Mg2+ , Y3+ , Ni2+ , etc.). he products may be hydroxides or hydroxicarbonates and their nanostructure may be kept when calcined to oxides. If some nanostructured particles spontaneously appear, homogeneous precipitation is efficiently performed with templates to design controlled nano-architectures. he most usual hard templates are anodic alumina membranes for 1D objects and colloidal crystal of silica or polymer spheres for inverse opals. Anodic alumina is interesting with ideas of preparing inorganic nanotubes (or in fact microtubes with nanometric wall thickness) by coating the internal surface of the nanochannels. As an example dealing with (Ba,Sr)TiO3 , S. Singh and Krupanidhi [10] impregnated anodic alumina membranes by sol–gel suspensions, and after drying, annealing at 650 ∘ C to crystallize the perovskite phase and template dissolution in NaOH solutions, they obtained nanotubes with walls composed of 4–8 nm particles. Soft templates are mesophases of surfactants such as cetyl trimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS), especially used for the existence of hexagonal phases in oil–water–surfactant ternary diagram. In any case, the nanostructure must be built without disturbing the shape imposed by the template and the template is preferably removed at the end of the process, since the idea is to use the porosity. Template removal may be performed by dissolution or calcination depending on its nature and on the nature of the produced materials. his step may be more problematic than the synthesis of the nanostructure, and sometimes nano-architectures collapse at this step. So systems with slow inorganic polymerization, sol–gel or homogeneous precipitation, are appropriate and it is not surprising if the first and main nanostructures obtained this way are silica-based from sol–gel as wellknown MCM (from Mobile Corporation) or Santa Barbara Amorphous (SBA) materials families. Some systems were thoroughly explored as Yada’s method, combining urea decomposition and dodecysulfate templating with practically

10.3

Dense Nanoceramics

always the same recipe (metal salt/dodecylsulfate/urea/water molar ratio equal to 1 : 2 : 30 : 60, heating to 80 ∘ C and waiting as long as necessary), whatever the targeted oxide, but with variable results (including mesoporous materials [11] and rare-earth oxide nanotubes [12]) and some difficulties to get rid of the surfactant. he method to prepare nanoparticles can also be chosen considering the shaping of the nanoceramics: solution methods with solvent replacement without intermediate drying are appropriate to prepare dispersed suspensions for membrane elaboration by dip coating, for instance. Aqueous chemistry produces particles with some defects or surface states that cannot be accepted for some applications in optics, but can be useful for functionalization and consequent redispersion in some liquids in view of coatings.

10.3 Dense Nanoceramics

he interest of nanoparticles is not restricted to nanoceramics and can provide some benefits for coarse grain ceramics too. As far as precursors are concerned, the use of nanoparticles with the same composition – at the nanoscale – as desired monophased materials with complex composition offers huge advantages as compared to a mixture of nanopowders of the simple oxides: all issues about intimate powder mixing and co-sintering of materials with different behaviors vanish. For instance, mixed 10 nm Tix Sn1−x O2 nanoparticles with homogeneous size and composition, prepared by co-precipitation in aqueous solutions, could be easily sintered into dense ceramics (5–10 μm grain size), whereas mixing TiO2 and SnO2 powders required sintering aids detrimental to the targeted application, higher sintering temperature, poor densification, and poor surface composition control due to tin oxide evaporation [2] (Figure 10.1).

(a)

(b)

Figure 10.1 Ti0.5 Sn0.5 O2 ceramics obtained by co-sintering TiO2 and SnO2 nanopowders (a) and by sintering Ti0.5 Sn0.5 O2 nanopowders (b). (Courtesy MH Berger, Mines-ParisTech.)

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he simplest system one can imagine to obtain nanoceramics is to start from nanoparticles with the same composition as the targeted materials and sinter them in conditions of limited grain growth. Nanopowders are generally easy to sinter at lower temperature as compared to microparticle, and sometimes do not need sintering aids. In order to prevent or hinder grain growth during the process, various processes are eligible. High-pressure sintering allows densification of ceramics while mitigating grain growth, thanks to lower temperatures as compared to conventional sintering. Other processes under high pressure such as electric current-activated sintering [13] and spark plasma sintering (SPS) rely on the fact that a very fast heating rate will promote dense sintering faster than grain growth. Uniaxial pressing is coupled to intense electric discharges (103 –104 A, a few milliseconds per pulse) for a few minutes. he electrical discharges generate spark plasma between grains, provoking impact pressure and local heating by Joule effect. So the zone between the grains is quickly melted and cooled, building necks and leading to densification without significant grain growth. Generally, at the end, grain size is much smaller as compared to conventional sintering. 10.3.1 Monophased Nanoceramics 10.3.1.1 Processes

If SPS is a sound approach, in some cases, it is also possible to use more classical sintering and get dense nanoceramics, starting from nanoparticles (as small as possible, under 20 nm). Y. Zhang et al. [14] started from nanocrystalline ZrO2 –Y2 O3 (+CuO as sintering aid) co-precipitates with crystal size in the range 10–15 nm, compacted them by uniaxial pressing, and sintered the pellets at 900 ∘ C for 4 h. Dense nanoceramics were obtained with crystal size below 50 nm. In comparison, one should remember that in some early studies on SPS sintering, some authors evidenced that grain growth could be fast and make it difficult to get nanoceramics (with grain size under 100 nm). For instance, Li and Gao [15] started from 10 nm precipitated ZrO2 (with 3% Y doping) and obtained dense ceramics only in conditions where the resulting grain size grew above 100 nm. X.H. Wang and I.W. Chen [16] demonstrated that the counterintuitive strategy opposite to SPS, that is a pressureless method with long sintering time, could work if a subtle two-step protocol was optimized: the idea consists in heating green pellets up to a temperature T 1 (at a rate of 10 ∘ C min−1 ) then immediately cooling down quickly to T 2 (generally 100–200 ∘ C lower than T 1 ) and maintain T 2 for a few hours. If the couple (T 1 ,T 2 ) is well chosen, it is possible to get dense ceramics with limited grain growth. he interpretation is that, once a critical density is reached, it is possible to lower the temperature and let surface energy finish the densification, whereas if high temperature is maintained (conventional method), significant grain growth goes along with densification. In the best case, the size of the nanoparticles before sintering gives the grain size of the nanoceramics. he authors claim for instance dense BaTiO3 ceramics with 8 nm grain size, thanks to

10.3

Dense Nanoceramics

this method [17]. Other studies had shown the benefit of a two-step protocol to limit grain growth in the case of bigger crystal size; for instance, Li and Ye [18] produced 95% dense α-Al2 O3 ceramics with grain size around 70 nm from 10 nm particles. he point is the protocol needs to be adapted for each case, and some authors such as A. Polotai et al. [19] proposed some refinements with sintering profile optimization. Nevertheless, this method is more difficult to apply, starting from powder mixture. It is also noteworthy that nanoceramics may result from the transformation of a metastable phase; in this case, the key point is to promote nucleation of the new phase versus grain growth. his strategy – transformation-assisted consolidation – was used by S.C. Liao et al. [20] to produce rutile dense nanoceramics from anatase nanopowder by high-pressure/low-temperature sintering (1.5 GPa/445 ∘ C), with a decreasing rutile grain size (44–36 nm) and increasing sintering temperature (400–445 ∘ C). he same way, they also obtained α-Al2 O3 dense nanoceramics (50 nm grain size) from metastable γ-Al2 O3 (8 GPa/460 ∘ C) [21]. If the main strategy consists in starting from nanopowders and finds ways to sinter them with mitigated grain growth, X. Chen et al. [22] found that it seems possible to start from 1–10 μm particles (PMN-PT in the cited article) and reduce their grain size under 100 nm during SPS sintering, using a pulsed direct current of 400 A (5.6 × 104 pulses in 3 min). According to the authors, starting particles were shattered into smaller ones in the process due to intense thermomechanical stresses locally induced by the pulsed electric field. 10.3.1.2 Properties

he main benefits expected from grain size reduction lie in improvement of mechanical properties, sometimes associated with another function (optical property, for instance). Mechanical Properties In microceramics, critical defects inducing cracks and fracture are typically surface grain boundaries. Grain size reduction significantly increases fracture toughness and the defects are no more due to grain size but due to the process by itself. he elastic limit and hardness increase with grain size reduction. he reason lies in the mechanisms of dislocation propagation. When a dislocation appears in a grain, it moves until it is blocked by energy barrier at grain boundaries. Other dislocations accumulate until their interactions (repulsion) provide enough energy to allow the propagation of the dislocation through the barrier. If grain size is reduced, under the same strain, the maximum number of dislocation in the grain is reduced and their potential energy does not overcome the barrier anymore. A higher strain is therefore necessary to propagate the dislocations. he Hall–Petch relation quantifies this behavior �y = �0 + √k , with �y being the d

elastic limit, k a constant, and d the grain size. his law cannot be extrapolated to grain size below 10–20 nm where grain boundary thickness becomes significant as compared to grain size. In fact, there is an experimental maximum, a so-called inverse Hall–Petch law being observed when grain size is lowered to a few

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nanometers. Hardness follows the same behavior since it is proportional to �y in a first approximation. In addition to this reinforcement of ceramics by grain size reduction, another effect may be useful for shaping, even if examples are scarce up to now: superplasticity. he superplastic deformation, demonstrated in several families of polycrystalline nanoceramics, is mainly explained by a sliding of the grains along boundaries and can result in spectacular extensions. his effect was used to form pieces with complex or unusual shapes (for ceramics) in some niche applications. A well-known example is given by yttria-stabilized tetragonal zirconia (YTZ) hemispherical caps for missile heads obtained by gas-pressure deformation at 1500 ∘ C [23]. Optical Properties: Example of Transparent Nanoceramics Nanoceramics can bring

better mechanical properties as compared to glasses or microceramics and ease of formation as compared to monocrystals. To avoid loss of transparency due to defects, one has to ensure phase purity, excellent densification, nanocrystal phase control, and no secondary phase at grain boundaries. According to a recent review [24], development of transparent nanoceramics is still a difficult challenge. More often, transparent ceramics have grain size well above microns, and studies involving nanosized grains (90% in the wavelength range between 400 and 1200 nm were measured for the PEDOT:PSS/CNT composite films, and a film thickness of about 60 nm was determined. On top of these films, we deposited a transfer length method (TLM)-type contact structure, consisting of various Al pads, forming gaps with increasing spacing distance, in order to compare the resistivities of the different spin-coating deposited films (see Figure 12.5a). In Figure 12.5b, we observe for both films a linear film resistance increase with increasing TLM gap-width (li ) and a 46% higher resistivity of the composite film (low-conductivity PEDOT:PSS with 7% MWCNTs) as compared to the pure PEDOT:PSS film (high-conductivity type PEDOT:PSS). After the formation of heterojunctions by spin coating of the same films as emitters on top of the n-type crystalline silicon substrates as absorber, “large” area solar cells with an area of 1 cm2 were fabricated by adding a full-area aluminum back contact and the top metal grid. A sketch of the obtained device structure is shown in Figure 12.6a. he comparison of the forward current characteristics of

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Multiwalled Carbon Nanotube Network-Based Sensors and Electronic Devices

2 × 107

I1 R1

I2 R2

I3 R3

I4 R4

Resistance (Ω)

Low conductivity PEDOT:PSS + MWCNTs

1 × 107

High conductivity PEDOT:PSS

0 (a)

0

10 20 30 40 Contact distance (mm)

(b)

50

Figure 12.5 (a) TLM test structure and (b) comparison of the resistance values as a function of the contact distance between a high conductivity PEDOT:PSS film (Baytron) and a low conductivity PEDOT:PSS film with MWCNTs. 2 × 10−2

Current (A)

1 × 10−2

0

Top contact grid PEDOT:PSS(+CNT) emitter n-type crystalline silicon absorber

(a)

Aluminum back contact

PEDOT + MWCNTs on n-Si (illuminated) PEDOT + MWCNTs on n-Si (dark) High conductive PEDOT on n-Si (dark) High conductive PEDOT on n-Si (illuminated)

−1 × 10−2 0

(b)

0.1

0.2 0.3 0.4 Voltage (V)

0.5

0.6

Figure 12.6 (a) Device structure and (b) current–voltage characteristics (dark and with AM 1.5 light illumination) of PEDOT:PSS (+MWCNTs) on n-type c-Si heterojunction solar cells.

the resulting heterodiode solar cells with the different emitter layers under dark and light conditions (AM 1.5 illumination) is shown in Figure 12.6b. Comparing the dark current–voltage characteristics, we find a lower voltage threshold for the inset of conduction and a higher series resistance in the case of the sample with highly conductive PEDOT:PSS emitter. When illuminating the solar cells with AM 1.5 light (100 mW cm−2 ) for both devices, a nice photovoltaic characteristic was obtained with short circuit current densities of about 8.4 mA cm−2 for the hetero-emitter device and about 11.5 mA cm−2 for the nanocomposite hetero-emitter. Regarding the open circuit voltage, a clearly higher value was obtained using the low conductive PEDOT:PSS emitter with MWCNTs. hese

12.3

Crystalline Silicon/Polymer Heterojunctions

early, not yet optimized, devices that served more as a proof of concept, suffered still from a rather low fill factor, and the overall efficiency was only around 1%. Nowadays, efficiencies between 9% and 11% have been reported for cells with n-type silicon substrate and PEDOT:PSS emitter [24, 25], and the manufacturing of a single-walled CNT/n-type c-Si heterojunctions with a conversion efficiency above 11% has been shown [26]. 12.3.2 PMMA with MWCNTs on c-Si Heterodiodes

In order to investigate the heterojunction between CNTs and crystalline silicon alone, without a conducting polymer matrix, we applied spin coating to deposit a nonconducting PMMA film with and without different CNT concentrations on top of an n-type crystalline silicon (c-Si) substrate. he solution of PMMA with CNTs was prepared using 5 mg of the Nanocyl type “3100” non-functionalized MWCNTs that were solved in 2 ml of dimethylformamide (DMF). he solution was sonicated at room temperature for 30 min. Successively, the MWCNT solution was mixed with the PMMA solution in order to obtain three different concentrations of MWCNTs. he different solutions were for 60 min at a temperature of 40 ∘ C. Subsequently, heterodiodes were prepared by spin coating the different PMMA + MWCNTs solutions and the PMMA alone without CNTs for reference on top of the crystalline silicon substrates (resistivity: 0.07–0.013 Ω cm, oriented), and the samples were subsequently annealed at 170 ∘ C on a hot plate for 2 min. Full area back contacts and small area front contacts (about 0.025 cm2 ) have been added using silver paste. A detailed description of the morphology and of the optical properties of the PMMA/MWCNT composite films is reported in [27]. In this case, the PMMA polymer matrix serves only for the stabilization of the CNN and cannot be seen as a hetero-emitter itself, in contrast to the case of the PEDOT:PSS films shown before in this chapter. he device with the pure PMMA film did not show diode characteristics, and the current values, measured in the voltage range below 10 nA, confirm the good electrical isolation properties of the pure PMMA film. he resulting current–voltage characteristics for the devices with different CNT contents are shown in Figure 12.7. We observe a diode behavior for every CNT concentration. he onset of conduction in forward direction decreases monotonically with the increase in CNT content. he prepared devices can be seen as a mixture between a silicon/CNT Schottky-diode and a metal–insulator–semiconductor (MIS) diode, in which the Schottky-diode character becomes stronger with increasing CNT concentration. According to the single diode equation model [28], the ideality factor (n), the diode saturation current (IS ), and the series resistance (RS ) for the organic/c-Si heterostructure, obtained from these measurements, were calculated for the heterodiodes with the different CNT concentrations and are given in Table 12.1. he ideality factor decreases monotonically from a value of 5.20 for the device with 1% CNTs to a value of 4.00 for the device with 7% CNTs, and the diode saturation

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2 × 10−5

PMMA + MWCNTs Crystalline silicon

Current (A)

234

1 × 10−5

0

PMMA + 1% CNTs PMMA + 4% CNTs PMMA + 7% CNTs

0

0.2

0.4

0.6 0.8 1 Voltage (V)

1.2

1.4

1.6

Figure 12.7 Current–voltage characteristics under forward bias of PMMA/MWCNT on n-type c-Si heterojunction diodes with different CNT concentrations in the PMMA film. Table 12.1 Diode characteristic parameters of PMMA + MWCNT organic film on n-type c-Si heterojunction diodes with three different CNT concentrations of the solutions used for spin coating of the organic emitter. CNT concentration (%)

1 4 7

n

IS (nA)

RS (k�)

5.20 4.88 4.00

7.06 8.24 15.3

20.8 25.8 11.1

currents increase from 7 to 15 nA. hese values are reasonable for heterodiodes with a crystalline silicon base, including also an isolation layer [29]. 12.3.3 Polymerized Oxadiazole/Crystalline Silicon Heterojunction as Electrical Memory Element

Electronic memories based on organic films are in general based on the insertion of thin organic films sandwiched between two metal contacts. A large variety of different organic films has been used for the realization of this kind of resistive memories; in some cases, simple single layers of common polymers, like poly(N-vinyl carbazole) (PVK) [30], and in other cases conductive nanoparticles were embedded into a nonconducting polymer matrix, such as PMMA [31] Here, we used a heterojunction between a crystalline silicon bottom layer and a single organic top layer without nanoparticle inclusion for the fabrication of a simple electronic memory element.

12.3

Crystalline Silicon/Polymer Heterojunctions

he devices were fabricated by spin-coating deposition of polymerized oxadiazole (POD) films that were solved in chloroform onto the c-Si substrates. Oxadiazole is an organic electron conductor, and in its polymerized form, it was also used for the fabrication of a blue-emitting polymer light emitting diode (PLED) [32]. he synthesis and structure of the molecule are described in [33] in detail and the results presented here are part of a more detailed study including switching devices, realized by POD deposition on p-type crystalline silicon substrates [34]. he n-type Czochralski crystalline silicon substrates were shortly immersed in buffered HF solution and subsequently rinsed with deionized water in order to remove the natural oxide on top of the crystalline silicon before heterojunction formation. he back contact was made by evaporation of about 100 nm thick aluminum film and the front contact by silver paste dots on top of the spin-coated POD film with a dot diameter of about 2 mm. he current–voltage characteristics of this organic/inorganic heterodiode are shown in a voltage interval between −1 V and +1 V in Figure 12.8. he voltage scan directions are indicated by the arrows. An asymmetry of the maximum currents with a rectification ratio at 1 V of about 2 orders of magnitude has been found. Various hysteresis effects have been observed in both forward and reverse bias directions. In particular, sharp switching below 0.1 V in forward direction and below 0.5 V in reverse direction can be observed. In the next step of the experiments, we decided to use the relatively wide hysteresis in the reverse current–voltage characteristics of the “isotype” POD/n-type c-Si heterojunction and to apply a sequence of three voltages, as shown in the lower trace of Figure 12.8 in order to demonstrate the bistable memory operation of the devices. In particular, we chose a sensing voltage of −0.3 V, a set voltage of −0.6 V and a reset voltage of 0 V. he resulting currents, shown in the upper trace of Figure 12.8, demonstrate clearly flip-flop operation. In this case, again a

Absolute current value (A)

10−4 10−5 10−6 10−7 10−8 POD Crystalline silicon

10−9 10−10 10−11 −1

−0.5

0 0.5 Applied voltage (V)

1

Figure 12.8 Current–voltage characteristics of a POD/n-type c-Si heterojunction during positive and negative voltage ramp.

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−6 −7 −8

1. cycle 2. cycle 3. cycle

−9 −10

0

Reset Read

Voltage (V)

Set

0

5

Read

10

15 20 25 Time (s)

Set

30

35

−0.5

Voltage (V)

Log current (A)

236

40

Figure 12.9 Current–voltage characteristics of a POD/n-type c-Si heterojunction during positive and negative voltage ramp shown for three consecutive cycles.

conductivity change between on state and off state of 2 orders of magnitude was obtained. he bistable operation is extremely reproducible, so that the traces of the monitored current, taken during three consecutive cycles, are practically indistinguishable. It can be noted that during the sensing periods with an applied bias voltage of −0.3 V, no current level drift has been observed. his let us hope that good information retention times can be achieved with this technology. Finally, in Figure 12.9, the repetition of the voltage sequence for three times is shown, with practically identical behavior during all three cycles. his confirms again the good reproducibility of the heterodiode characteristics. With the presented measurements, we could demonstrate that a very simple inorganic/organic semiconductor heterojunction system that is compatible with classical silicon technology can be used for information storage at very low voltage levels.

12.4 Bio-Nanocomposites with CNTs and Fungal Cells with Sensing Capability

As a last example of manufacturing nanocomposites, always with the same type of MWCNTs, we present a new class of materials, based on the combination of biological cells that form, in our case a tissue, only due to the nanotube addition. As an example, we used Candida albicans yeast cells that were grown in suspension with agitation at 25 ∘ C in RPMI medium and collected at an absorbance of 0.36 OD600. We dispersed the MWCNTs with 1% SDS in MilliQTM water. CNTs were added to the SDS solution and left for 150 min. he CNT suspension was then sonicated at room temperature for 20 min, and the supernatant was collected and allowed to form a precipitate for 18 h. he supernatant was collected, centrifuged

12.4

Bio-Nanocomposites with CNTs and Fungal Cells with Sensing Capability

Figure 12.10 Optical microscopy image of Candida albicans/MWCNTs tissue.

at 10 000 rpm for 5 min at room temperature, and the obtained supernatant was again collected. he suspension obtained is saturated with CNTs. he final CNT concentration depends on the SDS concentration. An amount of 750 μl of CNTs was added to 3 ml of C. albicans culture with a 20% final concentration of the MWCNT suspension in the growth medium [35]. After incubation at 25 ∘ C for one day, the artificial tissue was collected and deposited on coplanar gold electrodes, evaporated on top of the oxidized p-type silicon substrate. he distance between the coplanar contacts was 0.6 mm. After deposition of the material, the device was dried for one day at room temperature. For control experiments (RPMI medium with SDS both with and without C. albicans) after growth, C. albicans in absence of MWCNTs was centrifuged and the current–voltage characteristics were measured before drying. In this case, cells did not form a mechanically stable layer, and after subsequent drying, only a powder has been obtained. When observed by optical microscopy (Figure 12.10), the artificial tissue composed of highly packed cells is clearly visible. he effect of cell drying is manifested by their “ghost cell” appearance. A rather specific physical interaction between MWCNTs and C. albicans was observed by SEM (Figure 12.11). he cell wall (the outermost part of C. albicans and other yeast cells) appears to play a major active role in establishing a CNT network and in its stabilization. Subsequently, the dried C. albicans/MWCNT composite samples were subjected to slow temperature cycles. Figure 12.12a shows typical linear I–V characteristics of C. albicans/MWCNTs tissue with gold contacts for two different temperatures. Figure 12.12b shows resistance values of the sample, measured at 1 V, at four different temperatures between 25 and 100 ∘ C, and it is observed that the composite resistance decreases strictly linearly with increasing temperature. We used living C. albicans cells to self-structure a C. albicans/MWCNTs composite material and applied it as a temperature-sensing element operative up to 100 ∘ C. Microscopy showed that C. albicans/MWCNTs formed a sort of artificial tissue. Likewise, dried cells still acted as a stable matrix for the MWCNT network.

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Multiwalled Carbon Nanotube Network-Based Sensors and Electronic Devices 1 μm

Figure 12.11 SEM image of a single cell in a Candida albicans/MWCNTs tissue.

600

1900

100 °C

1850 25 °C

200

Resistance (Ω)

Current (μA)

400

0 −200

(a)

1750 1700 1650

−400 −600 −1

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1 (b)

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Figure 12.12 (a) Current–voltage characteristics at 25 ∘ C (full line) and at 100 ∘ C (dotted line), and (b) resistance values, measured at four different temperatures, of a Candida albicans/MWCNTs tissue with gold contacts.

Good stabilization of the temperature response of the material has been obtained. he artificial tissue also exhibited perfect linear current–voltage characteristics when combined with coplanar gold electrodes. he produced bio-nanocomposite is inexpensive and may be useful in a wide range of electronic applications, ranging from heating to sensing and microwave shielding.

12.5 Conclusions

After introducing shortly a variety of CNT-based physical and chemical sensors, we demonstrated the application of MWCNTs in very simple test structures for reproducible temperature sensing. Furthermore, we demonstrated devices

References

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Acknowledgments

he authors wish to thank Prof. Bruno Maresca from Salerno University for the help in conceiving and realizing the experiments concerning the bionanocomposites, Prof. Christian Boit and Dr. Jürgen Bruns from the TU Berlin for the planning and production of the of the micro-gap structures, and Helmut Wegner for the SEM and FIB imaging. Furthermore, we thank Marcel Leinhos, Stefan Schwertheim, and Katrin Meusinger for the fabrication of the PEDOT:PSS/silicon heterojunctions; Dr. Paolo Vacca, Dr. Simona Concilio, and Prof. Pio Ianelli for the help to produce the POD/silicon heterojunctions; M. Henninger and Dr. Anna Di Girolamo del Mauro for the fabrication of the PMMA + CNT on silicon heterodiodes; and last but not least, we thank Dr. Carlo Barone and Prof. Sergio Pagano for the low-temperature resistivity measurements on the CNT in micro-gap sensors. References 1. Arai, F., Ng, C., Dong, L., Imaizumi, Y.,

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13 Thin Film Piezomaterials for Bulk Acoustic Wave Technology Jyrki Molarius, Tommi Riekkinen, Martin Kulawski, and Markku Ylilammi

13.1 Introduction

he main application for BAWs is in the telecommunications, especially in mobile phones. here is an ever-ongoing development of making smaller and smarter mobile phones than before. One phone should be able to work around the world on different frequencies (bands), which of course increases the amount of filters needed in a given phone. he number of radio frequency (RF)-filters in a smart “world” phone is up to 17 filters or duplexers [1]. his has been resulting in a world market of billions of filter components per year. Because of the large size of the telecommunications market and the needs for performance increasing, combined with miniaturization, also the research activity around the world on the subject of BAW has been high [1–8]. here are two ways to make phones smaller; shrinking the size of individual devices and increasing integration. BAW in the current form achieves the first goal by its capability to produce very small, thin, and light filters. Comparison to the current market leaders, SAW filters (which overtook the bulky ceramic filters), shows that BAW filters have steeper passband skirts, smaller temperature coefficient of frequency (TCF), smaller chip size, and better power handling capability [7, 8]. All these differences are significant, and furthermore the comparison is between mature SAW technology and the first generations of commercial BAW devices, SMR-type (solidly mounted resonator, see below) or bridge-type. BAW also shows promise for future integration with RF circuits as materials, processing, and thermal budget can easily be designed to be compatible with, for example, Complementary Metal Oxide Semiconductor (CMOS) processing. he BAW structure lends itself also to other applications (gas-, bio, and pressure-sensors have been suggested). he performance of these sensors using ZnO as piezolayer and SMR-type structure with mirrors has been calculated and found to be excellent [7]. here are two basic BAW structures: namely, bridge (also called membrane) resonators or solidly mounted (also called mirror) resonators. he piezoelectric layer is vibrating between two electrodes and in bridge-type device the substrate and the resonator are decoupled by an air gap. he air gap, in principle, provides almost The Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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2.5 × 2.0 × 0.76 mm Figure 13.1 Commercial packaged BAW filters (left) SMR- and (right) bridge-type (courtesy of Avago and Triquint, respectively).

ideal isolation, but in practice, the lower electrode as well as the supporting structure cause losses. he bridge structure has been utilized to make filters using the resonators in a ladder configuration [6]. Bridges or membranes are usually made by surface (or bulk) micromachining. Mirrors for isolating the resonator from the substrate was first proposed by Newell and Nothanson [9] already in 1965, and then 30 years later developed to modern SMR structure by Lakin et al. [10]. Here the resonator is isolated from the substrate by an acoustical mirror, built from alternating layers of high and low acoustical impedance materials, whose thicknesses are a quarter of the acoustic wavelength at the operation frequency. Depending of the choice of materials, typically two to four layer pairs are needed. If molybdenum is used as the high impedance material and SiO2 as the low impedance material, three layer pairs are needed, but substituting Mo with W, two pairs are sufficient for adequate resonator substrate isolation. Mirrors can also be made of dielectric materials like AlN and SiO2 , which would give the benefit of easier processing as the mirror would not need any patterning. Metals in the mirror layers need patterning, because otherwise the parasitic capacitances associated with the conductive metal layers would cause problems in the device operation. Heavy metals have high acoustic impedance and high acoustic reflectivity and two layer pairs provide enough reflectivity. A mirror made of AlN/SiO2 requires four reflective pairs. here are commercial producers for bridge- [8] and SMR-type [1] BAW passband filters and duplexers for frequencies around 2 GHz and beyond (see Figures 13.1 and 13.3). Both technologies seem to be viable from both technological and economical point of view [8].

13.2 Zinc Oxide (ZnO)

In this paragraph, we are discussing not only ZnO piezoelectric film but also the materials science of piezoelectric film growth applied for BAW resonators.

13.2

Zinc Oxide (ZnO)

he main advantage of zinc oxide is its high acoustic coupling coefficient (k mat = 0.282, k 2 = 7.95%) [5]. PZT promises highest coupling coefficient between 0.28 and 0.5, after annealing, but low Q-values (about 220 at 2 GHz) [3]. Aluminum nitride (AlN) on the other hand, has a lower TCF (∼−25 ppm/K) than zinc oxide (∼−50 ppm/K). he smaller TCF of AlN in some BAW filter applications can nullify the benefit of the higher acoustic coupling coefficient of ZnO. Almost all materials get softer when heated, causing negative TCF. But silicon dioxide works the other way around. herefore, SiO2 used in the reflector also reduces the overall temperature drift (TCF) of BAW significantly [1]. he longitudinal sound velocity in AlN is 10 400 m s –1 , which is over 60% higher than that in ZnO, 6400 m s –1 . As the thickness of the piezolayer largely determines the frequency of the device, it is advantageous, at low frequencies, to have low sound velocity as the films will be thinner and therefore faster to deposit resulting in increased productivity. At high frequencies, the effective coupling becomes low when employing a piezomaterial with a low sound velocity, because of the small thickness of the layer. his would indicate that ZnO is better at low frequencies and AlN at high frequencies. he most important parameter determining the quality of piezoelectric layer (AlN or ZnO) is a strong preferred orientation of the film. For BAW devices operating in the longitudinal wave mode this is (0 0 0 1). he wurtzite crystal is thus growing c-axis perpendicular to the substrate and its hexagonal basal plane is interacting with the seed layer. here are applications where different orientation is desired, but in these cases as well, very strong preferred orientation is needed [4]. Piezoelectric films can and have been deposited by several different ways, like CVD (chemical vapor deposition), laser ablation, and PVD (physical vapor deposition) methods. In the PVD methods, magnetron sputtering has been used for decades in microelectronics fabrication, because of the advantages including precise control of film composition, crystalline structure and stress, thickness, and uniformity. It has been applied either by RF sputtering from ZnO target or by DC or pulsed DC in reactive mode from zinc target in oxygen-containing atmosphere, as the temperatures remain low during deposition. Beside the sputtering parameters themselves, other issues affecting the piezoelectric film quality are the seed layer and the sputtering environment (affecting contamination). If the seed layer is used as the bottom electrode of the device, it has to be highly conducting to keep the electrical losses to a minimum. herefore, it is advantageous to separate these functions to a highly conducting bottom electrode and to a separate seed layer, which can be optimized to promote piezo film growth and acoustical properties of the BAW stack (see Section 13.3.1). Device-quality ZnO can be grown on several metals – at VTT this has been realized on gold and molybdenum [5, 6, 11, 12]. It has been shown that good-quality AlN, which has the same wurtzite-type crystal structure as ZnO, can be grown on different seed materials [13]. Löbl et al. [14] and Lee et al. [15] for AlN, and Lee et al. [16] for ZnO identified the surface roughness of the seed layer as the decisive factor on piezoelectric film quality; the smoother the seed layer, the better the piezoelectric film quality. he film quality was measured by X-ray rocking curve of ZnO film and the FWHM (full-width half

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Wafer Slurry

Mounting Rotating wafer chuck

pad Wafer

Polishing pad Slurry

Rigid platen

Pad

(a)

Platen motion

(b)

Figure 13.2 Schematics of chemical mechanical polishing in system level (left) and microscale (right).

maximum) of the (0 0 0 2) peak was shown to correlate with the effective acoustic coupling coefficient, k eff [17]. k eff , on the other hand, determines the bandwidth and insertion loss of a filter [18]. Quality factors, Q, are determined at both series and parallel resonance. hey are calculated according to the IEEE standard [19]. he reason for the correlation between surface roughness and film quality is quite simple. Since the deposition takes place at low temperature and with low particle energy, adatoms on the surface have low mobility and they do not reach their energetically favored positions for the growth in the preferred orientation. On a smooth substrate, the movement of adatoms is easier and this results in improved piezolayer quality. Control of the surface roughness of a given metal can only be achieved to a certain degree with adjustment of the sputtering parameters, as other film properties, especially stresses in the film, will also be strongly affected. herefore, nanolevel control of the surface is needed. Chemical mechanical polishing (CMP) is usually used to planarize device structures, as seen in the basic schematics in Figure 13.2. he wafer is held on a carrier and pressed with a defined force against a microporous polyurethane polishing cloth, which is glued on the rigid polishing platen of the tool. While the platen and the chuck are rotating, a suspension with adjusted pH value of deionized water and abrasive particles (slurry) is dispensed on the platen. he abrasive particles are made from silica or ceria with diameters in the 50 nm range. During polishing, the particles are accelerated by the micropattern of the polishing pad and impinge on the surface of the wafer, thus weakening the strength of the atomic network. he pH-adjusted liquid can penetrate into the weakened network and dissolve atomic clusters from it. Due to the height variation of the patterned surface, a different local pressure is applied to elevated and lower areas of the wafer leading to increased removal on the higher regions. his leads to a planarization of the pattern on a large scale. In Figure 13.2b, the principle of the removal is presented in detail in microscale. In this chapter, the emphasis is on surface smoothening by CMP, which can be achieved with a modified CMP planarization process. Any kind of CMP, however, will lead to a heavy contamination of the polished substrates with particles left on the surface. Since these particles have strong adhesion, a special cleaning is an important issue after polishing. Besides soft

13.2

Air

Zinc Oxide (ZnO)

Air

Electrode

Electrode

Piezolayer

Piezolayer

Electrode Support Substrate

Electrode

Air

Low-Z Pa 5 = 1.454 μm

High-Z

Pa 5

Low-Z High-Z

Substrate

Figure 13.3 Bridge and mirror resonator film stacks with cross section SEM of the mirror BAW.

etching methods and standard cleaning with megasonic agitation, we use a special post-CMP cleaner, which scrubs the surface with a soft polyvinyl alcohol (PVA) brush and removes particles also by mechanical force. Besides, the particles slurry often contains metallic contamination. hus, by including chemistry to the post-CMP cleaning process, care has to be taken for lowering the metal contamination down to the stringent levels for CMOS compatible production. he CMP smoothening was developed (in the first edition of this chapter) and applied to BAW to achieve high-quality ZnO for resonators and filters. Schematic cross-sections of the thin film stacks for both bridge and SMR are shown in Figure 13.3. In surface micromachining, the air gap is formed by dissolving a sacrificial layer from underneath the bridge, for example, copper below silicon nitride bridge [6]. SMR, schematic in Figure 13.3, has the designed layer thicknesses, whereas the lowest high-Z layer in the actual scanning electron microscopy (SEM) cross-section micrograph of a BAW is thicker than designed. Fortunately, it does not affect the mirror performance substantially. his can be deciphered from Figure 13.4, which shows the relative calculated displacement amplitude in a resonator stack of the longitudinal wave in z-direction with silicon dioxide/tungsten mirror. he relative displacement at the substrate is less than 2% of the maximum at the series resonance frequency of 1857 MHz; therefore, it is not necessary to increase the amount of mirror layers in this stack. he highly columnar structure of the metals in the mirror and bottom electrode is clearly depicted in Figure 13.3, as well as the amorphous nature of silicon dioxide. Top electrode is sputtered aluminum and it has been deformed during sample cleaving. he ZnO piezolayer is also highly columnar as desired for strongly preferred orientation. But as can be seen in Figure 13.5, the ZnO film

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100

At series resonance frequency 1857.36 MHz

90 80 Relative amplitude (%)

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70

SiO2 Al ZnO Mo 300 nm 1050 nm 300 nm 807 nm

W 707 nm

SiO2 807 nm

W 707 nm

SiO2 807 nm

60 50 40 30 20

Si substrate

10 0 0.0

1.0

2.0 3.0 4.0 Location from the surface (μm)

5.0

Figure 13.4 Relative displacement in a resonator stack at 1857 MHz. Free surface is on the left.

= 1.038 μm

Mag = 101.83 K X WD = 7 mm

200 nm

EHT = 2.15 kV Detector = InLens

Store resolution = 1024 × 786

Date :22 May 2003 Time :18:15:14 VTT Microelectronics centre

Figure 13.5 Cross section SEM micrograph with non-CMP ZnO piezoelectric film on resonator.

on a layer stack, which is not CMP-smoothened, is porous and the ZnO surface appears to be very rough. It is not feasible to smoothen the top electrode metal layer (though it would be directly acting on growing piezoelectric film) by CMP, due to contamination issues. Gold, one of our electrode materials, is the most feared yield killer in microelectronics. herefore, we decided to smoothen the top mirror layer SiO2 ,

13.2

Zinc Oxide (ZnO)

249

3.00

5.00

2.00 2.50 1.00

0

2.50 (μm)

0 5.00

0

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2.00 (μm)

Figure 13.6 AFM nanographs of SiO2 (a) before and (b) after CMP smoothening.

as this is compatible with other work done on our CMP tool. A CMP smoothening process for the silicon dioxide was developed and the topological properties of the films were measured using atomic force microscopy (AFM). As one can see in AFM nanographs in Figure 13.6, the surface appearance of plasma-enhanced chemical vapor deposition (PECVD)-deposited SiO2 film changes completely in CMP. During the removal of 70–80 nm of oxide by CMP the rms roughness is dramatically reduced from 4–5 nm to less than 0.3 nm. After the first trials with actual BAW samples, a smooth surface was achieved, but large amount of particles were detected on the surface even after post-CMP cleaning. his was resolved by adding an Standard Clean (SC)-1 cleaning step at 55 ∘ C into the post-CMP cleaning procedure. Another issue with CMP smoothening is how our resonator stacks survive through the CMP. his is illustrated in Figure 13.7, where a stylus trace (in fact a cross-section, compare to Figure 13.3) of the resonator stack is shown before and after the CMP smoothening. he corners are rounded during CMP, but a large center area of the mirror stack remains flat and uniform. It does seem to be possible to reduce the rounded area further by CMP process development. When including CMP into the BAW process flow, one has to take into account not only the removal of the oxide by CMP but also the rounding of the corners by allocating some extra area on the resonator mirrors (designing for manufacturability). Although we lose some chip “real estate,” future integration of CMP smoothening into the filter processing seems feasible. In Figure 13.8, AFM nanographs of zinc oxide surface from the process without CMP smoothening of the silicon oxide and with CMP are shown. Surface roughness has been reduced from 23 to 4.4 nm. he ZnO film (non-CMP) in cross-section SEM micrograph in Figure 13.5 is from the same sample as AFM picture in Figure 13.8a. he cross-section microstructure and surface roughness

0 3.00

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

1200 1000 800 Height (nm)

250

600 400 200 0 −200 −200

0

200

400 600 Location (μm)

800

1000

1200

Figure 13.7 Dektak stylus trace of the BAW film stack (a) before, and (b) after CMP smoothening.

are also closely related in case of the CMP-smoothened ZnO film, where smooth surface also results in dense and featureless SEM cross-section (not shown here). Smoothening of SiO2 layer seems to result in better smoothness of the grown ZnO as expected and has been reported before [16]. On smoothest ZnO film, we have achieved the surface rms roughness of 4.4 nm with CMP, which compares favorably with the best achieved smoothness of non-CMP ZnO, where rms roughness is 13 nm. ZnO roughness was measured by AFM on the as-deposited samples. Data show that the smoothest ZnO is achieved on those wafers where the top SiO2 has been smoothened by CMP and the worst roughness was on non-CMP wafers. Another trend is that the ZnO on the non-CMP resonators is getting better with time (more runs). Due to the instabilities in the ZnO sputter deposition and small number of samples, evidence however is not unambiguous. One has to keep in mind that the wavelength of the acoustical waves in ZnO in these resonators is 3 μm, but the scale of the surface roughness is in (tens of ) nanometers. herefore, strong physical coupling between the acoustical waves and the surface roughness is not expected. One can speculate that a smoother surface would result in smoother and denser ZnO, because of the effect on film growth during sputtering. However, this theorem has not been completely verified, as the evidence is inconclusive. he fabricated experimental unpackaged ladder-type filter (Figure 13.9) worked well with clear sound for years, when tested in a real mobile phone at Global System for Mobile Communications (GSM) frequency.

13.2

Peak

Surface Area Summit Zero crossing

Stopband Execute

Zinc Oxide (ZnO)

Cursor

Roughness analysis Image statistics 3.00

2.00

1.00

0

2gb26 Zn0 2gb26c.001 Peak on Peak

0 1.00 2.00 3.00 μm

Summit on

Img. Img. Img. Img. Img. Img. Img.

Z range Mean Raw mean Rms (Rq) Ra Rmax Srf. area

155.18 nm 0.039 nm 6.506 nm 23.341 nm 18.676 nm 155.46 nm 10.403 μm2

Box statistics Z range Mean Raw mean Rms (Rq) Mean roughness (Ra) Max height (Rmax) Max peak ht (Rp) Av max ht (Rpm) Max depth (Rv) Av max depth (Rvm) Surface area Summit density Box x dimension Box y dimension

Zero cross. off Box Cursor

Surface area Summit Zero crossing

Stopband Execute

Cursor

Roughness analysis Image statistics 3.00

2.00

1.00

Img. Img. Img. Img. Img. Img. Img.

Z range Mean Raw mean Rms (Rq) Ra Rmax Srf. area

42. 720 nm −0.00003 nm 8.143 nm 4.422 nm 3.494 nm 42.793 nm 9.310 μm2

Box statistics Z range Mean Raw mean Rms (Rq) Mean roughness (Ra) Max height (Rmax) Max peak ht (Rp) Av max ht (Rpm) Max depth (Rv) Av max depth (Rvm) Surface area Summit density Box x dimension Box y dimension

0 1.00 2.00 3.00 μm 2gb37 Zn0 at center 2gb37c. 001 Peak on Summit on Zero cross. off Box Cursor 0

Figure 13.8 AFM nanographs of ZnO surface after sputter deposition (a) non-CMP (b) CMP smoothening applied to SiO2 .film.

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

FBAR filter 0 Reflection S11, insertion loss S21 (dB)

252

Ladder filter with six resonators.

5

10

Properties of resonator D41o11: fs 944.7 MHz, fp 971.6 MHz Qs 460 Qp 890, Radius 0.943 keff 0.234, FoM 48.5 Nonc. 0.37 %, RL 53 kOhm Co 3.70 pF Cm 213.7 fF LM 132.8 nH Rm 0.91 Ohm Rx 0.82 Ohm

VSWR spec.

S21 925 MHz 2.95 dB 960 MHz 2.33 dB 3.5 dB BW 38.2 MHz 1.26 dB ILmin 1.69 dB Ripple 2.17 VSWR Stopband 23.38 dB

15 S11

20

EGSM

25

30 800

S21

850

900

950 Frequency (MHz)

1000

1050

BAWFILTER 2W#69 D4G6o11 b

Figure 13.9 Microscope image of a six resonator 3-stage ZnO ladder filter for ∼1 GHz. The die size is approximately 1.4 × 2.0 mm2 (left) and the electrical response fulfilling the EGSM specifications (right).

13.3 Aluminum Nitride (AIN)

It has been shown that good-quality piezoelectric AlN thin film can be grown on different seed materials [13]. Löbl et al. [14] and Lee et al. [15] identified the surface roughness of the seed layer as the decisive factor on piezoelectric film quality; the smoother the seed layer, the better the piezoelectric film quality. his agrees with our results for ZnO, which also has the same wurtzite crystal lattice as AlN.

13.3

Aluminum Nitride (AIN)

C = 4.978 Å

N AI

a = 3.11 Å Figure 13.10 Schematic illustration of the wurtzite lattice structure of AlN [41].

AlN is the material of choice for the piezoelectric material in BAW devices [20–24], as it exhibits good electromechanical coupling, stability, nontoxicity, environmental friendliness, and compatibility with micro/nanoelectronic integrated circuit (IC) processing. AlN film quality must be very high to meet the requirements of smart mobile devices [20–22, 24–28]. Material requirements include exact stoichiometry, hexagonal wurtzite crystallographic structure with well-defined (0 0 0 1) orientation (see Figure 13.10), and strict control over film stress, roughness, and purity. Oriented AlN film growth requires optimization of the deposition parameters and of substrate and seed layer combinations. Several methods to deposit AlN layers include CVD, pulsed-laser deposition (PLD), molecular beam epitaxy (MBE), and RF- and DC-magnetron sputtering. Reactive pulsed-DC magnetron sputtering is the dominating method both in research and production. Even low levels of oxygen are detrimental for high-quality AlN growth [29]. hermodynamics dictate that Al reacts more preferably with oxygen than with nitrogen, and the unwanted Al2 O3 will deteriorate the columnar-oriented growth of AlN. hus, ultrahigh vacuum (UHV) with a base pressure before sputtering less than 1 × 10 –6 Pa is required. Moreover, moisture has to be excluded by using a load-lock, substrate heating, and by using high sputtering rates to minimize oxygen incorporation. Extended research of electrode materials include (1 1 1)-oriented face-centered cubic (fcc) metals such as Al, Pt, and Ni [21, 23, 24, 26, 30–34], (110)-oriented body-centered cubic (bcc) materials such as Mo and W [20–23, 29–32, 34–39], and hexagonal metals with a (0 0 0 1) orientation including Ti and Ru [22, 30, 31, 33]. Especially Mo electrodes fulfill the device requirements: low resistivity, high degree of (1 1 0) crystalline texture, high density, and surface smoothness. he growth of Mo film is, naturally, mostly influenced by the deposition parameters. However, the crystalline orientation and morphology of Mo electrodes is strongly influenced by the seed materials (and their optimized deposition).

253

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

TiW seed (8 nm)

Ni seed (10 nm)

Ti seed (20 nm)

300 nm Figure 13.11 SEM images (same magnification) of the Mo surface morphology after sputtering on thin TiW, Ni and Ti seed layers [41].

AIN mixed orientation AIN (0 0 2) Mo Si/SiO2

200nm

Figure 13.12 AlN on patterned Mo electrode (AlN film roughening at the edges) [T. Riekkinen, personal communication].

Several metallic seed layers have been studied for Mo electrode including Ti [34, 38, 40], Ta [38], Cr [38], TiW (10/90 wt%) [40], Ni [40], and bilayers Au/Ti, Ag/Ti, and Pt/Ti [36]. hese seed layers provide different templates for Mo crystalline growth. Both the grain size and surface roughness of the Mo film increases in the order Ti, Ni, and TiW seed (see Figure 13.11). his reflects to the crystalline structure of Mo film, where the (1 1 0) orientation of Mo film is more pronounced, when optimum Ti seed layer is used instead of TiW or Ni seed. he smooth surface morphology in Figure 13.12 and (110) film texture of the Ti-seeded Mo electrodes provide the best base for high-quality AlN piezoelectric films for resonators and filters for mobile devices. X-ray diffraction (XRD) clearly shows that nanoscale materials control with seed layers affects Mo film orientation, and influences the crystalline growth of AlN piezoelectric films. he preferred orientation of AlN films (0 0 0 1) is easily measured by X-ray rocking curve measurement of the AlN (0 0 0 2) reflection and

13.3

Normalized intensity

1.0

Aluminum Nitride (AIN)

AlN on Mo/TiW AlN on Mo/Ni AlN on Mo/Ti

0.5

0.0 10

15

20

25

ω (°) Figure 13.13 XRD rocking curve of the AlN (0002) reflection [T. Riekkinen, personal communication].

Top eletrode Mo Piezoelectric AIN Bottom electrode Mo #1 mirror SiO2 #1 mirror W #2 mirror SiO2

1 μm

#2 mirror W SiO2 Substrate {Si}

Figure 13.14 A cross-sectional SEM picture of the fabricated BAW resonator structure with layers depicted [41].

the FWHM of the X-ray peak. he FWHM values of the X-ray rocking curves are 2.3∘ for Ti seed, 5.0∘ for Ni seed, and 12.3∘ for TiW seed below Mo film (smallest value is best) (see Figure 13.13). he maximum intensities of the AlN peaks were 16000, 4600, and 530 counts s –1 on Ti/Mo, Ni/Mo, and TiW/Mo, respectively (highest is best). his further underlines the growth control with Ti nanoseed. Nanocontrol of materials properties is fine, but one needs to find out whether these material properties also reflect to the electrical performance of real devices. herefore, we fabricated SMR-type BAW resonators using the above nanoseed layers in the resonator structure (Figure 13.14). he difference between the series f s and parallel f p resonance frequencies is a direct measure of the electromechanical coupling coefficient; therefore, BAW resonators were measured with a network analyzer and the impedances of the

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

|Z| (Ω)

103 102

fs

fp TiW+Mo Ni+Mo Ti+Mo

101 100

1900

1920

1940

1960 1980 f (MHz)

1200

2020

2040

2 arg(Z)(rad)

256

TiW+Mo Ni+Mo Ti+Mo

1 0 −1 −2

1900

1920

1940

1960 1980 f (MHz)

1200

2020

2040

Figure 13.15 Impedance magnitude (upper plot) and phase of 50 Ω resonators [41].

devices with different seed layers are shown in Figure 13.15. To facilitate clear comparison, the data is plotted against a frequency normalized to f p and rescaled to match the f p of the Ti/Mo-based resonator. As the impedance plots clearly show, there is a drastic improvement in the electro-acoustic coupling coefficient K 2 , when TiW/Mo bottom electrode in the BAW resonator is replaced by Ni/Mo as indicated by an increase of spacing between f p and f s . Still a further improvement is achieved with Ti/Mo bottom electrodes. he most important performance values of a BAW resonator are Qmax , K 2 , and FoM = K 2 Q (Figure of Merit), which are 1276, 6.28%, and 80, respectively, for Ti/Mo electrode, for 50 Ω devices [41]. When substrate is heated during titanium sputtering, Ti/Mo electrode can be further optimized for highly c-axis-oriented AlN deposition. hese values fulfill the requirements of mobile RF devices, for example, smart phones. AlN has become the only piezoelectric material to be able to address the demands made upon duplexers because of, for example, steep passband skirts [8]. As the BAW device frequency is a direct function of the film thicknesses in the resonator stack (see Figure 13.14), any thickness nonuniformity would be a yield killer. herefore, localized ion beam etching is used for frequency trimming [42]. 13.3.1 Layer Transfer Method

An alternative processing method to decouple the nanoseed and electrode functions is the layer transfer method. his offers complete freedom to select a

13.4

Scandium-Alloyed Aluminum Nitride (Sc:AIN)

nanoseed for optimal AlN piezoelectric film growth. Moreover, as the electrodes are deposited after AlN film, any kind of multilayer electrodes with optimal acoustic and electrical performance may be used. Acoustic mirror can also be patterned after AlN deposition. Values obtained with this method are 1060, 6.04%, and 64, respectively, for Qmax , K 2 , and FoM. hese values are comparable to our normal fabrication (see Section 13.3), showing the potential of this method, if combined with innovative seed layers, multilayer electrodes, and special acoustic mirrors [41]. Layer transfer method has been recently applied to other piezoelectric materials: an energy harvester has been made using PZT as the piezoelectric material (see Section 13.5) grown on sapphire and transferred on polyethylene (PET) [43]. hen lithium niobate, LiNbO3 , piezoelectric wafer was bonded on SiO2 layer to fabricate piezoelectric microelectromechanical systems (MEMS) devices [44]. Demonstrated results for lithium niobate are high electromechanical coupling combined with high Q. hese high values will enable fabrication of acousto-optic modulators, chip-scale frequency combs, and piezoelectric gyroscope [45]. Some form of layer transfer and bonding can be used for integration of resonators and filters with control electronic circuitry. Heterogenous technology integration combining piezoMEMS, MEMS sensors, and electronic circuitry, for example, radios, is increasing in the future to enable smaller and more complex 3D system in package (3D-SiP).

13.4 Scandium-Alloyed Aluminum Nitride (Sc:AIN)

As discussed in Section 13.3, in thin film BAW filters for high-frequency applications up to 20 GHz, AlN is the material of choice. However, to fulfill the demanding device requirements for smart mobile applications, AlN films are close to their performance limits in terms of bandwidth and thermal compensation. herefore, there is need for a novel low-loss piezoelectric material with tailored properties for frequency filtering, actuating, and sensing applications [25]. Recent research has shown that the piezoelectric response of AlN can be improved by distorting the crystal lattice with additional element, namely, scandium, Sc. Akiyama et al. [46] have successfully improved the piezoelectric properties of AlN thin films by the addition of Sc. his was enabled by the discovery of a metastable hexagonal form of ScN, which can exhibit extensive solid solubility with AlN. Consequently, Akiyama et al. fabricated the nonequilibrium Sc0.45 Al0.55 N alloy that exhibits a piezoelectric strain coefficient d33 of approximately 24.6 pC N –1 , which is about four times that of AlN [47]. he marked increase in the piezoelectric response in the novel Scx Al(1–x) N thin film system has been attributed mainly to the intrinsic alloying effects and the resulting softening of the structure along the c-axis [48]. he different bonding characteristics of the ScN (rocksalt structure with octahedral coordination of nitrogen) and AlN (wurtzite structure with tetrahedral coordination for

257

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

nitrogen) has been proposed to lead to a “frustrated” system due to the structural phase competition [48]. he situation is quite similar to that encountered in the fabrication of amorphous diffusion barriers for IC applications [49]. Scx Al(1–x) N has inherently large electromechanical coupling coefficient [50], which provides wide frequency bandwidth for acoustic wave filters and it also makes it possible to incorporate temperature compensation in filters. Furthermore, key parameters for realizing good-quality piezoelectric energy harvesters are a high piezoelectric coefficient and a low relative dielectric permittivity. From this perspective, the power generation FoM for AlN is comparable to or even higher than that of PZT due to the lower relative dielectric constant. his was experimentally confirmed recently (2013), as Sc17 Al83 N increases the energy harvesting potential by 60% in comparison to pure AlN (or PZT) [51]. Sputtering method is our choice for ScAlN deposition, because it is a very versatile enabling deposition of practically all solid materials and several of them in situ without breaking vacuum in between. Furthermore, this method is UHV compatible. his is needed due to the detrimental effect of even trace amounts of

200 nm

(a)

(b) 0

1.00

2.00

3.00

3.00

2.00

2.00

1.00

1.00

0 3.00 μm 0

1.00

2.00

Figure 13.16 (a) SEM cross section, and (b) AFM surface image of ScAlN film on SiO2 /Ti/Mo seed [T. Riekkinen, personal communication].

0 3.00 μm

13.4

Scandium-Alloyed Aluminum Nitride (Sc:AIN)

oxygen, which deteriorates the preferred columnar growth of AlN or ScAlN films. Oxygen “contamination” is often induced into the chamber in water vapor, either from chamber walls or with the wafer. Baking of the chamber and preheating of the wafers is therefore a necessity. his is very important for nanoscale control of piezoelectric material growth as the seed layer/bottom electrode can be deposited without contaminating the interfaces, for instance, with oxide. Seed layer and sputtering geometry contribute to the nucleation and growth of ScAlN films in the same way as with wurtzite AlN and ZnO films. Sputtering parameters, that is, heating and substrate bias increase adatom surface diffusion resulting in smooth and dense film. he apparent compressive stress of the ScAlN films can be compensated by increasing the deposition pressure in the sputtering chamber. Same seed layer bottom electrode combination – Ti/Mo – as with AlN (described in Section 13.3) was chosen for ScAlN piezoelectric film growth. See Figure 13.16. Both AlN and ScAlN samples show preferred highly textured Mo (1 1 0) seeding (see Figure 13.17). Both piezoelectric films have hexagonal wurtzite phase with c-axis perpendicular to the surface. Furthermore, there is no indication of cubic ScN phase, which means that Sc is indeed incorporated into the AlN lattice. For electrical characterization of the ScAlN films, they were sputtered on seed bottom electrode on Bragg mirror wafers and fabricated to RF resonators. Comparison to similar AlN devices sputtered with the same tool is shown in Table 13.1. he 100 000 ScAIN(002) Mo(1 1 0)

1000 ScAIN(0 0 4)

Ti(0 0 2)

100

W(2 1 1)

Mo(2 2 0)

Si

Intensity (arb. units)

10 000

AIN ScAIN7

10

1 30

40

50

60 2θ (°)

70

80

90

Figure 13.17 XRD �-2� scans of AlN and Sc doped AlN films (Sc5 Al40 N55 ). Ti and Mo peaks originate from the seed and W (211) from the Bragg mirror [T. Riekkinen, personal communication].

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Thin Film Piezomaterials for Bulk Acoustic Wave Technology

Table 13.1 Summary of the electrical properties of the piezoelectric films on resonators at 2 GHz.

AlN Sc5 Al40 N

K 2 (%)

Q

6.91 9.52

1000 900

Source: T. Riekkinen, personal communication

effective electromechanical coupling coefficient K 2 is calculated from K2 =

� 2 fp − f s 4 fs

(13.1)

where f p and f s are the parallel and series resonances, respectively. Quality factor, Q, of the resonances is calculated from Q=

� || d� || 2 || d� ||

(13.2)

where � is the angular frequency and � the phase of the impedance in radians. A definitive increase of the effective electromechanical coupling coefficient for Sc-doped AlN film is observed compared with pure AlN layer, while maintaining comparable Q-value. his electromechanical coupling of Sc5 Al40 N55 is a major improvement resulting in larger MEMS actuation or wider bandwidth (see Figure 13.18) for RF frequency filtering applications. 103 ScAIN AIN

3.7% 102

|Z| (Ω)

260

101

100 2.8% 10−1 1.9

1.95

2 f (Hz, scaled)

2.05

2.1 × 109

Figure 13.18 Impedance magnitude of AlN and Sc14 Al86 N BAW resonators matched to 50 Ω [T. Riekkinen, personal communication].

13.5

Lead Zirconate Titanate (PZT)

13.5 Lead Zirconate Titanate (PZT)

PZT in bulk ceramic form has been used for decades in piezoelectric applications due to its high electromechanical coupling. Recently, polycrystalline perovskite PZT thin film piezoelectric material has been utilized for low-frequency MEMS applications, for example, gyro sensors, microphones, and energy harvesters as well as high-density capacitors and memory devices. he most studied composition of PZT is Pb(Zr0.52 Ti0.48 )O3 resulting in the highest piezoelectric coefficients being close to the morphotropic phase boundary. However, the application of well-crystallized PZT is limited by harsh deposition conditions that, for example, most practical electrode materials cannot survive. Crystalline structure of PZT is also highly dependent on Pb concentration. At high deposition temperature, lead is volatile and needs to be compensated during film growth. hus, development of advanced PZT deposition process is extremely important. Lead diffusion into silicon substrate causes clear cavities underneath the bottom electrode (see Figure 13.19a). Lead diffusion and the formation of cavities can be completely suppressed with TiO2 diffusion barriers (see Figure 13.19b). Both PZT films were deposited with identical sputtering parameters at 600 ∘ C. Maximizing the piezoelectric coefficient is of considerable importance in reducing the drive voltage or increasing the speed or sensitivity of many MEMS devices. For applications where large thin film piezoelectric coefficients are required, ferroelectric compositions, for example, PbZrx Tiy O3 (PZT), are very attractive compared to wurtzite AlN or ZnO. he resulting properties are dependent on film grain size, thickness, and orientation, with the best responses reported to date in {0 0 1}-oriented films near the morphotropic phase boundary, that is, Zr/Ti close to 50/50 [52]. Properties can be further increased with doping. Niobium-doped PZT produces two times the displacement of the nondoped PZT with the same excitation voltage [53]. For mass production, high-volume PZT deposition is needed. his has been achieved in the EU project piezoVolume using well-textured Pt (1 1 1) seed layers on TiO2 diffusion barriers [54]. Layer transfer techniques utilizing PZT/Si wafer bonding have been developed to uncouple seeding from substrate. Here also, CMP smoothening has been applied to PZT as well [55]. Although PZT has a perovskite structure, in order to grow it in preferred orientation, which is needed for good properties, similar smooth surface and suitable nanoseed films are needed as shown earlier with wurtzite-structured ZnO and AlN. PZT is best in low frequencies, but nevertheless RF-MEMS PZT has been developed to fabricate tunable, low-loss (high Q), compact, and linear components including tunable inductors and varactors and electromechanical filters with k eff 2 up to 8% [56].

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=1.007 μm

200 nm

(a)

EHT = 10.00 lV WD = 7 mm

Signal A = inLens Photo No = 6

Date : 22 Oct 2012 Time :15:28:56

ZEISS

Date : 24 Oct 2012 Time :11:28:44

ZEISS

=1.158 μm

200 nm

(b)

EHT = 5.00 lV WD = 6 mm

Signal A = inLens Photo No = 35

Figure 13.19 Crosssectional SEM of PZT (a) without, (b) with TiO2 diffusion barrier [T. Riekkinen, personal communication].

13.6 Lead-Free Piezoelectric Materials

Environmentally friendly lead-free piezoelectric materials have been developed recently. Within (K,Na)NbO3 (KNN) system, with orthorhombic perovskite lattice, (K0.5 Na0.5 )NbO3 was regarded as a promising candidate by Saito et al. [57]. his was in bulk ceramic form. For thin film MEMS a chemical solution deposition route has been developed. he piezoelectric coefficient (effective d33 ) value of the

13.7

Future Trends and Applications

KNN film was 46 pm V –1 [58]. Lately, KNN thin films have been epitaxially grown on Nb : SrTiO3 single-crystalline substrates with different crystallographic orientations by the sol–gel processing. Comparatively large piezoelectric response (d33 ) of 66.1 pm V –1 (peak value) was measured along the [0 0 1] direction [59]. hese piezoelectric values are comparable to those of thin film PZT. Another lead-free niobate family is based on lithium. LiNbO3 (LNO) films were first deposited as optical waveguides [60]. he deposition of the Si3 N4 film is a key to obtaining exclusively c-oriented LiNbO3 thin films. Silicon nitride layer provides a diffusion barrier to prevent the diffusion of Li (or Li2 O) into the substrate during deposition and postdeposition high-temperature processing needed to obtain the c-oriented films [61]. An original two-step growth process of sputtering and pyrosol deposition of LiNbO3 thin films has been demonstrated. his deposition technique results in highly c-oriented LiNbO3 /Si (1 1 1) and LiNbO3 /Al2 O3 (0 0 1) heterostructures with reduced surface roughness and fine columnar microstructures. hus, this method appears as promising for the deposition of high-quality thin films for SAW applications [62]. Many more environmentally preferred good alternatives have been developed, such as many component systems, for example, textured (K0.44 Na0.52 Li0.04 ) (Nb0.84 Ta0.10 Sb0.06 )O3 . hey are, however, only in bulk ceramic form [57]. hese kind of precise compositions of several elements are very difficult to deposit reproducibly as thin films on MEMS structures.

13.7 Future Trends and Applications

Further performance increase of BAW devices can be reached with thorough understanding of the electroacoustic devices and materials with simulation and modeling [63]. However, modeling needs correct electroacoustical materials parameters of the thin films to provide reliable results. Laser interferometry is a noncontact optical method that enables direct measurement of wave fields in an acoustic component, for example, in a BAW resonator [64, 65]. Optical probing has proved to be a powerful characterization method for studying mechanical wave fields in microacoustic components, enabling us to gain valuable insight into resonator physics as well as providing information for component design and modeling [63, 66, 67], thus, facilitating to the best performance attainable with given piezoelectric thin film material. here are many applications utilizing piezoelectric thin films, especially PZT: Ferroelectric random access memory (FeRAM) is one of a growing number of alternative nonvolatile memories, as it offers lower power usage, faster write speed, and a much greater maximum number of write–erase cycles than other techniques [68]. Another technology is piezoelectric-based micromachined ultrasound transducer (pMUT), which is a membrane operated by a thin layer of piezoelectric material [69, 70]. Energy harvesters are studied all over the

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world and piezoelectric films on MEMS structures (piezoMEMS) are especially suitable for miniature independent sensor units [43, 71]. Ultrasmall microphone applications use piezoelectric thin films [72]. An imaginative application, which is not science fiction anymore, is microrobotics, where motion is enabled by piezoelectric MEMS devices. Parts for these devices are currently developed for making flying microrobots [56]. As the BAW devices have matured, there is now increasing interest in integration. One developed platform is FBAR Metal Oxide Silicon (FMOS) (BAW, metal oxide silicon), which is an integrated high-frequency piezoelectric MEMS resonator integrated with an oscillator. It has very good performance (e.g., low current consumption) and proven manufacturability in (1 mm × 0.9 mm2 ) miniature hermetic package [73]. Others are also on the way of integrating electronics with MEMS for sensing and actuating [74]. Piezoelectric material in the former case is AlN and in the latter PZT. Integration of low-voltage CMOS chips with the MEMS structure can enable unforeseen applications [70]. Finally, monolithical integration of CMOS and piezoelectric resonators has been achieved. his reduces power requirements in radios and would enable tunable filters and oscillators in the future [75]. his is equivalent to the “holy grail” in radio technology – a narrowband low-loss filter with a small size which has an electrically tunable center frequency. One such tunable filter would eliminate a significant amount of switches and filters [76, 77].

13.8 Conclusions

In this chapter, the thin film piezoelectric materials were reviewed from the point of view of RF-BAW (radiofrequency BAW) technology used in all mobile smart devices (e.g., phones, tablets). hough the crystal structures of the discussed piezoelectric materials differ, there is a clear consistency with all the piezoelectric films described above. It is the need for strong preferred orientation of the polycrystalline film to exploit the full performance capability of the piezoelectric materials. he quality of the piezoelectric thin film material depends of: (1) optimized growth conditions (for each material), (2) seed layer underneath the piezoelectric thin film (3) surface roughness of the seed layer. Conditions (2) and (3) influence the piezoelectric material nucleation, which determines (to large extent) the density of the film, the crystal orientation, and piezoelectric poling of the films. For all nitride piezoelectric materials (AlN, ScAlN, etc.) it is paramountly important to avoid any contamination of the vacuum by oxygen in gas (O2 or CO2 ) or water vapor (H2 O), because of the thermodynamical tendency of the film to form oxides (e.g., AlOx ), which would hinder the proper microstructure evolution. he thin film material quality approaches, or even surpasses known bulk properties [78]. CMP is an enabling technology to secure the very flat and smooth surface for the growth of piezoelectric thin films.

References

Deposition of the piezoelectric films is the key to manufacturing of BAW and other piezoelectric components. Nanotechnology control of the interfaces is needed through piezoelectronic material microstructure and properties to achieve micro electro mechanical BAW devices.

Acknowledgments

We thank Dr Tapani Makkonen for thorough proofreading of the manuscript.

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14 Properties and Applications of Ferroelectrets Xunlin Qiu, Dmitry Rychkov, and Werner Wirges

14.1 Introduction

he demand for advanced functional materials in transducer technology is growing rapidly. A functional material performs the desired functions through a mechanism of correlation or feedback. Specifically, electromechanical (piezoelectric/electrostrictive) materials transform mechanical variables (displacement or force) into electrical signals (charge or voltage) and vice versa. hey are suitable for a large range of existing or conceivable applications. Several, but not all, piezoelectric materials exhibit pyroelectricity, which transforms temperature variations into electrical currents, and is used mainly in sensors, whereas the reverse electrocaloric effect still awaits real application. Furthermore, piezoelectricity is often connected with ferroelectricity – the existence of a spontaneous and remanent polarization that can be reoriented in sufficiently high electric fields. Piezoelectricity arises from the non-centrosymmetry in certain materials. Up to now, commercially available materials with strong piezoelectricity have usually been inorganic single crystals or ceramics. Compared with their inorganic counterparts, piezoelectric polymers have advantages such as low density, high flexibility and softness, suitability for large-area thin-film applications, low cost, low dielectric constant, and rather small acoustic impedance that is quite well matched to air and other fluids. herefore, the discovery of piezoelectricity in poly(vinylidene fluoride) (PVDF) in 1969 sparked intensive research on piezoelectric polymers especially on PVDF and its copolymers [1]. However, the application of the materials of PVDF family is limited by their relatively weak piezoelectricity (for PVDF: d33 = 15 … 20 pC N−1 ; d31 = 25 … 30 pC N−1 ). Cellular polymers (polymer foams) were produced as early as during the 1960s. hey are now widely used in our daily life for thermal insulation, shock and sound absorption, packaging, and so on. During the last two decades, a number of nonpolar cellular and voided polymers were discovered to exhibit strong electromechanical (piezoelectric) responses [2–5]. heir piezoelectric d33 coefficient is comparable or even higher than that of piezoelectric ceramics. The Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Table 14.1 Typical material parameters of several ferroelectret and ferroelectric polymers. Polymer

Cellular PP Cellular PET

®

Porous Teflon AF Tubular-channel FEP Layered Teflon film stack β-PVDF P(VDF-TrFE) Polyamide 11

Thickness (�m)

f p (MHz)

d33 (pC/N)

c33 (MPa)

70 90

0.6 0.2

200 … 1000 500

1.3 0.3

55 200 200 40 98 68

0.1 0.03 0.04 25.5 12.1 16.2

550 150 300 25 27 3

0.2 0.35 0.3 9.0 × 103 9.1 × 103 3.9 × 103

hese materials are now more and more often called ferroelectrets because their polarization behavior and other related properties are phenomenologically similar to those of typical ferroelectrics, whereas the microscopic charge trapping and de-trapping are the same as in other space-charge electrets. Some of the typical material parameters of ferroelectret and ferroelectric polymers are given in Table 14.1. Since ferroelectrets combine high piezoelectricity with the inherent advantages of polymers, they have attracted considerable interest in research and industry. In this chapter, we focus on the description of electromechanically active ferroelectret polymers. We describe the preparation of such polymer foams or polymer-film systems, the charging process and the resulting piezoelectricity, their optimization, as well as some of the proposed applications.

14.2 Preparation of Polymer Foams or Void-Containing Polymer Systems 14.2.1 Polymer Foams

In order to produce polymer foams, various procedures were developed. he traditional way is to use chemical or physical nucleating agents in molten polymer [6, 7]. he pressure in extruder, where plastic material is melted, compressed, and mixed, is sufficiently high to keep the melt non-foamed. Immediately after the pressure drop in the head of the extruder or die, the foam bubbles appear and grow, introducing a cellular structure in the polymer. Another widely used method is stretching filler-loaded polymers under suitable conditions. Tiny mineral particles are often employed as fillers that serve as stress concentrators for micro-cracks during biaxial stretching of the film. Simultaneous or sequential stretching in two perpendicular directions results in films with lenslike cavities. With a suitable pressure and temperature treatment, so-called gasdiffusion expansion (GDE) process, the size of the cavities can be adjusted [8].

14.2

Preparation of Polymer Foams or Void-Containing Polymer Systems

he external gas pressure is usually raised and kept at a high value for a certain period of time, so that the gases diffuse into the cavities until the internal pressure of the cavities equalizes the external pressure. he polymer foam is inflated by a subsequent sudden release of the external gas pressure. he thickness expansion of the foam is stabilized by heat treatment at elevated temperatures during or right after the pressure treatment. More recently, cellular polyester films including poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) have been fabricated through physical foaming with supercritical carbon dioxide (scCO2 ) [9, 10]. Sample preparation consists of a sequence of steps as schematically shown in Figure 14.1. A nonvoided commercial film is first exposed to pressurized CO2 at room temperature. he CO2 gas turns into supercritical phase at certain high pressures. With storage time, scCO2 penetrates into the bulk of the polymer film and eventually saturates. he penetration of gas molecules depends on parameters such as the gas pressure and the gas temperature. hen the pressure is quickly released (Figure 14.1a). he film filled with scCO2 is thermally treated at elevated temperature. Consequently, the scCO2 inside the film undergoes a phase change into gas, and foams the film (Figure 14.1b). he foamed structure can be further optimized by means of wellcontrolled biaxial stretching and sometimes subsequent GDE. Figure 14.2 shows an SEM image of the cross-section of a PET sample that was foamed, stretched, and expanded. Cellular polymer foams typically show a lateral Young’s modulus of the order of gigapascal and a thickness Young’s modulus of the order of megapascal. he special mechanical characteristic is one of the most important origins for the large piezoelectricity of ferroelectrets.

CO2 Polymer film

Pressure

Pressure release

Glass plate

Heating plate

Supercritical CO2

Temperature (a)

(b)

Figure 14.1 Preparation of polymer foams using supercritical CO2 . (a) Penetration of scCO2 into the polymer matrix. (b) Foaming of the polymer resulted from the phase change of the scCO2 .

273

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Properties and Applications of Ferroelectrets

60 μm

Figure 14.2 SEM image of the cross-section of a cellular PET film. The sample is foamed with scCO2 and the foam structure is further optimized by biaxial stretching and gasdiffusion expansion.

14.2.2 Void-Containing Polymer Systems

In polymer foams, the cavities always have a rather wide and not so well controlled size and shape distribution so that only some of the cavities are optimal for charging and for transducer operation. For industrial applications, ferroelectrets with well-controlled distributions or even uniform values of cavity size and cavity shape are very desirable. Such ferroelectrets may be easily produced on a large scale with good reproducibility. Several strategies were proposed for preparing ferroelectrets of this kind. Fluoroethylenepropylene (FEP) film systems with uniform cavities were obtained by thermal fusion combined with vacuum evacuation. A stack of two FEP films was placed between two cylindrical metal plates, which can be independently heated. One plate (top) is completely solid, while the other one (bottom) has tiny holes that are connected to a vacuum pump. An additional metal grid was placed between the stack of FEP films and the bottom plate. Most of the air was removed through the holes of the bottom plate by means of the vacuum pump and the adjacent FEP film was sucked into the openings of the metal grid. By heating and pressing the upper plate onto the stack, air cavities with the same diameter as the grid openings were created [11]. he aforementioned method was modified and further improved by Zhang et al. [12]. In their study, a metal mesh with (sub)millimeter spacing was pressed on stacks of alternating FEP and polytetrafluoroethylene (PTFE) films. With proper thermal treatment, the polymer layers were fused underneath the wires of the metal mesh, and cavities were formed between the fused areas because of the thermal expansion of trapped air and the thermal softening of the fluoropolymer films.

14.2

Preparation of Polymer Foams or Void-Containing Polymer Systems

More recently, ferroelectrets with well-controlled and uniform cavities have been developed by a straightforward lamination process [13]. In this process, two polymer electret films are laminated around a template between them. he template, which can be made of metal foils or of polymers with a melting temperature higher than that of the electret films, contains regular openings through which the electret films can be fused with each other. Lamination is performed at a temperature substantially higher than the melting temperature of the electret films yet lower than that of the template. After the outer layers have been fused, the template is removed, resulting in a polymer-film system with open tubular channels. Figure 14.3a [13] schematically shows the preparation for tubular-channel FEP ferroelectrets. he template is made of a 100 μm thick PTFE by means of laser cutting. It consists of several well-cut stripes with clearly defined and evenly distributed openings between them. he PTFE template is sandwiched between two solid FEP films with a thickness of 50 μm each, and then the sandwich is laminated at 300 ∘ C. After lamination, the stack is naturally cooled down under laboratory conditions. he two FEP layers are permanently fused with each other through the openings of the template. A cellular FEP structure with tubular voids is obtained after removal of the PTFE template. Figure 14.3b [13] shows an optical image of the cross-section of such an FEP film system.

1 Cut off FEP PTFE FEP

(a)

(b)

Heater Heater

2 Pull out

1.0 mm

Figure 14.3 (a) Schematic view of the preparation process for tubular-channel ferroelectrets. (b) Optical micrograph of the cross section of an FEP ferroelectret sample.

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14.3 Charging Process 14.3.1 Dielectric Barrier Discharges in Cavities

In order to render polymer foams piezoelectric, the cavities inside the material must be internally charged [14]. Charging can be achieved by means of direct contact charging, corona discharge without a grid at high corona-point voltages or electron beam charging. he charging process in ferroelectrets requires dielectric barrier discharges (DBDs). In DBDs, at least one side of the discharge gap is insulated from the electrodes by a dielectric layer [15]. Gas inside the cavities is ionized when the electric field reaches the threshold value for breakdown [16, 17]. DBDs in ferroelectrets are always accompanied by light emission that can be easily photographed. Based on the investigation of the light emission, a schematic model for the charging process has been proposed, as shown in Figure 14.4 [18]. Internal breakdown (Paschen breakdown) in the cavities is initiated when the voltage reaches the required threshold value (in this sense, the electric field in the cavities is comparable with the “coercive field” in ferroelectrics). Charges of opposite polarity are separated during the DBDs and are subsequently trapped on the top and bottom surfaces of the cavities (point A in Figure 14.4). he trapped charges induce an electric field opposite to the externally applied field and thus eventually extinguish the discharge. As the applied voltage increases further, a second series of breakdown events may occur, and the density of the internally trapped charges strongly increases (point B in Figure 14.4). When the applied voltage is reduced, the electric field of the trapped charges may overcompensate the applied field and may thus be able to trigger back discharges (point C in Figure 14.4). B

Vmax Charging voltage

276

A Vthr

C

0 0

t1

Figure 14.4 Schematic view of the DBD charging process in a single polymer cavity. When the charging voltage reaches the threshold value V thr , Paschen breakdown is ignited (A). At higher voltages, a second

Time

t2

t3

discharge may occur (B). During ramping down the voltage, the reverse electric field from the trapped space charges may lead to back discharges (C).

14.3

Charging Process

Paschen’s law governs the onset of the DBDs in the cavities. According to Townsend’s model, the critical breakdown field of common gases in a uniform electric field is a function of both the gas pressure p and the electrode spacing d (which in a ferroelectret context is equal to the cavity height). herefore, the dimensions of the cavities, the composition of the gas inside the cavities, and its pressure all strongly influence the charging process [19–22]. 14.3.2 Polarization versus Electric-Field Hysteresis

he existence of a polarization versus electric-field (P(E)) hysteresis is an essential feature of ferroelectric materials. It is often investigated in order to assess some of their properties such as the spontaneous polarization, the coercive field, and the polarization reversal under various conditions. As nonpolar polymers, ferroelectrets contain no intrinsic molecular dipoles. However, the internally charged cavities can be considered as man-made macroscopic dipoles, whose direction can be reversed by switching the polarity of the applied electric field. he density of the macroscopic dipoles determines the effective polarization in ferroelectrets. Using a modified Sawyer–Tower circuit, we obtained the P(E) hysteresis loops for several ferroelectrets [23]. Figure 14.5 shows a typical hysteresis curve for cellular polypropylene (PP) foam. he sample structure is optimized via GDE prior to the measurement. From the figure, the coercive field EC (the field at which the polarization goes through zero) and the remanent polarization Pr (the polarization that remains at zero field) are determined. Another feature of the P(E) hysteresis curve in Figure 14.5 is that P reduces significantly when the absolute value of the applied electric field is reduced from its maximum to zero. Pr is only about half of P at the maximum electric field. he

Effective polarization (mC m–2)

0.8 0.6 Pr

0.4 0.2 0.0

–Ec Ec

–0.2 –0.4

–Pr

–0.6 –0.8 –100 –80 –60 –40 –20

0

20

Electric field (mV

40

m–1

60

80 100

)

Figure 14.5 Polarization as a function of the electric field for a cellular PP ferroelectret sample.

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Properties and Applications of Ferroelectrets

large reduction of P during reduction of the absolute value of the external electric field is caused by back discharges triggered by the internal electric field of the space charges on the air–polymer interfaces inside the cavities [18].

14.4 Piezoelectricity of Ferroelectrets and its Stability

he macroscopic dipoles (internally charged cavities) deform when ferroelectret films are subjected to mechanical stress. he resultant change of the density of macroscopic dipole moments introduces a voltage (open circuit) or current (short circuit) between the two electrodes (Figure 14.6). his is known as direct piezoelectric effect. As for inverse piezoelectric effect, the macroscopic dipoles change their dimension upon the application of an additional voltage to the two electrodes. Due to the anisotropic structure of ferroelectrets, the cavities are highly compressible in the thickness direction. hus, ferroelectrets show very large piezoelectric d33 coefficient. Values of hundreds of pC/N are often achieved, more than 1 order of magnitude greater than those found in conventional ferroelectric polymers. he transverse piezoelectric coefficient (d31 or d32 ) is typically around 2 pC N−1 , 2 orders of magnitude lower than the d33 coefficient. In addition, the pyroelectric coefficient of ferroelectrets (∼0.25 μC m−2 K−1 ) is much smaller than that of polar polymers such as PVDF (∼27 μC m−2 K−1 ). he stability of the piezoelectricity in ferroelectrets is a critical issue for most applications. Obviously, temporal and thermal stability of piezoelectricity in ferroelectrets is very much dependent on the charge trapping properties of the polymeric material, that is, on how effectively charges deposited on the inner surfaces of the voids can be retained in the wide range of times and temperatures. For example, cellular polypropylene is one of the most common materials in ferroelectret field [8, 19, 24–27]. he piezoelectric coefficients in this material are much larger than those of conventional piezoelectric polymers such as PVDF and its

Figure 14.6 Schematic representation of the primary piezoelectricity of ferroelectrets.

14.4

Piezoelectricity of Ferroelectrets and its Stability

279

copolymers. However, ferroelectrets made of cellular PP films exhibit rather low thermal stability of piezoelectricity. At about 50 ∘ C, d33 coefficients in cellular PP films begin to decay rapidly, and at 100 ∘ C, these coefficients are lower than those observed in conventional ferroelectric polymers [25–27]. For this reason, the use of cellular PP is restricted in many applications that require thermal stabilities in excess of 60 ∘ C (e.g., in the automotive industry). One possible solution would be to use fluorocarbon polymers – namely PTFE and its copolymers that have markedly better thermal and temporal stability of charge. Indeed, a number of ferroelectret devices based on porous PTFE, or on solid FEP and PTFE in layered systems, have shown very good thermal stability of piezoelectric coefficients [12, 13, 28, 29]. For example, the graph adapted from [30] (Figure 14.7a) shows that a tubular channel ferroelectrets made of FEP films at temperatures above 120 ∘ C still retain more than half of their initial piezoelectricity. Figure 14.7b [31] shows the decay of d33 coefficients in laminated FEP ferroelectrets at 120 ∘ C as a function of time. Obviously, even at elevated temperatures, these ferroelectrets exhibit high and stable values of piezoelectric coefficients. he second approach to creating thermally stable ferroelectrets deals with the improvement of charge-trapping properties of existing polymers. Since the charge stability in most nonpolar polymers used in ferroelectrets largely depends on the surface properties of these materials [32], a surface modification can be an effective tool for charge stabilization. Early research [33] and later work [34–40] have shown that the thermal stability and charge transport properties in nonpolar polymers can be controlled by various chemical treatments. For example, Figure 14.8a [35] indicates more than 100 ∘ C improvement in charge stability of positively charged PTFE films treated with titanium-tetrachloride vapor, whereas very similar results (Figure 14.8b [40]) were obtained on FEP films charged both positively and negatively. hese charge-stability-control techniques can be applied directly to improve thermal and temporal stability of piezoelectricity in polymer ferroelectrets. Indeed, whether it is gas-phase fluorination of cellular PP samples (Figure 14.9a

(a)

10 000

0.9

–1

0.8

coefficient (pC N )

1.0 Quasistatic piezoelectic d33

Normalized piezoelectric coefficient d33

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0.7 0.6 0.5 0.4 0.3 0.2

1000

100

Sample Thickness 75 μm No.1 82 μm No.2 191 μm No.3

0.1 0.0

10 0

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40

60 80 100 120 140 Annealing temperature (°C)

160

180

(b)

0

500

1000

1500

2000

Time (min)

Figure 14.7 Temperature (a) and time (b) decay of d33 coefficients in laminated ferroelectret systems.

2500

3000

3500

14

Properties and Applications of Ferroelectrets 50 122 °C 40 30 1 20

dV/dT (V °C−1)

1600

Surface potential (v)

1400 1200 1000 800

2

100 200 300 Temperature (°C)

2

1

600

10 0 0

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1 2 3

0.8

+500 V –500 V +500 V, TiCl4

4

–500 V, TiCl4

0.6

1

3

2

4

0.4 0.2 0.0

0 50

(a)

1.0 227 °C

Normalized surface potential

280

100

150 200 250 Temperature (°C)

300

350

0

(b)

40

80

120 160 200 Temperature (°C)

240

280

Figure 14.8 Surface potential decay in PTFE (a) and FEP (b) electrets treated with titaniumtetrachloride vapor. 120

80

60

40

20

0 1.2

(c)

(b)

(d)

–1

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500 d33 - coefficent (pC N–1)

100

Piezoelectric coefficient d33 (pC N )

600

40

100%

95%

35 30

87%

100%

25

2

70%

66%

20 15

1

29%

37%

10 13%

5

3%

0 20

40

60 80 Temperature (°C)

100

Figure 14.9 (a) d33 decay in fluorinated LDPE ferroelectrets (black squares – virgin (solid circles) and virgin (open circles) cellusamples; red triangles – modification with lar PP ferroelectrets at 70 ∘ C. (b) Temperature orthophosphoric acid). dependence of d33 coefficients in laminated

[41]) or direct treatment of LDPE tubular channels with orthophosphoric acid (Figure 14.9b [42]), the resultant ferroelectrets exhibit very much improved stability of piezoelectricity.

14.5 Applications

Ferroelectrets combine a large piezoelectricity with elastic compliance and mechanical flexibility. Consequently, they attract considerable attention in fundamental research and have a good potential for use in numerous applications. Owing to their low acoustic impedance and good matching to air, other fluids and the body, ferroelectrets are particularly suitable for ultrasound sensors used

14.5

Applications

in communication, in materials testing and in medical applications [43–49]. For medical applications, the rather small pyroelectricity of ferroelectrets is another advantage as compared with ferroelectric polymers. he devices are generally insensitive to temperature oscillations of human or animal bodies under test. he suitability of ferroelectrets for microphones and loudspeakers was investigated [25, 50, 51]. Ferroelectret microphones are attractive for a wide range of applications as described below. For loudspeakers made of polymer foams, two working modes were developed: (i) Small sound-pressure levels can be generated using the intrinsic piezoelectricity of ferroelectrets [52]. (ii) he membrane-mode operation relies on the electret effect of the charges trapped on the film outer surfaces. Two one-side metalized cellular polymer films with opposite charges were put together via the respective metalized surface. he stack was then stretched and glued between a specially prepared electrode structure with regular cavities [25]. High sound pressure >100 dB can be obtained, resulting from the large elongation of the transducer films under the driving field between the metalized electrode and the grounded external electrodes. Various additional applications are also proposed. Examples include micromovement actuators [53], control panels, and keyboards [4]. Also reported are sensors for the monitoring of pressure distributions in shoe soles as well as quantitative dynamic force measurements on moving animals or the body. Based on soft and flexible polymer films, the fabrication of flexible sensors is possible if the electronics are separated from the sensor film and connected via cables. he sensors can be easily made into almost any shape, and can be conformably attached to uneven surfaces. Sensors can also be manufactured in large area. Large ferroelectret sensors that can be mounted below beds are employed in hospitals. Such bed sensors can monitor the movement, the respiration, the heartbeat, as well as the blood pressure of patients. Surveillance of rooms and of the surroundings of machines can be easily achieved using large area floor sensor systems [54]. In the following sections, we briefly demonstrate investigations and prototypes of some of the applications. 14.5.1 Concept for Focusing Ultrasound

A simple device for focusing air-borne ultrasound can be fabricated by using a Fresnel zone plate (FZP) or Fresnel phase plate (FPP) electrode pattern [55]. Figure 14.10 schematically shows an FZP electrode pattern on top of a piezoelectric film which could be done by standard photolithography. he other side of the film is coated with continuous electrode. Since acoustic signals are generated over the patterned electrodes only, the transmitted radiations interfere at some points determined by the zone radii. he intensity and resolution of FZP transducer can be improved by using FPP pattern. In an FPP, alternate zones are poled in opposite directions and both sides of the film are finally deposited with continuous electrodes.

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Properties and Applications of Ferroelectrets

Z

Focus

X

Electrode Figure 14.10 Schematic view of a Fresnel zone plate for focusing ultrasound.

Ferroelectret films are very suitable for such applications due to their low acoustic impedance that matches quite well with those of water and air. his concept was demonstrated with a cellular PP ferroelectret film with a thickness of around 70 μm [56]. A five-element FZP with a maximum diameter of 120 mm was tested as a sound source. he device shows a clear sound focusing behavior both along the main axis Z and along a line within the focal plane X, which is in excellent agreement with the calculation based on the Fresnel theory. An accessible frequency of up to 1 MHz is sufficient for most applications in air-borne ultrasound. 14.5.2 Ferroelectret Microphone

Ferroelectret film-based piezoelectric microphones (so-called piezoelectret microphones) are proposed owing to the high piezoelectricity of the film. Such microphones are simple devices compared with classical electret condenser microphones. he devices consist simply of a piece of two-side metalized ferroelectret film with connectors and housing. No miniature air gaps, as in electret microphones, are needed. herefore, piezoelectret microphones can be manufactured at very low cost. Cellular PP ferroelectrets optimized with GDE were used to construct such piezoelectret microphones [57, 58]. Microphones of a single cellular PP film show sensitivities of around 2.3 mV Pa−1 at 1 kHz. he sensitivities may be further improved by increasing the piezoelectricity of the film by increasing the charge density and by decreasing the Young’s modulus of the films. Multilayer structures, prepared by folding a single film or stacking different films, are employed in order to significantly enhance the sensitivity of ferroelectret devices. In early studies, micromovement actuators were manufactured with multilayer ferroelectret stacks in order to superimpose the thickness variation of each single film under electrical stress [25]. Improvements of the sensitivity of piezoelectret microphones were also achieved by this simple technique. A five-layer

14.5

Applications

Sensitivity (mV Pa–1)

20

10

5

2

1 10

Single-film microphone Five-film microphone 100

1000

10 000

Frequency (Hz) Figure 14.11 Frequency response of cellular-PP piezoelectret microphones with a single film and with a stack of five films.

stacked cellular PP piezoelectret microphone has a sensitivity of approximately 10.5 mV Pa−1 , well comparable to the respective values of traditional electret condenser microphones. Figure 14.11 [57] shows the measured frequency dependence of microphones with one and five films of cellular PP ferroelectrets. A flat frequency response over the whole audio range is demonstrated. Besides their simple design, piezoelectret microphones have advantages such as low harmonic distortion, low cost, lightweight, as well as ease of fabrication into different shapes and sizes. hese features make such microphones very suitable for a wide range of applications. 14.5.3 Control Panels and Keyboards

Very thin control panels, keyboard pushbuttons, and tactile sensors can be prepared with ferroelectret polymer films [59, 60]. he principle is simple. Changing the mechanical pressure on a ferroelectret film (with a load of certain weight, for instance) leads to a pulse-like sensor signal which can be easily detected with standard electronics. Ferroelectret films can be placed behind thin metal plates in order to achieve vandal-proof control panels. Due to the very small piezoelectric d31 and d32 coefficients, ferroelectret films are highly suitable for rollable and bendable keyboards and tactile sensors. he polarization in ferroelectret films has two states, that is, up (+1) and down (−1). he two polarization states together with the inactive state (i.e., unpoled (0)) can be patterned into a ferroelectret film using suitable poling methods. Different regions in the pattern can be identified with different sensor signals. By combining several layers to a multilayer stack, the number of identifiable regions is increased. Figure 14.12a [60] schematically shows a stack of three layers of ferroelectret films

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Properties and Applications of Ferroelectrets

L1 L2 L3

Electrical connections

T

0

(a)

Ferroelectret polarization metallization lamination layer

(b)

Figure 14.12 (a) Schematic view of a three-layer ferroelectret keyboard. (b) Three-layer ferroelectret keyboard prototype with electronic reading device.

with patterned polarization states. In order to detect the inactive combination (0, 0, 0), a fourth layer with uniform polarization is employed as a trigger layer. Without a trigger layer, the number of different keys k = 3l − 1, where l is the number of layers. Figure 14.12b [60] shows a three-layer ferroelectret keyboard prototype with reading electronics. he challenge in this concept is to achieve effective polarization with good edge resolutions between alternating regions in the pattern.

14.6 Conclusions

Internally charged polymer foams and void-containing polymer systems are a new class of electromechanically active materials. hese soft polymer materials contain gas-filled cavities that can be internally charged under high electric fields. Space charges of opposite polarity are separated and deposited at the top and bottom inner surfaces of the cavities. he charged cavities can be considered as man-made macroscopic dipoles, which – in combination with the nonuniform mechanical properties of the heterogeneous structure – induce the desired electromechanical properties. Several procedures for preparing thin polymer foams or void-containing polymer systems and for their electrical charging were introduced. he poled materials are called ferroelectrets because their macroscopic polarization and other related properties are phenomenologically similar to the behavior observed in typical ferroelectrics, while the internal charge trapping is the same as in other space-charge electrets. Due to their high electromechanical activity combined with high mechanical flexibility and good elastic compliance, ferroelectrets are considered or employed for a large range of applications shown in Table 14.2.

References

Table 14.2 Proposed applications of ferroelectrets. Field of application

Proposed devices and their application areas

Ultrasonic

Fresnel zone plate for focusing air-borne ultrasound Ultrasonic transducer for noncontact tests, medical diagnostics, communications, bionic research and technology, etc. Piezoelectric microphone for communication technology Pick-up for music instrument Piezoelectric loudspeaker for home-audio system, active noise control, etc. Pressure transducer for diagnostics and (bio-)sensorics, flexible keyboards and control panels, etc. Flat floor sensor for medical and child care, surveillance, etc. Motion detector and actuator for (bio-)sensorics, robotics, control systems, etc.

Electroacoustic

Electromechanical

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electrothermomechanical film (ETMF). J. Audio Eng. Soc., 38, 364–371. Kressmann, R. (2001) New piezoelectric polymer for air-borne and water-borne sound transducers. J. Acoust. Soc. Am., 109 (4), 1412–1416. Nykänen, H., Antila, M., Kataja, J., Lekkala, J., and Uosukainen, S. (1999) Active control of sound based on utilizing EMFi-technology. Proceeding of the Active 99, Fort Lauderdale, FL. Hämäläinen, M.K., Parviainen, J.K., and Jaaskelainen, T. (1996) A novel micromovement actuator manufactured using plastic electromechanical film. Rev. Sci. Instrum., 67, 1598–1601. Oliviero, C., Pastell, M., Heinonen, M., Heikkonen, J., Valros, A., Ahokas, J., Vainio, O., and Peltoniemi, O.A.T. (2008) Using movement sensors to detect the onset of farrowing. Biosyst. Eng., 100, 281–285. Mortezaie, M. and Wade, G. (1984) in Acoustic Imaging (eds M. Kaveh, R.K. Mueller, and J.F. Greenleaf), Plenum Press, New York, pp. 345–354.

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Schwödiauer, R., Bauer-Gogonea, S., and Bauer, S. (2004) Charged cellular polymers with ferroelectretic behavior. IEEE Trans. Dielectr. Electr. Insul., 11 (2), 255–263. Hillenbrand, J. and Sessler, G.M. (2004) High-sensitivity piezoelectric microphones based on stacked cellular polymer films. J. Acoust. Soc. Am., 116, 3267–3270. Hillenbrand, J. and Sessler, G.M. (2006) Stacked piezoelectret microphones of simple design and high sensitivity. IEEE Trans. Dielectr. Electr. Insul., 13 (5), 973–978. Buchberger, G., Schwödiauer, R., and Bauer, S. (2008) Flexible large area ferroelectret sensors for location sensitive touchpads. Appl. Phys. Lett., 92, 123511. Kogler, A., Buchberger, G., Bauer, S., and Schwödiauer, R. (2010) Heteropolar ferroelectrets for ultrathin flexible keyboards and tactile sensors. Proc. Eng., 5, 717–720.

Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jorg ¨ Fecht The Nano-Micro Interface Volume 2

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Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jorg ¨ Fecht

The Nano-Micro Interface Bridging the Micro and Nano Worlds

Volume 2

Second Edition

Editors Prof. Marcel Van de Voorde

TU Delft Fac. Techn. Natuurwetenschappen Eeuwige Laan, 33 1861 CL Bergen he Netherlands

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Dr. Matthias Werner

NMTC Soorstr. 86 14050 Berlin Germany Prof. Hans-Jorg ¨ Fecht

University of Ulm Inst. Micro & Nanomaterials Albert-Einstein-Allee 47 89081 Ulm Germany

Library of Congress Card No.: applied for British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library. Bibliographic information published by the Deutsche Nationalbibliothek

he Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at . © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Print ISBN: 978-3-527-33633-3 ePDF ISBN: 978-3-527-67922-5 ePub ISBN: 978-3-527-67921-8 Mobi ISBN: 978-3-527-67920-1 oBook ISBN: 978-3-527-67919-5 Cover Design Adam Design, Weinheim,

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Printed on acid-free paper

V

Contents

Volume 1 List of Contributors XV Foreword XXIII Acknowledgment XXV Introduction XXVII Part I Nanotechnology Research Funding and Commercialization Prospects – Political, Social and Economic Context for the Science and Application of Nanotechnology 1 1

A European Strategy for Micro- and Nanoelectronic Components and Systems 3 Neelie Kroes

2

Governmental Strategy for the Support of Nanotechnology in Germany 19 Gerd Bachmann and Leif Brand

3

Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region 37 Lerwen Liu

4

Near-Industrialization Nanotechnologies Developed in JST’s Nanomanufacturing Research Area in Japan 55 Yasuhiro Horiike

5

Quo Vadis Nanotechnology? 79 ́ Witold Łojkowski, Hans-Jörg Fecht, and Anna Swiderska Sroda

VI

Contents

Part II Development of Micro and Nanotechnologies

95

6

Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces 97 Jared J. Victor, Uwe Erb, and Gino Palumbo

7

Multisensor Metrology Bridging the Gap to the Nanometer – New Measurement Requirements and Solutions in Wafer-Based Production 115 Thomas Fries

8

Nanostructural Metallic Materials – Nanoengineering and Nanomanufacturing 135 Michael E. Fitzpatrick, Francisca G. Caballero, and Marcel H. Van de Voorde

9

Bulk Metallic Glass in Micro to Nano Length Scale Applications 159 Jan Schroers and Golden Kumar

10

From Oxide Particles to Nanoceramics: Processes and Applications 189 Jean-François Hochepied Part III Nanoelectronics and System Integration

205

11

Creating Tomorrow’s Applications through Deeper Collaboration Between Technology and Design 207 Jan Provoost, Diederik Verkest, and Gilbert Declerck

12

Multiwalled Carbon Nanotube Network-Based Sensors and Electronic Devices 225 Wolfgang R. Fahrner, Giovanni Landi, Raffaele Di Giacomo, and Heinz C. Neitzert

13

Thin Film Piezomaterials for Bulk Acoustic Wave Technology 243 Jyrki Molarius, Tommi Riekkinen, Martin Kulawski, and Markku Ylilammi

14

Properties and Applications of Ferroelectrets 271 Xunlin Qiu, Dmitry Rychkov, and Werner Wirges Volume 2 List of Contributors XVII Foreword XXV Acknowledgment XXVII Introduction XXIX

Contents

Part IV

Biomedical Technologies and Nanomedicine 289

15

Translational Medicine: Nanoscience and Nanotechnology to Improve Patient Care 291 Bert Müller, Andreas Zumbuehl, Martin A. Walter, Thomas Pfohl, Philippe C. Cattin, Jörg Huwyler, and Simone E. Hieber

15.1 15.2 15.3 15.4 15.5 15.6 15.7

Introduction 291 Nanoanatomy 294 Nanorepair 297 Nanoorthopedics 297 Nanovesicles 299 Nanodentistry 301 Interactions of Disciplines in Nanomedicine Acknowledgements 303 References 303

16

Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine 311 Costas Kiparissides and Olga Kammona

16.1 16.2 16.2.1 16.2.2 16.3 16.3.1 16.3.2 16.3.3 16.3.4 16.4 16.4.1 16.4.2 16.5 16.6

Introduction 311 Diagnostics 311 In vitro Diagnostics 312 In vivo Diagnostics 314 Drug Delivery 316 Nanocarrier-Based DDSs 316 Novel Design Considerations 323 heranostics 324 Administration Routes 325 Regenerative Medicine 328 Tissue Engineering 329 Cell herapies 331 Personalized Medicine 333 Conclusions – Future Challenges 334 References 335

17

Biofunctional Surfaces 341 Wolfgang Knoll, Amal Kasry, and Jakub Dostalek

17.1 17.2

Introduction 341 Supramolecularly Controlled Oligonucleotide Architectures for PCR (DNA Amplicon) Biosensing 344 Polymer Brushes for the Ultrasensitive Detection of Antibodies 349 Monitoring Bacteria Binding to Functional Surfaces 352 he t-BLM: A Novel Model Membrane Platform 355 Conclusions 359

17.3 17.4 17.5 17.6

302

VII

VIII

Contents

Acknowledgments References 360

360

18

Biomimetic Hierarchies in Diamond-Based Architectures Andrei P. Sommer, Matthias Wiora, and Hans-Jörg Fecht

18.1 18.2

Introduction 363 Biocompatibility Derived from Biomimetic Principles and Nanoscopic Interfacial Water 364 Design and Fabrication of Biomimetic Diamond Layers Precursor of the 3D Diamond Petri Dish 370 Biocompatibility of Biomimetic Surfaces 373 Surface Mechanical Properties at Nanoscale 375 Bottom Up–Top Down 376 Conclusions 377 References 378

18.3 18.4 18.5 18.5.1 18.5.2 18.6

363

367

Part V Energy and Mobility 381 19

Nanotechnology in Energy Technology 383 Baldev Raj, U. Kamachi Mudali, John Philip, and Sitaram Dash

19.1 19.2 19.3 19.4 19.4.1 19.4.2 19.4.3 19.4.4

Introduction 383 Nanofluids for Efficient Cooling of Miniature Devices 386 Nanofluid-Based Optical Sensors 388 Intelligent Coatings for Corrosion Mitigation 389 Synthesis of Nanocontainers 389 Preparation of Hybrid Coatings 390 Protective Properties of Coatings 391 Superhydrophobic Engineering Surfaces for Corrosion Mitigation 392 Superhydrophobic Surface Modification 393 Superhydrophobic Surfaces with Enhanced Corrosion Resistance 394 Nano-structured Coatings for Energy Technologies 395 Studies on Titanium Aluminum Nitride (TiAlN) 395 Oxidation-Resistant Hard Coatings 397 Super-Low Friction Ultrananocrystalline Diamond Films 398 Conclusions 399 Acknowledgements 400 References 400

19.4.5 19.4.6 19.5 19.5.1 19.5.2 19.6 19.7

20

The Impact of Nanoscience in Heterogeneous Catalysis 405 Sharifah Bee Abd Hamid and Robert Schlögl

20.1 20.2 20.3

Introduction 405 Nanocatalysis 408 Nano in Catalysis 409

Contents

20.4 20.5 20.6 20.7 20.8 20.9 20.10

Electronic Structure and Catalysis 411 Geometric Structure and Catalysis 411 Large Nano-objects in Catalysis 415 Nanostructured Carbons 415 he “Semiconductor” Approach 419 he Combicat Approach 420 Conclusions 423 References 424

21

Processing of Nanoporous and Dense Thin Film Ceramic Membranes 431 Tim Van Gestel and Hans Peter Buchkremer

21.1 21.1.1 21.1.2 21.1.3 21.2 21.2.1 21.2.2 21.2.3 21.3

Introduction 431 General 431 Ceramic Gas Separation Membranes 433 hin Film Solid Oxide Fuel Cells 434 Synthesis and Coating Methods 435 Porous Support Materials 435 Formation of hin Films and Membranes 436 Synthesis of Coating Liquids 436 Examples of Mesoporous, Microporous, and Dense hin Film Membranes 440 Mesoporous Membranes 440 γ-Al2 O3 Membranes 440 ZrO2 Membranes 441 Microporous Membranes 444 SiO2 Microporous Membrane for H2 Purification 444 Doped SiO2 Membranes for H2 Purification 445 Microporous Hybrid Membranes for CO2 Purification 446 Dense hin Film 8YSZ Membranes 449 Summary and Additional Comments 452 References 453

21.3.1 21.3.1.1 21.3.1.2 21.3.2 21.3.2.1 21.3.2.2 21.3.2.3 21.3.3 21.4

22

Nanotechnology and Nanoelectronics for Automotive Applications 459 Matthias Werner, Vili Igel, and Wolfgang Wondrak

22.1 22.2 22.3 22.3.1 22.3.2 22.3.2.1 22.3.2.2 22.3.2.3 22.3.2.4

Introduction 459 Effects and heir Application Potential 459 State of the Art and Future Development of Nanoelectronics Down-Scaling and Its Limits 460 Nanoelectronic Approaches 462 Crossbar Structures with Carbon Nanotubes 463 Spintronics 463 Magnetoresistive Memories 463 Single-Electron Tunneling (SET) 463

460

IX

X

Contents

22.3.2.5 22.3.2.6 22.3.3 22.4 22.4.1 22.4.2 22.4.2.1 22.5 22.5.1 22.5.2 22.5.3 22.5.4 22.6 22.7 22.7.1 22.7.2 22.7.3 22.7.4 22.8 22.8.1 22.8.2 22.8.3 22.9

RTDs (Resonant Tunneling Diodes) 463 Wide Bandgap Devices 464 Comparison of Nanoelectronic Applications 464 Nanotechnology for Passive Components 464 Li Ion Batteries 465 Supercapacitors as Energy Storage in Hybrid and Electric Cars DC Link Capacitors 465 Assembly Processes in Automotive Electronics 465 CNT Bumps 466 CNT Lawn 466 Solder Pastes with Nanoparticles 466 Silver Sintering 466 Reliability 467 Nanotechnology for Sensors, Actuators, and Optics 467 Magneto-Rheological Fluids for Damping Systems 468 Electro-Chrome Coatings for Rear-View Mirrors 468 Transparent Electrodes 468 Magnetic Sensors 468 Other Applications 469 Filled Nanoglues 469 Nanostructured Catalysts 469 hermal Management 469 Outlook 470 References 470

465

Part VI Process Controls and Analytical Techniques 473 23

Characterization of Nanostructured Materials 475 Alison Crossley and Colin Johnston

23.1 23.2 23.2.1 23.3 23.3.1 23.3.2 23.4 23.4.1

Introduction 475 Materials on the 1D Nanoscale 477 Atom Probe 478 Materials on the 2D Nanoscale 480 Raman Spectroscopy 481 Raman Spectroscopy of CNTs 481 Materials on the 3D Nanoscale 483 Photon-Correlation Spectroscopy (PCS) or Dynamic Light Scattering (DLS) 487 Separation Methods 488 he Basics of Differential Sedimentation 489 Other Important Parameters for Nanoparticle Characterization 490 Zeta Potential 490 Surface Area Determination 491

23.4.2 23.4.2.1 23.4.3 23.4.3.1 23.4.3.2

Contents

23.5

Conclusions 495 References 495

24

Surface Chemical Analysis of Nanoparticles for Industrial Applications 499 Marie-Isabelle Baraton

24.1 24.2 24.2.1 24.2.2 24.2.3

Introduction 499 Surface Chemistry of Nanoparticles 500 Importance of the Surface in Nanoparticle Properties 500 Characterization of Nanoparticles: Needs and Challenges 501 Relevance of the Surface Characterization for Industrial Applications of Nanoparticles 503 Biomedical Applications 505 Electrical Properties 505 Energy Applications 506 Environmental Applications: Catalysis, Photocatalysis, Gas Sensors 506 Other Properties and Applications 507 Analytical Instruments for Surface Characterization 507 Challenges in Surface Analysis of Nanoparticles 507 Techniques for Surface Analysis 508 Photoelectron Spectroscopy: X-Ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS) 509 Auger Electron Spectroscopy (AES) 509 Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) 510 Scanning Probe Microscopy: Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) 510 Low-Energy Ion Scattering (LEIS) 511 Other Techniques for Surface Analysis 511 Fourier Transform Infrared (FTIR) Spectroscopy 512 Background 512 Surface Characterization of Nanoparticles by FTIR Spectroscopy: Some Examples 514 Comparison of Silicon Nitride (Si3 N4 ) and Silicon Carbide (SiC) Surfaces 514 Comparison of Alumina (Al2 O3 ) and Aluminum Nitride (AlN) Surfaces 515 Comparison of Differently Synthesized Boron Nitride (BN) 515 Comparison of Differently Synthesized Titanium Dioxide (TiO2 ) 516 Surface Functionalization of Nanoparticles 518 Surface Study of Semiconductor Nanoparticles 519 Drude-Zener heory 519 Application to the Functionalization of Semiconductor Nanoparticles 520

24.2.3.1 24.2.3.2 24.2.3.3 24.2.3.4 24.2.3.5 24.3 24.3.1 24.3.2 24.3.2.1 24.3.2.2 24.3.2.3 24.3.2.4 24.3.2.5 24.3.2.6 24.4 24.4.1 24.4.2 24.4.2.1 24.4.2.2 24.4.2.3 24.4.2.4 24.4.3 24.4.4 24.4.4.1 24.4.4.2

XI

XII

Contents

24.4.4.3 24.5 24.6 24.6.1 24.6.2

Applications to Chemical Gas Sensors Based on Semiconductor Nanoparticles 521 Conclusions 523 Annex: Nanomaterials, Nanotechnology, and “Nanotools” 524 Nanomaterial and Nanoparticle: Definition 524 Markets for Nanotechnology, Nanoparticles, and “Nanotools” 525 Acknowledgments 527 References 527

25

Nanometer-Scale View of the Electrified Interface: A Scanning Probe Microscopy Study 537 ̈ Peter Muller, Laura Rossi, Santos F. Alvarado

25.1 25.2 25.3 25.3.1 25.3.2 25.4

Introduction 537 STM z–V Spectroscopy 538 Experimental Details 543 Alq3 hin Films on Au(1 1 1) 543 CuPc hin Films on Au(1 1 1) 544 Concluding Remarks 546 Acknowledgments 547 References 547 Part VII Creative Strategies Connecting Nanomaterials to the Macroscale World 551

26

Nanostructured Cement and Concrete 553 Henning Zoz, Reinhard Trettin, Birgit Funk, and Deniz Yigit

26.1 26.2 26.3 26.4 26.5 26.6 26.7 26.8

Introduction 553 Innovation and Performance 554 Costs/Benefits, Hard Facts 557 CO2 -Savings in Figures and Non-Cash Benefits 558 National and Global Importance 560 Market and Ready-to-Market 560 Realization and Planning 561 Benefits for the Construction Industry, FuturZement versus HPPC 563 Acknowledgments 565 References 565

27

Hydrogen and Electromobility Agenda 567 Henning Zoz and Andreas Franz

27.1 27.2 27.3 27.3.1 27.3.1.1

Introduction 567 H2 Tank2Go and isigo H2.0 569 he H2 -OnAir+ Project, “Iron Bird,” and Economical Fuel Cells 571 So What Is H2 -OnAir+? 572 he Case for Including Fuel Cell Development into his Project 575

®

®

Contents

27.4 27.5

Zoz ZEV Fleet and Project “REMONET” 577 Power to Gas to Fuel 578

28

Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials 583 Seok-Woo Lee and Julia R. Greer

28.1 28.2 28.2.1 28.2.2 28.2.3 28.3

Introduction 583 Size Matters: Mechanical Behavior at Nanoscale 584 Smaller is Stronger in Single Crystalline Metals 584 Smaller is Weaker in Nanocrystalline Metals 588 Emergence of Ductility in Nanometer-Sized Metallic Glasses 590 Capturing Size Effects and Using hem in Developing hree-Dimensional Hierarchical Metamaterials 593 References 597

29

Position and Vision of Small- and Medium-Sized Enterprises Boosting Commercialization 599 Torsten Schmidt, Nadine Teusler, and Andreas Baar

29.1 29.2 29.3 29.3.1

Challenges for SME in Nano-Industrialization: A Case Study 599 Scope 600 Four Propositions 602 Proposition 1: Cooperation in Large Industry Customer-Supplier Networks Allows SMEs to Launch New Product Ideas Successfully 602 Proposition 2: Packaging the Innovation into a Solution for the Global Market is a Key Success Factor in SMEs 604 Proposition 3: Competencies of SMEs and Research Institutions are Complementary Rather than Competing 605 Proposition 4: Suitable Networks Provide Special Skill Sets for Assuring Access to Partnering SMEs, Universities, and Public Funding 608 Summary and Future Outlook 609 he Authors 610 References 610

29.3.2 29.3.3 29.3.4

29.4 29.5

30

Optical Elements for EUV Lithography and X-ray Optics 613 Stefan Braun and Andreas Leson

30.1 30.2 30.3

Development and Trends in Microelectronics 613 Optics for EUV Applications 614 Fabrication and Characterization of EUV and X-ray Multilayer Mirrors 616 Multilayer Fabrication 616 Multilayer Characterization 618 Latest Developments in the Field of EUV Mirrors 621 EUV Mirrors with Reduced Reflectance for IR Radiation 621

30.3.1 30.3.2 30.4 30.4.1

XIII

XIV

Contents

30.4.2 30.5 30.6

Broadband EUV Mirrors 621 Multilayers as Nano-Focusing Optics for X-ray Microscopy 622 Summary and Outlook 624 References 625

31

Industrial Production of Nanomaterials with Grinding Technologies 629 Stefan Mende

31.1 31.2 31.2.1 31.2.2 31.2.3 31.2.4 31.3 31.3.1

Introduction 629 Wet Grinding in Agitator Bead Mills 629 Development of Agitator Bead Mills 629 Advantages of Wet Grinding Processes 631 Basic Setup of an Agitator Bead Mill 631 Influence of Operating Parameters 632 Real Comminution in Agitator Bead Mills 633 Influence of the Grinding Media Diameter and the Stirrer Tip Speed 634 Concept of Energy Transfer and Energy Utilization 635 Real Comminution of Titanium Dioxide (TiO2 ) 637 Mild Dispersion 638 Desagglomeration of Titanium Dioxide 640 Desagglomeration of Barium Titanate (BaTiO3 ) 642 Desaggregation of Zinc Oxide 643 Conclusions 644 References 645

31.3.2 31.3.3 31.4 31.4.1 31.4.2 31.4.3 31.5

32

Guidelines for Safe Operation with Nanomaterials 647 ́ ́ Iwona Malka, Marcin Jurewicz, Anna SwiderskaSroda, Joanna Sobczyk, Witold Łojkowski, Sonja Hartl, and Andreas Falk

32.1 32.1.1 32.1.2 32.2 32.3 32.3.1 32.3.2 32.3.3

Introduction 647 Terms and Definitions in Nanotechnology 649 Safety Guidelines for Nanotechnology Development 650 he Nanomaterials Characterization Methods 652 Safe Working Condition for Nanotechnology in Industry 652 Nanomaterial SDS 661 Labeling of Nanomaterials 667 International Organizations for Nanomaterials Standardizations 668 Nanomaterials Industrialization 670 Conclusions 671 Acknowledgments 673 Appendix 674 References 674

32.4 32.5

Contents

Part VIII Visions for the Future

677

33

Industrialization – Large-Scale Production of Nanomaterials/Components 679 Marcel Van deVoorde

33.1 33.2 33.3 33.4 33.5

Nanomanufacture and Process Control 679 Potential Industrial Nanotechnology Sectors 680 Standardization Procedures 681 Routes to Commercialization 683 Looking Ahead 683 Index

685

XV

XVII

Foreword Curiosity-driven fundamental research is part of human culture, the benefit of which is improved knowledge and understanding of phenomena, behavior, processes, and organic and inorganic matter. An integral part of curiosity is raising the question on intelligent and sustainable use of the knowledge, for example, for improving the quality of life. Society not only tolerates but also favors and finances research work; not forever, as at a certain point, the proof of usefulness of new results and dedicated innovation becomes evident. Fantasy and imagination have to be followed by innovation with market potential, economic benefit, and creation of working places. he fascination of nanoscience has been based on curiosity. An unexploited body of phenomena, matter, and behavior offered almost unlimited development for fantasy and imagination. For most fields of human needs like housing, daily water and food, health, communication, mobility, and power providing comfort for life nanoscience principally offers great potential for advanced solutions. he potential is based on some of the main characteristics of nanoscience and nanotechnology: small mass and volume (a small number of atoms and molecules) per material unit with a high ratio of atoms/molecules of different behavior at surfaces, a very large number of material units to be built together with new architecture (“architectonics”*), potentially interface-dominated stringent space limitations for electric charges, and consequences on electric, magnetic, and optic behavior of building blocks. he great potential for innovation offered by nanoscience and nanotechnology is evident. As a matter of fact, for the last decades, nanoscience and nanotechnology has been a university and research center topic to a large extent. Nano-Industry is still in its infancy: nano-Electronics and nano-Chemistry are already on the way of industrialization, nano-Health and nano-Biotech made a good start, and nano-Structural materials have still to find their way and need to be promoted. Nano-Industrialization needs development of fabrication and manufacturing. Top-down approaches based on continuous tailoring and miniaturization from the microscale as well as bottom-up approaches based on assembling nanoscale units or new collective phenomena based on nanoscale effects need to be developed for the production of new sustainable and safe devices in industrial quantities.

XVIII

Foreword

his book is an important and early contribution to the development of nanoManufacturing. It provides some directions for nano-Industry developments in the near future, especially for nano-Electronics and nano-IT, nano-Power and nano-Health, it describes examples with successful industrialization, and shows visions for the future in Europe, United States, and Asia. Tsukuba April 2014

Louis Schlapbach Prof. em. ETH/Empa, Scientist at NIMS Tsukuba

XIX

Acknowledgement he editors gratefully acknowledge the technical support of H. Faisst, C. Kotlowski and Dr. K. Bruehne of the ULM (D) University, Nanomaterials Institute, as well as various technical contributions and academic editing by Professor M. E. Fitzpatrick, Executive Dean of the Faculty of Engineering, Coventry University, UK. he generous support by the EUREKA programme through the research cluster Metallurgy Europe is gratefully acknowledged.

XXI

List of Contributors Sharifah Bee Abd Hamid

Marie-Isabelle Baraton

University of Malaysia Nanotechnology & Catalysis Research Centre (NANOCAT) Malaysia

University of Limoges and CNRS SPCTS Centre Europ. de la Céramique 12 rue Atlantis 87068 Limoges Cedex France

Santos F. Alvarado

ETH Zürich Magetism and Interphase Physics HPP N22 Hönggerbergring 64 8093 Zürich Switzerland Andreas Baar

Innos-Sperlich GmbH Bürgerstraße 44/42 D-37073 Göttingen Germany Gerd Bachmann

VDI Technologiezentrum GmbH Innovation Management and Consultancy VDI-Platz 1 40468 Düsseldorf Germany

Leif Brand

VDI Technologiezentrum GmbH Innovation Management and Consultancy VDI-Platz 1 40468 Düsseldorf Germany Stefan Braun

Fraunhofer Institut für Werkstoff- und Strahltechnik Winterbergstraße 28 01277 Dresden Germany

XXII

List of Contributors

Hans Peter Buchkremer

Raffaele Di Giacomo

Forschungszentrum Jülich Institute for Energy and Climate Research (IEK) IEK-1: Materials Synthesis and Processing 52425 Jülich Germany

Salerno University Department of Industrial Engineering (DIIn) Via Giovanni Paolo II 132 84084 Fisciano (SA) Italy Jakub Dostalek

Francisca G. Caballero

National Center for Metallurgical Research (CENIM-CSIC) Physical Metallurgy Department Av. Gregorio del Amo, 8 E-28040 Madrid Spain Philippe C. Cattin

University of Basel Department Biomedical Engineering Spitalstrasse 21 4031 Basel Switzerland

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Uwe Erb

University of Toronto Department of Materials Science and Engineering Wallberg Building College Street 184 (Suite 140) Toronto, ON M5S 3E4 Canada Wolfgang R. Fahrner

Alison Crossley

University of Oxford Department of Materials Begbroke Science Park Begbroke Hill Oxford OX5 1PF UK

Faculty of Mathematics and Computer Science Fernuniversitaet Hagen Universitaetsstrasse 1 58084 Hagen Germany Andreas Falk

Sitaram Dash

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India Gilbert Declerck

imec Kapeldreef 75 3001 Leuven Belgium

BioNanoNet Forschungsgesellschaft mbH Graz Austria

List of Contributors

Hans-Jorg ¨ Fecht

Sonja Hartl

University of Ulm Institute of Micro and Nanomaterials Albert-Einstein-Allee 47 89081 Ulm Germany

BioNanoNet Forschungsgesellschaft mbH Graz Austria

Michael E. Fitzpatrick

Coventry University Faculty of Engineering and Computing Priory Street Coventry CV1 5FB UK Andreas Franz

Zoz Group Maltoz-Straße 57482 Wenden Germany

Simone E. Hieber

University of Basel Biomaterials Science Center c/o University Hospital Basel 4031 Basel Switzerland Jean-Franc¸ois Hochepied

MINES ParisTech PSL Research University Centre for Materials Sciences CNRS UMR 7633 BP 87 91003 Evry France and

Thomas Fries

Fries Research & Technology GmbH Friedrich-Ebert-Straße 51429 Bergisch Gladbach Germany

ENSTA ParisTech UCP, 828 Bd des Maréchaux 91762 Palaiseau cedex France Yasuhiro Horiike

Julia R. Greer

California Institute of Technology Division of Engineering and Applied Science MC 309-81 California Blvd. 1200 E. Pasadenam, CA 91125 USA

University of Tsukuba Department of Graduate School of Pure and Applied Science Tennodai 1-1-1 Tsukuba 3058571 Ibaraki Japan

XXIII

XXIV

List of Contributors

Jorg ¨ Huwyler

Olga Kammona

University of Basel Department of Pharmaceutical Sciences Division of Pharmaceutical Technology Klingelbergstrasse 50 4056 Basel Switzerland

Chemical Process & Energy Resources Institute Centre for Research and Technology Hellas P.O. Box 60361 57001 hessaloniki Greece Amal Kasry

Vili Igel

NMTC Nano & Micro Technology Consulting Soorstraße. 86 Reichsstr. 6 14052 Berlin Germany Colin Johnston

University of Oxford Department of Materials Begbroke Science Park Begbroke Hill Oxford OX5 1PF UK Marcin Jurewicz

Bialystok University of Technology Faculty of Management Bialystok Poland U. Kamachi Mudali

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Costas Kiparissides

Aristotle University of hessaloniki Department of Chemical Engineering P.O. Box 472 54124 hessaloniki Greece Wolfgang Knoll

AITAustrian Institute of Technology Donau-City-Straße 1 1220 Wien Austria Neelie Kroes

European Commission Vice-President and Commissioner for the Digital Agenda Rue de la loi 200 B-1049 Bruxelles Belgium

List of Contributors

Martin Kulawski

Lerwen Liu

Oy Advaplan Inc. Alakartanontie 6 A 17 02360 Espoo Finland

NanoGlobe Pte Ltd Battery Road 4 Bank of China Building #25-01 049908 Singapore Singapore

Golden Kumar

Texas Tech University Texas USA Giovanni Landi

Faculty of Mathematics and Computer Science Fernuniversitaet Hagen Universitaetsstrasse 1 58084 Hagen Germany Seok-Woo Lee

California Institute of Technology Division of Engineering and Applied Science MC 309-81 California Blvd. 1200 E. Pasadenam, CA 91125 USA

Witold Lojkowski --

Bialystok university of Technology Faculty of management ojca tarasiuka 2 16-001 kleosin Poland Iwona Malka

Polish Academy of Sciences Institute of High Pressure Physics Warsaw Poland Stefan Mende

NETZSCH-Feinmahltechnik GmbH Sedanstraße 70 P.O. Box 14 60 95100 Selb Germany

Andreas Leson

Fraunhofer Institut für Werkstoff- und Strahltechnik Winterbergstraße 28 01277 Dresden Germany

Jyrki Molarius

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland

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List of Contributors

Bert Muller ¨

Jan Provoost

University of Basel Biomaterials Science Center c/o University Hospital Basel 4031 Basel Switzerland

imec Kapeldreef 75 3001 Leuven Belgium Xunlin Qiu

Peter Muller ¨

IBM Zurich Research Laboratory Säumerstrasse 4 8803 Rüschlikon Switzerland Heinz C. Neitzert

Salerno University Department of Industrial Engineering (DIIn) Via Giovanni Paolo II 132 84084 Fisciano (SA) Italy Gino Palumbo

Integran Technologies Inc. 6300 Northam Dr Mississauga ON L4V 1H7 Canada Thomas Pfohl

University of Basel Department of Chemistry Klingelbergstrasse 80 CH-4056 Basel Switzerland John Philip

Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakkam 603 102 Tamil Nadu India

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany Baldev Raj

National Institute of Advanced Studies (NIAS) Bengaluru 560012 Karnataka India Tommi Riekkinen

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland Laura Rossi

IBM Zurich Research Laboratory Säumerstrasse 4 8803 Rüschlikon Switzerland

List of Contributors

Dmitry Rychkov

Andrei P. Sommer

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany

Institute of Micro and Nanomaterials University of Ulm Albert-Einstein-Allee 47 89081 Ulm Germany

Robert Schlogl ¨

Abteilung Anorganische Chemie Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4-6 14195 Berlin Germany Torsten Schmidt

GXC Coatings GmbH Im Schleeke 27-31 D-38642 Goslar Germany Jan Schroers

Yale University Department of Mechanical Engineering and Materials Science Becton Center 217 Prospect Street 15 New Haven, CT 06520 USA Joanna Sobczyk

Institute of High Pressure Physics Polish Academy of Sciences Warsaw Poland

Anna S´widerska-S´roda

Institute of High Pressure Physics Polish Academy of Sciences Sokolowska 29/37, 01-142 Warsaw Poland Nadine Teusler

Innos-Sperlich GmbH Bürgerstraße 44/42 D-37073 Göttingen Germany Marcel H. Van de Voorde

University of Technology DELFT Faculty of Applied Science Materials and Engineering Department Eeuwigelaan, 33 1861 CL, Bergen he Netherlands Tim Van Gestel

Forschungszentrum Jülich Institute for Energy and Climate Research (IEK) IEK-1: Materials Synthesis and Processing 52425 Jülich Germany

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List of Contributors

Diederik Verkest

Werner Wirges

imec Kapeldreef 75 3001 Leuven Belgium

University of Potsdam Faculty of Science Institute of Physics and Astronomy, Applied Condensed Matter Physics Karl-Liebknecht-Straße 24/25 14476 Potsdam Germany

Jared J. Victor

University of Toronto Department of Materials Science and Engineering Wallberg Building College Street 184 (Suite 140) Toronto, ON M5S 3E4 Canada Martin A. Walter

Institute of Nuclear Medicine University Hospital Bern Freiburgstrasse 4 3010 Bern Switzerland Matthias Werner

NMTC Reichsstr. 6 14052 Berlin Germany

Wolfgang Wondrak

Daimler AG Power Electronics Advanced Engineering Hanns-Klemm-Straße 45 71034 Böblingen Germany Markku Ylilammi

VTT Technical Research Centre of Finland Microsystems and Nanoelectronics Tietotie 3 02044 Espoo Finland Henning Zoz

Matthias Wiora

Institute of Micro and Nanomaterials University of Ulm AlbertEinstein-Allee 47 89081 Ulm Germany

Zoz Group Maltoz-Straße 57482 Wenden Germany Andreas Zumbuehl

University of Fribourg Department of Chemistry Chemin du Musée 9 1700 Fribourg Switzerland

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds Marcel H. Van de Voorde, Matthias Werner, and Hans J. Fecht

1 Introduction

his book is about bridging the gap between nanoscience and technology, microsystem engineering, and the macroscale world. he interface between micro- and nanoscale technologies becomes a key field of endeavor. he first edition of this book, published in 2004, dated from an international workshop in 2003 in Berlin, Germany, and highlighted these emerging technology trends through contributions from 25 authors representing international research groups. he first edition was rather successful, but there have been many advances in the last 10 years that require an upgraded and extended second edition. In the new edition, featuring 6 parts and about 30 chapters, we have expanded the scope and coverage, as well as updated the book to cover recent developments and innovations. he book maintains the theme of addressing the interface between micro- and nanotechnology, with a strong focus on benefits that arise from exploiting synergy effects. he book’s contributions cover the entire range of basic technology aspects with special emphasis on industrial manufacturing of nanotechnology products and on potential applications. Moreover, business activities such as market expectations and market growth, transnational networking, and investment opportunities are highlighted and explained. Nanotechnology is gaining more and more interest also in the financial community. More than $US 3 billion is being spent around the globe on nanotechnology research this year alone. Recently published articles concerning possible future applications of nanotechnology predict a big commercial impact on nearly any industry branch. However, only very limited information is available on the market situation today as well as on the future prospects and the time-to-market span for nanotechnology products. How likely is the predicted huge impact on the global economy? What does that mean for established and start-up companies?

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The Nano–Micro Interface: Bridging the Micro and Nano Worlds

2 Nanotechnology

“Nanotechnology” is a loosely applied term, often understood as a kind of ultimate miniaturization of high-tech devices. But in fact, it does not refer simply to objects whose dimensions are entirely in the nanometer range; rather, it can be applied generally to refer to

• functional objects where one of the dimensions, upon which the function relies, is less than 100 nm. Some dimensions of the objects may lie in the microscale or above; • any equipment used in the fabrication or measurement of nanoscale objects, including those where the function relies on a feature or features with dimension less than 100 nm. Most fundamental physical properties change if the geometric size in at least one dimension is reduced to a critical value below 100 nm, depending on the material. his allows tuning of the physical properties of a macroscopic material, if the material is fabricated from nanoscale building blocks with controlled size and composition. By altering the sizes of those building blocks, controlling their internal and surface chemistry, their atomic structure, and their assembly, it is possible to engineer properties and functionalities in completely new ways. Nanoparticles and nanomaterials exhibit radically different phenomena and behaviors compared to their macroscale counterparts. hese include quantum effects, statistical time variations (fluctuations) of properties, surface and interface interactions, and the consequences of the absence of defects in the nanocrystals observed in conventional crystalline materials. Nanoparticles and nanomaterials have unique mechanical, electronic, magnetic, optical, and chemical properties, opening the door to enormous new possibilities for engineered nanostructures and integrated nanodevice designs, with application opportunities in information and communications, biotechnology and medicine, photonics, and electronics. Examples include developments in ultrahigh-density data storage, molecular electronics, quantum dots, spintronics, and others. Atomic or molecular units, with their well-known subatomic structure, offer the ultimate building blocks for bottom-up, atom-by-atom synthesis and, in some cases, self-assembly manufacturing. Advanced nanostructured materials such as high-purity single-wall carbon nanotubes are being considered for microelectronics, sensors, and thermal management for micro- and optoelectronics, including flat panel displays. he latest developments in “nanobiotechnology” clear the way to revolutionary cancer diagnosis and treatment, bone repair, and tissue regeneration.

3 Nano-Industry is Arriving

he new nanotechnologies are driven by two approaches to their manufacture:

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

• “top-down” approaches based on continuous miniaturization from the microscale;

• “bottom-up” approaches based on nanoscale building blocks or nanoscale effects for the production of new devices. As nanotechnologies become increasingly embedded in products and processes, their integration with the microscale will be critically important. his has many challenges both in understanding the fundamental scientific principles that underlie the integration, and also in the industrial realization of components that exploit nanoscale phenomena. he extrapolation of engineering principles and mechanical and physical properties from the macroscale to the nanoscale is not straightforward: some scaling laws may reach their limit of validity, for instance in mechanical properties of ceramics due to the drastic change in properties during the transition from the macro to nano phases. Similarly, manufacturing techniques and methodologies for macromaterials and components cannot be simply extrapolated for the fabrication of nanocomponents. For example, nanofabrication requires to some extent expensive clean rooms, new expertise, and new techniques for quality control during manufacturing. As a consequence, companies will not be able to use their existing production lines for newly developed nanoscale technologies. New measurement techniques and newly developed standards for engineering processes will be needed, alongside novel methods for lifetime prediction and the assurance of reliability in use. Mass-production demands reliable and reproducible properties for materials and products. his means good control in manufacturing, with in situ measurements for quality control. Methods are needed for joining materials and components at the nanoscale, and the assessment of properties such as fatigue, creep, and corrosion in volumes that are minute compared to conventional testing requirements. here is a critical role for developments in nanomeasurement techniques for nanotechnology products and applications, underlined by the increasing involvement of metrological institutes in the new field of “nanometrology.” Standardization of nanotechnology from production to application is an important element in its fundamental engineering development, and these elements are covered within this book. In addition, standardization will be critical in tackling societal issues around nanotoxicology and other concerns frequently associated with rapidly growing new technologies. Nanotechnologies are subject to the same requirements as any of the systems that they integrate or replace, in terms of performance, safety, risk management, economy, and biocompatibility. Nanotechnology gives the potential for the creation of new products, but also the possibility to upgrade conventional technologies: an example presented in the book is the application of “nanoconcrete” in bridge construction. Because of the impacts on existing applications, there is the opportunity for industries in Europe and the United States to recapture global markets in well-established fields, such as steel and textiles, for example, by the development and application of advanced nanotechnologies.

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4 Applications and Markets

Many consumers are already unknowingly using products based on nanotechnology. A case in point is high-performance sun protection cream, based on nanocrystalline titanium dioxide that provides UV absorption but, because of the fine particle size, does not appear white on the skin. Another example is the Giant Magneto Resistive Effect (GMR), used in computer hard disk drives. he current high storage densities may only be obtained through the use of nanotechnologies. he breadth of applications, and the potential contribution of nanotechnologies, is shown in Figure 1.

5 Research and Development

European industry is a world leader in nanotechnology, alongside the United States and Japan, as it becomes evident by the number of patents and scientific publications. Although there are many advantages for industry in the development and application of nanomaterials and components, production costs are considerably high, particularly initially, and products often require more intensive quality control. As a consequence, the added value brought by nanotechnology must be very significant in terms of improved or new properties and functionalities. his book highlights the competitive advantages that will be available to companies that invest in nanotechnologies. he performance of microsystems depends on the understanding of the properties on both the nano- and microscales. In the words of the Review Committee of the National Nanotechnology Initiative in the United States: “Revolutionary Quantum dots Opto-electronics Improved reliability Enhanced eletrical properties

Hydrogen storage Batteries Solar cells

Improved transport kinetics

Enhanced properties

Catalysis High surfaceto-volume ratio

Enhanced reactivity

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Green tyres Tools Increased wear resistance

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Coatings Increased hardness

Higher resistivity Electronics Sensors

Figure 1 An overview of the potential applications of nanotechnology.

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

change will come from integrating molecular and nanoscale components into high order structures … To achieve improvements over today’s systems, chemical and biologically assembled machines must combine the best features of the top-down and bottom-up approaches.” his requires extensive research, building upon current knowledge, and practice. he research needs to move from demonstration of nanoscale possibilities to the development of new ways of working in manufacturing. here is a particular challenge for small-to-medium enterprises (SMEs). hey can benefit greatly from new technologies, but often cannot afford the research and development costs. New models of partnership between SMEs and major industrial players, academic, and national laboratories are required. SMEs in the future will play a key role in the industrialization of nanotechnology because of their flexibility.

6 The Infinite Space at the Bottom and the Tremendous Opportunities to Climb Up

Figure 2a illustrates schematically the tremendous opportunities nanotechnology offers for engineering and improving the performance of materials, systems, and devices, as well as for scientists on fundamental grounds searching for unexpected effects. In Figure 2, materials engineering, with support of materials science, seeks to optimize materials properties by varying the materials’ chemical composition, phase structure, and microstructure (e.g., dislocations, grain boundaries, phase boundaries, point defects density, and arrangement). Figure 2b shows the great opportunities offered by new degrees of freedom in shaping properties of matter. Further, nanoarchitectures and nano-micro architectures combine the nano-micro building blocks into microsystem technologies. he new degrees of freedom produced through combining multiple effects at the nanoscale gives a vastly increased range of potential properties than was available before the nanotechnology era. When considering the further step of the combination of nanosized pieces of material (nano-building blocks) and micro-sized materials into nano-micro systems (the art of doing this can be called nano-micro architecture) the new space for discoveries and applications becomes very large indeed. he new, virtually infinite space of parameters that can be tuned to control material properties opens up opportunities for new discoveries, particularly to solve key societal needs: supply of energy without irreparable damage to the environment, delivering clean water, radically improving the efficiency of medical treatments, supporting developing countries to improve quality of life, and accelerating economic growth in technologically advanced countries. hus an exponentially growing, new space for research and development is opening for humanity that holds great promise for all citizens of the globe.

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Figure 2 (a) Materials science and engineering optimize materials properties, by varying materials’ chemical composition, phase structure, microstructure (e.g., dislocations, grain boundaries, phase boundaries, point defects, etc.) density, and arrangement. (Image courtesy W. Lojkowski, Unipress, Poland.) (b) Nanotechnology exploits

in addition to microstructure and chemical composition the effect of size and shape of matter on its properties. Further, nanoarchitecture and nano-micro architecture combines the nano-micro building blocks into nano-micro systems. (Image courtesy W. Lojkowski, Unipress, Poland.)

7 The Second Edition, 2014

his second edition maintains the theme of addressing the interface between micro- and nanotechnology, with a strong focus on the benefits that arise from exploiting synergy effects. he book’s contributions cover the entire range of basic technology aspects with the goal of developing new and improved

The Nano–Micro Interface: Bridging the Micro and Nano Worlds

1. A European Strategy for Micro- and Nanoelectronic Components and Systems

Part VIII: Visions for the future Part I: Nanotechnology Research Funding and Commercialization Prospects – Political, Social and Economic Context for the Science and Application of Nanotechnology

33. Industrialization – Large-Scale Production of Nanomaterials/Components Part VII: Creative Strategies Connecting Nanomaterials to the Macroscale World

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26. Nanostructured Cement and Concrete

2. Governmental Strategy for the Support of Nanotechnology in Germany 3. Overview on Nanotechnology R&D and Commercialization in the Asia Pacific Region 4. Near-Industrialization Nanotechnologies Developed in JST’s Nanomanufacturing Research Area in Japan 5. Quo vadis Nanotechnology?

27. Hydrogen and Electromobility 28. Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials 29. Position and Vision of Smalland Medium-Sized Enterprises Boosting Commercialization 30. Optical Elements for EUV Lithography and X-ray Optics

Part II: Development of Micro and Nanotechnologies 6. Micro/Nanoroughness Structures on Superhydrophobic Polymer Surfaces 7. Multisensor Metrology Bridging the Gap to the Nanometer – New Measurement Requirements and Solutions in Wafer-Based Production

The Nano-Micro Interface: Bridging the Micro and Nano Worlds

8. NanostructuralMetallic Materials – Nanoengineering and Nanomanufacturing

31. Industrial Production of Nanomaterials with Grinding Technologies

9. Bulk Metallic Glass in Micro to Nano Length Scale Applications 10. From Oxide Particles to Nanoceramics: Processes and Applications

32. Guidelines for Safe Operation with Nanomaterials Part VI: Process Controls and Analytical Techniques

Part III: Nanoelectronics and System Integration

23. Characterisation of Nanostructured Materials

11. Creating Tomorrow’s Applications through Deeper Collaboration between Technology and Design

24. Surface Chemical Analysis of Nanoparticles for Industrial Applications

12. Multiwalled Carbon Nanotube NetworkBased Sensors and Electronic Devices

25. Nanometer-Scale View of the Electrified Interface: A Scanning Probe Microscopy Study

13. Thin Film Piezomaterials for Bulk Acoustic Wave Technology 14. Properties and Applications of Ferroelectrets

Part V: Energy and Mobility 19. Nanotechnology in Energy Technology

Part IV: Biomedical Technologies and Nanomedicine

15. Translational Medicine: Nanoscience and Nanotechnology to Improve Patient Care

20. The Impact of Nanoscience in Heterogeneous Catalysis

16. Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine

21. Processing of Nanoporous and Dense Thin Film Ceramic Membranes

17. Biofunctional Surfaces

22. Nanotechnology and Nanoelectronics for Automotive Applications

18. Biomimetic Hierarchies in Diamond-Based Architectures

Figure 3 The 8 parts of the book and the subsequent 33 chapters.

applications. Moreover, business aspects such as potential markets, roadmaps, transnational networking, and investment opportunities are highlighted and explained. he book comprises eight parts and is subdivided into 33 chapters. PART I represents an overview of the state-of-the-art in commercializing nanotechnology, with particular case studies of the strategies being implemented in

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Germany and Japan. It highlights the global research efforts and gives a summary of the engineering and manufacturing developments, as well as the key markets. PART II features the main classes of materials – metals, ceramics, and polymers – and how nanotechnology can in each case have benefits for properties and applications. Novel materials such as bulk metallic glasses are also considered. Part III looks at the integration of nanoelectronics devices into larger systems, with examples of carbon nanotubes, piezomaterials, and ferroelectrets, and how there will need to be collaboration in the future between technology and design. Part IV looks at applications in biomedical technologies and nanomedicine. Bioactivation, biomimicry, and biofunctionality are all critical properties for the development of transformative applications in medicine, including diagnostics, drug delivery, and regenerative treatments. Part V covers energy and mobility applications. For transport applications, nanomaterials can have impact in areas as diverse as catalysis for exhaust treatments to nanoelectronics for vehicle sensing and improvements in fuel efficiency. Part VI covers process control and analytical techniques, specifically characterization techniques, surface chemical analysis, and interface studies, and gives guidelines for their application in industrial manufacturing. Part VII is devoted to creative strategies connecting nanomaterials to the macro world and gives insights into the engineering challenges of manufacturing at the nano- to macrolength scales, and shows cases in the development of production technologies for nanomaterials and components. he standardization of nanomaterials will be essential both for manufacturing and marketing purposes. he part gives examples of successful developments of large-scale production technologies for nanoproducts, including novel techniques such as grinding. PART VIII concludes the book with a vision for the future of nanomaterials, through industrialization and large-scale production of components.

References 1. Roco, M. et al. (2010) Nanotechnology

Research Directions for Societal Needs in 2020, Springer, Heidelberg.

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Part IV Biomedical Technologies and Nanomedicine

he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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15 Translational Medicine: Nanoscience and Nanotechnology to Improve Patient Care Bert Müller, Andreas Zumbuehl, Martin A. Walter, Thomas Pfohl, Philippe C. Cattin, Jörg Huwyler, and Simone E. Hieber

15.1 Introduction

Nanomedicine, also termed nanotechnology-enabled medicine [1], is the science and technology of diagnosing, treating, and preventing diseases and traumatic injuries, of relieving pain, and of preserving and improving health using molecular tools and molecular knowledge of the human body according to the European Science Foundation [2]. To clearly distinguish nanomedicine from established treatment forms, it can alternatively be defined as characterizing hard and soft tissues on the nanometer scale and tailoring nanostructured man-made materials for improving human health. he understanding of tissue organization down to its nanometer-size components and the development of interrelated tools to prevent, diagnose, and treat diseases are essential steps in current clinically applied science. he societal need for cost-effective improvements of patient health thereby motivates the research activities in nanomedicine and their scientific approaches. he present chapter focuses on selected clinically relevant challenges that can realistically be overcome by nanomedicine approaches in the near future. he four most prevalent diseases in Europe are cancer, cardiovascular and neurodegenerative diseases, as well as disorders of the musculoskeletal system. Here, we will focus on selected solutions to cardiovascular diseases and musculoskeletal disorders. In these fields, therapeutic strategies are based upon quantitative understanding of the nanostructure and mechanical properties of human hard and soft tissues. Deeper understanding of diseases based on nanometer- and micrometer-scale mechanical characterization methods and, above all, structural imaging down to the molecular scale help in clarifying the roots of underlying pathological processes, allowing for elaborating preventive strategies and enabling the development of adaptive local drug delivery. For instance, one main focus is the design of mechanosensitive nanocarriers and nanocontainers to deliver active substances at target locations in predefined doses [3]. hese efforts are converged on targeting applications in orthopedics and dentistry; oral and musculoskeletal biology are both largely driven by mechanical he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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forces, and the prosthesis materials in both applications require matching the unique nanostructure and material properties of the host tissues [4]. Mechanical stresses are present not only in the musculoskeletal but also in the cardiovascular system [5]. Similar mechanical and structural approaches will target vascular ischemic disease and stroke with drugs released by mechanosensitive nanocontainers. To target cardiac insufficiency, containers sensitive to mechanical forces generated by the beating heart should become employed. his approach will allow for efficient, localized drug delivery that can increase the pump function. It is evident that the clinical realization of these envisioned applications, moving beyond very recent proof-of-concept studies [5, 6], will require careful design and manufacture of nanometer-sized containers and carriers. Dealing with structural units ranging from 1 to 100 nm in size is a challenging feature of nanomedicine and nanotechnology (see Figure 15.1). Since, precisely at this size range, a variety of biological mechanisms are regulated, the design of man-made materials at these scales offers a huge potential to significantly improve patient management. While the understanding and manipulation of the human body at the nanometer scale will eventually revolutionize medicine, the challenges to realize the related innovations are considerable. Figure 15.1 illustrates the wide Human

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Figure 15.1 The logarithmic length scale for one direction in space classifies the life science disciplines: medicine from meter to submillimeter regime, cell biology on the micrometer scale, and biochemistry dealing

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with entities in the nanometer range. Below the scale, engineering and natural sciences are represented via man-made materials applied for diagnosis and therapy.

15.1

Introduction

variety of disciplines involved and shows that all medical considerations start with the human body. Physicians consider and treat their patients in their entirety. For an increasing number of patients, medical doctors in general and radiologist in particular apply imaging techniques to diagnose or even assist treating a multitude of diseases. Current medical imaging is restricted to a spatial resolution down to a fraction of a millimeter, that is, far from the limits of imaging techniques applied not only in other life sciences such as cell biology and biochemistry but also in other natural sciences and engineering especially in materials science and solid state physics. Significant efforts have to be invested to bridge the gap between imaging techniques used in microtechnology and nanotechnology and those used in clinical practice. Frequently, these challenges in bridging nanoscience and medicine are simply considered as a matter of scale. For instance, the number of cells within the human body and of atoms within a single cell corresponds to the huge figure of 1013 to 1014 , which is at least three orders of magnitude larger than the number of stars in the Milky Way. herefore, visualization of the entire human body cell-by-cell has not yet been achieved and the description of the body using individual atoms or molecules is currently impossible. Nonetheless, models and other tools [7] can be successfully applied to describe macroscopic and microscopic material properties in terms of the arrangement of atoms in crystalline structures. hese tools can yield useful insights into human tissue organization as well as diseases and healing processes. Such approaches, however, still require substantial developments in physics, chemistry, and engineering to effectively translate knowledge to solving challenges that clinicians are faced with in their daily practice. And in particular, it requires a convergence of all disciplines, focusing on one goal. he research efforts in nanomedicine require a detailed understanding of the human body down to the molecular level using highly sophisticated methods for post mortem, ex vivo, and in vivo structural characterization. his knowledge will allow for not only the regeneration and repair of diseased tissue in a biomimetic, this means in a nature-analog manner, but also the fabrication of implants with mesoscopic surfaces to optimize the material–tissue interfaces. Figure 15.2 shows how the Humboldt principle of coexistence of research and teaching forms the basis for nanomedicine’s translation to the industry and the clinic. Essential to this approach is the idea of research-oriented teaching and the transfer of knowledge and technology developed in research. Students and teachers are joined in a rather flat hierarchy with the endeavor to critically examine traditional bodies of knowledge and to actively advance learning. hesis projects on the distinct academic levels will become the seed for clinical research in hospitals (translation) and research and development (R&D) in MedTech and related industries with the final aim to create employment in clinics and high-tech companies. In this way, the clinically relevant knowledge and technology can be efficiently transferred to MedTech industry and the benefitting patients of the aging society.

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Knowledge and technology transfer Figure 15.2 Translational research offers several pathways from the academic research via industry to clinics.

15.2 Nanoanatomy

Current medical imaging in clinical environment is restricted to the submillimeter range at its best. he next coherent step is the imaging of human tissues, that is, an entire organ or a reasonable part of the organ, down to the molecular scale ex vivo. Analog to the well-established macroanatomy and microanatomy, one considers this emerging field as nanoanatomy. hese basic research activities in translational nanomedicine not only are limited to the characterization and understanding of human tissues in health and disease but also embrace its interrelation with body functions. hey require a set of sophisticated tools that allow for probing the relevant parts of organs and tissues at the nanometer scale. hrough cross-pollination from condensed matter physics, methods based on X-ray scattering have been developed to investigate human tissue function and disease progression [8–10]. Figure 15.3 illustrates a currently available experimental setup for spatially resolved X-ray scattering using synchrotron radiation. A highly intense, monochromatic X-ray beam is focused to a few micrometers in diameter, which perpendicularly impinges tissue slices about 100 μm thick. Although most of the X-ray photons pass the tissue and are absorbed on the beam stop, a significant fraction is scattered from the nanometer-size features of the tissue slice and counted on the highly efficient detection system. Moving the tissue in x- and y-directions and acquiring the related scattering patterns, micrometer resolution

15.2

Nanoanatomy

Beamstop Through beam

q ϕ

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2θ Dsd x Focused X-ray beam

Scattered X-rays SAXS pattern Specimen

Figure 15.3 X-ray scattering using monochromatized synchrotron radiation can be performed in a spatially resolved manner combining micrometer resolution in real space and averaged nanometer information from reciprocal space.

in the real space is achieved and an enormous amount of data in reciprocal space covering the entire range from atomic distances to several 100 nm are obtained. Comparing these X-ray scattering data with histological characterizations, the abundance and the preferential orientation of numerous nanometer-size components including collagen fibers and elongated hydoxyapatite crystallites can be extracted. Such an experimental setup has been used to quantitatively characterize the nanometer-size components of hard and soft tissue slices from bone/cartilage, urethra, human teeth, and brain (see, for example, Ref. [11]). Figure 15.4 shows an example of the nanostructure orientation of nanostructures within the sheep urethra [12]. he left image is a virtual cut through synchrotron radiation-based micro-computed tomography data of the sheep urethra, which displays the orientation of characteristic micrometer-sized anatomical features. One can clearly differentiate between the lumen of the urethra and the well-organized surrounded tissues. he epithelium and the lamina propria form the 1 to 2 mm-thick tunica mucosa. Caverns in the lamina appearing in black are characteristic for connective tissue in mammalians. As in histological slices, an interface separates clearly between the tunica mucosa and the tunica muscularis (muscular tissue) with a highly oriented microstructure. he color image on the right exhibits the scattering signal related to the presence of oriented nanostructures in the range between 7 and 11 nm. he main orientation of these nanostructures is given according to the color wheel. Overall, both cross-sectional modalities demonstrate the high similarity between the microanatomic and nanoanatomic features of the urethra. Similar to the extension of two-dimensional (2D) radiography to threedimensional (3D) hard X-ray computed tomography, tomographic imaging can be developed on the basis of these scattering approaches. For example, the spatial distribution of bio-membranes formed by myelin was recently revealed in the

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2 mm (a) Figure 15.4 Virtual cut through a sheep urethra, as seen in the synchrotron radiation-based micro computed tomography (a). Main orientation of the scattering

(b) signal related to nanostructures with sizes between 7 and 11 nm according to the color wheel (b).

rat brain by applying small-angle X-ray scattering (SAXS)-tomography [13] at the Swiss Light Source, Paul Scherrer Institute that currently hosts one of the world’s premiere beamlines for spatially resolved X-ray scattering [14]. Other X-ray-based techniques at the Paul Scherrer Institute, above all the highresolution microscopy technique and ptychographic coherent diffractive imaging (P-CDI), have recently been expanded from two to three dimensions and applied to bony tissues [15]. Next to taking a snapshot of the current state of tissues, assessing tissue dynamics constitutes an integral part of understanding human nanoanatomy. Interfacing microfluidics with state-of-the-art microscopy and SAXS is a strong emerging tool for investigating self-assembly processes of biomaterials and cell motility in vitro [16–20]. his microfluidics-based approach allows for deeper insights into the formation of tissue networks of different complexity [21, 22] and understanding of the self-organization, invasion, disruption, and healing of human membranes [23–25]. Data acquisition through probing tissues at the mesoscopic scales is a complex step, but only the first of several ones that will lead to the understanding of human nanoanatomy. he acquired imaging data are of tremendous size, often coming from multiple modalities with dissimilar spatial and density resolutions. he data thus require registration (i.e., alignment and merging) to unleash their full potential. Various image registration approaches have been proposed in the last two decades [26] and future developments may focus more on the handling of large data sets [27]. Past research efforts mainly concentrated on the task of co-registering thousands of images [28], but the registration of highly resolved images in three dimensions requires more efficient algorithms with respect to data size. Current image registration techniques can be separated into two main approaches, the landmark-based [29] and intensity-based methods [30]. While

15.4

Nanoorthopedics

the landmark-based approaches seem to be attractive for registering large data sets due to their inherent dimensionality reduction ability, matching the landmarks between images of different modalities can be challenging. Nevertheless, first steps in the direction of multimodal landmark matching have been made recently [31]. In intensity-based registration, in contrast, mutual information is used as a well-established similarity measure for multimodal registration [32]. Future intensity-based approaches may also be able to handle large data sets efficiently. heir development is already in progress for image data registration [33, 34] and for their application to mesoscopic scale three-dimensional imaging problems [35, 36].

15.3 Nanorepair

Human tissues are generally organized in three dimensions as known for the inner organs and the musculoskeletal system, but the membranes of the inner ear, for example, are two-dimensional arrangements of cells. he hierarchical organization of microstructures and nanostructures is characteristic for both the 2D and 3D human tissues. herefore, the repair of human tissues should not only be restricted to 3D bony tissues but also include membranes commonly present in the human body. he increasing number of prenatal diagnostics, for example, is resulting in an increasing number of procedures penetrating the fetal membrane. Although its healing capacity is well appreciated, the risk for premature rupture is high [37]. herefore, strategies have to be developed to suitably repair the membrane after amniocentesis. Such research initiatives might be termed nanorepair. One approach to form biomimetic materials is given in a bottom-up fashion. Biomimetic materials have been shown to control cell migration and tissue regeneration [38]. he controlled hierarchical organization using layer-by-layer and printing approaches has allowed for the in vitro formation of tissue-like structures [39]. It is obvious that by taking such approaches to the next level, the border between implant material and tissue becomes more and more diffuse. he implant becomes basically a replacement tissue. Indeed, using growth factor immobilization and release methods [40, 41], cyclic loading protocols [42], techniques to mimicking fetal membranes tissue formation, injury, and healing in vitro have been developed. Additionally, gluing materials have been tested for their properties to seal fetal membranes [37, 43].

15.4 Nanoorthopedics

Nanoanatomy will help to identify nature-analog implant surfaces. In principle, nature-analog implant surfaces have been available for decades. For example,

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titanium bone implants exhibit a surface with a distinct roughness on the micrometer and nanometer scales generated via sandblasting and/or etching procedures to achieve improved osteointegration [44]. Nevertheless, the effects of the microstructured and nanostructured surfaces are only partly understood [7]. herefore, the roughness of load-bearing implants on these length scales has to be further optimized to avoid, for example, inflammatory reactions and oral diseases such as peri-implantitis. Several underlying mechanisms were revealed, but the optimal roughness for the numerous man-made implants has not yet been found and further extended studies will be initiated. Such research activities for loadbearing implants might be summarized as nanoorthopedics. he understanding of nanoanatomy is necessary for intelligent and targeted manipulation of artificial materials at the nanometer scale to interface with human tissue. he importance of the interaction between tissues and engineered materials has been known ever since the first implants were investigated. A clinically successful, functionally stable tissue transition from host to implant requires orderly tissue ingrowth that is influenced by the implant surface chemistry and surface topography [45–48]. he development of next generation biomaterials will feature nanometer and micrometer scale surface structures designed to elicit specific host responses to control tissue ingrowth to an implant and avoid tissue scarring [49]. Orthopedic medicine is on the frontline of such developments, posing important clinical challenges [50–52]. Nanotechnology to tailor surfaces requires state-of-the-art techniques that allow processing of various materials, starting from ones that can be applied for exploratory in vitro studies to those finally used as constituents of medical implants for patients. Submicron scale patterns have been applied to surfaces and embedded in materials by using various techniques [53–55]. Advanced polymer constructs with mesoscopic surface patterns have been fabricated using up-scalable techniques including injection molding and roll embossing [56, 57], allowing for the application of secondary nanostructuring by use of hybrid molds [58–60]. Other methods include the grafting of polymer brushes onto chemically inert polymers such as fluoro-polymers and poly-olefins based on selective plasma activation [61]. Electron beam lithography exposures can be used to produce polymer brush structures with high spatial resolution and complexity [62–64]. Despite the smart application of specific nanostructures or the production of biomimetic materials, only testing of the respective tissue’s response can guarantee the viability of an implant. he host–implant response is often characterized via phenotypic cell behavior by assessment of gene and protein expression [65–70]. Murine, rat, equine, and human fibroblast model systems are used to elucidate cell and matrix interplay in healing and implant integration [71–74]. Quantitative microscopy [73, 75, 76] has been applied to explore and understand the function of tissue structures [71–74] and cell–matrix interactions [69, 70, 77–79]. Nanostructured and microstructured sensors were employed to explore inflammatory reactions [7, 80] and contractile cell forces that have been relevant to myofibroblast behavior [81].

15.5

Nanovesicles

15.5 Nanovesicles

A wide variety of medical applications might benefit from nanometer-size components for targeted drug delivery. hereby, liposomes offer a rather natural path to transport and release pharmaceuticals at desired locations. A recent prominent example is the shear-sensitive release of vasodilators [5, 6]. Such approaches can be classified as nanovesicles. Given that the human body is based on nanostructures, it is intuitive that the tools to intervene in the body’s function in a highly targeted fashion should also be of that scale. Building such small structures with classical engineering tools such as lithography is expensive and cumbersome. However, nature can guide us toward better approaches: self-assembly of amphiphiles into soft matter nanosystems, a fundamental principle of nature [82]. Arguably, nature’s most important amphiphiles are phospholipids. hey contain both a hydrophilic or polar head and hydrophobic or water-insoluble tails on the same molecule. In water, this arrangement leads to a hydrophobic effect and aggregation of the molecules into ordered structures. his association of phospholipids into superstructures minimizes the contact between bulk water and the hydrophobic parts of the molecules [83]. Depending mainly on the geometry and concentration of the phospholipids, various structures can be formed, the most attractive being self-closed and water-filled spherical particles composed of lipid bilayers [84]. hey are termed liposomes or phospholipid vesicles. Drug delivery systems made from liposomes have shown a high potential as therapeutics in the past decades in selected fields such as cancer and antifungal therapy, where the vesicle can be loaded with drugs such as amphotericin B (AmBisome) or doxorubicin (Caelyx) [85]. his technology is currently in use in the clinic [86]. he formulations show high tolerability and can be designed to have a prolonged circulation in the blood stream. Liposomal formulation can be lyophilized and have a shelf life of up to 2 years. he fundamental research on liposomes has, however, for a long time, diverged from medical goals. Instead, fundamental soft matter physics has taken the upper hand in the study of, for example, supported bilayers [87] and nanocontainer morphology [88]. Recent years have seen a trend in soft matter physics to study facetted vesicles which, for example, have a capsid-like icosahedral morphology [89]. he studies showed how liposome shapes are governed by the membrane bending energy and its in-plane elasticity [90]. he conclusion is that rigid bilayers show a multi-curvature, facetted morphology with in-built membrane defects at the vertices that will have an impact on membrane permeability [91]. Although the membrane bilayers consist of tightly packed phospholipids, the application of an external physical trigger such as changes in osmolarity, pH, or shear stress can induce a transient increase in the passive trans-bilayer membrane transport of vesicle payload. his phenomenon promises attractive applications in the field of nanomedicine.

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Artificial 1,3-diamidophospholipids that have been synthesized [92] selfassemble into faceted, lentil-shaped vesicles [5]. Indeed, as predicted by theory, liposomes formulated from these molecules were found to maintain their payload in the resting state; but upon the application of shear stress, triggered by simple shaking, the entrapped molecules were released from the vesicle. his fact stands in contrast to liposomes derived from natural sources that either release their cargo both spontaneously and when shaken or do not release their payload at either conditions. herefore, the vesicles formulated from the artificial 1,3-diamidophospholipid Pad–PC–Pad represent an unprecedented category of nanocontainers [92]. his fact has led to a convergence of soft matter physics with phospholipid chemistry and has shown fresh perspectives in medical applications for liposomes that react to the mechanical forces that occur in the human body. Y. Barenholz [93] pointed out that “because non-spherical liposomes release their contents only at elevated shear stress, drugs can be targeted and released only in regions with rheological changes (such as inside a clogged artery) without the need for any recognition molecules or a remote trigger.” Using lentil-shaped nanocontainers, a preferential release for clinically relevant stenosed artery models was demonstrated in vitro [5, 94]. In a constricted artery, wall shear stresses were found to be one order of magnitude higher than in a healthy artery. his change in shear stress may be used as a purely mechanical trigger for targeted drug delivery. herapies for diseases in which mechanical effects are involved can thus be envisioned. his includes drug delivery to address heart insufficiency (beating of the heart acts as the mechanical trigger), to open occluded arteries sufficiently to achieve a sufficient blood flow in the case of heart attack or stroke (local hemodynamic changes are the trigger), and intra-articular applications to medicate osteoarthritis in load-bearing joints such as the temporomandibular joint. Nanoparticle-based drug delivery systems are tools with the potential to improve efficacy and reduce systemic toxicity of a variety of drugs [95, 96]. In order to trace the in vivo distribution and functionality of those delivery systems, they can be enhanced with imaging functionalities such as for positron emission tomography (PET) [91]. In general, imaging-based drug development has shown promise for speeding up drug evaluation by supplementing or replacing preclinical and clinical pharmacokinetic and pharmacodynamic evaluations [91, 97, 98]. With radiolabeled drug compounds, the additional functionality allows for noninvasive imaging of bio-distribution and pharmacokinetics. his approach has shown the potential to monitor drug activity during preclinical and clinical drug development. Additionally, it might facilitate an early decision to select promising investigational compounds from compounds that seem likely to fail [99]. Furthermore, addition of the imaging functionality allows trace amounts of a drug to be tracked, leading to the development of the principle called microdosing. PET-based microdosing involves the administration of only microgram amounts of the respective drug. hus, the potential toxicological risks to human subjects are limited. As a consequence, microdosing is anticipated to permit smarter candidate selection by taking investigational compounds into humans earlier. Microdosing might allow safer human studies and reduce the use of animals

15.6

Nanodentistry

in preclinical toxicology [100]. Clinical microdose studies are anticipated to be feasible with a variety of radiolabeled nanovesicles. hese microdose studies have the potential to shorten time lines and cut costs along the critical path of clinical translation [101].

15.6 Nanodentistry

As aforementioned, human hard and soft tissues that generally exhibit preferential alignment of microstructures and nanostructures according to the loading directions form a sound basis of biomimetic implants. Although current dental fillings, for example, show superior mechanical stability, they have an average life span of only one or two decades, while the human crown can remain stable for many decades. Building bioinspired dental fillings with oriented and elongated nanocomposites might significantly improve the mechanical properties of artificial crown tissues [102]. Furthermore, remineralization of quality-reduced hard tissues, for example, of caries lesions, might reduce the volumes to be treated in a conventional manner. We classify the related topics as nanodentistry [103, 104]. Having the tools to characterize human nanoanatomy, to produce biomimetic materials, and to test their interaction with tissues opens the door to clinical applications. One of them is dentistry, where innovative implants have found widespread use [103, 105, 106]. he enamel that forms the outer surface of teeth has a complex anisotropic nanostructure as a result of biomineralization during formation and subsequent mechanical loading [107]. Such structural anisotropy is also observed for the underlying dentin. he anisotropic nature of human crown tissues became available for use in bioinspired dental fillings [102, 104]. he Clinical Editor of the journal Nanomedicine: Nanotechnology, Biology, and Medicine pointed out at the end of the article abstract [108] that synchrotron radiation-based X-ray scattering enabled a groundbreaking study of the caries pathology. It has been demonstrated that while bacterial processes dissolve ceramic components in enamel and dentin, the dentinal collagen network remains unaffected, enabling the development of future caries treatments that remineralize the dentin [108]. Inside teeth, mineral loss usually accompanies root canal infections, globally one of the most frequent dental disease indications. When developing improved root canal treatments, reliable binding of canal sealants to dentin and remineralization of root dentin for biomechanical re-constitution of the affected tooth would be immensely valuable [109]. Likewise, in bones, development of treatments for complex-shaped defects demand for “bone glues” where mineral release has been found to be a key advantage for bonding hard tissue interfaces. Re-establishing bone density after trauma or osteoporosis demands significant mass and release of minerals. For highly mineralized tissues, the highly active, inorganic biominerals and bioactive glass nanoparticles are among the most promising solutions [110]. Production methods were developed to

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access nano-biomaterials at the ton scale, hence enabling their use in global clinical product development. A number of preclinical tests on nano-bioglass and amorphous (glassy) nano-calcium phosphates have proven the methods’ capability to prepare materials of adequate purity and under quality protocols amenable to biomedical manufacturing.

15.7 Interactions of Disciplines in Nanomedicine

he five areas of nanomedicine selected above are closely related (see Figure 15.5), since equivalent materials and the same methods for characterization are applied, as recently reflected in a large national research proposal for Switzerland. he list of such emerging medical fields, which are based on nanoscience and nanotechnology, can be continued. he final goal is always the translation from basic research to clinical applications and its benefit for patients. he translation will succeed gradually and the developments are expected to appear in clinics step by step, as illustrated in Figure 15.6. Imaging methodologies

Nanoorthopedics

Nanoanatomy

Nanodentistry

Nanorepair

Nanovesicles

From basic research to clinics clinical use. Method- and material-related Figure 15.5 Selected research fields in nanomedicine with high translational impact: interactions are represented as dotted and dashed lines, respectively. certain fields are clearly related to basic research whereas others are already in

References State of the art

Challenges

2014 Increase of multi-functionality, bioinspiration toward nanometer scale

2018

Nanoimaging/ Nanoanatomy Nanostructured surfaces for implants

Breakthrough 2022

Nanoscienceenabled targeted therapy Bioinspired implants

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2026 (Raman-based) Nanodiagnostics Human brain – computer interface

Increase of complexity

Figure 15.6 From current research activities toward the major breakthroughs one expects more than a decade, a time period, which is characterized by increasing complexity.

being currently only available for nanoscience may become applicable for clinical diagnostics in more than a decade. Insights from nanoanatomy and technical capabilities may enable the design of bioinspired implants and might lead to functional interfaces, such as a human brain–computer interface. In general, the achievements are expected to become more and more complex when the mimicking of nature will approach the nanometer scale. he successful completion of these complex tasks, however, is anticipated to generate improvements in patient care in a wide variety of clinical disciplines. Acknowledgements

he authors express their special thanks of gratitude to the network “Nanomedicine for Human Health,” in particular to Oliver Bunk, Martin Ehrbar, Vartan Kurtcuoglu, Jess Snedeker, Katharina Maniura, Wendelin Stark, and Marco Wieland for their valuable input.

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16 Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine Costas Kiparissides and Olga Kammona

16.1 Introduction

Nanomedicine is defined as the application of nanotechnology to achieve breakthroughs in health care. It exploits the improved and often novel physical, chemical, and biological properties of materials at the nanometer scale. At this scale, man-made structures match typical sizes of natural functional units in living organisms, thus allowing them to interact with biomolecules. Nanomedicine has the potential to enable early detection and prevention, and to essentially improve diagnosis, treatment, and follow-up of diseases with a real benefit for patients [1]. Every scientific discovery in nanomedicine has to pass through various long-lasting developmental stages, including pre-clinical and clinical studies, in order to reach commercialization (Figure 16.1). Currently approved nanomedicine products are mainly intended for use in cancer treatment, hepatitis and other infectious diseases, anesthetics, cardiac/vascular disorders, inflammatory/immune disorders, endocrine/exocrine disorders, degenerative disorders, and so on. However, it should be noted that the major part of the research efforts are focused on cancer treatment [2].

16.2 Diagnostics

Many diseases, including cancer, originate from mutations and alterations to normal cellular regulatory and metabolic pathways at molecular level. Accurate and sensitive diagnosis has been constrained by the lack of biosensors and molecular probes capable of rapidly recognizing the distinct molecular features of these diseases. he ability of nanomaterials to interact with biological molecules combined with their optical, magnetic, or electrical properties and their large surface area, enabling the attachment of target-specific molecules, offer remarkable opportunities to detect and monitor molecules and cells in complex biological environments and thus enable the early diagnosis of diseases (i.e., detection of defective cells or he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Nanomedicine technology development pipeline Years to commercialization 7–20 years

1–7 years

Nanomedicine applications in development

Nanomedicine clinical investigations

Basic Pre-clinical nanoscience Application animal development research study

Clinical study

Theory

Near-term impact Now Commercial nanomedicine products

Commercial products

Use

Figure 16.1 Development pipeline of nanomedicine products [2].

biomarkers predicting the onset of the disease) [3–8]. Nanotechnologies, applied to molecular diagnostics and incorporated in cutting-edge molecular diagnostic methods, such as DNA and protein microarray biochips, enable diagnosis at the single-cell and single-molecule levels [9]. 16.2.1 In vitro Diagnostics

An in vitro diagnostic tool can be a chemo- or biosensor, capable of recognizing the presence, activity, or concentration of a specific molecule of biological importance in solution [1]. he goals of in vitro diagnostics for the next 5–10 years can be summarized in (i) the design of a new generation of molecular probes to trigger cellular metabolism and/or extracellular secretion of molecules that will be analyzed, when circulating in the body fluids, with a better sensitivity, at lower costs, and with possible multi-parametric analysis and (ii) the development of nanoscale sensors (e.g., mechanical, electrical, optical) and their integration into microscale devices for cheap, highly sensitive point-of-care (POC) diagnostics [3]. Various types of nanomaterials developed during the past decade have been extensively used in the field of in vitro diagnostics of cancer and infectious diseases (Table 16.1) [5]. However, realizing the full potential of nanotechnology, as it pertains to disease diagnosis, requires the ability to fabricate nanoscale devices and materials with a high degree of precision and accuracy. Fabrication of such nanoscale constructs can proceed from either a “top-down” or “bottom-up” approach. Examples of nanoscale biosensing devices with potential to significantly impact POC diagnosis due to their high sensitivity and capability for high-throughput screening of biological samples are mesoporous silica chips, allowing serum fractionation by a rapid four-step on-chip strategy and analysis of the low-molecular-weight proteome (LMWP) reflecting ongoing pathological conditions (Figure 16.2); nanowire biosensors (i.e., nanowires functionalized with

16.2

Diagnostics

Table 16.1 Selected nanoprobes and their potential applications. Nanoprobes

Analytical methods

Potential applications

QDs

Fluorescence resonance energy transfer (FRET) Bioluminescence resonance energy transfer (BRET)

Detection of DNAs, proteins, and enzymes Detection of disease-related protease

Metal NPs

Surface plasmon coupling Localized surface Plasmon resonance (LSPR) Surface-enhanced Raman scattering (SERS)

Single-molecule detection Detection of disease-related biomarkers Detection and identification of biomolecules

Magnetic NPs

Magnetic capture Diagnostic magnetic resonance

Bacterial detection Detection of infectious agents, nucleic acids, proteins, antibodies, and circulating tumor cells Multiples detection of protein Detection and differentiation of cancer cells, detection of biomarkers

CNTs

Giant magnetoresistive sensor Raman imaging

Si-nanowires

Field-effect device

Detection of biological species (proteins, DNAs, and viruses) and their interactions

Multifunctional nanomaterials

Multiplexed methods

Detection and tracking of biomolecules and cells, multimodal imaging

Adapted from [5].

different biorecognition elements) capable of achieving simultaneous detection of multiple biomolecular targets; nanocantilevers; and single-electron transistors (SETs). Nanocantilevers have been used to detect a variety of biomarkers (e.g., prostate-specific antigen, angiogenic factors, etc.). hey impart significant advantages over other molecular-based diagnostic technologies because of their sensitivity and capacity for microfluidic integration. he breakthrough potential in nanocantilever technology is the ability to sense a large number of proteins at the same time, in real time. Efforts are currently underway to develop SETs operating based on the quantum mechanical phenomenon of tunneling. he merging of top-down and bottom-up fabrication should also allow for the fabrication of large arrays of SETs capable of multiplexed biosensing [6]. Lab-on-a-chip (LOC) platforms have also become important tools for diagnostics due to advantages such as reduced sample volume, low cost, portability, and possibility to build new analytical devices or to integrate into conventional ones [10]. Finally, recent advances in micro/nanofabrication and biotechnology have led to the development of aptamer-based sensors [11]. So far, aptasensors have been applied to clinical diagnostics and applications are foreseen in the

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High Mw, abundant proteins LMWP

Nanoporus surface Step 1 – Spot samples on the chip (a)

Step 2 – LMWP harvesting (b)

Intensity

314

m/z Step 4 – Transfer to MALDI plate for MS analysis (c)

Step 3 – LMWP elution (d)

Figure 16.2 Schematic of the harvesting protocol consisting of (a) the deposition of plasma directly onto the chip surface, (b) the washing away of unbound substances, (c) the extraction of bound molecules, and (d) mass spectrometry analysis [6].

areas of biomarker detection, cancer clinical testing, and detection of infectious microorganisms and viruses [12]. 16.2.2 In vivo Diagnostics

In vivo imaging is focused on the detection of abnormal lesions differentiating a cluster of cells from the surrounding cells [13]. he main benefits of molecular imaging for in vivo diagnostics are the early detection of diseases and the monitoring of disease stages (e.g., in cancer metastasis), leading to individualized medicine and real-time assessment of therapeutic and surgical efficacy [1]. Various labeling agents like fluorescence, quantum dots (QDs), upconversion nanoparticles (UCNPs) (i.e., nanomaterials doped with rare-earth ions), magnetic nanoparticles (NPs), and radioisotopes can be tagged on nanomaterials for effective imaging such as optical, magnetic resonance, computed tomography (CT), positron emission tomography (PET), and so on. [14]. he advantages of NPs in comparison to molecular contrast agents are the variety of structures, shapes, and sizes that can be used to carry labels for different kinds of imaging [15] as well as the possibility to combine two or more agents in a single NP, and the surface functionalization of the NPs (e.g., with DNA, RNA, aptamers, peptides, proteins, enzymes, antibodies (Abs), tumor cell receptors, carbohydrates, etc.) to enable targeting and long circulation times with minimal nonspecific binding. For example, combining the anatomical resolution of magnetic resonance imaging (MRI) with the sensitivity of optical imaging could prove to be a powerful technique for quantifying the size of tumors, especially of those that are too small for MRI detection alone. Table 16.2

16.2

Diagnostics

Table 16.2 NP-based contrast agents for imaging techniques. In vivo imaging technique(s)

NP-based contrast agents

Near-infrared fluorescence (NIRF) imaging

QDs, dye-doped silica NPs, upconverting NPs, carbon nanomaterials, indocyanine green (ICG)-doped calcium phosphate NPs, luminescent porous silicon Iron oxide NPs, gadolinium-based agents, paramagnetic liposomes, lanthanide-based paramagnetic complexes Isotopes chelated or incorporated in NPs, silica NPs loaded with NIRF agents, MRI agents conjugated with iron oxide NPs. NPs incorporating radioisotopes

MRI PET Single-photon emission computed tomography (SPECT) X-ray imaging and CT

US PAI MRI/optical imaging PET/NIRF SPECT/fluorescence PET/MRI MRI/ photoacoustic tomography (PAT) Thermoacoustic tomography (TAT)/PAT US/MRI MRI/NIRF/PET

PET-CT/MRI/NIRF MRI/PET/BRET/ fluorescence

Iodinated NPs, gold-based NPs, bismuth sulfide NPs, composite ceramics containing iron oxide, and lanthanide materials Microbubble-based contrast agents Gold nanoshells, nanorods, and nanocages; SWNTs, golden carbon nanotubes (GNTs), dye-doped NPs. Gadolinium chelates, functionalized QDs, and iron oxide NPs [16] ICG, QDs SWNTs SWNTs SWNTs SWNTs Perfluorocarbon (PFC) NPs [17] Dextranated, diethylene triamine pentaacetic acid (DTPA)-modified magnetofluorescent NP [18], dextranated superparamagnetic iron oxide NPs [19] Dextranated and DTPA-modified magnetofluorescent NP [18] Magnetic-fluorescent-bioluminescent-radioisotopic MFBR, cobalt ferrite-based NP [20]

Adapted from [13].

gives an overview of the most commonly used in vivo imaging modalities and their combinations along with the developed NP-based contrast agents [13]. Stimuli-responsive (SR) polymers may be very useful in the detection of diseases that are usually accompanied by significant variations of analytes and/or physical variables (e.g., pH, temperature) [21]. Implantable sensors utilizing nanotechnology are at the forefront of diagnostic, medical monitoring, and biological technologies. hey are often equipped with nanostructured carbon allotropes, such as graphene or carbon nanotubes (CNTs). Multi-walled carbon nanotubes (MWNTs) have shown great promise in orthopedic implant systems, for monitoring bone growth via electrochemical

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sensing techniques. he optical properties of semiconducting single-walled carbon nanotubes (SWNTs) make them advantageous for biolabeling, imaging, and sensing in biological tissues. SWNTs have been also recently used as implantable bone strain sensors for the real-time monitoring of musculoskeletal conditions. Neuronal interfacing is yet another area in which SWNTs have become of interest for the monitoring and stimulation of neurons. Graphene has received a lot of attention due to its unique optoelectronic and physical properties. To date, graphene has found applications in implantable sensor technologies as a glucose detection system, neural stimulator and signal recorder, antigen detection system, and so on. Although graphene, along with graphene oxide (GO), has been found to be biocompatible under specific conditions and able to be interfaced with biological molecules, its toxicity is a continuing debate among the scientific community [22].

16.3 Drug Delivery

Major goals of nanomedicine in terms of controlled drug delivery are the maximization of drug bioavailability and efficacy, the control of pharmacokinetics, pharmacodynamics, nonspecific toxicity, immunogenicity, and biorecognition as well as the overcoming of obstacles arising from low drug solubility, degradation, fast clearance rates, relatively short-lasting biological activity, and inability to cross biological barriers (e.g., air–blood barrier, blood–brain barrier (BBB)) [23]. Modern drug delivery systems (DDSs) are being developed in response to the broad spectrum of novel therapeutic agents ranging from small molecules, (glyco)proteins (including Abs and antibody fragments (fAbs)), carbohydrates, polymer-drug adducts, anticodon molecules, genes and gene carriers (i.e., plasmids, disabled viruses), cells, and so on. [24]. 16.3.1 Nanocarrier-Based DDSs

he goals of nanomedicine in the field of drug delivery are expected to be achieved through the development of highly selective carrier-based DDS. However, since drug characteristics differ substantially with respect to chemical composition, molecular size, hydrophilicity, bioavailability, optimum concentration range, and so on, the essential characteristics that identify the efficiency of the nanocarriers are highly complex [23]. In comparison to microcarriers, nanocarriers have a number of advantages as potential DDS. For example, they can travel through the bloodstream without sedimentation or blockage of the microvasculature, they can circulate in the body and penetrate tissues such as tumors, they can be taken up by cells via endocytosis, and they can be engineered to recognize biophysical characteristics that are unique to the target cells, thus minimizing drug loss and toxicity associated with delivery to non-desired tissues [23].

16.3

Drug Delivery

Additionally, following drug incorporation into NPs, drug properties (e.g., solubility, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, thus allowing a greater flexibility in the design of drug molecules themselves [25]. Nanocarrier-based DDS are usually made of biocompatible and/or biodegradable materials such as synthetic proteins, lipids, polymers, inorganic materials, and so on. [26, 27] (Table 16.3). Successful nanocarrier-based formulations should be nontoxic, protect their therapeutic payload and exhibit biocompatibility, biodegradation, colloidal stability, controlled-release kinetics, and improved pharmacokinetics [28]. he use of multifunctional nanocarriers should be also considered for improved cancer therapies (i.e., delivery of drug-nucleic acid combinations such as siRNA-doxorubicin) [29]. he multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers which should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor

Table 16.3 Nanocarrier types. Nanocarriers

Drug

Functionalization

Advantages

Disadvantages

Micelles

Lipophilic

Folic acid, Arg-Gly-Asp (RGD) peptide, antibodies, RNA aptamer, carbohydrates

Control size and morphology, effective drug protection, in vivo stability, prolonged blood circulation times Long circulation time, targeting efficacy [31] Colloidal stability, tunable membrane thickness, and permeability, ability to encapsulate or integrate a broad range of drugs Incorporate multiple therapeutic agents, highly tailorable release profiles

Low drug loading, difficulty in transport through cell membrane

Immunomicelles Anti-cancer drugs, siRNA Polymersomes

Hydrophilic, lipophilic

Dendrimers

Hydrophilic, lipophilic

Monocloanal antibody (mAb)

Targeting ligands, PEG

Lacking specific cellular interactions

Toxicity

(continued overleaf )

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Table 16.3 (Continued) Nanocarriers

Drug

Functionalization

Liposomes

Hydrophilic, amphiphilic, lipophilic

Long-circulating Glycolipids, sialic acid, PEG, (PEGylated targeting ligands liposomes), triggered release, improved tumor accumulation, and therapeutic efficacy, reduced side effects [30, 32]

Hydrophilic, lipophilic

Increased encapsulation efficiency, high transdermal flux, safety, efficacy Targeting efficacy, increase of circulation time (release of payload at pathological areas in the presence of certain stimuli) Efficient, nontoxic

Niosomes Virosomes Ethosomes

Anti-cancer Immunoliposomes (stimulus- drugs sensitive)

Solid lipid NPs

PEG, mAb (stimulussensitive moieties) [31]

Hydrophilic, lipophilic

Lipoproteininspired NPs

NPs

Hydrophilic, lipophilic

PEG, targeting ligands

Advantages

HDL-like NPs can deliver molecules directly to the cytoplasm of cancer cells Drug protection against chemical and enzymatic degradation, accumulation in tumors, inflammatory and infectious sites

Disadvantages

Possible steric interference of PEG with Ab’s recognition ability

Low drug loading, drug expulsion during storage

16.3

Drug Delivery

Table 16.3 (Continued) Nanocarriers

Drug

Functionalization

Polysaccharidebased NPs Chitosan NPs

Poly(lactic acid) (PLA), Poly(lactic-coglycolic acid) (PLGA) NPs Poly(εcaprolactone) (PCL) Polyplexes

Lipopolyplexes Albumin NPs

Nanobees

Hydrophilic, lipophilic

Hybrid NPs Drug nanocrystals Nanoemulsions

Lipid nanoemulsions

Disadvantages

Mucoadhesive and permeationenhancing properties Burst effect FDA approved, biodegradable, biocompatible

Biodegradable, FDA approved Form non-covalent complexes with nucleic acids (polyplexes) Charged molecules

Targeting ligands nontoxic, nonimmunogenic, biocompatible, biodegradable

Cytolytic peptides

Silk fibroin

Inorganic NPs

PEG, targeting ligands

Advantages

Chemotherapeutics, nucleic acids, biological drugs

Hydrophilic, lipophilic

Anti-cancer drugs

Biocompatible, slowly biodegradable Well-established Potential chemistries diagnostic and therapeutic systems, hyperthermia 100% drug loading Thermodynamic stability, optical clarity, ease of preparation Cell/tissue targeting, barrier permeability (continued overleaf )

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Table 16.3 (Continued) Nanocarriers

Drug

Functionalization

Selfnanoemulsifying drug delivery systems (SNEDDSs)

Hydrogels (self-regulated hydrogels)

Insulin

Polymer/protein Anti-cancer therapy conjugates

Immunoconjugates

(Glucosesensitive moiety to control swelling and de-swelling) [33]

Advantages

Disadvantages

Spontaneously form nanoemulsions upon mixing with water/or gastrointestinal fluids, can be filled into gelatine capsules for oral delivery SR release Fast drug release

Reduced toxicity, prevention of immunogenic, or antigenic side reactions, enhanced blood circulation times Improved targeted accumulation in pathological sites while decreasing its undesirable side effects in healthy tissues [31]

A limited number of drugs can be attached to the Ab [31]

Based on [23].

lesion relative to healthy tissues, remote controlled or tumor stimuli-sensitive extravasation from blood at the tumor’s vicinity, internalization motifs to move from tumor bounds, and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing [30]. To date, several distinct therapeutic NP platforms have been approved for human use or entered clinical development for disease therapy (see Table 16.4 and Figure 16.3). Despite the success of the liposome, albumin NPs and micelle systems in the clinic, their wide medical applications have been hindered due to the lack of sustained release and compatibility with diverse pharmaceutically active molecules (e.g., broad range of small molecules, proteins, and nucleic acids). On the other hand, the combination of targeted and controlled-release

16.3

Drug Delivery

Table 16.4 Clinically approved NP-based therapeutics and their benefits and risks. Formulation

Application

Benefits

Potential risks

Liposomal amphotericin B

Antifungal

Decrease of toxicity, increase treatment success

Hypersensitivity reactions to liposomal drugs emerging from complement activation-related pseudoallergies

Liposomal daunorubicin

Cancer therapy (HIV-related Kaposi’s sarcoma (KS), leukemia)

Liposomal doxorubicin

Cancer therapy (metastatic breast cancer) Cancer therapy (metastatic breast cancer, ovarian cancer, HIV-related KS) Neovascularization

Increase drug concentration at the site of KS lesions, escape multi-drug resistance Decrease of cardiotoxicity, total retention of activity Less frequent dosing Skin toxicity in areas of vitilgo related to pegylated schedule and liposomal doxorubicin reduction in cardiotoxicity for breast cancer First and only drug therapy approved for treatment of macular degeneration Reduction of neurotoxicity, less frequent dosing schedule Less frequent dosing schedule and delaying neurological progression) 100% seroprotection in infants/children, increase in immunogenicity

Liposomes

Liposomal-PEG doxorubicin

Liposomal verteporfin

Liposomal vincristine

Cancer therapy (non-Hodgkin’s lymphoma)

Liposomal cytarabine

Cancer therapy (neoplastic and lymphomatous meningitis)

Liposomal immunopotentiating reconstituted influenza virus (IRIV) vaccine Liposomal morphine

Antiviral (Hepatitis A, influenza)

Postsurgical analgesia

Increase in analgesia for hip arthroplasty

Polymers

PEGylated formation

Less frequent dosing PEGylation is well tolerated Cancer therapy (acute lymphoblastic schedule leukemia) (continued overleaf )

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Table 16.4 (Continued) Formulation

Application

Benefits

Cancer therapy (acromegaly) Cancer therapy

Increase in half-life of clearance Increase of serum half-life

Potential risks

Liposomes

PEGylated formation PEGylated formation PEGylated formation PEGylated formation

Poly(alylamine hydrochloride)

Immunosuppresion Anemia (anemia treatment with associated chronic kidney disease) Antiviral (Hepatitis B, C) Macula treatment (age-related macular degeneration) Inflammation (Crohn’s disease) Immunomodulator (multiple sclerosis) Chronic kidney disease

Colesevelam hydrochloride

Anti-diabetic (type 2 diabetes)

PEGylated formation PEGylated formation

PEGylated formation Glu-Ala-Tyr copolymer

Less frequent dosing schedule

Longer half-life, reduced clearance First available ophthalmic anti-VEGF agent

PEGylated proteins possibly trigger antibody formation against PEG, leading to accelerated clearance

Detection of PEG antibodies in patient treated with PEG-asparaginase

Less frequent dosing

Reduction in mortality for elderly people, decrease in bone disease, vascular calcification

Iron NPs

SPIONS

Imaging (liver, gastrointestinal)

Iron oxide based

Anemia

Dextran-coated SPIONS complement activation and further clearance by the liver or spleen

Other platforms

Albumin-bound paclitaxel Nanocrystalline Nanocrystalline

Cancer therapy (metastatic breast cancer) Antiemetic (brain targeting) Antihyperlipidemic

Increase of response efficiency, decrease of toxicity Increase of bioavailability Increase of bioavailability

16.3

Drug Delivery

323

Table 16.4 (Continued) Formulation

Application

Benefits

Potential risks

Immunosuppressant Antianorectic

Increase of bioavailability Increase of bioavailability

Other platforms

Nanocrystalline Nanocrystalline Emulsions

Menopause treatment

Adapted from [35]. Liposomes

Targeted PEGylaled liposomes

1960s 1976

Controlledrelease polymeric systems

1980 1978

Dendrimers

DOXIL

Abraxane

1995

PLGApolyethylene glycol (PEG) NPs

Figure 16.3 Historical timeline of clinical-stage NP technologies. Liposomes, controlled-release polymeric systems for macromolecules, dendrimers, targetedPEGylated liposomes, first FDA-approved liposome (DOXIL), long-circulating PLGAPEG NPs, iron oxide MRI contrast agent NP

2005 1996

1994

Ferumoxide

CALAA-01

BIND-014

2008

2011

2007

Genexol-PM

SEL-068

(ferumoxide), protein-based DDS (Abraxane; nab technology), polymeric micelle NP (Genexol-PM), targeted cyclodextrin-polymer hybrid NP (CALAA-01), targeted polymeric NP (BIND-014; Accurint Technology), and fully integrated polymeric NP vaccines (SEL-068, tSVPt Technology) [25].

polymer NP technologies has recently resulted in the clinical translation of BIND-014 (i.e., targeted polymeric NPs) for cancer treatment [25, 34]. 16.3.2 Novel Design Considerations

Over the past decades, a variety of spherical nanocarriers (e.g., liposomes, micelles, NPs, polymer-drug conjugates), synthesized by “bottom-up” approaches, have shown promising results as potential drug delivery vehicles. Extensive studies have revealed the effect of particle size on nanocarriers’

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circulation, extravasation, and distribution in vivo. In contrast, the importance of particle shape has only recently begun to emerge. For example, disc-shaped NPs have demonstrated higher in vivo targeting specificity to endothelial cells, expressing intercellular adhesion molecule receptors in mice than spherical particles of similar size. he effect of nanocarriers shape on biological functions has led to the development of multiple shape-specific particulate platforms for nanomedicine applications [36, 37]. Advancements in nanofabrication processes (e.g., step and flash imprint lithography, particle replication in non-wetting templates, solvent molding-based fabrication) have generated the potential for producing uniform NPs of precise shape and size. Such top-down fabrication methods can provide precise, pre-designed control over particle geometry (shape, aspect ratio) and composition, which is often difficult to achieve using bottom-up approaches that tend to rely on emulsions or self-assembly [38]. Effective drug delivery requires successful navigation of carriers through complex biological paths in the body. Hence, control of particle properties (e.g., size, surface chemistry, shape) in real time provides temporal control over their interactions with cells or subcellular compartments. Particles with changeable size, surface chemistry, and shape have been recently developed and their benefits have been already demonstrated in vitro and in vivo. Recent studies have also shown the significance of additional properties such as internal architecture and mechanical flexibility in the function of drug carriers [39]. Indeed, the value of tailoring these parameters with the purpose of minimizing toxicity, unfavorable interactions with the immune system, rapid renal clearance, and accumulation in organs such as the liver and spleen is beginning to be more systematically recognized and increasingly adopted [25, 40]. 16.3.3 Theranostics

he term theranostics indicates an integrated nanotherapeutic system which can diagnose, deliver targeted therapy, and monitor the response to therapy. It is assumed that the combination of diagnosis and therapy could result in the acceleration of drug development, improved disease management, reduced risks and cost [4], and more personalized treatment [41, 42]. Multifunctional NPs have been designed as nanocarriers for simultaneous delivery of therapeutic and imaging agents in vivo [43–45] (Figure 16.4). he ideal theranostic NP should selectively and rapidly accumulate in diseased tissue, report biochemical and morphological characteristics of the area, deliver a noninvasive therapeutic, and degrade without toxic by-products. Although NPs have been FDA approved for clinical use as transport vehicles for nearly 15 years, full translation of their theranostic potential is incomplete. Still, remarkable successes with NPs have been realized in the areas of drug delivery and MRI. Emerging applications include image-guided resection, optical/photoacoustic imaging (PAI) in vivo, contrast-enhanced ultrasound (US), and thermoablative therapy [46]. Table 16.5 presents examples of theranostic NPs currently in clinical and pre-clinical studies.

16.3

(a)

(b)

Liposome or micelle encapsulation

Imaging

Therapy Thermal therapy GNP and MNP

+

Photoacoustic imaging GNP and MNP

− +

+ +

−

−

+ +

−

Photodynamic therapy UCNP Radiation therapy HfO

X-ray computed tomography GNP

− − +

Mesoporous silica coating

Magnetic resonance imaging MNP Optical imaging GNP, MNP, QD, and UCNP −

Drug Delivery

Targeting ligand − +

−

+

Drug molecule

−

+

+ −

−

+

− +

Radiotracer

−

Flurophore Layer-by-layer assembly

(c)

Surface modification

siRNA

(d)

Figure 16.4 Schematic diagram of multifunctional NPs. Four typical coatings developed for inorganic nanocrystals are (a) liposome or micelle encapsulation, (b) mesoporous silica coating, (c) LbL assembly, and

(d) surface conjugation. Abbreviations: GNPs, gold nanoparticles; HfO, hafnium oxide; MNPs, magnetic nanoparticles; QD, quantum dot; UCNPs, upconversion nanoparticles [45].

In the past decade, we have seen tremendous attention and effort focused on the development of novel DDS to circumvent the BBB (Figure 16.5) in seeking effective drug therapies for brain pathologies such as brain tumors and lysosomal storage disorders with neurological involvement [47, 48]. Ideally, the treatment for a brain disease should be constantly monitored and modulated. he idea of using magnetic or bubble-filled and drug-loaded nanocarriers, in combination with MRI and US, may provide a solution for achieving both the diagnosis and treatment purposes [47]. 16.3.4 Administration Routes

Macromolecular drugs have the unique power to tackle challenging diseases, but their structure, physicochemical properties, stability, pharmacodynamics, and

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Table 16.5 Examples of theranostic NPs in clinical and pre-clinical studies. NP Type

Therapeutic Agent

Diagnostic Agent Disease State

Target

Iron oxide

Anti-EGFRIgG

Iron oxide

Brain cancer

Epidermal growth factor receptor (EGFR)a)

Silica Liposome

Paclitaxel Paclitaxel

Iron oxide pH-responsive membrane

Folic acid EPR

Gold nanorod QD

Heat Doxorubicin

Thermal/CT QD

Many Ovarian cancer/many types Many Prostate cancer

Cyclodextrin

RNAi

Transferrin

Melanoma

Gold nanoshell (Aurolase) Silica Iron oxide

Nanoshell Nanoshell (MR (photothermal) and optical) cyclic RGD (cRGD) Injected cell Iron oxide (Endorem) Tumor necrosis Gold NP factor

Transferrin receptor EPR

Pre-clinical

EPR PSMAb)

Clinical

Gold

Head and neck cancer Melanoma Healthy volunteers Solid tumors

avB3Integrin None EPR

a) Epidermal growth factor receptor. b) PSMA, prostate-specific membrane antigen. Adapted from [46].

pharmacokinetics place stringent demands on the way they are delivered into the body (e.g., inability to cross mucosal surfaces and biological membranes). Carrier-based DDSs can diminish the toxicity of therapeutic biomolecules, improve their bioavailability, and make possible their administration via less invasive routes (e.g., oral, nasal, pulmonary, etc.). At present, protein drugs and antigens are usually administered parenterally (i.e., by subcutaneous or intramuscular injections as well as intravenous infusions), but this route is less pleasant and also poses problems of oscillating blood drug concentrations. In addition, the short biological half-lives of protein- and peptide-based drugs (P/P drugs), usually in the range of few hours, necessitate in some cases multiple injections per week that cause considerable discomfort to the patients, especially when long-term or chronic treatment is necessary. A prominent example is the treatment of diabetes mellitus by insulin, where patient compliance and long-term complications are closely associated. hus, a lot of research efforts have been undertaken regarding the replacement of injection therapy by non-parenteral delivery of protein drugs and vaccines via the development of efficient nanocarrier-based mucosal (e.g., oral, nasal, etc.) delivery systems [49]. Despite the significant barriers (i.e., chemical, enzymatic, and penetration related) to drug delivery in the gastrointestinal tract (GIT), the oral route [50]

16.3 Paracellular aqueous pathway Water-soluble agents

Drug Delivery

327

Transcellular Transport proteins Efflux lipophilic pumps pathway

Receptor-mediated transcytosis

Adsorptive transcytosis

Cell-mediated transcytosis

Lipid-soluble Glucose, amino acids, agents nucleosides

Insulin, transferrin

Albumin, other plasma proteins

Monocytes Liposomes

Blood Tight junstion

Endothelium Continuous membrane

Brain Pericyte Perivascular macrophage

Liposomes Monocytes Astrocyte

Microglia

Neuron Neuron

Neuron

Figure 16.5 Transport routes across the BBB. Pathways (a) to (f ) are commonly for solute molecules; the route (g) involves monocytes, macrophages, and other immune cells and can be used for any drugs or drug-loaded liposomes/NPs [47].

continues to be the most intensively studied for P/P administration. he interest in the oral route is well appreciated by considering its obvious advantages (e.g., ease of administration without requiring sophisticated sterile manufacturing facilities and/or the direct involvement of health-care professionals, large patient acceptability, etc.). Currently, a number of formulations of P/P drugs are in clinical trials [49]. Inhaled medications have been available for many years for the treatment of various lung diseases. hey are widely accepted as being the optimal route of administration of first-line therapy for asthma and chronic obstructive pulmonary diseases [23]. Administration of drugs via the pulmonary route can be achieved using nebulizers, metered dose inhalers (MDIs), and dry powder inhalers (DPIs) [51] containing nanostructures such as liposomes, micelles, NPs, and dendrimers. In the past decade, a lot of effort has been placed in the development of inhalable insulin formulations. However, due to the market failure of Exubera (i.e., a rapidly acting inhalable insulin manufactured by Pfizer in collaboration with Nektar herapeutics), most of the developed inhaled insulin formulations were discontinued, by March 2008 (NanoBioPharmaceutics, Pulmonary Delivery: Assessment Report, CPERI/CERTH, 21.03.2008, unpublished data). Nasal delivery has been also recognized as a very promising route for delivering therapeutic compounds, including biopharmaceutics (Table 16.6). Additionally, the soft palatal mucosa has been found to be a convenient, easily accessible novel site for the systemic delivery of therapeutic agents [52]. he use of nanotechnology is also being investigated for several different ophthalmic applications for the treatment of posterior segment disorders via

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Table 16.6 Marketed nasal formulations [53]. Company

Sanofi-Aventis Novartis Unigene’s laboratories/Upsher-Smith Laboratories, Inc. Ferring Pharmaceuticals, Inc. Sanofi-Aventis Sanofi-Aventis

Product

Description

® Miacalcin® Fortical®

Nasal formulation of LHRHa)

Kryptocur

Desmospray

Nasal spray of salmon calcitonin Nasal spray of salmon calcitonin

®

Suprecur Suprefact

Nasal desmopressin (analog of 8-arginine vasopressin (ADH)) Buserelin (LHRH agonist) Buserelin (LHRH agonist)

a) LHRH, Luteinizing-hormone-releasing hormone.

NPs-based drug and gene delivery to the target tissue [54]. In addition, nanocarrier-aided dermal/transdermal delivery are in the center of attention and are expected to be increasingly applied. In both cases, the stratum corneum (SC), the main barrier of the skin, has to be overcome [55]. Finally, intravaginal microbicide delivery systems are providing a new option for preventing the transmission of sexually transmitted infections (STIs) and (immunodeficiency virus) HIV [56]. 16.4 Regenerative Medicine

Regenerative medicine (RM) is an emerging multidisciplinary field that aims to restore tissues and hence organ functions applying tissue engineering (TE) and cell therapy. Regeneration of tissues can be achieved by the combination of living cells (ideally stem cells), which provide biological functionality, and various types of materials, which act as scaffolds to support cell proliferation [57]. he application of nanomaterials to RM has gained a lot of interest in recent years, partly due to the realization that control of cellular behavior, and therefore optimal tissue regeneration, can be achieved by the provision of an appropriate nano–bio interface. As compared to scaffold-free cell delivery, nanomaterials are advantageous in terms of providing a means to control the biochemical and mechanical microenvironment of the cells [58, 59]. Nanomaterials used in RM are usually fabricated by bottom-up (e.g., polymeric and inorganic NPs, CNTs, dendrimers, QDs, layer-bylayer (LbL) structures) and top-down (e.g., nanopatterned substrates) approaches (Figure 16.6) [60]. Beyond the advanced areas of orthopedics (e.g., implant and prosthetic design) and wound healing [61], others, such as the regeneration of cardiac, spine, and neural tissue [62], are still in their infancy and numerous challenges remain to be overcome before they can become a clinical reality. Suitable cell sources need

16.4

Regenerative Medicine

329

(a)

Polymeric/inorganic nanoparticles

Cell motif/peptide/ probe/drug-modified nanoparticles

Quantum dots

Dendrimers

(b)

Carbon nanotubes and nanofibers

Irradiation

Press Mas

Dip-pen nanolithography

Develop

Remove Transfer pattern

Inkjet printing

Photolithography

Nanoimprinting

Layer-by-layer structures

Resist Substrate

Ph

Writing direction Water meniscus

Self-assembled peptide nanofibers

Colloidal lithography

Electron beam resist layer Substrate Electron beam lithography

Figure 16.6 (a) Bottom-up and (b) top-down approaches for the production of nanomaterials [60].

to be identified and the rules governing cell growth and differentiation on biomaterials need to be understood [3, 63]. Nano-assisted RM has the potential to create a paradigm shift in the health-care systems of tomorrow by aiming at two major objectives: first, leveraging the self-healing potential of endogenous stem cells by identification of signaling systems and second, developing efficient targeting systems for stem cell therapies, thus aiming to trigger endogenous self-repair mechanisms rather than just managing or palliating the symptoms. he future research will thus aim at understanding the mechanisms of stem cell recruitment, activation, control, and homing with the help of nanomaterials in various forms, such as NPs, nanofibers, and CNTs. Of huge impact would also be the ability to implant cell-free, intelligent, bioactive materials that would effectively provide signaling to utilize the self-healing potential of the patient’s own stem cells [60]. 16.4.1 Tissue Engineering

he goal of TE is the in vivo or alternatively the in vitro regeneration of a complex functional organ consisting of a scaffold made of synthetic or natural materials that have been loaded with living cells (Figure 16.7) [57]. Human tissues are intricate ensembles of multiple cell types embedded in complex and well-defined

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Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine 3D structure with interconnected porosity

Zoom 1 Bioreactor

Zoom 2

In vitro regeneration of the tissue Porous scaffold + In vitro implantation

Cells

Nanoparticles entrapped into the scaffold for the controlled delivery of growth factors, drugs, DNA, and and so on.

Biomolecules immobilized to enhance cell functions (RGD peptides, adhesive proteins, and so on) TRENDS in Biotechnology

Figure 16.7 TE approach for tissue regeneration [57].

structures of the extracellular matrix (ECM). he organization of ECM is frequently hierarchical from nano to macro, with many proteins forming large-scale structures with feature sizes up to several hundred microns [64]. Nanofibrous materials that mimic the native ECM and promote the adhesion of various cells are being developed as tissue-engineered scaffolds for the skin, bone, cartilage, vasculature, heart, cornea, nervous system, and other tissues. A range of novel materials has been developed to enhance the bioactive or therapeutic properties of these nanofibrous scaffolds via surface modifications, including the immobilization of functional cell-adhesive ligands and bioactive molecules such as drugs, enzymes, and cytokines [65, 66]. As a new approach, nanofibers prepared by using industrial-scale needleless technology have been recently introduced, and their use as scaffolds to treat spinal cord injury or as cell carriers for the regeneration of the injured cornea is the subject of various current studies [65]. In addition to surface chemistry, nanotopography dictates initial protein adsorption and bioactivity as well as subsequent cellular adhesion [67]. Nanotopography-guided approaches have been increasingly investigated, especially in applications in which guiding the cell orientation is essential to achieve a functional tissue [57, 64]. Results demonstrate that the nanotopography itself can activate tissue-specific function in vitro – for example, protection (skin), mechano-sensitivity (ligament/tendon, bone), electro-activity (heart, skeletal muscle, neurons), and shear stresssensitivity (blood vessels) – as well as promote tissue regeneration in vivo upon transplantation presumably due to nanotopographical guidance and better cell-to-cell communications [64]. A better understanding of the interactions between cells and nanoscale surfacing is expected to advance the field of TE [68]. he nanofabrication methods that have been developed to mimic complex and well-organized ECM structures in vitro can be classified into template-assisted

16.4

Regenerative Medicine

Table 16.7 Potential cell sources for cell therapies [74]. Source

Definition donor/recipient

Autologous

Same individual

Allogenic Xenogenic Syngenic or isogenic

Drawbacks

Not always available (genetic diseases, age) Same species Immunological issues Different species Ethical issues and rejection Genetically identical Most appropriate for research individuals (clones, inbred) with animal model

Origin/di erentiation

Primary Secondary Embryonic stem cells induced pluripotent stem cells (iPSCs) Adult stem cells

Tissue or organ/specialized Large expansion needed Cell bank Cryopreservation/immunological issues Undifferentiated Ethical issues/purification/teratoma Committed

Selection of type/source

(e.g., replica molding (RM), nanoimprint lithography (NIL), microcontact printing (μCP), electrochemical deposition, etc.) and template-free (e.g., E-beam lithography, direct laser writing, salt leaching/gas foaming, electrospinning [69–71], etc.) methods [64]. Despite the great potential of the nanotopographyguided approach, there are a number of limitations for clinical applications, including the lack of ability to create 3D, highly organized structures for ECMs, the difficulty to prepare highly ordered nanoscale features over a large area, and the fact that an optimal nanostructure for a certain cell type is not necessarily optimal for another cell type [64]. Recently, structures (e.g., well-ordered nanofibers, nanotubes, and nanovesicles) based on chiral self-assembly peptides have been used for 3D tissue cultures of primary cells and stem cells, sustained release of small molecules, growth factors and monoclonal Abs, accelerated wound healing in reparative and regenerative medicine, as well as TE. It should be mentioned that one of such self-assembling peptides has been already used in human clinical trials for accelerated wound healings [72]. 16.4.2 Cell Therapies

Cell therapy refers to the process of introducing new cells (Table 16.7) into a tissue in order to treat various diseases or injuries. It utilizes transplanted cells, in particular stem and progenitor cells, to replace or regenerate damaged or diseased tissue (i.e., bone marrow transplant performed on leukemia patients, autologous cultured chondrocytes for the treatment of cartilage defects). Transplanted cells may home to diseased tissue, regenerate tissues through (trans)differentiation, and/or provide regenerative cues that facilitate regeneration through trophic factors and cell–cell interactions [73]. Promising approaches include stem cell transplants for

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Isolation

Biopsy

(a)

(b)

Cell-secreted factors

Isolated cells

(c)

Engineered tissue

(d)

In vitro

Cell expansion and differentiation

Functionalized matrix

In vivo

Intracoronary injection

Myocardial infarction

Intramyocardial injection

Epicardial implantation

Figure 16.8 Cell therapy approaches for myocardial infarction [74].

myocardial infarction (Figure 16.8) [74] and neurodegenerative disease, and dendritic cell vaccinations for cancer therapy. Recently, cardiac stem cells have been discovered, thus challenging the dogma that adult heart does not regenerate [74]. Currently, thousands of clinical trials around the world involve some form of cell therapy. While pre-clinical results have been very promising, few approaches have been translated into humans. his is likely in part due to the lack of a comprehensive understanding of the fate of transplanted cells, their distribution after injection, and the level of engraftment in local microenvironments. Traditionally, monitoring of therapeutic cells is conducted by histological analysis, which is laborious and invasive, requiring multiple tissue biopsies. Noninvasive imaging methods are urgently needed for qualitatively and quantitatively monitoring transplanted cells to understand their fate and function, which will facilitate prediction of treatment efficacy, reveal optimal transplantation conditions, including cell dose, delivery route, and timing of injections, and ultimately improve patient treatment. Recently, approaches using available imaging techniques, particularly optical imaging, MRI, and radionuclide imaging, have been utilized for tracking transplanted cells. NPs-based contrast agents have also received enormous attention for cell tracking due to their unique properties [66, 73]. Current techniques

16.5

Personalized Medicine

333

for cell tracking include fluorescence tracking with QDs, MRI tracking using magnetic NPs, and PET imaging with radioisotope containing NPs [73]. 16.5 Personalized Medicine

Recent advances in nanotechnology adequately address many of the current challenges in biomedicine. However, to advance nanomedicine, there is an urgent need for personalized treatments which require the combination of nanotechnological progress with genetics, molecular biology, gene sequencing, and computational design [75]. Personalized nanomedicine (Figure 16.9) could be defined as the management of a patient’s disease or drug response by combining nanotechnology with clinical and molecular knowledge (e.g., genomics, proteomics, epigenomics, and metabolomics) as well as bioinformatic tools to achieve the best possible medical outcome for that individual [76]. Advances in nanotechnology are enabling the nanofabrication of nanoscale biomaterials and nanosensor devices which are expected to significantly facilitate diagnosis and personalized medical therapies through minimally invasive procedures. Further optimization of nanobiomaterial systems will eventually result in a technology which will be based on a kit that a patient can operate from home. Such a nanobiomedical device will allow, for instance, the encapsulation and controlled release of therapeutic molecules Multidisciplinary experimental approaches Biomaterials Nanomaterials

Artificial tissue and organs

HTS Molecular Genomic Innovative Bioinformatics diagnostics technologies drug targets Assays Nanoinformatios

Nanomedicine

Imaging technologies

Translational medicine

Clinical validation

Advanced cell therapies Pharmacogenomics

Nanotechnology

Personalized Nanoscale clinical systems

Practical clinical utility

Targeted nanodelivery drug systems

Drug development and delivery

Nanomedicine

Innovative drugs

Patient stratification for individualised therapy Improved clinical and drug delivery outcomes

Figure 16.9 Schematic overview of personalized nanomedicine [76].

Pharmacotyping

Maximum safety

Maximum efficacy

Disease prognosis and diagnosis

Drug-related disciplines

Personalized medicine

Health-related disciplines

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Nanotechnology Advances in Diagnostics, Drug Delivery, and Regenerative Medicine

identified through genomic screening of the specific patient [75]. Complementary to this, personalized nanomedicine could create improved profiles for specific populations and individual patients for prognosis, diagnosis, and therapy [76]. Clinical application of nanotheranostics would enable earlier detection and treatment of diseases and earlier assessment of the response, thus allowing screening of patients who would potentially respond to therapy and have higher possibilities of a favorable outcome and elaborating personalized therapeutic protocols for achieving the maximal benefit along with a high safety profile [77].

16.6 Conclusions – Future Challenges

As the field of nanomedicine evolves, a wide range of innovations impact nearly every medical specialty (e.g., internal medicine, orthopedics, ophthalmology, dentistry, etc.). Nanotechnology’s applications in surgical oncology include tumor localization, tumor margin detection, identification of important adjacent structures, mapping of sentinel lymph nodes, and detection of residual tumor cells or micrometastases via nanoimaging [78] as well as nanocarrier-aided targeted delivery of anti-cancer drugs. With respect to cardiovascular science, nanotechnology developments comprise among others nanofiber-based scaffolds for vascular grafts mimicking the structural properties of the endothelium, nanostructured drug-eluting stent coatings with improved biocompatibility, thromboresistivity and enhanced vascular healing, and functional heart tissue constructs [79]. Nanostructured scaffolds with enhanced material–cell interaction for bone and cartilage repair are important nanotechnology applications in orthopedics. Nanostructured scaffolds have been also used for the growth of human dermal fibroblasts (e.g., cases of chronic wounds such as diabetic ulcers or burns), and wound dressings containing silver NPs have been used with excellent results against gram-positive and gram-negative bacteria. Monitoring of intraocular pressure for glaucoma management using a nanosensor embedded in a contact lens [80] and scaffolds for delivery of stem cells to replace defective retinal pigmented epithelial cells in age-related macular degeneration [81] are nanotechnology applications in ophthalmology together with the treatment of choroidal new vessels using NPs, treatment of oxidative stress, prevention of scaring after glaucoma surgery, and so on [80]. Nanotechnology advances in the field of dentistry include dental implants with nanostructured surface-enhancing osteoblast adhesion, implementation of NP technology into restorative materials with superior esthetic features, nanocomposite-based artificial teeth, treatment of periodontal diseases with DDS, and so on [82]. Nanoendoscopy has been introduced with the PillCam capsule endoscope, which allows peristaltic movement of a video-camera capsule down to the gut to produce intermittent imaging of the small intestine. A pill-sized camera could potentially be also used to replace the existing and much more invasive colonoscopy [83]. Beyond the current nanotechnology applications lies the promise of surgical operations using

References

nanorobots introduced into the body through the vascular system, development of a nanoneedle that can be accurately inserted into the nucleus of a cell without causing fatal damage, hemostasis during surgery using peptides that self-assemble into a nanoscale protective barrier that seals the wound and stops bleeding in

CS-N > CS > bare substrate (BS). After 7 days of immersion, barrier property of both CS and CS-N was reduced considerably compared to CS-NI. he coatings modified with inhibitor-loaded nanocontainers showed highest values of impedance mode for the region of time constant associated to sol–gel coatings properties and for the low-frequency region. his suggests that the hybrid coatings modified with inhibitor-loaded nanocontainers render active corrosion protection keeping the value of the impedance at low frequency almost constant.

19.4.4 Superhydrophobic Engineering Surfaces for Corrosion Mitigation

he lotus leaf [37] is a famous example of a naturally occurring superhydrophobic (SHP) surface, where water droplets falling onto them bead up and roll off. hese rolling droplets pick up small particles of dirt so that the lotus leaves are self-cleaning, which is the so-called lotus effect. Surface whose contact angles exceed 150∘ are known as SHP surfaces. he advent of nanotechnology has ended SHP coatings in numerous real-life applications. Self-cleaning glasses, clothes, anti-snow sticking, monument protection [38–40] are some of the applications of SHP surfaces. Surface energy and surface roughness are the two dominant factors for wettability which determine the water contact angle on the surface. When the surface energy is lowered by the incorporation of apolar groups on the metal surface, the hydrophobicity is enhanced. Motivated by the lotus effect in nature, a simple and novel approach has been developed for the SHP surface modification of titanium [41–43] and 9Cr-1Mo ferritic steels [44]. Titanium is used as condenser material for seawater applications in nuclear power plants and dissolver vessel in nitric acid environment of spent nuclear fuel reprocessing plants. here is a constant need to increase the corrosion resistance properties of titanium for prolonged service. In addition, titanium faces an unresolved problem of biofouling in seawater applications owing to biocompatibility concerns and surface hydrophilicity. Modified 9Cr-1Mo ferritic steel is widely used as a structural material for steam generator applications in thermal and nuclear power generations. Prolonged time lag is experienced during storage, fabrication, commissioning, and installation stages of the large projects. During this inevitable period, these materials are exposed to coastal atmosphere and are prone to general and localized corrosion. hus, generating “SHP” surface with water repellency is an attractive option to prevent and delay the onset of corrosion processes at the surfaces of engineering components in natural atmosphere. SHP titanium and SHP 9Cr-1Mo steel are obtained by creating micro-nano-roughness using anodization/chemical etching, followed by dip coating in low surface energy materials.

19.4

Intelligent Coatings for Corrosion Mitigation

19.4.5 Superhydrophobic Surface Modification

SHP titanium was made by employing anodization followed by coating with a low surface energy material. Anodization provides the required surface roughness, and low surface energy material coating provides the surface repellency. Coating after anodization with higher fatty acids such as myristic or stearic acid or silane as the low surface energy material generates the desired surface features and properties. here is a phenomenal increase in the order of superhydrophobicity as the low surface energy material is changed from myristic acid to stearic acid to silane. he wetting properties of the samples were elucidated using contact angle meter which showed contact angle around 150∘ and the water just rolled off the surface with a tilting angle of less than 5∘ . SHP 9Cr-1Mo steel was fabricated by etching the samples and coating with silane, the samples showed contact angles as high as 150∘ . SEM image of SHP surfaces show micro-nano-projections which increase the effective surface area [45] and enable the titanium surface to give high contact angle. It is believed that the gaps between the projections act as valleys [46], where air gets trapped so that water minimizes contact area with the surface leading to an increase in the contact angle as shown in Figure 19.3.

Figure 19.3 SEM micrograph of SHP 9Cr1Mo steel. Inset shows (a) the AFM (atomic force microscopy) image of the surface, (b) Nyquist plot of superhydrophobic coated

and uncoated 9Cr-1Mo steel in 0.01 M NaCl, and (c) water contact angle of 150∘ on the SHP surface.

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(a)

(b)

μm

μm

16

2 1 0 20

12 8

15 10

4 5

AFM study

Water contact angle > 150°

0

(c) –600000

(d)

Uncoated SHP coated

–500000

Z” (Ω cm2)

–400000 –300000 –200000 –100000 0 0

100000

200000 300000 Z’ (ohm cm2)

400000

‘‘Zero’’ microbial activity

High impedance for SHP coating

1 μm

EHT = 20.00 kV WD = 10.8 mm

Signal A = SE2 Photo No. = 6176

Mag = 6.00 K X Date :22 Feb 2011 Time :10:15:44 Vacuum mode = High vacuum

Figure 19.4 SEM micrograph of SHP titanium. Inset shows (a) the 3D AFM (atomic force microscopy) image of the surface, (b) water contact angle of 150∘ , (c) Nyquist

ZEISS

plot of SHP and polished titanium in 1 N HNO3 , and (d) epifluorescence micrograph of SHP titanium with no microbial attachment.

he SHP titanium and 9C-1Mo steels are well characterized and the results are consolidated in Figures 19.3 and 19.4.

19.4.6 Superhydrophobic Surfaces with Enhanced Corrosion Resistance

To examine the stability of the SHP coating, the change in corrosion resistance with immersion time in the corrosive environment was studied by immersing the surface-modified titanium samples in 1 N HNO3 for 30 min, 24 h, and 72 h. he corresponding EIS results demonstrate that with increase in immersion time, the corrosion resistance reduction is negligible and therefore, the coatings are stable in the HNO3 environment. Similarly, SHP 9Cr-1Mo steel also show good corrosion resistance in chloride medium. In order to check the stability of the coatings, the Ti and 9Cr-1Mo steel samples, were immersed in 1 N HNO3 and seawater

19.5

Nano-structured Coatings for Energy Technologies

for 15 days, respectively. he contact angles measured after the immersion tests were on an average 5–10∘ less as compared before immersion condition thus revealing reasonably the stability of the coatings. Further work needs to be carried out to realize applications. Antifouling activity of SHP titanium was evaluated by exposure studies in 10% nutrient broth culture of slime-forming Pseudomonas sp., a predominant biofilm former on titanium surfaces. SHP titanium samples were exposed for about 24 h and the samples were stained and observed under an epifluorescence microscope. SHP titanium surfaces showed “negligible microbial attachment” compared to the polished titanium samples. It is reported that the SHP coatings lower the free energy of surfaces [47]. Hence, microorganisms could not adhere firmly to such low-energy surfaces and got cleaned off at the slightest movement of surrounding media.

19.5 Nano-structured Coatings for Energy Technologies

Engineering applications are critically dependent on surface coatings. Major beneficiaries include power generation, automotive, and aerospace sectors, though there is hardly any application which does not consider surface tailoring to enhance performance. For example, biomedical community too uses surface engineering tools to enhance performance in a big way and for surgical tools. Surface coatings, on the one hand, rely on surface analysis and surface science methodologies for characterization, evaluation, and validation. On the other hand, principles of nanotechnology and material design are harnessed for creating tailored high-performance materials as protective coatings against vagaries of corrosion, oxidation wear, and erosion. In this context, three different materials have been extensively investigated by the authors. hese include hardoxidation-resistant TiAlN, tribology of diamond-based carbon-based materials and flame-pyrolysis-based oxidation-resistant zirconia coatings. A glimpse of all these studies is given. 19.5.1 Studies on Titanium Aluminum Nitride (TiAlN)

Transition metal nitrides display high hardness, metallic conduction, and structural stability arising out of d–d orbital interactions. In this context, state-of-the-art nitride thin films were synthesized by microstructural and compositional design to achieve the requirements [48]. TiN is one among the strong candidates for the above applications requiring high hardness, corrosion resistance, and relatively high conductivity. However, the stability of TiN beyond 350∘ C is poor and needs to be improved for realizing applications. Although several phases exist in TiN, the primary phase crystallizes in the rock salt structure

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with space group Fm3m having a lattice parameter of 4.24 Å with near perfect stoichiometry. Implantation induced hardness in Ti surface to form TiN is also ideally suited for microelectronics industries [49]. Furthermore, many of these materials are mostly nonstoichiometric and have impurities or growth-induced defects, which depend on synthesis technologies. Bond strength depends on stoichiometry, vacancy concentration, and impurities in the system. A stoichiometry deviation, either under or over, exhibits a lower hardness due to poor bond strength [50]. In the nitride family, recently AlN has attracted attention in both fundamental as well as in applied research and is pursued to develop hard coatings and optical devices, respectively [51]. Since AlN has wide band gap (6.2 eV), good thermal conductivity (∼260 W/(m⋅K) –1 ) and mechanical properties (∼17 GPa), this material is expected to be a surface acoustic wave (SAW) generator and substrate to grow GaN thin films [52]. To add, in superconductor electronics, it is a good barrier material in superconductor–insulator–superconductor (SIS) junctions, since it can support a much larger current density [53]. High-density grain boundaries and defects such as dislocations generate internal stresses in thin films. Alloying addition to TiN is considered as an alternative to improve the performance above 350∘ C. An ab initio calculation on alloying addition to TiN to assess the brittle to ductile transition behavior is reported; if grain to grain boundary volume fraction (G/B) < 0.5, the material behaves in ductile manner else in brittle manner [54]. Dissociations of TiN at the interfaces and Ti diffusion into Al layer forms ordered intermetallic compounds, but Al diffuses at a much slower rate in TiN, and thus the stability increases [48]. Of many ternary nitrides, Ti-Al-N is the one widely studied due to its good oxidation resistance properties. his system has local minimum but not the lowest possible Gibbs free energy and, thus, these nitrides are in metastable nonequilibrium state. Spinodal decomposition in TiAlN is responsible to form new phases by a continuous process and the phases therefore remain coherent during separation process [55]. he importance of these coatings is attributed to superior properties such as hardness, oxidation resistance, low coefficient of thermal expansion and low friction against steel. In particular, anti-oxidation and thermal stability at high temperature and chemical stability in demanding environments make TiAlN coatings preferred ones for industrial applications. Nanoindentation hardness measured for TiAlN with different Al% exhibited an increase in hardness at 64 Al% due to spinodal decomposition (Figure 19.5). Oxygen diffusion into TiAlN system was studied by Secondary Ion Mass Spectrometric (SIMS) technique. So, the oxidation resistance of TiAlN system up to 800∘ C is good and beyond this temperature, catastrophic failure occurs due to sudden diffusion of oxygen. Figure 19.5a shows the nano-indentation hardness of TiAlN thin films as a function of Al concentration. Results for annealed and as deposited specimen are depicted. Figure 19.5b provides oxidation depth obtained from SIMS studies as a function of temperature.

19.5

Nano-structured Coatings for Energy Technologies 1200

40 35

1000

As deposited

30

800

25 20 Annealed 1073 K

15

Depth (nm)

Hardness (Gpa)

397

10

600 400 200

5

0

0 50

60

(a)

70

80

A1 %

400 500 600 700 800 900 1000 1100 1200 (b)

Temperature (°C)

Figure 19.5 (a) Nanoindentation hardness of TiAlN thin films as deposited and annealed at 1073 K, (b) Oxygen diffusion in TiAlN thin films at high temperatures.

19.5.2 Oxidation-Resistant Hard Coatings

Flame-Assisted Spray Pyrolysis and Combustion Chemical Vapor Deposition (C-CVD) were developed to synthesize nanostructured oxide coatings. Coatings/thin films of high-temperature oxides such as nanostructured alumina (Al2 O3 ) [56] and yittria-stabilized zirconia (YSZ) which are important for thermal barrier and high-temperature oxidation resistance were achieved. A laser-assisted analog was used to get localized coatings [57]. For making alumina coatings, aluminumacetylacetonate (0.005 M) in ethanol solvent was used as a precursor. A schematic of the flame pyrolysis setup is shown in Figure 19.6. his original version was customized from time to time based 9 6

7

8 2 Air 1

3

4

5

1.

Precursor

2.

HPLC pump

3.

Atomizer

4.

LPG tank

5.

Split rastor X-stage

6.

Coax. burner

7.

Flame

8.

Substrate

9.

Y-Z stage

10. Base plate

10 Figure 19.6 A schematic of the flame pyrolysis (C-CVD) apparatus.

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on synthesis requirements. A customized premixed-diffusion combination type burner with an extra coaxial oxygen inlet placed proximally at the burner mouth enabled variation of deposition temperature from 600 to 1100∘ C in steps of 100 (±10)∘ C. he presence of γ- and θ-Al2 O3 phases was observed at deposition temperatures in the range of 600 to 800 ∘ C. At higher deposition temperatures of 900 and 1100∘ C, θ-Al2 O3 and α-Al2 O3 phases could be obtained. Adherent coatings could be obtained at temperatures beyond 700∘ C. Scratch-adhesion tests revealed a critical failure load of ∼10 N. his indicated acceptable coating substrate adhesion. he coefficient of friction of alumina coated Si specimen was measured using a tribometer and it was found to depend upon surface roughness. Oxidation resistance of alumina-coated Ni–20Cr specimens were studied using a thermogravimetric analyzer by exposing the coatings to isothermal heating at 1000∘ C in 20% O2 –Ar gas mixture. he results indicated that the CSs are 18 times more oxidation resistant compared to uncoated specimens. his deposition technique was also utilized to synthesize dense YSZ thin films [58]. Zirconium(IV) 2-ethyhexanoate and yttrium(III) 2-ethylhexanoate dissolved in ethanol was used as precursors. he depositions were carried out at various temperatures ranging between 900 and 1100∘ C. he effect of yttria concentrations (0, 4, 8, and 12%) on zirconia films has been studied. he films were characterized using SEM, energy dispersive spectroscope (EDS), glancing incident X-ray diffraction (GIXRD), and micro-Raman spectroscopy. he films were found to be uniform and dense.

19.6 Super-Low Friction Ultrananocrystalline Diamond Films

Minimization in wear loss of materials is an engineering challenge manifestation. Both machine dynamics and machine performance are impeded by wear. Although lubrication is applicable in certain instances to mitigate wear losses, low-friction coatings imparting near frictionless surfaces constitute an attractive alternative. In this context, plasma chemical vapor deposited carbon-based coatings have been investigated. Carbon-based films comprise an impressively broad and continually expanding class of materials that range from the building blocks of biology to carbon allotropes with extreme properties including outstanding tribology performance under various operating conditions [59, 60]. In this material, most critical compositional variables are distribution of carbon hybridization states and hydrogen content. In this respect, tribology properties of plasma chemistry dependent ultrananocrystalline diamond (UNCD) films deposited by microwave plasma enhanced chemical vapor deposition (MPECVD) system, were carried out on silicon substrate. UNCD films synthesized with 1.5% H2 in Ar/CH4 plasma consist of a large number of clustered diamond grains with small volume fraction of grain boundaries and sp2 /a-C in the film. However, films grown in Ar/CH4 plasma shows formation of ultra-nano grains with high volume fraction of grain

19.7

Conclusions

boundaries occupied by sp2 /a-C phases. hese phases reduce shear resistance, thereby, resulting in ultra-low friction coefficient with typical value of 0.02 [61]. UNCD films were chemically modified by N+ ion implantation and subsequently annealed [62]. Friction coefficient is found to be 0.15 in as-prepared film. his coefficient decreased to 0.09 and 0.05 in N+ ion implanted and post-annealed films, respectively. Such a modification of friction coefficient is a characteristic of the transformation of sp3 to graphitized/amorphized sp2 bonded carbon network. Transformation of sp3 to sp2 carbon network causes conversion of higher surface energy state (hydrophilic) to lower (hydrophobic) one, which results in ultra-low friction coefficient. Graphitization/amorphization in wear track observed by micro-Raman spectroscopy is found to be the prominent mechanism for the reduction in friction coefficient. Moreover, super-low friction coefficient with a value ∼0.0001 was obtained in hydrogen plasma treated ultrananocrystalline diamond nanowire (DNW) films deposited by N2 -based MPECVD system [63]. It was observed that as-grown DNW films mainly consist of diamond nano-crystals with sp2 /a-C bonded grain boundaries. However, the grain boundaries do not exist after H2 plasma treatment and the film possesses large fraction of sp3 phase. Such a super-low value of friction coefficient in this film resulted from passivation of carbon dangling bonds by hydrogen content and adsorption of atmospheric H2 O molecules. he surface passivation reduces adhesive interaction with sliding counter body during tribology tests. Consequently, O2 -plasma-treated DNW film resulted in chemical and microstructural modification. Boundary of the DNW is chemically constituted by sp2 /a-C-like bonding. However, nanowires transformed into ultra-small spherical grains after the O2 plasma treatments. In this condition, sp2 /a-C bonding is significantly reduced due to plasma etching caused by oxygen atoms. he O2 -plasma-exposed DNW film exhibited surface charging and caused formation of dangling bonds. his state of material has resulted in significant decrease in contact angle and superhydrophilic behavior. he friction coefficient of this film showed super-low value ∼0.002 with high wear resistance 2×10 –12 mm3 (Nm) –1 [64]. In the reciprocating pin-on-disc tribology test, only ∼80 nm wear loss was observed after the 1 km of sliding distance at 10 N loads. Such an advanced tribology property is explained through passivation of covalent carbon bonds and transformation of sliding surfaces by weak van der Waals and hydrogen bondings. hese ultra-low wear and ultra-low friction properties are useful for several applications in machine tools and mechanical components where low friction coefficient and high wear resistance are desirable for energy efficiency and component longevity.

19.7 Conclusions

Recent research findings show that magnetic nanofluids can provide dramatic thermal conductivity enhancement (>300%) due to efficient transport of heat through the percolating nanoparticle paths under a magnetic field, paving way

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for innovations in energy applications. Since the application of magnetic field enhances not only the thermal conductivity but also the rheological properties of the magnetic nanofluid, these are promising materials for applications in smart cooling-cum-damping devices. Nanofluid-based defect sensors offer visualization of defects by naked eye. Such sensors eliminate the need for electronics devices and processing of electronic data. In brief, nanofluid-based sensors and cooling devices are promising because of their energy efficiency. he inhibitor-loaded nanocontainer-impregnated coatings are proved to be potential candidates for active corrosion protection. he hybrid coating containing inhibitor-loaded nanocontainers could effectively delay the corrosion process by releasing the loaded inhibitor molecules. Taking a clue from the “lotus effect,” the SHP titanium and chrome-moly steel surfaces of contact angle 150 ± 2∘ show better corrosion resistance in chloride as well as in nitric acid medium. Biofouling studies have revealed that the SHP titanium surface not only hates water but also repels microbial attachment. his study paves the foundation for more rigorous research to utilize the SHP surface modified materials with corrosion and biofouling resistance in several energy related industrial applications. Nanotechnology can push the energy technologies to greater pinnacle, provided new capabilities for the processing and control of nano-sized particles and structures through innovative research evolves in a sustained manner. he research should focus on development of nano-sized materials in larger industrial scale. he energy industry should take lead to collaborate with world-class researchers from different R&D and academic institutes to develop the required nanotechnology. Nanotechnology can benefit both industry and environment, and hence the government funding agencies should initiate goal-oriented research in this area. Research, Development, Demonstration, and Deployment with vectors of business solutions to unsolved challenges is an approach being favored by the authors. he involvement of young students and researchers in ecosystems of new impressive applications is impetus to bring energy and creativity in the domain of nanotechnology for energy applications.

Acknowledgements

he inputs and technical discussions during the preparation of the manuscript by Dr Tom Mathews, Dr R. Ramaseshan, Dr Niranjan Kumar, and Dr Ch. Jagadeeswara Rao of IGCAR, Kalpakkam, are acknowledged and appreciated.

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of Al2O3 and yttria stabilized zirconia nanostructured coatings. Surf. Eng., 27, 407–409. Dhonge, B.P, Mathews, T., Rajagopalan, S., Dash, S., Dhara, S., and Tyagi A.K. (2011) Cubic fluorite yttria stabilized zirconia (YSZ) film synthesis by combustion chemical vapour deposition(C-CVD). 2011 International Conference on Nanoscience, Engineering and Technology (ICONSET), IEEE Xplore, pp. 65–68, doi: 10.1109/ICONSET.2011.6167913. Novoselov, K.S., Geim, A.K., Morozov, S.V., Jiang, D., Zhang, Y., Dubonos, S.V. et al. (2004) Electric field effect in atomically thin carbon films. Science, 306, 666–9. Grierson, D.S. and Carpick, R.W. (2007) Nanotribology of carbon-based materials. Nanotoday, 2, 12–21. Sharma, N., Kumar, N., Sundaravel, B., Panda, K., Wang, D., Kamarrudin, M., Dash, S., Panigrahi, B.K., Tyagi, A.K., Lin, I.N., and Raj, B. (2011) Effect of CH4/H2 plasma ratio on ultra-low friction of nano- crystalline diamond coating deposited by MPECVD technique. Tribol. Int., 44, 980–986. Panda, K., Kumar, N., Panigrahi, B.K., Polaki, S.R., Sundaravel, B., Dash, S., Tyagi, A.K., and Lin, I.N. (2013) Tribological properties of N+ ion implantedultrananocrystalline diamond films. Tribol. Int., 57, 124–136. Sankaran, K.J., Kumar, N., Chen, H.C., Dong, C.L., Bahuguna, A., Dash, S., Tyagi, A.K., Lee, C.Y., Tai, N.H., and Lin, I.N. (2013) Near frictionless behavior of hydrogen plasma treated diamond nanowire films. Sci. Adv. Mater., 5, 1–12. Radhika, R., Kumar, N., Sankaran, K.J., Dumpala, R., Dash, S., Rao, M.S.R., Arivuoli, D., Tyagi, A.K., Tai, N.H., and Lin, I.N. (2013) Extremely high wear resistance and ultra-low friction behavior of oxygen plasma treated nanocrystalline diamond nanowire films. J. Phys. D Appl. Phys., 46, 425304–425313.

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20 The Impact of Nanoscience in Heterogeneous Catalysis Sharifah Bee Abd Hamid and Robert Schlögl

20.1 Introduction

Heterogeneous catalysis is the science and technology of changing the rates of chemical reactions. he technology is needed to produce all liquid fuels, polymers, functional materials, and artificial biological molecules. In the future, catalysis will also be needed to integrate renewable primary electrical energy in sustainable energy systems through chemical energy conversion reactions such as water splitting and CO2 reduction. his application will be much larger in dimension than all existing chemical applications together. For this reason, it is mandatory to develop the respective catalytic systems to the ultimate of their performance. In this endeavor, the exact control of surface morphology for performance and stability will be critical. his can be achieved with the help of the concepts of nanoscience to catalysis (see Figure 20.1). he present chapter aims at discussing the state of affairs in this respect without giving a detailed account on the concepts of nanostructuring themselves. Catalysis is engaged with the making and breaking of specific chemical bonds. he specificity of the process in terms of chemo- and regio-selectivity leading to economical and sustainable production processes is a sensitive function of the local electronic structure of the interaction zone of a few atoms between reactants and catalyst. From molecular catalysis, we learn that also on the mesoscopic dimension, important control is executed on the function of the molecular ensemble that we call “active site.” his occurs through molecular dynamics and noncontact interactions between the active site, the reagent, and the dynamical matrix, which being the protein shell or the weakly coordinated ligands for smaller molecules. he analog in heterogeneous catalysis where we deal with solid systems is still not clear. One dimension of nanostructuring may thus be the surface termination being in its properties strongly modified [1] by reactions of the catalyst surface with reactant molecules. his aspect is usually not meant when the effect of “nano” is discussed in catalysis. It rather refers to size effects. Both aspects will be treated in the following text. he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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1800 1600 1400 1200 Citations

1000 800 600 400 200 0 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

406

Year Figure 20.1 Citations of the term nanocatalysis according to the web of science as seen in January 2014.

he catalytic reaction depends, however, not only on the molecular properties of the system, but also, in several domains of space and time, on the properties of the system catalyst-reactor with respect to transport of energy and materials. he direct correlation between catalytic performance and molecular properties is thus weak and can barely alone be used as guide for catalyst development. he nanoscience literature takes little notice when happily referring observed catalytic functions directly to nanoscopic attributes such as size and shape. Figure 20.2 shows main layers of dimensional effects that all interact to give an observable reaction in catalytic processes. he origin of the multidimensional nature of catalysis lies in the unavoidable coupling of molecular processes at the active site with transport phenomena in various dimensions. hese are essential, in order to produce a detectable amount of products scaling with Avogadro’s constant. In the present context, it is also relevant that the dynamical nature of catalysts involves side reactions of reactants with the catalyst phase. hese reactions are essential [2] to bring about the active sites. Simultaneously, they stabilize the nature of the catalyst matrix. As this matrix is often nanostructured, adverse effects ranging from surface reconstruction to sintering and segregation will limit the stability and thus the long-term performance of nanostructured catalysts. his effect alone puts a severe limit to the selection of nanostructuring strategies for enhancing the performance of a catalyst material. High-throughput experimentation (HTE) and combinatorial methods were advocated to solve the problem of lacking success of empirical optimization

20.1

Introduction

Time

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Segregation

Reactor transport

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s Surface restructuring

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μm

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m

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Figure 20.2 Catalysis is a multidimensional science. In order to observe the function of a catalyst, all layers of the space–time coordinate system have to cooperate.

strategies. After a decade of utilizing the combinatorial approach, it becomes clear [3] that also here a knowledge-based strategy is required to define compositional libraries and experimental procedures with a reasonable success rate. he target of testing nanostructured materials by high-throughput techniques has developed as an indispensable tool for rapidly acquiring data for either understanding selected topics in the structural evolution [4] of catalysts or probing the kinetic parameter space [5] of practical reactions comprising cascades of reactions. he initial concept of using “combinatorial chemistry” as a substitute for rational development is now replaced by the view that rational design and HTE are not competing with each other, but rather complementing each other within an integrated workflow, combining theory and experiment as indicated in Figure 20.3. Such a workflow is still a concept as many interdisciplinary boundaries within chemistry and outside chemistry have to be surmounted. he enormous parameter space – now available with the many attributes of nanostructuring of a given compound – makes it essential to leave the tradition of empirical search for a compound and then look for application. Rather a predefined application profile should enable the catalytic material scientist to suggest an experimental campaign leading with relatively few experiments to a useful catalyst.

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Active site

Atomistic reaction model

Spectroscopic observables

Material library

Structure

Synthesis

Dynamical

Static

Failure analysis

Formulation transport properties

Process and operation

Microkinetic model Evaluated hit for scale up Function

Intrinsic

Relation to theory

Analysis of potential

Figure 20.3 A still hypothetical workflow for rational catalyst development. The multitude of synthetic possibilities for shaping a given compound into various nanostructures renders prohibitive the traditional empirical search for optimized catalysts.

20.2 Nanocatalysis

he term nanocatalysis was introduced about 10 years ago and was initially designating the application of loose metal nanoparticles in solution. hese nanoparticles were generated by organometallic synthesis methods and revealed novel homogeneous size distributions. By varying solvents, even different shapes of particles were accessible. In selected organic reactions, such systems showed interesting performances in laboratory applications. Later, the meaning of the term was expanded, designating many approaches to prepare new catalysts. his includes model systems with nanoparticles deposited on well-ordered substrates. Today, there is a tendency to use the term synonymously for all kinds of solid catalytic materials. hus, it is difficult to interpret the overproportional growth of the number of citations one can find in the web of science as indicated in Figure 20.1. he term signals that there may be a difference in function or structure between “nanocatalysts” and “conventional” catalysts. his is not the case. All performance catalysts are nanoscopic in their functional structuring that is responsible in bringing about the active sites either as static surface defects or as dynamical process involving the reactant to be present. he idea that catalysts are static objects

20.3

Nano in Catalysis

when executing their function and may thus be different from their nanoscopic counterparts; being more dynamical is not correct as all performance catalysts are composed of nanoparticular objects. he nanoscience age has contributed enormously to catalysis by providing analytical techniques such as advanced electron microscopy, scanning probe techniques, and sophisticated model systems that were motivated by other fields of applications of nanoscopic concepts treated in this book. In addition, synthetic procedures used in generating catalysts could be understood in terms of nanostructuring approaches leading to a much better design of size and shape of active particles in aggregated solids used as practical catalysts. Loose nanoparticles can hardly be used in catalysis, as separation and isolation are critical. Nanoscopic objects need fixation on a support or agglomeration into macroscopic materials of millimeter size. In these aggregates, the individual nanoparticles expose only part of their surface to reactants, whereas another part of the surface is used to generate binding used for supporting and aggregation. he non-innocent interaction between nanoparticles and supports creates an additional tuning parameter which allows influencing the exact geometric and electronic structure: wetting interactions are a detectable measure of this specific bonding between nanoparticles and their environment. he nanoscience age is generating an enormous number of potential catalytic materials. his is triggered by the attention of synthetic chemists to needs of catalysis science for novel material concepts. Very few of these possible developments make it into technical testing or even in commercial application. his is due to enormous challenges in synthesizing sufficient quantities of the required material as chemical applications are intrinsically material-intensive. Challenges in supporting and fixing nanoparticles with retention of their beneficial properties and finally the cost of production are additional adverse factors. herefore, conventional systems made by precipitation and impregnation are prevailing in all large-scale applications as even the most spectacular success of nanostructuring in catalysis, namely the activation of gold-support systems, have found little practical use so far. he origin of these discrepancies between academic and technical catalysis research as well as the identity of the functional concepts between “nanocatalysis” and “conventional” catalysis is now discussed in detail.

20.3 Nano in Catalysis

Heterogeneous catalysis knows about size effects [6] as the dependence of performance on an average geometric size of the active material. As strong as these effects can be, as difficult is their rationalization. he simple argument that highly dispersed active materials expose more active sites per unit weight is correct, but it is an insufficient explanation as the properties of materials do change with

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size when their dispersion, defined as the ratio between bulk and surface atoms, reaches finite values. his effect leads to nonlinear structure-activity relations. Chemical bonds are typically 0.2 nm long, whereas typical stable catalytic particles are 2–6 nm in size. he ratio between the two sizes can be called size parameter, and it is found that a maximum of catalytic function occurs at values of the size parameter much larger than unity. It is thus justified to interrogate the impact of nanostructuring on catalysts [7]. his does not deny that catalysis relying on the deliberate synthesis of nano-sized particles as active masses is probably the oldest and single most successful realization of nanotechnology. he widespread attention that nanoscience has received in many areas of material and life sciences led to a loose definition of this field, including molecular objects as well as small crystals of many thousands of identical atoms or molecules. he geometric size of a few nanometer [8] is thus not a sufficient definition for the term nanocatalysis. It is rather useful to define nano-objects in catalysis as supramolecular ensembles in sizes that allow metastable bulk and surface configurations to be kinetically stabilized at conditions of application. Such objects are intermediates between crystals, aggregates, and molecules; they are defined by sharp boundaries between them, even when the objects are embedded in a matrix. hese conditions are fulfilled for metallic elements with objects containing 2–5 atoms per edge of its polyhedron (often cubooctahedra or icosahedra), or in semiconductors with 1–3 chemical bonds per edge. Figure 20.4a recalls the 8

1

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0.15 0.1 0.05 0 10

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Number of valence electrons

Figure 20.4 (a) Relation between size and number of atoms for a typical metal with close-packed structure in cubooctahedral shape. (b) Dispersion (ratio between bulk and surface atoms) for the same geometry.

(c) Evolution of the Kubo gap as function of the number of valence electrons. The dashed line indicates the energy of room temperature excitation of electrons.

20.5

Geometric Structure and Catalysis

relation between particle size and number of atoms contained. Operating catalysts are made of particles with sizes between 2 and about 7 nm; only in cases of encapsulated systems, smaller particles can occur. Figure 20.4b reveals that the ratio between surface and bulk atoms, for such particles, is still much larger than for bulk materials, pointing to a property of nanoparticles extremely important for catalysis: the fraction of coordinatively unsaturated (cus) atoms is large as compared to bulk materials.

20.4 Electronic Structure and Catalysis

Nanoparticles are large enough to reveal the bulk electronic structure of metals or semiconductors. hey are much larger than cluster objects, which are defined as entities at the transition from bulk to molecular properties (typically a few metal atoms for elements with highly delocalized valence electrons (alkali metals) and about 100 atoms for elements with strongly localized valence states (heavy main group metals)) [9] . Nanostructures may be defined alternatively as objects exhibiting a significant fraction of their total number of atoms as cus with respect to the regular bulk structure. If 20% cus sites are accepted as lower level of significance, objects of about 8000 atoms are nano-objects, falling for isotropic geometries in the same size range up to 6 nm (see Figure 20.4a) as defined above. he cus sites exhibit local electronic structures decoupled from the band structure of the part of the object with regular structure. Consequently, an energy gap opens (Kubo gap), whose width depends on the number of valence electrons in the nano-object [10]. his size effect on the integral electronic structure is significant for small objects as can be seen from Figure 20.4c. he band gap vanishes at 300 K (equivalent to about 25 meV) for objects with about 300 atoms. As catalytic reactions occur usually at elevated temperatures, the band gap effect is of significant influence only for small objects [11] of about 1 nm in size. Such objects are – despite their desirable catalytic function [12] in nonencapsulated forms [13] – usually not very stable under reaction conditions and tend to sinter. hus, a ground-state electronic structure modification well known to exist in small clusters [11, 14] is in most cases not responsible for a beneficial “nano-effect” in catalysis.

20.5 Geometric Structure and Catalysis

he relevance of the surface geometric structure is extensively known in heterogeneous catalysis and was originally designated with the term structure sensitivity [15]. Typical stable metallic nano-objects that are active in catalysis are depicted in Figure 20.5. Plates (a) show a Pt particle supported on silica [16] typical for

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(a)

200

2 nm

(b)

2 nm

Figure 20.5 (a) Pt nanoparticle deposited on a model silica support (see Ref. [10]). The internal structure is compatible with bulk Pt (see power spectrum at the right panel), but the surface of the three-dimensional particle

is rough and facetted. (b) A multiple-twinned Cu particle prepared by the gas aggregation technique (see Ref. [11]). The power spectrum reveals its perfect icosahedral symmetry by the satellite spot structure.

a hydrogenation catalyst. It is clearly seen that the bulk is well-ordered metal (see also Fourier pattern), whereas the surface is blurred and facetted. Object (b) is a copper multiple-twinned particle (MTP) of icosahedral symmetry [17] (see Fourier pattern). It shows regular defect sites at the edges of the subunits and exhibits a significant deviation from the bulk lattice constant [18]. he sizes of both classes of objects exclude the operation of an integral ground-state electronic effect. heir perimeters (surfaces) are nonuniform and exhibit irregularities and roughness. Such local geometric irregularities [19] are well known to exhibit strong variations in local electronic structure [20] and, for example, can easily revert the character of chemisorption from molecular to dissociative [21], a key feature in activating molecules for chemical reactions. An example of the control of chemical reactivity with the localization of cus sites was found in the interaction of methanol with Pd [22] where edge atoms exhibit a different

20.5

50

Conversion (%)

Fraction of Co diss. (%)

60

40 30 90 K

20

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10 10 (a)

100 Number of Rh atoms

Figure 20.6 Case studies of nano-effects in catalysts with supported metal nanoparticles. (a) From Ref. [18] reveals that the deposition temperature of identically sized particles plays a decisive role in their function probed in chemisorption of CO. (b) Structure-activity

1000 (b)

Geometric Structure and Catalysis

100 90 80 70 60 50 40 30 20 10 0

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C Au/Oxide C Au/C

3

5

7 Size (nm)

relationships for gold particles in glycol oxidation for two families of catalysts on different supports. The strong effect of support properties on the relation is obvious (adapted from Ref. [22]).

reactivity than terrace atoms, albeit both types are cus. he examples indicate that fine details and a variation in the local geometric structure of metastable objects exhibiting nonequilibrium surface termination are a key element in the action of nano-objects in catalysis. A nano-object is metastable and thus not defined in its properties uniquely by the combination of chemical identity and size; its synthetic prehistory and its interaction with the substrate are equally important as illustrated with the data of Figure 20.6. he ratio between molecular and dissociative chemisorption of the CO probe molecule depends on the deposition temperature of equally sized objects [21] (example (a) in Figure 20.6), and in example (b) of Figure 20.6, the relation between geometric size and catalytic performance depends strongly on the chemical identity of the support of “inert” gold particles [23]. In recent years, many examples of the resolution of catalytic size effects into nanostructural effects have been described. his is due to the advent of multiple model systems in which due to suitable physical synthesis methods a high degree of identical particle shapes could be achieved in samples large enough to be studied experimentally. An example is given in the review article [24] where Pt nanoparticles of comparable size but different shapes exhibited pronounced differences in catalytic activity measured by model reactions. In another example [12], trimers of silver were used as model catalysts for selective oxidation of propene. It was found that the silver metal had to be slightly oxidized, exhibiting an open d-shell electronic structure for good performance. It was found that roughly 3 nm particles on alumina fulfill these requirements, explaining the enormous sensitivity of the technical realization of Ag/alumina on the details of synthesis and support structure for obtaining rough and reactive Ag nanostructures. For a broader review of the subject with a multiplicity of examples, including gold catalysts, see the review [25] on CO oxidation. his review on

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utilization of CO oxidation [25] as probe reaction for the multidimensional nature of catalysis exhibits more examples of the specificity of size effects. he possibility of studying CO adsorption and its oxidation on free-flying nano-objects and deposited particles in comparison shed light on the concept that size is not the controlling variable. he size of particles is rather a convenient proxy, integrating over many geometric and electronic phenomena related to nonequilibrium portions of matter as they are useful in catalysis. he advent of aberration-corrected transmission electron microscopy (TEM) instrumentation renders it now possible to investigate the surface of nano-objects [26], with atomic resolution. With this method, it is possible to visualize the deviations from minimal-energy configurations at a catalyst surface. his was shown for a silver particle as this element is so frequently studied [27] in conceptual experiments. In reference [26], the cooperation of theory and experiment is demonstrated to rationalize the clearly visible deviation of translational ordering at the edge of the nanoparticle. his is caused by the presence of an adsorbate such as oxygen that changes the local electronic structure (bond elongations) and leads to a certain dynamics which is visible as blurring on the time scale of the image acquisition (1 s). In Figure 20.7, a realistic situation of gold nanoparticle supported on the tip of a carbon nanotube is shown. We recognize surface terminations compatible with low-indexed planes and step edges. On the same particle, we also see rough terminations created by a complex sequence of monatomic steps. Such sites are expected to serve as active sites for breaking chemical bonds, whereas the flat surfaces are suitable landing sites for molecules. he multifunctionality of a nano-object created by its nanostructuring is evident. Likewise, it is clear that this complex situation is only crudely described with the parameter size.

2 nm

Figure 20.7 A gold nanoparticle supported on a nitrogen-modified carbon nanotube. The image was recoded at 300 keV using a FEI TITAN instrument equipped with a CEOS image corrector. Note the atomic resolution

both for the gold particle and the carbon in basal and prismatic directions. The contrast inversion on some of the terminating atoms points to the action of chemical bonds from adsorbates at these locations.

20.7

Nanostructured Carbons

20.6 Large Nano-objects in Catalysis

he examples discussed so far are densely packed objects. Extended isolated objects with non-dense structures may carry a sizable amount of nonequilibrium surface features with the desired local chemical properties. Nanostructuring enhances the number density of such features and prevents the equilibration into a macroscopic solid (Ostwald ripening). Figure 20.8a illustrates this with vanadium oxide nanorods [28] that were obtained with an extremely textured arrangement of the (001) atomic planes along the needle axis. he rods are accessible by seeding an oxide solution with carbon nanotubes of high hydrophilicity. he high magnification image reveals that the surface of the rods is covered with a monolayer of a one-dimensional ordered material most relevant for catalytic functions [29]. Bulk vanadium oxide crystallizing in platelets is free of such a termination layer [30] even when grown in identical conditions. Figure 20.8b shows a carbon nanofiber highly active in dehydrogenation of ethylbenzene to styrene [31]. he nanostructure allows for an angle between the graphene sheets and the needle axis, giving rise to the tiled surface structure (arrows). he resulting carbon edges carry the active centers as oxygen heteroatomic terminations (prism faces (110)). Would the surface as a whole be terminated like this, the particle would oxidize under reaction conditions [32] and hence exhibit no lifetime in the reaction. No catalytic activity is obtained on defect-free basal (0001) terminations. he left image illustrates that nanostructuring of carbon into onion-like carbon optimizes the abundance of stabilizing basal planes and hence leads to a maximum catalytic activity [33] per unit mass carbon.

20.7 Nanostructured Carbons

Following this early example of carbon in catalysis, the field of application of carbon in catalytic reactions either as support or as metal-free catalyst [34] has expanded enormously in recent years. Besides the advent of multiple synthesis or preparation techniques [33, 34c, 35] letting the “family” of carbon nanostructures grow substantially, both the graphene effect and the search for electro-catalytic systems [36] in the context of energy applications can be seen as drivers for this trend. he last example is a useful illustration how nanosizing brings about functions that cannot be expected at all from bulk forms of the same material. Manganese oxides are sought as electro-catalysts for water splitting and there of oxygen evolution. On a molecular scale, this seems to be an excellent choice as a Mn–oxo cluster is performing this function in nature’s green leaves. In biomimetic approaches, the transport of electrons to the reactive surface is a problem with Mn oxides as they are poor electron conductors. Combining now in a composite, the excellent electron conducting properties of nanocarbons with

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(a)

50 nm

2 nm

(b)

O2 20 nm

Figure 20.8 Large nano-objects. (a) Vanadium pentoxide nanorods grown from seeding a vanadate solution with carbon nanofilaments (bamboo type, see bottom right). The HRTEM image reveals the perfect internal ordering of the V2 O5 structure and the amorphous termination layer. (b) A carbon nanofilament with a stepped outer surface (arrows) after use as catalyst in oxidative

2 nm dehydrogenation of ethylbenzene to styrene. Some polystyrene covers as loose debris the surface of the still active catalyst. The onionlike carbon object exhibits a minimum of non-reactive stabilizing basal planes at the surface and a maximum catalytic performance in the reaction schematically shown is attained.

20.7

Mn3O4 Hausmannit Figure 20.9 A nano-composite solution for the catalysis of oxygen evolution in the water splitting reaction. Note that both electron conductor (carbon nanotube) and

Nanostructured Carbons

5 nm catalyst (Hausmannit particle, arrow) are nanoscopic in dimension but of quite different shapes and sizes. (Adapted from Ref. [36].)

the catalytic potential of nanostructured MnxOy species can bring unexpected solutions as exemplified in Figure 20.9. Besides the quests to generate many novel carbons from polymeric precursors [37] as method to predetermine their structural features, the rich variation in local electronic structure is the most relevant feature in applying nanocarbon in catalysis. he nanoscopic dimension is so important in this context, as in all macroscopic forms of carbon, the anisotropic structure of graphene sheets would give rise to an overwhelming presence of “aromatic” sp2 carbon atoms that are not reactive as evidenced many times [38] with the “gold standard” of highly oriented pyrolytic graphite (HOPG) material. his is counterintuitive and needs some comment: he concept that, in nanostructured carbon, all atoms are electronically equal and of sp2 bonding geometry is only true to a crude approximation. Even in graphene, the edge atoms are coordinatively unsaturated in sp2 hybridization. Hence, they tend to undergo many reactions, leading to reconstructions, rendering them locally different from the archetype “benzene” structure (surface functional groups, interlayer bonding, reconstruction to a non-six-membered heterocyclic ring and others). Deviations from planarity, being frequent in nanostructured carbons, create localization of double bonds into a polyene-type local bonding again with sp2 configuration. In-plane defects [39] cause local deviations from perfect planar sp2 configuration. For graphitic (multilayered) objects, the interaction of guest species again leads to distortions of the planar structure and another family of local electronic structures results. Figure 20.10 shows that even for a simple reduction in

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Figure 20.10 C1s photoelectron spectra of HOPG macrocrystalline and natural nanocrystalline (300–100 nm average particle size, dashed) graphite. The clear differences in line profiles indicate the distributions of local bonding geometries caused by interacting

280

and non-interacting sp2-coordinated atoms. Heteroatoms as functional groups in many bonding geometries give additionally rise to signals at energies higher than 286 eV. (From Ref. [38].)

particle size of graphite from HOPG to nanostructured flakes of natural graphite, there is a substantial distribution of the local electronic structure detectable as line profile distortion in the C1s photoemission. he in situ observation of graphene growth from atomic precursors over catalysts [40] as shown in Figure 20.11 gives the calibration for the assignment of the species distribution. In summary, we understand now that a wide distribution of local electronic structures is possible in carbon when graphite is reduced to nanoscopic sizes in each dimension. As multiple mixed forms can and do occur in practical synthesis, a wide range of new reactivity and novel support effects are possible [34a, 41], the description of which is stretching far beyond this book chapter.

Intensity (arb. units)

20.8 C–C C–Fe

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Binding energy (eV) Figure 20.11 In situ observation of graphene synthesis on a metal catalyst: first non-interacting sp2 carbons are forming nuclei, then rapidly a layer of islands of

carbon is forming, followed by the incorporation of defects at later times as can be seen by the high-energy shoulder. Adapted from Ref. [40].

20.8 The “Semiconductor” Approach

he advent of nanotechnology in catalysts has also led to extended activities in catalytic reactor design. he aim here is to replace large reactors with highly parallelized arrays of small reactors [42] that are microfabricated. In this way, the control of mass and energy flow can be managed to great extent and the technologies of semiconductor device fabrication may be applied to a rigorous physical preparation strategy for the active catalyst. Further, the gap between model systems susceptible to structural characterization and the scale up to a large “chemical” system would vanish as the large system is a parallelized version of the small model. his approach was recently reviewed [43] and validated as promising development for future catalysis research. In the present context, it

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is critical to understand that the active catalyst mass inside such a microreactor has to fulfill additional requirements rather than being highly active. As there is little space, the density of active sites must be high per unit volume of material, excluding low surface area bulk catalysts and fluffy forms of supported systems. In addition, special requirements for adhering the active forms to the reactor material are also required which cannot be chosen freely in order to fulfill the conditions of heat exchange and of easy multiplication. Lastly, mechanical degradation of the catalyst bed is detrimental, as it quickly will lead to blocking of channel structures or of mixing and dosing elements of the reactor assembly. In summary, this field of performance catalyst development critically depends upon synthetic procedures from nanoscience and can tolerate also more exotic strategies, as the amount of functional material is limited in comparison to normal reactor applications, where tons of catalyst materials are needed on the industrial scale of reactors. For multifunctional catalytic processes such as selective oxidation, this seems a futuristic alternative due to the complexity of the catalytically active material that requires chemical means of preparation.

20.9 The Combicat Approach

he design principle of nanometer-sized objects with nonequilibrium surface structures seems to work well for metals and selected other compounds. In the large field of catalysis with metal oxides, the concept is only of limited success due to the lack of preparative methods [44] to access active nanostructured particles with predefined properties. he common approach [45] is to modify a given structure by chemical substitution. he active structure is always a “defect” structure with respect to the thermodynamically stable bulk oxide. It needs to be generated by very difficult-to-control thermal treatments called calcination and activation, leading inevitably to phase mixtures and chemically complex materials referred to as multi-phase-multi-element oxides (MMOs). In recent years, it was possible to identify a structure of molybdenum suboxide as essential single phase [46] in a variety of catalysts for a selection of selective oxidation processes of small alkane molecules. he essential motif [47] is shown as mechanical model in Figure 20.12a. It is a cluster of a central pentagonal bipyramid surrounded by five distorted octahedra. he atoms shown in the model are oxygen; the metal (Mo, W, Nb, V) are at the center of each polyhedron. he object is about 1 nm in diameter and 0.41 nm thick. For catalytic function, it seems essential that this active cluster is isolated [48] from the matrix to prevent excessive flow of active oxygen atoms and of electrons. During conventional synthesis, the cluster (Figure 20.12b) is condensed into a highly disordered polymer [49] with some long-range order (chains in one direction, see Figure 20.12c). his inadequate structure needs to be defected [50] by calcination in dilute air, creating a defective matrix Mo5 O14 and a second phase of ortho-MoO3 . he latter material

20.9

The Combicat Approach

(a)

(b)

(c)

(d)

Figure 20.12 The polyoxometalate functional unit in catalysts for selective oxidation of alkanes (a) can be realized with a variety of transition metal cations. The monomer (b) condenses during conventional preparation into a “glassy” state with close contact between the units (chains in (c)). By

introducing suitable linkers, a structure can be created (d) in which the units are isolated from each other and a hierarchical pore system will result. The nanostructure is of a layer type with structure-directing ions filling some of the channels to account for a stacking order.

is detrimental for catalysis [51] as it accelerates the burning of all valuable initial products formed on the cluster. If the correct nanostructure (Figure 20.12d) could be achieved by using linker structures during the initial synthesis such as in model cases with heteropolyoxomolybdates (HPOM) [52], then the detrimental calcination may be omitted. he polymerization of the clusters into a stable nano-object with perfect isolation of the active sites is desired. Only if the final polymer is nanoscopic in size, sufficient

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dispersion (see Figure 20.5b) at stability against chemical reduction and sintering can be achieved. In contrast to the empirical addition of heterocations to the solution of monomeric anions, the Combicat approach [53] utilizes detailed understanding to arrive at initial synthesis conditions, allowing using the same element (Mo, Nb, V) for building the clusters and the linkers. he Combicat approach aims at the minimum of chemical complexity in contrast to, for example, the HPOM structures. his is motivated by the severe stability problems encountered with practical reaction conditions: elevated temperatures, steam, and reducing conditions are aggressive to metal–oxygen chemical bonds involving two different metals with different degrees of polarization and differing redox properties. A homo-nuclear structure is the preferred option in order to minimize the decomposition processes during catalytic operation. he nanostructuring of the linked clusters can be achieved by controlling the polymerization kinetics. his is required to optimize the transport of molecules and of energy to and from the active material. he necessary porosity and sufficient geometric surface area need to be incorporated without allowing the system to become too susceptible towards hydrothermal sintering during catalytic operation. It is obvious that for executing the control over the synthesis, a set of independent variables is required. he identification and validation of these variables such as concentration ratios of reagent, temperature, presence of auxiliary ions to stabilize complexation equilibria, mode of solidification (variable or constant concentration), extrinsic variables (reactor design and operation), post-precipitation treatments, drying, and thermal treatments are an immense effort, being ideally suited for HTE strategies [54] adapted with special equipment to perform such controlled synthesis tasks. he usual processes of uncontrolled parallel precipitation in small quantities are unsuitable for such a task. Computer-automated larger scale reactors are required to allow the same amount of kinetic control of the synthesis reaction as it is exerted in the kinetics of catalytic performance tests. he results are diagrams of state for each unit operation, allowing defining recipes for reproducible and scalable synthesis. he general procedure is outlined in Figure 20.13. he metal monomer is simultaneously linker and building block for a homo-polymer. his needs to be grown into nanoparticles and investigated for stability against crystallization into orthoMoO3 . If this cannot be achieved, the linkers may be chosen from a different element much in the same way as glasses [55] are being produced. As the catalytic function is very difficult to assess from a structural analysis, it is mandatory to use HTE catalytic screening in parallel with the material development in order not to develop the system towards maximum stability by depriving it from the essential [55, 56] metastable structural features (defects) that are necessary for selective oxidation catalysis [57]. he dual application of HTE technology is thus vital for operating a rational nanostructuring strategy for such a complex functional material as a bulk selective oxidation catalyst.

20.10

Conclusions

MoO4–2 Polymolybdates

Homo-polymer

Hetero-polymer

Stabilization by condensation or supporting into nanostructures Ball milling Deactivation to bulk ortho-MoO3

Hydrothermal regeneration

Figure 20.13 Scheme of a preparation strategy to arrive at the desired nanostructure depicted in Figure 20.11d. Several alternatives are shown for the case that the homonuclear polymerization will not result in

sufficiently active and stable materials. Even samples deactivated during synthesis may be reactivated by mechanical or chemical treatments, providing ample chance to arrive at the desired structure.

he Combicat approach has recently found substantial [58] methodical developments. Both the search strategies for useful libraries of experiments and the practical synthesis of large and diverse libraries are highly developed [59] now. What has been left out, however, are methods to effectively control particle morphologies of catalyst libraries. his has led to a degree of realism about the usefulness of the combinatorial approach as stand-alone methodology. he consequence is that integrated approaches such as indicated in Figure 20.2 seem to be more suitable to really execute morphological control over a catalytic material as needed to bring out its optimum performance.

20.10 Conclusions

Nanostructured objects are essential tools in shaping catalysis towards the needs of modern economy, including the energy challenge. It is the optimization between maximal exposure of dynamical surface features and the necessary stability of the functional material that can be achieved by nano-objects. Neither the size minimization nor the operation of collective electronic effects is alone relevant for catalysis, being the characteristics of nanostructured objects that are so important in non-catalytic applications. Nanostructured objects in catalysis must not necessarily be nanoparticles [60] supported on mesoscopic structures. It was demonstrated that also bulk materials with open crystal structures are nanostructures in the sense that they form

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locally clusters of oxidic polyhedra, being relevant for catalysis operating through active sites. It remains open for the future to decide how large such an active site really is: the support [61] of nanoparticles is not “innocent” but plays a role in controlling transport processes and may even exert long-range electronic influences. In more massive catalysts, the site isolation [62] through chemical bonding may not be as isolating as thought. It may well be that oxidic local nanostructures are linked through charge carrier dynamics that we cannot clearly assign at present. Remote sensing of the relation between electrical conductivity and catalytic activity showed [1b] that such electron exchange plays a role in catalysis. Refined in situ characterization methods [1] for detecting the relevant local electronic features and rational synthesis protocols, replacing the “black art” of catalyst manufacture, are required to fully exploit the possibilities of nanoscience for a new generation of catalyst development concepts based on knowledge rather than on empirical methods. Despite the enormous growth of empirical descriptions of successful applications of nanostructured catalysts as exemplified by carbon materials, photocatalysts on titania basis or gold nanoparticles, to name a few, there is still no systematic strategy allowing to rationally approach the issue of controlling reactive surface properties by nanostructuring. he term nanocatalysis is not justified for the current mode of catalyst development as the element of rational influencing the morphology of a catalysts is still absent. he present work also revealed that existing performance catalysts do not justify the introduction of a special designation as they consist, necessarily and often unintentionally, of nanostructured units carrying the relevant functions. he best example of “nanocatalysis” is the application of deliberate nanostructures prepared by physical methods for generating model system in catalysis research. hrough such well-defined systems, phenomena like restructuring, sub-surface chemistry and metal-support intergrowth can be addressed [25] with chemical precision. he transfer of such knowledge to practical performance catalysts is a great challenge for the future that could bind together model and performance catalysis science.

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Schlögl, R. (1997) Relevance of a glassy nanocrystalline state of Mo4 VO14 for its action as selective oxidation catalyst. Catal. Lett., 44 (3–4), 153–163. Schlögl, R., Knop-Gericke, A., Hävecker, M., Wild, U., Frickel, D., Ressler, T., Jentoft, R.E., Wienold, J., Blume, A., Mestl, G., Timpe, O., and Uchida, Y. (2001) In situ analysis of metal-oxide systems used for selective oxidation catalysis: How essential is chemical complexity? Top. Catal., 15 (2–4), 219–228. Ressler, T., Timpe, O., Neisius, T., Find, J., Mestl, G., Dieterle, M., and Schlögl, R. (2000) Time-resolved XAS investigation of the reduction / oxidation of MoO3-x . J. Catal., 191 (1), 75–85. (a) Bouchy, C., Pham-Huu, C., Heinrich, B., Derouane, E.G., Derouane-Abd Hamid, S.B., and Ledoux, M.J. (2001) In situ TPO, TPD and XRD characterisation of a molybdenum oxycarbohydride catalyst for n-butane isomerisation. Appl. Catal., A, 215, 175; (b) Jentoft, F., Klokishner, S., Kröhnert, J., Melsheimer, J., Ressler, T., Timpe, O., Wienold, J., and Schlögl, R. (2003) he structure of molybdenum-heteropolyacids under conditions of gas phase selective oxidation catalysis: a multimethod in-situ study. Appl. Catal., A, 256, 291–317. (a) Schüth, F., Baumes, L., Clerc, F., Demuth, D., Farrusseng, D., Llamas-Galilea, J., Klanner, J., Klein, C., Martinez-Joaristi, A., Procelewska, J., Saupe, M., Schunk, S., Schwickardi, M., Strehlau, W., and Zech, T. (2006) High throughput experimentation in oxidation catalysis: higher integration and “intelligent” software. Catal. Today, 117 (1–3), 284–290; (b) Schüth, F., Busch, O., Hoffmann, C., Johann, T., Kiener, C., Demuth, D., Klein, J., Schunk, S., Strehlau, W., and Zech, T. (2002) Highthroughput experimentation in oxidation catalysis. Top. Catal., 21 (1–3), 55–66. (a) Szijjarto, G.P., Tompos, A., Heberger, K., and Margitfalvi, J.L. (2012) Synergism between constituents of multicomponent catalysts designed for ethanol steam reforming using partial least squares regression and artificial neural networks.

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61. (a) Villa, A., Wang, D., Spontoni, P., Comb. Chem. High hroughput Screen., 15 (2), 105–113; (b) Tompos, A., Arrigo, R., Su, D.S., and Schlögl, R. Margitfalvi, J.A., Vegvari, L., Hagemeyer, (2010) Nitrogen functionalized CNTs A., Volpe, T., and Brooks, C.J. (2010) supported Pd and Au-Pd NPs as catalyst Visualization of large experimental space for alcohols oxidation. Catal. Today, using holographic mapping and artificial 157 (1–4), 89–93; (b) Hävecker, M., neural networks. Benchmark analysis of Cavalleri, M., Herbert, R., Follath, R., multicomponent catalysts for the water Knop-Gericke, A., Hess, C., Hermann, gas shift reaction. Top. Catal., 53 (1–2), K., and Schlögl, R. (2009) Methodol100–107; (c) Tompos, A., Margitfalvi, ogy for the structural characterisation J.L., Szabo, E.G., and Vegvari, L. (2010) of VxOy species supported on silica Combinatorial design of Al2 O3 supunder reaction conditions by means of in situ O K-edge X-ray absorption ported Au catalysts for preferential spectroscopy. Phys. Status Solidi B, 246 CO oxidation. Top. Catal., 53 (1–2), (7), 1459–1469; (c) Hess, C., Wild, U., 108–115. and Schlögl, R. (2006) he mechanism 60. (a) Cormary, B., Dumestre, F., Liakakos, for the controlled synthesis of highly N., Soulantica, K., and Chaudret, B. dispersed vanadia supported on silica (2013) Organometallic precursors of SBA-15. Microporous Mesoporous Mater., nano-objects, a critical view. Dal95, 339–349. ton Trans., 42 (35), 12546–12553; (b) Chaudret, B., Gomez, M., and Philippot, 62. Grasselli, R.K. (2001) Genesis of site isolation and phase cooperation in selecK. (2013) Metal nanocatalysts in solutive oxidation catalysis. Top. Catal., 15 tion: characterization and reactivity. Top. (2–4), 93–101. Catal., 56 (13–14), 1153–1153.

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21 Processing of Nanoporous and Dense Thin Film Ceramic Membranes Tim Van Gestel and Hans Peter Buchkremer

21.1 Introduction 21.1.1 General

he history of ceramic membranes dates back more than 50 years when such membranes were developed for uranium enrichment. To apply uranium as a nuclear fuel in a light water reactor it is necessary to increase the 235 U content in natural uranium from 0.7% to about 3–5% [1]. his was achieved by utilizing a Knudsen diffusion process. Knudsen diffusion is a means of diffusion that occurs in mesoporous ceramic membranes. In this case, the pore diameter is smaller than the mean free path of the diffusing gas molecules and the gas molecules collide with the pore walls more frequently than with each other. he theoretical maximum achievable selectivity in such a process is given by (MA ∕MB ) with MA and MB the molecular mass of the gases 235 UF6 and 238 UF6 , respectively. he selectivity is thus very small, which requires more than 1000 separation stages for the enrichment to 3% 235 U and very large membrane areas for practical applications [2]. Membrane technology has thereafter been dominated by polymeric membranes, because they are much cheaper and easier to prepare on a large scale. However, since the 1980s, a number of emerging applications started to require membranes with high thermal, chemical, and mechanical stability and since then there has been a rapidly growing interest in ceramic and other types of inorganic membranes. Examples of such applications are treatment of wastewater from the food and dairy industry, energy-efficient gas separation, H2 separation, pervaporation, membrane reactors, and high-temperature fuel cells. Other types of inorganic membranes include glass and metallic membranes, as well as hybrid polymer-inorganic materials [3–5]. Based on the number of applications in industry as well as in laboratory research, polymeric and ceramic oxide membranes are the two main classes of separation membranes. hey cover all kinds of membrane applications The Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Table 21.1 Application fields and properties of nanoporous and dense ceramic membranes. Application field

Membrane process

Pore size functional layer

Complexity of preparation process/ commercial availability

Separation liquid/ macromolecules Separation liquid/small molecules Separation liquid/ions

Ultrafiltration

Mesoporous >2 nm

Nanofiltration

Microporous 1–2 nm

Desalination, reverse osmosis

Microporous 50 nm), mesoporous (50 > pore size > 2 nm), and microporous (pore size < 2 nm) [10]. he mesoporous membranes in our work are made by wet-deposition processes, which involve the deposition of nanoparticles from a sol or nanodispersion. he specific examples are a mesoporous γ-Al2 O3 and a stabilized ZrO2 (8% Y2 O3 ) membrane. For these membranes, the gas separation efficiency is moderate to very low, dependent on the molar mass of the gases. On the other hand, such membranes are very suitable for filtering out large organic molecules Table 21.2 Main applications of gas separation membranes. Gas separation

Membrane application

O2 /N2 H2 /O2 H2 /hydrocarbons H2 /N2 H2 /CO CO2 /hydrocarbons (e.g., CH4 ) H2 O/hydrocarbons (e.g., CH4 ) H2 S/hydrocarbons He/hydrocarbons He/N2 Hydrocarbons/air H2 O/air Volatile organic species (e.g., ethylene)/light gases (e.g., N2 )

O2 -enriched air production, N2 gas generation Fuel cell Hydrogen recovery in refineries Hydrogen recovery from ammonia purge gas Syngas ratio adjustment Natural gas sweetening, landfill gas upgrading Natural gas dehydration Sour gas treating Helium separation Helium separation Hydrocarbons recovery, pollution control Air dehumidification Polyolefin purge gas purification

Taken from Ref. [6].

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in ultrafiltration processes, which is today one of the most frequent applications of ceramic membranes. To improve the separation efficiency in gas separation, we developed in parallel microporous membrane layers. To this end, we use a mesoporous membrane as an underlayer to form a graded membrane. Processing methods for the microporous membrane involve sol–gel processing, which is a special kind of wet-deposition process. he specific examples given in this review are an amorphous SiO2 and a hybrid organic-SiO2 membrane. We refer the interested reader to a few papers which have been published on other materials such as zeolites [11–14], microporous carbon [15–17], and SiC [18]. he gas transport in a microporous membrane occurs through different mechanisms (Knudsen diffusion, micropore diffusion, surface diffusion) depending on the ratio between the sizes of the pores and the gas molecules, as well as on the temperature and pressure used. In practice, Knudsen diffusion is also found as the dominating mechanism for microporous membranes with larger micropores (>1 nm). hus, our major task is to develop a tight microporous membrane with a pore size significantly below 1 nm and a narrow pore size distribution. 21.1.3 Thin Film Solid Oxide Fuel Cells

he focus in the second part of this review is on dense thin film membranes for application in a SOFC. SOFCs are a class of fuel cells which are characterized by the use of a solid oxide material as the electrolyte. In a working SOFC, the solid electrolyte conducts oxygen ions from the cathode (the air side) to the anode, where oxidation of the oxygen ions with the fuel (usually hydrogen) occurs. SOFCs display some significant advantages in comparison with other fuel cell types, such as fuel flexibility (also, hydrocarbons can be used) and long-term stability. SOFCs consist of three main parts, macroporous anode, dense solid electrolyte, and macroporous cathode, which are all made of ceramic materials. he cell operates at very high temperatures, typically between 700 and 1000 ∘ C, since the typical materials used in an SOFC are not sufficiently electrically and ionically conducting at lower temperatures. One of the biggest breakthroughs in SOFC research was the development of the anode-supported cell design [19–22]. A major remaining challenge is to further reduce the thickness of the electrolyte to the micrometer range. hus, various techniques for the fabrication of thin films are being studied [23–28]. he most notable are CVD, PVD, pulsed laser deposition (PLD), and sol–gel. Attempts have also been made to reduce the thickness of the electrolyte by using conventional powder techniques, such as suspension casting, tape casting, screen printing, but after a certain point these techniques lead to untight layers. With the current state of the art, thin film deposition has only been successfully implemented in micro-SOFCs. However, scaling the coating technology to common highly porous anode substrates with a larger surface roughness remains particularly problematic.

21.2

Synthesis and Coating Methods

In our research, we introduced the wet-coating technology developed to prepare mesoporous and microporous membranes to achieve a dense thin film electrolyte membrane [29–32]. In this way, we avoided the often very complicated experimental methods reported on micro-SOFCs and were also able to coat large-area substrates. A few examples of thin film dense electrolytes with a thickness from 2 μm to H2 (0.289 nm) > CO2 (0.36 nm) > N2 (0.38 nm) is in line with expectations, since it follows the kinetic diameter of the test gases (given in brackets). As can be seen, the CO2 and N2 permeance was negligible in most samples, suggesting the presence of micropores with sizes of up to 0.3 nm. he success rate in the series of 10 samples was 8–10, and the average selectivity exceeded 50 and 150 for H2 /CO2 and for H2 /N2 , respectively. Comparison with literature data on SiO2 membranes revealed that the membranes synthesized are rather similar in terms of their properties to the denser membranes prepared with CVD by, for example, Oyama and co-workers [83]. hey reported that the He and H2 transport through the SiO2 top layer can be understood as a diffusion process through an amorphous structure which contains 5-, 6-, 7-, and 8-membered Si–O rings, similar to a vitreous SiO2 glass structure. Probably, a less well-defined material made by sol–gel processing may contain also larger ring structures. 21.3.2.2 Doped SiO2 Membranes for H2 Purification

An important drawback mentioned frequently for amorphous SiO2 membranes is degradation of the membrane material in an atmosphere containing water vapor. For this reason, a number of researchers focused on developing alternative SiO2 materials with an improved stability. One common approach is to improve the material stability by adding doping compounds, such as ZrO2 , TiO2 , Al2 O3 , NiO, and so on (e.g., Ref. [59–65]). An extension of the work on the doped silica

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membrane is the synthesis of metal-doped membranes (e.g., Ref. [66–69]). In our research, we adopted this approach and also fabricated Ni- and Co-doped SiO2 membranes. As shown in Table 21.4, these membranes exhibit a somewhat lower He permeance than the pure SiO2 membranes prepared under comparable conditions, while the H2 permeance is in the same range. Due to the importance of fast and reproducible processing routes, our research on H2 -separation membranes was further expanded by the introduction of RTP and ink-jet printing. As can be seen in Table 21.4, the behavior of the RTP membranes is similar to that of the membranes fabricated with a slow temperature program. In another series of coating experiments, ink-jet printing was introduced. For the ink-jet printed samples, three coating-calcination steps were employed. In each step, RTP was used so that the overall processing time was less than 2 h. he ink-jet printed SiO2 layer showed a remarkable similarity to the SiO2 layers made by dip coating, with a somewhat greater layer thickness and lower permeance [44]. 21.3.2.3 Microporous Hybrid Membranes for CO2 Purification

For applications which involve the separation of CO2 from other larger gases such as N2 and CH4 , alternative membrane types are developed. he retention of all gases larger than H2 makes the above-described membranes obviously unsuitable for such applications. A frequently considered approach is a templating approach. he preparation method of a templated membrane is based on similar sol–gel processes, whereby a template is incorporated in the membrane material and afterwards removed to create an (ordered) pore structure which is accessible for CO2 . To improve the selectivity for CO2 , the pore surface of the membrane is commonly modified. Modifying agents include simple organic compounds and amines, but in most cases an aminated organosilane compound is used, which can be coupled to the surface by a chemical reaction (e.g., Ref. [58, 73]). Another way to prepare such a hybrid membrane is to employ special precursors with organic or amine groups in the sol synthesis route. Figure 21.10 shows two membrane types which were successfully synthesized using two typical precursors, amino-propyl-triethoxy-silane (APTES) and bis-triethoxy-silyl-ethane (BTESE). he advantages of this approach lie in the fact that the microporous structure of the membrane can be controlled more easily than with a post-modification process. he synthesis method of the sols was similar to those of the amorphous SiO2 membranes in the previous sections. After the dip-coating process, the layers were fired in vacuum at 450 ∘ C. In both cases, it appeared that the achievable crack-free layer thickness was larger than for the pure membranes. Since a number of reports have recently appeared on the excellent stability of BTESE-derived membranes, this type of membrane was further investigated. It appeared that very homogeneous layers could be deposited on a mesoporous γ-Al2 O3 underlayer (Figure 21.10b) as well as on an 8YSZ underlayer (Figure 21.10c). he pore size distribution was analyzed using permporometry with helium as carrier gas and water as condensing/blocking compound.

4 4 4 4 4 4 4 4

�P (bar)

H2 (mol m –2 s –1 Pa –1 )

3.07 × 10 –8 2.10 × 10 –8 3.09 × 10 –8 4.50 × 10 –8 2.39 × 10 –8 1.59 × 10 –8 1.42 × 10 –8 2.84 × 10 –8

He (mol m –2 s –1 Pa –1 )

1.91 × 10 –7 9.54 × 10 –8 8.93 × 10 –8 1.10 × 10 –7 8.80 × 10 –8 5.27 × 10 –8 7.11 × 10 –8 8.85 × 10 –8

6.35 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 1.83 × 10 –10 3.66 × 10 –10

CO2 (mol m –2 s –1 Pa –1 )

2.1 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 < 1.78 × 10 –10 3.73 × 10 –10

N2 (mol m –2 s –1 Pa –1 )

S1: sample 1; S2: sample 2; < 1.78 mol m –2 s –1 Pa –1 means a value below the detection limit of the flow meter.

SiO2 SiO2 -Ni SiO2 -Co SiO2 -RTP SiO2 -Ni-RTP SiO2 -Co-RTP SiO2 -ink-jet-RTP-S1 SiO2 -ink-jet-RTP-S2

Membrane

Table 21.4 Gas permeance of membranes with SiO2 top layers and doped SiO2 top layers.

> 50 > 118 > 173 > 253 > 134 > 89 77 77

H2 /CO2

> 150 > 118 > 173 > 253 > 134 > 89 > 80 76

H2 /N2

21.3 Examples of Mesoporous, Microporous, and Dense Thin Film Membranes 447

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21

Processing of Nanoporous and Dense Thin Film Ceramic Membranes Microporous hybrid-SiO2 (C2H4-modified)

Microporous hybrid-SiO2 (C3H6NH2-modified)

Mesoporous γ-Al2O3 Mesoporous γ-Al2O3

(a)

(b)

Mesoporous graded ZrO2 (8% Y2O3)

He Permeance (m3 m−2 h−1 bar−1)

60 Microporous hybrid-SiO2 (C2H4-modified)

40

20

0 0

(c)

(d)

Figure 21.10 (a)–(c) SEM images of hybrid SiO2 membranes, coated with a polymeric sol. (a) mesoporous γ-Al2 O3 underlayer and top layer prepared with APTES precursor; (b) mesoporous γ-Al2 O3 underlayer and top layer prepared with BTESE precursor; (c) mesoporous 8YSZ underlayer and top layer prepared with BTESE precursor (two dip-coating steps; calcination at 450 ∘ C in vacuum; α-Al2 O3 disc substrate (d = 40 mm; pore size ∼100 nm)) ((a) scale bar = 200 nm; (b), (c) scale bar = 1 μm); (d) pore

1

2 3 Kelvin diameter (nm)

4

5

diameter of hybrid SiO2 membrane with mesoporous 8YSZ underlayer, measured with permporosimetry. As shown with red arrows, the half value of the average initial permeation corresponds with a Kelvin diameter of ∼0.6 nm (carrier gas He; blocking liquid water; tubular α-Al2 O3 substrate; length 105 mm, outer diameter 10 mm, inner diameter 7 mm; pore size ∼70 nm; two dip-coating steps; calcination at 450 ∘ C in vacuum).

While the pure SiO2 membranes were too tight for our test equipment, the pore size of the hybrid SiO2 membrane was significantly larger with an average value at around 0.6 nm. In Figure 21.11, the gas permeation behavior of a hybrid SiO2 and a pure SiO2 membrane are compared. It can be seen that the hybrid membrane shows no Knudsen diffusion (CO2 > N2 ), which confirms a microporous structure with relatively small pores, as observed in permporosimetry. he membrane, however, does not show micropore diffusion (H2 > He) either, which suggests the influence of a CO2 adsorption and surface diffusion mechanism. he influence of CO2

Examples of Mesoporous, Microporous, and Dense Thin Film Membranes

Permeation (mol s−1 m−2 Pa−1)

6 × 10−7

6000 Hybrid-SiO2 RT

5 × 10−7

Hybrid-SiO2 200 °C

5000

SiO2 200°C

4 × 10−7

4000

3 × 10−7

3000

2× 10−7

2000

1×10−7

1000

0

Permeation (l h−1 m−2 bar−1)

21.3

0

2.6 2.8 3.0 3.2 3.4 3.6 He 2.6 (Å) H2 2.89 (Å) CO2 3.3 (Å) N2 3.64 (Å) Kinetic diameter (Å) Figure 21.11 Gas permeance as a function of the kinetic diameter of the test gas for a membrane with a hybrid SiO2 top layer (black measuring points) and a membrane with a pure SiO2 top layer (red measuring

points) (two dip-coating steps; calcination at 500 ∘ C in air (SiO2 ) and at 450 ∘ C in vacuum (hybrid SiO2 ); α-Al2 O3 disc substrate (d = 40 mm; pore size ∼100 nm)).

adsorption can also be seen by the larger CO2 permeation measured at room temperature than at 200 ∘ C. In a series of 10 samples, an average CO2 /N2 selectivity of 5 was observed for this type of hybrid membrane. For comparison, the CO2 /N2 selectivity of a Knudsen membrane is 0.8. Despite this substantial improvement in separation efficiency, a selectivity of 5 is still too low for commercial application of the membrane. It should be noted that our results were obtained in single gas permeation tests and a significant increase of CO2 /N2 selectivity can be obtained in a mixed gas operating mode, as reported in several articles on CO2 adsorption membranes. However, the current membrane should be further improved by reducing the pore openings and/or increasing the CO2 adsorption. 21.3.3 Dense Thin Film 8YSZ Membranes

As mentioned in the introduction, a major challenge in SOFC research is the development of electrolyte membranes with a thickness in the micrometer range. Building upon the knowledge and experience acquired in the synthesis of mesoporous YSZ layers, a novel method using dispersions of nanoparticles with a size in the range of 50–100 nm was introduced [29–32]. Using the nanodispersions shown in Figure 21.12, a mesoporous layer with a thickness in the range of 1–2 μm was possible. For example, a single coating with 8YSZ nanodispersion (A) yields a mesoporous layer with a thickness of ∼2 μm after calcination. A single coating with 8YSZ nanodispersion (B) gives a mesoporous layer with a thickness of ∼1 μm after calcination.

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Processing of Nanoporous and Dense Thin Film Ceramic Membranes

(a) Mesoporous ZrO2 (8% Y2O3)

Macroporous anode layer

EHT = 15.00 kV Detectpr = QBSD WD = 7 mm

Macroporous anode layer

2 μm

Mesoporous graded ZrO2 (8% Y2O3)

EHT = 15.00 kV Detectpr = InLens WD = 7 mm

(c)

Macroporous anode layer EHT = 15.00 kV Detectpr = QBSD WD = 8 mm

EHT = 15.00 kV Detectpr = InLens WD = 9 mm

2 μm

Graded ZrO2 (8% Y2O3)

(d)

Macroporous anode layer

1 μm

EHT = 15.00 kV Detectpr = QBSD WD = 9 mm

(e)

Dense ZrO2 (8% Y2O3)

(b)

Dense ZrO2 (8% Y2O3)

1 μm

Figure 21.12 (a) SEM image of a mesoporous 8YSZ layer, coated with a 60 nm nanodispersion on a regular macroporous NiO/8YSZ anode substrate (two spin-coating steps; calcination at 500 ∘ C; 75 × 75 mm2 substrate). (b) SEM image after thermal treatment for 5 h at 1400 ∘ C in air (sintering) and 3 h at 900 ∘ C in Ar/H2 (reduction). (c) SEM image of a graded mesoporous 8YSZ layer, coated with a 60 nm nanodispersion and a 35 nm particulate sol on a regular macroporous NiO/8YSZ anode substrate (two spincoating steps for each layer; calcination at 500 ∘ C; 75 × 75 mm2 substrate). (d) Sample

1 μm

Dense ZrO2 (8% Y2O3)

EHT = 15.00 kV Detectpr = InLens WD = 7 mm

(f)

1 μm

with an additional coating step with a 6 nm polymeric sol (two spin-coating steps; calcination at 500 ∘ C). (e) SEM image after thermal treatment for 5 h at 1400 ∘ C in air. (f ) SEM image of a thin film 8YSZ membrane with a thickness < 1 μm, made by coating a 60 nm nanodispersion, a 35 nm particulate sol and a 6 nm polymeric sol on a regular macroporous NiO/8YSZ anode substrate (one spin-coating step for each layer; calcination at 500 ∘ C; thermal treatment for 5 h at 1400 ∘ C in air and 3 h at 900 ∘ C in Ar/H2 ). ((a), (b) scale bar = 2 μm; (c), (d), (e), (f ) scale bar = 1 μm).

21.3

Examples of Mesoporous, Microporous, and Dense Thin Film Membranes

Figure 21.12a,b show an example of a spin-coating experiment with the 60 nm 8YSZ nanodispersion (b). he substrate was a common NiO/8YSZ anode substrate made at our institute. he spin-coated sample was fired to 500 ∘ C to give a nondense mesoporous thin film. hen, the coating and calcination process was repeated, yielding a double mesoporous layer of electrolyte material with a thickness of approximately 2–3 μm, as shown in Figure 21.12a. he mesoporous layer can be sintered using the standard temperature program for conventional electrolytes at IEK-1 (1400 C, 5 h) yielding a dense thin film electrolyte with a thickness of ∼1 μm, as shown in Figure 21.12b. he average gas density in terms of He leakage was ∼3.10 –4 mbar l cm –2 s –1 ). Furthermore, we can modify the thickness of the mesoporous precursor layer, and thus the dense thin film electrolyte by adjusting the particle size and the number of coating steps. It became also apparent that the density of the sintered electrolyte improves by using a multiple coating process, with successive nanodispersion and sol coating steps, in a similar way to that described in the previous section for nanoporous membranes. Figure 21.12c illustrates a graded mesoporous design, consisting of a mesoporous layer made with the nanodispersion (B) and a mesoporous sol–gel layer created with the sol (C). In Figure 21.12d, an additional sol–gel layer made with the sol (D) is coated. he graded systems can also be sintered using the standard sintering program (1400 ∘ C, 5 h) yielding a dense thin film electrolyte with a thickness of ∼1 μm. he gas density in terms of He leakage of these layers was on average ∼1.10 –4 mbar l cm –2 s –1 and ∼5.10 –5 mbar l cm –2 s –1 , respectively. Furthermore, it has been shown that combinations, which included nanodispersion (A), yielded somewhat thicker electrolytes with a thickness of ∼2 μm and an improved gas density of up to ∼1.10 –5 mbar l cm –2 s –1 ) was achieved [32]. Development work is under way to prepare even thinner dense 8YSZ electrolyte layers. he first prototypes were made by spin coating single layers of a nanodispersion and a sol. he composition of the coating liquid was in addition further refined to improve the coverage of the substrate during the coating step. he substrate was the same NiO/8YSZ anode substrate as in the previous examples. he samples were end-sintered at 1400 ∘ C for 5 h to give a dense electrolyte. hereafter, the sample was reduced in Ar/H2 at 900 ∘ C for 3 h. he gas density in terms of air leakage was ∼1.10 –5 mbar l cm –2 s –1 ) before and 7.10 –4 mbar l cm –2 s –1 ) after reduction, and it can be clearly seen in the SEM (scanning electron microscope) image in Figure 21.12f that the thickness is significantly thinner than 1 μm. After its successful introduction, the method for depositing dense thin film 8YSZ membranes was applied to make novel SOFCs with a thin film electrolyte [84, 85]. Figure 21.13 shows SEM images of a finished cell, prepared by dip coating a mesoporous 8YSZ layer on a tape-cast NiO/8YSZ substrate, followed by sintering at 1400 ∘ C for 5 h. hereafter, a CeGd-oxide (CGO) Sr-diffusion barrier layer was coated with PVD and a LaSrCoFe-oxide cathode layer was deposited with screen-printing. he higher magnification micrograph (Figure 21.13b) confirms that the thickness of the novel electrolyte layer measures approximately 1 μm, which is one order of magnitude smaller than the electrolyte thickness in our regular SOFC and other values reported in the literature for conventional

451

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(a)

21

Processing of Nanoporous and Dense Thin Film Ceramic Membranes

Cathode compartment

(4)

(b)

(3) (2)

Anode compartment EHT = 15.00 kV Detectpr = QBSD WD = 9 mm

10 μm

Figure 21.13 Backscattering SEM images of a thin film SOFC. The cell comprises: (1) a Ni/8YSZ anode, (2) a thin film 8YSZ electrolyte, made by dip coating with a 60 nm nanodispersion, (3) a CeGd-oxide (CGO) electrolyte, made by physical vapor

EHT = 15.00 kV Detectpr = QBSD WD = 9 mm

1 μm

(1)

deposition, (4) a LaSrCoFe-oxide cathode, made by screen printing; (b) shows a detail of the 8YSZ (dark) and CGO (bright) thin film electrolyte layers. ((a) scale bar = 10 μm; (b) scale bar = 1 μm).

coatings. In this backscattering image, the two different electrolyte layers can be clearly distinguished. he first layer is the 8YSZ layer and the second brighter layer is the CGO Sr-diffusion layer, made by PVD. In a single cell test, it also appeared that the reduced electrolyte layer thickness improves the performance of the cell significantly. At the typical SOFC operating temperature of 800 ∘ C, the thin-film cell gave a superior average current density of 2.7 A cm –2 , which corresponds to a power density of approximately 1.9 W cm –2 (cell voltage 0.7 V). Another important consideration is that the cell also provides superior values at lower temperatures. For example, the current density at 650 ∘ C measures 1.6 A cm –2 , which represents an improvement of approximately 60% in comparison with the value obtained for the regular SOFC.

21.4 Summary and Additional Comments

In this chapter, we have seen that the deposition of sols containing nanoparticles is a very attractive method for the fabrication of ceramic thin film membranes. Furthermore, from the results obtained in our lab, it appeared that the method allows the deposition of mesoporous (pore size > 2 nm), microporous (pore size < 2 nm) and dense membranes. he mesoporous membranes in our work include, for example, a conventional γ-Al2 O3 membrane and a novel stabilized ZrO2 (8% Y2 O3 ) membrane. he latter membrane has, in contrast to conventional membranes, a sufficient chemical and thermal stability. In this way, typical separation applications in the industry which involve, for example, water vapor, a high temperature, and corrosive solutions can be considered. Such membranes are very suitable, for instance, for filtering

References

out large organic molecules in ultrafiltration processes, which is today one of the most frequent applications of ceramic membranes. In gas separation processes, the membranes show Knudsen selectivity, which is insufficient for current commercial applications. To improve the separation efficiency in gas separation, we developed in parallel microporous membrane layers. To this end, we use a mesoporous membrane as an underlayer to form a graded membrane. he specific examples provided in this chapter are an amorphous SiO2 and a hybrid organic-SiO2 membrane. he amorphous SiO2 membrane shows a relatively dense structure, in which H2 can permeate, while CO2 and N2 are excluded. he H2 /CO2 selectivity of the SiO2 membrane exceeded on average 50 and 150. he hybrid SiO2 membrane shows a more open structure, with an average pore size of around 0.6 nm. As opposed to the pure SiO2 membranes, the hybrid membrane is a candidate for the separation of CO2 from other larger gases such as N2 and CH4 . Currently, the membrane is further improved by reducing the pore openings and increasing the CO2 adsorption. he current hybrid SiO2 membrane is also under investigation for application in pervaporation, which is today one of the most important industrial applications of microporous membranes. Dense thin film membranes have a wide range of possible applications in the field of gas separation (e.g., O2 /N2 ), SOFCs, and solid-state batteries. In our work, successful synthesis of a 8YSZ dense thin-film membrane was demonstrated. his membrane can be deposited with a thickness of ∼2 μm, ∼1 μm, and even

less material High durability > build less often CO2 -savings in manufacturing

CO2 emission reduction relevant

Product relevance FuturBeton C.1

Product relevance HPPC

√

√

√

-indirect

√

√

√

√

√

√

√

√

√

Huge

—

100 μm

100 μm

(a)

OPC

(b)

HPPC

(c)

OPC vs. HPPC

Figure 26.11 (a–c) Optical microscopy of OPC-powder, HPPC-powder, and sculpture with complex structure by OPC and HPPC respectively [2].

durability. For concrete constructions that are subject to structural engineering, material can be saved and, thus, one can not only build in a more sustainable but also once again lighter, higher, and again, even more cost-effective (CA3) way. More sustainable here means that over the time one has to build less at the same benefit which is another reason for the materials cost-effectiveness (CA4). he new building material FuturZement/Beton C.1 offers in its manufacturing route in total a gigantic number of CO2 -emission savings compared to conventional concrete where next to the concern and for the care of our environment, such savings can already today be calculated into Cents and Euros. hus one can therefore build responsibly and for the fifth time more economically (CA5). And all this at an additional cost of currently approx. 7 € t –1 FuturBeton C.1. Particularly utilizing HPPC that is usually also mixed as a fraction with OPC, more complex and finer high-strength structures can be realized (Figure 26.11). By this, one can, for example, manufacture concrete facades at better quality with lighter components and even lighter lightweight concrete blocks with even better thermal insulation values.

References

Table 26.6 FuturBeton C.1 and/or HPPC, where to go and what to do. Country

CO2 emission is expensive

Large steel industry, GGBS waste product available

√ √

√

A B C D

— —

— √ —

Proper answer

FuturBeton C.1 HPPC HPPC/FuturBeton C.1 HPPC

In countries where CO2 emission is expensive and where the steel industry, and, therefore, GGBS as a waste product, is available in mega masses, FuturBeton C.1 is the right answer. In countries where at least one of the two conditions is not given, HPPC shall be given priority. Also in case of HPPC, still huge CO2 -emission savings could be generated because the CA1–CA4 mentioned above apply equally to HPPC, and CA1 and CA3–4 are directly CO2 -relevant (Table 26.6).

Acknowledgments

We very much appreciate the financial support from the BMBF, and we thank all partners in the project “FuturZement” and also all partners co-operating in previous and ongoing joint projects. Without their contribution, this work could not have been done, and we would like to mention especially Dr Carsten Geisenhanslueke, Mr Wilhelm Nolte, Mrs Miriam Ringwald, and Dr Josef Strunge (Dyckerhoff AG); Mrs Katrin Schumacher, (University of Siegen); Mr Frank Siedenstein (Runkel Fertigteilbau GmbH); Dr Albert Herrmann, Mr homas Hoeppner, and Mrs Birgit Mohrhardt (Fuchs Lubritech GmbH); Dr Sebastian Diaz de la Torre and Dr David Jaramillo Vigueras (CIITEC-IPN); Mr Bernd Knaebel, Mr Josef Zeppenfeld, and Mr Hans Venc (Civil Engineering Department of Olpe); Mr Ralf Rombach and Mr Manfred Funk (Straßen.NRW).

References 1. Zoz, H., Benz, H.U., Schäfer, G.,

Dannehl, M., Krüll, J., Kaup, F., Ren, H., and Jaramillo, D.V. (2001) High kinetic processing of Enamel, p. Ia/b. INTERCERAM Int. Ceram. Rev., 50 (5), 388–395and (6), 470–477. 2. Zoz, H., Jaramillo, D., Tian, Z., Trindade, B., Ren, H., Chimal-V, O., and Diaz de la Torre, S. (2004) High

performance cements and advanced ordinary portland cement manufacturing by HEM-refinement and activation. ZKG Int., 57 (1), 60–70. 3. Nolte, W. from Co. Dyckerhoff AG (2010) High performance cement and application, OZ-10. 3rd German-Japanese Symposium on Nanostructures Wenden, Germany, proceedings Vol. 3, p. V05. 4. Arteaga-Arcos, J.C., Chimal-Valencia, O.A., Delgado Hernández, D.J.,

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Yee-Madeira, H.T., and Diaz de la Torre, S. (2011) High energy ball mill parameters used to obtain ultra-fine portland cement at laboratory level. ACI Mater. J., 108-M39, 371–377. 5. Fuentes-Romero, M.T. (2013) María Teresa Fuentes Romero, Evaluación de la durabilidad del cement clase H Y compositos cementantes base scoria del alto horno, Master thesis. CIITEC-IPN, Mexico. 6. FuturZement (2009-2012) Project of the German Federal Ministry for Education and Research (BMBF). Project-No. 03X0068A. 7. FuturZement (2013) Project of the German Federal Ministry for Education and

8.

9.

10.

11.

Research (BMBF). Project-No. 03X0068. Weitzel, B. and Trettin, R.; Final Report 2013, part University of Siegen. Smolczyk, H.G. (1980) Slag structure and identification of slag. 7th ICCC, vol. 1, Paris, pp. 1–17. Communication with Dr. Eichhorn, U. (2013) Managing Director VDA, Association of the German Automotive Industry, Berlin (05-2013). Press release Federal Environment Agency of Germany (UBA) (26 February 2013). he Cement Sustainability Initiative Progress Report (2005).

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27 Hydrogen and Electromobility Agenda Henning Zoz and Andreas Franz

27.1 Introduction

he starting point of the Zoz hydrogen and electromobility agenda is the energy storage tank H2Tank2Go with the related concept of a revolution in the refueling infrastructure. his feasible concept in hydrogen mobility will ultimately contribute to the environment only if a replacement for fossil fuel is generated from renewable sources. And thus our application guides our well-known proposals for the base-loadable CO2 -free power plant and also the feasible approach “Power to Gas to Fuel.” hese together would and can provide a, if not substantial, contribution to the energy turn. hose virtually pressureless storage systems based on metal hydrides are nothing new, and on this topic, for example, Zoz had cooperated with Opel/GM already more than 10 years ago (test vehicles Opel Zafira). What is new is that the materials are getting better and the idea is quite simple with little exchange tanks “exchangeable at a vending machine.” From today’s point of view, the earlier and also still present demand of for an automotive to “refuel hydrogen at the vehicle” has been simply wrong since this would require complex, heavy, and expensive tanks. And so the problem raised by the auto industry of the lack of infrastructure for hydrogen refueling can not only be solved by the Zoz tanks but will be virtually nonexistent. One can, from now on, refuel at any home depot and/or get the filled tank through mail order. In order to bring this very safe and effective future technology into a commercial application, Zoz Group has been carrying out substantial R&D activities in H2 -powered vehicles. As a result, at the Hannover Fair 2011, a prototype of the hydrogen kickboard isigo H2.0 was presented to the public. One year later, at the Hannover Fair 2012, the semi-serial version of the isigo H2.0, powered by two H2Tank2Go tanks, was demonstrated. However, since the auto industry does not show any interest, the detour through the air according to Zoz might lead to the breakthrough: “ … since automotive insistently does not want to have a look, we go into the air and then just drop the

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he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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tanks” (on the road) … “and if everything keeps going well, our tanks could fly in 1–2 years.” his understanding led to the formation of a project called “H2-OnAir+.” he goal of the H2-OnAir+ project is to equip solar- and battery-powered aircraft with an additional fuel-cell range extender to increase the range to at least three times its current value (at zero sun, from notional 33 to >100 km), proving that hydrogen is a potential candidate for primary power supply of clean aviation. If this concept is successful, then the next step is the application in electric car propulsion and finally for the entire range of personal transportation systems. And what is equally important for its success is the availability of cost-effective fuel cells made by Zoz, that is, H2-OnAir+, which are also on our to-do list. “Exactly these fuel cells can then power the already known Zoz-H2 -kickboards and then soon a car,” says Dr. Henning Zoz, President of the Zoz Group. In order to follow up on the goal to effectively work on a H2 power pack solution, the Zoz Group recently purchased a fleet of electric passenger cars. hese vehicles will be visible on the road in the near future as they will be rented out to nearby communities and businesses in the Sieger/Sauerland area. hey also will be part of yet another project called REMONET, which is a collaboration between the University and also the city of Siegen along with various companies in the area, including the Zoz Group. he main purpose of REMONET is to gather knowledge about electromobility in a rurally structured city region. his will include a variety of issues such as car sharing, refueling infrastructure, customer behavior, the utilization of electrically driven vehicle fleets for certain businesses, and much more. At first, the electric vehicle fleet of Zoz (Zoz ZEV fleet/ZEV, zero-emission vehicle) will remain solely battery-driven, and all the data generated by their consistent usage will be thoroughly analyzed within the REMONET project. However, in the future, parallel to the development of the H2 -driven power platform for the H2-OnAir+ project, the plan is to also equip the Zoz ZEV fleet with the same fuel cell/H2 tank setup that is powering the electric aircraft and use it as a range extender. If possible, there will be no major changes to the system (same fuel cell for aviation and for ground application). If successful, both passenger cars and electric aircraft will significantly increase their range and will be completely independent of any hydrogen refueling infrastructure as a result of the use of the quickly replaceable H2Tank2Go . Finally, the last point on the Zoz Hydrogen Agenda would be the widespread utilization of hydrogen-driven mobility (using H2Tank2Go cartridges) but with hydrogen being produced completely by the so-called renewable energy sources such as wind or sunlight. As of today, most hydrogen (>90%) is produced as a byproduct of the chemical industry. Only if the hydrogen is produced via electrolysis of water using “clean” energy sources will it be possible for mobility to become independent of fossil fuels. herefore, the motto of the Zoz Group is “Power to Gas to Fuel.”

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27.2

27.2 H2Tank2Go

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H2Tank2Go

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and isigo

H2.0

® and isigo®H2.0

For over 3 years now, Zoz GmbH has been involved in the development and production of small hydrogen storage cartridges called H2Tank2Go (Figure 27.1), which are based on metal hydride technology. he method of storing hydrogen is based on metallic alloys that are able to absorb hydrogen “like a sponge” and therefore can store large amounts of the gas in a relatively small volume. At room temperature, the pressure inside one tank is only at about 5 bar, whereas the amount of hydrogen would easily surpass 700 bar if the storing method was based on high-pressure technology and there was no metal hydride powder inside the tank. When it comes to volumetric storage density, the H2Tank2Go even beats the so-called cryo tanks (see Figure 27.2), in which hydrogen is stored in the liquid form at extremely cold temperatures (−253 ∘ C). he H2Tank2Go itself is a bottle-sized (∼1 l) cartridge that is filled with a metallic alloy, produced by Zoz Gmbh, called Hydrolium . his alloy is able to reversibly store about 50 g (∼556 standard liters, which is equivalent to about 1.67 kWh of chemical energy) of hydrogen. It remains inside the tank in the form of a loose powder. Special filters ensure that no powder can ever leak out of the tank. he pressure inside the cartridge is basically related to its temperature. he higher the temperature, the more hydrogen is released, which leads to a higher pressure. However, at usual operating conditions the pressure does not exceed 10 bar. herefore, the H2Tank2Go offers a relatively safe method of storing large amounts of hydrogen in a limited volume. Regarding the stored energy, one has to take into account the fact that H2 has to be converted into water (adding the atmosphere’s oxygen) via fuel cells, whose efficiency factor is about 60%. So the 1.67 kWh of

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Figure 27.1 H2Tank2Go .

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120 Material capacity

Complex MH Chemical hydrides

System capacity

100 Volumetric capacity (g L–1)

570

80

Ultimate target

Liquid H2

Hydrolium®

60

HPMH 2015 target

40

Gas at 700 bar

H2Tank2Go® Liquid H2

20

700 bar

Gas at 350 bar

2010 target

350 bar

0

0

2

4

6

8

10

12

Gravimetric capacity (wt%) Figure 27.2 Volumetric and gravimetric storage capacities for different methods of storing hydrogen.

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chemical energy stored inside one H2Tank2Go cartridge is equivalent to about 1 kWh of electrical energy (of course, depending on the efficiency of the fuel cell). A good Li-ion battery today stores about 250 Wh l−1 and 150 Wh kg−1 of energy. he H2tank2Go weighs slightly more than 4 kg and thus offers about double the gravimetric and even four times the volumetric energy storage capacity compared to a regular Li-ion battery. So the potential use of H2Tank2Go technology for electromobility purposes is quite obvious. To bring the capabilities of the H2Tank2Go into practical use, a real demonstrator had to be developed. For this purpose, the reconstruction of a formerly solely battery-driven electro-kickboard called “isigo 1.0” was revealed to the public at the Hannover Fair 2010 as the prototype of the hydrogen-driven kickboard “isigo H2.0.” Whereas the battery-driven isigo has a range of about 20–25 km, the prototype of the isigo H2.0 could go to about 60 km with one H2Tank2Go cartridge. One year later, at the Hannover Fair 2012, the semi-serial version of the isigo H2.0 (Figure 27.3), powered by two H2Tank2Go tanks followed, increasing the theoretical range up to 120 km. For applications such as electric kickboards, for safety and complexity reasons, this could not even remotely be done with other hydrogen storage techniques such as cryo or high-pressure tanks. But the very high volumetric storage density and the relatively high safety of the H2Tank2Go are not the only advantages of the product. One of the main benefits is the very easy and superfast exchangeability of empty tanks against freshly charged ones via the so-called Click’n-Go system. As the charging operation to get gaseous H2 into the Hydrolium powder is not a fast process (typically more than 1 h), it basically makes no sense if one wants to charge hydrogen directly

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27.3

The H2-OnAir+ Project, “Iron Bird,” and Economical Fuel Cells

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Figure 27.3 isigo H2.0.

into the vehicle. In order to do so, one would need a very complex tank with a very advanced cooling system, which would make the tank heavy and expensive. his may be one of the main reasons why the automotive industry basically has no interest in metal hydride technologies (another reason may be the gravimetric storage density, which although much better than Li-ion batteries is, because of the weight of the hydride powder, worse than with other H2 storage techniques). But in case the vehicle is directly powered by a fuel cell, the charging or refueling time with the H2Tank2Go and its Click’n-Go system is only a few seconds (replacing an empty tank with a fresh one) and so time issues at the refueling station are basically nonexistent. One could from now on easily refuel at any home depot and/or get the fuel through mail order. Another way would be to install a kind of vending machine (Figure 27.4) at any gasoline station, where empty tanks can be exchanged against fully charged ones for very little cost (basically just for the cost of hydrogen inside the tanks). With this kind of “refueling stations,” the very huge problem of installing a proper hydrogen infrastructure, which is a major obstacle for the breakthrough of hydrogen-driven vehicles on the road, could be bypassed, as it is much easier to put vending machines anywhere than high-pressure hydrogen refueling systems. So in conclusion, the H2Tank2Go could totally revolutionize the existing H2 infrastructure.

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27.3 The H2-OnAir+ Project, “Iron Bird,” and Economical Fuel Cells

Because of the fact that the Zoz Group is a relatively small company with very limited resources, the step to finally turn this kind of H2 infrastructure revolution

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Figure 27.4 “Vending machine” for exchanging hydrogen tanks.

into reality cannot be done without financial and technical help. Large projects need proper funding and, since the automotive industry up to now has not shown any interest, maybe a detour through the air might lead to a breakthrough. Although the issue of hydrogen infrastructure at first was not a reason for the formation of a project called H2-OnAir+, the Zoz Group has made it a top priority within its list of targets. 27.3.1 So What Is H2-OnAir+?

H2-OnAir+ is a European cooperative project under the umbrella of the EUROGIA+ initiative, which is a bottom-up, industry-driven, market-oriented program which addresses all areas of the energy mix from renewable energy to efficiency and reduction of carbon footprint of fossil fuels. he main goal of the H2-OnAir+ project is to equip a solar- and batterypowered aircraft with an additional fuel-cell range extender to increase the range to at least three times its current value (at zero sun from notional 33 to > 100 km), proving that hydrogen is a potential candidate for primary power supply of clean aviation. If this concept is successful, then the next step is its application to electric car propulsion and, finally, for the entire range of personal transportation systems. he hydrogen-driven fuel-cell range extender will work in tandem with the existing Li-ion battery (by also recharging the battery in flight) and, for cost, performance, and particularly weight reasons, will be composed of different options of hydrogen tanks feeding PEM fuel cells (PEM-FCs).

27.3

The H2-OnAir+ Project, “Iron Bird,” and Economical Fuel Cells

Figure 27.5 Solar driven aircraft “Icaré 2.”

Air-breathing fuel-cell stacks (optimized for cost and weight) in the power range of about 2 kW each will be integrated as a twin system (redundancy) to achieve a total of about 4 kW rated electrical power. he complete additional weight of the range extender will not exceed 50 kg. For the hydrogen supply, different routes of storing hydrogen will be investigated. All tanks will have the same quick-connector system, thus a competitive investigation can easily be achieved. A strong synergy is given to the project with the presence of several German, French, and Polish partners. his project is based on the Icaré 2 aircraft platform (Figure 27.5) of the University of Stuttgart, which is operated today in cooperation with Steinbeis Flugzeugund Leichtbau GmbH (SFL). he Icaré 2 was built for solar flight. For this reason, it has been designed for extremely low power consumption in all flight conditions. he typical power requirement for sustained cruise flight is less than 2 kW of electric power. For take-off, the electric engine needs up to 14 kW, which is provided by a rechargeable battery system. With its low power consumption, particularly at cruising altitude, Icaré 2 is an ideal test platform for new energy systems. Moreover, Icaré 2 incorporates all features such as low energy consumption, solar generator, and battery system for future flying and other transportation platforms. Icaré 2 was also chosen because it can act as an experimental platform for a future HAPS (high-altitude pseudo satellite). Such platforms need to have solar cells on board for basic energy supply. Icaré 2 already has the solar cells. In addition, batteries are needed, which are already on board. his combination is currently not enough to keep HAPS on altitude during the night. Additional power coming from the PEM could be an alternative to keep advanced HAPS on altitude, and H2-OnAir+ will give us some insight into this issue (Figure 27.6).

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Data: Wing span: Wing area: Empty mass: max. take off mass: max. wing loading: Solar panel area: max. input power: min. power required:

25.0 m 25.7 m2 270 kg 360 kg 14.0 kg m–2 21.6 m2 14 kW 1836 W

Figure 27.6 Icaré 2 – technical specifications.

Figure 27.7 H2-OnAir+ project partners.

he project’s consortium consists of the following partners (see also Figure 27.7): – Zoz Group, Germany – H2 tanks, fuel cells – Steinbeis Flugzeug- und Leichtbau GmbH, Stuttgart, Germany – aircraft, installation, flight tests

27.3

The H2-OnAir+ Project, “Iron Bird,” and Economical Fuel Cells

– Institute of Chemical Engineering, Polish Academy of Sciences, Poland – analysis of metal hydrides – Centre National de la Recherche Scientifique CNRS, Montpellier, France – testing of fuel cells – MAHYTEC, France – H2 tanks – Airbus, Germany – consulting partner (not part of the project consortium). Zoz Group will develop a customized, air-cooled PEM-FC to significantly improve the performance of the Icaré 2. During the development of lightweight and cost-effective fuel cells, Zoz for the start-up phase of the project will utilize a (semi)commercial PEM-FC in the range of 2 kW, so that the H2 range extender can be built independently of the progress of fuel-cell development. Zoz will also be responsible for the implementation of the complete range-extender platform into the already existing (battery driven) electric passenger cars as an additional ground application. 27.3.1.1 The Case for Including Fuel Cell Development into This Project

Within the scope of the project, it is planned to work on an efficient and also cost-effective PEM-FC in the range of about 2 kW power. hese include the core components of membrane and gas diffusion layer, bipolar plates, and mechanical/thermal control engineering of hydrogen fuel as well as heat management. Indirect products are the automation of the “stack production,” including membrane assembly, stacking, and sealing. Further indirect products can be inexpensive and small pumps, valves, and control circuits as well as efficient back-up batteries, which, according to the current state of the art, are to be provided in each overall drive concept. No product can be economically viable without a market. It is therefore of crucial importance that, owing to lack of product availability, currently little or no existing market is addressed by the project partners where their own capacities can establish a breakthrough to the end user. hus it is in the nature of things that we should start small, and so with “small” fuel cells. It is also important to note that, within the power range of about 2 kW, all kinds of quasi-stationary applications in mobile homes as well as “grid-less” small applications like telephone booths, vending machines, sailboats, and so on, could be realized. he proposed power range would also be suitable application inside small electric passenger cars, which are already at the disposal of Zoz GmbH. It can recharge the corresponding batteries and is especially flexible and therefore future-oriented. And exactly this is the aim, that is, the attainment of a current target price of EUR 1000 per kW of power, which today, in the case of small cells, is completely unmatched and nowhere in sight! And one may safely assert that, for example, mobile home manufacturers are eagerly waiting for a cost-effective and safe fuel cell/hydrogen tank energy package to finally be able to replace the woefully heavy batteries for stationary power supply. Here, for example, a market is directly in sight and virtually present, but the product is still missing.

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To achieve the goal of an economical and cost-effective fuel cell, it is necessary to completely rethink the conventional build-up of the fuel cell stacks as well as the typically imposed technical requirements. Here, the main technical points of concern are the bipolar plates, the catalyst, and fuel-cell stack periphery. New bipolar plates should be fundamentally changed so that the use of graphite can be completely avoided. Consuming processes such as cutting or PIM (powder injection molding) would then be not required if bipolar plates are made of more favorably priced metal where the so-called flow fields are stamped by modern press facilities or even functionally shifted. In the case of the second significant cost driver, the catalyst, the coating process of the membrane should be fundamentally changed. Instead of, for example, spraying and rolling the material onto the membrane and thus generating loss through “overspray,” an optimal surface exposure with a significantly simplified joining mechanism to the polymer membrane and therefore greatly reduced loss of material and also labor/process costs could be done via modern gluing techniques. his allows for a saving of “expansive” precious metals in circulation; otherwise, a “premade catalyst layer” from the precious metal factory would significantly expand the catalytic surface exposure, which would also lead to a saving of precious metal within the product. Such a “premade catalyst layer” according to current estimates does not have to be costly but can, on the contrary, be cheaper than specific precious metal powders currently used. Also, the demanding attitude toward a fuel cell shall be addressed here. In this case, a fuel cell that offers cost effectiveness can be satisfactory even if it withstands less than 1000 h of lifetime. Regarding the periphery, which is the third cost driver, it can be noted that conventional fuel cells are equipped with a large number of tubes, sensors, pumps, valves, and switches. Here, the Zoz Group has demonstrated, at least in the most promising approaches, that a 320-W PEM-FC can also get by with just a hose and valve. In order to counteract the possible argument of a “disposable product” right away, there must be no more disposable products today! But, “products to be recycled after a defined operating life” can promise success. And an important environmental and resource aspect of the fuel cell is just its excellent ability to be recycled. he combination of the newly developed PEM-FC together with appropriate hydrogen supply (H2Tank2Go cartridges) and system management (current-, heat-, gas-flow regulations) basically makes up a “hydrogen power platform,” which in case of mobile applications, such as the Icaré 2 aircraft and small passenger cars, can act as a range extender (or even main power supply), but also be used for any other (stationary) applications that need an independent power supply. Project leader of Airbus Group Innovations calls this H2 power platform the “Iron bird” and will perform all the tests on ground. To demonstrate the technical capability of the finished H2-OnAir+ hydrogen range extender, SFL will perform a number of test flights within Germany.

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27.4

Zoz ZEV Fleet and Project “REMONET”

27.4 Zoz ZEV Fleet and Project “REMONET”

Also the fully developed range extender platform shall be used for ground application inside electric passenger cars. Like in the aircraft scenario, the range of the cars will be increased with a range extender based on hydrogen. he goal here is to simply put the “Iron bird” power platform out of the air and transfer it to the ground without any significant modification. Zoz Group has already taken the first steps in approaching this goal by the purchase of a small fleet of battery-driven electric cars (10 small passenger cars; Figures 27.8 and 27.9), of which some will be put into operation in public places for the communities of Wenden, Freudenberg, and Siegen as well as for local businesses in the area. he users of those cars are bound by a long-term rental contract and have already made commitments to establish highly visible parking places where only zero-emission vehicles (10–12 spots in the area of Siegen, Wenden, and Freudenberg) are allowed to park. As long as the H2-OnAir+ project and the development of the “Iron bird” power platform are going on, the Zoz ZEV fleet will remain solely battery-driven. Nevertheless, the vehicles will be in operation and visible on the road in the Sieger/Sauerland area of Germany. he users of the vehicles also have made commitments to install special vending machines for the replacement of old and empty hydrogen tanks against new and freshly charged ones within the next 3 years, so the reconstructed e-cars can be “refueled” with hydrogen by a simple clicking procedure. he integration of the H2 range extender in those vehicles along with the implementation of the “refueling stations” for the exchange of H2 cartridges will effectively showcase its commercial applicability as well as the independence from conventional hydrogen infrastructure (high-pressure tanking stations) and bring positive PR for the whole project.

Figure 27.8 Zoz ZEV fleet.

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Figure 27.9 Zoz ZEV fleet.

he whole strategy regarding electromobility and the Zoz ZEV fleet will also be a part of yet another project called “REMONET.” he REMONET project started in January 2014 and is funded by the federal ministery for education and research – Bundesministerium für Bildung und Forschung (BMBF). he project is led by the University of Siegen. Together with the city of Siegen and various companies from the local area (including Zoz Group), the topic of electromobility will be thoroughly analyzed by actively getting involved in various related endeavors, producing data, and drawing conclusions out of the results. he main purpose of REMONET is to gather knowledge about electromobility in a rurally structured city region. his will include a variety of topics such as car sharing, refueling infrastructure, customer behavior, the utilization of electrically driven vehicle fleets for certain businesses, and much more. Zoz Group will contribute with its ZEV fleet and installation of two recharging stations for electric vehicles in the center of Siegen.

27.5 Power to Gas to Fuel

Today’s political landscape basically dictates that one of the main problems in the world is the life-giving gas for all plants on the planet, namely, carbon dioxide. he man-made part of about 4% of the total amount of CO2 in the atmosphere (currently at about 400 ppm, measured near the active volcano at Mauna Loa, Hawaii) is declared the key cause of global warming. And although Germany’s output of CO2 emissions makes up for only 3.4% of the global figure and therefore a fraction of only 0.0000544% of the earth’s atmosphere, the use of fossil fuels in Germany is generally regarded as a sin against Mother Nature and to be avoided at all cost. Regardless of the scientific debate around this issue, the sociopolitical road map for the future points more and more in the direction of the so-called renewable

27.5

Power to Gas to Fuel

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energies such as wind and solar, which are heavily subsidized by the German government. After the incident at the Fukushima Daiichi nuclear power plant in Japan 2011 and the hurried decision to shut down all German nuclear power plants until 2020, this trend now seems to be irreversible. But sunshine and wind are naturally always subject to fluctuations, thus a constant flow of such renewable energies can never be achieved. In order to provide a base-load power supply without having a fossil-fuel-based backup, one has to somehow store the renewable energy during times of overproduction (strong wind, heavy sunshine). At times when there is neither wind or sunshine, or when the amount of produced energy simply is not enough, this stored energy could be used to guarantee the continuity of power supply until (enough) wind and sunshine become available. he sad news is that there is currently no method to store large amounts of energy, so that the so-called energy turnaround in Germany can actually function in a way that would make us independent of fossil fuels. All the pumped storage hydro power stations in Germany put together can only store enough energy to keep the country going for about 30 min, and unfortunately they are only available at a very small number of locations. herefore, one very important challenge for the future will be to find an alternative, feasible, and also economical storage solution. Although at the moment there is no large market neither for electrolyzers that convert water into hydrogen and oxygen using only electricity nor for large enough hydrogen storage tanks or even the appropriate methods for the reconversion of hydrogen into electricity (large fuel cells or H2 turbines, etc.), at CO2 + 4 H2

CH4 + 2 H2O

CH4 Regularwind, regular sunshine

CH4

Methanation (natural gas production)

H2

Household gas supply

Natural gas grid

H2-storage and -tanking-station 2H2 O O2

Renewable energies / power generation (e.g., windpark rothaarWind”)

H2

O2+ 2 H2 H2

Electrolyzer (hydrogen production)

H2

H2 H2Tank2Go®-distribution (exchange of empty against charged cartridges)

H2

Electric car (incl. fuel cell-range-extender and H2Tank2Go®-tanks) isigo® H2.0

H2Tank2Go® -cartridges

H2 H2

Power grid

H2 → electricity (energyreconversion)

Battery charging station (for electric vehicles)

Electric car (incl. gasoline-range-extender)

Figure 27.10 “Power to Gas to Fuel” – power plant scheme at normal conditions.

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Hydrogen and Electromobility Agenda

CO2 + 4 H2

CH4 + 2 H2O

CH4

CH4

Methanation (natural gas production)

H2 Overproduction (strong wind and sunshine)

Natural gas grid

Household gas supply

H2-storage and -tanking-station

H2

O2+ 2 H2

2H2 O O2

H2

H2

H2

H2

Electric car (incl. fuel cell-range-extender and H2Tank2Go®-tanks)

®

Renewable energies / power generation (e.g., windpark rothaarWind”)

H2Tank2Go -distribution (exchange of empty against charged cartridges)

Electrolyzer (hydrogen production)

H2Tank2Go® -cartridges

isigo® H2.0

H2 H2

H2 → electricity (energyreconversion)

Power grid

Battery charging station (for electric vehicles)

Electric car (incl. gasoline-range-extender)

Figure 27.11 “Power to Gas to Fuel” – power plant scheme at overproduction (strong wind and sunshine).

CO2 + 4 H2

CH4 + 2 H2O

CH4

CH4 Methanation (natural gas production)

H2

No wind, no sunshine

Natural gas grid

Household gas supply

H2-storage and -tanking-station 2H2 O O2

Renewable energies / power generation (e.g., windpark rothaarWind”)

H2

O2+ 2 H2 H2

Electrolyzer (hydrogen production)

H2

H2

H2 H2Tank2Go®-distribution (exchange of empty against charged cartridges)

H2Tank2Go® -cartridges

Electric car (incl. fuel cell-range-extender and H2Tank2Go®-tanks)

isigo® H2.0

H2 H2

Power grid

H2 → electricity (energyreconversion)

Battery charging station (for electric vehicles)

Electric car (incl. gasoline-range-extender)

Figure 27.12 “Power to Gas to Fuel” – power plant scheme at low input from renewable energies (no wind and no sunshine).

27.5

Power to Gas to Fuel

least it would be possible even today to build a demonstrator basically combining all of the above-mentioned technologies, giving an example for the possible decentralized clean energy of the future. As shown in Figures 27.10–27.12, Zoz Group has already proposed a kind of demonstration power plant, which as an alternative option even including the possible methanation of hydrogen using CO2 gas. he thus produced methane gas could be stored in the already existing natural gas grid. Although all the components of the proposed power plant already exist today, its technical realization would be an economic disaster because in terms of household power supply it cannot compete with the established technology based on fossil fuels. In the near future, this scenario can only be economical if gasoline for mobility purposes is also replaced by hydrogen technology. To avoid the complex and expensive construction of a high-pressure H2 infrastructure, the Zoz approach using H2Tank2Go technology could go a great way in mastering the “energy turnaround.”

®

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28 Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials Seok-Woo Lee and Julia R. Greer

28.1 Introduction

With the increasing use of nanotechnology, mechanical properties of nano-sized crystals with different initial microstructures are being have been actively investigated. Especially, the size effects on mechanical properties, especially strength and toughness, have attracted significant interest since those would be the most important parameters for the design of mechanically reliable devices such as micro-electro-mechanical systems (MEMS). he recent state-of-the-art experiments have demonstrated that the mechanical behavior of nano-sized metals is vastly different from that of their bulk counterparts. For example, a single crystalline metals exhibit a “smaller is stronger” trend, which is characterized by the empirical power law. In the case of face-centered cubic (fcc) metals, nano-cylinders with 200 nm in diameter are about 20 times stronger than 20 μm-diameter ones made of the same material. However, nanocrystalline nanopillars exhibit an opposite behavior, a “smaller is weaker” trend governed by the grain boundary (GB)-mediated mechanisms. Metallic glasses, which contain liquid-like atomic configurations, exhibit a “smaller is ductile” trend. A metallic glass sample, which is extremely brittle at the bulk scale, is capable of deformation without failure when its diameter is reduced down to 100 nm. For the past decade, the small-scale mechanical testing community has unraveled the fundamental mechanisms that govern the size effects in mechanical behavior, and the present time is just around the corner to turning toward a scalable engineered structures consisting of nanoscale components, a scalable three-dimensional architecture metamaterials where our knowledge on small-scale plasticity should be incorporated. he physical properties of metamaterials are controlled by engineered structure as well as the choice of materials, and the modern technology pushes the limit of the hierarchical length scales to smaller and smaller to achieve unique properties that do not exist at the bulk scale. It is crucial to understand both the mechanical properties that stem from the configuration of structural members and those from materials induced by the size reduction for the design of these architectured structures. hese studies would provide a pathway for us he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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to connect a bridge between nanoscience and useful engineering structures. In this chapter, we first introduce and overview some of the size effects that arise in the mechanical behavior of materials at small length scales and then discuss how these nanomechanical effects can be applied towards the fabrication of useful structural metamaterials.

28.2 Size Matters: Mechanical Behavior at Nanoscale

he most conventional way to control the material properties is through microstructural control. In the case of mechanical properties of metals, dislocation-based strengthening mechanisms, such as strain hardening, precipitation, solid solution, and grain size strengthening would be the best examples in materials science. he models for these mechanisms have been intensively studied for the last 100 years, and especially the strength of bulk materials can now be predicted very well in a quantitative manner. he key parameter here is an “intrinsic” length scale determined typically by the average distance between the governing defects, such as dislocations, precipitates solutes, and grain boundaries. At the bulk scale, the sample size is usually much larger than these intrinsic length scales, and all mechanical properties have been regarded as intensive properties, which means “no dependence of sample dimension.” Recent developments in nanotechnology have allowed us to investigate the properties of nano-sized materials where the sample dimensions, or “extrinsic” length scale to approaches the intrinsic length scale, and have demonstrated the emergence of size effects on the mechanical behavior of materials. Understanding the role of this “extrinsic size effect” at small scales is still a topic of rigorous investigation in small-scale mechanics testing community, and it is critical to develop an understanding of their interplay and mutual effects on the mechanical properties and material deformation, especially in small-scale structures. his section focuses on providing an overview of metal-based material classes whose properties as a function of external size have been investigated and provides a critical discussion on the combined effects of intrinsic and extrinsic sizes on the material deformation behavior. 28.2.1 Smaller is Stronger in Single Crystalline Metals

In the past decade, the small-scale mechanical experiments, mostly uniaxial compression tests, demonstrated that at the micro- and submicron scales, the sample dimension is a key parameter that affects the strength of crystalline metals with nonzero initial dislocation density [1–3]. In these studies, a pillar with a circular or square cross-section was fabricated mainly by the focused ion beam (FIB) and by some FIB-less methodologies, as well. All the experimental results remarkably demonstrated that the strength of single crystalline metals shows the power-law

28.2

700 600

Size Matters: Mechanical Behavior at Nanoscale

D = 7450 nm D = 960 nm

D = 870 nm D = 580 nm

585

D = 420 nm D = 400 nm

Stress (MPa)

500 400 300 200 100 0 0.00 (a)

(b)

0.05

0.10

0.15 Strain

0.20

0.25

Figure 28.1 (a) Post-deformation SEM image of Au nanopillar. (b) Stress versus strain data for Au nanopillars with different diameters. (Reprinted with the permission of Ref. [5].)

dependence between the strength (yield strength or flow strength) and sample dimension (pillar diameter), regardless of fabrication technique. Uniaxial compression tests with a nanoindentation technique, which adopts a flat punch tip, was first introduced by Uchic et al., who reported the strong sample size dependence of their FIB-machined Ni and Ni3 Al micropillars [4]. Greer and Nix further explored this phenomenon at the nanoscale and showed that single crystalline Au nanopillars at the submicron scale exhibit a remarkable strengths of nearly 50 times higher than bulk counterpart (Figure 28.1) [5]. his methodology has a significant advantage for the study of size effect becuase it enables the fabrication of samples of virtually any size above ∼100 nm in any crystallographic orientation for a given single crystal several research groups investigated the size effect on plasticity for various materials, and reported that most metals exhibit size effects in strength, with an empirical power-law dependence as � = A ⋅ D−n ,

(28.1)

where � is yield strength or flow strength, A is the prefactor, D is the pillar diameter, and n is the scaling exponent. For example, Figure 28.2 shows that various fcc metals exhibit a linear relationship, which dictates a smaller is stronger (italicize) trend. he physical mechanism driving this power law is still under debate, but the following two mechanisms are regarded as the major descriptions. At the submicron scale, the dimensions of nanopillars are so small that they contain only a few dislocations. he applied stress drives virtually all existing mobile dislocations to annihilate at the surfaces of the nanopillar, leading to a “dislocation starvation” state [6]. At that point the plasticity mechanism becomes dislocation-nucleation controlled, and the nucleation stress, which corresponds to the flow stress in a stress–strain curve, becomes higher in the smaller samples due to the greater

0.30

28

Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials Au Greer et al. (Acta Mater. 2005) Au Greer et al. (PRB 2006) Au Volkert et al. (Phil. Mag. 2006) Au Kim et al. (Acta Mater. 2009) Au Kim et al. Tension (Acta Mater. 2009) Au Kim et al. Tens./Comp. (Acta Mater. 2009) Au Lee et al. (Acta Mater. 2009) Cu Jennings et al. (PRL 2010) Cu Jennings et al. Tens (Phil. MAg. 2010) Cu Jennings et al. Com (Phil. MAg. 2010) Cu Jennings et al. (unpublished) Cu Kiener et al. Tens (Acta Mater. 2008) Ni Frick et al. (Mat. Sci. Eng. A. 2008) AI Ng et al. (Acta Mater. 2008)

0.1

0.01 τ/�

586

1E-3

1E-4 100

1000

10 000

D/b Figure 28.2 Shear flow stress normalized by shear modulus on appropriate slip system for most fcc metallic micro- and nanopillars tested in compression and tension to date. (Reprinted with the permission of Ref. [3].)

fraction of the surface area. his is a weakest link analogy for the statistical distribution of surface sources. At the micron-scale, the strength of micropillars might be controlled by the operation of “single arm dislocation sources” [7]. A single arm dislocation source can be thought of as a Frank–Read source truncated by the free surface, and the operation stress of the weakest single arm source determines the yield strength of micropillar. Typically, the operation stress of an isolated single arm source is determined approximately by �b∕R, where � is the shear modulus, b is the magnitude of the Burgers vector, and R is the pillar radius. hus, the smaller pillars contain dislocation sources which require the application of higher stresses, leading to the “smaller is stronger” behavior. Plasticity in body-centered cubic (bcc) metals is more interesting compared to the fcc metals. he power-law dependence of bcc pillars exhibit a strong dependence on the intrinsic lattice resistance, which is defined as the stress required to move an infinitely long straight dislocation through the lattice at finite temperature. Schneider et al. and Kim et al. found that Mo, Ta, W, and Nb pillars exhibit different size effects, manifested by the varying exponents is Eq. (28.1). hey argued that a critical temperature and the remaining Peierls barrier at room temperature is the key parameter that determines n [8, 9]. A critical temperature is defined as a temperature at which the mobility of screw dislocations becomes equal to that of edge dislocations. Peierls barrier is defined as the intrinsic lattice resistance at 0 K. Because the mobility of screw dislocation in bcc metals

28.2

Size Matters: Mechanical Behavior at Nanoscale

587

0.03

V, 0.82 0.02

0.01 0.009 0.008 0.007 0.006

Mo, Ta: –0.42 W: –0.32

τ/�

0.005 0.004

Mo Schneider, et al. (comp) Mo Kim, et al. (comp) Mo Kim, et al. (tension) Nb Schneider, et al. (comp) Nb Kim, et al. (comp) Nb Kim, et al. (tension) Ta Schneider, et al. (comp) Ta Kim, et al. (comp) Ta Kim, et al. (tension) W Schneider, et al. (comp) W Kim, et al. (comp) W Kim, et al. (tension) V Han, et al. (comp) MoAINi 4% Bei, et al. (comp)

0.003 0.002

1E-3 9E-4 8E-4 7E-4 6E-4 5E-4 200

400

600

800 1000

2000

4000

6000 8000 10 000

20 000

D/b

Figure 28.3 Resolved shear stress normalized by shear modulus on {1 1 0}/ slip system versus diameter normalized by the Burgers vector for all five tested bcc metals to date. Closed symbols correspond to compression and open ones to tension, with each metal having an individual color.

Three lines represent the average values for the slopes reported by referenced groups (compression only) split into three groups of metals delineated by the level of residual Peierls stress. (Reprinted with the permission of Ref. [3].)

has a strong temperature dependence associated with the double-kink pair nucleation/propagation, size effects also exhibit a strong dependence on the thermal parameter such as critical temperature or Peierls barrier. In fact, these two quantities have the similar relation with the temperature in that they both become higher at a lower temperature, and they are size-independent. If this size-independent effect becomes higher, then the size effect becomes smaller, leading to the smaller n [10]. For example, W has the highest critical temperature or Peierls barrier, shows the smallest size effect, while Nb and V exhibit the strong size effects due to their low critical temperature or Peierls barrier (Figure 28.3) [3]. Until now, more interesting findings have been reported on uniaxial deformation of various sized metallic systems. Especially, the development of in situ mechanical testing systems allows us to perform uniaxial tensile tests, enabling a further fundamental understanding of small-scale mechanical testing. Figure 28.4 shows recent examples of micro-/nanoscale tensile experiments. Furthermore, several research groups have tried to incorporate a temperature

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Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials

(b)

(a)

10 μm

ε = 0.8%

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10 μm

ε = 5.4%

(d)

10 μm

ε = 0.5%

(e)

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276.8 nm

12/23/2008 HV mag WD HFW dce 146.49 FM 1000 kV 60 000 x 118 mm 4.97 μm ETD

(h)

1800

2.89 nm

281.7 nm

ε = 10.9%

1600 1400 1200 1000 800 600 400 200

500

Figure 28.4 Uniaxial tension of (a–d) FIBfabricated Cu micropillars with different aspect ratios showing progressive slip initiation, (e) FIB-fabricated Nb nanopillar positioned inside the tensile grips, and (f–h)

0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Engineering strain

nm

50 nm

electroplated Cu nanopillar before and after necking with stress–strain and zoomed-in neck region. (Reproduced with permission from Refs. [11, 12].)

control system to understand the temperature effects on the size effect at the nanoscale. 28.2.2 Smaller is Weaker in Nanocrystalline Metals

In polycrystalline metals, GBs act as an obstacle for a dislocation motion, which results in the dislocation pileup near the GB. Because the higher stress is required to move this array of dislocations, it is more difficult to deform a polycrystalline metals with smaller grain size. his is the well-known Hall–Petch relation, which dictates that the yield strength is inversely proportional to the square root of grain size [13, 14]. However, in nanocrystalline metals, where the grain size is reduced to a few tens of nanometers, materials gets softer at smaller grain sizes, a phenomenon often referred to as the inverse Hall–Petch regime [15]. For a larger grain size, the motion of dislocations in grains usually mediates the plasticity, but nanocrystalline metals do not have enough room for this mechanism. Rather,

28.2

Size Matters: Mechanical Behavior at Nanoscale

589

1.2

2000 800 nm

100 nm

400 nm

0.8 200 nm

1000

0.6 Pt compression, 12 nm grains Cu, micron-sized grains (Yang et al.25) 16 Ni compression, 60 nm grains (Jang et al. ) 16 Ni tension, 60 nm grains (Jang et al. ) Bulk yield strength Theory (equation 2)

0.4 500 0.2 0

(a)

1.0

1500 σy /σyBulk

True compressive stress (Mpa)

1600 nm

0.0 0

0

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 True compressive strain

Figure 28.5 Deformation characteristics of 60 nm grained nanocrystalline Ni–4%W nanopillars. (a) Compressive for pillars of different diameters. (Reprinted with permission

(b)

10

30

20 D/d

from Ref. [17].) (b) Tensile and compressive strengths as a function of size showing “smaller is weaker” trend. (Reprinted with permission from Ref. [18].)

the GB-mediated process governs plasticity: for example, grain rotation, GB sliding, partial dislocation emission and absorption at the GBs, diffusional creep, and GB migration and grain growth. Freestanding nanocrystalline Al thin films with submicron thickness exhibit the enhanced ductility by the stress-induced grain growth and stress-coupled GB mitigation [16]. In the case of polycrystalline pillar, a grain size gets bigger, the size effects becomes close to those of single crystalline pillar, that is, smaller is stronger. his makes sense because coarse-grained pillar contains only a few grains, and a microstructure becomes similar with a single crystal. he dislocation source operation would be the major mechanisms in large-grained pillar as in a single crystal [7]. However, the grain size becomes smaller enough to prevent dislocation source mechanisms; nanocrystalline pillar does not obey a smaller is stronger trend. Instead, a “smaller is weaker” trend occurs due to the GB-mediated plastic deformation. Jang and Greer performed in situ uniaxial tension and compression tests of 60 nm grained nanocrystalline Ni–W nanopillars and demonstrated that nanopillars with 100 nm in diameter exhibits 42% smaller strength in compression and 36% smaller strength in tension than nanopillars with 1.6 μm in diameter [17]. Figure 28.5a shows the stress–strain curves of nanocrystalline Ni–W nanopillars with different diameters clearly demonstrate a smaller is weaker trend. Gu et al. also confirmed a similar trend in Pt nanocrystalline nanopillars. In this study, the large-scale molecular dynamics simulation was performed, and revealed that GB sliding near the free surface would be a governing process of plastic deformation. For a given average grain size, d, the smaller pillar has the low D∕d ratio, where D is the sample diameter. hen, GB sliding is relatively easier due to the small fraction of triple junction across the pillar. Gu et al. found the significant softening when D∕d is close to 5. After yielding, further plastic deformation

40

50

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Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials

occurs by the nucleation of partial dislocations for fcc crystals. Typically, they are nucleated at the triple junction where the stress is most highly concentrated. Figure 28.5b shows the yield strength, which is normalized by the bulk strength as the function of D∕d. For fcc Cu, Ni, Pt nanocrystalline pillars, the emergence of “smaller is weaker” trend occurs roughly for D∕d < 10. 28.2.3 Emergence of Ductility in Nanometer-Sized Metallic Glasses

In the previous section, we have discussed the size-dependent strength of nano-sized metals. he strength is an important parameter for the design of engineering systems. For a brittle material such as ceramic, however, the toughness is more important because the strength is already high enough. Strength itself does not guarantee the mechanical stability because any small flaw in a material can cause the stress concentration, leading the stress level much higher than the yield strength. Typically, a ductile material, such as metal, has an efficient energy dissipation mechanism to relieve the stress concentration. For example, the plastic deformation at the crack tip dissipates the elastic strain energy and reduces the stress level at the crack tip. Also, the dislocation multiplication at the crack tip causes a strain-hardening mechanism, leading to self-hardening to prevent the crack propagation. However, the brittle materials do not have this kind of mechanisms or cannot operate it at room temperature due to too strong atomic bonding between atoms. Amorphous materials correspond to the former because they do not have a dislocation, a line defect that carries plasticity. Ceramic materials correspond to the latter because too high atomic bonding does not allow dislocations to move at room temperature. Under a given stress, atomic bonding in brittle materials is simply broken sequentially, and catastrophic failure occurs. At a high temperature, however, thermal energy can help dislocations to move, leading to the plastic deformation as metals. herefore, it is crucial to improve the toughness or ductility of these brittle materials for an engineering use. he most traditional way to enhance the ductility is making a composite. A ductile second phase is typically used to prevent the sudden crack propagation. However, recent nanomechanical studies have demonstrated that the brittle materials can become ductile simply by size reduction, and we discuss a metallic glass as an example in this section. Most metallic system prefers a crystalline state under thermodynamic equilibrium because the periodic atomic arrangement provides the lowest energy state. However, if the liquid melt is cooled down above a certain critical cooling rate, the short time of cooling does not allow atoms to make the period array. Rather, the liquid melt is solidified with keeping a liquid structure, forming a kinetically frozen metastable solid. If we use the metallic elements for this process, we call a solidified alloy “metallic glass.” A metallic glass attracts a lot of interest due to its ultrahigh strength [19]. Because this amorphous alloy does not have a dislocation, which carries plasticity, the plastic deformation is caused by the nucleation/propagation of shear band, which required the high stress. Cobalt-based

28.2

Size Matters: Mechanical Behavior at Nanoscale

591

bulk metallic glass exhibits about 5 GPa of yield strength, which is closed to that of alumina, 5.5 GPa [20]. his exceptional strength is beneficial for a structural use, but the major drawback is its brittleness such as ceramic. Once a shear band is formed, it propagates rapidly, causing the catastrophic failure. Significant efforts to enhance their deformability have been focused on developing metallic glasses capable of uniformly distributing shear bands or to hinder their propagation. Recently, Jang and Greer demonstrated that FIB-machined metallic glass can be ductile by size reduction even under tension [21]. Figure 28.6a–f show the snapshots taken during an in situ nanomechanical tension tests. Figure 28.6e clearly shows a necking, which is the evidence of ductile deformation under (a)

(b)

(c)

(d)

A

B

C

2.0

B

1.5 1.0

D

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2.5

D True stress (GPa)

C

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2.0 1.5 1.0 0.5

0.5 A 0

D

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(g)

(f)

100 nm

100 nm

Engineering stress (GPa)

(e)

0

0.02

0.04

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Engineering strain

Figure 28.6 Monotonic nanotension results for the 100 nm diameter specimen. (a) SEM image of a typical as-fabricated 100 nm diameter tensile sample. (b–f ) Images captured from a movie recorded during an in situ tension test at �E of 0 (b), 0.04 (c), 0.06 (d), 0.07 (e), and the final fracture (f ). The square in (e) indicates the region where a neck is formed. (g, h) The engineering (g)

0

0.10 (h)

A 0

0.07

0.14

0.21

True strain

and true (h) stress–strain curves of the nanotension test. True stresses and strains after necking were obtained by directly measuring the diameter in the necked region. The error bars in (h) reflect the uncertainty in measuring pillar dimensions on the captured images of the movie. The value of strain in (g) and (h) has no units. (Reprinted with permission from Ref. [21].)

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Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials

tension. Figure 28.6g and Figure 28.6h show the engineering stress–strain curve and the true stress–strain curve, respectively. he true stress–strain curve shows enhanced ductility up to the fracture strain of 28. he metallic glass used in this study is Zr-based, which is typically extremely brittle at the bulk scale, but nanomechanical test shows that a nano-sized metallic glass shows an exceptional ductility. he reported phenomena may be understood by considering two competing processes: crack-like shear-band propagation versus homogeneous flow, and the contribution of each process to the overall deformation at different sample sizes. Analogously to Griffith’s crack-propagation criterion, the stress required to propagate a preexisting shear band to fracture is [22, 23]: √ √ 2 2ΓE �= , (28.2) ad where Γ is the shear-band energy density/unit area, E is Young’s modulus, a is the aspect ratio (height/diameter), and d is the diameter. Shear-band propagation stress gradually increases as the sample diameter decreases (Figure 28.7). If the shear-band propagation stress becomes higher than the stress required for the homogeneous deformation, metallic glass could be deformed in a homogeneous manner. Jang and Greer found that the critical diameter for homogeneous deformation for Zr-based metallic glass is closed to 30–100 nm, which agrees well with their observation. here were several considerations regarding the experimental artifact from the FIB damage at the surface. Chen et al. made FIB-less Ni–P metallic glass pillar by electroplating technique, and demonstrated that the significant plasticity still occurs for a nanopillar with D < 100 nm. So, metallic glass indeed becomes Homogeneous plastic deformation

σ Fracture strength

Ideal strength Stress required for Range of possible homogeneous deformation stress required for homogeneous deformation

Plasticity

Yield strength

Stress required for Shear-band propagation

d* Figure 28.7 Schematic representation of the applied stresses required to initiate shear-band propagation versus homogeneous deformation as a function of sample diameter, d. When the sample diameter is larger than the critical size, d∗ , defined as the intersection of the two curves, the

d material fails by shear-band propagation without notable plasticity. When d < d∗ , homogeneous plastic deformation precedes shear-band propagation, showing significant plasticity quantified by the height difference between the two curves. (Reprinted with permission from Ref. [21].)

28.3

Capturing Size Effects and Using Them

ductile by size reduction. Another interesting observation is strain hardening in stress–strain curve in Figure 28.6b. Because there is no dislocation multiplication in metallic glass, strain hardening looks mysterious. Recent molecular dynamics simulations in Chen’s work show that for smaller pillar, structural relaxation near the surface is not negligible in plastic deformation (D.Z. Chena and J.R. Greer, private communication). he initiation of homogeneous plastic deformation near the surface relaxes the surface structures, making the surface region stronger. hen, the further plastic deformation by the rearrangement of atomic configurations gets harder with strain.

28.3 Capturing Size Effects and Using Them in Developing Three-Dimensional Hierarchical Metamaterials

In the previous sections, we discussed the size effects on the mechanical behavior. he size effects are highly beneficial when we design any small structure with high strength and toughness. If there exist any structures with nanoscale constituents, they would be stronger by “smaller is stronger” trend and tougher by “smaller is ductile” trend than the prediction made from the typical handbook values at the bulk scale. So, the development of nanoscale architectured structures attracts a lot of interest because they are considered as one way to create a high-strength and high-tough metamaterial, and sometimes with low density. hese materials can have the multiple length scales of constitutes from the size of material microstructure (e.g., grain size) to the size of individual member to the size of the whole structure. he hierarchy of length scales provides various ways to control the physical properties of structure by controlling each length scale. Especially, if the dimensions of structural member were close to the nanoscale, the overall properties would be unusually superior due to the emergence of the size effects. In fact, it is easy to find out these examples in biological materials. Hard biological materials often consist of hierarchically arranged constituents, whose dimensions can span nanometers to micrometers to centimeters and larger. Figure 28.8 shows scanning electron microscope and optical images of silicified cell walls from diatoms and a radiolarian, which has periodic skeletal arrangements of bioceramics [24, 25]. hese organisms are known to be mechanically strong and lightweight, properties that provide an efficient defense way again to predator. Biominerals such as nacre, mollusk shells, and crustaceans have been reported to have higher fracture toughness than man-made monolithic ceramics of the same composition because they have the nano-sized constituents at the lower level of hierarchy [26]. Recent development of nanofabrication successfully has produced the hierarchical nanostructures. Jang et al. reported the fabrication and mechanical properties of periodically arranged hollow titanium nitride (TiN) nanolattices with the dimensions of individual components spanning from nanometers to hundreds of micrometers [27]. hese hierarchical length scales are similar with those of the

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Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials Natural materials

Length scales

>100 μm

(b)

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Computer-aided design

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Substrate

(h)

(i)

(j)

Figure 28.8 Skeletal natural biological materials versus TiN nanolattices. (a, b) SEM images of silicified cell walls with periodic lattice structures from different diatom species. (c) Optical image of a radiolarian with a kagome lattice. (d, e) Computeraided design of octahedral nanolattices. (f, g) SEM image of a fabricated nanolattice with a three-dimensional kagome unit cell. (h–j) SEM (h, i) and transmission electron microscope dark-field (j) images of an

Grain

10 nm

(k)

engineered hollow nanolattice synthesized with TiN. The inset in (i) shows the crosssection of a strut. The TiN thin film in (j) was deposited in the same batch with the nanolattice samples. (k) Schematic representation of the relevant dimensions of such fabricated nanolattices. Scale bars, 500 nm (b), 20 μm (h), 5 μm (f, i), 1 μm (inset of i), 20 nm (j). (Reprinted with permission from Ref. [27].)

cell walls in diatom organisms (Figure 28.8). hese structures are constructed of hollow tubes of TiN. he fabrication process consists of the following steps: digital design of a three-dimensional structure (Figure 28.8d,e), direct laser writing (DLW) of this pattern into a photopolymer using two-photon lithography (TPL) to create freestanding three-dimensional solid polymer skeletons, conformal deposition of TiN using atomic layer deposition (ALD), and etching out of the polymer core to create hollow ceramic nanolattices. he resulting structure was approximately 100 μm in each direction. he dark-field transmission electron microscope

Load (mN)

28.3

0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00

0

400

800

Capturing Size Effects and Using Them

1200

595

1600

Displacement (nm)

(a) Monotonic loading

Loading direction

(b)

(c) I.

As-fabricated

(d) II. At maximum load

Figure 28.9 Compression experiments on a single unit cell. (a) Load versus displacement data from a monotonic-loading experiment. The arrow in (a) indicates the onset of nonlinearity; (b)–(d) SEM images taken at zero

III.

After fracture

(b) and maximum loads (c), and after failure (d) during the monotonic loading experiment. Arrows in (d) point to the location of fracture. (Reprinted with permission from Ref. [27].)

image in Figure 28.8j shows the characteristic nanostructural length scale of TiN, represented by its grain size, was between 10 and 20 nm, as can be seen. Figure 28.8 also contains scale bars showing all relevant sizes within these structures. In situ compression experiments on the octahedral unit cell were done by applying an axial load along the vertical axes of the unit cells (Figure 28.9). Experimentally observed force versus displacement data were used for a finite element method (FEM) framework to estimate the stress distribution within the structure under the maximum applied load. Surprisingly, the FEM analysis confirmed that the maximum local von Mises stress reaches 2.50 GPa, which corresponds to the tensile stress of 1.75 GPa and a strain 1.8%. Typically, the tensile strength of bulk TiN is the order of magnitude lower than this value. Because of its brittleness, the measured strength of TiN is usually between the order of a few tens and hundreds of megapascals. he emergence of such high strength and failure resistance of this TiN can be understood in a similar fashion with a metallic glass, which exhibits a “smaller is ductile” trend discussed in Section 2.3. As described in Section 2.3, the propagation stress of shear band in metallic glass can be understood by the analogy with crack propagation. he propagation stress of shear band or the crack opening stress is closely related to the preexisting flaw

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Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials

Fracture strength

Theoretical limiting strength

σ f ∝ (1/ t)1/m

t∗

Wall thickness (t)

Figure 28.10 Schematic representation of theoretical strength, which is independent of sample size, and fracture strength described by Weibull statistics. (Reprinted with permission from Ref. [27].)

size, which is a shear-band size for metallic glass and is a micro-crack size near the surface for a ceramic. According to Griffith’s theory, the increase in total energy by producing a new surface competes with the release of elastic strain energy, resulting in a critical stress of defect propagation, which is typically inversely proportional to the square root of the initial length of shear band or crack. For a ceramic, the number of initial flaw is proportional to the surface area because most micro-cracks are formed near the surface by the material processing. If we assume the Gaussian distribution of crack length, and the smaller volume has the benefit in the perspective of toughness because it has a smaller chance to contain a bad, that is, long initial crack. Also, even though it exists, the initial length crack is so small that due to already small dimension of an individual member, the crack opening stress would be higher than the material theoretical strength. In this case, materials would be fractured by the atomic-bonding breakage anywhere of materials regardless of the location of flaw. his phenomenon is often called fracture tolerance at the nanoscale. Figure 28.10 depicts an illustrative plot of strength as a function of sample thickness, which shows the intersection of the theoretical strength and that described by �f ∝ (1∕t)1∕m at the critical thickness of t ∗ , where �f is the fracture strength, t is the wall thickness, and m is the Weibull modulus. Based on Jang et al.’s calculation, the theoretical strength of TiN is 3.27 GPa (estimated by E/30� with E = 98 GPa), and which is close to the estimated tensile yield strength, 2.50 GPa of TiN nanolattice member. his indicates that the artificially made TiN nanolattice consists of the TiN member whose strength is nearly theoretical limit, which offers the ultrahigh strength architectured structure.

References

hus, the attainment of such exceptionally high strength in TiN results from the low probability of preexisting flaws in nano-sized solids. Failure in such materials initiates at a weakest link, which is determined by the competing effects of stress concentrators at surface imperfections and local stresses within the microstructural landscape. hese findings may offer the potential of applying hierarchical design principles offered by hard biological organisms to create damage-tolerant lightweight engineering materials.

References 1. Uchic, M.D., Shade, P.A., and Dimiduk,

2.

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D.M. (2009) Plasticity of micrometerscale single crystals in compression. Annu. Rev. Mater. Res., 39, 361–386. Kraft, O., Gruber, P.A., Mönig, R., and Weygand, D. (2010) Plasticity in confined dimensions. Annu. Rev. Mater. Res., 40, 293–317. Greer, J.R. and De Hosson, J.T.M. (2011) Plasticity in small-sized metallic systems: intrinsic versus extrinsic size effect. Prog. Mater Sci., 56 (6), 654–724. Uchic, M.D., Dimiduk, D.M., Florando, J.N., and Nix, W.D. (2004) Sample dimensions influence strength and crystal plasticity. Science, 305, 986–989. Greer, J.R., Oliver, W.C., and Nix, W.D. (2005) Size dependence of mechanical properties of gold at the micron scale in the absence of strain gradients. Acta Mater., 53 (6), 1821–1830. Greer, J.R. and Nix, W.D. (2006) Nanoscale gold pillars strengthened through dislocation starvation. Phys. Rev. B, 73, 245410. Parthasarathy, T.A., Rao, S.I., Dimiduk, D.M., Uchic, M.D., and Trinkle, D.R. (2007) Contribution to size effect of yield strength from the stochastics of dislocation source lengths in finite samples. Scr. Mater., 56 (4), 313–316. Schneider, A.S., Kaufmann, D., Clark, B.G., Frick, C.P., Gruber, P.A., Mönig, R., Kraft, O., and Arzt, E. (2009) Correlation between critical temperature and strength of small-scale bcc pillars. Phys. Rev. Lett., 103, 105501. Kim, J.-Y., Jang, D., and Greer, J.R. (2010) Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale. Acta Mater., 58 (7), 2355–2363.

10. Lee, S.-W. and Nix, W.D. (2012) Size

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dependence of the yield strength of fcc and bcc metallic micropillars with diameters of a few micrometers. Philos. Mag., 92 (10), 1238–1260. Kiener, D., Grosinger, W., Dehm, G., and Pippan, R. (2008) A further step towards an understanding of size-dependent crystal plasticity: in situ tension experiments of miniaturized single-crystal copper samples. Acta Mater., 56 (3), 580–592. Jenning, A.T. and Greer, J.R. (2011) Tensile deformation of electroplated copper nanopillars. Philos. Mag., 91 (7-9), 1108–1120. Hall, E.O. (1951) he deformation and ageing of mild steel. 3. Discussion of results. Proc. Phys. Soc. London, Sect. A, 64, 747–753. Petch, N.J. (1953) he cleavage strength of polycrystals. J. Iron Steel Inst., 174, 5–28. Meyers, M.A., Mishra, A., and Benson, D.J. (2006) Mechanical properties of nanocrystalline materials. Prog. Mater Sci., 51 (4), 427–556. Legros, M., Gianola, D.S., and Hemker, K.J. (2008) In situ TEM observations of fast grain-boundary motion in stressed nanocrystalline aluminum films. Acta Mater., 56 (14), 3380–3393. Jang, D. and Greer, J.R. (2011) Sizeinduced weakening and grain boundaryassisted deformation in 60nm-grained Ni nano-pillar. Scr. Mater., 64 (1), 77–80. Gu, X.W., Wu, Z., Zhang, Y.-W., Srolovitz, D.J., and Greer, J.R. (2013) Microstructure versus flaw: mechanisms of failure and strength in nanostructures. Nano Lett., 13 (11), 5703–5709. Telford, M. (2004) he case for bulk metallic glasses. Mater. Today, 7, 36–43.

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20. Inoue, A., Shen, B., Koshiba, H., Kato,

24. Kröger, N. (2007) Prescribing diatom

H., and Yavari, A.R. (2003) Cobaltbased bulk glassy alloy with ultrahigh strength and soft magnetic properties. Nat. Mater., 2, 661–663. 21. Jang, D. and Greer, J.R. (2010) Tensile and compressive behavior of tungsten, molybdenum, tantalum, and niobium at the nanoscale. Nat. Mater., 9, 215–219. 22. Volkert, C.A., Donohue, A., and Spaepen, F. (2008) Effect of sample size on deformation in amorphous metals. J. Appl. Phys., 103, 083539. 23. Gao, H.J., Ji, B.H., Jager, I.L., Arzt, E., and Fratzl, P. (2003) Materials become insensitive to flaws at nanoscale: lessons from nature. Proc. Natl. Acad. Sci., 100, 5597–5600.

morphology: toward genetic engineering of biological nanomaterials. Curr. Opin. Chem. Biol., 11, 662–669. 25. Robinson, W.J. and Goll, R.M. (1978) Fine skeletal structure of the radiolarian Callimitra carolotae Haeckel. Micropaleontology, 24, 432–439. 26. Sarikaya, M. and Aksay, I.A. (1992) Nacre of abalone shell: a natural multifunctional nanolaminated ceramicpolymer composite material. Results Probl. Cell Differ., 19, 1–26. 27. Jang, D., Meza, L., Greer, F., and Greer, J.R. (2013) Fabrication and deformation of three-dimensional hollow ceramic nanostructures. Nat. Mater., 12, 893–898.

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29 Position and Vision of Small- and Medium-Sized Enterprises Boosting Commercialization Torsten Schmidt, Nadine Teusler, and Andreas Baar

29.1 Challenges for SME in Nano-Industrialization: A Case Study

he following contribution is dedicated to the general understanding of the challenges for growth as well as to the operational options small- and medium-sized enterprises (SMEs) are facing in nano-industrialization such as: 1) validation and verification of real customer needs with respect to a. feasibility b. cost c. timing, 2) access to the global market place by sales, inventory, production, and logistics management without draining the organization’s current capabilities, 3) keeping the innovation pipeline filled by updating their technologies, 4) mitigation of financial risks associated with innovation launch. For the sake of calibrating the proposed concepts, a case study is given: GXC Coatings GmbH (GXC) develops – based on chemical nanotechnology – manufactures, and applies transparent functional coatings for maintaining transparency under adverse environmental conditions. his SME was founded in 2000 by business entrepreneurs and inventors. he nanotechnological functionality was developed by the inventors. Adaptation and customizing to meet the full set of specification for automotive mass production was accomplished at GXC; its formation was driven by the entrepreneurs in cooperation with the inventors. GXC became independent from the inventors in 2004. Today, GXC is one of the leading suppliers of transparent functional coating technology for the automotive industry and optics industry. GXC received networking support by the “Landesinitiative Nano- und Materialinnovationen Niedersachsen (NMN).” NMN is an initiative of the government of the Federal State of Lower Saxony in the Federal Republic of Germany.

he Nano-Micro Interface: Bridging the Micro and Nano Worlds, Second Edition. Edited by Marcel Van de Voorde, Matthias Werner, and Hans-Jörg Fecht. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2015 by Wiley-VCH Verlag GmbH & Co. KGaA.

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Position and Vision of Small- and Medium-Sized Enterprises Boosting Commercialization

29.2 Scope

SMEs play an important role comprising economic as well as social and psychological aspects in German society. his economic field is constituted by economically and legally independent businesses. he primary trait is a close relationship between a person, that is, the entrepreneur, and an economic unit strongly influencing its market behavior and performance such as [1]

• the identity of ownership and personal responsibility for the enterprise’s activities,

• the identity of ownership and personal liability for the entrepreneur’s and the enterprise’s financial situation,

• the personal responsibility for the enterprise success or failure, • the personal relationship between employer and employees. In quantitative terms, the following classification (Table 29.1) is used by theInstitute for Mittelstandsforschung (IfM), Bonn [1]: he European Union has applied the following classification (Table 29.2) since January 1, 2005 [2]. Based on the aforementioned definition, IfM investigated for Germany in 1999:

• approximately 70% of the employees are employed with SMEs, • SMEs create approximately 60% of the gross value added, • SMEs create approximately 45% of all revenues subject to VAT, Table 29.1 SME classification used by the Institute for Mittelstandsforschung (IfM), [1]. Classification

Personnel

Annual revenues EUR million

Small Medium-sized Large

500

50

Table 29.2 SME classfication used by the European Union [2]. Classification

Micro Small Medium-sized

Personnel

Annual revenues EUR million