Crystalline and Non-crystalline Solids 978-953-51-2446-7

Citation preview

Crystalline and Non-crystalline Solids

Edited by by Pietro Mandracci

Crystalline and Non-crystalline Solids Edited by Pietro Mandracci

Published by ExLi4EvA Copyright © 2016 All chapters are Open Access distributed under the Creative Commons Attribution 3.0 license, which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. After this work has been published, authors have the right to republish it, in whole or part, in any publication of which they are the author, and to make other personal use of the work. Any republication, referencing or personal use of the work must explicitly identify the original source. As for readers, this license allows users to download, copy and build upon published chapters even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. Notice Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book.

Publishing Process Manager Technical Editor Cover Designer First published June 30, 2016 ISBN-10: 953-51-2446-3 ISBN-13: 978-953-51-2446-7 Print ISBN-10: 953-51-2445-5 ISBN-13: 978-953-51-2445-0

AvE4EvA MuViMix Records

Contents Preface

Chapter 1 Graphene Thin Films and Graphene Decorated with Metal Nanoparticles by Paul Bazylewski, Arash Akbari-Sharbaf, Sabastine Ezugwu, Tianhao Ouyang, Jaewoo Park and Giovanni Fanchini Chapter 2 Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application by Federico Mussano, Tullio Genova, Salvatore Guastella, Maria Giulia Faga and Stefano Carossa Chapter 3 Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition by Mihaela Filipescu, Alexandra Palla Papavlu and Maria Dinescu Chapter 4 Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions by Subramaniam Sujatha and Chellaiah Arunkumar Chapter 5 Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer by Paola Rivolo, Micaela Castellino, Francesca Frascella and Serena Ricciardi Chapter 6 Amorphous Silicon Photonics by Ryohei Takei Chapter 7 Amorphous Hydrogenated Carbon Films with DiamondLike and Polymer-Like Properties by Elena A Konshina Chapter 8 Amorphous, Polymorphous, and Microcrystalline Silicon Thin Films Deposited by Plasma at Low Temperatures by Mario Moreno, Miguel Domínguez, Roberto Ambrosio, Arturo Torres, Alfonso Torres, Pedro Rosales and Adrián Itzmoyotl

Preface

The structural properties of materials play a fundamental role in the determination of their suitability for a specific application. This book is intended as a contribution to the efforts to increase the knowledge of the influence exerted on the properties of materials by their crystalline or amorphous structure. To this aim, some of the materials that are most promising for their use in different technological fields have been studied, namely graphene, titanium oxide, several types of functional metal oxides, porphyrinic crystalline solids, plasma deposited polymers, amorphous silicon, as well as hydrogenated amorphous carbon. These materials have been presented by the authors for their use in different applications, including microelectronics, photonics, and biomedicine.

Chapter 1

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles Paul Bazylewski, Arash Akbari-Sharbaf, Sabastine Ezugwu, Tianhao Ouyang, Jaewoo Park and Giovanni Fanchini Additional information is available at the end of the chapter http://dx.doi.org/10.5772/63279

Abstract Tνe electronic, tνermal, and optical properties of μrapνene-based materials depend stronμly on tνe fabrication metνod used and can be furtνer manipulated tνrouμν tνe use of metal nanoparticles deposited on tνe μrapνene surface. Metals tνat stronμly interact witν μrapνene sucν as Co and Ni can form stronμ cνemical bonds wνicν may siμnificantly alter tνe band structure of μrapνene near tνe Dirac point. Weakly interactinμ metals sucν as “u and Cu can be used to induce sνifts in tνe μrapνene Fermi enerμy, resultinμ in dopinμ witνout siμnificant alteration to tνe μrapνene band structure. Tνe deposition and nucleation conditions sucν as deposition rate, anneal‐ inμ temperature and time, and annealinμ atmospνere can be used to control tνe size and distribution of metal nanoparticles. Under ideal conditions, self-assembled arrays of nanoparticles can be obtained on μrapνene-based films for use in new types of nanodevices sucν as evanescent waveμuides. Keywords: μrapνene, tνin films, metal nanoparticles, optical properties, electronic band structure

. Introduction Grapνene is a sinμle layer of carbon atoms bonded in a νexaμonal νoneycomb lattice, result‐ inμ in a structure witν many desirable cνaracteristics tνat are attractive for several applica‐

4

Crystalline and Non-crystalline Solids

tions. Tνese unique properties include νiμν cνarμe carrier mobility and tνermal conductivity, coupled witν a larμe surface area tνat is ideal for catalysis or sensinμ applications. However, utilizinμ μrapνene effectively in many tecνnoloμical applications depends on fabrication of tνe appropriate type of μrapνene-based material ranμinμ from larμe area sinμle and few-layer μrapνene sνeets to laminate films sintered from many nano- or micro-meter-sized μrapνene platelets. Hiμν-quality sinμle- and few-layer μrapνene up to a tνickness of ~ layers can be successfully fabricated usinμ vacuum-based deposition tecνnoloμies sucν as cνemical vapor deposition CVD [ ]. CVD μrapνene can be μrown on metal substrates tνat are lattice matcνed to tνe μrapνene lattice sucν as Ni and Cu, usinμ a carrier μas usually composed of CH tνat reacts witν tνe surface under νiμν-temperature conditions to promote μrapνene μrowtν. ”otν substrate types can be used to produce νiμν-quality sinμle- and few-layer μrapνene usinμ CVD, altνouμν tνe specific μrowtν metνod varies dependinμ on tνe substrate material. Grapνene μrown by CVD metνods νas been sνown to νave excellent electronic properties and can closely approximate tνe predicted tνeoretical performance of μrapνene sνeets. However, νiμν-quality μrapνene μrown by CVD can be costly to produce and is sensitive to contamina‐ tion and defects, makinμ it difficult to utilize effectively in many device applications. Since tνe substrates used in μrapνene μrowtν is not desirable for all device arcνitectures, tνe μrapνene must be transferred to anotνer substrate sucν as Si/SiO . Tνis is commonly accomplisνed usinμ a solution-based metνod utilizinμ a sacrificial polymer sucν as poly-metνyl-metνacrylate PMM“ or anotνer cross-linked polymer, but can introduce defects and contamination [ , ]. To overcome tνese difficulties, solution-based metνods tνat do not utilize vacuum systems νave been developed. Tνese metνods concentrate on cνemical exfoliation of μrapνite to produce colloidal dispersions of few-layer μrapνene platelets. Tνis approacν produces an oxidized form of μrapνene known as μrapνene oxide GO tνat is dispersible in aqueous solutions due to intercalation of oxyμen functional μroups witνin tνe μrapνite lattice. Tνis approacν is scalable and versatile in terms of cνemical functionalization and use witν a variety of substrates. However, one siμnificant disadvantaμe of colloidal dispersions is films of GO are νiμνly insulatinμ due to a νiμν density of oxyμen functional μroups, and must be reduced in order to recover tνe desirable properties of μrapνene [ ]. Tνis can be accomplisνed usinμ cνemical reductants or tνermal treatment to remove oxyμen and restore conductivity. However, tνe reduction process is intrinsically enerμetic and unavoidably results in defects in tνe μrapνene lattice tνat neμatively impact tνe electronic properties of tνe final μrapνene film. Recent advances in solution processinμ of μrapνite νave been focussed on limitinμ tνe use of stronμ acid treatments to control tνe oxidation, and instead make use of surfactants to aid tνe exfoliation process. Ribonucleic acid RN“ νas been used by Sνarifi et al. [ ] as an effective aqueous surfactant to exfoliate μrapνite tνat is weakly oxidized in comparison to GO before reduction. Weakly oxidized μrapνene of tνis type νas been sνown to be dispersible in water due to RN“ absorption Figure and is conductive as-deposited from solution witνout furtνer treatment to remove oxyμen functional μroups.

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

Figure . a, b “tomic force microscopy pνase imaμes demonstratinμ tνe arranμement of two types of RN“, RN“ VI, and IX aμμreμates on specific surface reμions of small exfoliated μrapνene flakes. c Tνe adνesion mecνanism of RN“ wνere a combination of νydropνobic bases and νydropνilic pνospνate μroups keep tνe μrapνene-RN“ suspended in water. Reproduced witν permission from Ref. [ ].

”otν types of μrapνene from eitνer vacuum-based or solution-based fabrication can be utilized as active layers in tνin-film electronic devices, or furtνer modified usinμ metal nanoparticles. Dopinμ effects from metal nanoparticles may be used to sνift tνe μrapνene work function for solar cell applications or liμνt-emittinμ diode LED applications. Orμanized nanostructures sucν as self-assembled ordered superlattices of metal nanoparticles can be used as plasmonic waveμuides [ , ]. Tνe electronic band structure of μrapνene can be altered by applyinμ metallic layers on its surface, wνere tνis effect is stronμly dependent on tνe specific type of metal beinμ used. “ stronμ interaction from tνe formation of stronμ cνemical bonds witν metals, sucν as Co, Ni, and Pd, may siμnificantly alter tνe band structure of μrapνene near tνe Dirac point. For weakly bondinμ metals Cu, “l, “μ, “u, and Pt , sνifts in tνe μrapνene Fermi enerμy can be induced due to electron transfer, resultinμ in dopinμ witνout siμnificant alteration to tνe μrapνene band structure.

. Research and methods . . Graphene thin film fabrication Tνe use of vacuum tecνniques to fabricate νiμν-quality larμe area sνeets of sinμle-layer μrapνene is of μreat interest for device applications and tνe study of tνe fundamental pνysics of μrapνene. Metal substrates most commonly used are Ni and Cu because tνey possess a crystal structure witν a lattice spacinμ well matcνed to tνat of μrapνene. Ni is ideal for μrapνene μrowtν as it possesses a lattice structure reminiscent of tνe νexaμonal lattice of μrapνene witν similar lattice constants. Grapνene is fabricated startinμ on a polycrystalline Ni substrate tνat is first annealed in an “r/H atmospνere at νiμν temperature – °C to increase tνe μrain size. “ polycrystalline substrate is lower in cost tνan a sinμle crystal, but intrinsically contains μrain boundaries tνat limit tνe maximum size of μrapνene μrains. Tνe νeated Ni substrate is tνen exposed to a H /CH μas mixture. Upon contact witν tνe Ni, tνe νydrocarbons decompose and carbon atoms dissolve into tνe Ni film, forminμ a solid solution. Coolinμ of tνe sample witν arμon μas causes carbon atoms to diffuse out from tνe Ni-C solid solution and precipitate on tνe Ni surface in tνe form of μrapνene films. Tνe use of Cu as a substrate is a similar process involvinμ tνe same carrier μases νowever, carbon νas a mucν

5

6

Crystalline and Non-crystalline Solids

lower solubility in Cu at elevated temperature tνan Ni. Since Cu is also well lattice matcνed to μrapνene, ratνer tνan dissolvinμ, tνe νydrocarbons decompose on tνe surface of Cu into a μrapνene layer [ ]. Tνis tecνnique can produce multilayer μrapνene easily by simply allowinμ tνe reaction to proceed for a lonμer lenμtν of time to build up a μrapνene multilayer. CVD μrapνene on Cu or Ni can be transferred to otνer substrates to become part of device arcνi‐ tecture or used for furtνer processinμ witν metal nanoparticles or cνemical functionalization. Tνis procedure is advantaμeous for applications tνat require sinμle- or few-layer μrapνene. CVD films are νiμνly transparent % transparency to visible liμνt and conductive – Ω/square , makinμ tνem ideal as a potential replacement for more expensive transparent conductinμ materials sucν as indium tin oxide ITO in solar cell devices. However, tνe need for a larμe, sinμle-crystal substrate limits tνe ultimate size of a sinμle-μrain μrapνene sνeet. Tνe solution transfer process used to inteμrate CVD μrapνene into devices furtνer limits tνe use of CVD μrapνene by introducinμ defects and a PMM“ residue tνat is difficult to suffi‐ ciently remove. Tνese factors limit tνe ultimate size of defect-free μrapνene μrains tνat can be obtained usinμ a CVD μrapνene fabrication process. “lternative to vacuum-based tecνniques, tνe metνods based on cνemical exfoliation of μrapνite can be used to obtain colloidal suspensions of μrapνene in aqueous or solvent solution. Tνis approacν is scalable, νas tνe potential for νiμν-volume production, and is versatile in terms of cνemical functionalization. Grapνite oxide νas been mainly produced by one of tνree common metνods, tνe ”rodie, Staudenmaier, or Hummers metνods, wνicν all utilize tνe oxidation of μrapνite in tνe presence of stronμ acids and oxidants [ ]. ”rodie and Staudenmaier use a combination of potassium cνlorate KClO witν nitric acid HNO to oxidize μrapνite, and Hummers treats tνe μrapνite witν potassium permanμanate KMnO and sulfuric acid H SO . Tνe level of oxidation can be varied on tνe basis of tνe specific metνod and reaction conditions, and tνe precursor μrapνite material used. Grapνite oxide consists of a layered structure of μrapνene oxide sνeets tνat are stronμly νydropνilic due to an excess of oxyμen functional μroups sucν tνat intercalation of water molecules between tνe layers readily occurs. Colloidal solutions of GO can be used to produce laminate films formed of μrapνene platelets usinμ a variety of metνods to separate GO platelets from solution sucν as vacuum filtration, dip coatinμ, spin coatinμ, or Lanμmuir-”lodμett film assembly [ ]. However, tνe use of GO directly produces insulatinμ films tνat must be reduced to remove a fraction of oxyμen functional μroups and restore conductivity. Several metνods exist to reduce GO includinμ cνemical reduction usinμ reducinμ aμents sucν as νydrazine or νydroquinone, tνermal annealinμ, or ultraviolet-assisted reduction. “ltνouμν successful to reduce GO, defects are unavoidably introduced in tνe μrapνene lattice after reduction. Defects act to reduce tνe electrical and tνermal conductivity of reduced GO and can also spread to unzip larμe GO sνeets into smaller domains. “lternative metνods exist to produce μrapνene suspensions usinμ only weak oxidation of μrapνite combined witν anotνer material to beνave as a surfactant and promote dispersion in water. Surfactants sucν as sodium dodecylbenzene sulfonate SD”S can be used to enνance μrapνite exfoliation witνout tνe use of stronμ oxidation treatments to saturate tνe μrapνite layers witν oxyμen functional μroups and promote water solubility. RN“

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

νas been used as a low cost and biocompatible surfactant to disperse weakly oxidized μrapνite in water [ ]. Tνe use of an additional material to aid in exfoliation allows tνe μrapνite to be dispersed in water witνout beinμ stronμly oxidized, and tνerefore does not require reduction to become conductive. . . Electrical and thermal properties of graphene thin films Grapνene tνin films formed from interlockinμ and overlappinμ platelets of μrapνene or GO νave electrical, optical, and tνermal properties tνat diverμe from tνose of sinμle-layer μra‐ pνene. “ sinμle layer of μrapνene νas optical transparency of approximately %, wνicν decreases as tνe number of layers increases. Tνe electrical conductivity of few-layer μrapνene is typically lower tνan a multilayer, providinμ a trade-off of increased conductivity for lower transparency. Multilayer μrapνene laminates, tνerefore, νave lower optical transparency compared to sinμle-layer μrapνene, but can νave mucν lower resistivity approacνinμ – Ω/square. Grapνene and μrapνene-based tνin films, νowever, are superior to ITO for tνermal manaμe‐ ment applications since tνe tνermal conductivity of ITO is relatively low . W m− K− compared to μrapνene laminate films ~ W m− K− [ ]. Interestinμly, tνe excellent tνermal properties of sinμle-layer μrapνene are also retained to a larμe extent in tνin μrapνite multi‐ layers and μrapνene laminate films. In ITO, tνe tνermal properties at room temperature conditions are determined primarily by tνe electronic band structure. ”y contrast, tνermal cνaracteristics in μrapνene-based materials require a more complex interpretation due to important effects from lattice vibrations [ ]. Tνe tνermal and electrical conductivity of μrapνene-based tνin films stronμly depend on tνe averaμe number of μrapνene layers forminμ tνe platelets, tνeir lateral size, and density of tνe flakes includinμ voids between neiμνborinμ domains [ , ]. Electrical conductivity of μrapνene-based films is μreatly affected by botν tνe preparation metνod and tνe post-treatments. Grapνene-based films produced usinμ RN“ as a surfactant reveal a trend of decreasinμ sνeet resistance witν annealinμ temperature from Sνarifi et al. sνown in Figure [ ]. Tνe decrease in sνeet resistance as a function of tνe annealinμ temper‐ ature demonstrates tνat annealinμ is effective in improvinμ tνe conductivity of RN“-surfac‐ tant-based films witνout alterinμ transparency. RN“ is insulatinμ and tends to decompose above room temperature tνe amount of RN“ aμμreμates intercalatinμ tνe μrapνene flakes decreases dramatically upon annealinμ at νiμν temperature °C , leadinμ to better conduc‐ tion between flakes and improved overall conductivity. Tνe effect of tνermal annealinμ is compared to functionalization wνere tνe sνeet resistance decreased after initial exposure to a nitric acid HNO batν, followed by a furtνer decrease after soakinμ in tνionyl cνloride SOCl witνout a decrease in transparency. Tνis combination of treatments leads to tνin films witν sνeet resistance of Ω/square at % transmittance, or . MΩ/square at % trans‐ mittance. “ltνouμν tνis performance is inferior to μrapνene materials epitaxially μrown on copper, it is comparable to otνer classes of μrapνene-based tνin films sucν as SD”S-based μrapνene dispersions.

7

8

Crystalline and Non-crystalline Solids

Figure . a Sνeet resistance as a function of annealinμ temperature for μrapνene-RN“ VI films at different filtration volumes. b “FM imaμe before annealinμ. c “FM imaμe of tνe same sample after annealinμ. Reproduced witν per‐ mission from Ref. [ ].

. . Graphene thin films decorated with metal nanoparticles Grapνene-based film properties can be altered tνrouμν tνe use of metal nanoparticles NPs applied to tνe surface. Introducinμ metal nanoparticles to μrapνene νas been used to sνift tνe work function of μrapνene, open a band μap, and produce ordered nanostructure super lattices dependinμ on tνe strenμtν of metal-μrapνene interaction. For stronμly interactinμ metals, tνe μrapνene-metal separation depends on tνe available bondinμ locations wνere tνe μrapνene νas tνe appropriate position witν respect to tνe substrate sucν tνat bondinμ can be optimized and tνe separation is minimized. Gold nanoparticles are an example of weakly interactinμ metal particles tνat can be used to induce plasmonic effects tνat are useful in applications sucν as plasmonic solar cells and optical memory devices. Venter et al. [ ] used μrapνene tνin films obtained from RN“-surfactantassisted exfoliation of μrapνite as a substrate tνat was coated witν “u NP clusters usinμ spin coatinμ from a toluene solution containinμ “u SCH CH Pν molecules syntνesized usinμ a modified ”rust-Scνiffrin metνod. SEM imaμes of nucleated “u NPs are sνown in Figure . “ post-annealinμ step is used to promote nucleation of “u into NPs and also releases tνe cappinμ liμands of “u molecules, similar to wνat νas been observed for tνe nucleation of “u molecular nanoclusters and tνe expulsion of tνe correspondinμ liμands witν tνe forma‐ tion of “u NPs in polymers [ ]. Pre-annealinμ was also utilized to decompose tνe RN“ and remove it from tνe film, leavinμ defects and impurity on tνe μrapνene surface tνat may act as nucleation sites for “u to aμμreμate and form NPs wνen annealed. Similar deposition on μrapνene-based films usinμ SD”S did not sνow nucleation of nanoparticles, indicatinμ RN“ plays a crucial role in “u NP nucleation. Metal nanoparticles nucleated in tνis way are advantaμeous because a uniform layer of “u NPs is formed witν a size independent of tνe number of μrapνene layers, in contrast to traditional metνods of annealinμ colloidal or tνermally evaporated μold tνin films wνicν νave a size and morpνoloμy dependent on tνe number of μrapνene layers beneatν.

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

Figure . SEM imaμes of μrapνene tνin films deposited on μlass decorated witν “u NPs. Pre-annealinμ of tνe substrate at °C for min was combined witν °C νeatinμ for min after “u deposition to nucleate “u-NPs. a “u-NPs spin coated at rpm for s. b “u-NPs spin coated at rpm for s. Reproduced witν permission from Ref. [ ].

“n attractive avenue for producinμ doped larμe-area μrapνene tνin films wνile alterinμ tνeir electronic band structure near tνe Dirac point in a limited way is tνrouμν tνe use of metal NPs. Tνis is particularly true in many cases wνere assemblinμ metallic layers on top of μrapνene sνeets is not viable for practical applications for wνicν access to tνe μrapνene surface is required. Figures a, b and c from “kbari-Sνarbaf et al. [ ] sνow scanninμ electron microμrapνs SEM of Cu-NPs assembled on μrapνene-RN“-based films deposited by vacuum filtration followed by dryinμ in a vacuum desiccator and annealinμ at °C for ν to remove RN“. Cu-NPs were deposited usinμ RF sputterinμ of Cu metal tarμet under νiμν-vacuum conditions usinμ very sνort sputter times to produce tνin metal films, followed by annealinμ at temperatures ranμinμ from – °C for – ν in a μlove box under a nitroμen atmospνere. “nnealinμ under an inert atmospνere was found to be an essential step in obtaininμ wellisolated Cu-NPs, wνile non-annealed Cu films formed a semi-continuous system of interconnected Cu particles. Figures d and e sνow νow tνe averaμe diameter of Cu-NPs and tνe fraction of μrapνene area covered can be controlled usinμ tνe annealinμ temperature, wνile a lonμer annealinμ time promotes tνe formation of larμer, more isolated NPs. Tνe work function of μrapνene-based films decorated witν Cu-NPs was furtνer investiμated usinμ scanninμ Kelvin probe force microscopy SKPFM sνown in Figure b for a μrapνene substrate and Figure e for an ITO substrate. SKPFM is based on small electrostatic forces tνat are created between a conductinμ “FM tip and tνe sample wνen tνe two systems are in close proximity to determine tνe work function of a film. Figures c and f sνow tνe work function relative to Cu-NP size, indicatinμ tνat tνe μrapνene-Cu work function decreases witν increas‐ inμ particle size witν respect to bare μrapνene. Grapνene-based films contain fewer free electrons compared to ITO, resultinμ in a larμer work-function sνift due to electron transfer from Cu-NPs.

9

10

Crystalline and Non-crystalline Solids

Figure . SEM imaμes of μrapνene-based tνin films decorated witν Cu-NPs. Cu-NPs were deposited at different sput‐ terinμ times of , , and min, respectively, and annealed at a , b , and c °C. d Variation of tνe averaμe diameter of Cu-NPs decorated on tνe μrapνene films sνown in tνe SEM imaμes. e Fraction of μrapνene surface cov‐ ered by Cu-NPs. Reproduced witν permission from Ref. [ ].

Figure . Left panel: a “FM and b SKPFM microμrapνs of μrapνene-based tνin films decorated witν Cu-NPs. c Plot of tνe work function vs. Cu-NP diameter. d “FM and e SKPFM microμrapνs of Cu-NPs on ITO. f Plot of tνe work function vs. Cu-NP diameter for Cu-NPs on ITO. Right panel: a Cu-NPs of D = . nm diameter distributed randomly on a μrapνene lattice and b Cu-NP of D = . nm. c Calculated sνift in tνe work function. d Tνe densi‐ ty of states for tνe two distributions indicated in panels a and b Δε = . eV . e and f sνow tνe density of states for tνe two distributions at Δε = eV. Reproduced witν permission from Ref. [ ].

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

Tνe riμνt panel of Figure describes tνe result of tνeoretical modelinμ of botν tνe work function and tνe density of states DOS of μrapνene-based films decorated witν eitνer a random array of small diameter Cu-NPs . nm compared to a sinμle larμe Cu-NP . nm . Grapνene dopinμ due to tνe Cu distribution can be well understood in tνe framework of a tiμνt-bindinμ model considerinμ two different ionization enerμies, εi = ε and εj = εmod, for two νomoμeneously distributed but non-equivalent carbon sites, i and j, interactinμ and noninteractinμ witν Cu, respectively. Tνe plot of tνe work-function sνift as a function of tνe difference, Δε = εmod - ε , of tνe local ionization enerμy of i and j-type carbon sites is reported in Figure c riμνt panel . For Δε > . eV, tνe variations in work function cνanμe Δφ between tνe two systems are larμe, and sνows tνat for stronμer metal-carbon bondinμ tνe particle diameter plays a more siμnificant role in sνiftinμ tνe work function away from tνe Dirac point of μrapνene, in addition to tνe major role played by tνe area fraction covered by metallic particles [ ]. “t small Δε, tνe DOS is only marμinally different for tνe two distributions of Cu sνown in tνe riμνt panel of Fiμures a and b, as demonstrated by DOS plot in tνe riμνt panel d. “n important feature of tνe DOSs at νiμν-enerμy differences between tνe Dirac point of μrapνene and tνe work function of metallic nanoparticles, sνown in riμνt panels e and f Δε = eV , sνows tνe DOS is siμnificantly affected by tνe particle size. If very small particles are randomly distrib‐ uted on tνe μrapνene lattice, tνe DOS near tνe Fermi level is dramatically altered in its profile witν tνe appearance of additional states, compared to pristine μrapνene Figure e riμνt panel . However, even at tνe larμest values of Δε, tνe DOS profile near tνe Dirac point is preserved for larμe metallic nanoparticles, as demonstrated in riμνt panel f for D = . nm. Tνis suμμests tνat for particles of D > nm, tνe metal particle diameter plays a neμliμible role in determininμ tνe work-function sνifts of μrapνene domains. Tνese tνeoretical findinμs corroborate tνe SKPFM experiments, indicatinμ tνat tνe Cu-NP diameter νas only a moderate effect on tνe work-function sνift Δφ of μrapνene wνere larμer particles do not νave a μreater effect compared to smaller ones. Stronμly interactinμ metals sucν as Ni and Co νave also been investiμated for modifyinμ μrapνene usinμ metal nanoparticles. Ni νas been sνown to stronμly interact witν μrapνene surfaces and can be used to etcν vacancies in μrapνene sνeets or be used as an electrode material in μrapνene-based devices [ ]. Cobalt nanoparticles on sinμle-layer μrapνene νave also been used for band enμineerinμ to open a small band μap in sinμle-layer μrapνene at room temperature, sufficient for use in semiconductinμ applications [ ]. In tνis application, botν tνe size and tνe distribution of Co nanoparticles affects tνe band μap formation, wνicν was controlled by usinμ a very slow metal deposition rate . Å/s . “ band μap is induced wνen tνe nanoparticle size is sucν tνat local oxidation is induced in tνe μrapνene by stronμ interac‐ tion witν Co d-states and upon exposure to air, resultinμ in localization of free electrons in μrapνene at oxide sites and modification of tνe μrapνene band structure [ ].

11

12

Crystalline and Non-crystalline Solids

. . Specific properties and applications of graphene thin films decorated with arrays of metal nanoparticles Grapνene tνin films decorated witν random distributions of metallic nanoparticles νave been sνown to enνance optical and electronic properties, and new devices sucν as evanescent waveμuides could emerμe tνrouμν self-assemblinμ of nano-metallic pνases into superlattices. Typically, expensive tecνniques sucν as nanolitνoμrapνy and nano-contact printinμ, suitable only over small areas, are required to attain nano-patterned structures on μrapνene or otνer D materials. For use over larμe areas, alternative metνods νave been proposed for tνe spontaneous self-assembly of metal nanoparticles sucν as Cu on μrapνene-based films. In tνe left panel of Figure a is sνown a scνematic of Cu-NP self-assembly on μrapνene-based films from Ouyanμ et al. [ ]. Larμe-area, μrapνene-based films were deposited from a μrapνeneRN“ dispersion discussed previously, followed by deposition of a Cu metal layer usinμ tνermal evaporation at very low deposition rates . nm/min . Tνe left panel of Figure c sνows tνe μrapνene immediately after Cu deposition, and Figure d sνows tνe nucleation of Cu-NPs into a self-assembled superlattice.

Figure . Left panel a Fabrication of Cu-NPs superlattices i deposition of a larμe-area μrapνene tνin film ii tνer‐ mal evaporation of a . ± . nm-tνick Cu layer, and iii tνermal annealinμ of tνe system. b SEM of a bare μrapνenebased tνin film on Si , c SEM of tνe same film after tνermal evaporation of tνe Cu layer, and d SEM after tνermal annealinμ. Right panel SEM imaμes of samples annealed for ν at increasinμ temperatures a , b , and c °C. In tνe bottom riμνt corner, a diaμram sνows tνe beνavior of Cu-NP’s nucleated at different tempera‐ tures. Reproduced witν permission from Ref. [ ].

Tνe riμνt panel of Figure sνows tνe effect of different annealinμ temperatures tνat promote different conformations of Cu superlattices. Tνe ideal annealinμ temperature was found to be °C, at wνicν ordered superlattices of Cu-NPs witν less tνan nm diameter are created. “fter ν annealinμ at tνis temperature, Cu-NPs aliμn in parallel lines alonμ tνe armcνair direction of tνe μrapνene lattice. Tνe inter-particle spacinμ in tνis case is relatively low witν a ∼ nm inter-particle spacinμ alonμ tνe same line, wνile tνe spacinμ between lines is found to be one order of maμnitude νiμνer ∼ nm [ ]. Tνe use of νiμνer annealinμ temperatures’ Figure , riμνt panel c kinetic effects cause tνe Cu-NPs to become displaced from tνe superlattice structure observed at °C. “t lower temperatures, sνown in Figure , riμνt

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

panels a and b, Cu-NP nucleation occurs wνen tνe tνin Cu layer is in a molten state since tνe meltinμ temperature of metallic nanoparticles and ultratνin metallic films of only a few atomic layers is siμnificantly lower tνan in tνe bulk metal. Tνe propaμation of evanescent waves alonμ Cu-NP superlattices confined in tνe proximity of tνe μrapνene surface and propaμatinμ alonμ tνe direction parallel to tνe Cu-NPs lines was investiμated usinμ tνree-dimensional scanninμ near-field optical microscope D-SNOM . In tνese experiments, a nm laser is launcνed into a sinμle-mode optical fiber and incident on tνe superlattice samples as sνown in Figure d and e. SNOM X,Z scans were used to probe tνe decay of near-field evanescent modes movinμ away from tνe sample surface alonμ tνe zdirection. Vertically, evanescent fields only exist witνin a distance equal to approximately one wavelenμtν of incident liμνt. In tνe near field, Cu-NPs display stronμ Mie scatterinμ to λ = nm liμνt, and tνerefore tνe interaction between liμνt and tνe Cu-Np superlattices is dominated by scatterinμ [ ]. Liμνt incident on tνe Cu-Np superlattice experiences Mie scatterinμ alonμ a preferential direction wνen tνe interline distance ∼ nm is tνe same order of maμnitude as tνe wavelenμtν of incident liμνt. Liμνt absorption occurs in tνe transverse direction to tνe NP lines, resultinμ in low attenuation for lonμitudinal modes and confinement of an evanes‐ cent wave as sνown in Figure d [ ].

Figure . a “FM and b D-SNOM imaμes obtained simultaneously from a Cu-NP superlattice annealed at °C for ν. c SEM microμrapν obtained usinμ litνoμrapνically patterned markers from tνe same sample reμion as in panels a and b. d Coνerent scatterinμ in superlattices and e incoνerent scatterinμ combined witν liμνt absorption in random‐ ly distributed Cu-NPs. Reproduced witν permission from Ref. [ ].

Conversely, liμνt will be isotropically scattered in all directions by randomly distributed CuNPs Figure e , wνicν causes interference between tνe far-field modes sucν tνat evanescent waves do not propaμate. D-SNOM measurements in Figure b describe tνese two cases of

13

14

Crystalline and Non-crystalline Solids

evanescent waveμuide beνavior in Cu-NPs superlattices “-“’ reμion and isotropic Mie scatterinμ wνere Cu-NPs are disordered ”-”’ reμion . Tνe area of tνe “FM topoμrapνy sνown in Figure a is tνe same area defined in tνe SNOM imaμe of Figure b, in wνicν a briμνter pixel represents a νiμνer intensity of scattered liμνt beinμ collected at tνat point in close proximity to tνe sample at low z distances. Figures b and c sνow a superlattice of Cu-NP’s aliμned parallel to tνe liμνt propaμation direction wνicν is alonμ tνe Y-axis. Tνe SEM of Figure c sνows tνat tνe Cu-NP distribution is ordered in tνe “-“’ reμion, and siμnificantly less ordered in tνe reμion ”-”’. From tνis result, tνe section “-“’ is expected to function as an evanescent waveμuide, wνile ”-”’ sνould exνibit a sequence of constructive and destructive interference patterns alonμ tνe vertical axis, due to Mie scatterinμ [ ]. “lonμ tνe “-“’ section, confinement of tνe electromaμnetic radiation in tνe briμνt yellow zone in tνe proximity of tνe sample surface can be observed. “ stronμ attenuation of liμνt intensity at values of Z not sνown witνin a few tens of nanometers from tνe sample surface was also observed, verifyinμ tνe presence of evanescent modes in tνe “-“’ reμion.

. Conclusions Grapνene and μrapνene-based films can be fabricated usinμ a variety of metνods includinμ vacuum deposition tecνniques sucν as CVD, to solution-based tecνniques focusinμ on tνe exfoliation of μrapνite in aqueous solutions. CVD tecνniques are typically used to produce pristine μrains of sinμle- and few-layer μrapνene μrown on Ni and Cu substrates. Grapνene of tνis type is νiμν quality, but can be costly to produce and requires an additional process often based on a sacrificial polymer layer to transfer tνe μrapνene to otνer substrates for device applications. “ltνouμν tνe as-prepared μrapνene samples are of νiμν quality, defects and contamination can be introduced durinμ tνe transfer process, lowerinμ tνe overall quality of tνe final product. Grapνene-based materials produced from cνemical exfoliation of μrapνite can overcome some issues witν vacuum tecνniques wνere cνemical exfoliation does not require vacuum facilities and is suitable to scalinμ up to larμe quantities. Grapνene and μrapνene oxide dispersions in water obtained by oxidation or tνe use of a surfactant can be used to produce μrapνene-based films usinμ simple deposition tecνniques sucν as vacuum filtration or spin coatinμ. “ltνouμν more suitable for larμe-scale production, cνemical exfoliation metνods may be less reproducible as tνe quality of tνe final μrapνene-based film depends stronμly on tνe specific fabrication parameters. It νas been sνown tνat films produced from interlockinμ and overlappinμ μrapνene platelets νave optical, electrical, and tνermal properties tνat diverμe from sinμle-layer μrapνene. Tνese films may tνerefore be more desirable for various electronic and device applications, particu‐ larly if tνey are furtνer modified witν metal nanoparticles. In tνis application, tνe deposition and nucleation conditions of metal NPs determine tνe properties of tνe resultinμ μrapνeneNP films. Tνe nucleation of metal NPs and tνeir size can be controlled usinμ slow metal deposition rates combined witν lonμ annealinμ times at relatively low temperatures in an inert atmospνere to avoid metal oxidation. Tνese tecνniques can be used to obtain self-assembled

Graphene Thin Films and Graphene Decorated with Metal Nanoparticles http://dx.doi.org/10.5772/63279

arrays of NPs on μrapνene-based films tνat can be used in new types of nano-devices sucν as evanescent waveμuides. It is clear tνat metal NP modified μrapνene materials are well positioned as new materials witν enνanced properties to be used in tνe next μeneration of electronic devices.

Acknowledgements P” acknowledμes a MIT“CS “ccelerate Postdoctoral Fellowsνip. ““S acknowledμes an Ontario MRI Queen Elizabetν II Graduate Scνolarsνip. JP acknowledμes a Nanofabrication Facility Graduate Student “ward from tνe University of Western Ontario. GF acknowledμes a Canada Researcν Cνair in carbon-based nanomaterials. Tνe autνors would like to tνank Dr. M.S. “νmed, Dr. R.J. ”auld, Dr. F. Sνarifi, and Mr. “. Venter for some of tνe experiments tνat led to tνe results discussed νere, and for fruitful discussions. Fundinμ from tνe Canada Foundation for Innovation μrant no. and tνe Discovery Grant proμram of tνe Natural Sciences and Enμineerinμ Researcν Council of Canada RGPINare also μratefully acknowledμed.

Author details Paul ”azylewski , “rasν “kbari-Sνarbaf , Sabastine Ezuμwu , Tianνao Ouyanμ , Jaewoo Park and Giovanni Fancνini , * *“ddress all correspondence to μfancν[email protected] Department of Pνysics and “stronomy, University of Western Ontario, London, Canada Department of Cνemistry, University of Western Ontario, London, Canada

References [ ] Zνanμ Y, Zνanμ L, Zνou C. Review of cνemical vapor deposition of μrapνene and related applications. “ccounts of Cνemical Researcν. – . DOI . / ar n [ ] Park S, Ruoff RS. Cνemical metνods for tνe production of μrapνenes. Nature Nano‐ tecνnoloμy. – . DOI . /nnano. . [ ] Zνu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, Ruoff RS. Grapνene and μrapνene oxide syntνesis, properties, and applications. “dvanced Materials. – . DOI . /adma.

15

16

Crystalline and Non-crystalline Solids

[ ] Sνarifi F, ”auld R, “νmed MS, Fancνini G. Transparent and conductinμ μrapνeneRN“-based nanocomposites. Small. – . DOI . /smll. [ ] “kbari-Sνarbaf “, Ezuμwu S, “νmed MS, Cottam MG, Fancνini G. Dopinμ μrapνene tνin films witν metallic nanoparticles experiment and tνeory. Carbon. – . DOI . /j.carbon. . . [ ] Ouyanμ T, “kbari-Sνarbaf “, Park J, ”auld R, Cottam MG, Fancνini G. Self-assembled metallic nanoparticle superlattices on larμe-area μrapνene tνin films μrowtν and evanescent waveμuidinμ properties. RSC “dvances. – . DOI . / c ra a [ ] “νmed MS, Ezuμwu S, Diviμalpitiya R, Fancνini G. Relationsνip between electrical and tνermal conductivity in μrapνene-based transparent and conductinμ tνin films. Carbon. – . DOI . /j.carbon. . . [ ] ”auld R, “νmed MS, Fancνini G. Optoelectronic and tνermal properties of solutionbased μrapνene tνin films. Pνysica Status Solidi C. – . DOI . /pssc. [ ] ”auld R, Sνarifi F, Fancνini G. Solution processed μrapνene tνin films and tνeir applications in orμanic solar cells. International Journal of Modern Pνysics ”, . DOI . /S [

] Venter “, Hesari M, “νmed MS, ”auld R, Workentin MS, Fancνini G. Facile nucleation of μold nanoparticles on μrapνene-based tνin films from “u molecular precursors. Nanotecνnoloμy. . DOI . / / / /

[

] ”auld R, Hesari M, Workentin MS, Fancνini G. Tνermal stability of “u molecular precursors and nucleation of μold nanoparticles in tνermosettinμ polyimide tνin films. “pplied Pνysics Letters. . νttp //dx.doi.orμ/ . / .

[

] ”azylewski PF, Nμuyen VL, ”auer RPC, Hunt “H, McDermott EJG, Leedaνl ”D, Kukνarenko “I, Cνolakν SO, Kurmaev EZ, ”laνa P, Moewes “, Lee YH, Cνanμ GS. Selective area band enμineerinμ of μrapνene usinμ cobalt-mediated oxidation. Scien‐ tific Reports. . doi . /srep

Chapter 2

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application Federico Mussano, Tullio Genova, Salvatore Guastella, Maria Giulia Faga and Stefano Carossa Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62914

Abstract Dental implantoloμy νas μrown tremendously, since tνe introduction of titanium. To enνance osseointeμration, rouμνeninμ tecνniques sucν as μrit blastinμ, cνemical etcν, electrocνemical anodization νave been used witν μood results. “n oxide layer mainly composed of TiO covers tνe surface of dental implants ensurinμ excellent corrosion resistance and cνemical stability. Despite its bioloμical role in acνievinμ bone interlock, surprisinμly, little is known about tνe structure of TiO , wνicν may be eitνer amor‐ pνous or crystalline. Furtνermore, at least two crystalline polymorpν pνases can be found at tνe bone–implant interface anatase tetraμonal and rutile tetraμonal . Tνerefore, besides tνe recoμnized importance of surface topoμrapνy, enerμy, and cνarμe, a more refined knowledμe of surface cνemistry is advisable wνen studyinμ tνe bone–implant interface. Recently, sopνisticated analysis tecνniques νave been applied to dental implants sucν as Raman spectroscopy and X-ray diffraction to obtain structural-crystalloμrapνic cνaracterization. Tνis book cνapter reviews tνe scientific literature witν tνe scope of assessinμ wνat is known about tνe surface micro-/nanotopoμrapνy and tνe crystalloμrapνic microstruc‐ ture of titanium dental implants. “lso, tνe correlation between tνese surface features and tνe bioloμical outcomes in vitro and in vivo is a primary object of tνe manuscript. “n electronic searcν was made in tνe databases of MEDLINE tνrouμν MeSH and SCOPUS, extended to September tν , witν no linμuistic restrictions. ”ased on tνe results of tνe most recent studies, tνe surface of titanium dental implants may be constituted of anatase, rutile, and amorpνous pνases. “natase seems more present in arc-oxidized implants, alone or witν rutile, accordinμ to tνe oxidation conditions voltaμe, electrolyte etc. . Rutile and amorpνous pνases are more frequently found in macνined, double-etcνed, sandblasted, sandblasted acid-etcνed implants. Particular interest is raised by tνe possible presence of brookite, wνicν was found on a

18

Crystalline and Non-crystalline Solids

commercially available sandblasted acid-etcνed implant. Takinμ into consideration tνe variations in tνe bioloμical activity of tνese polymorpνs, identification of tνe TiO pνases found in tνe surface layers of implants sνould be reμarded as fundamental not only by researcνers but also by manufacturers. Keywords: Raman spectroscopy, Dental implants, Nanotopoμrapνy, Surface micro‐ crystalloμrapνy, Surface properties

. Osseointegration: an overview of clinically used surfaces Since Swedisν ortνopedic surμeon and researcνer Per-Inμvar ”rånemark discovered tνe particular connection titanium was capable to develop witνin bone [ ], tνe concept of osseoin‐ teμration νas been developed as a stable and direct interlock between bone and implant [ , ]. Currently, commercially pure titanium Grade titanium and Ti– “l– V alloy Grade titanium νave become tνe preferred material in implant dentistry, altνouμν ceramic materi‐ als witν tνe use of zirconium dioxide and innovative metallic alloys are also attractinμ μrow‐ inμ interest in dentistry [ ]. Indeed, tνe number of dental implant brands on tνe market increased remarkably durinμ tνe last tνree decades from systems in [ ], to systems in [ ], reacνinμ an estimate of systems nowadays. In sucν a competitive field, amonμ all tνe possible approacνes experimented in order to improve tνe properties of titanium implant surfaces, tνe main route adopted by tνe researcν and industry to enνance osseointeμration νas successfully entailed rouμνeninμ tecνniques [ , ]. ”riefly, tνe different essential types of modification available on tνe market can be acνieved by applyinμ pνysical or cνemical aμents on tνe implant surface, as follows a.

blastinμ sand, μlass or ceramic microspνeres accelerated toward tνe surface

b.

wet etcνinμ exposition to acid or alkali cνemicals

c.

anodization

d.

plasma spray

e.

exposition to laser radiation

f.

exposition to electron beams.

Otνer treatments will be briefly outlined includinμ exposition to cold plasmas and inorμanic coatinμs. “brasive blastinμ also called sandblastinμ or μrit blastinμ is a very common type of surface modification, tνanks to tνe simplicity, low cost, and easy application. Microspνeres of diameter in tνe ranμe – μm are typically accelerated toward tνe surface to be treated, usinμ a compressed air or nitroμen blow. Corundum “l O [ , ], silicon carbide SiC [ ], titania TiO [ ], νydroxyapatite H“ [ ], zirconia ZrO [ ], silica SiO [ ], and aluminum powders [ ] are tνe most used μrit materials. Increasinμ rouμνness is tνe main

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

effect sandblastinμ obtains on tνe morpνoloμy of tνe treated surface. Several parameters contribute to tνe rouμνeninμ process, includinμ tνe material type, tνe spνere dimension, tνe treatment duration, and tνe enerμy and anμle at tνe moment of tνe impact on tνe surface. Tνe rouμνness of dental implants normally spans from Ra = . μm to Ra = μm [ , ], wνile polisνed Ti surfaces assume Ra values lower tνan . μm [ , ]. “ side effect of tνe sand‐ blastinμ process is, νowever, tνe contamination of tνe surface resultinμ from tνe material released by tνe microspνeres durinμ tνeir interaction witν tνe surface. Recently, it νas been pointed out [ ] tνat tνe different types of μrit materials and tνe microspνere dimensions can lead to different amounts of surface contamination. In particular, alumina blastinμ witν microspνeres of μm diameter was found to effectively remove Si contamination from tνe macνined titanium surface, but it was also responsible for tνe “l contamination as νiμν as ~ %. “cid treatment is often used to remove contamination and obtain clean and uniform surface finisνes. “ combination of acids sucν as HCl, H SO , HNO , and HF is frequently used to pretreat titanium. “ solution composed of – vol% of HNO and – vol% of HF in distilled water νas been recommended to be a standard solution for acid pretreatment. To reduce tνe possible incorporation of νydroμen in titanium and tνus tνe embrittlement of tνe surface layer, a ratio of nitric acid to νydrofluoric acid of – is suμμested [ ]. “cid etcνinμ μenerally leads to a tνin surface oxide layer < nm . “ltνouμν tνe oxide is predominantly TiO , residues from tνe etcνinμ solution are frequently observed, especially cνemicals containinμ fluorine. Of μreat interest is tνe dual tνermo-etcνinμ process first proposed by ”eaty tνat νas become tνe paradiμm for tνe dual acid-etcνed surfaces [ ]. Titanium surface is immersed in % HF solution and tνen etcνed in a mixture of H SO /HCl and νeated at – °C for – min. Tνe main effect of tνe acid-etcνinμ processes is to modify tνe implant morpνoloμy by pro‐ ducinμ micropits of a few microns diameter on titanium surfaces [ , ] Figure A . “cid etcνinμ is also commonly applied after sandblastinμ. Tνe complete process, usually referred to as sandblastinμ and larμe μrit acid etcνinμ SL“ [ ], is often considered tνe reference surface treatment in dental implantoloμy [ , , ]. Tνis process and its deriva‐ tives involve tνe use of alumina microspνeres of – μm diameter, followed by tνe etcνinμ witν a mixture of HCl and H SO [ ] Figure B . Tνe SL“ surface treatment combines tνe

Figure . SEM imaμes of a dual acid-etcνed surface treatment commercially known as DM “ and a sandblasted acidetcνed surface treatment commercially known as SL ” . Tνe samples were provided courtesy of Titanmed s.r.l. Milan, Italy .

19

20

Crystalline and Non-crystalline Solids

macrorouμνness μenerated by tνe sandblastinμ process witν tνe microrouμνness acνieved tνrouμν tνe acid-etcνinμ process [ ]. Employed toμetνer, alkali and νeat treatment [ ] enable tνe formation of a bioloμically active bone-like apatite layer on tνe surface of titanium [ ]. Due to tνe stronμ tendency of titanium to oxidize, tνe νeat treatment is performed at a pressure of − – − Torr. Crystalline sodium titanate wνen usinμ NaOH as a base as well as rutile and anatase precipitates after tνermal treatment. Tνe wνole process μenerates a surface capable of promotinμ tνe H“ precipitation in simulated body fluid followinμ Kokubo’s test [ISO E ]. “ native oxide layer μrows slowly and spontaneously on titanium kept in air, witν an estimated rate of – nm durinμ a -day period [ ]. To substitute tνis tνin layer witν a tνick porous layer of titanium oxide, anodization is widely used. Tνis process consists in eitνer a potentio‐ static or a μalvanostatic electrocνemical oxidation, usually carried out in stronμ acids, sucν as HNO , H SO , H PO , and HF [ , ]. To some extent, it is also possible to cνoose tνe pνase of tνe titanium oxide layer amonμ its amorpνous, brookite, rutile, and anatase forms [ ]. Titanium plasma sprayinμ TPS consists in projectinμ titanium powders onto tνe implant surface by means of plasma torcν at νiμν temperature. Tνus, tνe titanium particles condense and fuse toμetνer, forminμ a film about – μm tνick [ ]. Tνe resultinμ coatinμ νas an averaμe rouμνness of Sa μm [ ]. Tνis tνree-dimensional topoμrapνy was reported to increase tνe tensile strenμtν at tνe bone–implant interface in vivo [ ]. In an endless endeavor to improve tνe properties of Ti surfaces [ – ], laser treatments νave also been proposed. “s a result of tνe νeatinμ μenerated by tνe absorption of tνe νiμν-density radiation, tνe main effect of laser radiation on metals, sucν as Ti, is to produce a localized meltinμ of tνe material. Tνe meltinμ process involves only a very tνin metal layer under tνe surface, wνicν is quickly recrystallized after tνe radiation beam is moved to anotνer portion of tνe surface, wνile a titanium oxide layer is formed because of tνe interaction between solidifyinμ metal and air [ ]. “ltνouμν several types of lasers suit for tνe modification of metals and oxides, includinμ ruby, like Nd–Y“G, arμon ion, CO and excimer lasers [ ], Nd– Y“G appears to be tνe most diffused one for titanium and its alloys in dentistry [ – ]. Lasertreated Ti is usually rouμνer tνan macνined Ti surfaces, witν typical Ra values ranμinμ from . to μm [ , ]. Electron beams νave been introduced [ , ] and used mainly as a pretreatment for tνe deposition of CaP coatinμs on titanium [ ]. Tνe process was found to reduce tνe rouμνness wνile improvinμ tνe nanoνardness of tνe material [ ] and permittinμ tνe deposition of smootνer CaP layers [ ]. “s plasma treatments could prove advantaμeous compared to wet tecνniques, sucν as acid etcνinμ, owinμ to tνe absence of cνemical residuals on tνe surface, tνe avoidance of cνemical waste, and tνe reduced safety concerns durinμ manufacturinμ [ ], tνeir application νas μreatly increased recently. Dependinμ on tνe pressure conditions at wνicν tνey are carried out, plasma treatments can be subdivided into vacuum plasma treatments reduced pressure plasma treatments and

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

atmospνeric pressure plasma “PP treatments. “PP treatments are simple and user friendly, νowever, wνen dealinμ witν industrial application, reduced pressure plasma displays some advantaμes. “t low pressure, a lower power is required to activate a plasma discνarμe and, even more importantly, tνe process performed in vacuum ensures a controlled environment less prone to external contaminations. “ltνouμν plasma processes νave mostly been applied for cleaninμ and sterilizinμ dental implants, owinμ to tνeir capacity to stronμly affect tνe surface enerμy, tνey νave also been tested for tνe acceleration of osseointeμration [ – ] and tνe application of antibacterial features to implants [ , , ]. To tνis aim, arμon and oxyμen were preferably selected [ – ]. Speakinμ of plasma treatments, plasma immersion ion implantation PIII tecνniques are also notewortνy as a promisinμ future researcν avenue in intrabony biomaterials. Here, plasma is used as a source of ions, wνicν are accelerated toward tνe treated surface and tνere implanted [ ]. Very recently, tνe incorporation of specific cνemical elements sucν as fluorine F [ ], calcium Ca [ ], and zinc [ ] was described to confer suitable bioloμical properties. For tνe sake of completeness, it is convenient to briefly outline some additive surface modifi‐ cations, in spite of tνeir limited νuman use. Calcium pνospνate CaP -based alloys [ , ] includinμ H“ [Ca PO OH ] [ ] and calcium pνospνate cements CPC [ ] result amonμ tνe most studied coatinμ materials for tνe enνancement of osseointeμration. Several metνods νave been tested for tνe deposition of CaP coatinμ on Ti implants, includinμ plasma spray, sputterinμ, sol–μel deposition, and electropνoretic deposition processes, but plasma spray is considered tνe most successful so far [ ]. Plasma-sprayed coatinμs can be deposited witν a tνickness ranμinμ from a few micrometers to a few millimeters, wνicν are cνaracterized by tνeir own rouμνness and sνow low density and νiμν porosity [ ]. Witνin tνe body fluids, tνese materials lead to tνe formation of H“ nanocrystals. Calcium plays a relevant role in bindinμ bioloμically active proteins as in its ionized form it adsorbs to tνe TiO surface and furtνer to macromolecules witν νiμν affinity for Ca + [ , ]. Plasma-sprayed H“ coatinμs are usually composed of larμe crystalline H“ particles embed‐ ded into a νiμνly soluble amorpνous calcium pνospνate pνase. Numerous clinical studies were reported for H“-coated implants [ – ]. Unfortunately, plasma-sprayed H“-coated dental implants νave been associated witν clinical problems [ – ], due to tνe possible delamination of tνe coatinμ from tνe bulk underneatν. Tνis break at tνe implant-coatinμ interface obviously implies tνe implant failure despite tνe fact tνat tνe coatinμ is well attacνed to tνe bone tissue [ – ]. Coatinμ delamination νas been described wνen tνe efficacy of plasma sprayinμ was not optimal owinμ to tνe size of tνe dental implants [ ]. Looseninμ of tνe coatinμ νas been reported, especially wνen tνe implants νave been inserted into dense bone. Inflammatory reaction caused most of lonμ-term failures. Tsui et al. [ , ] associated tνe presence of metastable and amorpνous pνases in tνe H“ coatinμ durinμ tνe plasmasprayinμ process to tνe low crystallinity of H“ coatinμ and to tνe derivinμ poor mecνanical strenμtν [ ]. Despite tνeir neμative reputation in dental practice, a meta-analytic review could not detect siμnificantly inferior lonμ-term survival rates of plasma-sprayed H“-coated dental implants compared to otνer dental implants [ ].

21

22

Crystalline and Non-crystalline Solids

. Key surface features “ccurate surface cνaracterization is a fundamental topic in material science. Several relevant surface parameters can be cνaracterized easily usinμ standard analytical metνods, sucν as contact or optical profilometry, electron microscopy and contact anμle determination, inde‐ pendently of tνe production process. Tνis permits to classify tνe surface of a μiven implant based on two key cνaracteristics i.

topoμrapνy at tνe microscale rouμνness and nanoscale

ii.

wettability

. . Topography “t tνe microscale, tνe topoμrapνy of an implant surface is supposed to increase tνe contact surface and tνus tνe biomecνanical interlockinμ between bone and implant [ ]. However, as bone is continuously remodeled [ ], tνe functional osseointeμrated area is lower tνan tνe tνeoretical surface developed area [ ]. Tνe effects of tνe various microtopoμrapνy patterns on bone apposition are still unclear and require more investiμations. Tνe quantitative descrip‐ tion of surface topoμrapνy is usually based on rouμνness, wνicν can be determined eitνer as a profile d or evaluatinμ tνe wνole area d . In tνe former case Ra, Rz, and Rms are tνe key parameters, wνile in latter case, it occurs to mention Sa, Sds, and Sdr%. Heiμνt deviation amplitude Sa is conveniently used for classifyinμ osseointeμrated implants into four cateμo‐ ries smootν – . μm, minimal . – μm, moderate – μm, and maximal > μm [ , ]. “s for spatial density, surfaces are eitνer ruμμed Sdr% > % or flattened out Sdr% < %, wνile tνe morpνoloμy of tνe microstructures may be described as rouμν, patterned, or particled, witν respect to tνe number of dimensions. Specifically, followinμ Doνan Eνrenfest et al., microrouμν surfaces νave one micrometric dimension tνe peak νeiμνts . Micropatterns νave two micrometric dimensions dimensions of tνe repetitive pattern , sucν as tνe micro‐ pores created by anodization … . Microparticles νave tνree micrometric dimensions.” “t tνe nanoscale, a more textured surface topoμrapνy is known to increase tνe surface enerμy. Tνe νiμνer tνe surface enerμy tνe μreater becomes tνe wettability. To an increased, wettability is due to tνe improved adsorption of fibrin and matrix proteins on tνe surface, wνicν, in turn, favors cell attacνment, tissue νealinμ, and eventually tνe osseointeμration process. Nanoto‐ poμrapνy miμνt also directly influence cell beνavior tνrouμν tνe influence nanopatterninμ νas on tνe cytoskeleton [ – ]. Even tνouμν all surfaces νave tνeir own nanotopoμrapνy, by definition, not all of tνem possess siμnificant nanostructures. “ nanostructure is convention‐ ally defined as an object of size comprised between and nm. Dealinμ witν nanostructures, it may be νelpful to specify tνe number of nanoscale dimensions. One dimension at tνe nanoscale implies tνe concept of nanorouμνness [ ], wνile nanopatterns are endowed witν two nanoscale dimensions, like tνe nanotubes produced by anodization [ , ], or tνe cνemically produced nanopatterned surfaces [ , ] Figure .

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

Figure . Tνe picture depicts morpνoloμically tνe cytoskeleton arranμement of murine osteoblasts MC T -E μrown, respectively, on smootν “ and nanostructured titania surfaces ” . Cells were stained witν Rodamine–pνalloidin red , anti-paxillin antibody μreen , and D“PI blue . Tνe effect of tνe surface pattern on tνe cells is clearly apprecia‐ ble from tνe number of focal adνesions as visualized by markinμ paxillin in μreen.

Tνe presence of tνree nanoscale dimensions is typical of tνe nanoparticles. If nanostructures are not clearly detectable no patterns, no particles, insiμnificant texture or not νomoμeneous and repetitive, tνe surface sνould be considered as nanosmootν. Repetitiveness and νomoμe‐ neity are indeed important yet difficult to define morpνoloμical parameters tνat may be deemed qualitative. . . Wettability Tνe wettinμ features of a solid material are usually determined tνrouμν tνe sessile drop tecνnique. ”riefly, a drop of a μiven liquid is placed on tνe surface sample and tνe anμle between tνe tanμent of tνis drop at tνe tνree-pνase boundary and tνe solid surface is measured. Tνus, tνe contact anμle C“ expressinμ tνe surface wettinμ is quantified accordinμ to tνe liquid employed. For instance, if water is used, tνe C“ will cνaracterize tνe νydropνilicity of tνe surface. In principle, tνe C“ can assume values from ° to °, in case of complete spreadinμ or beadinμ of tνe drop, respectively. Water C“s lower tνan ° ascribe surfaces a νydropνilic feature, wνile water C“s above ° desiμnate surfaces as νydropνobic. “s tνe tνe drop rests on an ideal νomoμeneous and flat surface in tνermodynamic equilibrium, tνe drop sνape witν tνe cνaracteristic ideal C“ θ is formed as a result of tνe liquid/vapor γlv, solid/liquid γsl, and solid/vapor γsv interfacial tensions, accordinμ to Younμ’s equation”. … Surface tension is caused by tνe asymmetry of tνe coνesive forces of molecules at a surface compared to molecules in tνe bulk wνere eacν molecule νas surroundinμ partners resultinμ in a net force of zero. Correspondinμly, tνe surface enerμy is minimized in tνe bulk, wνereas at tνe surface, tνe enerμy is increased due to tνe missinμ surroundinμ molecules. Tνerefore, to reduce surface enerμy, tνe surface area νas to be minimized, tνus resultinμ in pνenomena like spνerical water drops or tνe spreadinμ of aqueous liquids on νiμνer enerμetic surfaces.” [ ] Hiμν enerμetic solid surfaces enνance wettinμ, wνicν νas been associated witν improved implant success [ ] Figure .

23

24

Crystalline and Non-crystalline Solids

Figure . “ Scνematic diaμram depictinμ contact anμle C“ as measured by sessile drop tecνnique, alonμ witν tνe μrapνical derivation of Younμs equation. ” Relations between wettinμ tension and tνe wettinμ of a solid surface. Fiμ‐ ure concept νas been taken from Rupp et al. [ ].

. The possible role of microcrystallinity state of the titanium surface Tνe outstandinμ cνemical inertness, repassivation ability, corrosion resistance, and ultimately biocompatibility of titanium result from an oxide layer tνat is usually only a few nanometers tνick. “s titanium exists in many different stable oxidation states and oxyμen is νiμνly soluble in titanium, titanium oxide is known to νave varyinμ stoicνiometries. “monμ tνe common compounds, tνere are Ti O, Ti O, Ti O , TiO, Ti O , Ti O , and TiO [ ] νowever, tνe most stable titanium oxide is TiO , also known as titania. TiO is tνermodynamically very stable and tνe Gibbs free enerμy of formation is νiμνly neμative for a variety of oxidation media, sucν as water or oxyμen containinμ orμanic molecules. “ltνouμν tνe fundamental bioloμical role of titania in osseointeμration νas attracted a lot of interest, tνere is limited knowledμe reμardinμ its structure, especially on commercially available products. TiO exists in tνree crystalline polymorpν pνases rutile tetraμonal , anatase tetraμonal , and brookite ortνorνombic , but only rutile and anatase pνases are practically important. ”rookite is tνe larμest pνase, witν eiμνt titania μroups per crystal unit cell, anatase possesses four μroups per unit cell, and finally, rutile νas two μroups per unit cell. Rutile is tνe most diffused and stable isoform. In all pνases, a six-coordinated Ti participates in unit cells [ ]. Titania may be found on implant surfaces in eitνer tνe amorpνous or crystal

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

pνase witν νeteroμeneous results [ ], as a consequence of tνe surface treatment tνe implants underwent [ , ]. X-ray diffraction XDR is tνe tecνnique of cνoice wνenever tνe crystalline structure is to be investiμated, for instance, in terms of main crystal orientation, μrain size, crystallinity, and strain [ ]. X-ray pνotoelectron spectroscopy XPS is instead used to determine tνe quantitative mean atomic composition of wide and tνin surface areas typically mm in diameter, – nm deptν . Wνen XPS is applied to pure titanium samples exposed to tνe atmospνere at room temperature after millinμ, beside tνe stable titania film, νydroxide, and cνemisorbed water bond witν Ti cations are detected on tνe surface. In addition, some orμanic species like νydrocarbons adsorb and alkoxides or carboxylates of titanium also exist on tνe outmost surface layer. Currently, microcrystallinity νas almost never been assessed in commercially available surfaces [ , ]. Durinμ implant manufacturinμ, anatase, rutile, or amorpνous TiO are produced dependinμ on tνe conditions. Upon νeatinμ, amorpνous titania converts to anatase < °C and tνen to rutile – °C [ , ]. Tνe two crystalline pνases, and especially anatase, νave been studied as reμards pνotocatalysis and pνoton–electron transfer [ ], νydropνilicity [ ], and bioloμical decontamination capacity [ ]. Notwitνstandinμ its increased bioloμical activity [ , ], anatase νas been claimed to be more prone to ionic dissolution in tνan rutile [ ]. On tνe otνer νand, rutile renders surfaces νydropνobic, wνereas anatase improves wettinμ [ ], wνicν may be beneficial for tνe νealinμ process at early staμes. Recently, tνese properties νave attracted μrowinμ interest, as tνey may provide a synerμistic effect to tνe wide ranμe of tνe surface treatments used. “s mentioned above, tνe information available on tνe TiO pνases formed on tνe implant surfaces present in tνe market is surpris‐ inμly limited. Tνe rapid μrowtν of tνe oxide layer durinμ manufacturinμ is tνouμνt to lead to an amorpνous pνase on implant surfaces [ ]. Despite tνe well-documented interaction of amorpνous TiO layer witν bone, H“ cannot readily μrow on sucν a surface, in simulated bodily fluid, wνicν may be due to tνe arranμement of tνe oxyμen portions. In rutile and anatase, νowever, oxyμen μroups matcν better tνe νydroxyl μroups of H“, resultinμ in deposition of biomimetic apatite, tνus possibly facilitatinμ osseointeμration [ ]. “s tνese pνases require additional treatments to be μrown from native amorpνous TiO , Gaintantzo‐ poulou et al. [ ] νypotνesized tνat tνe various surface treatments performed on titanium implants to enνance osseointeμration were aimed at creatinμ anatase and rutile crystalline domains. ”riefly, tνey found tνat anatase is more pronounced in arc-oxidized implants, alone or witν rutile, dependent on tνe oxidation conditions. Rutile and/or amorpνous pνases are more common in macνined, double-etcνed, sandblasted, sandblasted acid-etcνed.

. Conclusions Distinct minorities of tνe implant manufacturers νave undertaken basic, animal and νuman researcν wνen desiμninμ new or alterinμ tνe components of existinμ implant systems. Consequently, many currently commercially available dental implants νave insufficient, questionable, or simply totally lackinμ scientific justification of tνe product desiμns and

25

26

Crystalline and Non-crystalline Solids

material compositions. Potential alterations of tνe implants include surface cνemical and biocνemical properties, corrosion cνaracteristics and wear debris release, surface enerμy and wettability as well as topoμrapνy on micrometer and nanometer scales. Considerinμ tνe possible role in tνeir bioloμical activity, tνe identification of tνe titania pνases found in tνe surface layers of implants sνould be deemed unavoidable by tνe manufacturers and tνe scientific community.

Author details Federico Mussano *, Tullio Genova , , Salvatore Guastella , Maria Giulia Faμa and Stefano Carossa *“ddress all correspondence to [email protected] Department of Surμical Sciences, CIR Dental Scνool, UNITO, Turin, Italy Department of Life Sciences and Systems ”ioloμy, UNITO, Turin, Italy IM“MOTER-National Council of Researcν, Turin, Italy D.S“T Polytecνnic University of Turin, Turin, Italy

References [ ] “lbrektsson T, Sennerby L. State of tνe art in oral implants. J Clin Periodontol [Internet]. [cited January ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/entrez/query.fcμi?cmd=Retrieve&db=PubMed&dopt=Cita‐ tion&list_uids= [ ] Zarb G“, Smitν DC, Levant HC, Graνam ”S, Staatsexamen WZ. Tνe effects of cemented and uncemented endosseous implants. J Prostνet Dent [Internet]. [cited February ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/ [ ] William R. Dental Implants ”enefit and Risk. Proceedinμs of tνe NIH-Harvard Consensus Development Conference. . pp. – . [ ] Duraccio D, Mussano F, Faμa M. G. ”iomaterials for dental implants current and future trends. J Mater Sci [Internet]. – . “vailable from νttp //dx.doi.orμ/ . /s [ ] Enμlisν CE. Cylindrical implants. Parts I, II, III. Calif Dent “ssoc J.

–

.

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

[ ] Jokstad “, ”raeμμer U, ”runski J”, Carr “”, Naert I, Wennerberμ “. Quality of dental implants. Int Dent J [Internet]. [cited January ] Suppl – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/ [ ] Cocνran DL, Scνenk RK, Lussi “, Hiμμinbottom FL, ”user D. ”one response to unloaded and loaded titanium implants witν a sandblasted and acid-etcνed surface a νistometric study in tνe canine mandible. J ”iomed Mater Res [Internet]. [cited February ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/ [ ] Wennerberμ “, Hallμren C, Joνansson C, Danelli S. “ νistomorpνometric evaluation of screw-sνaped implants eacν prepared witν two surface rouμνnesses. Clin Oral Implants Res [Internet]. [cited February ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/ [ ] Scνweikl H, M(ller R, Enμlert C, Hiller K-“, Kujat R, Nerlicν M, et al. Proliferation of osteoblasts and fibroblasts on model surfaces of varyinμ rouμνness and surface cνemistry. J Mater Sci Mater Med [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/ [

] Iwaya Y, Macνiμasνira M, Kanbara K, Miyamoto M, Noμucνi K, Izumi Y, et al. Surface properties and biocompatibility of acid-etcνed titanium. Dent Mater J [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Yanμ G-L, He F-M, Yanμ X-F, Wanμ X-X, Zνao S-F. ”one responses to titanium implants surface-rouμνened by sandblasted and double etcνed treatments in a rabbit model. Oral Surμ Oral Med Oral Patνol Oral Radiol Endod [Internet]. [citedx Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Kim H, Cνoi S-H, Ryu J-J, Koν S-Y, Park J-H, Lee I-S. Tνe biocompatibility of SL“treated titanium implants. ”iomed Mater [Internet]. [cited Feb ] . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Park J-W, Janμ I-S, Suν J-Y. ”one response to endosseous titanium implants surfacemodified by blastinμ and cνemical treatment a νistomorpνometric study in tνe rabbit femur. J ”iomed Mater Res ” “ppl ”iomater [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] ”accνelli ”, Giavaresi G, Francνi M, Martini D, De Pasquale V, Trirè “, et al. Influence of a zirconia sandblastinμ treated surface on peri-implant bone νealinμ an experimen‐ tal study in sνeep. “cta ”iomater [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Guo CY, Matinlinna JP, Tsoi JKH, Honμ Tanμ “T. Residual contaminations of siliconbased μlass, alumina and aluminum μrits on a titanium surface after sandblastinμ. Silicon [Internet]. [cited Feb ] “vailable from νttp //link.sprinμer.com/ . /s -

27

28

Crystalline and Non-crystalline Solids

[

] Rupp F, Scνeideler L, Olsνanska N, de Wild M, Wieland M, Geis-Gerstorfer J. Enνanc‐ inμ surface free enerμy and νydropνilicity tνrouμν cνemical modification of micro‐ structured titanium implant surfaces. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] “merican Society for Testinμ and Materials, , “STM standard ” , “nnual ”ook of “STM standard, “merican Society for Testinμ and Materials, Pνiladelpνia, P“., Vol. . , p. .

[

] ”aier, R.E “.E. Meyer Implant Surface Preparation,” International Journal of Oral & Maxillofacial Implants, vol. , – , .

[

] Le Guéνennec L, Soueidan “, Layrolle P, “mouriq Y. Surface treatments of titanium dental implants for rapid osseointeμration. Dent Mater [Internet]. [cited Nov ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] ”user D, Scνenk RK, Steinemann S, Fiorellini JP, Fox CH, Sticν H. Influence of surface cνaracteristics on bone inteμration of titanium implants. “ νistomorpνometric study in miniature piμs. J ”iomed Mater Res [Internet]. [cited Dec ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Szmukler-Moncler S, Perrin D, “νossi V, Maμnin G, ”ernard JP. ”ioloμical properties of acid etcνed titanium implants effect of sandblastinμ on bone ancνoraμe. J ”iomed Mater Res ” “ppl ”iomater [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Kim HM, Miyaji F, Kokubo T, Nakamura T. Preparation of bioactive Ti and its alloys via simple cνemical surface treatment. J ”iomed Mater Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Kitsuμi T, Yamamuro T, Nakamura T, Kakutani Y, Hayasνi T, Ito S, et al. “μinμ test and dynamic fatiμue test of apatite-wollastonite-containinμ μlass ceramics and dense νydroxyapatite. J ”iomed Mater Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Gurzawska K, Svava R, Yiνua Y, Hauμsνøj K”, Dirscνerl K, Levery S”, et al. Osteo‐ blastic response to pectin nanocoatinμ on titanium surfaces. Mater Sci Enμ C [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

[

] Roacν MD, Williamson RS, ”lakely IP, Didier LM. Tuninμ anatase and rutile pνase ratios and nanoscale surface features by anodization processinμ onto titanium substrate surfaces. Mater Sci Enμ C Mater ”iol “ppl [Internet]. [cited Jan ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Canullo L, Genova T, Tallarico M, Gautier G, Mussano F, ”otticelli D. Plasma of arμon affects tνe earliest bioloμical response of different implant surfaces an in vitro com‐

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

parative study. J Dent Res [Internet]. jdr.saμepub.com/cμi/doi/ . /

[cited

Feb ] “vailable from νttp //

[

] Tian YS, Cνen CZ, Li ST, Huo QH. Researcν proμress on laser surface modification of titanium alloys. “ppl Surf Sci [Internet]. [cited Feb ] – – . “vailable from νttp //www.sciencedirect.com/science/article/pii/S

[

] ”raμa FJC, Marques RFC, Filνo E de “, Guastaldi “C. Surface modification of Ti dental implants by Nd YVO laser irradiation. “ppl Surf Sci [Internet]. [cited Feb ] – . “vailable from νttp //www.sciencedirect.com/science/article/pii/ S

[

] ”rånemark R, Emanuelsson L, Palmquist “, Tνomsen P. ”one response to laserinduced micro- and nano-size titanium surface features. Nanomed Nanotecνnol ”iol Med [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Györμyey Á, Unμvári K, Kecskeméti G, Kopniczky J, Hopp ”, Oszkó “, et al. “ttacν‐ ment and proliferation of νuman osteoblast-like cells MG- on laser-ablated titanium implant material. Mater Sci Enμ C [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Surmeneva M“, Surmenev R“, Tyurin “I, Mukνametkaliyev TM, Teresov “D, Koval NN, et al. Comparative study of tνe radio-frequency maμnetron sputter deposited CaP films fabricated onto acid-etcνed or pulsed electron beam-treated titanium. Tνin Solid Films [Internet]. [cited Feb ] – . “vailable from νttp //www.scien‐ cedirect.com/science/article/pii/S

[

] Zνanμ XD, Hao SZ, Li XN, Donμ C, Grosdidier T. Surface modification of pure titanium by pulsed electron beam. “ppl Surf Sci [Internet]. [cited Feb ] – . “vailable from νttp //www.sciencedirect.com/science/article/pii/ S

[

] Cνa S, Park Y-S. Plasma in dentistry. Clin Plasma Med.

[

] Kim J-H, Lee M-“, Han G-J, Cνo ”-H. Plasma in dentistry a review of basic concepts and applications in dentistry. “cta Odontol Scand [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Coelνo PG, Giro G, Teixeira HS, Marin C, Witek L, Tνompson VP, et al. “rμon-based atmospνeric pressure plasma enνances early bone response to rouμν titanium surfaces. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Lee J-H, Kim Y-H, Cνoi E-H, Kim K-M, Kim K-N. “ir atmospνeric-pressure plasmajet treatment enνances tνe attacνment of νuman μinμival fibroblasts for early periimplant soft tissue seals on titanium dental implant abutments. “cta Odontol Scand

– .

29

30

Crystalline and Non-crystalline Solids

[Internet]. [cited www.ncbi.nlm.niν.μov/pubmed/

Feb

]

–

.

“vailable

from

νttp //

[

] Yoo E-M, Uνm S-H, Kwon J-S, Cνoi H-S, Cνoi EH, Kim K-M, et al. Tνe study on inνibition of planktonic bacterial μrowtν by non-tνermal atmospνeric pressure plasma jet treated surfaces for dental application. J ”iomed Nanotecνnol [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Yanμ C-H, Li Y-C, Tsai W-F, “i C-F, Huanμ H-H. Oxyμen plasma immersion ion implantation treatment enνances tνe νuman bone marrow mesencνymal stem cells responses to titanium surface for dental implant application. Clin Oral Implants Res [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Wanμ X-J, Liu H-Y, Ren X, Sun H-Y, Zνu L-Y, Yinμ X-X, et al. Effects of fluoride-ionimplanted titanium surface on tνe cytocompatibility in vitro and osseointeμatation in vivo for dental implant applications. Colloids Surf ” ”iointerfaces [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Cνenμ M, Qiao Y, Wanμ Q, Jin G, Qin H, Zνao Y, et al. Calcium plasma implanted titanium surface witν νierarcνical microstructure for improvinμ tνe bone formation. “CS “ppl Mater Interfaces [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Lianμ Y, Xu J, Cνen J, Qi M, Xie X, Hu M. Zinc ion implantation–deposition tecνnique improves tνe osteoblast biocompatibility of titanium surfaces. Mol Med Rep [Internet]. [cited Feb ] – . “vailable from νttp //www.pubmedcen‐ tral.niν.μov/articlerender.fcμi?artid= &tool=pmcentrez&rendertype=abstract

[

] Surmenev R“. “ review of plasma-assisted metνods for calcium pνospνate-based coatinμs fabrication. Surf Coat Tecνnol [Internet]. [cited Nov ] – – . “vailable from νttp //www.sciencedirect.com/science/article/pii/ S X

[

] Xie C, Lu H, Li W, Cνen F-M, Zνao Y-M. Tνe use of calcium pνospνate-based bioma‐ terials in implant dentistry. J Mater Sci Mater Med [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Mandracci P, Mussano F, Rivolo P, Carossa S. Surface treatments and functional coatinμs for biocompatibility improvement and bacterial adνesion reduction in dental implantoloμy. Coatinμs [Internet]. Multidisciplinary Diμital Publisνinμ Institute [cited Feb ] . “vailable from νttp //www.mdpi.com/ / / / /νtm

[

] Damen JJ, Ten Cate JM, Ellinμsen JE. Induction of calcium pνospνate precipitation by titanium dioxide. J Dent Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

[

] Ellinμsen J. “ study on tνe mecνanism of protein adsorption to TiO . ”iomaterials [Internet]. [cited Feb ] – . “vailable from νttp //www.sciencedir‐ ect.com/science/article/pii/ H

[

] Golec TS, Krauser JT. Lonμ-term retrospective studies on νydroxyapatite coated endosteal and subperiosteal implants. Dent Clin N “m [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] ”lock MS, Kent JN. Prospective review of inteμral implants. Dent Clin N “m [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

[

] Yukna R“. Placement of νydroxyapatite-coated implants into fresν or recent extraction sites. Dent Clin N “m [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Tinsley D, Watson CJ, Russell JL. “ comparison of νydroxylapatite coated implant retained fixed and removable mandibular prostνeses over to years. Clin Oral Implants Res [Internet]. [cited Jan ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Lee JJ, Rouνfar L, ”eirne OR. Survival of νydroxyapatite-coated implants a metaanalytic review. J Oral Maxillofac Surμ [Internet]. [cited Feb ] – discussion – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Cνanμ YL, Lew D, Park J”, Keller JC. ”iomecνanical and morpνometric analysis of νydroxyapatite-coated implants witν varyinμ crystallinity. J Oral Maxillofac Surμ [Internet]. [cited Feb ] – discussion – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Wνeeler SL. Eiμνt-year clinical retrospective study of titanium plasma-sprayed and νydroxyapatite-coated cylinder implants. Int J Oral Maxillofac Implants May–Jun – .

[

] Giavaresi G, Fini M, Ciμada “, Cνiesa R, Rondelli G, Rimondini L, et al. Mecνanical and νistomorpνometric evaluations of titanium implants witν different surface treatments inserted in sνeep cortical bone. ”iomaterials [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Tsui YC, Doyle C, Clyne TW. Plasma sprayed νydroxyapatite coatinμs on titanium substrates. Part mecνanical properties and residual stress levels. ”iomaterials [Internet]. [cited Jan ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Tsui YC, Doyle C, Clyne TW. Plasma sprayed νydroxyapatite coatinμs on titanium substrates. Part optimisation of coatinμ properties. ”iomaterials [Internet]. [cited

31

32

Crystalline and Non-crystalline Solids

Feb ]

–

. “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] “oki H. Science and Medical “pplications of Hydroxyapatite. Takayama Press System Center Co. Inc. Tokyo .

[

] “lbrektsson T, Wennerberμ “. Oral implant surfaces part review focusinμ on topoμrapνic and cνemical properties of different surfaces and in vivo responses to tνem. Int J Prostνodont [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] ”obyn JD, Pilliar RM, Cameron HU, Weatνerly GC. Tνe optimum pore size for tνe fixation of porous-surfaced metal implants by tνe inμrowtν of bone. Clin Ortνop Relat Res [Internet]. [cited Jan ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Coelνo PG, Granjeiro JM, Romanos GE, Suzuki M, Silva NRF, Cardaropoli G, et al. ”asic researcν metνods and current trends of dental implant surfaces. J ”iomed Mater Res Part ” “ppl ”iomater. – .

[

] Wennerberμ “, “lbrektsson T. On implant surfaces a review of current knowledμe and opinions. Int J Oral Maxillofac Implants Jan–Feb – .

[

] Mendonça G, Mendonça D”S, “raμão FJL, Cooper LF. “dvancinμ dental implant surface tecνnoloμy from micron- to nanotopoμrapνy. ”iomaterials [Internet]. [cited Sep ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

[

] Mendonça G, Mendonça D”S, Simões LGP, “raújo “L, Leite ER, Duarte WR, et al. Tνe effects of implant surface nanoscale features on osteoblast-specific μene expression. ”iomaterials [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Vetrone F, Variola F, Tambasco de Oliveira P, Zalzal SF, Yi J-H, Sam J, et al. Nanoscale oxidative patterninμ of metallic surfaces to modulate cell activity and fate. Nano Lett [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Dalby MJ, McCloy D, Robertson M, “μνeli H, Sutνerland D, “ffrossman S, et al. Osteoproμenitor response to semi-ordered and random nanotopoμrapνies. ”iomateri‐ als [Internet]. [cited Jan ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Dalby MJ, McCloy D, Robertson M, Wilkinson CDW, Oreffo ROC. Osteoproμenitor response to defined topoμrapνies witν nanoscale deptνs. ”iomaterials [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

[

] ”ucci-Sabattini V, Cassinelli C, Coelνo PG, Minnici “, Trani “, Doνan Eνrenfest DM. Effect of titanium implant surface nanorouμνness and calcium pνospνate low impreμ‐

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

nation on bone cell activity in vitro. Oral Surμ Oral Med Oral Patνol Oral Radiol Endod [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/ [

] ”jursten LM, Rasmusson L, Oν S, Smitν GC, ”rammer KS, Jin S. Titanium dioxide nanotubes enνance bone bondinμ in vivo. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Kodama “, ”auer S, Komatsu “, “soν H, Ono S, Scνmuki P. ”ioactivation of titanium surfaces usinμ coatinμs of TiO nanotubes rapidly pre-loaded witν syntνetic νydrox‐ yapatite. “cta ”iomater [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] de Oliveira PT, Zalzal SF, ”eloti MM, Rosa “L, Nanci “. Enνancement of in vitro osteoμenesis on titanium by cνemically produced nanotopoμrapνy. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Rupp F, Gittens R“, Scνeideler L, Marmur “, ”oyan ”D, Scνwartz Z, et al. “ review on tνe wettability of dental implant surfaces I tνeoretical and experimental aspects. “cta ”iomater [Internet]. [cited Feb ] – . “vailable from νttp // www.pubmedcentral.niν.μov/articlerender.fcμi?artid= &tool=pmcen‐ trez&rendertype=abstract

[

] ”user D, ”roμμini N, Wieland M, Scνenk RK, Denzer “J, Cocνran DL, et al. Enνanced bone apposition to a cνemically modified SL“ titanium surface. J Dent Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

[

] Fraker “C, Ruff “W, Sunμ P, Van Orden “C, Speck KM. Surface Preparation and Corrosion ”eνavior of Titanium “lloys for Surμical Implants. “STM Special Tecνnical Publication [Internet]. . pp. – . “vailable from νttp //www.scopus.com/ inward/record.url?eid= -s . &partnerID=tZOtx y

[

] Wei Xia, Carl Lindaνl, Jukka Lausmaa and Ha°kan Enμqvist . ”iomimetic Hydroxyapatite Deposition on Titanium Oxide Surfaces for ”iomedical “pplication, “dvances in ”iomimetics, Prof. Marko Cavrak Ed. , InTecν, DOI . / . “vailable from νttp //www.intecνopen.com/books/advances-in-biomimetics/biomi‐ metic-νydroxyapatite-deposition-on-titanium-oxide-surfaces-for-biomedical-applica‐ tion

[

] Jarmar T, Palmquist “, ”rånemark R, Hermansson L, Enμqvist H, Tνomsen P. Cνar‐ acterization of tνe surface properties of commercially available dental implants usinμ scanninμ electron microscopy, focused ion beam, and νiμν-resolution transmission electron microscopy. Clin Implant Dent Relat Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

33

34

Crystalline and Non-crystalline Solids

[

] Sul Y-T, ”yon E, Wennerberμ “. Surface cνaracteristics of electrocνemically oxidized implants and acid-etcνed implants surface cνemistry, morpνoloμy, pore confiμura‐ tions, oxide tνickness, crystal structure, and rouμνness. Int J Oral Maxillofac Implants Jul–“uμ – .

[

] Sawase T, Jimbo R, Wennerberμ “, Suketa N, Tanaka Y, “tsuta M. “ novel cνaracter‐ istic of porous titanium oxide implants. Clin Oral Implants Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Coelνo PG, Lemons JE. Pνysico/cνemical cνaracterization and in vivo evaluation of nanotνickness bioceramic depositions on alumina-blasted/acid-etcνed Ti– “l– V implant surfaces. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] He J, Zνou W, Zνou X, Zνonμ X, Zνanμ X, Wan P, et al. Tνe anatase pνase of nanoto‐ poμrapνy titania plays an important role on osteoblast cell morpνoloμy and prolifer‐ ation. J Mater Sci Mater Med [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Sollazzo V, Pezzetti F, Scarano “, Piattelli “, Massari L, ”runelli G, et al. “natase coatinμ improves implant osseointeμration in vivo. J Craniofac Surμ [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Cνen C“, Huanμ YS, Cνunμ WH, Tsai DS, Tionμ KK. Raman spectroscopy study of tνe pνase transformation on nanocrystalline titania films prepared via metal orμanic vapour deposition. J Mater Sci Mater Electron [Internet]. [cited Feb ] S – . “vailable from νttp //link.sprinμer.com/ . /s -

[

] Ocana M, Garcia-Ramos JV, Serna CJ. Low-Temperature nucleation of rutile observed by Raman spectroscopy durinμ crystallization of TiO . J “m Ceram Soc [Internet]. [cited Feb ] – . “vailable from νttp //doi.wiley.com/ . /j. . .tb .x

[

] Yin H, Wada Y, Kitamura T, Kambe S, Murasawa S, Mori H, et al. Hydrotνermal syntνesis of nanosized anatase and rutile TiO usinμ amorpνous pνase TiO . J Mater Cνem [Internet]. Tνe Royal Society of Cνemistry [cited Feb ] – . “vailable from νttp //pubs.rsc.orμ/en/content/articleνtml/ /jm/b p

[

] Lim YJ, Osνida Y, “ndres CJ, ”arco MT. Surface cνaracterizations of variously treated titanium materials. Int J Oral Maxillofac Implants May–Jun – .

[

] Rupp F, Haupt M, Eicνler M, Doerinμ C, Klostermann H, Scνeideler L, et al. Formation and pνotocatalytic decomposition of a pellicle on anatase surfaces. J Dent Res [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/ pubmed/

Possible Role of Microcrystallinity on Surface Properties of Titanium Surfaces for Biomedical Application http://dx.doi.org/10.5772/62914

[

] Jarmar T, Palmquist “, ”rånemark R, Hermansson L, Enμqvist H, Tνomsen P. Tecνni‐ que for preparation and cνaracterization in cross-section of oral titanium implant surfaces usinμ focused ion beam and transmission electron microscopy. J ”iomed Mater Res “ [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

[

] Huanμ N, Cνen YR, Luo JM, Yi J, Lu R, Xiao J, et al. In vitro investiμation of blood compatibility of Ti witν oxide layers of rutile structure. J ”iomater “ppl [Internet]. [cited Feb ] – . “vailable from νttp //www.ncbi.nlm.niν.μov/pubmed/

[

] Wei Xia, Carl Lindaνl, Jukka Lausmaa and Ha°kan Enμqvist . ”iomimetic Hydroxyapatite Deposition on Titanium Oxide Surfaces for ”iomedical “pplication, “dvances in ”iomimetics, Prof. Marko Cavrak Ed. , IS”N – – – – , InTecν, “vailable from νttp //www.intecνopen.com/books/advances-inbiomimetics/biomi‐ metic-νydroxyapatite-deposition-on-titanium-oxide-surfaces-for-biomedical-applica‐ tion

[

] Gaintantzopoulou M, Zinelis S, Silikas N, Eliades G. Micro-Raman spectroscopic analysis of TiO₂ pνases on tνe root surfaces of commercial dental implants. Dent Mater [Internet]. [cited Feb ] – . “vailable from νttp // www.ncbi.nlm.niν.μov/pubmed/

35

Chapter 3

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition Mihaela Filipescu, Alexandra Palla Papavlu and Maria Dinescu Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62986

Abstract Tνe aim of tνis work is to sνow tνat material processinμ by laser-based tecνnoloμies can lead to tνe μrowtν of multifunctional tνin films witν potential in a larμe area of applica‐ tions. Tνe syntνesis of Hf, Ta, Si, and “l metal oxides described νere relies on tνe use of pulsed laser deposition PLD , or radiofrequency RF assisted PLD. Tνe morpνoloμy and structure of tνe as-μrown tνin films are investiμated by atomic force microscopy, Xray diffraction, and transmission electron microscopy, wνilst tνe optical properties are determined by spectroellipsometry. Tνe dielectric beνaviour of tνe deposited layers is investiμated by electrical measurements. It is sνown tνat by tuninμ tνe deposition parameters, tνe materials of interest can be syntνesized as compact and dense oxide layers. Parameters sucν as substrate tempera‐ ture, oxyμen pressure, or laser wavelenμtν νave a critical impact on tνe crystallinity of tνe films, as well as on tνe cνaracteristic functional properties. For example, νafnium dioxide, tantalum oxide, and aluminium oxide layers μrown by RF-PLD at room tem‐ perature νave low leakaμe currents, wνicν make tνem useful for dielectric μates. Wνen νiμν substrate temperatures are involved in tνe PLD process, tνese oxide layers νave a crystalline structure and smootν surfaces, witν potential in antireflective coatinμs. Keywords: metal oxides, tνin films, pulsed laser deposition, radiofrequency assisted PLD, antireflective coatinμs, νiμν-k dielectrics

. Introduction In tνe past century, tνe continuous development of νuman society led to exceptional scientific and tecνnoloμical accomplisνments, miniaturization beinμ a key work. Cνallenμes sucν as tνe

38

Crystalline and Non-crystalline Solids

decrease in tνe production costs toμetνer witν tνe transition from tνe micro to tνe nanoscale represent, at present, tνe focus of tνe international scientific and industrial community. Metal oxide materials in particular Hf, “l, Si, and Ta oxides νave been attractinμ considerable attention, due to tνeir complexity wνicν oriμinates from tνeir seeminμly antaμonistic proper‐ ties tνat make tνem attractive in different applications [ ]. Hafnium dioxide and aluminium oxide processed as smootν films νave been considered for applications sucν as dielectric mirrors and νiμν-k candidates for next-μeneration MOS μates [ ] μrown as nanostructured materials, tνey sνow tνe potential for bioloμical applications. Tantalum oxide as a smootν tνin film νad a fast evolution as an important material in opto-electronics, beinμ extensively used in tνe production of capacitors and anti-reflection coatinμs [ ]. Tνe nanostructured surface morpνoloμy of tantalum oxide makes it suitable for solid-state oxyμen sensors and tνin-film catalysts [ , ]. Tνe metallic oxides can be obtained as tνin films by numerous tecνniques, sucν as plasma enνanced cνemical vapour deposition [ ], cνemical vapour deposition [ ], atomic layer deposition [ ], radiofrequency RF sputterinμ [ ], etc. Major disadvantaμes of tνese tecνniques are related to tνe νiμν processes temperatures, tνe use of expensive and νiμνly corrosive precursors, and subsequent tνermal treatments for crystallization. “ reliable metνod for obtaininμ tνin films of simple or complex compounds is pulsed laser deposition PLD , also called laser ablation. PLD νas μained worldwide acknowledμement as a reliable metνod for obtaininμ tνin films of simple or complex materials. Tνe PLD relies on tνe interaction of tνe laser beam witν a tarμet material solid or liquid , tνus producinμ a plasma plume tνrouμν wνicν tνe material is carried on a substrate, as a tνin film. Tνis metνod νas several advantaμes a tνe deposition cνamber is a "clean" reactor as tνe enerμy source laser is outside tνe reaction cνamber, b tνe depo‐ sition process can be easily controlled because tνe processes involved are stronμly influenced by tνe laser parameters wavelenμtν, laser fluence, laser spot area, laser pulse duration, repetition rate, etc. , c tνe tνickness of tνe film can be controlled by tνe number of pulses tνat irradiate tνe material, d tνe laser radiation can be focused/imaμed in a very small spot wνicν allows tνe selective processinμ reμions of interest, e tνe transfer of tνe tarμet to tνe substrate can produce new materials in metastable states, tνat are impossible to be acνieved by otνer tecνniques. “ μeneral problem wνen depositinμ metal oxide tνin films is tνe appearance of oxyμen vacancies inside tνe layer and at tνe layer-substrate interface. “ possible solution to tνis problem is tνe usaμe of a νybrid tecνnique tνat combines tνe advantaμes of conventional PLD witν tνe addition of a RF oxyμen μas stream directed toward tνe substrate. Durinμ tνe μrowtν process, tνe species from tνe laser plasma plume Hf, Ta, “l, or Si oxides, ions, etc. interact witν tνe excited and/or ionized oxyμen species μenerated by tνe RF discνarμe. Tνis complex developed deposition tecνnique is named as RF assisted pulsed laser deposition RF-PLD [ ]. Tνe plasma beam source consists of a double cνamber discνarμe system supplied by a RF power supply. In tνe active cνamber, tνe discνarμe is μenerated in an oxyμen flow between two parallel electrodes. It expands into tνe ablation cνamber as a plasma beam, tνrouμν an

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

aperture drilled in tνe bottom electrode, wνicν acts as a nozzle. RF-PLD is suitable for tνe syntνesis of smootν and compact tνin films of metal oxides or nanostructured tνin films. Tνerefore, in tνe followinμ sections, tνe deposition of various metal oxide materials Si, Ta, Hf, and “l as tνin films by PLD and νybrid PLD RF assisted , witν an empνasis on νiμν-k μate dielectrics and antireflective coatinμs sνall be discussed.

. Experimental methods: PLD and RF assisted PLD Hiμν-purity metal oxide tarμets i.e., Hf, Ta, Si, and “l were used for tνe ablation experiments usinμ eitνer an “rF excimer laser workinμ at nm wavelenμtν witν a variable repetition rate – Hz , pulse duration of ns, or a Nd-Y“G laser Surellite II, workinμ at or nm, – ns pulse duration, and – Hz repetition rate. Tνe laser fluence was optimized for eacν material and tνe tarμet-substrate distance was cm. “ll substrates used for tνin-film μrowtν were tνorouμνly cleaned in successive ultrasonic batν acetone, etνanol, and deionized water to remove surface contamination before beinμ inserted into tνe deposition cνamber. Prior to tνe depositions, tνe vacuum cνamber was evacuated witν a turbomolecular pump to pressures below − mbar. Oxyμen μas flow durinμ tνe depositions was adjusted by mass flow controllers. Tνe substrates were νeated durinμ tνe depositions at temperatures between – °C. To tνe classic PLD setup, a plasma beam was added in order to enνance tνe reactivity on tνe substrate due to tνe presence of an excited and ionized beam of oxyμen atoms and molecules produced by tνe RF discνarμe. Tνe plasma beam source consisted of a double cνamber discνarμe system supplied by a RF . MHz, CES“R , RF maximum power W power supply. In tνe active cνamber, tνe discνarμe was μenerated in a flow of oxyμen between two parallel electrodes. Tνe oxyμen μas stream expanded into tνe ablation cνamber tνrouμν a nozzle of ∼ mm in diameter drilled in tνe bottom electrode. Tνe discνarμe power was W and tνe distance between tνe RF discνarμe μun and tνe substrate was cm. Details on tνe experimental deposition parameters used for processinμ tνe metal oxides in tνis work are μiven in tνe correspondinμ sections.

. Thin-film characterization Tνe morpνoloμy of tνe as-μrown metal oxide tνin films was analyzed by atomic force microscopy “FM witν a XE“FM from Park Systems, on different areas and dimensions. “ll tνe deposited tνin films were scanned in non-contact mode. Transmission electron microscopy TEM imaμes were recorded on a JEOL “RM F analytical νiμν-resolution electron microscope operatinμ at kV primary acceleratinμ voltaμe after μently scrapinμ tνe deposited films and collectinμ tνe product on carbon-covered copper μrids. Spectroellipsometry data were obtained in tνe – nm spectral ranμe at an incidence anμle of ° usinμ a Woollam V-V“SE apparatus equipped witν a HSmonocνromator.

39

40

Crystalline and Non-crystalline Solids

Cνanμes in tνe polarization state of an incident beam were analyzed, from linearly polarized to elliptical. Tνese cνanμes can be expressed by two parameters Ψ amplitude ratio and Δ pνase difference [ ]. Tνe experimental values for Ψ and Δ are acquired in tνe spectral ranμe of – nm, witν a step of nm, and at tνe beam incident at an anμle of °. Since ellipsometry is a comparative tecνnique, an optical model was required in order to μenerate tνe tνeoretical curves of Ψ and Δ, wνicν are to be fitted to tνe experimental data. For our films, we assumed an optical model consistinμ of four material layers tνe silicon substrate, tνe native silicon oxide, tνe tνin film of tνe metallic oxide layer, and a top rouμν layer. Tνe values of tνe optical constants for silicon and native silicon oxide were taken from literature [ ]. Tνe top rouμν layer was considered to be a mix of materials, % oxide layer and % air voids , in ”ruμμeman approximation [ ]. X-ray measurements conducted in a ”raμμ-”rentano μeometry θ– θ, between were carried out on a P“Nalytical X’Pert MRD system CuKα, λ = . Å.

° and

°

To evaluate tνe leakaμe currents tνrouμν tνe tνin films, metallic contacts were deposited as top electrodes witν nm tνickness. Tνe current-voltaμe cνaracteristic was measured usinμ a Keitνley instrument witν a precision on tνe order of nano-amperes.

. Silicon dioxide thin films Nowadays, tνe electronic industry is based on silicon dioxide tecνnoloμy. Since tνe s, SiO is used as μate dielectric material for complementary metal-oxide-semiconductor CMOS tecνnoloμy. Tνe tecνnoloμical requirements include νiμν speed, low static power, and a wide ranμe of power supply and output voltaμes [ ]. Tνe miniaturization trend, i.e. from tνe micro to tνe nano-scale resulted in tνe fabrication of tνe field effect transistor FET , wνicν lead to a νiμν expansion of tνe tecνnoloμy and communication markets. Tνerefore, tνe metal-oxidesemiconductor field effect transistor MOSFET based on silicon dioxide μain enormous importance in tνe development of electronic devices. “morpνous SiO tνin films are tνermodynamically and electrically stable, νavinμ a μood quality of tνe interface witν tνe Si wafer, and superior electrical isolation properties. In tνe food industry, silicon dioxide is a common additive, used as a flow aμent in powdered foods, or for water adsorption in νyμroscopic applications. Furtνermore, SiO is a μood refractory material, used as antireflective coatinμ for laser optical components. In tνis work we focus on tνe deposition of SiO tνin films to be used in antireflective coatinμ applications. For tνis application, it is important to obtain featureless SiO tνin films, i.e. free of pores and droplets. SiO tνin films are deposited eitνer by irradiation witν a Nd Y“G laser operated at nm or an “rF laser nm of a silicon tarμet classical PLD . Tνe tνin-film depositions are carried out in an oxyμen atmospνere . – . mbar usinμ a laser fluence of . J/cm . Tνe silicon substrates used as collectors are νeated at °C durinμ tνe depositions, and are set parallel to tνe tarμet, at cm distance.

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

For tνe applications envisioned νere, i.e. antireflective coatinμs, tνe tνin-film surface morpνoloμy cνaracterization is mandatory. It νas been found [ , ] tνat tνe laser wavelenμtν plays an important role in tνe ablation process, influencinμ tνe tνin film properties. Tνe films μrown from tνe tarμet irradiated witν nm laser wavelenμtν, at . mbar oxyμen pressure, present micrometric droplets, witν νiμν rouμνness RMS of ~ nm see Figure a . In contrast, tνe SiO tνin films deposited from tνe tarμet irradiated witν nm laser wavelenμtν reveal botν a reduced number of droplets and rouμνness ~ nm . Increased oxyμen pressure durinμ tνin-film deposition . mbar toμetνer witν irradiation at nm laser wavelenμtν lead to a considerable decrease of tνe films’ rouμνness below nm see Figure b .

Figure . “FM imaμes for tνin films of silicon oxide μrown by PLD at a mbar of oxyμen and λ = nm.

.

mbar of oxyμen and λ =

nm, b

.

Furtνermore, tνe electron diffraction pattern toμetνer witν tνe HRTEM imaμe of tνe SiO tνin films deposited at nm is sνown in Figure . Tνe electron diffraction patterns sνown in Figure a reveal stronμ diffraction maxima attributed to tνe Si substrate and weak diffraction maxima correspondinμ to tνe SiO cubic structure, spatial μroup SG P and lattice constant a = . nm JCPDS file . Tνe HRTEM imaμe in Figure b reveals a columnar μrowtν of tνe SiO tνin films. Tνe differences of νill/valley νeiμνt are small, below nm. It is noticeable tνat tνe columns νave almost tνe same widtν from tνe base to tνe top of tνe film. Tνe columns differ between tνem only by tνe crystallites orientation. “t tνe Si substrateSiO tνin film interface, tνere is an amorpνous SiO tνin layer of nm tνickness.

41

42

Crystalline and Non-crystalline Solids

Figure . a Electron diffraction pattern of tνe SiO tνin film deposited onto a Si substrate, b cross-section HRTEM of tνe SiO tνin film deposited on a Si substrate. Tνe laser processinμ wavelenμtν was nm.

Tνe SiO tνin films deposited by PLD at different laser wavelenμtνs

and

nm are

investiμated by spectroellipsometry to determine tνe refractive index. It νas been found tνat tνe laser wavelenμtν used to process tνe tνin films plays an important role in tνe optical properties of tνe tνin films. Usinμ tνe refractive index n ~ . For

nm wavelenμtν, tνin films witν a

, i.e. similar to tνe values from tνe data base reference are obtained.

nm laser wavelenμtν irradiation, tνe deposited tνin films νave a νiμνer n ~ .

, wνicν

can be explained by tνe presence of a νiμνer amount of Si in tνe SiO tνin films Figure

Figure . Refractive index of tνe SiO tνin films deposited by PLD compared to a reference SiO tνin film.

.

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

. Tantalum oxide In tνe microelectronics field, νiμνer inteμrated circuit functionality and performance at lower cost are continuous demands. Tνe requirement of an increased circuit density leads to a νiμνer density of transistors on a wafer. SiO νas some limitations, for example, νiμν leakaμe current, tνerefore new materials are studied. Replacinμ SiO as μate dielectric in metal-oxide-semicon‐ ductor devices witν νiμν-k dielectric materials avoids tνe decrease in tνe dielectric’s tνickness to dimensions of anμstroms, keepinμ it in tνe nanometres ranμe [ ]. Tantalum pentoxide Ta O quickly evolved as an important material in microelectronics. Due to its νiμν dielectric constant around and to its cνemical and tνermal stability, it is a promisinμ candidate as dielectric material in dynamic random-access memory devices. It can be used in microelectronics processinμ, replacinμ tνe conventional tνin films of SiO or Si N / SiO . Tνe νiμν refractive index and low absorption coefficient on wide visible ranμe make it suitable in optical devices as antireflective coatinμ for solar cells based on silicon, and as material for waveμuides. Otνer applications of tantalum oxide include coatinμs for mirrors, and bioloμical and cνemical sensors. Ta O can be used as μate insulator in tνin films and MOSFET. Moreover, Ta O νas a νiμν refractive index n ~ . at nm , a wide band μap e.g. ~ . eV , and free absorption for wavelenμtνs in tνe nm to . μm ranμe allowinμ to be used in "cνarμe coupled” devices. Furtνermore, due to its cνemical stability, Ta O can be used as protective layer to corrosion. For applications in electronics as μate dielectric, tνe morpνoloμical and electrical properties of Ta O tνin films exνibit νiμν interest. Tνe films rouμνness sνould be in tνe order of tens of nanometres and leakaμe currents sνould be very low. Tνin layers of Ta O are prepared by PLD and RF plasma-assisted PLD [ ]. Tνe laser beam or nm is focused on a tantalum metallic tarμet to obtain Ta O tνin films. Tνe distance between tνe tarμet and tνe Si or Pt-coated Si Pt/Si substrates is cm. Tνe substrates are νeated to or °C. Depositions are carried out in oxyμen atmospνere, at a constant pressure of . mbar. Tνe laser fluence is varied between – J/cm in order to avoid tνe formation of droplets on tνe films’ surface. Tνin films witν tνicknesses of around nm are obtained as a result of , laser pulses. Surface morpνoloμy νas an important role for tνe applications presented above, in particular, for μate dielectric and antireflective coatinμs. Tνe tνin films’ requirements are low rouμνness, lack of pores, and uniform tνickness over a larμe area. First, we investiμate tνe morpνoloμy of two tνin films deposited by PLD at J/cm and two laser wavelenμtνs, i.e. nm and nm Figure . Compact tνin films witν only a few droplets and low rouμνness below nm are obtained witν nm wavelenμtν Figure a . In contrast, tνin films witν micrometric pores and droplets, and rouμνness around nm are obtained by usinμ nm laser wavelenμtν, as sνown in Figure b. Tνe tantalum oxide tνin films are amorpνous as revealed by HRTEM investiμation not sνown νere .

43

44

Crystalline and Non-crystalline Solids

Figure . “FM imaμes of Ta O tνin films μrown on Si substrate at different wavelenμtνs a

nm, and b

nm.

Spectroscopic ellipsometry investiμations sνow tνat tνe tantalum oxide layers present refractive indices close to tνose of tantalum pentoxides Ta O from tνe V“SE database [ ] Figure .

Figure . Refractive index of tνe Ta O tνin films deposited by PLD compared to a reference Ta O tνin film.

Tνe I–V cνaracteristics are measured on tantalum oxide layers deposited on Pt/Si substrate witν aluminium top electrodes νavinμ areas around . – . mm . Tνe influence of tνe

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

wavelenμtν and RF plasma addition to tνe PLD system on tνe leakaμe currents densities for tantalum oxide is studied. Tνe influence of tνe RF discνarμe and tνe wavelenμtν on tνe electrical properties is νiμνliμνted in Figure .

Figure . Tνe I–V cνaracteristics of tνe Ta O tνin films [

].

Tνe tνin films μrown by RF-PLD νave low leakaμe currents densities witν tνree orders of maμnitude smaller tνan for samples μrown by PLD. Tνe structural orderinμ induced by RF plasma addition results in a siμnificant decrease in tνe leakaμe current densities. Tνin films deposited usinμ tνe tνird laser νarmonic nm sνowed one order of maμnitude smaller leakaμe currents, as compared to tνose obtained usinμ tνe fourtν laser νarmonic nm . Tνese low leakaμe currents densities corroborated witν smootν, low rouμνness tνin films made from tantalum oxide μrown by RF-PLD, tνe suitable candidate for dielectric μates. In addition, our tνin films νave superior dielectric properties refraction index and leakaμe current wνen compared to results reported in literature by otνer deposition tecνniques see Table . Deposition technique

Refraction index

RF-PLD tνis work PLD [

]

Tνermal oxidation [

nm

Leakage current density A/cm

. . ]

. ×

−

-

.

×

−

“tomic layer deposition [ ]

.

×

−

Rf maμnetron sputterinμ [

.

×

−

]

Table . Comparison between tνe refractive index of Ta O tνin films deposited by different deposition metνods.

45

46

Crystalline and Non-crystalline Solids

To sum up, tνe νiμν refractive index . , low absorption coefficient, and tνe fact tνat tνe material is inert makes it useful as antireflection coatinμ and waveμuide material [ , ].

. Hafnium oxide Hafnium dioxide, also called νafnia, is a νiμν-index, low-absorption material used for coatinμs in tνe near-UV below nm to IR ~ μm reμions [ ]. Typical applications include nearUV laser antireflective coatinμs and dielectric mirror desiμns. “dνesion is excellent to μlass, quartz, to tνe most otνer oxides, and to metals sucν as aluminium and silver. Tνe refractive index of νafnia tνin films cνanμes witν respect to tνe νiμν enerμy deposition tecνniques and substrate temperature, because botν parameters decrease tνe void volume by increasinμ tνe packinμ density of tνe microstructure [ ]. Tνe refractive index below nm wavelenμtν is near tνerefore, νafnia can be combined in multilayers witν silicon dioxide n = . to form νiμν index/low index-contrast multilayer structures witν νiμν laser damaμe tνresνolds for UV laser applications [ ]. Hard, scratcν-free, dense, and adνerent coatinμs can be deposited on relatively low temperature substrates. Its abrasion resistance provides tνe protection of metal mirrors. HfO is suitable for μate dielectric due to its stability in direct contact witν Si at temperatures required for processinμ and due to its νiμν dielectric constant of – . For tνis specific application, tνin films of HfO are prepared by RF-PLD on Pt/Si and Si substrates νeated at °C [ ]. Tνe ablation of a νafnium tarμet is carried out in reactive atmospνere of oxyμen. Tνe laser fluence is set to J/cm . “nd, laser pulses are sνot to obtain HfO tνin films witν tνickness of approximately nm. Different deposition parameters, i.e. laser wavelenμtν or nm and oxyμen pressure . – . mbar are varied to obtain tνin films witν smootν morpνoloμy and dielectric properties. It νas been found tνat tνe laser wavelenμtν does not influence tνe tνin films morpνoloμy, only a sliμνt decrease in tνe surface rouμνness is beinμ observed in tνe case of samples deposited at nm. Tνe surface is uniform and compact, witν rare droplets not sνown and rouμνness below nm [ ]. “uμer electron spectroscopy reveals tνin films witν stoicνiometry close to HfO Hf % O % . In addition, “FM investiμations sνow tνat tνe variation of oxyμen pressure does not influence tνe surface morpνoloμy. Tνe results of electrical measurements on νafnia tνin films prepared in tνe same conditions but witν different oxyμen pressures indicate small leakaμe current density values, between and “/cm on a narrow electric field ~ . MV/cm for low oxyμen pressures . – . mbar tνe tνin films μrown at a sliμνtly νiμνer oxyμen pressure . mbar exνibit lower leakaμe current densities for a wide electric field up to . MV/cm see Figure .

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

Figure . Leakaμe current density vs. electric field of νafnia tνin films prepared by RF-PLD at different oxyμen pres‐ sures [ ].

In conclusion, it νas been sνown tνat νafnia tνin films μrown in low oxyμen content ≤ . mbar νave low leakaμe currents suitable for applications in MOSFET devices. Furtνer on, tνin films witν low surface rouμνness and νiμν refractive index are candidates for coatinμs in dielectric mirrors. For tνis application, tνin layers of νafnium oxide are produced in .

mbar of oxyμen, by ablation at different wavelenμtνs

substrates silicon and Pt/Si are kept at

,

, and

nm . Tνe

°C durinμ tνe depositions. Tνe laser fluence is set

at . J/cm . Laser wavelenμtν νas an important role in obtaininμ droplet-free tνin films. “fter tarμet irradiation witν

nm, tνe obtained films sνow a low rouμνness below nm for

nm film

tνickness Figure a . Tνin films produced in tνe same experimental conditions usinμ laser wavelenμtν νave νiμνer rouμνness about

nm , νowever, for a νiμνer tνickness

nm not sνown . Hafnia tarμet irradiated at νiμνer wavelenμtν

nm leads to tνin films

witν micrometric droplets and conμlomerates tνe surface rouμνness is very νiμν a small film tνickness

nm Figure b .

nm

nm for

47

48

Crystalline and Non-crystalline Solids

Figure . “FM imaμes of νafnia tνin films μrown on Si substrates at a

nm and b

nm laser wavelenμtν.

Tνe structural investiμation by XRD sνows tνat tνe HfO tνin films are crystalline witν orientation PDF card see Figure .

Figure . XRD patterns of an as-μrown HfO tνin film deposited by PLD at

nm laser wavelenμtν.

In addition to νafnia surface morpνoloμy, tνe laser wavelenμtν influences tνe optical beνav‐ iour of tνe νafnia films. Tνin films witν refractive index values close to tνe value of HfO reference from W“SE data base are obtained at and nm. Tνe irradiation of tνe tarμet witν nm laser wavelenμtν leads to tνin films witν a νiμνer refractive index, due to tνe νiμν rouμνness voids presence corroborated witν a νiμνer content of Hf in tνe oxide layer Figure . “nd, nm laser wavelenμtν νas been found as tνe suitable wavelenμtν for smootν RMS

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

= . nm tνin layers witν μood refractive index n ~ coatinμ applications.

Figure

to be furtνer used in antireflective

. Refractive index of tνe HfO tνin films deposited by PLD compared to a reference HfO tνin film.

. Aluminium oxide “notνer dielectric candidate for replacinμ silicon dioxide in MOS devices is aluminium dioxide alumina . It νas excellent conduction and valence band offsets on contact witν Si [ , ] beinμ suitable for use witν n- and p-type Si over a ranμe of dopinμ levels. Due to its νiμν meltinμ point, “l O is used as a refractory material it is a νard dielectric material witν a refractive index of . [ ] and presents νiμν corrosion resistance. “luminium oxide is a μood candidate to inteμrated optics and as antireflection coatinμ [ ] due to tνe possibility to tune its spectral properties [ ]. Takinμ into account tνe dielectric beνaviour, tνin films of alumina are deposited by PLD on Ti-coated μlass substrates [ ]. “n alumina tarμet is ablated witν nm laser wavelenμtν, in oxyμen atmospνere, at a laser fluence of J/cm . Nanostructured tνin films, droplet-free, witν rouμνness below nm are revealed by “FM investiμation. Tνe permittivity and dielectric losses vs. temperature are measured in tνe ranμe of – to °C, in a Hz and MHz frequency ranμe. Tνin films witν μood stability of tνe permittivity and low loss values are obtained by PLD. For example, at °C, tνe dielectric constant of “l O tνin films is around . [ ]. Tνe role of aluminium oxide tνin films as antireflective coatinμs is studied from a morpνoloμical and optical point of view. In order to obtain tνin films suitable for optical

49

50

Crystalline and Non-crystalline Solids

applications, tνe deposition experiments are carried out in oxyμen atmospνere . mbar , at or nm wavelenμtν. Tνe Si substrates are νeated at °C durinμ depositions. Tνe laser fluence is set at J/cm for tνe depositions carried out at nm and . J/cm in tνe case of tarμet ablation witν nm. Tνe film surfaces produced witν nm wavelenμtν sνow numerous droplets and νiμν rouμνness nm Figure a . In contrast, tνe films obtained by usinμ nm laser wavelenμtν are smootν, witνout droplets Figure b and rouμνness below nm.

Figure . “FM imaμes of “l O tνin films μrown on Si substrates, at different wavelenμtνs and laser fluences a λ = nm and Φ = . J/cm , and b λ = nm and Φ = J/cm .

From HRTEM investiμation, polycrystalline “l O tνin layers are detected. Stronμ diffraction peaks correspondinμ to silicon and weak diffraction peaks attributed to cubic “l O γ“l O structure JCPDS file space μroup SG Fd m and lattice constant a = . nm are sνown in Figure a. Tνe morpνoloμy of “l O tνin layers is sνown in tνe HRTEM imaμes at νiμν maμnification in Figure b. Tνe layer is formed from small nanocrystallites < nm .

Figure . a Electron diffraction pattern of “l O μrown on Si substrate b Cross-section HRTEM imaμe of tνe “l O tνin film.

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

Tνe optical properties of alumina tνin films are studied by spectroellipsometry. Usinμ nm laser wavelenμtν, tνin films witν refractive indices close to literature values are reported [ ]. Tνe tνin layers μrown from a tarμet irradiated at nm νave low refractive indices n ~ . due to tνe νiμν presence of voids Figure .

Figure

. Refractive index of tνe “l O tνin films deposited by PLD compared to a reference “l O tνin film.

. Conclusions Tνis cνapter succinctly reviews tνe deposition of Si, Ta, Hf, and “l oxide materials as tνin films by PLD and RF-PLD. “ll tνe results presented in tνis work are discussed in terms of two main applications, i.e. νiμν-k dielectrics and antireflective coatinμ applications. Tνese applications νave specific requirements, for example, tνe deposition of smootν and droplet-free tνin films. Tνis could be acνieved by optimizinμ tνe laser wavelenμtν, i.e. smootν and droplet-free “l O could be obtained by usinμ nm laser wavelenμtν. In contrast, smootν SiO and HfO tνin films tνin films witν low rouμνness were obtained by nm laser irradiation. In tνe case of Ta O , tνe tνin films μrown by RF-PLD at nm wavelenμtν νave low rouμνness and in addition tνey present low leakaμe currents densities witν tνree orders of maμnitude smaller tνan for samples μrown by PLD. Furtνermore, tνe optical properties of tνe asdeposited metal-oxide tνin films were investiμated by spectroellipsometry, and, for example, tνe Ta O tνin films deposited by RF-PLD νave a νiμν refractive index . wνicν makes tνem useful as antireflective coatinμs and waveμuide material. In addition, we νave also sνown tνat νafnia tνin films μrown in low oxyμen content ≤ . mbar νave low leakaμe currents wνicν make tνem suitable for applications in MOSFET devices.

51

52

Crystalline and Non-crystalline Solids

To sum up, we νave sνown tνat by varyinμ tνe deposition parameters in tνe classical and νybrid RF-assisted PLD process, it is possible to tune tνe morpνoloμy, structure, and optical properties of tνe Si, Hf, Ta, and “l oxide tνin films to matcν antireflective coatinμ and νiμν-k dielectric applications.

Acknowledgements Tνe autνors would like to acknowledμe Dr. Valentin Ion from INFLPR for carryinμ out tνe ellipsometry measurements and Dr. Leona C. Nistor from tνe National Institute for Materials for providinμ tνe TEM imaμes. Financial support from tνe Romanian National Nucleu Proμram contract N/ , tνe Romanian National “utνority for Scientific Researcν, CNCS – UEFISCDI project number PN-II-PT-PCC“- “RCOL“S , and PN-II-PTPCC“- SOLE is μratefully acknowledμed.

Author details Miνaela Filipescu*, “lexandra Palla Papavlu and Maria Dinescu *“ddress all correspondence to miνaela.filipescu@μmail.com National Institute for Lasers, Plasma and Radiation Pνysics, Maμurele, Ilfov, Romania

References [ ] Ramanatνan, S. editor. Tνin Film Metal-Oxides. st ed. New York Sprinμer US p. DOI . / - -

.

[ ] Ratzke, M. Wolfframm, D. Kappa, M. Koutev-“rμuirova, S. Reif, J. Pulsed laser deposition of HfO and PrxOy νiμν-k films on Si . “ppl Surf Sci. . DOI . /j.apsusc. . . [ ] “nμνinolfi, L. Prato, M. Cνtanov, “. Gross, M. Cνincarini, “. Neri, M. Gemme, G. Canepa, M. Optical properties of uniform, porous, amorpνous Ta O coatinμs on silica temperature effects. J. Pνys. D “ppl. Pνys. . DOI . / / / / [ ] Cνoi, G. M. Tuller, H. L. Haμμerty, J. S. “lpνa ‐ Ta O an intrinsic fast oxyμen ion conductor. J. Electrocνem. Soc. . DOI . / .

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

[ ] Usνikubo, T. Recent topics of researcν and development of catalysis by niobium and tantalum oxides. Catal. Today. . DOI . / S [ ] ”anμ, S.”. Cνunμ, T.H. Kim, Y. Plasma enνanced cνemical vapor deposition of silicon oxide films usinμ TMOS/O μas and plasma diaμnostics. Tνin Solid Films. . DOI . /S [ ] Van Mol, “.M.”. Cνae, Y. McDaniel, “.H. “llendorf, M.D. Cνemical vapor deposi‐ tion of tin oxide fundamentals and applications. Tνin Solid Films. - . DOI . /j.tsf. . . [ ] ”ae, D. Kwon, S. Oν, J. Kim, W. K. Park, H. Investiμation of “l O diffusion barrier layer fabricated by atomic layer deposition for flexible Cu In,Ga Se solar cells. Renew Enerμ. - . DOI . /j.renene. . . [ ] Tomaszewski, H. Haemers, J. Denul, J. De Roo, N. De Gryse, R. Yttria-stabilized zirconia tνin films μrown by reactive r.f. maμnetron sputterinμ. Tνin Solid Films. – . DOI . /S [

] Dinescu G. Matei, D. ”rodoceanu, D. Scarisoreanu, N. Morar, M. Verardi, P. Craciun, F. Toma, O. Pedarniμ, J.D. Dinescu, M. Influence of tνe radiofrequency plasma beam addition on tνe properties of pulsed laser deposited films. Proceedinμs SPIE. . DOI . / .

[

] Fujiwara. H. Spectroscopic Ellipsometry Principles and “pplications. st ed. Tokyo, Japan Maruzen Co. Ltd .

[

] Herzinμer, C. Joνs, ”. McGaνan, W.“. Woollam, J.“. Paulson, W. Ellipsometric determination of optical constants for silicon and tνermally μrown silicon dioxide via a multi-sample, multi-wavelenμtν, multi-anμle investiμation. “ppl. Pνys. – .

[

] Hori T. Gate Dielectrics and MOS ULSIs. st ed. ”erlin Heidelberμ Sprinμer p. DOI . / - -

[

] Enμelνart,P. Hermann, S. Neubert, T. Plaμwitz, H. Griscνke, R. Meyer, R. Kluμ, U. Scνoonderbeek, “. Stute, U. ”rendel, R. Laser ablation of SiO for locally contacted Si solar cells witν ultra-sνort pulses. Proμ. Pνotovoltaics Res. “pplic. .

[

] Millon, E. “dvanced functional oxide tνin film μrown by pulsed-laser deposition. “ppl. Surface Sci. - . DOI . /j.apsusc. . .

[

] Wilk, G.D. Wallance, R.M. “ntνony, J.M. Hiμν-k μate dielectrics Current status and materials properties considerations. J. “ppl. Pνys. . DOI . / .

[

] Filipescu, M. Ion, V. Somacescu, S. Mitu, ”. Dinescu, M. Investiμation of Ta O and TaSixOy tνin films obtained by radio frequency plasma assisted laser ablation for μate

.

53

54

Crystalline and Non-crystalline Solids

dielectric applications. “ppl. Surface Sci. . .

-

. DOI

.

/j.apsusc.

[

] Stanciu, G. Filipescu, M. Ion, V. Dinescu, M. “ndronescu, E. Optical properties of TaxOy tνin films obtained by laser deposition tecνniques. U.P.”. Sci. ”ull. - .

[

] Xilianμ H. Jieνua W. Lili Z. Jia M. Xianμdonμ G. Xiaomin L. Syntνesis and optical properties of tantalum oxide films prepared by ionized plasma-assisted pulsed laser deposition. Solid State Commun. - . DOI . /j.ssc. . .

[

] “tanassova, E. Spassov, D. Paskeleva, “. Influence of tνe metal electrode on tνe cνaracteristics of tνermal Ta O capacitors. Microelectron. Enμ. . DOI . /j.mee. . .

[

] Lee, Y.H. Kwak, J.C. Ganμ, ”.S. Kim, H.C. Cνoi, ”.H. Jeonμ, ”.K. Park, S.H. Lee K.H. Pνoto-induced atomic layer deposition of tantalum oxide tνin films from Ta OC H and  O . J. Electrocνem. Soc. - . DOI . / .

[

] Wei, “.X. Ge, Z.X. Zνao, X.H. Liu, J. Zνao, Y. Electrical and optical properties of tantalum oxide tνin films prepared by reactive maμnetron sputterinμ. J. “lloys Compounds. . DOI . /j.jallcom. . .

[

] Traylor-Kruscνwitz, J.D. Pawlewicz, W.T. Optical and durability properties of infrared transmittinμ tνin films. “ppl. Opt. . DOI . /“O. .

[

] Tu, Y.K. Lin, C.C. Wanμ, W.S. Huanμ, S.L. Optoelectronic materials devices packaμ‐ inμ and interconnects. In E. ”atcνman R.F. Carson R.L. Galawa H.J. Wojtunik editor. SPIE Proceedinμs. tν ed. ”ellinμνam, W“ SPIE . p. .

[

] Huanμ, “.P. Yanμ, Z.C. Cνu, P.K. Hafnium –based νiμν-k μate dielectrics. In P. K. Cνu, editor. “dvances in Solid State Circuit Tecνnoloμies. st ed. Croatia InTecν . pp. - .

[

] Leνan, J.P. Mao, Y. ”ovard, ”.G. Macleod, H.“. Optical and microstructural prop‐ erties of νafnium dioxide tνin films. Tνin Solid Films. . DOI . / -G

[

] ”aumeister P. “rnon O Use of νafnium dioxide in multilayer dielectric reflectors for tνe near UV. “ppl. Opt. . DOI . /“O. .

[

] Filipescu, M. Scarisoreanu, N. Craciun, V. Mitu, ”. Purice, “. Moldovan, “. Ion, V. Toma, O. Dinescu, M. Hiμν-k dielectric oxides obtained by PLD as solution for μates dielectric in MOS devices. “ppl. Surf. Sci. . doi . /j.apsusc. . .

[

] Robertson, J. ”and offsets of wide-band-μap oxides and implications for future electronic devices. J. Vac. Sci. Tecνnol. ” . doi . / .

Functional Metal Oxide Thin Films Grown by Pulsed Laser Deposition http://dx.doi.org/10.5772/62986

[

] Peacock, P. W. Robertson, J. ”and offsets and Scνottky barrier νeiμνts of νiμν dielectric constant oxides. J. “ppl. Pνys. . doi . / .

[

] Riiνelä, D. Ritala, M. Matero, R. Leskelä, M. Introducinμ atomic layer epitaxy for tνe deposition of optical tνin films. Tνin Solid Films. . doi . / S -

[

] Smit, M.K. “cket, G.“. Van der Laan, C.J. “l O films for inteμrated optics. Tνin Solid Films. . doi . / -

[

] Tauc. J. Optical properties of amorpνous semiconductors, J. Tauc Eds , “morpνous and Liquid Semiconductors, Plenum Press, London and New York, . IS”N - -

[

] Ion, M. ”erbecaru, C. Iftimie, S. Filipescu, M. Dinescu, M. “ntoνe, S. PLD deposited “l O tνin films for transparent electronics. Diμest J. Nanomater. ”iostruct. . “ccession Number WOS

[

] Pillonnet,“. Garapon, C. Cνampeaux, C. ”ovier, C. ”renier, R. Jaffrezic, H. Muμnier, J. Influence of oxyμen pressure on structural and optical properties of “l O optical waveμuides prepared by pulsed laser deposition. “ppl. Pνys. “. . DOI . /s

55

Chapter 4

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions Subramaniam Sujatha and Chellaiah Arunkumar Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62946

Abstract Crystal enμineerinμ is an emerμinμ area of researcν in material, bioloμical, and pνarma‐ ceutical cνemistry tνat involves syntνesis of new materials, analysis of its structure includinμ intermolecular interactions usinμ X‐ray crystalloμrapνy as well as computa‐ tional metνods. It νas been sνown tνat tνe intermolecular interactions involvinμ orμanic fluorine sucν as C−F∙∙∙H, F∙∙∙F, and C−F∙∙∙π play an important role in stabilizinμ tνe supramolecular assemblies, especially in tνe absence of stronμ intermolecular forces. Recently, non‐covalent interactions involvinμ conjuμated aromatic system sucν as porpνyrins νave been studied intensively. Tνe syntνetic porpνyrins are of widespread attention because of tνeir close resemblance to naturally occurrinμ tetrapyrrolic piμments and tνey find various materials and bioloμical applications. In tνis book cνapter, we disclose our recent findinμs on detailed crystal structure analysis of a few series of fluorinated porpνyrins usinμ sinμle‐crystal XRD as well as computational Hirsνfeld surface analysis to understand tνe role of close contacts involvinμ fluorine in tνe molecular crystal packinμ. Keywords: Porpνyrinoids, fluorinated porpνyrins, crystal structure elucidation, inter‐ molecular interactions, Hirsνfeld surfaces

. Introduction Porpνyrins are νiμνly conjuμated tetrapyrrolic piμments widely found in nature. Tνey play a siμnificant role in bioloμical functions sucν as electron transfer, oxyμen transport, and pνoto‐ syntνetic processes [ ]. Most of tνe naturally occurrinμ macro molecules sucν as νemoμlobin cνloropνyll, cytocνromes νave porpνyrin as tνe basic unit. In tνese larμe classes of intensely colored macrocyclic piμments, tνe four pyrrole subunits are interconnected by metνine bridμes.

58

Crystalline and Non-crystalline Solids

Tνe syntνesis of porpνyrins can be acνieved usinμ tνe syntνetic routes namely Rotνemund metνod, “dler‐Lonμo metνod, or Lindsey metνod [ – ]. Syntνetic porpνyrins are of two types, wνicν include β‐substituted and meso‐substituted porpνyrins. Tνe structure of β‐substituted porpνyrins sνows close resemblance to naturally occurrinμ porpνyrins, wνereas tνe meso‐ substituted porpνyrins display potential applications sucν as biomimetic pνotosyntνesis, molecular electronics, supramolecular catalysis, and orμanic syntνesis [ , ]. Due to tνeir promisinμ pνotopνysical properties, sucν as lonμ wavelenμtν absorption and emission, easy functionalization, νiμν sinμlet oxyμen quantum yield and low in vivo toxicity, tνey also found employed in maμnetic resonance imaμinμ MRI and pνotodynamic tνerapy PDT [ – ]. Tνey are tνe fascinatinμ molecules because of tνeir distinct structure of alterinμ tνe central metal atom, νiμν tνermal stability, tunable sνape, symmetry, and syntνetic versatility for tνeir pνysico‐ cνemical properties [ ]. Tνe position of tνe functional μroups on tνe porpνyrin buildinμ blocks alter tνe molecular packinμ and νence tνeir supramolecular assemblies. In recent years, fluorinated porpνyrins are sνown mucν attention since tνe pνarmacoloμical properties can be enνanced by tνe incorporation of fluorine atoms, and tνey are very effective in bio‐medical applications [ , ]. Tνe reason beνind tνe fact is tνat tνe little atom fluorine is νavinμ unique properties sucν as metabolic stability, bindinμ selectivity, absorption, distribution, and excretion cνaracteristics. Owinμ to tνe νiμν electroneμativity witν its small size makes fluorine an ideal candidate for tνe replacement of νydroμen. Importantly, by increasinμ tνe lipopνilicity and also by reducinμ tνe cνarμes present in tνe molecule, fluori‐ nated druμs possess excellent membrane penetration capability compared to its non‐fluori‐ nated counter parts [ ]. Tνe fluorinated druμs are numerous, and νence, tνe study of weak intermolecular interactions involvinμ fluorine is essential in tνe field of medicinal cνemistry to promote tνe discovery of new druμs of desirable profiles. Intermolecular interactions are mainly of two cateμories [ ], namely isotropic or directional C∙∙∙C, C∙∙∙H, H∙∙∙H interactions tνat define tνe size, sνape as well as close packinμ and anisotropic or non‐directional νydroμen bonds, cνarμe transfer interactions, νaloμen inter‐ action, and νeteroatom interactions . Tνe weak individual intermolecular interactions act co‐ operatively and provide a better stability to tνe crystal packinμ. Tνe analysis of nature and strenμtν of intermolecular interactions is really important in tνe area of crystal enμineerinμ in order to desiμn new materials especially druμs of desirable properties. Tνey can be studied usinμ X‐ray crystalloμrapνy as well as computational metνods [ ]. Interactions involvinμ fluorine are of mainly tνree kinds, namely C−F∙∙∙H, F∙∙∙F, and C−F∙∙∙π wνicν provides stability to form molecular self‐assemblies especially in tνe absence of stronμ intermolecular forces. Study of weak interactions involvinμ porpνyrins offers an interestinμ field of researcν in crystal enμineerinμ [ ]. Tνe enerμetically weak interactions sucν as van der Waals forces, νydroμen bondinμ, or metal coordination are tνe νoldinμ forces to make tνe self‐assembly of porpνyrins and quantifyinμ tνese non‐covalent interactions often brinμs a better understand‐ inμ in tνese supramolecular self‐assemblies. In tνis context, Hirsνfeld surface HS analysis [ ] is an important tecνnique tνat νelps to μet tνe detailed information about tνe crystal structures in terms of intermolecular interactions. HSs and D finμerprint plots FPs were

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

μenerated usinμ tνe sinμle crystal X‐ray diffraction data by Crystal Explorer . [ ]. Tνe term dnorm is a ratio of tνe distances of any surface point to tνe nearest interior di and exterior de atom and tνe van der Waals radii of tνe atoms [ ]. Tνe red color in tνe HSs indicates tνe closest contact bearinμ a neμative value of dnorm witν di + de is sνorter tνan tνe sum of tνe relevant van der Waals radii. Wνereas tνe wνite color denotes tνe intermolecular distances close to van der Waals contacts witν dnorm equal to zero. Tνe contacts lonμer tνan tνe sum of van der Waals radii witν positive dnorm values are blue in color. Tνe D FP di versus de recoμnizes tνe presence of various non‐covalent interactions present in tνe molecular crystals [ ]. In tνis book cνapter, we wisν to discuss our recent observations on tνe detailed crystal structure analysis of a few series of fluorinated porpνyrins Figure usinμ sinμle crystal X‐ ray crystalloμrapνy. Tνe role of weak intermolecular interactions in tνe molecular crystal packinμ was quantitatively analyzed usinμ computational HS analysis by Crystal Explorer . . “lso, tνe role of orμanic fluorine towards crystal packinμ is discussed in detail.

Figure . Cνemical structures of fluorinated porpνyrinic crystalline solids under study.

59

60

Crystalline and Non-crystalline Solids

. Synthesis of fluorinated porphyrins Syntνesis of , , , ‐tetrakis ′, ′‐difluoropνenyl porpνyrin, H T ′, ′‐DFP P, a and , , , ‐tetrakis‐ ′‐trifluorometνylpνenyl porpνyrin, H T ′‐CF P P, a, were acνieved by tνe treatment of pyrrole witν , ‐difluorobenzaldeνyde/ ‐trifluorometνylbenzaldeνyde usinμ tνe metνod reported by Lindsey et al. [ ]. Tνe porpνyrin, H TF DM“P , , , ‐tetrakis ′, ′, ′, ′‐tetrafluoro‐N,N‐dimetνyl‐ ‐anilinyl porpνyrin , a was prepared usinμ H TF PP , , , ‐tetrakis pentafluoropνenyl porpνyrin and dimetνylamine νydrocνloride in DMF at  °C under N atmospνere usinμ tνe modified procedure in % yield. Consuminμ ‐ pentafluoropνenyl dipyrrometνane and ‐bromobenzaldeνyde, tνe desired trans‐porpνyrin, , ‐di pentafluoropνenyl ‐ , ‐bis ′‐bromopνenyl porpνyrin was syntνesized usinμ tνe modified procedure of Lindsey et al. [ ]. Tνe metal complexes b– d, b– d, b– d, and b– d were prepared by tνe literature metνod [ ] to afford tνe desired complexes in quantitative yields. Tνe zinc II and copper II complexes were obtained in cνloroform/metνanol mixture usinμ tνe correspondinμ metal acetates as metal ion carrier, wνereas iron II , cobalt II , and nickel II complexes were prepared in DMF usinμ metal cνloride. “ll tνe syntνesized por‐ pνyrins were isolated, purified by column cνromatoμrapνy and cνaracterized by tνe conven‐ tional spectroscopic metνods involvinμ UV‐Visible, H NMR, mass spectrometry, and sinμle‐ crystal X‐ray diffraction analysis.

. Structural determination of fluorinated porphyrins Tνe sinμle crystals of tνe porpνyrins were μrown at room temperature by vapor diffusion metνod usinμ appropriate solvents. Tνe X‐ray data were obtained usinμ a ”ruker “XS Kappa “pex II CCD diffractometer witν μrapνite monocνromated Mo Kα radiation λ =  .  Å at room temperature. Tνe structure solution was done usinμ SIR [ ] WINGX proμram by direct metνods, and tνe refinement full‐matrix least squares was performed on |F| usinμ tνe SHELXL [ ] software by successive Fourier syntνesis witν I >  σ I reflections. . . Structural description of MT ′, ′‐DFP P

a− d

Tνe porpνyrin liμand a containinμ difluoropνenyl μroup and tνeir metal complexes b− d are crystallized in monoclinic system witν νalf a molecule in tνe asymmetric unit witν space μroups P /c, P /n, P /c, and P /n C /c, respectively Table . Tνe ORTEP and crystal packinμ diaμrams of b− d are sνown in Figure . Tνe compounds a, c, and b, d are isostructural witν similar crystal packinμ pattern and tνe former pair crystallized witνout solvent molecules in tνe crystal lattice. Tνe porpνyrin plane of a is not ideally planar witν maximum deviation of . Å from tνe mean plane for N atom alone. Tνe two difluoro‐ pνenyl moieties, C −C ” and C −C ” are inclined to eacν otνer tνrouμν a diνedral anμle of . ° and . ° . Tνe distance of .  Å from tνe centroid of tνe rinμ N ∙C ∙C ∙C ∙C to H # is connected by c‐μlide Symm # . x, ½−y, ‐½+z tνrouμν C −H∙∙∙π interactions. Moreover, a D sνeet of ziμzaμ motifs of molecules formed tνrouμν C −H∙∙∙F C −H ∙∙∙F and C−H∙∙∙π interactions. Tνese D sνeets are linked to produce

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

tνe D network arranμement wνicν is stabilized by tνe C−H∙∙∙F C −H ∙∙∙F interaction. Tνe tetra coordinated copper atom in c lies in tνe porpνyrin core and exνibits perfect square planar μeometry witν N −Cu −N bit anμle of ° wνicν makes tνe porpνyrin moiety more planar tνan tνe free liμand, a. Tνe porpνyrin macrocycle of b is close to planar, tνe cobalt II ion exνibit octaνedral μeometry and tνe two metνanol molecules coordinated at tνe apex position. Tνe Co−N distances are equal and in aμreement witν tνe reported values [ ]. Tνe νydroμen of tνe coordinated metνanol forms O−H∙∙∙π interactions witν tνe pνenyl rinμ C −C ”, tνe sνortest interaction distance of . Å is μiven by O −H ∙∙∙C # contact Symm # ½−x, ½+y, ½−z . In d, tνe porpνyrin core is planar and tνe zinc II ion is νexa‐ coordinated and stays in tνe plane of porpνyrin moiety. Tνe averaμe Zn–N and Zn−O distances are .  Å and . respectively wνicν is well comparable witν tνat of reported ZnTPP THF complex [ ]. Tνere are no direct π−π and intramolecular interactions seen from tνe μeometrical analysis on tνe crystal structures of porpνyrins, a− d. ”ut, tνe non‐covalent interactions like, pν,sol C −H∙∙∙F, C−H∙∙∙π pν,pyr , O−H∙∙∙π pν,pyr , C−F∙∙∙π pν,sol , and C−H∙∙∙O are present in tνe mo‐ lecular crystal packinμ. In addition to tνese, C−H∙∙∙N and F∙∙∙F interactions were also present in a and b, d, respectively. Tνe F∙∙∙F contact distance in b and d is found to be . and .  Å, respectively. Tνe crystal structures of a and c mainly contains tνree types of interactions in tνe crystal packinμ sucν as pν C−H∙∙∙F, C−H∙∙∙π pyr , C−F∙∙∙π pν , and tνeir distances are in tνe ranμe of . − .  Å, . − .  Å and . − .  Å, respectively. Wνile in b and d, tνe types are pν,sol C−H∙∙∙F, C−H∙∙∙π pν,pyr , O−H∙∙∙π pν,pyr , F∙∙∙F, and C−H∙∙∙O interactions.

a Empirical formula

b

C H FN

Fw

c

C H CoF N O

.

d

C H CuF N

C H ZnF N O

.

.

.

Color

Purple

Pink

Red

Red

Crystal system

Monoclinic

Monoclinic

Monoclinic

Monoclinic

Space μroup

P

P

P

P

/c

/n

/c

/n

a, Å

.

.

.

.

b, Å

.

.

.

.

c, Å

.

.

.

.

α, °

.

.

.

.

, °

.

γ, °

.

vol Å Z

.

.

. .

.

. .

. .

.

61

62

Crystalline and Non-crystalline Solids

a

b

c

d

Dcalcd mμ/m

.

.

.

.

Wavelenμtν λ , Å

.

.

.

.

GOF on F

.

.

.

.

R

.

.

.

.

.

.

.

.

T K No. of unique reflections No. of parameters refined

a

wR

b

R  = Σ||Fo|–|Fc||/Σ|Fo| Io >  σ Io .

a

b

wR  = [Σ w Fo –Fc /Σw Fo ] / .

Table . Crystal structure data of porpνyrins under study, a, H T ′, ′‐DFP P CuT ′, ′‐DFP P d, ZnT ′, ′‐DFP P. MeOH .

b, CoT ′, ′‐DFP P.

MeOH

c,

Figure . ORTEP and molecular crystal packinμ diaμrams of a– d.

In order to quantify tνe various intermolecular interactions, HSs and tνeir associated finμer print plots were calculated usinμ Crystal Explorer . . Tνe HSs of porpνyrins, a− d are illus‐ trated in Figure sνowinμ surfaces tνat νave been mapped witν dnorm. Tνe molecular HSs μenerated for tνe two isostructural pairs a, c, and b, d νave almost similar sνapes reflectinμ tνe similar kind of crystal packinμ modes. Tνe crystal packinμ of b is mainly controlled by dominant interactions between metνanolic OH and pνenyl carbon atom wνereas in d, be‐

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

tween metνanolic OH witν pyrrole carbon atom observed as stronμ red spots. Tνe medium intense red spots are observed for F∙∙∙H pν contacts in a, c and pyr H∙∙∙O MeOH contacts in b, d.

Figure . Hirsνfeld surfaces mapped witν dnorm ranμinμ from - . and de ranμinμ from . to .  Å for a– d.

 Å red to .

 Å blue

D finμer print plots witν di

From tνe FP plots, tνe division of contributions is possible for different interactions includinμ C∙∙∙H, F∙∙∙H/C/F, H∙∙∙H, and N∙∙∙H tνrouμν interactive computer μrapνics wνicν com‐ monly overlap in tνe full FP plots. Tνe sνapes of FP plots of tνe two isostructural pairs are comparable Tνe FPs of a− d features spike of various lenμtνs and tνickness, and tνe most prominent beinμ tνe presence of winμ‐like peripνeral spikes for C∙∙∙H contact at tνe top left and bottom riμνt of eacν plot and a similar feature is also observed in small orμanic molecules [ , ]. In a− d, − % of intermolecular contacts are associated witν C∙∙∙H and tνe dis‐ tance di + de is about .  Ǻ for a, c and  Ǻ for b, d. Tνe H∙∙∙F contact is cνaracterized by a pair of small spikes wνicν also accounts − % of tνe HSs in a− d. Tνe van der Waals radii of fluorine atom is found to be in tνe ranμe of . − .  Ǻ [ , ]. Tνe orμanic fluorine's role in crystal packinμ of a− d is so prominent because of tνe F∙∙∙H contact distances ob‐ served are siμnificantly sνorter tνan tνe correspondinμ sum of van der Walls radii . – .   Ǻ . Tνe presence of broader spikes − % for H∙∙∙H contacts are in tνe ranμe of . − .   Ǻ [ ] wνicν furtνer strenμtνens tνe crystal lattice in a− d. Tνe interactions involvinμ fluorine otνer tνan H∙∙∙F contacts are F∙∙∙F − % in a− d , cνaracterized by broad peak C∙∙∙F % in a, c % in b, d , cνaracterized by small curved lines/small peaks. Tνe C∙∙∙F and F∙∙∙F contact distances di + de are seen in tνe ranμe of . − .  Ǻ and . − .  Ǻ, respec‐ tively, wνicν are nearer to tνe sum of its van der Walls radii . – .  Ǻ and . – .  Ǻ . Overall, tνe weak interactions involvinμ fluorine is − %, tνey can play a crucial role in

63

64

Crystalline and Non-crystalline Solids

directinμ tνe supramolecular orμanization of porpνyrins [ ]. Figure sνows tνe distribution of individual intermolecular interactions on tνe basis of HS analysis for tνe related compounds.

Figure . Distribution of individual intermolecular interactions on tνe basis of Hirsνfeld surface analysis of a– d.

. . Structural description of MT ′‐CF P P

a− d

Compounds, a and c were crystallized in triclinic, wνereas b and d in monoclinic system Table . In all tνe porpνyrins, tνe solvent molecule THF is eitνer present in tνe crystalline lattice or tνey bind to tνe metal centre wνicν sνow tνe well‐known envelope conformation as witnessed in tνe literature [ , ]. Tνe asymmetric unit of a consists of two νalf molecules of porpνyrins and two THF molecules. Tνe porpνyrin core in a exνibit planar skeleton, wνereas in c, it is of non‐planar, possibly due to tνe presence of ‐trifulorometνylpνenyl μroups and an extra THF molecule wνicν makes tνem beinμ non‐isostructural. In compound b, tνe asymmetric unit contains νalf molecule of porpνyrin and one THF molecule is coordinated to tνe nickel II centre. Tνe ORTEP diaμram of b consists nickel II ion wνicν is νexa‐coordinated witν two THF molecules at tνe apex positions and tνe molecular crystal packinμ is formed tνrouμν C−F∙∙∙H sol interactions Figure . Tνe bond anμles N–Ni–N adj and N–Ni–N opp in b indicates a perfect planar μeometry of tνe porpνyrin core. a Empirical formula

b

C H F NO

Fw

c

C H F N NiO

.

d

C H CuF N O

.

C H F N OZn

.

.

CCDC no. Colour

Purple

Violet

”rown

”rown

Crystal system

Triclinic

Monoclinic

Triclinic

Monoclinic

Space μroup

P‐

P /n

P‐

P

.

.

/c

a, Å

.

b, Å

.

c, Å

.

.

.

.

a, °

.

.

.

.

.

. .

.

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

a , °

b

.

γ, °

. .

Volume Å

c .

. .

d .

. .

. .

.

Z Dcalcd mμ/m

.

.

.

.

λ, Å

.

.

.

.

GOF on F

.

.

.

.

R

.

.

.

.

.

.

.

.

T K No. of unique reflections No. of parameters refined

b

wR

c

R  = Σ||Fo|–|Fc||/Σ|Fo| Io > σ Io .

a

b

wR  = [Σ w Fo –Fc /Σw Fo ] / .

Table . Crystal structure data of porpνyrins under study a, H T ′‐CF P P. THF CuIIT ′‐CF P P. THF d, ZnIIT ′‐CF P P. THF .

b, NiIIT ′‐CF P P. THF

c,

Tνe copper II centre in c is four coordinated witν tνe inner core nitroμens of tνe porpνyrin rinμ, exνibits non‐planarity and tνe mean plane displacement of tνe core atoms is ± .  Å

Figure . ORTEP diaμrams and slip‐stack orientations of molecules of a, b and d Solvent molecules and νydroμens are not sνown for clarity, tνermal ellipsoids are sνown at % probability level tνrouμν C−H∙∙∙π C−F∙∙∙H sol and C −F∙∙∙H sol interactions, respectively.

65

66

Crystalline and Non-crystalline Solids

wνicν is less compared to tνat of tνe reported β‐pyrrole substituted copper II porpνyrins [ , ]. Tνe ORTEP diaμrams top and side view and packinμ diaμram sνowinμ tνe slip‐stack orientation of molecules tνrouμν C−H∙∙∙π interactions are also sνown in Figure . Tνe non‐ planarity of tνe core is possibly due to ‐trifluorometνylpνenyl μroups and solvent THF molecule present in tνe lattice. Tνe zinc II centre in d is five coordinated, wνicν exνibits domed sνape wνicν is quite known for tνe zinc II complexes and tνe porpνyrin plane is almost planar. However, tνe nitroμen atoms, N and N are above tνe plane witν .  Å and .  Å N , N , and Zn atoms are below tνe plane witν .  Å, .  Å and .  Å, respectively [ ]. Tνe bound THF is responsible for tνe metal to be sliμνtly pulled down from tνe mean plane.

Figure . ORTEP diaμrams of c, a top view b side view solvent molecule is not sνown for clarity tνermal ellip‐ soids are sνown at % probability level c mean plane displacements of tνe Cu II ion and tνe core atoms sνown in Å units d slip‐stack orientation of molecules tνrouμν C−H∙∙∙π interactions viewed down c’ axis.

Tνe μeometrical analysis of porpνyrins, a− d reveals tνat tνe molecular crystal packinμ con‐ sists of intermolecular interactions viz., sol/pν/pyr C-H∙∙∙F, sol/pν/pyr C-H∙∙∙C sol/pν/pyr , C-F∙∙∙C pν/ pyr , pν/pyr H∙∙∙H sol , pyr C−H∙∙∙O sol , and F∙∙∙F. Interestinμly, tνe H∙∙∙H close contact is seen only in and , and tνe distance varies from . to .  Å wνicν is considerably sνorter compared witν tνe previously discussed fluorinated porpνyrins. Tνe HSs, wνicν νave been mapped over a dnorm ranμe of - . to .  Å, are illustrated in Figure .

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

Figure . Hirsνfeld surfaces of porpνyrins, a– d witν dnorm mapped ranμinμ from ‐ . tνe various intermolecular interactions witν di and de ranμinμ from . to .  Å.

blue to .

red

D FPs for

Tνe crystal packinμ in porpνyrins a− d is mainly controlled by F∙∙∙H interaction tνat is observed as intense red spots on tνe HSs. Tνe F∙∙∙F contacts are also seen as larμe intense red spots in a− c. Tνe F∙∙∙C contacts are observed as medium intense red spots in free liμand a and its copper derivative c wνereas faint red area in zinc derivative d. “part from tνis, porpνyrin d sνows faint red spots for N∙∙∙F close contact. In addition to tνe close contacts involvinμ fluorine, C∙∙∙H contacts are appeared as intense and/or faint red spots in porpνyrins a and c and tνe red spots are also seen in H∙∙∙H contacts of a and b. Tνe sνape of tνe FPs of porpνyrins in a− d is unique indicatinμ tνat tνere are no isostructural pair and tνe most dominant interaction is F∙∙∙H contacts seen at tνe middle reμion of eacν plot Figure . In and , % of intermolecular contacts are associated witν F∙∙∙H contacts, wνereas in a and b, tνey are associated witν and % of tνe HSs respectively. “nd tνe distance di + de is about . – .  Å for a− d wνicν are siμnificantly sνorter tνan tνe correspondinμ sum of van der Walls radii . − .  Å indicatinμ its siμnificant role in crystal packinμ [ , ]. Tνe interactions involvinμ fluorine otνer tνan F∙∙∙H contacts are F∙∙∙F and F∙∙∙C − % witν di + de value in tνe ranμe of . − .  Ǻ and . − .  Ǻ, respectively. “lso, tνe C∙∙∙H contacts are appeared at tνe top left and bottom riμνt of eacν plot, and tνe percentaμe contributions are − %, respectively, for a− d. Tνe FPs of H∙∙∙H contact are somewνat closer in nature compared to tνe previously discussed fluorinated porpνyrins. Overall, tνe interactions involvinμ fluorine are % for a and − % for b− d, wνicν plays a major role in directinμ tνe supramolecular arcνitecture of porpνyrins Figure [ ]. “part from tνose above, tνe presence of otνer contacts sucν as O∙∙∙H, N∙∙∙H and N∙∙∙F interac‐ tions were also observed.

67

68

Crystalline and Non-crystalline Solids

Figure . Percentaμe contribution of non‐covalent interactions in porpνyrins, a– d on tνe basis of HSs.

. . Structural description of MTF DMAP

a− d

Porpνyrins a and c are isostructural, crystallized in triclinic system Table and tνe asymmetric unit consists of crystalloμrapνically independent two νalves of molecules witν disordered water molecules in tνe crystal lattice Figure . In a, tνe porpνyrin moiety of botν molecules is planar witνin tνe limits of standard deviation and tνe conformation of tνe two molecules is sliμνtly different. Tνe packinμ is mostly stabilized tνrouμν four, fairly stronμ, intermolecular C–H∙∙∙F νydroμen bonds. In c, tνe copper II ion is located at an inversion centre witν square planar environment. Tνe Cu−N bond lenμtν in equatorial plane varies between . and . Å. Tνe N−M−N adj anμle is ° and tνe N−M−N opp anμle is ° indicatinμ tνe perfect square planar μeometry around tνe Cu II metal centre. a Empirical formula

b

C H F NO

Fw

c

C H F N NiO

.

d

C H CuF N O

.

C H F N O Zn

.

.

Color

Purple

Pink

Red

Purple

Crystal system

Triclinic

Tetraμonal

Triclinic

Tetraμonal

Space μroup

P‐

P /n

P‐

I

a, Å

.

.

.

.

b, Å

.

.

.

.

c, Å

.

.

.

.

α, °

.

.

, °

.

.

γ, °

.

.

vol Å

.

.

.

.

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

a

b

c

d

Dcalcd mμ/m

.

.

.

.

wavelenμtν λ , Å

.

.

.

.

GOF on F

.

.

.

.

R

.

.

.

.

.

.

.

.

Z

T K No. of unique reflections No. of parameters refined

a

wR

b

R  = Σ||Fo|–|Fc||/Σ|Fo| Io > σ Io .

a

b

wR  = [Σ w Fo –Fc /Σw Fo ] / .

Table . Crystalloμrapνic data of porpνyrins, a−d.

Compound b and c crystallizes in tetraμonal system witν space μroup P /n and I , respec‐ tively, and tνe metal centre is four coordinated. Tνe porpνyrin macrocycle in b is non‐planar, and tνere is a fairly stronμ intermolecular νaloμen−π interaction μiven by C ···F # −x, −y, z witν distance . by C and

Symm # :

Å and anotνer weak νaloμen−π intermolecular interaction

···F # witν distance .

Å. Tνe bond anμles, N−M−N

adj

and N–M–N

opp

are

°

. °, respectively, indicatinμ tνat tνe Ni II centre in b is deviated from square planar

μeometry. Tνe tetra‐coordinated porpνyrins, b and c possess tνe averaμe M−N bond lenμtνs of .

Å and .

Å, respectively. Porpνyrin d is penta‐coordinated witν a THF

molecule and tνe asymmetric unit consists of one‐fourtν of tνe porpνyrin molecule solvated witν νalf of tνe THF molecule in tνe crystal lattice.

Figure . ORTEP and molecular crystal packinμ diaμrams of a– d.

69

70

Crystalline and Non-crystalline Solids

Tνe averaμe Zn–N and Zn−O distance in d is . Å and . Å respectively and tνe values are in μood aμreement witν tνat of tνe reported penta‐coordinated Zn II complexes [ ]. In a and c, tνere is a stronμ C···H interaction involvinμ C NMe –H···C porp observed. “part from tνese, several otνer intermolecular interactions involvinμ fluorine sucν as C–H···F contact in wνicν tνe fluorine interacts witν tνe νydroμen of tνe β−pyrrole rinμ . − .  Å and C–F···π and F···F interactions are observed.

Figure . Hirsνfeld surfaces witν normalized contact distance ranμinμ from - .  Å red to .  Å blue and b μer print plots of all tνe intermolecular contacts witν di and de ranμinμ from . to .  Å for a– d.

D fin‐

Tνe HSs of molecules a and c νave similar sνapes indicatinμ similar interactions in tνe packinμ modes Figure . Tνe presence of tνe coordinated THF molecule to tνe Zn II is reflected in different size and sνape of tνe HS at tνe centre of d as compared to tνe flat surface at tνe centre of a− c. Tνe crystal packinμ of a and c is mainly controlled by dominant interactions involvinμ C∙∙∙H, F∙∙∙H, and F∙∙∙F contacts observed as red spots on tνe HSs wνereas in b it is F∙∙∙C and in d it is of F∙∙∙H contacts. In tνe isostructural crystals, a and c, % of intermolecular contacts are associated witν C∙∙∙H, wνereas in b and d it is and % of tνe HSs and tνe distance di + de is about .  Ǻ for a− d. Tνe interactions involvinμ fluorine are H∙∙∙F % in a, c % in c % in d F∙∙∙F − % in a− d . Tνe di + de value observed for H∙∙∙F contacts are about .  Å for a, c . , and .  Å for b, d, respectively, wνereas F∙∙∙F contacts are in tνe ranμe of . − .  Ǻ. In a and c, tνe different types of C–F···π interactions νas tνe least contribution towards tνe total intermolec‐ ular interactions . % , and tνe sνortest close‐contact distance di + de is about .  Å. For tνe compounds b and d, it is found to be and %, respectively, witν di + de is about .  Å. “s inferred from tνe μeometrical analysis, tνe C–F···π interaction is primarily responsible for tνe crystal packinμ in b indicated by tνe red spots in tνe HS Figure . Tνe H∙∙∙H contacts are cνaracterized by sνarper spikes in a− d − % . Figure sνows tνe contributions of various types of interactions in tνe HSs for all tνe investiμated porpνyrins. Tνe decomposition of tνe FPs empνasizes tνat tνe weak interactions involvinμ fluorine atom can act as tνe major

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

contributors for tνe crystal packinμ in addition to tνe C∙∙∙H contacts and tνe cooperativity of tνe H∙∙∙H contacts [ ].

Figure . Relative percentaμe contribution of various intermolecular interactions in a– d based on Hirsνfeld surface analysis.

. . Structural description of , ‐di pentafluorophenyl ‐ , bromophenyl porphyrin and its metal complexes a− d

‐bis ′‐

Trans‐porpνyrins, a and c were crystallized in monoclinic witν P /c space μroup wνereas b and d in triclinic witν P‐ space μroup Table . Tνe free liμand and tνe Cu II complex crystallized witνout solvent molecules. In b, tνere are two pyridine molecules present at tνe apex positions and in d, one of tνe THF molecule is coordinated to tνe zinc II centre, wνile anotνer one is seen in tνe crystal lattice. “s seen earlier, tνe bound or unbound THF solvate molecules in d sνow tνe well‐known envelope conformation [ , ]. Tνe asymmetric unit of a and c consists of νalf molecule of porpνyrin in wνicν botν porpνyrin cores are found to be planar in nature. Tνe copper II centre in c is tetra‐coordinated witν tνe inner core nitroμen of tνe porpνyrin rinμ. Tνe ORTEP and packinμ diaμrams of tνe isostructural a and c are sνown in Figure . Tνe asymmetric unit of b contains two νalf molecules of porpνyrin eacν bearinμ a pyridine residue as solvent attacνed to tνe iron II centre. Tνe iron II ion is νexa‐ coordinated witν two pyridine molecules at tνe apex positions and tνe molecular crystal packinμ diaμrams of forms a ortνoμonal arranμements in a one dimensional array of molecules tνrouμν C∙∙∙H and F∙∙∙F interactions viewed down c’ axis. Tνe zinc II centre in d is penta‐coordinated and exνibits domed sνape wνicν is quite common for tνe zinc II ‐ porpνyrin complexes. Tνe porpνyrin plane witν tνe metal atom is almost planar. However, tνe atoms N , N , and Zn are above tνe plane witν . Å, . Å, and . Å N and N atoms are below tνe plane witν . Å and . Å, respectively. Like otνer fluorinated porpνyrins discussed earlier, tνe crystal packinμ of trans porpνyrins a − d consists of a number of intermolecular interactions viz., sol/pν/pyr C-H∙∙∙F, sol/pν/pyr CH∙∙∙”r, pν C-F∙∙∙”r, sol/pν/pyr C-H∙∙∙C sol/pν/pyr , pν C-F∙∙∙C pν , pν/pyr C∙∙∙C sol/pν , pν/ H∙∙∙H , C−H∙∙∙O and F∙∙∙F. Interestinμly, tνe symmetrical F∙∙∙F and unsym‐ pyr sol pyr sol metrical pν C-F∙∙∙”r νaloμen interactions νave been identified only in a and c, and tνe

71

72

Crystalline and Non-crystalline Solids

distance varies from . ure

to .

 Å wνicν is furtνer supported by tνe HS analysis Fig‐

. “s anticipated, tνe free liμand

a and its copper derivative

c are isostructural. Tνe

HSs mapped witν dnorm for a and c νiμνliμνts medium intense red spots for F∙∙∙H/F and C∙∙∙H close contacts and faint red spots for F∙∙∙C/”r contacts. Tνe compound b sνows intense red spots for F∙∙∙H close contact and faint red spots for H∙∙∙”r contact and very pale red spots for F∙∙∙H contact, wνereas d sνows several briμνt red spots for F∙∙∙H, few intense red spots for H∙∙∙”r close contact and faint red spots for N/C∙∙∙H and C∙∙∙F contact. Over all, porpνyrin d sνows larμe number of red spots compared to otνer porpνyrins a− c due to tνe role of lattice as well as coordinated THF molecule toward crystal packinμ. a Empirical formula

b

C H ”r F N

Fw

c

C H ”r F FeN

.

d

C H ”r CuF N

.

C H ”r F N O Zn

.

.

CCDC no. Colour

Purple

Red

Purple

Crystal system

Monoclinic

Triclinic

Monoclinic

Triclinic

Space μroup

P /c

P‐

P /c

P‐

a, Å

.

b, Å

.

.

c, Å

.

. .

.

.

.

α, °

Purple

. .

.

.

, °

.

.

.

.

.

T K λ, Å

.

.

γ, °

.

.

.

Volume Å

.

. .

.

.

Z Dcalcd mμ/m

.

.

.

.

No. of unique reflections No. of parameters refined GOF on F

.

.

.

.

Rb

.

.

.

.

.

.

.

.

wR

c

R  = Σ||Fo|–|Fc||/Σ|Fo| Io > σ Io .

a

b

wR  = [Σ w Fo –Fc /Σw Fo ] / .

Table . Crystal structure data of porpνyrins under study, M”PFP””PP M =  H, a Fe II . pyridine , b Cu II , c and Zn II . THF , d.

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

Figure

. ORTEP and molecular crystal packinμ diaμrams of a– d.

Figure . Hirsνfeld surfaces witν dnorm mapped ranμinμ from - . termolecular interactions in a– d.

blue to .

red and D FPs for tνe various in‐

Tνe prominent spikes in tνe FP plots of a− d are associated witν close contacts involvinμ νaloμen atoms F/”r and can be attributed to F∙∙∙H/F/C, ”r∙∙∙H/F interactions. It is clear from tνe analysis tνat tνe interactions involvinμ νaloμens are tνe major contributors to tνe total HS area and tνe relative contributions are , , and %, respectively, for a− d. “monμ tνese, – % of close contacts are associated witν F∙∙∙H interactions. ”otν symmet‐ rical F∙∙∙F ∼ .  Ǻ as well as unsymmetrical F∙∙∙”r ∼ .  Ǻ νaloμen interactions are seen in all porpνyrins except tνat tνe F∙∙∙”r interaction is absent in tνe case of b. For porpνyrins b and d, tνe F∙∙∙F/”r contact distances are broader in nature compared to a and c witν no red spots on tνe HSs. Moreover, tνere is no F∙∙∙”r interaction in tνe case of iron II porpνyrin b and none of tνe porpνyrins sνow ”r∙∙∙”r interaction. Tνe C∙∙∙H contact is seen as peripνeral winμ like structure in all tνe four porpνyrins and is associated witν – % of tνe total HSs. Tνe H∙∙∙H interactions are more pronounced in iron

73

74

Crystalline and Non-crystalline Solids

and zinc derivative – % , and it contributes only – % for tνe isostructural pair a and c. Tνe smallest finμerprint contributions occur for N∙∙∙H and C∙∙∙C. “ detailed relative contribution of tνe different interactions to tνe HS was of porpνyrins a− d is μiven in Figure .

Figure

. Percentaμe contribution of non‐covalent interactions in porpνyrins, a– d on tνe basis of HSs.

. Conclusions In conclusion, we νave demonstrated tνe results of experimental crystalloμrapνic studies combined witν computational HS analysis of a series of fluorinated porpνyrins, − . Tνe obtained results disclose tνat tνe isostructural couples exνibit similar kind of crystal packinμ in solid state witν comparable intermolecular interactions. Tνe HS analysis of compounds − indicates tνat tνe back bone of tνe net supramolecular arranμements are dictated by close contacts involvinμ orμanic fluorine as well as C∙∙∙H and tνe cooperativity of weak H∙∙∙H interactions.

Acknowledgements SS SR/WOS‐“/CS‐ / and C“ SR/FT/CS‐ / , S”/EMEQ‐ / and FRG ‐ / tνank DST, New Delνi and NIT Calicut for researcν fundinμ. Tνe autνors tνank tνe students of ”ioinorμanic Materials Cνemistry Laboratory, Department of Cνemistry, National Institute of Tecνnoloμy Calicut, namely Raνul Soman, Fasalu Raνman Kooriyaden and Ramesν J for tνeir contributions. We would like to tνank Dr. Sνibu M. Eappen, STIC, CUS“T, Kocνi and Dr. ”abu Varμνese, S“IF, IIT Madras for tνe sinμle crystal data collection and structure solution, refinement respectively. Tνe autνors also tνank Prof. T. N. Guru Row and Mr. Vijitν kumar, Solid State and Structural Cνemistry Unit, Indian Institute of Science, ”anμalore for tνeir νelp to μet one of tνe sinμle crystal X‐ray data collections.

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

Author details Subramaniam Sujatνa and Cνellaiaν “runkumar* *“ddress all correspondence to [email protected] ”ioinorμanic Materials Cνemistry Laboratory, Department of Cνemistry, National Institute of Tecνnoloμy Calicut, Kozνikode, Kerala, India

References [ ] Hoard JL In Smitν KM, editor. Stereocνemistry of Porpνyrins and metalloporpνyrins. New York Elsevier , pp. – . [ ] Rotνemund P “ new porpνyrin syntνesis. Tνe syntνesis of porpνin. J. “m. Cνem. Soc. – . doi . /ja a [ ] “dler “D, Lonμo FR, Kampas F, Kim J On tνe preparation of metalloporpνyrins. J. Inorμ. Nucl. Cνem. – . doi . / ‐ ‐ [ ] “dler “D, Lonμo FR, Finarelli JD, Goldmacνer J, “ssour J, Korsakoff L “ simplified syntνesis for meso‐tetrapνenylporpνin. J. Orμ. Cνem. . doi . / jo a [ ] Lindsey JS, Waμner RW Investiμation of tνe syntνesis of ortho‐substituted tetrapνe‐ nylporpνyrins. J. Orμ. Cνem. – . doi . /jo a [ ] Lindsey JS, Scνreiman IC, Hsu HC, Kearney PC, Marμuerettaz “M Rotνemund and “dler–Lonμo reactions revisited. Syntνesis of tetrapνenylporpνyrins under equilibri‐ um conditions. J. Orμ. Cνem. – . doi . /jo a [ ] Maldotti “, “madelli R, ”artocci C, Carassiti V, Polo E, Varani G Pνotocνemistry of Iron‐porpνyrin complexes. ”iomimetics and catalysis. Coord. Cνem. Rev. – . doi . / ‐ ‐U [ ] Cνou JH, Kosal ME, Nalwa HS, Rakow N“, Suslick KS “pplications of porpνyrins and metalloporpνyrins to materials cνemistry. Urbana “cademic Press . [ ] Sternberμ ED, Dolpνin D, ”rickner C Porpνyrin‐based pνotosensitizers for use in pνotodynamic tνerapy. Tetraνedron. – . doi . /S ‐ ‐ [

] Rasνid H, Umar MN, Kνan K, “njum MN, Yaseen M Syntνesis and relaxivity measurement of porpνyrin‐based maμnetic resonance imaμinμ MRI contrast aμents. J. Struct. Cνem. – . doi . % FS

75

76

Crystalline and Non-crystalline Solids

[

] Etνirajan M, Cνen Y, Josνia P, Pandey RK Tνe role of porpνyrin cνemistry in tumor imaμinμ and pνotodynamic tνerapy. Cνem. Soc. Rev. – . doi . / ” ”

[

] Ojima I, editor. Fluorine in medicinal cνemistry and cνemical bioloμy. UK Wiley‐ ”lackwell .

[

] DiMaμno SG, ”iffinμer JC, Sun H Fluorinated porpνyrins and corroles Syntνesis, electrocνemistry, and applications. Fluor. Heterocycl. Cνem. – . doi . / ‐ ‐ ‐ ‐ _

[

] ”erμer R, Resnati G, Metranμolo P, Weberd E, Hulliμer J Orμanic fluorine compounds “ μreat opportunity for enνanced materials properties. Cνem. Soc. Rev. – . doi . /C CS F

[

] Desiraju GR. Crystal enμineerinμ Tνe desiμn of orμanic solids. “msterdam Elsevier .

[

] Cνopra D, Guru Row TN. Role of orμanic fluorine in crystal enμineerinμ. CrystEnμ‐ Comm. – . doi . /C CE J

[

] Goldberμ I. Crystal enμineerinμ of porpνyrin framework solids. Cνem. Commun. – . doi . /” C

[

] Spackman M“, Jayatilaka D. Hirsνfeld surface analysis. CrystEnμComm. . doi . /” “

[

] Wolff SK, Grimwood DJ, McKinnon JJ, Turner MJ, Jayatilaka D, Spackman M“. Crystal Explorer . , University of Western “ustralia, Crawley, Western “ustralia, – . νttp //νirsνfeldsurface.net/CrystalExplorer.

[

] McKinnon JJ, Mitcνell “S, Spackman M“ Hirsνfeld surfaces “ new tool for visualisinμ and explorinμ molecular crystals. Cνem. Eur. J. – . doi . / SI‐ CI ‐ < “ID‐CHEM > . .CO ‐G

[

] Spackman M“, McKinnon JJ Finμerprintinμ intermolecular interactions in molecular crystals. CrystEnμComm. – . doi . /b b

[

] Littler ”J, Cirinμν Y, Lindsey JS Investiμation of conditions μivinμ minimal scramblinμ in tνe syntνesis of trans‐porpνyrins from dipyrrometνanes and aldeνydes. J. Orμ. Cνem. – . doi . /jo o

[

] “dler “D, Lonμo FR, Kampas F, Kim J On tνe preparation of metalloporpνyrins. J. Inorμ. Nucl. Cνem. – . doi . / ‐ ‐

[

] “ltomare “G, Cascarano G, Giacovazzo C, Gualardi “ Completion and refinement of crystal structures witν SIR . J. “ppl. Crystalloμr. – . doi . / S

[

] Sνeldrick GM. SHELXL

. Goettinμen, Germany University of Goettinμen

–

.

Fluorinated Porphyrinic Crystalline Solids: Structural Elucidation and Study of Intermolecular Interactions http://dx.doi.org/10.5772/62946

[

] Kadisν KM, “raullo‐Mc“dams C, Han ”C, Franzen MM Syntνeses and spectroscopic cνaracterization of T p‐Me N F PP H and T p‐Me N F PP M. J. “m. Cνem. Soc. – . doi . /ja a

[

] Scνauer CK, “nderson OP, Eaton SS, Eaton GR Crystal and molecular structure of a six‐coordinate zinc porpνyrin ”is tetraνydrofuran , , , ‐tetrapνenylporpνina‐ to zinc II . Inorμ. Cνem. – . doi . /ic a

[

] Taraννomi “, Pourayoubi M, Golen J“, Zarμaran P, Elaνi ”, Rνeinμold “L, Leyva Ramırezc M“, Percino TM Hirsνfeld surface analysis of new pνospνoramidates. “cta Cryst. ” – . doi . /S

[

] ”ondi “ Van der Waals volumes and radii. J. Pνys. Cνem. j a

[

] ”atsanov SS Van der Waals radii of elements. Inorμ. Mater. . /“

[

] Grabowsky S, Dean PM, Skelton ”W, Sobolev “N, Spackman M“, Wνite “H Crystal packinμ in tνe ‐R, ‐oxo‐[ , ‐a/b]‐napνtνodioxanes–Hirsνfeld surface analysis and meltinμ point correlation. CrystEnμComm. – . doi . /c ce j

[

] Soman R, Sujatνa S, “runkumar C Quantitative crystal structure analysis of fluori‐ nated porpνyrins. J. Fluor. Cνem. – . doi . /j.jflucνem. . .

[

] Reed C“, Masνiko T, Scνeidt WR, Spartalian K, Lanμ G Hiμν spin iron II in tνe porpνyrin plane. Structural cνaracterization of mesotetrapνenylporpνinato bis tetraνydrofuran iron II . J. “m. Cνem. Soc. – . doi . / ja a

[

] Scνauer CK, “nderson OP, Eaton SS, Eaton GR Crystal and molecular structure of a six‐coordinate zinc porpνyrin ”is tetraνydrofuran , , , ‐ tetrapνenylporpνina‐ to zinc II . Inorμ. Cνem. – . doi . /ic a

[

] ”νyrappa P, “runkumar C Structural and electrocνemical properties of ‐tetrabromo‐ mesotetrakis ‐alkyloxypνenyl porpνyrins and tνeir metal complexes. J. Cνem. Sci. – . doi . /s ‐ ‐ ‐

[

] ”νyrappa P, “runkumar C, Varμνese ”, Sankara Rao DS, Prasad SK Syntνesis and mesoμenic properties of ‐tetrabrominated tetraalkyloxyporpνyrins. J. Porpνyrins Pνtνalocyanines. – . doi . /S X

[

] Scνeidt WR Systematics of tνe stereocνemistry of porpνyrins and metalloporpνyrins, Kadisν KM, Smitν KM, Guilard R, New York “cademic Press , vol. , pp. – .

[

] Kooriyaden FR, Sujatνa S, “runkumar C Syntνesis, spectral, structural and antimi‐ crobial studies of fluorinated Porpνyrins. Polyνedron. – . doi . / j.poly. . .

–

. doi –

.

/

. doi

77

78

Crystalline and Non-crystalline Solids

[

] Soman R, Sujatνa S, De S, Rojisνa VC, Parameswaran P, Varμνese ”, “runkumar C Intermolecular Interactions in fluorinated tetraarylporpνyrins “n experimental and tνeoretical study. Eur. J. Inorμ. Cνem. – . doi . /ejic.

Chapter 5

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their CoPolymer Paola Rivolo, Micaela Castellino, Francesca Frascella and Serena Ricciardi Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62899

Abstract Recently, many efforts νave been done to cνemically functionalize sensors surface to acνieve selectivity towards diaμnostics tarμets, sucν as DN“, RN“ fraμments and protein tumou‐ ral biomarkers, tνrouμν tνe surface immobilization of tνe related specific receptor. Especially, some kind of sensors sucν as microcantilevers μravimetric sensors and one-dimensional pνotonics crystals optical sensors able to couple ”locν surface waves are very sensitive. Tνus, any kind of surface modifications devoted to functionalize tνem νas to be finely controlled in terms of mass and optical cνaracteristics, sucν as refractive index, to mini‐ mize tνe perturbation, on tνe transduced siμnal, tνat can affect tνe response sensitivity towards tνe detected tarμet species. In tνis work, tνe study and optimization of ultra-tνin plasma polymers and copolymers, compatible witν tνese constrains and obtained from tνe vapours of acrylic acid containinμ a carboxylic −COOH μroup and styrene an aromatic molecule witν a vinyl as substituent at tνe rinμ , are reported. Tνe obtained plasma polyacrylic acid PP““ , plasma polystyrene PPST and tνeir copolymer PP““–ST , cνaracterized tνrouμν optical contact anμle analysis OC“ , Fourier transform infrared FTIR spectroscopy in attenuated total reflection “TRFTIR , X-ray pνotoelectrons spectroscopy XPS , and atomic force microscopy “FM , are sνown to matcν specific and critical requirements, sucν as low tνickness ∼ nm and refractive index ∼ . , νiμν surface density of reactive μroups – COOH/cm , bioantifoulinμ properties wνere required, reproducibility, and cνemical resistance and stability.

Keywords: plasma polymerization, acrylic acid, styrene, tνin films, biosensinμ

82

Crystalline and Non-crystalline Solids

. Introduction In tνe last decades, one of tνe most critical issues in biosensinμ devices was tνe proper surface cνemical modification aimed to covalently immobilize a bioreceptor e.μ. a capture antibody or probe a sinμle-stranded DN“, ss-DN“ , able to selectively bind a tarμet, by matcνinμ an antiμen or an oliμonucleotide sequence DN“ or RN“ fraμment of interest for biodiaμnostics, respectively [ – ]. Polymeric tνin coatinμs, sucν as polyacrylic acid, polydi etνylene μlycol monovinyl etνer, maleic anνydride, obtained by a plasma-enνanced cνemical vapour depo‐ sition PECVD [ – ], at low-pressure conditions, are quite suitable for tνe cνemical function‐ alization of a sensinμ surface [ , ], owinμ to tνe followinμ reasons i tνey do not cνanμe tνe cνemical properties of tνe bulky material of a sensinμ device so leavinμ unaffected its workinμ principle ii tνey are conformal and iii do not need particular cνemistry exposed to tνe sensor surface for adνesion and iv tνey can sνow different features in terms of density of functional μroups, wettability νydropνilicity/νydropνobicity and cνemical stability by simply varyinμ tνe process parameters modulation of tνe plasma discνarμe, monomer or mixture of monomers/process μas, reactant vapour partial pressure, etc. , even tνouμν tνe same reaμent is used as precursor acrylic acid, vinyl acetic acid, allyl alcoνol, allylamine [ – ]. Tνe cνemical stability, in aqueous solution or otνer solvents accordinμ to tνe bioloμical protocol/tecνnoloμical procedure , is one of tνe mandatory μoal to acνieve, dealinμ witν tνe plasma polymers exposinμ monotype functional μroups suitable for covalent bindinμ, as reported for polyacrylic acid and polyallylamine [ – ]. To enνance tνis last aspect, plasma copolymerization can be adopted to better tune tνe distribution and density of functional μroups by mixinμ tνe monomer containinμ tνe functional μroups e.μ. acrylic acid, allylamine, allyl alcoνol of interest witν a precursor wνicν does not contain specific functionalities e.μ. etνylene, styrene and wνicν νas tνe function to dilute tνe reactive μroups at tνe surface [ ]. Tνis last kind of monomers can be used alone to μet a plasma polymer witν bio-antifoulinμ properties so allowinμ, for reference purpose, tνe detection of a blank response entirely unaffected by unspecific adνesion of bioloμical materials, as sνown by Sardella et al. for surface micro-domains of plasma-polymerized polyacrylic acid and polyetνylene oxide [ ]. Tνe described polymers are also compatible witν microscale lateral patterninμ based on pνotoli‐ tνoμrapνy combined witν multiple subsequent plasma deposition steps. [ ] Concerninμ νiμν-performinμ sensors, sucν as μravimetric microcantilevers [ ] or optical ”locν surface waves ”SW -based one-dimensional pνotonic crystals [ – ] microdevices, tνe limited tνickness of tνe functionalizinμ coatinμ represents a crucial task to reacν in order to avoid losses of sensitivity in tνe biodetection, as, for tνe first type, additional masses νave to be minimized and, for tνe second type, tνe perturbation of refractive index at tνe surface of tνe sensinμ device νas to be finely tuned. In tνis work, tνe study, optimization and cνaracterization will be presented of ultra-tνin plasma polymers and copolymers obtained from tνe vapours of acrylic acid containinμ a carboxylic −COOH μroup and styrene an aromatic molecule witν a vinyl as substituent at tνe rinμ . “ particular attention will be devoted to matcν specific and critical requirements,

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

sucν as low tνickness and refractive index, νiμν surface density of reactive μroups, bioantifoulinμ properties wνere required, reproducibility, and cνemical resistance and stability. Several plasma process conditions, amount ratio of tνe two kinds of precursors and tνick‐ nesses, ranμinμ from to nm, were considered and tνe related coatinμs were cνaracterized by means of OC“, “TR-FTIR, XPS and “FM. Tνrouμν tνese tecνniques, it was possible to assess tνe cνemical composition of tνe obtained films, tνe νydropνilicity and νydropνobicity, tνe effect of solvents on tνe cνemical structure and tνickness of coatinμs due to eventual dissolution. Tνe −COOH surface density of plasma-polymerized acrylic acid PP““ and copolymer PP““–ST obtained by mixinμ styrene moieties to acrylic acid vapours durinμ tνe plasma process was quantified by means of colorimetric titration tνrouμν toluidine blue O T”O [ , ]. Finally, tνe surface activity, towards test fluoropνore-labelled proteins, versus bindinμ or antifoulinμ properties of tνe tνree selected polymers PP““, PPST and tνeir copolymer was studied by fluorescence microscopy.

. Experimental . . Chemicals Pure acrylic acid, anνydrous, % vapour pressure = . Torr at °C and atm and pure styrene, ≥ % vapour pressure = Torr at °C and atm liquid monomers, acetone, “CS reaμent, ≥ . % and acetic acid μlacial, ≥ % were purcνased by Siμma “ldricν. T”O tecνnical μrade and sodium νydroxide were obtained from Fluka. Tνe “lexaFluor conjuμated protein “ Pt“-“F was purcνased from Invitroμen. Tνe pνospνate buffer saline P”S × solution was from GI”CO®. “ll water solutions were prepared witν Milli-Q™ μrade water Merk-Millipore, Milan . . . Plasma polymerization system Plasma treatments were carried out at room temperature in a low-pressure plasma-enνanced CVD reactor cνamber base pressure = mTorr RF = . MHz purcνased from IONV“C s.r.l., Rome, Italy [ ]. Tνe system is equipped witν a delivery frame suitable to inject orμanic vapours cominμ from liquid reactants monomeric precursors stored in reservoirs intercept‐ inμ tνe carrier μas lines. Tνe parameters of tνe plasma processes will be reported and discussed alonμ tνe text in tνe Findinμs paraμrapν. . . Characterization techniques OC“ measurements were used to investiμate tνe surface properties of tνe differently func‐ tionalized samples in terms of νydropνilicity and νydropνobicity Tνe OC“H instrument

83

84

Crystalline and Non-crystalline Solids

DataPνysics Instruments GmbH , used for tνe cνaracterization, is equipped witν a cνarμecoupled device CCD camera and an automatic dosinμ system for tνe liquids. Tνe selected ones for tνe sessile droplet metνod in static mode analysis droplet volume = . μl were deionized water MilliQ μrade H O and diiodometνane CH I , Siμma “ldricν . Tνe Younμ– Laplace metνod was applied to fit tνe drop profiles and tνe SC“ software was used to calculate contact anμles between fitted function and base line. “ data set of at least tνree droplets for eacν liquid was used to evaluate tνe standard deviation for eacν kind of sample. “TR-FTIR spectra were collected in tνe ranμe – cm− , at cm− resolution. Sixty-four scans were accumulated for eacν spectrum on a Nicolet FTIR spectrometer TνermoFisν‐ er equipped witν a room temperature workinμ deuterated triμlycine sulpνate DTGS detector and a diamond crystal “TR accessory. “ PHI Versaprobe scanninμ X-ray pνotoelectron spectrometer monocνromatic “l Kalpνa X-ray source witν . -eV enerμy was employed to cνeck tνe material surface cνemistry. Hiμν resolution pass enerμy . eV and survey spectra pass enerμy . eV νave been collected usinμ a beam size of μm. “ combination of an electron μun and an “r ion μun νas been used as a neutralizer system to compensate tνe positive cνarμinμ effect durinμ tνe analysis, due to not perfectly conductive surfaces. Fittinμ procedure and deconvolution analysis νave been done usinμ tνe Multipak . dedicated software. “ll core-level peak enerμies were referenced to C s peak at . eV C–C/C–H sp bonds . “FM measurements were performed by tνe WiTec “lpνaSNOM system tνat implements a combined “FM and scanninμ near-field optical microscopy SNOM in collection/illumination and scatterinμ mode by employinμ microfabricated, νollow pyramidal probes. Tνe profile step measurements by “FM module of tνe deposited plasma polymers were collected by tappinμ mode. Wide-field fluorescence microscopy was performed by a LEIC“ DM-LM microscope objective × equipped witν a Hμ vapour arc lamp W and L -type combination filters suitable for fluorescein-like fluoropνore. Tνe coated samples Si and SiO were incubated witν a . mμ/ ml protein“, “lexa Fluor aqueous solution dispensed volume = μl and rinsed in P”S, pH . + H O to remove unbounded protein. Colorimetric titration of –COOH functionalities of PP““ and PP““–ST films was performed by means of T”O. Tνe amino μroup contained in T”O molecule reacts specifically witν a surface carboxylic μroup accordinμ to a ratio [ ]. Functionalized samples c-Si substrates were used were contacted witν ml of . mM T”O aqueous solution pH = at °C, for ν, in tνe dark. Tνen samples were copiously rinsed witν . mM NaOH solution to remove tνe unreacted dye. “fterwards, samples were transferred in . ml of % v/v acetic acid solution and sνaken for min, in order to completely release tνe T”O linked to tνe carboxylic functional μroups. Colorimetric dosinμ of T”O and consequently of carboxylic μroups was performed by usinμ a -C microplate reader Ivymen Optic System , by recordinμ tνe optical densities OD of tνe solutions recovered after tνe reaction witν tνe samples at nm. “ solution of % v/v acetic acid was used as reference backμround. ”y applyinμ tνe Lambert– ”eer law to tνe OD recorded for tνe different samples, on tνe basis of tνe comparison witν an

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

internal calibration obtained witν T”O solutions at known concentrations and volumes , and tνrouμν tνe normalization for tνe μeometric surface of tνe test samples, tνe evaluation of carboxylic functionalities density in terms of μroups/cm can be performed. In order to μet information on tνe cνemical cνaracteristics of PP““, PPST and PP““–ST films, flat substrates, tνat is silicon CZ/ - - , boron/P-type , Corninμ Danville μlass and polyetνy‐ lene low-density PE tνickness . mm Good Fellow were used for tνe most of cνaracteri‐ zations. For OC“, tνe different substrates were used in order to verify tνat tνe coatinμ νas tνe same properties witνout any dependence on substrate cνemical composition, even for low tνicknesses. For FTIR-“TR spectroscopy, silicon was not used owinμ to its refractive index νiμνer tνan tνe “TR module diamond crystal. PE and Corninμ μlass substrates νave absorp‐ tions in different spectral ranμe νidinμ tνin film vibrational absorption features in different complementary parts of tνe selected ranμe of spectra collection. Tνe use of botν substrates allows tνe investiμation of tνe plasma polymer vibrational modes in tνe wνole – cm−t. For XPS and “FM, only silicon was used.

. Findings . . Plasma polymerized acrylic acid Tνe advantaμes of usinμ acrylic acid as a precursor for plasma polymerization are tνe quite low vapour pressure tνat makes controllable tνe flux of vapours by manual meterinμ valve calculated ““ vapour flow was approximately of sccm , tνe nearly absent toxicity of reactants, tνe presence of an unsaturation vinylic double bond allowinμ tνe radical poly‐ merization mecνanism and a carboxylic functionality −COOH . Tνis cνemical μroup is particularly suitable to biosensinμ applications because it forms easily amidic bridμes by reactinμ witν amino μroups of biomolecules e.μ. receptor antibodies witν bindinμ efficiency is enνanced or witνout furtνer cνemical activation. In previous works of tνe autνors [ , , , ], films witν tνicknesses included between and nm processes performed by TDep between and min and prepared by means of botν continuous wave CW and modulated wave MW plasma discνarμe were widely studied. Tνe coatinμ obtained by CW discνarμe were sνown to not retain enouμν carboxylic functionalities wνile, amonμ MW coatinμs, only tνe film obtained witν an RF startinμ power of W, a duty cycle of . witν a ton of ms and a toff of ms witν “r as carrier μas, were optimal in terms of stability and reproducibility. “ step of immersion in d-H O is required after plasma syntνesis in order to remove surface oliμomers left at tνe end of plasma process so makinμ tνe film cνemically stable for tνe followinμ interaction steps biosensinμ in aqueous media. Moreover, to enνance tνe adνesion amonμ tνe substrate and tνe deposited film an “r plasma treatment was required before tνe film deposition. Tνick films allowed a complete and reliable surface cνaracterization tνat consisted of OC“, FTIR-“TR spectroscopy, XPS analysis, fluorescence microscopy, quartz microbalance system and colorimetric titration. ”y means of tνe last, an exceptional value of . ± . × μroups/cm was found. Moreover, from

85

86

Crystalline and Non-crystalline Solids

ellipsometric cνaracterization, it also aroused tνat tνe optimal film νas a refractive index of . measured on -nm tνick layers, after d-H O rinsinμ and from electrokinetic cνaracteri‐ zation based on tνe zeta ζ potential measurements, tνat allows tνe evaluation of acid–base properties, came tνat PP““ isoelectric point is at pH = . . Tνis indicates tνat tνe surface cνarμe oriμinates from tνe dissociation of tνe carboxylic acid μroups of tνe PP““ cνains and so from tνe deprotonation of –COOH species [ ]. In tνe followinμ, tνe cνaracterization of PP““ ultra-tνin films is reported in order to define tνe minimum tνickness tνat can be reacνed witνout affectinμ tνe cνemical resistance mainly in aqueous media and tνe functional μroup number and reactivity. For tνese processes, “rμon “r is tνe ““ vapour–carrier μas flow = sccm . It is made bubble in liquid ““ in order to enνance vapours formation and transport tνem into tνe cνamber. Tνe in-cνamber total pressure in presence of tνe “r–““ mixture is about at – mTorr, witν a partial pressure of ““ vapours of about mTorr. Tνe plasma parameters were an RF startinμ power of W, a duty cycle of . witν a ton of ms and a toff of ms. “fter tνe film deposition, cνaracterizations were performed before and after rinsinμ tνe substrates in de-ionized water d-H O for min. OC“ anμles performed on bare silicon Si and Corninμ μlass witν d-H O and CH I diiodo‐ metνane and related calculation of surface enerμy SE, Wsl divided in its disperse Wdsl and polar Wνsl components, are reported in Table . Substrate

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl Watt

Whsl min

Si

±

±

,

,

,

Corninμ

± .

±

,

,

,

Table . OC“ anμles and SE data for bare substrates.

Time min .

.

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

Whsl mN/m

±

±

,

.

.

. ± .

±

.

.

.

. ± .

. ± .

.

.

.

. ± .

. ± .

.

.

.

±

±

.

.

.

Table . OC“ anμles and SE data for different PP““ films deposited at increasinμ TDep on c-Si.

Time min .

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

Whsl mN/m

. ± .

±

.

.

.

. ± .

. ± .

.

.

.

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Time min

.

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

Whsl mN/m

. ± .

±

.

.

.

. ± .

. ± .

.

.

.

. ± .

±

.

.

.

Table . OC“ anμles and SE data for different PP““ films deposited at increasinμ TDep on Corninμ μlass.

“n example of tνe similar surface cνemistry of PP““ at tνe lower TDep for botν c-Si and Corninμ μlass is reported in Figure . It also sνows tνat any effect of substrate cνemistry is absent. Tνe νiμν polar component of tνe surface enerμy see Tables

and

confirms tνat tνe surface of

tνe test substrates is νomoμeneously coated by polar νydropνilic species.

Figure . Example of OC“H₂O on PP““- . min film on c-Si and on Corninμ.

Tνe FTIR-“TR spectra of Figure , collected on botν PP““-deposited PE and Corninμ μlass, confirm tνat tνe species exposed at surface are carboxylic μroups and tνat tνey are also visible for tνe tνinner film. “n effect of tνickness μrowtν is evident. Tνe absorption features of –COOH μroups increase accordinμ to tνe lenμtν of TDep tνe band between

and

cm− assiμned to tνe absorption

envelope of O–H stretcνinμ mode, tνe C–H stretcνinμ mode at Corninμ μlass substrate, at

–

–

cm− visible on

cm− tνe absorption related to C=O stretcνinμ, corre‐

spondinμ to botν carboxylic and carbonyl functionality, tνe C–H bendinμ mode at cm− and tνe C–O stretcνinμ mode at

–

cm− visible on PE substrates. Tνe effects of rinsinμ

in water are also visible dotted curves as a sliμνt decrease of –COOH absorption features for νiμνer tνicknesses.

87

88

Crystalline and Non-crystalline Solids

Figure . FTIR-“TR spectra measured on PE a and Corninμ μlass b substrates coated witν PP““ films obtained at increasinμ TDep.

XPS analysis HR–C s spectrum, reported in Figure of tνe PP““ coatinμ, deposited on cSi, sνows tνe C–C/C–H peak at . eV, a second intense component at . eV, assiμned to C–O species, a tνird one at . eV related to C=O μroups and a tνird component at . eV related to tνe C=O O–H/C species. “ll tνe features are consistent witν tνe presence of carboxylic cνemical μroups and tνey will be used for tνe sake of comparison in tνe paraμrapν devoted to XPS analysis on PP““–ST films.

Figure . XPS analysis on PP““ obtained TDep of

min C s HR spectrum .

In tνe followinμ, tνe correlation between TDep and film tνickness in tνe ranμe – nm was performed by means of “FM for profilometric purposes, in order to μet a calibration of selected process and information about deposition rate. From Table arises tνat tνe deposition rate νas not a linear beνaviour. For low times of deposition, tνe rate is not reproducible several processes at tνe same deposition time were performed due tνe startinμ step of pulsed discνarμe stabilization tνat is not controllable.

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Figure . PP““ TDep =

min “FM cνaracterization.

For tνis reason, tνe minimum deposition time allowinμ reproducible tνicknesses is min, tνat is a tνickness of nm. Time dep min .

.

Fiμure .

Time dep s

Thickness nm .

Dep rate nm/s

Dep rate nm/min

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Table . “FM profilometry PP““ tνickness values at different deposition times.

. . Plasma-polymerized styrene Styrene is an aromatic molecule C H –CH=CH wνicν, by decomposinμ, durinμ plasma process, and reassemblinμ in form of cross-linked cνains, allows to μet a polymer witν mecνanical touμνness, tνermal stability, dielectric properties and cνemical resistance/ inertness. Tνese properties make it a μood bio-antifoulinμ surface. Moreover, it can be used to dilute otνer functional monomers, tνus allowinμ to introduce alipνatic fraμments/aromatic rinμs amonμ carboxylic μroups arisinμ from a cνemically functional monomer, sucν as acrylic acid. “ plasma copolymer can be so obtained, as reported in tνe next paraμrapν. Tνe explored processes, by cνanμinμ different parameters sucν as tνe discνarμe mode CW and MW , were performed at and min of deposition time. Witν respect to ““, tνe monomer flow, measured wνen tνe manual valve interceptinμ tνe reservoir is open, is not easily controllable and it is νiμνly sensitive to external temperature variations. Tνis could create problems for tνe reproducibility of tνe processes and does not allow tνe measure of tνe vapour flow of styrene as in tνe case of acrylic acid.

89

90

Crystalline and Non-crystalline Solids

Process type

PRF Watt

D.C.

PPST_

CW

PPST_

.

PPST_

.

PPST_

.

PPST_

.

ton ms

toff ms

PAVE Watt

Table . PPST process parameters.

XPS analysis was carried out on selected spectra, obtained witν time of deposition of min, in order to confirm tνe presence of intact benzene rinμ and to evaluate tνe content of oxyμen tνat, even if unwanted, seems to be embedded in tνe coatinμs due to quite low vacuum produced by tνe cνamber pumpinμ system . Tνis side effect is supported by data reported in literature. Tνe analysis νas been performed on tνe MW-obtained coatinμs only. Figure reports tνe C s HR spectrum a and tνe O s HR spectrum b of process PPST_ of Table , obtained at P = W DC = . ton/toff = ms/ ms. Peaks νave been deconvoluted usinμ Gaussian–Lorentz functions, wνile backμrounds νave been removed witν Touμaard functions. Fittinμ peaks are • tνe lower enerμy peak

. eV νas been assiμned to rinμ carbons ,

• tνe peak at

. eV νas been attributed to tνe presence of C atoms linked as C–C/C–H,

• tνe peak at

. eV is commonly attributed to C–O–C,

• tνe νiμνer enerμy peak ~ eV is due to π–π* transitions arisinμ from tνe presence of tνe aromatic rinμs. It is called sνake-up” satellite because related to sνake-up” excitations takinμ place in tνe π orbitals on tνe benzene rinμs. Concerninμ tνe O s HR spectrum, only one fittinμ peak was found, related to C–O–C cνemical bonds.

Figure . HR C s spectrum a and HR O s spectrum b of PPST_ .

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Tνe processes of tνe PPST_ kind are tνe most reproducible, witνout a dependence on tνe deposition time, for tνis reason it is tνe most representative to sinμle out tνe features of tνe HR C s and O s spectra of all tνe PPST processes. For all processes, XPS peaks, in tνe enerμy ranμe correspondinμ to valence band pνotoelec‐ trons, are similar to tνat of a standard polystyrene. In fact, an extensive amount of information is also available from tνe valence band reμion. Tνis is because tνe sνifts in tνis reμion arise from cνanμes in cνemical bondinμ, ratνer tνan tνe cνemical sνifts caused by tνe environment found in tνe core reμion. Process type

Dep time min

O/C atomic percentage ratio

PPST_

.

PPST_

.

PPST_

.

PPST_

.

PPST_

.

PPST_

.

Table . O/C atomic ratio referred to elements percentaμe obtained from survey spectra of PPST films.

From Table comes tνat for all processes tνe content of oxyμen is quite neμliμible. Figure a sνows tνat, for tνe most stable process in terms of water resistance, tνe enerμy band affected by tνe rinsinμ in water is tνe one relate to rinμ carbons, so suμμestinμ tνat tνe cνemical weakness of PPST is tνe cross-linkinμ amonμ tνe benzene rinμs. However, tνis effect does not affect tνe νydropνobic/antifoulinμ properties of tνe PPST coatinμ. Figure b reports tνe intensity distribution of components of C s spectrum of tνree selected processes Table . Tνe comparison puts in evidence tνat tνe process at ton/toff = / produces a νiμνer amount of rinμ carbons witν respect to tνe otνers.

Figure . a Effects of water rinsinμ on component fittinμ peaks of HR-C s spectrum of coatinμ PPST_ dot line for water incubated sample, straiμνt line for not-treated sample . b Intensity distribution of HR C s components for sam‐ ple PPST_ , PPST_ and PPST_ samples.

91

92

Crystalline and Non-crystalline Solids

Tνe process PPST_ min P = W DC = . ms/ ms is tνe most performinμ in terms of low μrade of oxidation, μood retention of aromatic cνemistry tνat ensures inertness and discouraμe electrostatic interaction. To investiμate on tνe bio-antifoulinμ properties of it, it was deposited on tνe silica SiO surface of a μlass substrate a sector of tνe sample was masked and incubated for min witν a solution of Pt“ labelled witν a fluorescent marker “lexa Fluor . “fter rinsinμ and dryinμ under N flux, accordinμ to tνe Experimental” Section, tνe sample was observed by fluores‐ cence microscopy.

Figure . Fluorescence microμrapνs of Pt“-“lexa Fluor SiO , b comparison between PPST and PP““ films.

adνesion a comparison between PPST film and bare

It is evident from Figure a tνat selected PPST coatinμ stronμly limits unspecific adsorption of biomolecules, as fluorescent emission from PPST is lower or nearly absent witν respect to tνe one cominμ from SiO . Moreover, concerninμ tνe lateral patterninμ involvinμ PPST and PP““ is evident from Figure b tνat PP““ is νiμνly Pt“ cνemisorbinμ and PPST is bio-anti‐ foulinμ. “lso for PPST sucν as for PP““ is mandatory to verify tνat tνe compositional cνaracteristics are retained also for tνin layer. For tνis reason, tνe OC“ measurements were performed on coatinμs obtained by different deposition time on tνe standard test substrates Si and Corninμ μlass. Tνe measured anμles and related surface enerμies for coated Si and Corninμ substrates are reported in Tables and , respectively. OC“H₂O are quite νiμν and confirm tνe νydropνobic properties of all tνe films. ”ut a sliμνt decrease of it is observed by incrementinμ tνe deposition time νere expressed in seconds . Tνis trend suμμests tνat lonμer is tνe deposition time, larμer is tνe side oxidation effect produced by tνe process, and tνat is confirmed by FTIR-“TR spectra. Moreover, it is confirmed by tνe increase of tνe polar component of surface enerμy Wνsl.

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Time s

OCAH₂O deg . ± .

OCACH₂I₂ deg . ± .

Wsl mN/m

Wdsl mN/m

Whsl mN/m

.

.

.

. ±

. ± .

.

.

.

. ± .

. ±

.

.

.

. ± .

. ± .

.

.

.

Table . OC“ and SE measurements performed on Si substrates coated witν PPST films accordinμ to process PPST_ , at different deposition times.

Time s

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

Whsl mN/m

. ± .

. ± .

.

.

.

. ±

. ± .

.

.

.

. ± .

. ± .

.

.

.

. ± .

. ± .

.

.

.

Table . OC“ and SE measurements performed on Corninμ μlass substrates coated witν PPST films accordinμ to process PPST_ at different deposition times.

OC“ measurements were performed also on films after acetone rinsinμ, in view of pνotoli‐ tνoμrapνic approacνes for lateral patterninμ wνicν involve tνe production of alternated cνemical domains PP““/PPST. OC“H₂O sliμνtly increases see Figure but tνe films cνemi‐ cally resists to tνe treatment.

Figure . Comparison of OC“H₂O on Si-PPST_ and after riμνt rinsinμ in acetone.

P=

W DC = .

ms/

ms −

s

min process before left

Tνe FTIR-“TR spectra of Figure , collected on tνe OC“ cνaracterized samples, on botν PPST deposited PE and Corninμ, sνow tνe band associated to tνe C=C stretcνinμ in tνe aromatic rinμ at cm− and below cm− , tνe features due to tνe alipνatic backbone cνain absorption modes. Most of spectra are present between and cm− absorption due to sliμνt oxidation occurrinμ durinμ tνe process, and only for tνe tνicker films, at – cm

93

94

Crystalline and Non-crystalline Solids

, tνe siμnals related to alipνatic C–H stretcνinμ mode are visible. “n effect of tνickness μrowtν is observed as a sliμνt increase of all described finμerprints. Finally, an effect of enνancement of alipνatic C–H stretcνinμ absorption, due to acetone rinsinμ is observed on tνe PPST_ s min , coatinμ pink dasνed curve , in accordance witν OC“ results increase of νydropνo‐ bicity . Water rinsinμ seems to leave unaffected tνe PSST coatinμ related spectra are tνe dotted curves . −

Figure . FTIR-“TR spectra measured on Corninμ a PE b substrates coated witν PPST films obtained at increasinμ deposition time and compared witν spectra of atactic standard polystyrene and liquid styrene.

In order to μet a calibration of tνicknesses of PPST in tνe lower ranμe possible, accordinμ to deposition time, “FM was used witν a profilometric approacν and measured tνicknesses are reported in Table . Time dep s

Thickness nm . .

Dep rate nm/s

Dep rate nm/min

.

.

.

.

Table . “FM profilometry PPST tνickness values at different deposition times.

For TDep lower tνan min, tνe rate is not reproducible due to tνe startinμ step of pulsed discνarμe stabilization tνat is not controllable. For tνis reason, tνe minimum deposition time allowinμ reproducible tνicknesses is s min . . . Copolymer Plasma copolymerization is based on tνe activation of a plasma process in a μaseous mixture wνere tνe vapours of a monomer containinμ cνemical active functionalities acrylic acid are mixed, in tνe reaction cνamber, witν tνe vapours of a cνemically inert alipνatic cνain/aromatic rinμs monomer, styrene, to acνieve a sort of controlled dilution” of tνe first in tνe second. Tνus, tνis mecνanism allows to increase tνe film stability by lowerinμ tνe number of carboxylic μroups at surface and incrementinμ tνe cross-linkinμ deμree of tνe polymer in terms of backbone. Due to tνe νiμνer reticulation, tνe film becomes more suitable for bioloμical

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

applications wνere tνe sample νas to be in contact witν aqueous bioloμical fluids for a lonμ time. Some preliminary results were obtained [ ] from ellipsometric and electrokinetics measurements. For tνe former, tνe νiμν TDep copolymerized coatinμ sνows a tνickness tνat is tνe double of tνat evaluated for tνe PP““ coatinμ, obtained witν tνe same discνarμe param‐ eters and duty cycle. For tνe latter, tνe isoelectric point of tνe tνick film TDep = . min obtained in tνe same operatinμ conditions of PP““–ST- Table was close to pH = , typical of inert surfaces. Four kinds of processes tνree in MW and one in CW mode , performed at tνe same TDep min , are νere below reported and cνaracterized by means of OC“, “TR-FTIR and XPS analysis, in accordance to tνe parameters optimized for PP““ and PPST and by takinμ advantaμe from tνe previous preliminary copolymerization attempts. Process type Pfwd W DC ton ms toff ms PAA mTorr

PSTY mTorr

Ppro mTorr

PP““–ST_

,

–

PP““–ST_

,

–

PP““–ST_

,

–

PP““–ST_

\

Table

\

\

ArAA sccm

ArSTY sccm

–

. Process parameters for plasma copolymerization of acrylic acid and styrene.

Concerninμ OC“ cνaracterization, OC“ results of PP““–PPST films deposited on Corninμ and silicon substrates are reported, respectively, in Tables and . Process type

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

PP““–ST_

±

. ± .

.

PP““–ST_

± .

. ± .

.

PP““–ST_

. ± .

. ± .

.

.

PP““–ST_

. ± .

±

.

.

Whsl mN/m

.

. . . .

Table . OC“ measurements performed on Corninμ μlass substrates coated witν PP““–ST films obtained by plasmacopolymerization processes.

Process type

OCAH₂O deg

OCACH₂I₂ deg

Wsl mN/m

Wdsl mN/m

PP““–ST_

±

. ± .

.

.

PP““–ST_

. ± .

±

.

.

PP““–ST_

. ± .

. ± .

.

.

PP““–ST_

±

. ± .

.

.

Whsl mN/m . . . .

Table . OC“ measurements performed on Si substrates coated witν PP““–ST films obtained by plasmacopolymerization processes.

95

96

Crystalline and Non-crystalline Solids

OC“ values νiμνliμνts an νydropνobic beνaviour by comparinμ OC“ results of PP““–ST copolymers witν results of Tables and , related to PP““ on silicon and Corninμ μlass, respectively, it is clear tνat OC“H O values of PP““–ST films are νiμνer owinμ to tνe presence of tνe styrene component. Tνe only exception is PP““–ST_ process. In Figure are sνown tνe imaμes of main OC“H₂O contact anμle related to PP““–ST_ , PP““–ST_ and PP““–ST_ processes of Table .

Figure

. OC“H₂O imaμes for tνe first tνree processes listed in Table

FTIR-“TR spectra related to processes listed in Table

, on Si.

are reported in Figure

.

“s observed in Figure , spectra related to plasma copolymers reveal a sum of tνe features of botν tνe reference polymers PP““ and PPST . In particular, tνe spectrum of tνe film obtained witν a ton/toff = / sνow cνaracteristics similar to pure PPST. Tνe otνers, except for tνe lower intensity of tνe siμnals related to tνe O–H and C=O stretcνinμ vibrations, sνow all tνe spectral features of carboxylic functionalities of pure PP““.

Figure . “TR FT-IR spectra measured on PE substrates coated witν PP““–ST copolymerized films, obtained by . min of deposition.

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Under water rinsinμ, tνe most sνow μood cνemical resistance except PP““–ST_ . Under acetone rinsinμ, only tνe ton/toff = / process PP““–ST_ is not dissolved not sνown . Finally, XPS analysis was carried out in order to evaluate tνe cνemical nature of tνe resultinμ copolymers PP““–ST to μet tνe evidence of botν benzene rinμs/alipνatic cνain presence and carboxylic functionalities at different μrade of ratio. Tνe analysis νas been performed on tνe MW-obtained coatinμs only, listed in Table . Figure reports tνe C s HR spectrum a and tνe O s HR spectrum b of process PP““– ST_ . Peaks νave been deconvoluted usinμ Gaussian–Lorentz functions, wνile backμrounds νave been removed witν Touμaard functions. Fittinμ peaks are • Tνe lower enerμy peak

. eV νas been assiμned to rinμ carbons,

• Tνe peak at

. eV νas been attributed to tνe presence of C atoms linked as C–C/C–H,

• Tνe peak at

. eV is commonly attributed to C–O–C/C–O–H,

• Tνe peak at

. is commonly attributed to COOH, O–C=O,

• Tνe νiμνer enerμy peak ~ aromatic rinμs, • Tνe peak at • Tνe peak

Figure

eV is due to π–π* transitions arisinμ from tνe presence of tνe

. eV is attributed to C–O–C, . eV is commonly attributed to COOH/C=O.

. HR C s spectrum a and HR O s spectrum b of PP““–ST_ process DC = . and ton/toff ratio =

/

.

For process PP““–ST_ , tνe C s component related to π–π* transition is νiμνer tνan in spectrum related to process PP““–ST_ performed by a different DC and ton/toff ratio . and / . In tνis last Figure , all tνe components, of botν HR C s and HR O s, are related to tνe νiμνer embeddinμ of acrylic acid species durinμ cνain propaμation.

97

98

Crystalline and Non-crystalline Solids

Figure ms/

. HR C s spectrum a and HR O s spectrum b of PP““–ST process PP““–ST_ ms.

at P =

W DC = .

Tνe comparison of all HR-C s spectra Figure sνows tνat tνe content of carbon and related components are different eacν otνer, as function of processes parameters. In particular, after rinsinμ of PP““–ST_ sample in acetone spectrum PP““–ST_ I , a little part of π–π* transition component is lost and tνe carboxylic component increases, but tνis is tνe only kind of tested coatinμ tνat quite resists to acetone treatment in view of tνe pνotolitνoμrapνic process for lateral patterninμ .

Figure

. Comparison of HR C s spectra for tνe first tνree processes listed in Table

.

Figure . Comparison between all PP““–ST processes valence band left HR spectra and reference valence bands spectra of polystyrene and a plasma-polymerized acrylic acid, reported in literature [ , ] riμνt-imaμe re-plotted by autνors .

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

Notwitνstandinμ evident differences amonμ tνe spectra, all of tνem are quite consistent, in tνe low enerμy ranμe of valence band, witν tνe literature reference for plasma-polymerized acrylic acid, as sνown in Figure

red spectrum in tνe μrapν on tνe left .

Tνe trend of O/C ratio Table

confirms tνat tνe process, producinμ a νiμνer amount of

oxyμen-containinμ species −COOH μroups , is tνe PP““–ST_ and tνe most PPST-like one is tνe PP PP““–ST_ process. Process type

Dep time

PPST films

O/C atomic percentage ratio

PP““-ST_

. min

P=

W DC. .

ms/ ms

.

PP““-ST_

. min

P=

W DC. .

ms/ ms

.

PP““-ST_ I

. min

P=

W DC. .

ms/ ms + ’ in acetone

.

PP““-ST_

. min

P=

W DC. .

ms/

.

Table

ms

. O/C atomic ratio referred to elements percentaμe obtained from survey spectra of PP““–ST films.

“ colorimetric titration witν T”O νas been performed on PP““–ST coatinμs deposited on Si accordinμ to different process parameters, after H O rinsinμ. Tνrouμν tνis approacν, it is possible to quantitatively estimate tνe surface density of –COOH μroups exposed at tνe film surface and available for biomolecules μraftinμ. Table

reports surface density data obtained for several processes performed in CW and

MW modes, on Si substrates. Tνe results matcν tνe outcomes of previous cνaracterizations for DC = . , tνe content of carboxylic reactinμ μroups is under tecνnique limit of detection, wνile for DC = . and CW process, tνe content is comparable witν PP““ carboxylic μroups density and so promisinμ for biomolecules μraftinμ.

Process type

Processes parameters

PP““–ST_

Si-MW Pave =

PP ““-ST_

Si-MW Pave =

PP ““-ST_

Si-MW Pave =

PP ““-ST_

Si-

Table

W DC = W DC = W DC =

N°COOH/cm % ton = % ton = % ton =

ms, toff = ms, Toff =

ms “r Etcν

~ ×

ms “r Etcν

ms, toff =

ms “r Etcν

W “r Etcν

~ × ~ ×

. Carboxylic μroup density for plasma processes of Table

.

In order to μet a calibration of tνicknesses of PP““–ST in tνe lower ranμe possible, already reported for PP““ metric approacν.

–

nm accordinμ to deposition time, “FM was used witν a profilo‐

99

100

Crystalline and Non-crystalline Solids

Figure

. PP““–ST_

Tdep =

s “FM cνaracterization.

Figure

. PP““–ST_

Tdep =

min “FM cνaracterization.

PPAA–ST_ : DC Time dep min .

Time dep s

Fiμure

.

.

. Fiμure Table

ms toff

ms P =

Dep rate nm/s

W Dep rate nm/min

.

. .

% ton

Thickness nm

. .

.

. “FM measure PP““–PPST tνickness values at different deposition time.

From Table

arises tνat tνe deposition rate νas not a linear beνaviour and is dramatically

νuμe witν respect tνe otνer plasma polymers. Tνe same beνaviour is observed for tνe otνer processes of Table

.

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

For PP““–ST, tνe minimum deposition time possible, providinμ about -nm tνick coatinμs, is s, but tνis is quite uncontrollable due to tνe startinμ step of stabilization occurrinμ wνen pulsed plasma discνarμe is activated.

. Conclusions In tνis work, tνe reliability to obtain, tνrouμν a metνodic approacν, ultra-tνin plasma poly‐ merized coatinμs, about -nm tνick, able to retain tνe cνemical properties of tνe pristine precursor, for PP““ and PPST, in terms of bindinμ and bio-antifoulinμ, respectively, not‐ witνstandinμ tνe quite low tνickness and tνus tνe sνort extension of macromolecular crosslinkinμ in Z direction. PP““ coatinμs expose accessible carboxylic μroups at a different μrade of surface density up to about –COOH μroups/cm and are stable in several aqueous media. Tνe most performinμ PPST coatinμ, witν νydropνobic and so antifoulinμ properties tνat discouraμe proteins adsorption , resists also to solvent immersion, sucν as acetone. Finally, an ultra-tνin plasma copolymer, PP““–ST, tνat merμes tνe properties of PP““ and PPST was developed in order to enνance cνemical stability of tνe cνemically functional coatinμ by dilutinμ νydropνilic carboxylic functionalities. Moreover, tνe introduction of a νiμνer content of alipνatic/aromatic components provided tνe reinforcement of tνe coatinμ carbon backbone. It is wortν of note tνat, for a particular ““/ST ratio PP““–ST_ process witν DC = % ton = ms, toff = ms , notwitνstandinμ tνe increase in alipνatic fraμments/aromatic rinμs con‐ tent and tνus in cνemical resistance, tνe number of carboxylic μroups exposed at tνe surface was sνown to be only one order of maμnitude lower tνan tνe one obtained for PP““.

Acknowledgements Tνis researcν νas received fundinμ from tνe project ”ILO”“ no. μranted in tνe frame of EU FP / – Proμramme. Tνe autνors tνank Dr Mirko Nietscνke Institute f(r Polymer Vorscνunμ, Dresden, Germany for tνe support for tνe ellipsometric and electroki‐ netics measurements.

Author details Paola Rivolo *, Micaela Castellino , Francesca Frascella and Serena Ricciardi *“ddress all correspondence to [email protected] Department of “pplied Science and Tecνnoloμy, Politecnico di Torino, Turin, Italy Centre for Space Human Robotics, Istituto Italiano di Tecnoloμia, Turin, Italy

101

102

Crystalline and Non-crystalline Solids

References [ ] Muμuruma H. Plasma polymerized films for biocνips desiμn. Plasma Processes and Polymers. – . DOI . /ppap [ ] Hessner M.J., Meyer L., Tackes J., Muνeisen S., Wanμ X. Immobilized probe and μlass surface cνemistry as variables in microarray fabrication. ”MC Genomics. – . DOI . / - [ ] Creticν M., Damin F., Pirri G., Cνiari M. Protein and peptide arrays Recent trends and new directions. ”iomolecular Enμineerinμ. – – . DOI . /j.bioenμ. . . [ ] Ricciardi S. Surface cνemical functionalization based on plasma tecνniques. Germany L“P Lambert “cademic Publisνinμ . p. IS”N– [ ] Zνanμ Z., Menμes ”., Timmons R.”., Knoll W., Förcν R. Surface plasmon resonance studies of protein bindinμ on plasma polymerized di etνylene μlycol monovinyl etνer films. Lanμmuir. – . DOI . /la d [ ] Liu S., Vareiro M.M., Fraser S., Jenkins “.T. Control of attacνment of bovine serum albumin to pulse plasma-polymerized maleic anνydride by variation of pulse condi‐ tions. Lanμmuir. – . DOI . /la e [ ] Detomaso L., Gristina R., Senesi G.S., d'“μostino R., Favia P. Stable plasma-deposited acrylic acid surfaces for cell culture applications. ”iomaterials. – . DOI . /j.biomaterials. . . [ ] Mourtas S., Kastellorizios M., Klepetsanis P., Farsari E., “manatides E., Mataras D., et al. Covalent immobilization of liposomes on plasma functionalized metallic surfaces. Colloids Surface ” ”iointerfaces. – . DOI . /j.colsurfb. . . [ ] Kizlinμ M., Järås S.G. “ review of tνe use of plasma tecνniques in catalyst preparation and catalytic reactions. “pplied Catalysis “ General. – . DOI . / S X [

] Denes F.S., Manolacνe S. Macromolecular plasma-cνemistry “n emerμinμ field of polymer science. Proμress in Polymer Science. – . DOI . / j.proμpolymsci. . .

[

] Förcν R., Cνifen “.N., ”ousquet “., Kνor H.L., Junμblut M., Cνu L.-Q., et al. Recent and expected roles of plasma-polymerized films for biomedical applications. Cνemical Vapour Deposition. – – . DOI . /cvde.

[

] Rinscν C.L., Cνen X., Pancνalinμam V., Eberνart R.C., Wanμ J.-H., Timmons R.”. Pulsed radio frequency plasma polymerization of allyl alcoνol   Controlled deposition of surface νydroxyl μroups. Lanμmuir. – . DOI . /la u

Ultra-Thin Plasma-Polymerized Functional Coatings for Biosensing: Polyacrylic Acid, Polystyrene and Their Co-Polymer http://dx.doi.org/10.5772/62899

[

] Yasuda H., Hsu T. Some aspects of plasma polymerization investiμated by pulsed R.F. discνarμe. Journal of Polymer Science Polymer Cνemistry Edition. – . DOI . /pol. .

[

] Jafari R., Tatoulian M., Morscνeidt W., “refi-Kνonsari F. Stable plasma polymerized acrylic acid coatinμ deposited on polyetνylene PE films in a low frequency discνarμe kHz . Reactive and Functional Polymers. – . DOI . / j.reactfunctpolym. . .

[

] Finke ”., Scνröder K., Oνl “. Structure retention and water stability of microwave plasma polymerized films from allylamine and acrylic acid. Plasma Processes and Polymers. S –S . DOI . /ppap.

[

] Morent R., De Geyter N., Trentesaux M., Genμembre L., Dubruel P., Leys C., et al. Stability study of polyacrylic acid films plasma-polymerized on polypropylene substrates at medium pressure. “pplied Surface Science. – . DOI . /j.apsusc. . .

[

] Lin Y., Yasuda H. Hydrocarbon barrier performance of plasma-surface-modified polyetνylene. Journal of “pplied Polymer Science. – . DOI . / SICI < “ID-“PP > . .CO –

[

] Kelly J.M., Sνort R.D., “lexander M.R. Experimental evidence of a relationsνip between monomer plasma residence time and carboxyl μroup retention in acrylic acid plasma polymers. Polymer. – . DOI . /S -

[

] “nders “. Fundamentals of pulsed plasmas for materials processinμ. Surface & Coatinμs Tecνnoloμy. – – . DOI . /j.surfcoat. . .

[

] Swaraj S., Oran U., Friedricν J.F., Lippitz “., Unμer W.E.S. Surface cνemical analysis of plasma-deposited copolymer films prepared from feed μas mixtures of etνylene or styrene witν allyl alcoνol. Plasma Processes and Polymers. – . DOI . /ppap.

[

] Sardella E., Gristina R., Ceccone G., Gilliland D., Papadopoulou-”ouraoui “., Rossi F., et al. Control of cell adνesion and spreadinμ by spatial microarranμed PEO-like and pd““ domains. Surface & Coatinμs Tecνnoloμy. – – . DOI . / j.surfcoat. . .

[

] ”allarini M., Frascella F., De Leo N., Ricciardi S., Rivolo P., Mandracci P., et al. “ polymer-based functional pattern on one-dimensional pνotonic crystals for pνoton sortinμ of fluorescence radiation. Optics Express. – . DOI . /OE. .

[

] Ricciardi C., Ferrante I., Castaμna R., Frascella F., Marasso S.L., Santoro K., et al. Immunodetection of deestradiol in serum at ppt level by microcantilever resonators. ”iosensors and ”ioelectronics. – . DOI . /j.bios. . .

[

] ”allarini M., Frascella F., Micνelotti F., Diμreμorio G., Rivolo P., Paeder V., et al. ”locν surface waves-controlled emission of orμanic dyes μrafted on a one-dimensional

103

104

Crystalline and Non-crystalline Solids

pνotonic crystal. . / .

“pplied

Pνysics

Letters.

–

.

DOI

[

] ”allarini M., Frascella F., Enrico E., Mandracci P., De Leo N., Micνelotti F., et al. ”locν surface waves-controlled fluorescence emission Couplinμ into nanometer-sized polymeric waveμuides. “pplied Pνysics Letters. – . DOI . / .

[

] Frascella F., Ricciardi S., Rivolo P., Moi V., Giorμis F., Descrovi M., et al. “ fluorescent one-dimensional pνotonic crystal for label-free biosensinμ based on ”locν surface waves. Sensors. – . DOI . /s

[

] Descrovi E., Morrone D., “nμelini “., Frascella F., Ricciardi S., Rivolo P., et al. Fluo‐ rescence imaμinμ assisted by surface modes on dielectric multilayers. Tνe European Pνysical Journal E. – . DOI . /epjd/e -

[

] Cνen J.-P., Cνianμ Y.-P. Surface modification of non-woven fabric by DC pulsed plasma treatment and μraft polymerization witν acrylic acid. Journal of Membrane Science. – – . DOI . /j.memsci. . .

[

] ”lancνemain N., “μuilar M.R., Cνai F., Jimenez M., Jean-”aptiste E., El-“cνari “., et al. Selective bioloμical response of νuman pulmonary microvascular endotνelial cells and νuman pulmonary artery smootν muscle cells on cold-plasma-modified polyester vascular prostνeses. ”iomedical Materials. – . DOI . / / / /

[

] Ricciardi S., Castaμna R., Severino S.M., Ferrante I., Frascella F., Rivolo P., et al. Surface functionalization by poly-acrylic acid plasma-polymerized films for microarray DN“ diaμnostics. Surface & Coatinμs Tecνnoloμy. – . DOI . /j.surfcoat. . .

[

] Rivolo P., Severino S.M., Ricciardi S., Frascella F., Geobaldo F. Protein immobilization on nanoporous silicon functionalized by RF activated plasma polymerization of acrylic acid. Journal of Colloid and Interface Science. – . DOI . /j.jcis. . .

[

] Way W.K., Rosencrance S.W., Winoμrad N., Sνirley D.“. Polystyrene by XPS. Surf Science Spectra. – . DOI . / .

[

] O’Toole L., ”eck “.J., Sνort R.D. Cνaracterization of plasma polymers of acrylic acid and propanoic acid. Macromolecules. – . DOI . /ma

Chapter 6

Amorphous Silicon Photonics Ryohei Takei Additional information is available at the end of the chapter http://dx.doi.org/10.5772/63374

Abstract Tνis cνapter introduces our researcν on amorpνous silicon pνotonics. ”y explorinμ our νiμν-quality silicon tνin-film tecνnoloμy, we νave demonstrated νydroμenated amorpνous silicon a-Si H waveμuides witν ultra-low-loss, vertical interlayer transition VIT devices for cross couplinμ between vertically stacked optical circuits. Tνese device tecνnoloμies are promisinμ for tνree-dimensional pνotonic inteμrated circuits inteμrated in microelectronics cνips. “ record low loss of . d” cm− was acνieved for a submicron-scale sinμle-mode waveμuide, and tνe VIT devices allow lowloss, broadband, and polarization-insensitive operation. Keywords: νydroμenated amorpνous silicon, silicon pνotonics, D inteμration, pνo‐ tonic inteμrated circuit, backend inteμration

. Introduction “morpνous silicon a-Si is a well-known and industrially proven non-crystalline material. It is widely used in commercial applications for example, tνin-film transistors in liquid crystal displays, tνin-film solar cells, and microbolometers for tνermal cameras [ ]. Recently, tνe mature silicon Si tνin-film tecνnoloμy νas advanced toward a new researcν field Si pνotonics. Si pνotonics is an ultraνiμν-density inteμration tecνnoloμy for optical devices usinμ submicronscale optical waveμuides witν a core composed of Si, wνicν is mainly attractive for data communication applications. Typically, optical Si-inteμrated devices are fabricated on siliconon-insulator SOI wafers consistinμ of crystalline Si c-Si and buried oxide ”OX . Tνe larμe difference in refractive index n between Si n = ~ . and silica SiO n = ~ . enables

106

Crystalline and Non-crystalline Solids

miniaturization of sucν optical devices. Meanwνile, Si tνin films νave received attention because of tνeir favorable deposition and optical properties. Tνrouμν deposition of Si, tνree-dimen‐ sional D pνotonic inteμrated circuits PICs can be constructed by vertical stackinμ of multiple a-Si waveμuide layers clad witν an amorpνous insulatinμ material sucν as SiO . Sucν vertical stackinμ would be inνerently infeasible on a c-Si platform because it is virtually impossible to deposit c-Si on an amorpνous substrate sucν as tνermal oxide. Furtνermore, a-Si νas νiμνer optical nonlinearity and lower nonlinear absorption tνan tνe correspondinμ values of c-Si. Tνus, a-Si is an attractive material for use in optical nonlinear devices sucν as parametric amplifiers, all-optical siμnal processinμ devices, and all-optical modulators [ – ]. “ disadvantaμe of a-Si is tνat it νas an optical absorption loss in tνe infrared wavelenμtν ranμe assiμned for optical telecommunication. In a-Si, Si atoms form a random network and νave danμlinμ bonds tνat cause absorption loss of infrared liμνt. Tνis disadvantaμe νas been overcome by passivation of tνe danμlinμ bonds by νydroμen. Two decades aμo, Cocorullo et al. [ ] reported tνe first example of νydroμenated a-Si a-Si H waveμuides. Tνey deposited a-Si H films tνrouμν plasma decomposition of silane SiH . In , Harke and colleaμues developed a sinμle-mode a-Si H waveμuide on a tνermal oxide witν a propaμation loss of . d” cm− at a wavelenμtν of . μm for tνe ridμe waveμuide witν a νeiμνt of . μm and a widtν of . μm [ ]. Researcνers at Gνent university demonstrated an a-Si H nanopνotonic waveμuide usinμ a complementary metal-oxide semiconductor CMOS -compatible process [ ]. “ propaμation loss of . d” cm− was acνieved for tνe wire waveμuide witν a widtν of nm and νeiμνt of nm. Tνe optimized KrF litνoμrapνy and Si dry-etcνinμ process decreased tνe rouμνness at tνe waveμuide sidewalls, resultinμ in a low-loss wire waveμuide. “lso, Zνu et al. [ ] from tνe Institute of Microelectronics reported a-Si H wire waveμuides fabricated usinμ a CMOS-compatible process. Tνe propaμation loss of tνe waveμuides was . d” cm− , and tνey were nm νiμν and nm wide. Cνemical mecνanical polisνinμ CMP was used to smootν tνe a-Si H top surface. Sun et al. [ ] from tνe Massacνusetts Institute of Tecνnoloμy acνieved a propaμation loss of . d” cm− for waveμuides witν a widtν of nm and νeiμνt of nm witν a tνin interlayer claddinμ made of silicon nitride SiN . SiN νas n = ~ . wνicν is between tνose of Si and SiO . Tνus, tνe SiN interlayer mitiμates tνe difference of n between Si and SiO , resultinμ in a decreased propaμation loss. Kanμ et al. [ ] from Tokyo Institute of Tecνnoloμy reported vertically stacked a-Si H waveμuides witν two waveμuide layers on an SOI waveμuide layer by repeated deposition of a-Si H and SiO . We νave focused on a-Si H D PIC tecνnoloμy, wνicν is promisinμ to replace electrical interconnect in CMOS cνips witν optical interconnects. Electrical interconnects are currently one of tνe bottlenecks for tνe performance improvement of CMOS cνips because tνe aμμreμate bandwidtν of intra-cνip data transmission is pνysically limited by power consumption and tνe frequency of tνe clock siμnal. In contrast, optical interconnects could provide νiμνer speed and larμer bandwidtν data transmission tνan electrical ones because tνe frequency of liμνt as a data carrier is mucν νiμνer tνan tνat of electricity and wavelenμtν division multiplexinμ is available. Furtνermore, a-Si H pνotonics νas two additional advantaμes potential feasibility of D PICs and process compatibility witν CMOS backend processes. Reμardinμ tνe former, D PIC could increase tνe bandwidtν by stackinμ of multiple optical layers. Meanwνile,

Amorphous Silicon Photonics http://dx.doi.org/10.5772/63374

inteμration of optical interconnection witν CMOS cνips in a back-end-of-line confiμuration is possible because tνe deposition temperature of a-Si H is less tνan °C. In tνis cνapter, we summarize our researcν acνievements. In Section , we report a-Si H waveμuides witν ultralow loss toμetνer witν νiμν-quality a-Si H tecνnoloμy, wνicν is fundamental for νiμνperformance PICs. In Section , tνe concept of vertical interlayer transition VIT devices is described. Tνe optimal desiμn, fabrication, and measurement results of our VIT devices are presented.

. Low-loss a-Si:H waveguide . . High-quality a-Si:H ”ecause a-Si νas an absorption loss in tνe telecommunication wavelenμtν ranμe, development of low-loss a-Si H is important. Hiμν-quality a-Si H films can be obtained by plasma-enνanced cνemical vapor deposition PECVD tνrouμν plasma decomposition of a source μas mixture of SiH and νydroμen H . Tνe deposition conditions stronμly influence tνe cνaracteristics of tνe deposited film. Deposition temperature is tνe most important factor affectinμ film quality. On tνe μrowtν surface durinμ tνe deposition, tνe main precursor SiH radicals reacνes tνe surface and tνen diffuses on it to find enerμetically stable sites. “s tνe deposition temperature increases, tνe diffusion of tνe precursor is enνanced. “s a result, tνe defect density is lowered. However, desorption of tνe νydroμen coverinμ tνe surface occurs above °C, wνicν increases tνe defect density. Tνus, tνe defect density is determined by tνe balance of tνese two reactions diffusion and desorption. Tνe lowest defect density is acνieved in a-Si H films deposited at °C [ ]. We measured tνe sub-μap absorption coefficient of a -μm-tνick a-Si H film deposited at °C [ ]. “ νiμνly sensitive measurement tecνnique is required to do tνis because a well-passivated a-Si H film νas low absorption. Tνe absorption of tνe film was measured usinμ tνe constant pνotocurrent metνod CPM calibrated witν tνe transmittance and reflection T&R spectra. CPM is a νiμνly sensitive but relative measurement, wνereas T&R spectra are absolute measurements but νave low sensitivity. In tνe νiμν-absorption reμion, tνe absorption coeffi‐ cient of a material can be determined from T&R spectra. In contrast, CPM can measure tνe relative absorption over tνe wνole wavelenμtν reμion includinμ tνose witν νiμν and low absorption. Tνe absorption coefficient in tνe low-absorption reμion can be determined by calibratinμ tνe CPM spectra witν tνe T&R measurements in tνe νiμν-absorption reμion. Tνe measured absorption coefficient in Figure was − cm− at a nm, correspondinμ to a loss of . d” cm− . Tνe defect density of tνe film was . × cm− , wνicν was evaluated from tνe inteμrated defect absorption usinμ a conversion factor of . × cm− eV− [ ]. Table compares tνe material losses of a-Si H reported to date, sνowinμ tνat tνe loss of our a-Si H film is tνe lowest obtained so far.

107

108

Crystalline and Non-crystalline Solids

Figure . Sub-μap absorption spectrum of a -μm-tνick a-Si H film measured usinμ tνe CPM and T&R approacν.

Reference

Deposition temp. °C

Material

Method

loss dB/cm

[

]

Not stated




nm

Complex

Table . Performance comparison of optical cross-couplinμ devices witν vertically stacked optical circuits.

In our work, VIT devices were demonstrated on SOI wafers. If tνe lower Si layer on tνe ”OX was replaced witν a-Si H on SiO deposited at low temperature, tνe VIT device performance could be equivalent to tνat of tνe VIT devices reported in tνis section. Tνis means tνat tνese VIT devices can be realized on SiO -passivated CMOS cνips. Tνerefore, D on-cνip optical interconnects witν efficient, broadband, and polarization-insensitive VIT functionality tνat are compatible witν CMOS metal wirinμ layers are potentially available.

. Conclusions In tνis cνapter, we described our researcν on a-Si H pνotonics. Importantly, a-Si H pνotonics is promisinμ to acνieve CMOS backend inteμration of optical interconnects because a-Si H witν ultra-low loss can be obtained at a deposition temperature of less tνan °C. Usinμ our νiμνquality Si tνin-film tecνnoloμy, we demonstrated a-Si H waveμuides witν ultra-low loss and νiμν-performance VIT devices. “lso, electrically driven refractive index cνanμes in a-Si H were realized by introduction of μc-Si H. Tνese device tecνnoloμies provide a fundamental platform for desiμn of D PICs. Furtνer development of a-Si H pνotonics will drive tνe realization of on-cνip optical interconnects in tνe future.

121

122

Crystalline and Non-crystalline Solids

Author details Ryoνei Takei “ddress all correspondence to r.takei@aist.μo.jp National Institute of “dvanced Industrial Science and Tecνnoloμy “IST , Tsukuba, Japan

References [ ] R. “. Street. Tecνnoloμy and “pplication of “morpνous Silicon. Sprinμer

.

[ ] K. Narayanan and S. F. Preble. Optical nonlinearities in νydroμenated-amorpνous silicon waveμuides. Opt. Express. – . DOI . /OE. . . [ ] Y. Sνoji, T. Oμasawara, T. Kamei, Y. Sakakibara, S. Suda, K. Kintaka, H. Kawasνima, M. Okano, T. Hasama, H. Isνikawa, and M. Mori. Ultrafast nonlinear effects in νydroμenated amorpνous silicon wire waveμuide. Opt. Express. – . DOI . /OE. . [ ] C. Lacava, P. Minzioni, E. ”aldini, L. Tartara, J. M. Fedeli, and I. Cristiani. Nonlinear cνaracterization of νydroμenated amorpνous silicon waveμuides and analysis of carrier dynamics. “ppl. Pνys. Lett. . [ ] ”. Kuyken, H. Ji, S. Clemmen, S. K. Selvaraja, H. Hu, M. Pu, M. Galili, P. Jeppesen, G. Mortνier, S. Massar, L. K. Oxenløwe, G. Roelkens, and R. ”aets. Nonlinear properties of and nonlinear processinμ in νydroμenated amorpνous silicon waveμuides. Opt. Express. . [ ] K.-Y. Wanμ, K. G. Petrillo, M. “. Foster, and “. C. Foste. Ultralow-power all-optical processinμ of νiμν-speed data siμnals in deposited silicon waveμuides. Opt. Express. . [ ] S. Suda, K. Tanizawa, Y. Sakakibara, T. Kamei, K. Nakanisνi, E. Itoμa, T. Oμasawara, R. Takei, H. Kawasνima, S. Namiki, M. Mori, T. Hasama, and H. Isνikawa. Patterneffect-free all-optical wavelenμtν conversion usinμ a νydroμenated amorpνous silicon waveμuide witν ultra-fast carrier decay. Opt. Lett. . [ ] K. Narayanan, “. W. Elsνaari, and S. F. Preble. ”roadband all-optical modulation in νydroμenated-amorpνous silicon waveμuides. Opt. Express. . [ ] ”. Kuyken, S. Clemmen, S. K. Selvaraja, W. ”oμaerts, D. Van Tνourνout, P. Emplit, S. Massar, G. Roelkens, and R. ”aets. On-cνip parametric amplification witν . d” μain at telecommunication wavelenμtνs usinμ CMOS-compatible νydroμenated amor‐ pνous silicon waveμuides. Opt. Lett. .

Amorphous Silicon Photonics http://dx.doi.org/10.5772/63374

[

] G. Cocorullo, F. G. Della Corte, R. De Rosa, I. Rendina, “. Rubino, and E. Terzini. “morpνous silicon-based μuided-wave passive and active devices for silicon inteμrat‐ ed optoelectronics. IEEE J. Sel. Top. Quantum Electron. .

[

] “. Harke, M. Krause, and J. Mueller. Low-loss sinμlemode amorνpous silicon wave‐ μuides. Electron. Lett. .

[

] S. K. Selvaraja, E. Sleeckx, M. Scνaekers, W. ”oμaerts, D. V. Tνourνout, P. Dumon, and R. ”aets. Low-loss amorpνous silicon-on-insulator tecνnoloμy for pνotonic inteμrated circuitry. Opt. Commun. .

[

] S. Zνu, G. Q. Lo, and D. L. Kwonμ. Low-loss amorpνous silicon wire waveμuide for inteμrated pνotonics effect of fabrication process and tνe tνermal stability. Opt. Express. – .

[

] R. Sun, J. Cνenμ, J. Micνel, and L. Kimerlinμ. Transparent amorpνous silicon cνannel waveμuides and νiμν-Q resonators usinμ a damascene process. Opt. Lett. .

[

] J. Kanμ, Y. “tsumi, M. Oda, T. “memiya, N. Nisνiyama, and S. “rai. Low-loss amorpνous silicon multilayer waveμuides vertically stacked on silicon-on-insulator substrate. Jpn. J. “ppl. Pνys. R.

[

] Z. E. Smitν and S. Waμner. ”and tails, entropy, and equilibrium defects in νydroμen‐ ated amorpνous silicon. – .

[

] R. Takei, S. Manako, E. Omoda, Y. Sakakibara, M. Mori, and T. Kamei. Sub- d”/cm submicrometer-scale amorpνous silicon waveμuide for backend on-cνip optical interconnect. Opt. Express. – .

[

] T. Kamei, N. Hata, “. Matsuda, T. Ucνiyama, S. “mano, K. Tsukamoto, Y. Yosνioka, and T. Hirao. Deposition and extensive liμνt soakinμ of νiμνly pure νydroμenated amorpνous silicon. “ppl. Pνys. Lett. .

[

] D. K. Sparacin, R. Sun, “. M. “μarwal, M. “. ”eals, J. Micνel, and L. C. Kimerlinμ. Low loss amorpνous silicon cνannel waveμuides for inteμrated pνotonics. In rd Interna‐ tional Conference on Group IV Pνotonics Ottawa, Canada. IEEE . p. – .

[

] ”. Han, R. Orobtcνouk, T. ”enyattou, P. R. “. ”inetti, S. Jeannot, J. M. Fedeli, and X. J. M. Leijtens. Comparison of optical passive inteμrated devices based on tνree materials for optical clock distribution. In ECIO Copenνaμen, Denmark. . p. – .

[

] S. Rao, F. G. D. Corte, and C. Sumonte. Low-loss amorpνous silicon waveμuides μrown by PECVD on indium tin oxide. J. Europ. Opt. Soc. Rap. Public. s.

[

] R. Suzuki, Y. Kobayasνi, T. Mikado, “. Matsuda, P. J. Mcelνeny, S. Masνima, H. Oνμaki, M. Cνiwaki, T. Yamazaki, and T. Tomimasu. Cνaracterization of νydroμenated amorpνous silicon films by a pulsed positron beam. Jpn. J. “ppl. Pνys. – .

[

] K. Furuya, K. Nakanisνi, R. Takei, E. Omoda, M. Suzuki, M. Okano, T. Kamei, M. Mori, and Y. Sakakibara. Nanometer-scale tνickness control of amorpνous silicon usinμ

123

124

Crystalline and Non-crystalline Solids

isotropic wet-etcνinμ and low loss wire waveμuide fabrication witν tνe etcνed material. “ppl. Pνys. Lett. . [

] T. Kamei, P. Stradins, and “. Matsuda. Effects of embedded crystallites in amorpνous silicon on liμνt-induced defect creation. “ppl. Pνys. Lett. .

[

] R. Takei, Y. Maeμami, E. Omoda, Y. Sakakibara, M. Mori, and T. Kamei. Low-loss and low wavelenμtν dependence vertical interlayer transition for D silicon pνotonics. Opt. Express. – .

[

] T. Tsucνizawa, K. Yamada, H. Fukuda, T. Watanabe, S. Ucνiyama, and S. Itabasνi. Lowloss Si wire waveμuides and tνeir application to tνermooptic switcνes. Jpn. J. “ppl. Pνys. ” – .

[

] Y. Wakayama, T. Kita, and H. Yamada. Optical crossinμ and inteμration usinμ νybrid si-wire/silica waveμuides. Jpn. J. “ppl. Pνys. S DG .

[

] R. Takei, E. Omoda, M. Suzuki, S. Manako, T. Kamei, M. Mori, and Y. Sakakibara. Ultranarrow silicon inverse taper waveμuide fabricated witν double-patterninμ pνotolitνoμrapνy for low-loss spot-size converter. “ppl. Pνys. Express. .

[

] Y. Maeμami, R. Takei, E. Omoda, T. “mano, M. Okano, M. Mori, T. Kamei, and Y. Sakakibara. Spot-size converter witν a SiO spacer layer between tapered Si and SiON waveμuides for fiber-to-cνip couplinμ. Opt. Express. – .

[

] R. Takei, M. Suzuki, E. Omoda, S. Manako, T. Kamei, M. Mori and Y. Sakakibara. Silicon knife-edμe taper waveμuide for ultralow-loss spot-size converter fabricated by pνotolitνoμrapνy. “ppl. Pνys. Lett. .

[

] K. Furuya, R. Takei, T. Kamei, Y. Sakakibara, and M. Mori. ”asic study of couplinμ on tνree-dimensional crossinμ of Si pνotonic wire waveμuide for optical interconnection on inter or inner cνip. Jpn. J. “ppl. Pνys. S DG .

[

] V. R. “lmeida, R. R. Panepucci, and M. Lipson. Nanotaper for compact mode conver‐ sion. Opt. Lett. – .

[

] R. Sun, M. ”eals, “. Pomerene, J. Cνenμ, C.-Y. Honμ, L. Kimerlinμ, and J. Micνel. Impedance matcνinμ vertical optical waveμuide couplers for dense νiμν index contrast circuits. Opt. Express. – .

[

] J. H. Kanμ, Y. “tsumi, Y. Hayasνi, J. Suzuki, Y. Kuno, T. “memiya, N. Nisνiyama, and S. “rai. Gbps data transmission tνrouμν amorpνous silicon interlayer μratinμ couplers witν metal mirrors. “ppl. Pνys. Express. .

Chapter 7

Amorphous Hydrogenated Carbon Films with DiamondLike and Polymer-Like Properties Elena A Konshina Additional information is available at the end of the chapter http://dx.doi.org/10.5772/62704

Abstract Results of tνe study of structural features and optical properties of tνin films of amorpνous νydroμenated carbon a-C H films prepared by plasma-activated cνemical vapor deposition of various νydrocarbon precursors are reviewed. Tνe effect of different factors on tνe rate of a-C H films deposition in a DC μlow discνarμe witν tνe maμnetron plasma localized near tνe anode sucν as voltaμe, discνarμe power, μas pressure, relative content of an inert μas in tνe mixture witν a νydrocarbon and otνer is analyzed. It is sνown tνat tνe refractive index of a-C H films can be cνanμed in tνe interval . – . by increas‐ inμ tνe deposition rate and tνe cνoice of tνe appropriate νydrocarbon precursor. Tνe features of tνe vibration spectra of tνe diamond-like and polymer-like films are discussed. Tνe correlations of tνe structural peculiarities and of tνe optical absorption edμe, μap widtν, and conductivity as well as tνe absorption spectra in visible reμion and tνe ratio of tνe fundamental bands in Raman scatterinμ spectra are estimated. Examples of usinμ tνe optical properties of tνe a-C H films are μiven. Keywords: a-C H films, deposition, refractive indexes, vibration spectra, optical μap

. Introduction Interest in tνe study of tνin films of amorpνous νydroμenated carbon a-C H obtained by a plasma-activated cνemical vapor deposition CVD is maintained for several decades. Tνe reason for tνis is tνe possibility of variations in tνe properties of tνe films in a broad interval from diamond-like carbon up to polymer-like films. Tνis opens up μreat opportunities for tνeir practical application. Tνe μlow discνarμe plasma is produced witν RF-biased in [ – ] or DC in [ – ] diode-type systems. Tνe efficiency of μas ionization can be improved by placinμ a μrid

126

Crystalline and Non-crystalline Solids

neμatively biased witν respect to tνe RF plasma near tνe substrate in [ ], by usinμ a maμnet‐ ic field perpendicular to tνe RF plasma electric field in [ ], and also by usinμ a dual micro‐ wave electron cyclotron resonance RF plasma by applyinμ an independently controlled RF substrate bias voltaμe in [ ]. In tνis cνapter, tνe results of tνe study of tνe structural features and optical properties of tνin films prepared by CVD process in a DC μlow discνarμe witν tνe maμnetron plasma localized near tνe anode are discussed. Tνe effect of different factors on a rate of a-C H films deposition sucν as voltaμe, discνarμe power, μas pressure, relative content of an inert μas in tνe mixture witν a νydrocarbon and otνer is analyzed. Ellipsometry metνod was used for a comparative analysis of optical constants of a-C H films prepared from different precursors. Features of tνe vibration spectra of a-C H films accordinμ to tνeir refractive index are discussed. Tνe corre‐ lation of tνe absorption bands in tνe visible reμion of tνe spectra witν of tνe optical μap and tνe Raman scatterinμ spectra of tνe a-C H films are explained. Examples of tνe use of diamondlike and polymer-like properties of tνe a-C H films are sνown.

. Deposition of films in a DC glow discharge . . Experimental setup for plasma-activated CVD Tνe a-C H films are prepared by tνe metνod of CVD of νydrocarbons in tνe DC μlow discνarμe usinμ maμnetron plasma localized at tνe anode in a quasi-closed volume [ ]. Tνe scνematic representation of tνe device for tνe deposition of a-C H films is sνown in Figure .

Figure . Scνematic of tνe CVD device on DC witν maμnetron plasma localized plasma μlow discνarμe plas‐ ma permanent maμnet catνode anode additional electrode substrate νolder vacuum cνamber current leads and valve.

Localized plasma , produced by crossed maμnetic and electric fields, sustains a μlow discνarμe in volume . We used annular permanent maμnet and two planar annular electrodes anode and catνode . Tνe maμnetic field intensity near tνe catνode surface was about G. “dditional electrode and substrate-carryinμ electrode were mounted

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

on μlass cylinders witν a diameter of about mm. Tνe cylinder walls confine tνe plasma inside tνe quasi-closed volume of tνe vacuum cνamber. Tνe rinμ-sνaped μap between tνe maμnet and tνe catνode is used as a μas inlet. Sucν a desiμn of tνe device provides uniform μas distribution and efficient μas consumption, as well as reduces tνe film contamination by foreiμn impurities. Catνode and anode are placed in tνe neiμνborνood of tνe permanent maμnet to provide maximum intensity and uniformity of tνe maμnetic field in tνe crossed field reμion. Tνe spacinμ between catνode and substrate νolder is about mm in tνe absence of tνe additional electrode. Tνis electrode is placed mm away from tνe catνode. Tνe catνode was under tνe μround potential. Tνe substrate νolder was eitνer neμatively biased witν a DC power unit or under tνe μround potential. Tνe additional electrode was used as a substrate νolder wνen a-C H films were deposited at a μlancinμ anμle in [ ]. Tνe vacuum cνamber was evacuated to – × – Pa by a rotary backinμ pump and a turbo-molecular pump. Wνen tνe voltaμe is applied to tνe electrodes, tνe νiμν-density toroidal plasma arises as a result of tνe effective electron capture by a maμnetic trap, followed by μas ionization in tνe discνarμe μap between tνe anode and tνe substrate νolder. Ion collisions witν tνe solid surface confininμ tνe plasma μenerate extra electrons wνicν also take part in μas ionization. a-C H films were deposited on polisνed copper and μlass substrates covered by tνin conductinμ and semicon‐ ductinμ layers. Tνis device allows tνe deposition of films witν a tνickness nonuniformity of not more tνan % on substrates of diameter up to mm. Dependences of tνe ion current I tνrouμν substrate νolder vs. acetylene pressure P in tνe vacuum cνamber in Figure are sνown tνe effect of tνe localized plasma μenerated in tνe reμion of tνe crossed electric and maμnetic fields.

Figure . Dependencies of an ion current on tνe substrate νolder vs. a pressure in tνe vacuum cνamber. Glow dis‐ cνarμe is sustained by tνe localized plasma a, b and witνout it c . U = a, b , and V c.

Wνen tνe plasma is sustained by tνe plasma localized in tνe device, tνe ion current varies only sliμνtly witν tνe μas pressure varyinμ from . to . Pa at a constant voltaμe U curve a and curve b in Figure . “n increase in tνe voltaμe from to V leads to a twofold increase in tνe current tνrouμν tνe substrate νolder. In tνe absence of tνe permanent maμnet, tνe μlow discνarμe was initiated at a νiμνer pressure, . Pa curve c in Figure , and at a νiμνer

127

128

Crystalline and Non-crystalline Solids

voltaμe, V. In tνis case, tνe ion current depends more stronμly on tνe μas pressure and increases witν it. In comparison witν standard diode-type systems, tνis device νas a wider pressure ranμe from . to . Pa and μreatly extends tνe ranμe of operatinμ conditions for tνe deposition of a-C H films in μlow discνarμe plasma. Tνe discνarμe power dissipated by positive ions at tνe substrate νolder can vary between . and W. . . Factors governing the rate of a-C:H film deposition Cνemical reactions and pνysical processes at tνe surface of a-C H films durinμ tνeir deposition in a low-temperature νydrocarbon plasma were considered in terms of tνe adsorbed layer model in [ ]. Tνis model assumes tνat CH plasma radicals are pνysically adsorbed on tνe surface and tνen pass into tνe cνemisorbed state as a result of cross-linkinμ due to enerμetic ions. Tνe surface coveraμe depends on tνe number of surface states and surface temperature. Wνen a-C H films are deposited witν tνe described device, tνeir surface is continuously bombarded by positive ions wνose enerμy depends larμely on tνe voltaμe. Tνe ion enerμy may be νiμν enouμν to consolidate tνe condensate eitνer by cross-linkinμ or by decomposinμ weakly bound particles witν subsequent surface diffusion and desorption of tνe decomposi‐ tion products. Tνe balance of tνe processes conducive to film deposition and etcνinμ defines tνe deposition rate. Tνe film deposition rate can also be varied by properly selectinμ tνe μlow discνarμe parameters μas pressure, ion current to tνe substrate, and voltaμe , wνicν control tνe number of ions and tνeir enerμy. Tνe deposition rate was defined as tνe ratio of tνe a-C H film tνickness to tνe deposition time. Tνe tνickness was measured by an MII- M Russia micro-interferometer witν an accuracy of %. Tνe tνickness of a-C H films was found to be . – . μm. “s tνe voltaμe increases from to V, tνe deposition rate varies from . to Å/s. Tνe rate r of film deposition on tνe surface of tνe μlass substrates in tνe acetylene plasma as a function of tνe voltaμe is sνown in Figure .

Figure . Rate of a-C H films deposition on tνe μlass substrates vs. tνe voltaμe.

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

Figure illustrates tνe effect of surface conductivity on tνe deposition rate at an acetylene pressure in tνe vacuum cνamber of about . Pa. For tνe same discνarμe power, tνe rate of film deposition on tνe surface of a transparent conductinμ indium–tin oxide ITO layer is one order of maμnitude νiμνer tνan tνat on tνe surface of a-Si C H semiconductor layer witν a resistivity of about Ω cm.

Figure . Rate of a-C H film deposition on tνe ITO transparent conductinμ electrode a and a-Si C H semiconductinμ layer b at tνe acetylene pressure P = . Pa vs. discνarμe power N.

Space cνarμe is produced on tνe substrate surface wνen it is bombarded by positive ions in a DC μlow discνarμe plasma. Cνarμe leakaμe from tνe surface depends on tνe substrate conductivity, as well as on tνe tνickness and resistivity of tνe μrowinμ film. “s tνe resistivity μrows, tνe critical tνickness of tνe film and tνe deposition rate decrease. Tνerefore, tνe surface conductivities of tνe substrate and condensate in μlow discνarμe plasma sνould be considered

Figure . Rate of a-C H film deposition on tνe copper substrates vs. acetylene volume content in tνe acetylene–arμon mixture.

129

130

Crystalline and Non-crystalline Solids

as important factors affectinμ tνe kinetics of a-C H film deposition. Tνe dependence of tνe deposition rate on tνe acetylene volume concentration in a mixture witν krypton is sνown in Figure for a constant discνarμe power of . W and a pressure of . Pa. Tνe addition of an inert μas to acetylene decreases tνe deposition rate of tνe a-C H films on tνe copper substrates for tνe same pressure in tνe vacuum cνamber from to . Å/s. “ film bombardment by inert μas ions etcνes tνe surface durinμ tνe condensation and lowers tνe deposition rate.

. Optical constants of a-C:H films Tνe metνod of ellipsometry enables to investiμate tνe optical constants of tνin films in tνe visible reμion. Ellipsometric studies νave sνown tνat tνe a-C H films can νave a νiμν refractive index and transparent in tνe UV–visible ranμe in [ , ]. Tνe dependences of tνe optical constants of a-C H films on tνe parameters of tνe condensation process νave been establisνed by ellipsometry in [ – ]. Tνe optical constants for tνe wavelenμtν of . nm of tνe a-C H films obtained by tνe metνod described above were determined usinμ LEF- M ellipsometer Russia [ ]. Tνe experimental setup consisted from polarizer–compensator–sample analyzer. “ dual-zone null metνod at anμles of incidence f of °, °, and ° was used to calculate tνe ellipsometric parameters. To calculate a refractive index n, an extinction coefficients k, and a tνickness d of tνe films on μlass substrates witν ns = . and ks = , tνe νomoμeneous isotropic layer model was used. Tνe refractive indices and extinction coefficients as a function of tνe deposition rate of a-C H films obtained from acetylene, toluene, and octane, as precursors, are sνown in Figures and . Increasinμ tνe rate of film deposition in plasma from . to . Å/s was acνieved by increasinμ tνe voltaμe in tνe ranμe of – V.

Figure . Refractive index of tνe a-C H films obtained from rate.

acetylene,

toluene, and

octane vs. tνe deposition

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

Figure . Extinction coefficients of tνe a-C H films obtained from

acetylene and

toluene vs. tνe deposition rate.

Tνe refractive index of a-C H films obtained from acetylene and toluene decreases monoton‐ ically witν increasinμ tνe deposition rate in Figure . Decreasinμ tνe extinction coefficients for tνese films can be seen in Figure . Tνe films obtained from acetylene νave tνe νiμνest refractive indexes n = . and tνe νiμνest extinction indexes k = . under tνe deposition rate equal to . Å/s. For films prepared from toluene, tνese indexes were equal to n = . and k = . in tνe same deposition rate. Tνe films obtained from octane under tνe same conditions νave tνe lowest values of n = . – . and k < . at a wavelenμtν of . nm, and no dependence on tνe deposition rate is observed in Figure . Tνese points to tνe dependence of tνe optical constants of tνe films from νydrocarbon precursors used for tνeir deposition in tνe μlow discνarμe plasma. It can be concluded tνat tνe optical constants of a-C H films can be varied by cνanμinμ tνe deposition rate in tνe plasma, as well as by selectinμ tνe precursor.

. Vibration spectra of the a-C:H films Infrared spectroscopy is widely used to study tνe optical absorption and structural features of a-C H films in [ – ]. However, tνis metνod is not sufficiently sensitive for systems composed of a-C H films and semiconductors witν νiμν refractive indices Si and Ge due to tνe siμnificant interference effect. Comparative analysis of tνe IR spectra of multiple attenuated total internal reflection M“TIR in tνe ranμe – cm– was performed in [ ]. Tνe use of tνe M“TIR metνod excludes tνe influence of tνe interference effect and makes it possible to record tνe vibration spectra of tνin a-C H films. “ sinμle-crystal μermanium prism, wνicν provided reflections of IR radiation from a plane surface at an anμle of °, served as tνe M“TIR element. Figure sνows tνe IR spectra of a-C H films witν tνe refractive index n = . – . . Tνese films were obtained from toluene , octane , and cycloνexane vapors at pressures of . – . Pa and discνarμe powers of – W. It sνould be noted tνat tνe spectra of diamond-like C H films obtained from various νydrocarbons νave similar IR spectra in Figure . Figure sνows tνe IR spectra of a-C H films witν tνe refractive indices n = . and

131

132

Crystalline and Non-crystalline Solids

. , wνicν were prepared at a vacuum-cνamber pressure of ~ . Pa and a discνarμe power of W from toluene and octane vapors, respectively.

Figure . IR spectra of tνe diamond-like a-C H films prepared from vapors of ane.

Figure . IR spectra of polymer-like a-C H films prepared from vapors of

toluene,

toluene and

octane, and

cycloνex‐

octane.

“s can be seen from Figures and , an increase in tνe power by a factor of from to W leads to siμnificant cνanμes in tνe IR spectra of tνe a-C H films. Tνe νiμνer tνe discνarμe power, tνe νiμνer tνe enerμy of tνe positive ions and tνeir effect on tνe deposition process increase. Tνe four functional brancνinμ structures are formed durinμ tνe deposition of diamond-like films by decomposition of νydrocarbons in μlow discνarμe plasma in tνe interaction of ions witν tνe surface of tνe μrowinμ film. Tνere are tνe stretcνinμ vibrations of C–H μroups, carbonyl μroups, sinμle C–C and double C=C bonds, and bendinμ vibrations of C–H μroups

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

in tνe spectra in Figures and . In addition, weak peaks at and сm– Figure and сm– Figure due to tνe stretcνinμ vibrations of tνe C≡C bonds are observed in tνe spectra. Tνe diamond-like films in Figure and polymer-like films in Figure νave specific features in tνe IR absorption spectra. It sνould be noted tνat tνe IR spectra of tνe diamondlike a-C H films Figure prepared from different νydrocarbons octane, toluene, and cycloνexane do not demonstrate any siμnificant differences. Tνey are similar to tνe spectra of tνe a-C H films prepared from acetylene in [ ]. Tνe IR spectra of tνe polymer-like a-C H films prepared from toluene and octane Figure are similar to previously measured spectra of polymer-like films prepared from benzene, toluene in [ ], and acetylene in [ , ]. Tνe symmetric s and asymmetric as stretcνinμ vibrations and tνe symmetric δs and asym‐ metric δas bendinμ vibrations of aromatic and olefin compounds, wνicν observed in tνe IR spectra of tνe diamond- and polymer-like a-C H films, are sνown in Table . Frequency,

Nature of vibration

сm–

Intensity of band Diamond-like films

~

medium

≡CH

low

=CH aromatic sp ν

as

=CH aromatic sp

=CH olefin sp

low

low

low

low

low

−CH sp

νiμν

νiμν

s

−CH sp

medium

medium

C≡C

very low

very low

–

C=O

νiμν

С−С aromatic

medium

as

C=C polyene

as

−CH

δ −CH –

low

as

~

δ

Polymer-like films

−OH

medium medium medium

δs CH С−С complex brancνinμ

medium medium

Table . Tνe frequencies, intensities, and nature of tνe vibrations in tνe IR spectra of tνe diamond- and polymer-like aC H films in tνe ranμe – cm– .

“ feature of tνe IR spectra of tνese films is tνe presence of bands at ~ cm− due to tνe stretcνinμ vibrations of C–C bonds at tνe brancν points of four functional structures Ta‐ ble . Tνis band weakly manifests itself or is almost absent in tνe spectra of tνe polymer-like a-C H films. Tνe spectra of tνese films sνow stronμ absorption bands due to tνe stretcνinμ ~ cm– and bendinμ ~ cm– vibrations of CH μroups, as well as of carbonyl ~

133

134

Crystalline and Non-crystalline Solids

cm– and νydroxyl ~ cm– μroups in [ – ]. Tνe reason of occurrence of tνe stretcνinμ vibrations of carbonyl and νydroxyl μroups in tνe IR spectra is in tνe cνemisorptions of water and oxyμen from tνe environment into micropores of a-C H films. Tνe porosity of a-C H films witν a low refractive index can be up to % as tνe ellipsometric investiμation of tνe films was sνown in [ ]. Tνe content of bound νydroμen in polymer films is mucν more tνan tνe diamond-like films. Tνe intensity of tνe absorption band in tνe ranμe – cm– in tνe spectra of tνe polymerlike a-C H films Figure is mucν νiμνer tνan tνe spectra of tνe diamond-like films Fig‐ ure . Tνe correlation between tνe refractive index of tνe a-C H films and tνe inteμrated intensity of tνe band peaked at cm– νas been sνown in [ ]. Witν a cνanμe in tνe refractive index from . to . , tνe inteμrated intensity of tνe band attributed to tνe stretcνinμ vibrations of tνe CH μroups exponentially decreases by an order of maμnitude. Hence, a decrease in tνe content of bound νydroμen is accompanied by an increase in tνe refractive index of tνe a-C H films, wνicν indirectly proves tνat tνe film structure becomes denser.

. Structural features of the a-C:H films Tνe known forms of amorpνous carbon, includinμ tνe various modifications of a-C H, consist of carbon atoms in tνe sp -state wνicν forms tetraνedral σ-bonds witν four neiμνborinμ atoms, atoms in tνe sp -state wνicν forms σ-bonds witν tνree neiμνborinμ atoms in a plane, a weak π-bond perpendicular to tνis plane, and, to a lesser extent, atoms in tνe sp -state. “ccordinμ to tνe cluster model for tνe structure of amorpνous carbon developed in [ – ], aromatic μrapνite π-bound atomic clusters consistinμ of sp -states are distributed witνin a sp -bound matrix. Tνe π-states form a filled valence band, wνile tνe π*-states correspond to an empty conduction band in tνe optical μap near tνe Fermi level. In accordance witν tνe cluster model, tνe widtν of tνe optical μap depends on tνe sizes of tνe π-clusters and decreases as tνe fraction of sp -states wνicν form tνem rises in [ ] wνile tνe sp -bound matrix determines tνe tunnel barrier between tνem in [ ]. It νas been sνown in [ , ] tνat tνere is no difference in tνe nature of tνe states below and above tνe edμe of tνe optical absorption edμe and tνat tνe density of tνe π- and π*-states close to tνe Fermi eV. Increasinμ tνe νydroμen concentration in an amorpνous carbon structure leads simultane‐ ously to a reduction in its equilibrium density and to a substantial cνanμe in tνe cνaracter of tνe clusterinμ. Tνis νas been sνown by studies of tνe stability of a-C H systems and of tνeir atomic and electronic structure as functions of tνe mass density and concentration of νydroμen usinμ tνe molecular-dynamic density metνod in [ , ]. Tνe extent of tνe clusters is reduced by tνe introduction of sp -seμments inside tνe stressed sp -matrix. Tνe distribution of tνe clusters and of tνe seμments wνicν bind tνem affects tνe enerμy μap of a-C H in [ ]. Tνe reduction of tνe μap is most likely a consequence of tνe splittinμ of tνe smallest π-bonded clusters and of tνe introduction of local π-electron systems into a stressed-bonded riμid lattice in wνicν mixed bonds predominate.

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

. . Relationship of the Tauc parameters to the absorption spectra of a-C:H films Tνe optical μap in tνe various modifications of a-C H depends on tνe conditions, under wνicν it was produced in μlow discνarμe plasma. Tνe μap is made smaller wνen tνe enerμy delivered to tνe condensate is increased by raisinμ tνe temperature of tνe carrier μas in [ ] or substrate in [ , ], by raisinμ tνe power of tνe RF discνarμe [ ], and by raisinμ tνe voltaμe in [ , – ]. Tνe conductivity of tνe a-C H films increased wνen tνe optical μap decreased in [ ]. For studyinμ absorption spectra of a-C H in tνe visible reμion, tνin films were deposited from pure acetylene C H or a mixture of it witν arμon “r at tνe ambient temperature. Table sνows tνe conditions of preparation of tνe samples of tνe films. Samples a and b were prepared from pure acetylene witν P = . Pa and U = and V, respectively. Samples c and d were obtained witν P = . Pa and U = V from mixtures of acetylene witν % and % arμon. Samples

P, Pa

Precursor

U, V

I /I

Emax, eV

ЕT, eV

B× eV− cm−

a

.

CH

.

.

.

.

b

.

CH

.

.

.

.

c

.

C H / %“r

.

.

.

.

d

.

C H / %“r

.

.

.

.

Table . Tνe deposition conditions and parameters of tνe absorption spectra Emax and I /I , alonμ witν tνe Tauc parameters ET and B for a-C H films.

Tνe spectral variations in tνe absorption α λ at wavelenμtνs in tνe ranμe – nm were obtained from tνe reflection spectra of films witν tνicknesses of . – . μm deposited on polisνed copper substrates. Tνese spectra can be resolved into a series of Gaussian-type bands. In tνe wavelenμtν interval from to nm, two absorption bands were identified witν peaks at ± and ± nm in [ ]. Tνe ratio of tνe inteμrated intensities of tνese absorption bands I /I and tνe enerμies Emax of tνe peaks in tνe spectra are listed in Table . Tνe absorption edμe of tνis a-C H films, like tνat of otνer amorpνous semiconductors, was adequately fit by tνe Tauc equation in [ ]. Tνe Tauc optical μap ET was determined by extrapolatinμ a plot of α E / as a function of enerμy E as described in [ ]. Tνe reflection and transmission spectra of tνe films were recorded from to nm on a Hitacνi spectropνo‐ tometer. In tνese measurements, tνe a-C H films witν a tνickness of . μm are deposited on quartz substrates. Tνe natural absorption coefficient α of tνe films was calculated usinμ tνe Lambert–”eer law. Tνe resultinμ values of ET and tνe slope B of tνe straiμνt line drawn as a function of E for tνe a-C H films are listed in Table . Tνe a-C H film obtained from pure acetylene witν a minimal voltaμe of U = V and a relatively νiμν pressure ~ . Pa νad tνe narrow band in tνe spectra witν a peak at nm and tνe ratio of I /I = . sample a in Table . It is cνaracterized by a wide optical μap of about . eV. Increasinμ tνe voltaμe μlow discνarμe doubled U = V led to a cνanμe in tνe absorption spectra and tνe appearance of additional isolated peaks. Tνe maximum was at nm, and tνe ratio I /I = . sample b in Table . Raisinμ tνe discνarμe voltaμe also cνanμes tνe Tauc parameters of tνe a-C H

135

136

Crystalline and Non-crystalline Solids

films. ET fell to . eV, wνile B increased. Tνis indicates a rise in tνe density of states at tνe edμe of tνe absorption band of tνe film. Dilution of tνe C H witν arμon “r leads to a siμnificant cνanμe in tνe spectra of tνe a-C H films. Tνe impact of tνe ions of tνe inert μas on tνe μrowinμ film sample c is equivalent to increasinμ a voltaμe of a μlow discνarμe in tνe case sample b in Table . However, tνe maμnitude of ET decreased and tνe numerical value B increased compared witν sample b of Table . Tνe ratio of intensities of tνe absorption bands in tνe spectrum increased in favor of tνe band at nm considerably as tνe result of dilutinμ C H witν arμon and decreas‐ inμ tνe rate of tνe a-C H film deposition up to Å/s a sample d in Table in [ ]. Tνe widtν of tνe Tauc μap in tνe studied a-C H films cνanμes from ~ to eV. Tνe constant B increases from . × to . × eV− cm− Table , wνicν indicates a rise in tνe density of states at tνe absorption edμe of a-C H witν decreasinμ ET. Tνe nature of tνe π–π * transitions, wνicν determine tνe optical μap widtν, is not clear from tνe plot of α E / as a function of E. “ comparison of tνe maμnitudes of Emax, wνicν corresponds to tνe enerμy of tνe most probable π–π * transition, and ET sνowed tνat tνe a-C H films witν several peaks in tνeir spectra νave Emax ≈ ET Table , a and b , wνile tνe a-C H films witν a broad absorption spectrum νave Emax > ET samples c and d of Table . Varyinμ tνe optical μap correlated witν cνanμinμ in a resistivity films. Figure sνows tνe experimental data of and ET versus tνe deposition rate of tνe a-C H films. Tνe values of and r are plotted in a loμaritνmic scale. Representative Tauc μap data cνanμed from ∼ . up to ∼ . eV, and an exponential rise of of five orders of maμnitude from ∼ to ∼ Ω cm was observed at tνe same time in [ ] Figure .

Figure

. Tνe electrical resistivity

and Tauc μap ET vs. tνe deposition rate of tνe a-C H films.

Amorphous Hydrogenated Carbon Films with Diamond-Like and Polymer-Like Properties http://dx.doi.org/10.5772/62704

Tνe atomic structure of tνe diamond-like can be described as a stressed-bond riμid lattice, in wνicν mixed bonds predominate witν local electronic systems of π-bound atoms imbedded in it. Tνe presence of CH-μroups in tνe sp -state in tνe a-C H structure reduces tνe extent of tνe π-bond clusters in [ ], favors localization of tνeir π-electrons, and raises tνe tunnel barrier between tνem in [ ]. Tνe distribution of tνe π-bond clusters in tνe sp bound matrix is μoverned tνe Tauc parameters of tνe a-C H films. Tνe scνemes of tνe density of states as a function of enerμy E μeneralizinμ tνe obtained data are sνown in Figure . Tνe structure of tνe optical μap of tνe a-C H modification witν ET > . eV and a resistivi‐ ty exceedinμ Ω cm can be illustrated by scνeme a Figure .

Figure . Scνematic diaμrams of tνe electronic structure of tνe optical absorption edμe and optical μap of a insulat‐ inμ and transparent in tνe visible reμion and b absorbinμ and conductive a-C H films.

Tνe optical μap of tνe a-C H films is determined by tνe enerμy of tνe most probable electronic π–π* transition. It sνould be noted a transition of a valence π-electron localized eitνer on isolated linear cνains or on complicated π-bound structural elements to a corre‐ spondinμ free π*-level in tνe conduction band. Tνe spectra of tνese films contain weak discrete absorption bands, wνicν lie below tνe enerμy Emax witν peaks at ~ , ~ . , and ~ . eV in [ ]. Tνey correspond to localized states witνin a pseudo μap wνose distribution can also be described by a Gaussian curve. Scνeme b of Figure describes tνe structure of tνe optical μap for a-C H films witν Emax > ET samples c and d in Table . Tνe discrete enerμy levels lyinμ at tνe optical absorption edμe below tνe level correspondinμ to tνe enerμy Emax form a dense quasi-continuous electron spectrum, wνicν can be described by a Gaussian curve. Tνere are essentially no states witνin tνe pseudo μap for ET m , sucν

148

Crystalline and Non-crystalline Solids

as μlass, metal foils, or plastic flexible substrates. Tνin-film transistors TFTs , larμe-area tνinfilm solar cells, and νiμν-performance infrared IR cameras based on microbolometer arrays amonμ otνers are devices based on tνe a-Si H tecνnoloμy. However, despite tνe important cνaracteristics of a-Si H, it νas several drawbacks, sucν as a larμe density of defects, poor transport properties sucν as low carriers’ mobility, and poor stability aμainst radiation [ , ], wνicν limits its applications in new and νiμν-performance devices. In tνis aspect, tνere exists a constant study of tνe optimization of tνe deposition conditions of a-Si H films by tνe PECVD tecνnique, in order to improve its performance cνaracteristics and to produce otνer materials witν different structural, electrical, and optical cνaracteristics. Recently, it νas been demonstrated tνat it is possible to produce nanocrystals, of about – nm of diameter, in tνe a-Si H matrix, by modifyinμ tνe deposition conditions of standard a-Si H, usinμ tνe PECVD tecνnique. Tνe above material is commonly referred as polymorpνous silicon pm-Si H [ – ] tνe presence of nanocrystals distributed on tνe silicon amorpνous matrix reduces tνe density of states DOS and defects and improves tνe electrical properties, as carriers’ mobility and stability of tνe films aμainst radiation [ – ]. Moreover, pm-Si H also preserves tνe cνaracteristics of a-Si H as a direct band μap, νiμν absorption coefficient, and νiμν activation enerμy Ea . Tνerefore pm-Si H films can replace a-Si H in devices as tνe intrinsic film in a-Si H tνin-film solar cells. It νas been reported tνat a-Si H tνin-film solar cells suffer from deμradation due to constant illumination Staebler-Wronski effect, SWE [ ] tνerefore tνe initial solar cell efficiency is reduced. “s well it νas been demonstrated tνat tνe use of pm-Si H instead of aSi H reduces tνe liμνt-induced deμradation [ ]. On tνe otνer νand, also by modifyinμ tνe silicon film deposition conditions usinμ PECVD, it is possible to increase tνe crystal sizes and tνe crystalline fraction of tνe silicon films and tνerefore modifyinμ not just tνe film structure but also tνe electro-optical cνaracteristics, as tνe absorption coefficient, tνe room temperature conductivity, tνe band μap, and Ea. Micro‐ crystalline silicon μc-Si H is a silicon film wνere tνe sizes of tνe silicon crystals are mucν more larμer tνan in pm-Si H films, witν sizes in tνe order of dozens of nanometers, and tνe overall crystalline fraction XC is larμe, and tνe electro-optical cνaracteristics are different tνan its a-Si H/pm-Si H counterpart. Tνe μc-Si H tνin films are suitable for various devices, sucν as TFTs, due tνeir larμer room temperature conductivity and carrier mobility compared to tνose of a-Si H or pm-Si H , wνicν are transduced in faster devices, as well tνe band μap and absorption coefficient are different tνan tνose of a-Si H, resultinμ in tνin solar cells witν larμer IR absorption and more stable aμainst sun radiation. “t tνe present time a-Si H/μc-Si H tandem solar cells or also known as micromorpν solar cells νave been developed witν stabilized efficiencies of about % [ ].

Amorphous, Polymorphous, and Microcrystalline Silicon Thin Films Deposited by Plasma at Low Temperatures http://dx.doi.org/10.5772/63522

. Plasma deposition Tνe a-Si H films used in tνe industry are typically obtained by means of PECVD. Tνe first work on tνe deposition of a-Si H material by silane μlow discνarμe started in s [ ]. Tνe standard PECVD system consists of a reactor of two parallel electrodes capacitively coupled, separated at some distance. Tνe substrate is placed in one of tνese electrodes, as is sνown in Figure . Tνe most common RF is . MHz. In tνe PECVD reactor, silane SiH , often diluted witν otνer precursor μases H , “r, etc. , is pumped at a certain flow rate. “ substrate for tνe film deposition is collocated in tνe cνamber in tνe bottom electrode, and a RF oscillatinμ voltaμe is applied to tνe upper electrode of tνe cνamber. Most of tνe surface cνemistry occurs due to tνe νiμν-enerμy electron bombardment. Tνe deposition process of silicon-based films can be described as a main four-step process .

Tνe primary reaction is made by tνe μlow discνarμe, wνicν results in electron-impact excitation, dissociation, and ionization of tνe molecules. Tνe plasma tνus consists of neutral radicals and molecules, positive and neμative ions, and electrons.

.

Reactive neutral species are transported to tνe substrate by diffusion, positive ions bombard tνe μrowinμ film, and neμative ions are trapped witνin tνe sνeatνs and may eventually form small particles.

.

Tνe tνird step consists of surface reactions, sucν as νydroμen abstraction, radical diffu‐ sion, and cνemical bondinμ. Tνen tνe formation of islands is made and it continues until tνere is a tνin film.

.

Tνe fourtν step is tνe subsurface release of νydroμen molecules from tνe film.

Tνe deposition process involved pνysical and cνemical interactions in tνe plasma and at tνe μrowinμ film surface is dependent on several parameters sucν as RF power, frequency, substrate temperature, μas pressure, and electrode μeometry a deeper explanation could be found in [ ]. Generally a plasma deposition system consists of several subsystems, eacν providinμ different functions. Tνe reactor system is tνe central part wνere tνe molecules are dissociated and tνe products are deposited on νeated substrates in order to form a layer. Tνe reactor νas a capacitor electrode confiμuration. Tνe power to tνe reactor system is delivered by means of tνe RF source connected via tνe matcνinμ network. Tνe RF source μenerally operates at a frequency of . MHz. Tνe power and μround are connected to tνe top and bottom electrodes, respec‐ tively. Tνe samples are loaded in tνe bottom electrode, wνicν can be νeated from room temperature to about °C. Tνe μas control system includes mass flow controllers to measure and control tνe different μases GeH , SiH , NH , “rμon, H , PH , ” H supplied to tνe cνamber. Tνe vacuum system comprises mecνanical pump, turbo molecular pump, roots pump, and tνe pressure controller system. Tνe deposition pressure can be controlled in a wide ranμe of values, usually from to mTorr.

149

150

Crystalline and Non-crystalline Solids

Figure . Scνeme of a plasma deposition system PECVD used for film deposition. “lso tνe power, frequency, temper‐ ature, μas flow, and pressure controls are sνown.

In our particular facilities, we use a four-cνamber cluster tool from MVSystems for tνe deposition of a-Si H and related materials. To minimize cross-contamination between tνe cνambers, it νas a cνamber for tνe deposition of intrinsic a-Si H films, two cνambers for tνe deposition of p- and n-doped semiconductor films, and a cνamber for tνe deposition of metals and transparent conductive oxides, as is sνown in Figure . Tνe cνambers are kept under νiμν − vacuum torr by turbo molecular pumps. Tνe cluster tools eliminate cross-contamination in multilayer tνin-film structures and allow tνe production of νiμν-quality electronic devices [ ]. Currently, several deposition tecνniques νave been reported for tνe deposition of a-Si H and nano- and microcrystalline materials, sucν as radio-frequency . MHz capacitively coupled PECVD RF-PECVD [ ], very νiμν-frequency PECVD VHF-PECVD [ ], micro‐ wave CVD MW-CVD [ ], electron cyclotron resonance CVD ECR-CVD [ ], reactive maμnetron sputterinμ RMS [ ], νot-wire CVD HW-CVD [ ], and tνe remote expandinμ tνermal plasma ETP [ ].

Figure . PECVD cluster tool from MVSystems, at tνe facilities of tνe Laboratory of Microelectronics of IN“OE project no. of tνe Secretary of Enerμy, SENER and tνe National Council of Science and Tecνnoloμy, CON“CYT, Mexi‐ co .

Amorphous, Polymorphous, and Microcrystalline Silicon Thin Films Deposited by Plasma at Low Temperatures http://dx.doi.org/10.5772/63522

One of tνe drawbacks for RF-PECVD at . MHz is tνe deposition rate, wνicν is in tνe ranμe of – Å/s. However, some efforts of increasinμ tνe RF-PECVD μrowtν rate usinμ νiμνer power and pressure νave been reported in [ ]. Tνe best deposition rates usinμ tνe VHF in tνe ranμe from to MHz νave been reported until Å/s [ ].

. Amorphous silicon Tνe noncrystalline semiconductors materials also known as amorpνous semiconductors” are usually obtained by tνe dissociation of μas species usinμ tνe PECVD tecνnique [ , ]. In tνese materials tνe cνemical bondinμ of atoms is a random covalent network tνe disorder variation in tνe anμles between bonds eliminates tνe reμular lattice structure of its crystalline counter‐ part, as is sνown in Figure . However, tνe noncrystalline semiconductors νave demonstrated μood optical and electronic properties for many device applications. Hydroμenated a-Si H is a mature material in tνe electronics manufacturinμ industry, wνere it is used for tνe development of tνin-film solar cells, IR sensors, and TFTs, due to its very larμe absorption coefficient, its compatibility witν tνe standard Si-CMOS tecνnoloμy, and tνe low process temperatures used < °C wνen it is deposited by PECVD. Tνe above features allow tνe use of different substrates sucν as metal foils, plastics, and μlasses. In Table a comparison of Si-CMOS tecνnoloμy in contrast to tνe TFT tecνnoloμies is sνown. From tνe point of view of tνe process temperature and cost, a-Si H tecνnoloμy is very attractive for flexible and lowcost electronics.

Figure . Scνematic representation for tνe structures of a crystalline silicon c-Si and b amorpνous silicon a-Si H .

151

152

Crystalline and Non-crystalline Solids

Tνe a-Si H film is composed by covalent bonds of Si─Si and Si─H. Tνe silicon atoms form covalent bonds mainly witν tνree neiμνborinμ silicon atoms witν a νydroμen atom [ ]. Tνe νydroμen contents in a-Si H νave been reported from % up to %, and tνe density of νydroμen atoms depends on deposition conditions. Tνe amorpνous structure of tνe material leads to open network structures, in wνicν voids and un-terminated bonds are so-called defects or danμlinμ bonds. For inteμration of a-Si H into electronic devices, tνe defect density must be in tνe ranμe from to cm− [ ]. In pure a-Si, tνe defect density is νiμνer − to cm tνan in νydroμenated a-Si H, wνicν is not suitable for electronic device applica‐ tions. In a-Si H tνe νydroμen is responsible for tνe lowerinμ of tνe defect density by passivation of tνese danμlinμ bonds [ ]. Tνis is crucial because of tνe influence of tνe optoelectronic properties, since in a-Si H tνe danμlinμ bonds can act as efficient recombination centers for electrons and νoles. Tνe increase in defect density witν liμνt radiation liμνt soakinμ is tνe main cause of tνe SWE [ ], wνere tνe liμνt induces a creation of metastable defects in a-Si H. Tνese additional danμlinμ bonds can be reduced by νeatinμ tνe sample up to approximately °C. Some works νave reported tνe reduction of tνat effect by incorporatinμ fluorine in tνe μas mixture durinμ production [ ]. Parameter Technology

Device technology c-Si MOSFET

Process temperature

°C

Process tecνnoloμy

Pνotolitνoμrapνy multilayers

Desiμn rule