NANOTECHNOLOGY SCIENCE AND TECHNOLOGY SERIES NANOTECHNOLOGY: NANOFABRICATION, PATTERNING AND SELF ASSEMBLY No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form orby any means. The publisher has taken reasonable care in the preparation of this digital document, but makes noexpressedorimpliedwarrantyofanykindandassumesnoresponsibilityforanyerrorsoromissions.Noliabilityisassumedforincidentalorconsequentialdamagesinconnectionwithorarisingoutofinformationcontained herein. This digital document is sold with the clear understanding that the publisher is not engaged inrendering legal, medical or any other professional services. NANOTECHNOLOGY SCIENCE AND TECHNOLOGY SERIES Safe Nanotechnology Arthur J. Cornwelle2009. ISBN: 978-1-60692-662-8 National Nanotechnology Initiative: Assessment and Recommendations Jerrod W. Kleike (Editor) 2009. ISBN: 978-1-60692-727-4 Nanotechnology Research Collection - 2009/2010. DVD edition James N. 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ISBN: 978-1-60876-125-8 Bio-Inspired Nanomaterials and Nanotechnology Yong Zhou (Editor) 2009. ISBN: 978-1-60876-105-0 Nanopowders and Nanocoatings: Production, Properties and Applications V. F. Cotler (Editor) 2010. ISBN: 978-1-60741-940-2 Nanomaterials: Properties, Preparation and Processes Vinicius Cabral and Renan Silva (Editors) 2010. ISBN: 978-1-60876-627-7 Nanomaterials Yearbook - 2009. From Nanostructures, Nanomaterials and Nanotechnologies to Nanoindustry Gennady E. Zaikovand Vladimir I. Kodolov (Editors) 2010. ISBN: 978-1-60876-451-8 Nanotechnology: Nanofabrication, Patterning and Self Assembly Charles J. Dixonand Ollin W. Curtines (Editors)2010. ISBN: 978-1-60692-162-3 NANOTECHNOLOGY SCIENCE AND TECHNOLOGY SERIES NANOTECHNOLOGY: NANOFABRICATION, PATTERNING AND SELF ASSEMBLY CHARLES J. DIXON AND OLLIN W. CURTINES EDITORS Nova Science Publishers, Inc. New York Copyright 2010 by Nova Science Publishers, Inc. 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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Nanotechnology:nanofabrication,patterning,andselfassembly/editors,CharlesJ.DixonandOllinW. Curtines. p. cm. Includes index. ISBN 978-1-61761-771-3 (Ebook) 1.Nanostructured materials. 2.Nanotechnology.I. Dixon, Charles J. II. Curtines, Ollin W. TA418.9.N35N3574 2009 620'.5--dc22 2009004990 Published by Nova Science Publishers, Inc. New York CONTENTS Preface xi Research and Review Studies1 Chapter 1 Electrochemical Nanofabrication3Di Wei Chapter 2 Fabrication and Application of Novel Two-Dimensional Nanowebs via Electrospinning51Bin Ding, Chunrong Li, Dong Wang and Seimei Shiratori Chapter 3 Nano-scale Characterization and Spectroscopy of Strained Silicon71Norihiko Hayazawa and Alvarado Tarun Chapter 4 Nanotechnologies for Cancer Diagnostics and Treatment107Phong Tran and Thomas J. Webster Chapter 5 Mechanical Characterization at Nanometric Scale of Ceramic Superconductor Composites151J.J. Roa, X.G. Capdevila and M. Segarra Chapter 6 ZnO Nanowire Arrays: Template-free Assembly Growth and Their Physical Properties237Bingqiang Cao and Weiping Cai Chapter 7 Spatially Resolved Control of Electrical Resistivity in Organic Materials Development of a New Fabrication Method of Junction Structures275Toshio Naito Chapter 8 Fabrication of Electrical Contacts on Individual Metal Oxide Nanowires and Novel Device Architectures293Francisco Hernandez-Ramirez, Juan Daniel Prades, Roman Jimenez-Diaz, Olga Casals, Albert Cirera, Albert Romano-Rodriguez, Joan Ramon Morante, Sven Barth and Sanjay Mathur Contentsviii Chapter 9 Functionalization of Nanoparticles, Nanotubes and Nanowires by Surface-Initiated Atom Transfer Radical Polymerization309Jinying Yuan, Mi Zhou and Yingwu Yin Chapter 10Synthesis and Applications of Nano-sized Ferroelectrics via Mechanochemical Activation331L.B. Kong, Z. Xu and T.S. Zhang Chapter 11 Preparation and Characterization of Monoatomic Carbon Chains: Unraveling, Field Ion Microscopy, and Field Emission371Igor M. Mikhailovskij Chapter 12 Sequential Nucleation and Growth of Complex Nanostructures by a Two-Step Strategy409Li Yang, Paul W. May and Lei Yin Chapter 13 Progress of Self-standing Diamond Film Fabricated by DC Arc Jet Plasma CVD435G.C. Chen, F.X. Lu, B. Li, C.M. Li, W.Z. Tang, J.H. Song, L.F. Hei and Y.M. Tong Chapter 14 Nanoshell Arrays: Fabrication and Enhanced Photoluminescence459Zhipeng Huang and Jing Zhu Chapter 15 A Strategy for the Incorporation of Trivalent Lanthanide Ions into Anatase Tio2 Nanocrystals479Wenqin Luo, Chengyu Fu, Renfu Li and Xueyuan Chen Chapter 16 Nanocrystallite Superhard Titanium Nitride Film in Multi-arc Ion Plating509Xiang Yu, Chengbiao Wang, Meng Hua, Yang Liu and Shengli Ma Chapter 17Embedded Optical-electrical Nanomateriales Fabricated by Ion Implantation525X.T. Zu, X. Xiang, S. Zhu and L.M. Wang Chapter 18Structural, Dynamical and Optical Properties of Self-assembled Porphyrins at the Mesoscopic Scale559Valentina Villari, Norberto Micali and Luigi Mons Scolaro Short Communications 603 Short Communication A The Influence of Thiophene Addition on Catalytic Pyrolysis of Poly (Dimethyl Siloxane)605K.F. Cai, C.W. Zhou, A.X. Zhang and J.L. Yin ContentsixShort Communication B Nanofinishing of Cotton Textiles615N. Vigneshwaran and Virendra Prasad Index621 PREFACE This new book is dedicated to outstanding research in nanotechnology which is a catch-all description of activities at the level of atoms and molecules that have applications in the real world. A nanometer is a billionth of a meter, about 1/80,000 of the diameter of a human hair, or 10 times the diameter of a hydrogen atom. Nanotechnology is now used in precision engineering, new materials development as well as in electronics; electromechanical systems aswellasmainstreambiomedicalapplicationsinareassuchasgenetherapy,drugdelivery and novel drug discovery techniques. Nano-andmicro-fabricationshavebeenlargelyusedintheapplicationssuchas integratedcircuits,micro/nanoelectro-mechanicalsystems(M/NEMS),micro-opticsand countlessothers.Themethodologyofnanofabricationcanbedividedintotwotypes,top-down and bottom-up processes, which themselves can be further divided. Top-down process refers to approaching the nanoscale from the top (or larger dimensions), such as lithography, nanoimprinting,scanningprobeandE-beamtechniqueetc..Inbottom-upfabrication processes, the nanotechnology process builds nanoscale artifacts from the molecular level up, through single molecules or collections of molecules that agglomerate or self-assemble. Using abottom-upapproach,suchasself-assemblyenablesscientiststocreatelargerandmore complexsystemsfromelementarysubcomponents(e.g.atomsandmolecules).Ingeneral, top-down processes that transfer minute patterns onto material are more matured than bottom-upprocesses.Anexceptionisepitaxialprocessesthatcreatelayersthroughlayer-by-layer growth with registry at the atomic level.Electrodepositionhasactuallybeenusedfordecadestoformhighquality,mostly metallic, thin films. It has recently been shown that high quality copper interconnects for ultra largescaleintegrationchipscanbeformedelectrochemicallyonSiwafer[1;2]. Electrodepositionhasthusbeenshowncompatiblewithstateoftheartsemiconductor manufacturingtechnology.Thelargestsemiconductorcompanies,forexample,IBM,Intel, AMD,Motorolaetc.areinstallingwafer-electroplatingmachinesontheirfabricationlines [1]. The electrodeposition of Cu with the line width 250 nm was used in the mass-production ofmicro-processorPentiumIIIin1998.In2003,thelinewidthoftheCPUwasreducedto 130nminPentiumIV.Electrochemistrywaslargelyusedinchipfabrication[3]andthe packagingofmicro-electronics[4].However,comparingwithothernanofabrication techniques,electrochemicalnanofabricationisstillamaidenareawhichneedsfurther development and fulfilment. Charles J. Dixon and Ollin W. CurtinesxiiChapter 1 summarized the most recent developments in electrochemical nanofabrications. Itincludesnotonlytheconventionaltechnique,underpotentialdeposition(UPD),which dealswiththedepositionofasinglemetal-iononadefinitesubstratebutalsosomenew developmentsusingultrashortvoltagepulsingandtemplatemethodsfor3Dconstructionof nano-materials.Electrochemicalnanofabricationisaversatilemethod,whichincludesboth top-downnanofabrication(e.g.electrochemicallithography)andbottom-upprocesssuchas electrochemicalatomiclayerepitaxy(EC-ALE).Nano-templatesincludinganodized aluminumoxide(AAO)membranes,colloidalpolystyrene(PS)latexspheres,single/aligned carbonnanotubes,selfassembledmonolayers (SAMs),blockedcopolymersandcyclodextrin molecules can be used for the preparation of various types of nanowires, nanotubes, ordered arraysofnanoparticlesandnanodotselectrochemically.Combiningelectrochemistrywith other nanofabrication techniques such as focused ion beam (FIB) and self-assembly provides many novel strategies in the fabrication of nanomaterials with specific design. Selective areas inthenanoscalecanbemodifiedbyelectrochemicalnanostructuringwithmetals,metal oxidesandconductingpolymersusingabipolarelectrochemicaltechnique.Thetraditional lithographyandpatterntechniqueiscostly.Intheconstructionofsoftmatterssuchas conducting polymers, traditional spin casting cannot guarantee nanostructures due to the fast speed of solvent evaporation. Electrochemical technique provides an innovative, versatile and economicwayofnanofabrication.Itespeciallyoffersbetteralternativetoconstructthesoft matter nano-structures in a controllable manner.In general, electrochemical nanofabrication offers simplicity, efficiency, low-temperature processing,cost-effectiveness,thepossibilityinpreparinglargeareadepositsandprecise control of the deposit thickness, which are the essential advantages than other nanofabrication techniquestilldate.Additionally,itcanbeusedtoprepareawiderangeofmaterials comprisingtheinorganicandtheorganic.Theformerincludesquantumdots,metallicand semiconducting(e.g.ZnO,TiO2)nanotubesandnanorods.Thelatterincludesconducting polymer nanotubes and nanowires.Chapter2reviewsourrecentprogressonthenoveltwo-dimensionalnanowebsbythe optimization of processing parameters during electrospinning. Using high applied voltage and low relative humidity in chamber, the by-product ofmicro-sized defect films can be splitted into nanowebs due to the fast phase separation of the charged droplets which flight with high moving speed in electric field from capillary tip to collector. The electrospun fibers act as a supportforthefishnet-likenanowebscomprisinginterlinkedone-dimensionalnanowires. Theaveragediameterofthenanowirescontainedintypicalnanowebsisaboutoneorderof magnitudesmallerthanthatofconventionalelectrospunfibers.Nanowebstogetherwith commonelectrospunnanofiberscanbeassembledintoathree-dimensionalfibrousmat.So far,nylon-6,polyacrylicacid(PAA),poly(vinylalcohol)(PVA)/SiO2nanoparticles,and PVA/zinc acetate have been found to have the possibility forming nanowebs. The formation, morphology,andareadensityofthenanowebsinelectrospunfibrousmatsarestrongly affectedbytheappliedvoltage,ambientrelativehumidity,kindsofsolvents,solution concentration and conductivity, and distance between capillary tip to collector. The expanded applications of electrospun fibers are expected due to the formation of nanowebs, such as the nano-sizedcontrollablefilters,highefficientcatalysts,catalystsupporter,andsensors.The preliminarydatashowingthatthesensitivityofPAAnanowebstoammoniais2.5times higherthanthatofelectrospunPAAnanofibers.Additionally,PAAnanowebsshowmuch PrefacexiiiquickerabsorptionspeedandlargercapacitiesthanthatofPAAnanofibersduringthe ammonia absorption test.Strainedsilicon(-Si),thefundamentalmaterialofintegratedcircuit,isfinding tremendousattentionbecauseitbooststhespeedandreducesthepowerconsumptionsof electronicdevices.However,poorhomogeneitydistributionofstrainin-Silayerscan degradeperformanceofelectronicdevices.Ramanspectroscopyisusedtostudystrain fluctuationsinsiliconbecausetheoptical phonons in Ramanspectra arestronglyinfluenced bystrain.ThoughsiliconareRamanactivedevices,theRamanefficiencyofananometer layerof-SiisextremelyweakandisofteneclipsedundertheRamanscatteringof underlying buffer substrates. Micro Raman measurements show only uniform features in the nano-scalebecauseofaveragingeffectfromdiffraction-limitedspatialresolution. In Chapter 3, the authors utilized surface enhancement in Raman scattering to overcome weak emission problems and to suppress averaging effect. Thin -Si layers were covered with thin AglayertoinvokesurfaceenhancedRamanspectroscopy(SERS).ResultsshowthatSERS effectively enhanced the Raman signal from -Si layer and it stands distinctly apart from the Ramansignaloriginatingfromthebufferlayer.Thistechniqueispromisingbutitlacksthe spatial resolution in the nano-scale due to diffraction limit from the probing light. In order to achievenano-scalespectroscopy,point-surface-enhancementwasused,ratherthanalarge surface enhancement. The authors used a silver-coated sharp tip, just like SERS, but only the sampleregionveryclosetothetipapexischaracterized.Thistechnique,knownasthetip-enhanced Raman spectroscopy (TERS), provides nanometric resolution in ourmeasurement. The authors observed localized strains by employing TERS. The TERS spectra revealed clear nano-scale variation in Raman frequency. Now that the authors can distinctively separate -Si from underlying buffer layer, signal-to-noise ration (SNR) needs further improvement. They improveTERSSNRintwoways:opticalfieldenhancementusing differentmetallictipand backgroundsignalsreductionarisingfrombulkmaterials.Thetip-enhancementismore important for homogenous nano-materials or for samples with very weak signals whereas the background signal reduction is indispensable for nano-materials that consist of different thin layerswithstrongsignalssuchas-Siorsampleswithstrongsignallevel.Accordingly,the authorsintroduceseveralapproachesmainlyforthesuppressionofbackgroundsignals arising from other bulk materials. The authors will discuss the utilization of UV light source, specializedtip,sampleorientationrelativetoprobingpolarization,anddepolarization configuration to obtain high contrast Raman signal. The characterization techniques describe above is applicable to other nano-materials. Cancertreatmentusuallyusesdrugs(chemotherapy)toreducetumorsize,followedby surgery to remove the tumor (if possible). Then, more chemotherapy and radiation therapy is used to kill as many tumor cells as possible. The goal of this collective treatment is to target andkillcanceroustissuewhileminimizingsideeffectsonhealthycells.Duetotheirnon specificity,currentcancertherapieshavepoortherapeuticefficacyandcanalsohavesevere side effects on normal tissues and cells. In addition, cancer is often diagnosed and treated too late,i.e.,whenthecancercellshavealreadyinvadedandmetastasized(i.e.spread)toother partsofthebody.Atthisstage,treatmentmethodsarehighlylimitedintheireffectiveness. Thus, scientists have been focusing efforts into finding alternative methods to detect cancer at earlier stages and kill such cancerous tissues more effectively. Nanoparticles (that is, particles withatleastonedimensionlessthan100nm)havebecomeveryattractiveforimproving Charles J. Dixon and Ollin W. Curtinesxivcancerdiagnosisandtreatmentduetotheirnoveloptical,magneticandstructuralproperties notavailableinconventional(ormicron)particlesorbulksolids.Nanoparticleshavebeen extensivelystudiedforvariousapplicationsincludingdeliveringanti-cancerdrugsto tumorous tissues and/or enhancing imaging capabilities to better diagnose and treat cancer. In Chapter 4, recent work related to the improved targeted therapy for specific cancers (whether bydevelopingmorespecificanti-canceragentsorbyalteringdeliverymethods)are summarized.Discussionsontheadvantagesanddisadvantagesofthemostwidelystudied nanoparticles(i.e.,liposomenanoparticles,polymer-basednanoparticles,quantumdots, nanoshells, and superparamagnetic particles) in cancer imaging followed by anti-cancer drug deliveryarehighlighted.Lastly,bonecancerandcurrentresearchinusingnanoparticlesfor treatingbonecancer,withanemphasisonthenoveluseofselenium(anaturalanti-cancer element found in our bodies), are addressed. The nanoindentation or indenter testing technique (ITT) is a functional and fast technique that can give us a lot of information about the mechanical properties of different materials at nanometricscale,fromsoftmaterials,suchascopper,tobrittlematerials,suchasceramics. Theprincipleofthetechniqueistheevaluationoftheresponseofamaterialtoanapplied load. In a composite material, if the size of the residual imprint resulting from a certain load is lowerthanthesizeofthestudiedphase,thenispossibletodetermineitsmechanical properties, and therefore its contribution to the global mechanical properties of the composite. Dependingonthetippedindenterused,differentequationsshouldbeappliedtostudythe responseofthematerialandcalculatestress-straincurvesandparameterssuchashardness, Youngsmodulus,toughness,yieldstrengthandshearstress.Theseequationsarerelatedto thedifferentdeformationmechanisms(elastic,plasticorelastoplastic)thatthematerial undergoes.Inthecaseofmostoftheceramiccomposites,whenasphericaltippednanoindenteris used, elastic deformation takesplace,andHertzequationscanbe usedto calculate theyield stress,shearstressandthestrain-stresscurves.Ontheotherhand,whenaBerckovich indenterisused,plasticdeformationtakesplace,thenOliverandPahrrequationsmustbe appliedtoevaluatethehardness,Youngsmodulusandtoughness.Nevertheless,inthe hardness study, Indentation Size Effect (ISE) must be considered. In Chapter 5, the mechanical properties of a ceramic superconductor material have been studied.YBa2Cu3O7-(YBCOorY-123)texturedbyBridgmanandTopSeedingMelt Growth(TSMG)techniqueshavebeenobtainedandtheirmechanicalpropertiesstudiedby ITT. This material presents a phase transition from tetragonal to orthorhombic that promotes a change in its electrical properties, from insulating to superconductor, and that can be achieved by partially oxygenating the material. On the other hand, the structure of the textured material isheterogeneous,andtwodifferentphasesarepresent:aY-123asamatrixandY2BaCuO5 (Y-211) spherical inclusions. Moreover, the texture process induces an anisotropic structure, thus being the ab planes the ones that transport the superconductor properties while the c axis remains insulating. Thepurposeofthisstudyisthecharacterizationofthemechanicalproperties,inelastic andplasticrange,oforthorhombicphasesofYBCOsamplestexturedbyBridgmanand TSMGtechnique.WiththeITTtechnique,theoxygenationprocesscanbefollowedandits kinetics established. InChapter6,growthandphysicalpropertiesofZnOnanowirearrayswerereviewed.It begins with some general remarks on semiconductor nanowires and basic properties of ZnO. PrefacexvInthesecondpart,differentkindsofgrowthmethodsthathavebeenappliedtogrowZnO nanowiresaresummarized.VaporphasemethodsusuallybasedonVSLorVSmechanism, depending on the presence or absence of a metal catalyst, were discussed in general. Typical solutionmethodsforgrowthofZnOnanowireswerediscussedseparatelyasthereisno commongrowthmechanismthatcanbeappliedtodescribethem.Anewtemplate-free strategy based on self-assembly process to grow ZnO nanowire into arrays were emphasized anddiscussedindetail.Theobtainedsamplequalitieswerecharacterizedwithscanning electronmicroscopy,transmissionelectronmicroscopy,X-raydiffractionandenergy-dispersive X-ray spectrum. The third part deals with the physical properties of ZnO nanowire arrays. Raman spectrum, including resonant Raman spectrum, was applied to test the crystal qualityandphononinteractionofZnOnanowires.Temperature-dependent photoluminescencespectraweremeasuredtoprobetheintrinsicexcitonanddefect-related emission process of ZnO nanowires. Field emission properties of such ZnO nanowire arrays werealsostudiedinviewofthepossibleapplicationforflat-paneldisplays.Somebrief conclusions were summarized at the end.Organicmaterials(OMs)arediverseandareinterestingintermsofapplicationin electronicdevices.Inparticular,organicchargetransfersalts(OCTSs),whicharetypically composedofpositiveandnegativeionic(andoftenradical)organicmolecules,attract continuedattention.Withoutcarrierdoping,theygenerallyhavehighconductivity, magnetism, and well-defined unique nanostructures in their crystalline form. In order to apply the OCTSs to electronic devices, they should be made junction structures. Although there are establishedwaysandadvancedmethodsfordopingandfabricationofjunctionstructuresin thecurrentindustrialtechniquesforthesilicondevices,fewofthemareapplicabletothe OMs due to totally different chemical and physical properties between inorganic and organic materials.InChapter7,theauthorswouldliketodiscussanewmethodforsimultaneous realization of doping and junction structures beginning with the single crystals of the OCTSs. Themethodutilizesaphoto-inducedchemicalreaction,andproducesastablesolidstate composedofwell-defineddifferentpartsofdifferentconducting/magneticproperties.With referencetoourrecentandpreviousworkaswellasrelatedstudiesofothergroups, discussion will briefly cover experimental methods, preparation of materials, examination of irradiationconditionsandresultantsolidscharacterization,outlineofmechanismofthis photochemical modification, and remaining problems to be explained or overcome. Metal oxide nanowires exhibit novel properties due to their high surface-to-volume ratio andhighsurfacestability.Forthisreason,theyareconsideredexcellentcandidatestobe incorporatedintoanewgenerationofdeviceswithimprovedperformance.Nevertheless, reachingcompletecontroloftheirphysical,chemicalandelectricalpropertiesisneeded beforetheycanbewidelyusedinoureverydaylife.Thisobjectivecanbeonlyfulfilledif reproducibleelectricalmeasurementsonindividualnanomaterialsareperformed.However, thefabricationofelectricalnanocontactsinafastandwell-controlledprocessisstillan unsolved issue. In Chapter 8, the main nanofabrication techniques that are commonly used to electrically access individual metal oxide nanowires, and to study their intrinsic properties are presented.Advantagesandlimitationsofthesemethodologiesarediscussedindetail.By integratingbottom-upandtop-downtechniques,thefirstfunctionalprototypesbasedon individualnanowireshavealreadybeenimplemented,pavingthewaytothefuture developments of nanoscale electronics, optoelectronics and chemical sensing devices. Charles J. Dixon and Ollin W. CurtinesxviThe inorganic-polymer hybrid nanomaterials have many excellent properties. So they are becomingincreasinglyimportantforvariousapplicationsrangingfrombiomaterialsto semiconductorsinmanyfieldsandarousemuchinterestofscientistsallovertheworld. Chapter 9 highlights the development of surface-initiated living radical polymerizations from the inorganic materials, including nanoparticles and one-dimensional (1D) nanostructures, by surface-initiatedatomtransferradicalpolymerization(SI-ATRP).Theemphasisisputupon the new developments of SI-ATRP taken to prepare hybrid nanomaterials in the recent years.Ferroelectricmaterialshavebeenfoundtobepromisingcandidatesinapplicationsofa widerangeofelectronicdevices,suchashigh-dielectricconstantcapacitors,piezoelectric sonar or ultrasonic transducers, pyroelectric security sensors, medical diagnostic transducers, electro-opticallightvalves,andultrasonicmotors,andsoon.Ferroelectricmaterialswere conventionally fabricated via solid-state reactions at relatively and sometimes extremely high temperatures for calcining and sintering. Due to the presence of volatile components, such as lead(Pb),bismuth(Bi)orlithium(Li),inmostferroelectriccompounds,hightemperatures processing would brought out the problems of losing of the elements, which often resulted in thedeteriorationsinmicrostructuresandthuselectricalperformancesoftheferroelectric materials.To reducethefabricationtemperatures offerroelectricceramics,itis necessaryto useultrafinepowders.High-energymechanochemicaltechnique,asanalternativemethod, hasbeenusedtosynthesizenanosizedferroelectricpowdersdirectlyfromtheiroxideand otherprecursors.Chapter10servesasanoverviewofprogressinthesynthesisofvarious ferroelectricmaterialsbyusingvariousmechanochemicalmillingfacilities.Inaddition, applicationsofnanosizedferroelectricpowdersinmaterialspreparationanddevice fabrication will be also be included. Linearformsofcarbonareimportantinawidevarietyofapplication,rangingfrom highlyconductinginterconnectstofieldemissionmaterials.Bymethodsoffieldion microscopy(FIM)andmass-spectrometry,itwasrevealedthepresenceoflinearcarbon chainsatthesurfaceofcarbonfibersafterhigh-voltagetreatment.Theauthorspresentin Chapter11abriefreviewoftheseresearchemphasizingrecentdevelopments.Thecarbon chainsattachedtothespecimentipscan beproducedinsituinafieldionmicroscope using low-temperaturepulsedevaporationbyelectricfieldsoftheorderof1011 V/m.AtomicC-chainsareproducedduringthehigh-fieldunravelingofnanofibers.Theexperimental procedures usedinFIMcarbonchainsstudiesarereviewedandthe resultsinrelation to the atomisticsofunravelingprocessesarediscussed.Moleculardynamicssimulationsandhigh resolutionFIMexperimentsareperformedtoassesstheevaporationofatomicchainsunder high-fieldconditions.Carbonexhibitsaveryrichdynamicsofbond-breakingthatallows transformationfromgraphenestoatomicchains.High-fieldexperiments,theoriesleadingto carbon chain formation, and methods to extract quantitative information on a variety of chain-surface interactions are described indetail.Isolatedatomiccarbon chainscan be obtained at differenttemperatures,pullingspeedsandforces.Currentversusvoltagefieldelectron characteristicsofmonoatomiccarbonwireswereinvestigated.Theseresultslendstrong supporttotheconjectureofSmalleythatlinearcarbonchainsmayprovidetheultimate atomic-scale field emitters.Self-assemblednanostructuresarenewformsofmaterialswhichareinterestingfroma fundamentalscientificperspective,aswellashavingmanypotentialtechnological applications.AsexplainedinChapter12,itisbelievedthattheabilityofnanostructuresto self-assemblewithcontrolledcrystallineorientation,size,complexityandcrystal Prefacexviimorphology,providepotentialapplicationsindatastorage,functionaldevices, communications and technology. Recently, a two-step strategy was successfully developed in ourlabtoproducetwo-dimensionalorthree-dimensionalcarbonnitridewell-defined hierarchicalcomplexstructures.Thisstrategyisacombinationofanovellaser-induced depositiontechniquefollowedbyself-assembly.Inthefirststep,asuspensionofcarbon nitridenanoparticleswaspreparedbyliquid-phasepulsedlaserablation(LP-PLA).Inthe secondstage,thissuspensionwasdepositedontoasiliconsubstratetoactasaseedlayer. Via controlling the rate of evaporation of the liquid phase part of the seed suspension, and the sizeandthequantityofnanocrystalswithinthedroplet,itwaspossibletocreatearangeof nanoscalestructures,includingdensenanospheres,highly-symmetricflowers,hollowcore-shell and uniform grass-like structures. The growth of such complex structures is governed by an evaporation-driven self-assembly process. As the droplet dries, small building blocks, such asnanoparticles(NPs)ornanorods(NRs)nucleateupontheexistingcrystalsandtemplate, sharingthesameedges,toformaclose-packedarrangement.Byvaryingthedesignofthe building blocks, materials combination, interfacial chemistry, and confining dimensions, it is expected to extend this synthetic approach to a range of new structured materials with useful functional properties.Self-standingdiamondfilmswerefabricatedbya30kWDCArcjetCVDsystem.The novelprogresses,includinglayer-structuredfilm(nano-/micro-crystallinelayer)fabrication, high orientated film deposition with high growth rate at very high ratio of CH4/H2, crack-free thick and large area films growth, and single crystal fabrication, were reported.Layer-structuredself-standingfilms,2-and4-layeredones,werefabricatedby fluctuating the ratio of methane to hydrogen with deposition time. Results of scan electronic microscopy (SEM) and Raman spectra showed that the layered films were constructed by the micro-crystallinegrainslayer/nano-crystallinegrainslayer.Theresidualstresswithinthe filmswerebalanced,andevendiminishedinthecertainlayer.Thelayercontainingnano-crystalline grains due to a plenty of secondary nucleation could weakly inherit the columnar growthfeatureoftheoverlaidlayercontainingmicro-crystallinegrains.Thegrainsizeand growthorientationofthelayercontainingmicro-crystallinegrainscouldbeadjustedby introduction a mid-layer containing nano-crystalline grains. Growth rate was over 10m/hr in layered film fabrication.The effect of very high concentration of CH4 in H2, 10%CH4/H2 25%, was studied on thefilmmorphologyandorientation.Diamondfilmswithmorphologycontainingnice facetedmicro-sizedgrainswereobtainedwithCH4/H2upto17%.Thefilmcomposition changewasfoundbyRamanspectra.High(111)-orientedfilmsweredepositedunderthe conditionofCH4/H2=15%atthemaximumgrowthrateabout50m/h.Deposition temperaturecouldinfluenceboththemorphologyandorientationof the diamondfilms.The higherdepositiontemperature,thehigherCH4/H2couldbeallowedtodepositmicro-sized grain-containingfilms.However,highdepositiontemperaturewouldspoil(111)-orientation. As a consequence, (220) and (311) would be enhanced.Crackpatternsoccurringinself-standingfilmswereclassifiedasnetworkshape,river shape and circle shape. The distribution and style of dominating crystalline surface was found toinfluencethestrengthofself-standingfilm.Thefilmswith60-120mmofdiameterand 2mmofthicknessweresuccessfullydepositedbycontrollingofdominatingcrystalline surface in the films. Charles J. Dixon and Ollin W. CurtinesxviiiAnewapproachtosinglediamondcrystalfabricationbyarcjetwasproposedand discussed in Chapter 13. This method was named as stable-tip method which was applied to overcomethemorphologyinstability.Singlecrystal,110.6mm3 insize,wassuccessfully fabricated by this method. The synchrotron radiation topography was adopted to characterize this single crystal diamond.Lowemissionefficiencyofsilicon(Si)basedlightemissiondevices(LED)stillblocks applicationofSi-LED.Therefore,studiesfocusingonimprovinglightemissionofSi-LED stillattractresearchespassion.Recently,theauthorshavedevelopedanewmethod combiningnanospherelithographyandpulsedlaserdepositiontofabricateSi-basedarrays nanostructures,andhaveobtainedremarkablyenhancedphotoluminescence(PL)fromthese structures.TheSibasednanostructuresarehemisphereshellarrays(HSSAs)ornanoflower arraysassembledbysilicon-germanium(SiGe)alloy.Thesestructuresincludenon-close-packed and close-packed ones, single layer and multilayer ones, as well as arrays on different substrates. In Chapter 14, the authors investigated the photoluminescence of these arrays structures, andfoundthatallthesestructurescouldenhancethephotoluminescenceintensities.Among them, the enhancement of light emission from SiGe double layer HSSAs (DL-HSSAs), which is as high as 700 folds, is the highest among those of all structures.Employingtransmissionelectronmicroscopy(TEM),scanningelectronmicroscopy (SEM),time-resolvedPL,andelectromagneticsimulationetc,theauthorsfoundthe enhancement of light emission in Si based nanostructures originated mainly from the increase ofextractionefficiencyofphotonsfromthenanostructures.Theelectromagneticsimulation ofenhancementmatchedwelltheexperimentdata.Theauthorsalsofoundthatthese enhancements are related to degree of order of arrays. In highly order arrays, the enhancement is higher than that in other arrays.Trivalentlanthanide(Ln3+)ion-dopedsemiconductornanocrystalshaveattracted extensiveattentionduetotheabilitytotailortheiropticalpropertiesviasizecontrolandto achievehighlyefficientluminescencethroughsensitizationbythehost.Todate,findinga waytodopetheundopableLn3+ionsintosemiconductornanomaterialsviachemical methodsremainsachallenge.InChapter15,recentprogressinthedopingofLn3+ionsin TiO2nanomaterialshasbeenreviewed.Anovelsol-gel-solvothermalmethodhasbeen developed to effectively incorporate Ln3+ ions (Eu3+, Er3+, Nd3+ and Sm3+) into anatase TiO2 nanoparticlesviatheself-assemblyandcrystallizationprocessofpreviousamorphous nanoparticles, in spite of a large mismatch in ionic radius and charge imbalance between Ln3+ andTi4+.ThecrystallizationprocessofLn3+dopedTiO2nanoparticlesweresystematically studiedbymeansofthermogravimetric-differentialthermalanalyses(TG-DTA),powderX-raydiffraction(XRD),andtransmissionelectronmicroscope(TEM).Photoluminescence (PL)spectraofLn3+:TiO2samplesexhibitresolvedandsharpemissionandexcitationlines from the intra f-f transitions of Ln3+ ions (Ln=Nd, Sm, Eu, Er), indicating regular crystalline surroundingsofLn3+ions.MultiplesitesofEu3+,Sm3+andNd3+ionsinanataseTiO2 were detected by means of high- resolution site-selective spectroscopy at 10K, whereas only single site emission of Er3+ in TiO2 were observed. Very intense near-infrared luminescence around 1.53mwasalsoobserved,whichoriginatedfromthesinglelatticesiteofEr3+ions incorporatedinTiO2nanocrystals.TheluminescencedynamicsandCFlevelsofLn3+at different sites have been analyzed. Highly efficient emissions of Nd3+ and Sm3+ sensitized by theTiO2hostwereobservedupontheexcitationabovetheTiO2bandgapenergyatroom Prefacexixtemperature(RT),whichisofparticularinterestformaterialapplications.Agrowth mechanism for the incorporation of Ln3+ in the anatase lattice is also suggested.Titanium nitride (TiN) films synthesized by multi-arc ion plating (AIP) normally have a columnarmicrostructure,andarelikelytoinducesurfacedefectsduetotheformationof macroparticlesandneutralparticlesinthevicinityofcathodearcsources.Hence,the achievablemicrohardnessofthenormalAIPTiNfilmsonlyrangesbetween20~30GPa.A systematicstudyforfabricatinganadherentnano-superhardtitaniumnitride(TiN)filmon M2highspeedsteelsubstratebyavacuumcathodemulti-arcion-plating(AIP)systemwas initiated.Tounderstandtherelationshipofthefilmprocessing-structure-property,their microhardness, film-to-substrate adhesion, frictional property, and microstructure of the film wereinvestigatedusingVickershardometer,scratchtester,ball-on-disctester,X-ray diffractometer, and transmission electron microscope. Results in Chapter 16 show that: (i) the achievable film microhardness ranges between 35 GPa and 45 GPa; (ii) the critical load (Lc) of the superhard TiN film is at 64 N approximately; (iii) the friction coefficient, under a high-loadandahighrotating-speed,ofthefilmisrangingfrom0.5to0.8;and(iv)thenmscale mean main grain-sizes of the film are approximately 12.7 nm for TiN111, 19.7 nm for TiN200 and 9.6 nm for TiN220. The maximum achievable microhardness 45 GPa is more than twice of the 22 GPa for standard TiN film. Such hardness enhancement is anticipated as mainly due to: (a) the formation of nanoscaled crystalline grains; (b) the preferential orientation and growth of grains in the close-packed plane (111); and (c) the induced residual stress within the film by ion bombardment. InChapter17,nanoparticlesembeddedininsulators,e.g.,Al2O3,MgO,YSZandTiO2 singlecrystals,werefabricatedbyionimplantationandsubsequentthermalannealing, including metallic Ni, Zn and their oxides, and intermetallic nanoparticles. Optical, magnetic and mircostructural properties of nanoparticles have been studied. The metallic nanoparticles havesurfaceplasmonresonanceabsorption,andoxidenanoparticlesshowgood photoluminenscence. The magnetic nanoparticles, e.g., metallic Ni and intermetallic CoxNi1-x nanoparticles,showstrongferromagnetismbehaviors.Theionfluencecanaffectthe concentrations and the intensities of the surface plasmon absorption of metallic nanoparticles. Ionfluxisanotherimportantparametertofabricatenanoparticles.Anexampleofeffectsof ion flux on the nanoparticles has been presented in this data review. The relationship between annealingtemperatureandoptical,magneticandmicrostructuralpropertiesofnanoparticles has also been systematically studied. Ion implantation provides a versatile and powerful technique for synthesizing nanometer-scaleclustersembeddedinthenear-surfaceregionofavarietyofhostmaterials.The embedded nanoparticles have attracted considerable attention because of their unique optical-electricalpropertiesthataredifferentfromthoseofthebulkmatrix.Metallicnanoparticles embedded in insulators have pronounced optical effects, including surface plasma resonance (SPR)absorption,andstrongthird-ordernonlinearoptical(NLO)susceptibility.Theformer suggestsapplicationsasopticalfilters,includingeye-glasscoatings.Thelatterhaspotential applicationinall-optical-memoryorswitchingdevices.Oxidenanoparticleshavegood photoluminescence.Theyhavepromisingapplicationinlight-emittingdevices.Magnetic metallic nanoparticles often show a ferromagnetic behavior with a larger coercivity than that ofthecorrespondingbulkmaterials,whichmayprovidepotentialapplicationofthe nanocomposite as magneto-optical materials for a high density magnetic data storage device. Charles J. Dixon and Ollin W. CurtinesxxOrganized self-assembly of molecules, driven by noncovalent intermolecular interactions, isthemostversatiletoolforaccessingnewmaterialswithdesiredopticalandelectronic properties.Porphyrinsareparticularlyattractivespeciestoincorporateintosupramolecular assembliesbecausetheirrichphotochemistrymayimpartfunctionality,provideinsightinto themechanismsofbiologicalprocessessuchasphotosynthesis,serveasprobesintothe featuresofself-assembledstructuresandasmodelsformolecularorganizationand energy/electrontransferprocesses.Theclosemolecularpackinginaself-assembled porphyrin aggregate leads to different electronic coupling and delocalization of the excitation energy,whichcanbeexploitedforapplicationsinnon-linearopticaldevices,photoelectric cells,recordingdevices.Thepossibilitytocontrolandtuneeithershapeandsizeofthe porphyrinclustersopensthewayfortheiruseaspotentialnanodevices.Chapter18aimsto collect some recent developments in the field of porphyrin self-assembly and to frame all the reported topics into the current theories. The influence of thiophene addition on the pyrolysis of poly(dimethyl siloxane) catalyzed byferroceneat~1050 oCinArwasstudiedinthefirstShortCommunication.Theas-synthesizedproductwascharacterizedbyX-raydiffraction,scanningelectronmicroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The thiophene addition caused several changes. Firstly, the yield of the product was increased by severaltimesandthediametersoftheproductweresomewhatincreased.Secondly,the productwaschangedfromonlySiC/SiO2nanocablestoamixtureofSiC/SiO2nanocables andSiC-SiO2side-by-sidenanowires.Thirdly,moreYtypenanostructureswerefound. Finally,thegrowthprocessoftheproductwasalteredasthenanostructureseachhada polyhedralFeSnanoparticleratherthansphericalFenanoparticle.However,lengthsofthe productwerestillonthemillimeterscale.Thepromotionmechanismofthiopheneaddition was also analyzed. As discussed the second short communication, nanotechnology revolutionized every field inscienceandtechnology.Recently,itsusefulnessinnanofinishingofcottonfabricsby impartingfunctionalpropertieslikeantimicrobial,UV-resistance,self-cleaninganddrug-delivery is well documented. In addition, enhancement in comfort properties of cotton textiles isalsobeingevaluatedwiththehelpofnanofinishing.Withjudicialuseofnanomaterials, keepinginviewtheirbio-safetyandenvironmentalimpactissues,nanofinishingwillbea great boon to the users of cotton textiles. RESEARCH AND REVIEW STUDIESIn: Nanotechnology ISBN: 978-1-60692-162-3Editors: C.J. Dixon and O.W. Curtines, pp. 3-50 2010 Nova Science Publishers, Inc.Chapter 1ELECTROCHEMICALNANOFABRICATIONDi WeiNokia Research Centre, c/o Nanoscience Centreat University of Cambridge,11 JJ Thomson Avenue, CB3 0FF, Cambridge, UKAbstractNano-andmicro-fabricationshavebeenlargelyusedintheapplicationssuchasintegratedcircuits,micro/nanoelectro-mechanicalsystems(M/NEMS),micro-opticsandcountlessothers.Themethodologyofnanofabricationcanbedividedintotwotypes,top-downandbottom-upprocesses,whichthemselvescanbefurtherdivided.Top-downprocessreferstoapproachingthenanoscalefromthetop(orlargerdimensions),suchaslithography,nanoimprinting,scanningprobeandE-beamtechniqueetc..Inbottom-upfabricationprocesses, the nanotechnology process builds nanoscale artifacts from the molecular level up,through single molecules or collections of molecules that agglomerate or self-assemble. Usingabottom-upapproach,suchasself-assemblyenablesscientiststocreatelargerandmorecomplex systems from elementary subcomponents (e.g. atoms and molecules). In general, top-down processes that transferminute patterns ontomaterial aremorematuredthanbottom-upprocesses. An exception is epitaxial processes that create layers through layer-by-layer growthwith registry at the atomic level.Electrodepositionhasactuallybeenusedfordecadestoformhighquality,mostlymetallic, thin films. It has recently been shown that high quality copper interconnects for ultralargescaleintegrationchipscanbeformedelectrochemicallyonSiwafer[1;2].Electrodepositionhasthusbeenshowncompatiblewithstateoftheartsemiconductormanufacturingtechnology.Thelargestsemiconductorcompanies,forexample,IBM,Intel,AMD,Motorolaetc.areinstallingwafer-electroplatingmachinesontheirfabricationlines[1]. The electrodeposition of Cu with the line width 250 nm was used in the mass-productionofmicro-processorPentiumIIIin1998.In2003,thelinewidthoftheCPUwasreducedto130nminPentiumIV.Electrochemistrywaslargelyusedinchipfabrication[3]andthepackagingofmicro-electronics[4].However,comparingwithothernanofabricationtechniques,electrochemicalnanofabricationisstillamaidenareawhichneedsfurtherdevelopment and fulfilment.Di Wei 4Thischaptersummarizedthemostrecentdevelopmentsinelectrochemicalnanofabrications.Itincludesnotonlytheconventionaltechnique,underpotentialdeposition(UPD), whichdealswiththedepositionofasinglemetal-iononadefinitesubstratebutalsosomenewdevelopmentsusingultrashortvoltagepulsingandtemplatemethodsfor3Dconstructionofnano-materials.Electrochemicalnanofabricationisaversatilemethod,whichincludesbothtop-downnanofabrication(e.g.electrochemicallithography)andbottom-upprocesssuchaselectrochemicalatomiclayerepitaxy(EC-ALE).Nano-templatesincludinganodizedaluminumoxide(AAO)membranes,colloidalpolystyrene(PS)latexspheres,single/aligned carbon nanotubes, selfassembled monolayers (SAMs), blocked copolymers andcyclodextrinmoleculescanbeusedforthepreparationofvarioustypesofnanowires,nanotubes,orderedarraysofnanoparticlesandnanodotselectrochemically.Combiningelectrochemistrywithothernanofabricationtechniquessuchasfocusedionbeam(FIB)andself-assembly provides many novel strategies in the fabrication of nanomaterials with specificdesign.Selectiveareasinthenanoscalecanbemodifiedbyelectrochemicalnanostructuringwith metals, metal oxides and conducting polymers using a bipolar electrochemical technique.The traditional lithography and pattern technique is costly. In the construction of soft matterssuchasconductingpolymers,traditionalspincastingcannotguaranteenanostructuresduetothefastspeedofsolventevaporation.Electrochemicaltechniqueprovidesaninnovative,versatileandeconomicwayofnanofabrication.Itespeciallyoffersbetteralternativetoconstruct the soft matter nano-structures in a controllable manner.In general, electrochemical nanofabrication offers simplicity, efficiency, low-temperatureprocessing,cost-effectiveness,thepossibilityinpreparinglargeareadepositsandprecisecontrol of the deposit thickness, which are the essential advantages than other nanofabricationtechniquestilldate.Additionally,itcanbeusedtoprepareawiderangeofmaterialscomprisingtheinorganicandtheorganic.Theformerincludesquantumdots,metallicandsemiconducting(e.g.ZnO,TiO2)nanotubesandnanorods.Thelatterincludesconductingpolymer nanotubes and nanowires.Electrochemical DepositionUnder Potential Deposition (UPD)Surface limited reactions are well known in electrochemistry and are generally referred toasunderpotentialdeposits[5;6].Underpotentialdeposition(UPD)istheformationofanatomic layer of one element on a second element at a potential under, or prior to, that neededtodeposittheelementonitself.Theshiftinpotentialresultsfromthefreeenergyofthesurface compound formation.;EarlyUPDstudieswerecarriedoutmostlyonpolycrystallineelectrodesurfaces[7].Thiswasdue,atleastinpart,tothedifficultyofpreparingandmaintainingsingle-crystalelectrodes under well-defined (and controlled) conditions of surface structure and cleanliness[8]. Forexample,cadmium(Cd)can beunderpotentiallydeposited onCu(111)and Cu(100)[9]. There are a number of excellent reviews on this topic [5;6].Electrochemical Atomic Layer Epitaxy (EC-ALE)Electrochemicalatomiclayerepitaxy(EC-ALE)isthecombinationofUPDandALE,whichusesUPDforthesurfacelimitedreactionsinanALEcycle[10].Fundamentaltoforminghighqualitystructuresanddeviceswiththinfilmsofcompoundsemiconductorsisthe concept of epitaxy. The definition of epitaxy is variable, but focuses on the formation ofElectrochemical Nanofabrication 5singlecrystalfilmsonsinglecrystalsubstrates.Thisisdifferentfromotherthinfilmdepositionmethodswherepolycrystallineoramorphousfilmdepositsareformedevenonsinglecrystalsubstrates.Homoepitaxyistheformationofacompoundonitself.Heteroepitaxyistheformationofacompoundonadifferentcompoundorelement,andismuch more prevalent. The principle of ALE is to growthe deposit one atomic layer at a time[11]. Surface limited reactions are developed for the deposition of each component element inacycletodirectlyformacompoundvialayer-by-layergrowth,avoiding3Dnucleations.With cycle, a compound monolayer is formed, and the deposit thickness is controlled by thenumberofcycles.InanEC-ALEprocess,eachreactanthasitsownsolutionanddepositionpotential, and there are generally rinse solutions as well.Controlofgrowthatthenanoscaleisamajorfrontierofmaterialsscience.Themanipulationofacompoundsdimensions,orunitcell,atthenanoscale,canresultinmaterials with unique properties. By constructing superlattices, nanowires and nanoclusters orforming nanocrystalline materials, the electronic structure (bandgap) of a semiconductorcanbeengineered.EC-ALEhasbeendevelopedasanelectrochemicalmethodologytogrowcompound semiconductors with nanoscale or atomic layer control. In an EC-ALE synthesis ofCdTe, for example, atomic layers of tellurium and cadmium are alternatively electrodepositedtobuildupathinlayerofCdTe[12;13].Thenecessaryatomiclevelcontrolovertheelectrodeposition of these two elements is obtainedbydepositingbothelementsusingUPD.ThethicknessoftheCdTelayerpreparedbyEC-ALEcanbespecifiedbycontrollingthenumber of Cd and Te layers that are deposited.Figure 1. Transmission electron micrograph (TEM) of a CdTe deposit formed using 200 cycle of CdTevia EC-ALE [14]. Reproduced by the kind permission from the publisher.Di Wei 6Fig.1showstheTEMfigureoftheCdTeusngEC-ALEwith200cycles[14].Theregularlayeredstructure,parallelwiththesubstrateAulatticeplanes,suggeststheepitaxialnatureofthedeposit.ThereareanumberofwaystointroducedopantsintoanEC-ALEdepositandtheycanbeintroducedhomogeneouslythroughoutthedeposit.InitialdopingstudiesofZnSwererunwiththeideaofformingphosphorscreensforflatpaneldisplayapplications [15].Electrochemical Deposition Methods for Semiconducting NanocompoundsElectrodepositionnormallyleadstosmallparticlesize,largelybecauseitisalowtemperaturetechnique,therebyminimizinggraingrowth.It,however,possessestheadditionalfeatureofaveryhighdegreeofcontrolovertheamountofdepositedmaterialthroughFaradayslaw,whichrelatestheamountofmaterialdepositedtothedepositioncharge. This feature is particularly desirable when isolated nanocrystals are to be deposited ona substrate.Severalmethodsandvariationshavebeendevelopedtoelectrodepositcompounds.Oxidesareprobablythelargestgroupofelectrodepositedcompounds(forexample,aluminiumanodization).TheelectrodepositionofII-VIcompoundshasbeenextensivelystudiedandiswellreviewedinanumberofarticles[16-18].Anumberofreviewsofsemiconductor electrodeposition also exist which describe the various methods used [19;20].Themostprominentelectrodepositionmethodsforsemiconductingcompoundsinclude:codeposition, precipitation and various two-stage techniques.SemiconductorfilmcanbeelectrodepositedeitherbyEC-ALEorbyco-deposition[21].ThemostsuccessfulmethodologytoformII-VIcompoundshasbeencodeposition[22-26],wherebothelementsaredepositedatthesametimefromthesamesolution.Stoichiometryismaintainedbyhavingthemoreinactiveelementasthelimitingreagent,and poising the potential where the less noble element will underpotentially deposit only onthemorenobleelement.TheclassicexampleisCdTeformation[22],wherethesolutioncontains Cd2+ and HTeO2+, usually at pH 2. The potential is set to reduce HTeO2+ to Te onthesurfaceatalimitingrate,whileCd2+isreducedontheTeatanunderpotential,apotentialwherenobulkCdisformed.Cd2+ionsarepresentinalargeexcess,todepositquantitativelyonTeasitisformed,resultinginstoichiometricCdTe.Althoughthestructureandmorphologyofcodepositedcompoundsarevariable,somehavingbeendescribedascauliflowerlike,highqualitydepositshavebeenformed[27].Thereareanumberofpapersintheliteratureconcerningtheformationofcompoundsemiconductordiodesbyelectrodeposition,themostpopularstructurebeingaCdS-CdTebasedphotovoltaic.CdSwasgenerallydepositedfirstonanITO/glasssubstrate,followedbyalayerofCdTe,usuallybycodeposition[28-34].SailorandMartinetal.grewanarrayofCdSe-CdTenano-diodesin200nmporealumite[35-37],usingacompoundelectrodepositionmethodologycalledsequentialmonolayerelectrodeposition[38].AcommercialprocessisbeingdevelopedbyBPSolartoformCdTebasedphotovoltaicsusing codeposition. Relatively rapid deposition rate has been achieved by codeposition anditispresentlythemostpracticalcompoundsemiconductorelectrodepostionmethodology.Codepositionholdsgreatpromiseifgreatercontrolcanbeachieved.Atpresentthemainparametersofcontrolaresolutioncompositionandthedepositionpotential.TherehaveElectrochemical Nanofabrication 7beenanumberofattemptstoimprovetheprocessbyusingvariationsinreactantconcentration, pH [39;40], and the potential program [38;41-45]. In most cases, the depositsareimprovedbyannealing.Intheapplicationofphotovoltaicapplications,annealingisusedtoconvertCdTefromtheas-depositedn-typematerialtothedesiredp-type[34;46].SemiconductorssuchaspolycrystallineITOonglasshavebeenusedtoformdepositsofZnSwithnoobviousproblems[15].Ideallylatticematchedsemiconductorsubstratescould be used to form deposits. For instance,InSbis latticematchedwithCdTeand couldbe used as a substrate. Good quality deposits of CdSe have beenformed onInPandGaAssubstratesusingcodepositionbyMaurinandFromentetal.[47;48].Theirworkclearlyshowtheapplicabilityofhighqualitycommercialcompoundsemiconductorswafersassubstrates for compounds electrodeposition.The precipitation method involves electrochemical generation of a precursor to one of theconstituentelements,inasolutioncontainingprecursorstotheotherelements[49-52].Thereactionisessentiallyhomogeneous,butasonereactantisformedattheelectrodesurface,mostoftheproductprecipitatesonthesurface.Thismethodresemblespassiveoxidefilmformation onreactivemetals,wheremetalionsreactwiththesolvent,oxygenorhydroxide.The film thickness is controlled by the amount of electrogenerated precursor. However, as themethodresemblesprecipitation,thequalityoftheresultingdepositisquestionable,andtheprocess is difficult to control. Film thickness is necessarily limited by the need for precursortransportthroughthedeposit.AclassicexampleistheformationofCdSbyoxidizingaCdelectrode in a sulphide solution [49;53-57].Twostagemethods arewherethinfilmsofthe compoundelement,oranalloy,arefirstdeposited,atleastonebyelectrodeposition[58].Asecondstage,annealing,thenresultsininter-diffusion and reaction of the elements to form the compound. The deposits are annealedinair,inertgas,oragaseousprecursortooneofthecompoundscomponentelements.Forinstance, electrodeposited CuIn alloys have been annealed in H2S to form CuInS2 [59]. Giventhe needforannealing,thismethodology haslimitationsfortheformationofmoreinvolveddevice structures. In general, annealing has been used to either form or improve the structuresofcompoundfilmsformedbytheelectrodepositionmethodsdescribedabove.Theprimarytoolforunderstandingcompoundelectrodepositionandforimprovingcontrolovertheprocess has been the methodology of EC-ALE [60;61].Electrochemical Synthesis of Quantum DotsQuantumdotsaresemiconductorparticleshavingdiametersthataresmallerthanabout10nm.Suchsemiconductornanoparticlesexhibitabandgapthatdependsontheparticlediameter:thesmallernanoparticle,thelargerthebandgap.Becausequantumdotspossessasize-tunablebandgap,thesediminutiveparticleshavepotentialapplicationsindetectors,light emitting diodes, electroluminescent devices, and lasers.Electrochemicalmethodscansynthesizesize-monodispersequantumdotsongraphitesurfaces, which provide an electrical connection to the graphite in situ. The essential featuresof these methods can be depicted as in Fig. 2.Di Wei 8Figure2.Theelectrochemicalandchemicalmethodtosynthesizethequantumdotsandothersemiconductor nanocrystals on graphite.Thefirststepinvolvestheelectrodepositionofmetalnanoparticlesontoagraphitesurface from a solution containing the corresponding metal ions. The metal nanoparticles areelectrochemicallyoxidizedtoyieldametaloxide(MO),inwhichtheoxidationstateofthemetalmatchestheoxidationstateinthefinalproduct.Finallymetaloxidenanoparticlesareconvertedintonanoparticlesofasemiconductingsalt(MX)viaadisplacementreactioninwhichoxideorhydroxideisreplacedbythedesiredanions(X).ExamplesofusingthesemethodscanbeshowninthesynthesisofCuI[62],CdS[63]andZnO[64]quantumdots.Ultrathin films of quantum dots with deposits of non-connected nanocrystals and thick filmsof more than 10 nm in average thickness can be made by electrochemical methods [65-67].Electrochemical Deposition Methods for Metallic NanostructuresInorganic nanoparticles can be fabricated by many different techniques. Electrochemicalandwet-chemicalmethodsaredemonstratedtobeeffectiveapproachestomakemetalnanostructures under control without addition ofareducingagentor protectingagent.Aninsituelectrochemicalreductionmethodforfabricatingmetalnanoparticlesoncarbonsubstratessimultaneouslyassemblingintoorderedfunctionalnanostructureswasdeveloped[68].Ag+wasadsorbedonahighlyorientedpyrolyticgraphitesurfacemodifiedby4-aminophenyl monolayer with coordination interaction, and then homogeneously dispersed Agnanoparticlescouldbeobtainedthroughpulsedpotentiostaticreduction.Multilayeredmetalnanostructuresonglassycarbonelectrodeshavebeenobtainedbyextendingthismethod[69;70].Thelargerelectrochemicalwindowofionicliquidsincomparisonofaqueouselectrolytesenablestheinvestigationofelectrodepositionofmetalandsemi-conductorelements and compounds in nanoscale. Nanoscale electrocrystallization of metals such as Ni,Co and the electrodeposition of semiconductors (Ge) on Au (111) and Si (111):H have beenstudied in the underpotential and overpotential range from ionic liquids [71]. For example, 3Dgrowth in Co electrodeposition on Au (111) from ionic liquids based on imidazolium cationsstarts at potentials below -0.17 V vs. Co/Co(II). 3D and 2D structures of Co and Ni depositionin the nanoscale were illustrated.In addition, nanocrystalline aluminium can be obtained byelectrodepositionfromionicliquidscontainingimidazoliumcationswithoutadditives[72].Electrochemical Nanofabrication 9The crystal refinement is due to a cathodic decomposition of the imidazolium ions to a certainextent giving rise to nanocrystalline aluminium.Metal nanowires can be obtained using solution phase reduction [73], template synthesis[74-77], and physical vapour deposition (PVD) [78] onto carbon nanotubes. Metal wires withwidthsdownto20nmandlengthsofmillimetrescanbepreparedonsiliconsurfaceusingelectron beam lithography [79] or by PVD [80].However, none ofthesemethodsare usefulto prepare free-standing metal nanowires that are longer than 20 m. Penner et al. [81] haveused the step edge defects on single crystal surfaces as templates to form metal nanowires byelectrochemicalstepedgedecoration.Metallicmolybdenum(Mo)wireswithdiametersrangingfrom15nmto1mandlengthsofupto500mwerepreparedinatwo-stepprocedureonfreshlycleavedgraphitesurfaces[82].Molybdenumoxidewireswereelectrodepositedselectivelyatstepedgesat-0.75VSCEandthenreducedinhydrogengasat500 C to yield Mo metal. Such nanowires can be obtained size selectively because the meanwire diameter was directly proportional to the square root of the electrolysis time.Parrallelarraysoflong(>500m),dimensionallyuniformnanowirescomposedofmolybdenum,copper,nickel,gold,andpalladiumcanalsobeelectrodepositedbythesamestrategy[81].Theywerefirstlypreparedbyelectrodepositingnanowiresofaconductivemetal oxide such as NiO, Cu2O or MoO2. Nanowires of the parent metal were then obtainedby reducing the metal oxide nanowires in hydrogen at elevated temperature. Nanowires withdiametersintherangefrom15nmto750nmwereobtainedbyelectrodepositionontothestepedgespresentonthesurfaceofhighlyorientedpyrolyticgraphiteelectrode.Afterembeddingthenanowiresinapolymerfilm,arraysofnanowirescouldbeliftedoffthegraphitesurfacetherebyfacilitatingtheincorporationofthesearraysindevicessuchassensors. Vertical arrays of metal nanowirehold promiseformakingchemicaland biologicalsensorsinadditiontoelectronemittersinfield-emissiondisplays.Butthedifficultyofgrowingwell-definedarrayshaskeptthesetechnologiesatbay.Electrochemicalnanofabrication using crystalline protein masks solved this problem [83]. A simple and robustmethod was developed to fabricate nanoarrays of metals and metal oxides overmacroscopicsubstrates using thecrystallinesurfacelayer(S-layer)proteinofdeinococcusradioduransasanelectrodepositionmask.SubstratesarecoatedbyadsorptionoftheS-layerfromadetergent-stabilizedaqueousproteinextract,producinginsulatingmaskswith2-3nmdiameter solvent-accessible openings to the deposition substrate. Thecoating processcan becontrolled to achieve complete or fractional surface coverage. The general applicability of thetechnique was demonstrated by forming arrays of Cu2O,Ni,Pt,Pd,andCoexhibiting long-range order with the 18 nm hexagonal periodicity of the protein openings. This protein-basedapproachtoelectrochemicalnanofabricationshouldpermitthecreationofawidevarietyoftwo-dimensional inorganic structures.Electrochemical NanolithographyInadditiontoitswell-knowncapabilitiesinimagingandspectroscopy,scanningprobemicroscopy(SPM)hasshowngreatpotentialsforpatterningofmaterialstructuresinnanoscaleswithprecisecontrolofthestructureandlocation.ElectrochemicalnanolithographyusingSPM,whichincludesscanningtunnellingmicroscopy(STM)andatomicforcemicroscope(AFM),hasbeenusedtofabricateofpatternedmetalstructuresDi Wei 10[84-87], semiconductors [87;88]and soft matters such as conducting polymers [89;90]. Theelectrochemical processing of material surfaces at nanoscale both laterally and vertically canbeconductedbyscanningprobeanodization/cathodization,whichusedthetip-samplejunctionofascanningprobemicroscopeconnectedwithanadsorbedwatercolumnasaminuteelectrochemicalcell.Areviewonnanofabricationbyscanningprobemicroscopelithography examines various applications of SPM in modification, deposition, removal,andmanipulationofmaterialsfornanoscalefabrication[91].ComprehensivereviewsofSPM-related lithography can be found in the literature [92].STMhasatremendouspotentialinmetaldepositionstudies.Theinitialstagesofmetaldeposition and the Ag adlayer on Au (111) have been studied by Kolb et al. [93].The inherentnatureofthedepositionprocesswhichisstronglyinfluencedbythedefectstructureofthesubstrate, providing nucleation centres, requires imaging in real space for a detailed picture ofthe initial stage. This is possible with an STM, the atomic resolution helps to understand theseprocessesonatrulyatomisticlevel.Thefollowingfiguredemonstrateswealthofstructuraldetail supplied by STM. In situ STM investigations for Ag UPD on Au (111) in the potentialrange from 600 to 200 mV vs. Ag/Ag+ were carried out [93]. Underpotentially deposited Agrevealedaseriesoforderedadlayerstructureswithanincreasingdensityofadatomswhendecreasing applied potentials.Nanostructuringcanbealsoachievedbyinvolvingelectrochemicalprocessesintotheoverall procedures. For example, Li et al. [94;95] deposited Ag and Pt clusters on a graphitesurfacebyapplyingpositivevoltagepulsestotheSTMtipinasolutioncontainingtherespectivemetalcations.Thiseffectwasattributedtonucleationwithinholeswhichwerecreated on the graphite substrate surface by the voltage pulses. Kolb et al. [96], on the otherhand,wereabletodetachCuclustersfromatip,wheretheyhadbeenpreviouslydepositedelectrochemically, onto a Au substrate by mechanical contact. However, all these techniquessuffer from restrictions, which could be largely avoided if controlled nanostructuring could beachieved by a direct local electrochemical reaction on the substrate, with the geometry beingdeterminedbythelocationofthetipwhichactsasalocalcounterelectrode.Byapplyingultrashort voltage pulses ( 100ns), holes of about 5 nm in diameter and 0.3 to 1 nm depth onAu substrate can be created by local anodic dissolution, while cathodic polarization led to thedepositionofsmallCuclusters[97].Thedevelopmentofallowingthegenerationofsmallmetalclusters,withthehelpofanSTMtip,andplacingthematwillontosinglecrystalelectrode surfaces was reported [96;98]. This so-called tip-induced metal deposition involvesconventionalelectrolyticdepositionofametalontothetipofanSTM,followedbyacontrolled tip approach during which metal is transferred from the tip to the surface (so-calledjump-to-contact[99]).Smallcopperclusters,typicallytwotofouratomiclayersinheight,werepreciselypositionedonaAu(111)electrodebyaprocessinwhichcopperwasfirstdeposited onto the tip of the STM, which then acted as a reservoir from which copper couldbetransferredtothesurfaceduringanappropriateapproachofthetiptothesurface[100].Tip approach and position were controlledexternallybyamicroprocessor unit, allowing thefabricationofvariouspatterns,clusterarrays,and''conductingwires''inaveryflexibleandconvenient manner [96]. The formation of such clusters with the tip of a STM is simulated byatom dynamics and subsequently the stability of these clusters is investigated by Monte-Carlosimulations in a grand-canonical ensemble. It leads to the conclusion that optimal systems fornanostructuringarethosewherethemetalsparticipatinghavesimilarcohesiveenergiesandElectrochemical Nanofabrication 11negativeheatsofalloyformation.Inthisrespect,thesystemCu-Pd(111)ispredictedasagood candidate for the formation of stable clusters [101].Inadditiontoproducingthemetalnano-clusters,STMscanalsobeappliedtoformnanoscale pits in thin conducting films of thallium (III) oxide [102] as well as to write stablefeatures on an atomically flat Au (111) surface [103]. Pit formation was only observed whentheprocesswasperformedinhumidambientconditions.Themechanisminvolvedinpitformation was attributed to localized electrochemical etching reactions beneath the STM tip.Byapplyingvoltagepulses(closeto3V)acrossthetunnellingjunctionincontrolledatmospherewiththepresenceofwaterorethanolvapour,nano-holecanbeproduced.Thesmallest hole formed is 3 nm in diameter and 0.24 nm in depth. This nano-hole represents thelossofabout100Auatomsinthetopatomiclayerofgoldsurface,thereisnoatomicperturbationseeninsideandoutsidethenano-hole.Differentnanostructures(latticeofdots,legends, map, etc.) can also be fabricated. The threshold voltage for the formation of a nano-holedependsontherelativehumidity,however,therelationshipbetweenthethresholdvoltage and the relative humidity is basically independent of the tip material.The application of conducting AFM probe anodization to nanolithography was also usedinthefabricationandpatterningofmaterialsinasimilarmannerasSTMprobes.AFM-tip-inducedandcurrent-inducedlocaloxidationofsiliconandmetalswerereportedandthisnovellocaloxidationprocesscanbeusedtogeneratethinoxidetunnelingbarriersof10-50nm.[88]. The direct modification of silicon and other semiconductor and metal surfaces by theprocessofanodizationusingtheelectricfieldfromaSPMisonepromisingmethodofaccomplishingdirect-writinglithographyfortheelectrondevicefabrication.Thistechniqueinvolvestheapplicationofanelectricalbiastoboththeconductingprobeandthesamplesubstratetolocallyoxidizeselectedregionsofasamplesurface.Sincemostoflithographicworkswithorganicresistshavebeenexclusivelycarriedoutonsiliconsurfaceforpracticalapplication,soseveralorganicresistswithdifferentfunctiongroupshavebeenstudiedinorder to investigate the surface group effect on the anodic anodization using AFM.Silicon(Si)sampleswhosesurfaceswereterminatedwithhydrogen(Si-Hsamples)orcoveredwithanorganosilanemonolayerweregenerallyusedtodepositmetallicand/orsemiconductor nanomaterials [86]. Silicon oxide (SiO2) patterns can be prepared on the Si-HsamplesurfacesbytheuseofanodizationofSi,whileinthesecondcasetheorganosilanelayerwasselectivelydegradedbyanodiccorrosion.Furthermore,patterntransferprocessesthatfabricatedmetalnanostructuresusingthesepatternedSiO2ororganosilanelayersastemplatesweredeveloped.Theseprocessesarebasedonarea-selectiveelectrolessplatingwhereselectivitydependsonthedifferenceinthechemicalreactivitybetweenthesurfacemodified by scanning probe anodization and the unmodified surface. Nanostructures down toafewtennanometersinsizehavebeenfabricatedwithLangmuirBlodgett(LB)filmsandself-assembledmonolayers(SAMs)usingSPMlithography[104].TheSAMscanbepreparedwithorganosilaneetc.asultrathinresistsonSisubstrate.Theeffectofsuchfunctional groups of molecules on the AFM anodization, which was performed under contactmodehasbeenstudiedintheoptimizedprocessconditions.AppliedvoltagebetweentheAFMtipandsample,thescanningspeedandtherelativehumidityinairarealsoimportantfactorsfornanometer-scalelithographyoftheultrathinfilms.Thehighstructuralordernessandperfectthicknessofultrathinorganicmolecularassembliesarethemajoradvantagesasrequired for nanoscale lithography.Di Wei 12Cleanedp-typeSi(100)waferwasfirstlyoxidizedbypiranhasolution(3:1mixtureofsulfuricacidand30%hydrogenperoxide)tomakethesurfacehydrophilic.Theoctadecyldimethylmethoxysilane (ODMS) molecules react with OH groups on a silicon oxidesurface resulting in the formation of a SAM in a thickness of 1.7 nm. The local degradation ofthemonolayeronselectedareawheretheprobetipoftheAFMwasscannedwithabiasvoltageoccurredduetotheanodicreaction.ThedegradedregionsbecamehydrophilicindicatingthattheODMSmoleculesweredecomposedandreplacedwithOHgroupsasaresultoftheprobescan.AFMimagesshowedthatthetipscannedregionswereprotrudedcomparedtothesurroundingregionsasFig.3shows.ThisisduetovolumeexpansionresultingfromanodizationoftheSisubstrate,whichimmediatelyfollowedthetip-induceddegradation of the SAM.Figure3.AnodizedpatternformationonSi-wafer.SiwaferwasfirstlyoxidizedtoformhydrophilicoxidelayerfortheselfassemblyofODMS.ODMSSAMsactastheresist.Reproducedbythekindpermission from the publisher.Figure 4. The AFM image of ODMS monolayer after AFM anodization at the different applied currents[104]. Reproduced by the kind permission from the publisher.Fig. 4 shows the AFM image of ODMS monolayer after AFM anodization at the differentcurrent conditions. Typically with ODMS monolayers, protruded patterns are fabricated withline-width of 70 nm at a scan rate of 120200 m/s and an applied voltage of 2025 V. TheElectrochemical Nanofabrication 13heightofprotrudedlinescanbecontrolledbychangingthecurrentbetweenthetipandsubstrate.Whentheappliedcurrentwas57nA,theheightofprotrudedlinewas1.0nm.With increasing thecurrentupto 2023nA,theanodizedheight increasedto3.0nm.Thus,theheightoftheprotrudedlinesincreasesduetotheeffectiveelectricfieldstrengthforagivenappliedvoltageandascanrate.Theelectricfieldplaysanimportantroleintheformationofprotrusion.AFManodizationwassuccessfullycarriedoutwithSAMsonthesiliconsubstrate.AppliedvoltagebetweentheAFMtipandsample,thescanningspeed,surfacegroup,andtherelativehumidityinthelaboratoryareveryimportantfactorsfornanometer-scalelithographyoftheultrathinfilms.Thehighstructuralordernessandperfectthicknessof ultrathinorganicmolecularassembliesarethemajoradvantagesasrequiredfornanoscale SPM lithography.Soft matters such as conducting polymers can also be patterned in the nanoscale by suchlithographicmethod.Caietal.describedthefirstobservationoflocalizedelectropolymerizationofpyrroleandanilineonhighlyorientedpyrolyticgraphite(HOPG)substratesunderAFMtip-sampleinteractions[89].AscanningoroscillatingAFMtip,providingthehorizontalscratchingforceandtheverticaltappingforce,isessentialasthedrivingforceforthesurfacemodificationwiththeconductingpolymer.ItwasshownthatundertheAFMtipinteraction,theelectropolymerizationcanbeblockedonthebareHOPGsubstrateorenhancedontheas-polymerizedfilm.Thelocalizedelectropolymerizationinselected surface areas enables the nanomodification of lines, square platforms, or hollows ofpolypyrrole and polyaniline on the substrates. The result indicates that AFM can be used as aunique tool for nanofabrication of conducting polymers.Nano-writingofintrinsicallyconductingpolymerwasalsoachievedviaanovelelectrochemicalnanolithographictechniqueusingtappingmodeelectrochemicalAFM.Conductingpolymer(polythiophenederivatives)nanolinesassmallas58nminwidthwereobtainedandthelinewidthiscontrolledasafunctionofthewritingspeedandwritingpotential [90].Figure 5. Electrochemical nanolithography [90]. Reproduced by the kind permission from the publisher.Di Wei 14TheelectrochemicalnanolithographyprocessisshowninFig.5.ConductiveAFMprobes,goldcoatedsiliconnitride(SiN4)areusedasworkingelectrode.Silverwireandplatinumwirewereusedasreferenceelectrodeandcounterelectrode,respectively.Higherwriting potential and slower writing speed produce wider conducting polymer nanolines dueto enhanced propagation. The great benefit of this method lies in no specific restriction in thechoice of substrates and the ease of controlling feature size, which is expected to facilitate tofabrication of all plastic nanoelectronic devices.Asstatedpreviously,manySPMlithographytechniquesbasedonanodizationofSisurfaces[88],electrochemicalreactionsinsolutionusingelectrochemicalSTMtips[96;98]and electrochemical decomposition of self-assembled monolayers [104] have been developedinthepastdecade.Morerecently,adippennanolithography(DPN)methodwasinventedthat uses an AFM tip as a nib to directly deliver organic molecules onto suitable substratesurfaces, such as Au [105-107]. When AFM is used in air to image a surface, the narrow gapbetween the tip and surface behaves as a tiny capillary that condenses water from the air. Thistiny water meniscus is actually an important factor that has limited the resolution of AFM inair. Dip-pen AFM lithography uses the water meniscus to transport organic molecules fromtiptosurface.Byusingthistechnique,organicmonolayerscanbedirectlywrittenonthesurface with no additional steps, and multiple inks can be used to write different molecules onthe same surface. By coupling electrochemical techniques, the DPN are not limited to deliverorganicmoleculestothesurface.Electrochemicaldip-pennanolithography(EC-DPN)techniquecanbeusedtodirectlyfabricatemetalandsemiconductornanostructuresonsurfaces.Figure6.SchematicsketchoftheEC-DPNexperimentalsetup[108].Reproducedbythekindpermission from the publisher.The tiny water meniscus on the AFM tip was used as anano-sizedelectrochemicalcell,inwhichmetalsaltscanbedissolved,reducedintometalselectrochemicallyanddepositonthe surface as shown in Fig. 6. In a typical experiment, an ultrasharp silicon cantilever coatedwith H2PtCl6 is scanned on a cleaned p-type Si (100) surface with a positive DC bias appliedonthetip.Duringthislithographicprocess,H2PtCl6dissolvedinthewatermeniscusiselectrochemicallyreducedfromPt(IV)toPt(0)metalatthecathodicsiliconsurfaceanddeposits as Pt nano-features as shown in the result below [108].Electrochemical Nanofabrication 15Figure 7. AFM image and height profile of two Pt lines drawn at different scan speed. a) line at 10 nm/sandb)lineat20nm/s.Thevoltageappliedatthetipis3Vforbothlinesandtherelativehumidityis43% [108]. Reproduced by the kind permission from the publisher.ElectrochemicalAFM"dip-pen''nanolithographyhassignificantlyexpandedthescopewhereDPNnanofabricationcanbeapplied.ItcombinestheversatilityofelectrochemistrywiththesimplicityandpoweroftheDPNmethodtoproducenanostructureswithhighresolution.ElectrochemicalSTM-basedmethodsrequirethatthesubstratesbemetallic,butsubstrates used in EC-DPN do not have to be metallic since the control feedback of the AFMdoes notrelyonthecurrentbetweenthetipandsurface.Siwaferscoatedwithnativeoxideprovidesenoughconductivityforthereductionoftheprecursorions.ThisdevelopmentsignificantlyexpandsthescopeofDPNlithography,makingitamoregeneralnanofabrication technique that not only can be used todeliver organicmoleculestosurfacesbut is also capable of fabricating metallic and semiconducting structures with precise controlover location and geometry.Localelectrochemicaldepositionoffreestandingverticallygrownplatinumnanowireswas demonstrated with a similar approach, electrochemical fountain pen nanofabrication (EC-FPN)[109].TheEC-FPNexploitsthemeniscusformedbetweenanelectrolyte-fillednanopipette('thefountainpen')andaconductivesubstratetoserveasaconfinedelectrochemical cell for reducing and depositing metal ions. Freestanding Pt nanowires werecontinuouslygrownoffthesubstratebymovingthenanopipetteawayfromthesubstratewhile maintaining a stable meniscus between the nanopipette and the nanowire growth front.Highqualityandhighaspect-ratiopolycrystallinePtnanowireswithdiameterofsimilarto150 nm and length over 30 m were locally grown with EC-FPN. The EC-FPN technique isshown to be an efficient and clean technique for localized fabrication of a variety of verticallygrownmetalnanowiresandcanpotentiallybeusedforfabricatingfreeform3Dnanostructures.Di Wei 163D Electrochemical NanoconstructionIncombinationwithlithographicpatterns,electrochemistryhastakenakeypositioninproductsandmanufacturingprocessesofmicrotechnology,whichhasestablishedamulti-billiondollarmarketwithapplicationsininformation,entertainment,medical,automotive,telecom and many other technologies such as lab on a chip etc. [110]. Different strategies andtechniques such as electrochemical etching, LIGA and ultrashort voltage pulsing, which havebeen used in microtechnology, were also applied to construct 3D structures in the nanoscale.Electrochemical EtchingandLIGA TechniqueElectrochemicaletchingwithultra-shortvoltagepulsesallowstodissolveelectrochemicallyactivematerialswithinanextremelynarrowvolumeandtomanufacturethreedimentional(3D)microstructures.Micro-andnanoporoussiliconcanbegeneratedbyanodizationofsiliconwafersinhydrofluoricacid.Sinceetchingproceedspreferablyinthe(100) direction of the single-crystalline silicon wafer, the pore shape is nearly straight and thedepth is equal for all pores. The pores start to grow on a polished wafer in a random pattern,andtheirarrangementisusuallydefinedbytransferringasuitablelithographicpatternandgenerating a corresponding pattern of pits by alkaline etching as shows in Fig. 8. The patternof the deep pores generated subsequently by the electrochemical etching process correspondsto the pattern of the shallow starter pits. The cross section of the pores is usually square withrounded corners and their size can be varied by changing the etching current. More complexcrosssectionscanbegeneratedbyoverlappingofporesusingadditionaletchingstepsandcorresponding pattern definition (e.g. by means of lithography).Figure8.Macroporoussiliconstructuregeneratedbymeansofelectrochemicaletchingofsingle-crystalline silicon (Source: V. Lehmann, Siemens AG) [110]. Reproduced by the kind permission fromthe publisher.Electrochemical Nanofabrication 17Themacroporoussiliconstructuregeneratedbymeansofelectrochemicaletchingofsingle-crystalline silicon was demonstrated above. In the electrochemical set-up, hydrofluoricacid(HF),withorwithoutethanoland/orwaterisusedaselectrolyteandplatinumisthestandard cathode. The etch rate of ca. 1 m/min is observed. Both electro-polishing and poreformationtakeplaceintheanodicregime.Dependingoncurrentdensity,siliconcanbeetched in such two different modes: pore formation and electro-polishing. In pore formation,etchingproceedsverticallydownwards,leavingasiliconskeletonwithupto80%emptyspace, whereas in electropolishing, the whole surface is being etched. Pore formation starts atthewafersurfacefromadefectoranintentionalinitialpit.Electronicholesfromthebulksilicon are transported to the surface, and they react at the defect or pit. Further etching occursatthenewlyformedporetips,becausetheyattractmoreholesduetohigherelectricfieldstrength, and the process leads to a uniform porous layer depth as the holes are consumed bythe growing tips and other surfaces are depleted of holes. This etching mode takes place underlowholeconcentrationanditislimitedbyholediffusion,andnotbymasstransferintheelectrolyte cell. If hole density increases, some holes reach the surface and react there, leadingtosurfacesmoothing.Thisistheelectro-polishingregime,inwhichionictransferfromtheelectrolyteplaysarole.Illuminationcontributestoholeconcentrationinn-typesilicon(butnotinp-typesilicon)andtheanodicetchingofn-typesiliconhappensunderilluminationwhilst p-type silicon etches in dark. A very wide range of pore size from 0 to 20 m can beetched by varying electrolyte concentration, current density and illumination [111]. As a ruleofthumb,porediameterinmicrometreishalftheresistivityinohm/cm:for1umpore,2ohm/cm n-type silicon is suitable. For small pores, low resistivity is needed; for large pores,high resistivity material has to be used. If pore formation starts from an unobstructed surface,a random pore array results. If initial pits are prepared by lithography and etching, pores canbearrangedatwill[112].Whenann-typesiliconwaferisananodeinanalkalineetchingsolution(e.g.KOH)biasedpositivelyabovepassivationpotential,thesurfacewillbeoxidized, which stops silicon dissolution whilst p-type silicon was etched. The n-type layer ofa p/n-structure can similarly be protected. Etching of p-type silicon continues until the diodeisdestroyed,andn-typesiliconisthenpassivated.Theconfinedetchantlayertechniquehasbeen applied to achieve effective three-dimensional (3D) micromachining on n-GaAs andp-Si.Thistechniqueoperatesviaanindirectelectrochemicalprocessandisamaskless,low-cost technique for microfabrication of arbitrary 3D structures in a single step [113]. It has alsobeen presented that free-standing Si quantum wire arrays can be fabricated without the use ofepitaxialdepositionorlithographybyelectrochemicalandchemicaldissolutionofwafers[114].Thisnovelapproachuseselectrochemicalandchemicaldissolutionstepstodefinenetworks of isolated wires out of bulk wafers.Electrochemicalmethods,eitheraloneorincombinationwithothertechniques,havebeen developed for shaping materials. 3D microstructures with extremely high precision andaspectsratiocanbemanufacturedbymeansofLIGAtechnology,whichcombinesdeeplithography,electrodepositionandmouldingprocesssteps.TheacronymLIGAisderivedfrom the German expressions for these manufacturing steps and offer high potential regardingminiaturization, freedom of design and mass production. Micro-gear system produced from anickel iron alloy by means of LIGA was shown in Fig. 9.Di Wei 18Figure 9. Micro-gear system produced from a nickel iron alloy by means of LIGA technology (Source:Micromotion, IMM) [110]. Reproduced by the kind permission from the publisher.However,theultraprecisemicrostructureswithextremeaspectratiocouldonlybegeneratedbydeepX-raylithography.Difficulties,forexample,theaccesstosynchrotronradiation facilities have limited the commercialization of LIGA technique in mass fabrication.Micro- and Nano-machining by Ultrashort Voltage Pulsing TechniqueTheapplicationofelectrochemistryinmicro-machiningcanbefoundinbook[115].Incontrasttotheconventionalprocessesofelectrochemicalmicromachining,wherethegapbetweentheelectrodesisusually0.1mmanddirectcurrentisapplied,anovelelectrochemicalmicofabricationmethodusingagapinmrangeandveryshortvoltagepulses of some tens of nanoseconds was developed. The short pulse confines electrochemicalprocessescorrespondingly,removalofmaterial to averynarrowvolumetoenableaprecisenanomachining.Ultrashortpulsescanbeemployedtomachineconductingmaterialswithlithographicprecision[116].Resolutioncanbeimprovedsignificantlythroughtheuseofultrashortvoltagepulsescomparingtotheuseofconventionaldirectcurrentanodization.Threedimensionalcomplexnanostructures,lines,curvedfeatures,andarrayscanbemachined in substrates in single-step processing.Themethodisbasedontheapplicationofultrashortvoltagepulsesofnanosecondduration, which leads to the spatial confinement of electrochemical reactions, e.g. dissolutionof material. The electrochemical dissolution rate of the material has to be intentionally variedovertheworkpiecesurfacebyapplyinginhomogeneouscurrentdensitydistributionintheelectrolyte and at the workpiece surface. This can be achieved by the geometric shape of thetool, locallyverysmalltool-workpiecedistances,partialinsulation ofthetoolorworkpiece,and high overall current densities etc. This situation is illustrated in Fig 10. The workpiece ispreferentiallyetchedwithinthegapregionbetweenthefrontfaceofthetoolandtheworkpiece surface. This approach for local confinement of electrochemical reactions is basedonthelocalchargingoftheelectrochemicaldoublelayer(DL)andtheresultingdirectinfluence on the electrochemical reaction rates.Electrochemical Nanofabrication 19Figure10.Sketchoftheexperimentalsetupandprincipleofelectrochemicalmicromachiningwithultrashort pulses. RE and CE are abbreviates of reference and counter electrode.Thepotentialsoftheworkpieceandtoolarecontrolledbythelow-frequencybipotentiostat.Thevoltagepulsesaresuppliedbythehighfrequencypulsegenerator.Anultrashort voltage pulse limits the charging of double layercapacitanceto thevicinity ofthetool.The current distribution betweentheDLisalso illustratedinFig.10.The pulsing timeconstant is given by the DL capacitance multiplied bytheresistance oftheelectrolytealongthe current path. The latter factor is locally varying, depending on the local separation of theelectrode surfaces [116]. Therefore, upon proper choice of the pulse duration, DL areas wherethe tool and workpiece electrodes are in close proximity are strongly charged by the voltagepulses,whereasatfurtherdistancesthechargingbecomesprogressivelyweaker.Thepulsedurationprovidesadirectcontrolforthesettingthemachiningaccuracy.Machiningprecisions below 100 nm were achieved by the application of 500 ps voltage pulses [117].Figure 11. Spiral trough with a depth of 5 mm, machined into a Ni sheet with a W tool in 0.2 M HCl (3ns,2Vpulses,33MHzrepetitionrate,workpiece-0.1VAg/AgCl,tool-0.3VAg/AgCl[117].Reproduced by the kind permission from the publisher.Di Wei 20The application of ultrashort voltage pulses between a tool electrode and a workpiece inanelectrochemicalenvironmentallowsthethree-dimensionalmachiningofconductingmaterials with nanoscale precision. The principle is based on the finite time constant for DLcharging,whichvarieslinearlywiththelocalseparationbetweentheelectrodes.Duringnanosecondpulses,theelectrochemicalreactionsareconfinedtoelectroderegionsincloseproximity.Theperformanceofelectrochemicalmicromachiningwithultra-shortvoltagepulseswasdemonstratedinanumberofexperimentswheremicrostructuresweremanufacturedfromvariousmaterialslikecopper,siliconandstainlesssteels[116].Threedimentionalstructureswithhighaspectratioscanbeachievedbyusingsuitablemicroelectrodesandpiezo-drivenmicropositioningstages.ThespiralshowninFig.11wasmanufacturedbymachiningtheNisheetwith3nspulses.Wallsofsimilarthicknesswithsurface roughness and radii of curvature less than 100 nm were readily machined [117].Figure12.Scanningelectronmicrographs.(a)thetool;(b)structureinNisubstrate.Experimentalconditions:Usub=-0.35V,Utool=-0.3V,2nspulseduration,2.2Vamplitude,1:10pulsetopauseratio,and0.05MHClelectrolyte.Thestructurewasmachined400nmintothesurfaceinlessthan2min [118]. Reproduced by the kind permission from the publisher.Smalltoolscanbeusedtomakeverysmallfeatures.Highaspectrationanometreaccuratefeaturesweremachinedinnickelusingultrashortvoltagepulseelectrochemicalmachining[118].Twotools(oneistherotundatool,presentedinFig12aandotheris22arrayofcubes,presentedinFig.13a)werefirstlyfabricatedbyfocusedionbeam(FIB)milling and then used in the machining. The potentials of the shaped tungsten tool and nickelsubstrate electrodes were controlled with a bipotentiosts which kept the potentials of the toolandsubstrateconstantversusanAg/AgClreferenceelectrodebyapplyingapotentialtoPtcounterelectrode.AllexperimentswereconductedinanaqueousHClsolutionwithvariousconcentrations.Supplementarycircuitrywaspresenttoallowtheadditionalofultrashort(order of 1 ns) pulses to the potential of the tool electrode. The separation of the tool and thesubstrateworkpieceelectrodeswascontrolledwithpiezoactuatorsandthetoolwasfedintotheworkpiecewithaconstantfeedingspeed,avoidingmechanicalcontactbetweentheelectrodesbymonitoringthedccurrentbetweentoolandworkpiece.Structureswith90nmwidthsweremadebyapplying2nsvoltagepulsesfortheparallellinesinthecentreofthestructure in Fig 12b. To reach a depth of 400 nm, total electrochemical machiningtimeof1Electrochemical Nanofabrication 21min 45s was applied. Examples of patterns made with the 22 array of cubes tool are shownin Fig. 13b. It indicates that the feature resolution improves with decrease in pulse duration.Figure 13. Scanning electron micrographs. (a) Tungsten tool; (b) machined Ni substrate. Experimentalconditions: Usub=-1.7 V, Utool=-1.0 V, pulse duration indicated, 2 V amplitude, 1:10 pulse to pause ratio,and 0.2 M HCl electrolyte. Feature resolution and edge sharpness increased as pulse duration decreased[118]. Reproduced by the kind permission from the publisher.Three-dimensionalmachiningofelectrochemicallyactivematerialsincludingconstructionofunconventionalislandpatternsonasurfacewithnanoscaleresolutionwasrealizedbythismethod[97;119-121].Thus,electrochemicalmachiningcanbeappliedtomicroelectro-mechanicalsystems(MEMS)[12