CorrespondingauthorFax14048949140EmailaddresszhongwangmsegatecheduZLWangwwwelseviercomlocatecplett ChemicalPhysicsLetters4172005359 ID: 191384
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Formationofdouble-sideteethednanocombsofZnOandself-catalysisofZn-terminatedpolarsurfaceChangShiLao,PuXianGao,RuSenYang,YueZhangYingDai,ZhongL.WangSchoolofMaterialsScienceandEngineering,GeorgiaInstituteofTechnology,Atlanta,GA30332-0245,USA Correspondingauthor.Fax:+14048949140.E-mailaddress:zhong.wang@mse.gatech.edu(Z.L.Wang).www.elsevier.com/locate/cplett ChemicalPhysicsLetters417(2005)359 363 ARTICLEINPRESS (FE-SEM,eldemissionLEO1530FEG)andtransmis-sionelectronmicroscopy(TEM,eldemissionTEMHit-achiHF-2000).Fig.1aisalowmagnicationSEMimageoftheas-grownsingle-sidedZnOcombswithasymmetricteethdis-tributiontion.Theyieldofthenancombsis100%.Atypicalnanocombismagniedandisinserted,showingmanythinteethofsimilarlengthsanddiametersgrowingoutofastraightprimaryribbon.Theseteethhavespacingaround200nm,diameter50nmandlengthFig.1bisanothercongurationforthesingle-sidedcombs,inwhicharowofhexagonalnanowireswithtwosegmentsofdierentdiametersstackingoneontheotheralongthelengthdirection.Fromthehexagonalsymmetryofthenanowire,itsgrowthdirectionis[0001].Fig.1cshowsacombstructurewithaseriesoflongthinbelts(40 50inlength,0.5 4minwidth),growinginparalleloutofonesideoftheribbonandformingawaterfall-likeuration.InFig.1d,thenanocombshaveasetofmuchwiderteeth,withawiderangeofinter-teethspacing,alengthfrom1to5mandawidthof200 500nm.Theupperinsetimagerevealsthequasi-rectangularshapeofthecrosssectionoftheteeth.Fig.1eisaTEMimageofatypicalsingle-sidedcombstructureandthecorrespond-ingelectrondiractionpattern.Thediractionpatternshowsthatthegrowthdirectionoftheteethis[0001]andoftheprimaryribbonis[210],andbothsharethesametopandbottomsurfacesof±(0110).Theformationofone-sidedasymmetricnanocombshasbeenattributedtotheself-catalysiseectofpolarsurface Fig.1.(a)As-grown,single-sideteethedZnOcombstructures.Insetisamagniedimageofasingle-sidedcomb;(b)to(d)areSEMimagesofsingle-sidcombswithdierentmorphologies.(e)AtypicalTEMimageofthesingle-sidednanocomb.Insetdiractionpatternisfromthecircledareashowingthathegrowthdirectionoftheteethis[0001].C.S.Laoetal./ChemicalPhysicsLetters417(2005)359 363 ARTICLEINPRESS .Duetothenon-centralsymmetriccharacteristicofZnO,the(0001)ofZnOisterminatedwithZncations,andthe(0001)isterminatedwithoxygenanions,whicharethetwotypicalpolarsurfacesofZnO,andtheyinducesagroupofuniquenanostructuresstructures.TheZn-(0001)sur-faceischemicallyactiveanditsself-catalysisresultsinthegrowthofteethononeside.Theoxygenterminated(000surfaceisrelativelychemicallyinertandproducesnogrowth.Thisisthereasonthattheasymmetricnanocombsaremostfrequentlyreceivedreceived,andtheycanbegrownalmostat100%purity.However,symmetricnanocombswithdouble-sidedteeth(sh-ribbontype)havealsobeenproducedinoursyn-thesis,andsometimestheyieldcanbemorethan80%.InFig.2a,alowmagnicationSEMimageshowsahighyieldofthedouble-sidedteethcombstructure.Fig.2bisamag-niedimageofasymmetriccomb,whichclearlydisplaysthattheteethgrowfrombothsidesoftheribbon.Fig.2isanothertypeofdouble-sidedcombswithtworowsofdumbbell-likeshapedteeth.Theformationofthesymmetricnancombscannotbeex-plainedbythepolarsurfacemodelifthemainribbonisasinglecrystalwithbothsidesofthecombsbeingterminatedbyZn-(0001)andO-(0001),respectively.Tondouttheformationprocessofthedouble-sidednanocombs,wehaveusedconvergentbeamelectrondiraction(CBED)todeter-minethepolarityofthetwosides.Fig.3aisalowmagni-cationTEMimagefromthenanocomb,displayingasymmetricdistributionoftheteethatbothsidesoftherib-bon.Thecorrespondingelectrondiractionpatternre-cordedfromagroupofteethisgiveninFig.3b,showingtheconventionalspottypatternof[0110],butthereisaradialangulartwistproleasindicatedbythedashedlinesforthe{000}seriesofthediractionspots,indicatinga Fig.2.SEMimagesofthedouble-sideteethedZnOcombstructures.(a)AlowmagnicationSEMimageshowingthehighyieldofthesymmetriccombs.(b)and(c)double-sidedZnOnanocombswithdierentmorphologies.C.S.Laoetal./ChemicalPhysicsLetters417(2005)359 363 ARTICLEINPRESS