December
[Article]物理化学学报(WuliHuaxueXuebao)ActaPhys.?Chim.Sin.,2010,26(12)：3369-33723369www.whxb.pku.edu.cn ZnO纳米线阵列的电沉积法制备及表征 王丹丽阮永丰*张灵翠
300072)杨红波(天津大学理学院,天津
摘要：利用直流电沉积方法在多孔氧化铝模板的孔洞中生成锌纳米线,在氧气氛围中,于800°C下氧化2h,
将氧化铝中的锌氧化成氧化锌.本研究利用氧气氛围进行锌的氧化,大大提高了传统方法的氧化锌纳米线的制
备效率.用场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)和X射线衍射仪(XRD)对其形貌及成分进
行表征和分析,结果表明,氧化铝模板的有序孔洞中填充了大尺寸、均匀连续的多晶态氧化锌纳米线.纳米线具
有约1000:1的高纵横比,其长度等于氧化铝模板的厚度,直径约为80nm.光致发光(PL)光谱表明,氧化锌纳米
线在504nm处有由于氧空位引起的较强蓝绿光发射.这为进一步研究ZnO/AAO组装体发学性质和开发新型 功能器件提供了基础.
关键词：阳极氧化铝;
中图分类号：O646;氧化锌;纳米线阵列;电沉积;氧化O78;O61 PreparationbyElectrodepositionandCharacterizationofZnO NanowireArrays
WANGDan-LiRUANYong-Feng*ZHANGLing-CuiYANGHong-Bo (SchoolofScience,TianjinUniversity,Tianjin300072,P.R.China) Abstract：
Orderedzinc(Zn)nanowirearraysembeddedinanodicaluminumoxide(AAO)templates werepreparedbyaneffectiveelectrodepositionmethod.Oxygenwasusedtooxidizetheelectrodeposited
zincnanowirearraysintheAAOtemplates.Bythermaltreatmentinanoxygenatmosphereat800°Cfor2
h,thedepositedZnwascompletelyoxidized.Themicrostructuresandopticalpropertiesofthesynthesized
zincoxide(ZnO)nanowirearrayswereinvestigatedbyfieldemissionscanningelectronmicroscopy
(FE-SEM),transmissionelectronmicroscopy(TEM),X-raydiffraction(XRD),andphotoluminescence(PL)
spectrumanalyticapparatus.WefoundthatlargescalepolycrystallineZnOnanowirearrayswereuniformly
assembledinthenanochannelsoftheAAOtemplate.Thenanowireshaveaveryhighaspectratioofabout
1000:1withthelengthequalingthetemplatethicknessandadiameterofabout80nm.PLmeasurements
oftheZnO/AAOassemblyshowedastronggreenemissionat504nm,whichwasattributedtotheoxygen
vacancydefectsoftheZnOnanowires.Theseresultscanbeusedinfurtherstudiesofthestructuraland
functionalpropertiesofelectroluminescencedevicesbasedontheZnO/AAOassembly. KeyWords：
Anodicaluminumoxide;Zincoxide;Nanowirearray;Electrodeposition;Oxidization ThemultifunctionalmaterialZnOhasbeenusedtomakeva- ristors,gassensors,solarcells,andotherdevicessince1950s.It hasattractedgreatinterestrecentlyinthesemiconductorfield[1-5]becauseofitslargedirectbandgap,strongexcitonbindingenergyandimportantapplicationprospectsinoptoelectronicdevices.MostresearcheshavebeenfocusedonitsnanostructuresandReceived:August30,2010;Revised:October8,2010;PublishedonWeb:October22,2010. ?Correspondingauthor.Email:ruanyf@tju.edu.cn;Tel:+86-22-27406635.
TheprojectwassupportedbytheNaturalScienceFoundationofTianjin,China(07JCZDJC00600,07JCYBJC06000).
天津市自然科学基金(07JCZDJC00600,07JCYBJC06000)资助项目?EditorialofficeofActaPhysico?ChimicaSinica 3370
ActaPhys.?Chim.Sin.2010
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p-typedoping[6-7],whilefewresearcheshavebeendoneontheluminescenceofZnOwithnon-p-njunction.ItispossibletofabricateanewtypeofZnOelectroluminescencedevicewithnon-p-njunctionbyinsertingZnOintoanodicaluminumoxide(AAO)templates[8].BasedonthepropertiesofAAOphotoniccrystals,theluminescenceofZnOinthedevicementionedabovewouldbeenhanced[9].AAOhasalsobeenextensivelyusedtosynthesizenanometer-
sizefibril,rods,wires,andtubulesthroughavarietyofmethods[10-11].OrderedZnOnanowiresplayanim-portantroleinthoseapplications.ZnOnanowirearraysweresynthesizedbyone-stepelectrodeposition[12]inanAAOtemplate.ThedepositionofZn(OH)2introducedbyaqueoussolutioncompeteswiththeformationofZnO[13]andtheZn(OH)2canquenchthenearbandemissionofZnO[14].Lietal.[15]alsosuc-cessfullypreparedZnOnanowirearraysinanAAOtemplatethroughthermallyoxidizingtheZnnanowirearraysinair.However,thethermaloxidationtimewasverylong(about35h)andthedepositedareawasquitesmall.BecauseoftheabsenceofsuitablepretreatmentoftheAAOtemplate,thechallengeistofabricateuniformZnOnanowirearrayswithlargedepositedarea.ThosedrawbacksofthecurrentmethodstoprepareZnO/AAOassemblywouldlimititsapplicationsinelectroluminescencedevices.
Inthispaper,amoreefficientmethodwasdevelopedtopreparelargescaleuniformZnOnanowires.Theoxidizingtimewasgreatlydecreasedfrom35to2handthedepositedareaofZnOnanowirearrayswasincreased.Fieldemissionscanningelectronmicroscopy(FE-SEM),transmissionelectronmicroscopy(TEM),X-raydiffraction(XRD),andphotoluminescence(PL)techniqueswereemployedforsamplecharacterization. 1Experimental
TheAAOwasfabricatedbyatwo-stepanodizationprocess[16].Briefly,ahighpurity(99.999%)aluminumplatewasannealedat550℃inair.Afterbeingelectro-polished,theAlplatewasan-odizedin0.3mol·L-1oxalicacid(>99.5%,analyticalreagent,(AR))solutionunderconstantvoltageof40Vatroomtempera-turefor10h.Afterremovaloftheanodicaluminalayer,thetexturedAlwasanodizedagainunderthesameconditionasthestepone,andthentheAllayerwasremovedinasaturatedCuCl2(>99%,AR)solution.Asubsequentetchingtreatmentwascarried
outin5%(w)phosphoricacid(>85%,AR)solutionat30℃for30mintoremovethebarrierlayerandenlargetheporediameter.ThethicknessoftheresultedAAOtemplateisabout100μmandtheporediameterisabout80nm.
OrderedZnOnanowirearraysembeddedinAAOtemplateswerefabricatedbyelectro-depositingZnfollowedbyoxidationofthedepositedZn.Astandardthree-electrodeelectrochemicalcellwasusedfortheelectricdeposition,withasaturatedcalomelelectrodeasthereferenceelectrode,aPtsheetabout3cm2inareaservedasthecountelectrode.APtlayerwasplacedbymagnetronsputteringmethodontoonesideoftheAAOtemplateusedastheworkingelectrode.Beforemountingintotheelectrochemicalcell,theAAOwasimmersedinanele
ctrolytesolutionunderultrasonicagitationfor10mintoremovethecontaminantsonthetemplatesurfaceandtoimprovetheinternalsurfacewettability.Thetreatmentiscriticaltoobtainhomogeneousnanowiresinthewholegrowingarea.Thedepositionexperimentwascarriedoutinasolutioncontaining80g·L-1ZnSO·47H2O(>99.5%,AR)and -1 20g·LH3BO3(>99.5%,AR)atroomtemperatureforabout30min.Thevoltagerangewasbetween1.25Vand1.30V,andthetimeusedwasbetween20minand30min.Thehighervoltagewasapplied,thelessdepositiontimewasneeded.Afterelectro-depositing,theZnnanowirearrayswereembeddedintheAAO.ThesubsequentstepwastomechanicallypolishthePtelectrode,whichwasonthesurfaceofAAO.ItisessentialforZnnanowirearraystobeoxidizedsufficientlyandefficiently.Throughathermaltreatmentinoxygenatmosphereat800℃for2h,thedepositedZnwasoxidizedcompletely.ThedepositedZn/AAOassemblywasblackwithmetallicluster.Afteroxidation,awhiteZnO/AAOassemblywasobtained.ForFE-SEMstudy,thesampleswerequenchedinliquidnitrogenfor1mintoobtainaregularcrosssection.ForTEMobservation,ZnOnanowireswiththeAAOtemplateweredissolvedin1mol·L-1NaOHsolutiontoremovetheAAOtemplateandsomedissociativeZnOnanowiresweregotten.
2Resultsanddiscussion
ThesurfacemorphologyandthestructureoftheAAOwereobservedbyfieldemissionscanningelectronmicroscopy(FE-SEMNANOSEM430,FEI,USA).AsshowninFig.1A,theAAOhasahighlyorientedporousstructureofuniform
Fig.1FE-SEMimagesofAAOtemplate (A)topview,(B)crosssectionview No.12
WANGDan-Lietal.：
PreparationbyElectrodepositionandCharacterizationofZnONanowireArrays
3371 Fig.2FE-SEMimagesof(A)ZnOnanowirearrayembeddedinAAOand(B)asinglenanowireoutofthechannelofAAO,
(C)TEMimageofZnOnanowires
TheinsetinfigureAshowstheenlargedimageofZnOnanowirearrays.
Fig.3XRDpatternsoftheZnnanowireembeddedinAAObefore(A)andafter(B)calcinationat800℃for2h
poresizes,whichcouldbeorganizedinaprecisehexagonalstructure.TheaverageporediameteroftheAAOobtainedisabout80nm,whiletheinterporedistanceisabout120nm.Fig.1BshowstheFE-SEMimagefromcrosssectionviewoftheAAO.Itdisplaysthattheporechannelsarenearlyinparal-lelandtheinternalsurfaceissmooth. TypicalFE-SEMimagesofaZnO/AAOassemblyareshowninFig.2A.ItisobservedclearlythatthelongZnOnanowiresuniformlyembeddedinAAOareofperfectstraight-nessandcontinuity.Theupperrightinsetisanenlargedmagni-ficationimageoftheZnOnanowirearrays.Itcanbeseenthatthesurfaceofthenanowiresissmooth.TheaveragediameteroftheZnOnanowiresisabout80nm,almostequalstotheporesizesofthetemplateused.Thenanowiresarewithveryhighaspectratioofabout1000:1,withthelengthofabout100μm,whichequalingtotemplatethickness.AscanbenoticedinFig.2B,asinglenanowireisoutofthechannelofAAO.Itwasformedwhenthesamplewassplitforacrosssectionexamina-tion.OurdataconfirmedthattheZnOnanowireswerecom-pactedbytheelectrodepositionmethod.
Tofurtherconfirmourexperimentresults,ZnOnanowireswerealsoobservedbytransmissionelectronmicroscopy(TEMTECNAIG2F20,PHILIPS).Fig.2CdisplaysaresultobservedbytheTEM.TwoseparateZnOnanowiresareshowninFig.2C,anditisnoticedthatthesenanowiresareverystraight,thediameterofthesenanowiresisabout80nm,almostequalstothediameterofthenanochannels.
ThecrystallinestructurewasdeterminedbyXRDwithCuKαradiationusingaRigakuX-raydiffractometer,asshowninFig.3.Fig.3AshowstheXRDpatternofas-depositedZn/AAOassembly.TherewasnoanyotherfeaturelineinthesamplebutthoseofdepositedZn.Fig.3BshowstheXRDpatternofthesampleannealedinoxygenatmosphereat800℃for2h.NoZnfeaturelinescanbeseeninFig.3B,whileZnOphasewasdetected.ItindicatesthattheZnnanowiresimbeddedinAAOchannelscanbecompletelyoxidizedin2hunderoxy-genatmospherecondition.However,thesameoxidationpro-cesswouldtake35hinair.Itshortensthepreparationtimeof 4Photoluminescence(PL)spectrumofZnOnanowires TheinsetisthePLspectrumofablankAAOtemplate. 3372
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