ZnO纳米线阵列的电沉积法制备及表征 - 英文 - 解析

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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ZnO/AAOassembliesenormouslybytheelectrodepositionmethod.Furthermore,theXRDpatternsindicatethattheZnOnanowiresareofpolycrystallinestructureswithoutpreferredorientation.WealsofoundthattherewasAl2O3featuredetect-edneitherinFig.3AnorinFig.3B,whichisbecauseanodicalu-minumoxideisamorphousuntilheatedupto824℃[17-18]. Photoluminescence(PL212,SPEX)measurementswereper-formedtostudytheluminescencepropertyofZnOnanowires.Astrongemissionbandwasobservedat504nm,whichwasat-tributedtotheoxygenvacancydefectsofZnO[19],asshowninFig.4.Ablueemissionbandat430nmwasobserved.Compar-ingthePLspectrumofablankAAOtemplate(theinsetinFig.4)withthatoftheZnO/AAOassembly,weconcludethatthebroademissionbandaround430nmoriginatesfromtheAAOtemplate. 3Conclusions

Inconclusion,largescaleuniformZnOnanowirearraysbasedonhexagonallyarrangedAAOwasfabricatedbyanef-fectiveelectrodepositionmethod.TheirFE-SEMimagesshowthattheZnOnanowirearraysarelong,continuous,anduni-form.XRDpatternsindicatethatZnnanowiresinAAOcanbeoxidizedcompletelyin2hat800℃inoxygenatmosphere.TheZnO/AAOassemblyhasastronggreenemissionbandat504nmandablueemissionbandat430nm.Thegreenemis-sionisattributedtooxygendefectsandtheblueemissionorigi-natesfromAAO.TheaboveconclusionssuggestthattheZnO/AAOassemblycouldbeusefulforthepreparationofZnOelec-troluminescencedevices.References 1

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