PREPARATION AND CHARACTERIZATION OF PS-SiO2 NANOCOMPOSITE MICROSPHERES

JournalofCrystalGrowth311(2009)3889–3897

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JournalofCrystalGrowth

journalhomepage:www.1mpi.com

Precursor-controlledsynthesisofhierarchicalZnOnanostructures,usingoligoaniline-coatedAunanoparticleseeds

DeeptiKrishnan,T.PradeepÃ

DSTUnitonNanoscience(DSTUNS),DepartmentofChemistryandSophisticatedAnalyticalInstrumentFacility,IndianInstituteofTechnologyMadras,Chennai600036,India

articleinfo

Articlehistory:

Received6May2009Receivedinrevisedform26May2009

Accepted9June2009

CommunicatedbyK.NakajimaAvailableonline18June2009PACS:61.46.Àw61.46.Df81.10.Aj68.37.Lp68.37.Àd

Keywords:

A1.CrystalmorphologyA1.Nucleation

A2.GrowthfromsolutionsB1.Zinccompounds

B2.SemiconductingII–VImaterials

abstract

Shape-selectedsynthesisofalargenumberofzincoxide(ZnO)nano-andmicrostructureswasachievedbytheseed-mediatedgrowthofoligoaniline-coatedgoldnanoparticleprecursors.DistinctiveZnOstructuressuchasnanoplates,nanospheres,microstars,micro owers,microthornsandmicromultipodsweresynthesizedbythismethod.Slightlydifferentshapeswereobtainedintheabsenceoftheseedsolution.Thisisafast,lowtemperature(601C)andbiomimeticroutetomakeawidevarietyofstructures.Thestructureandmorphologyofthenanostructureswerestudiedbytransmissionelectronmicroscopy(TEM)andscanningelectronmicroscopy(SEM),respectively.Ramanspectroscopy,Fourier-transforminfrared(FTIR)spectroscopyandX-raydiffraction(XRD)wereutilizedforthecharacterizationofthenanostructures.Agrowthmechanismforthesenanostructureswasproposedbasedontheseresults.Theconcentrationsofthereactingspecieswerethemainparametercausingthechangesinthemorphologies.Thevariationinmorphologiesofthesestructuresisbelievedtobeduetotheabilityoftheseedsolutionaswellaspolyvinylpyrrolidone(PVP)toselectivelysuppress/depressthegrowthofcertainplanes,allowinggrowthtooccuronlyincertainspeci cdirections.Changesintheamountofgrowthnucleiwithvaryingsodiumhydroxide(NaOH)concentrationisalsoseentoaffectthemorphologyofthesestructures.

&2009ElsevierB.V.Allrightsreserved.

1.Introduction

Zincoxide(ZnO),asemiconductorwithadirectwidebandgap(3.37eV–387nm,deepviolet/borderlineultraviolet(UV))andalargeexciton-bindingenergy(60meV)[1],isahighlypreferredmultitaskingmetaloxidehavingavastlistofattractiveproperties.Duetoitsuniqueopticalandelectricalproperties[2,3],itisregardedasapotentialmaterialinoptoelectronicapplicationsoperatinginthevisibleandnearultravioletspectralregions.Theareasinwhichitisusedinclude,UVlight-emittingdiodes[4–6],nanolasers[7],gassensors[8],highly-ef cientgreenphosphors[9],photo-catalystsandphotovoltaicdevices[10,11], eld-effecttransistors[12],chemicalsensors[13],transparentconductorsandvaristors[14,15].Alsoitpossessesexcellentthermalandchemicalstability,alargepiezoelectriccoef cient,andaneasilymodi ableelectricalconductivity.Itisnon-toxic,compatiblewithskin,antimicrobialandisusedasanUV-blockerinsunscreens.

ThetremendousinterestinZnOisduetoitsuniqueabilityofpossessingstructure-dependentproperties.Propertieslikeelectricalandthermaltransport,inadditiontoopticaland

ÃCorrespondingauthor.Tel.:+81757535445/+914422574208;

fax:+914422570545.

E-mailaddress:pradeep@iitm.ac.in(T.Pradeep).

0022-0248/$-seefrontmatter&2009ElsevierB.V.Allrightsreserved.doi:10.1016/j.jcrysgro.2009.06.019

mechanicalproperties,couldbevariedwithrespecttoparticlesize,shape,morphology,orientationandaspectratio.Hence,morphologyanddimensionality-controlledgrowthofzincoxidehasbecomeachallengingtopiclatelytodesignnovelfunctionaldevices.Sofar,numerousnanostructuredZnO’swithvariousmorphologieshavebeenfabricatedlikeplates[16],wires[17],belts[18],rods[19],pyramids[20],cagesandshells[21],dandelions[22],branchedcrystallites[23],organic-cappednano-crystals[24],urchins[25],hollowspheres[26],bridgesandnails[27],hemisphericalbowls[28],ellipsoidsandnanocolumns[29],towers[30],conesandreefs[31]andstars[32].Themostcommonroutesforpreparingthesestructuresfallintoeithervapor-phasesynthesis[33–41]suchasvapor-liquid-solid(VLS)growth,chemicalvapordeposition(CVD),metalorganicchemicalvapordeposition(MOCVD),thermaldecompositionandthermalevaporationorsolution-phasesynthesis[42,43]likehydrother-mal,microemulsionandtemplate-assistedsol–gelprocesses.Amongthetwocategories,solution-phasetechniquesarehighlypreferredastheyinvolvelowtemperatureandarecheaperforscale-up.Vapor-phasetechniquesrequirehightemperature(ofmorethan2501C)andareexpensive,besidesdemandstringentconditions.Hence,itishighlydesirabletodevelopasynthesiswhichrequiresmildconditions,duetoitseasyincorporationinbiologicallyrelevantprocessesaswellasinpracticalapplications.