Electrodeposition of silver nanoparticle arrays on ITO coated glass and their

AppliedSurfaceScience258 (2011) 1831–1835

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AppliedSurfaceScience

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ElectrodepositionofsilvernanoparticlearraysonITOcoatedglassandtheirapplicationasreproduciblesurface-enhancedRamanscatteringsubstrate

Jun-CaoBian,ZheLi,Zhong-DongChen,Hai-YanHe,Xi-WenZhang?,XiangLi,Gao-RongHan

StateKeyLaboratoryofSiliconMaterials,DepartmentofMaterialsScienceandEngineering,ZhejiangUniversity,Hangzhou,310027,China

article

info

abstract

Articlehistory:

Received17September2011Accepted12October2011

Available online 18 October 2011

Keywords:Silver

NanoparticlearraysDouble-potentiostaticElectrodepositionSERS

Inthispaper,adouble-potentiostaticmethodisusedforpreparationofhighlyef?cientanduniformsurface-enhancedRamanscattering(SERS)substrate.Themethodtakesadvantageofthequicknucleationandslowgrowthprocess,yieldingsilvernanoparticlearrays(NAs)containinglargeamountofhotspots,whichbringaboutthesedensesilverNAsforreproducibleSERSapplication.

© 2011 Elsevier B.V. All rights reserved.

1.Introduction

Nobelmetalnanoparticles(e.g.AgandAu),withthestronglocalizedsurfaceplasmonsresonance(LSPR),haveattractedcon-siderableattentionduetotheirpotentialapplications,suchaselectronics,photonics,biosensorsandsurface-enhancedRamanscattering(SERS)[1–4],etc.Amongnoblemetalnanoparticles,nanosilverisidealasithasthelowestplasmoniclossesinthevisiblespectrum[5].However,asacrucialprocedurefortheactualappli-cation,e.g.,toensurethereproducibilityoftheSERSsubstrate,theassemblingofsilvernanoparticlearrays(NAs)withsmallsizevari-ationanduniformspatialdistributiononasolidsubstrateremainschallenging.Althoughthiscanbeachievedbylithographicpro-cess[6–8],itiseitherexpensiveortimeconsumingforscalinguptomm-dimensions.Moreover,seed-mediatedgrowthprocessinvolvesseedphysisorptiononsubstrateandseedgrowth[9–11],whichresultsinthecomplexmanipulationandlowef?ciency.Asforphysicalprocesssuchasthermalevaporation,hightemperatureorlowpressureenvironmentisalwaysindispensable[12].

Electrodepositionisattractiveasitiseconomical,versatileandef?cienttoprepareNAsontosubstrate.Uptonow,sev-eralstrategieshavebeenproposedsuchasutilizingatemplate[13],applyingdoublepotentialpulses[14–16]orpotentialstep[17],oremployingacyclicvoltammetryscan[18].However,

fabricationofsilverNAsbythedouble-potentiostaticmethodol-ogyisrarelydocumented.Itiswellknownthattherearetwobasicprocessesduringelectrodeposition:nucleationandgrowth[19,20].Tonarrowthesizedistribution,aquicknucleationandslowgrowthprocessisfavorable.Althoughthedouble-pulsemethodcanreal-izethegoal,ahighprecursorconcentrationisneeded[15,16],whichinevitablyincreasesthesizevariations.Onthecontrary,thedouble-potentiostaticmethodismoredesirable,whichhasfollow-ingadvantages:(A)denseanduniformlydistributednucleicanberapidlygeneratedunderthehighnucleationpotentialandlowsil-verprecursorconcentration,(B)thesubsequentlowerpotentialcanmaintainasuitablegrowthrateofgrowthphaseandinhibitthefor-mationofnewnuclei.AllthesecharacteristicsarecrucialtoobtainuniformanddensemetallicNAs.

Inthisreport,directelectrodepositionofsilverNAswithuniformsizeandspacialdistributionwasrealizedbyadouble-potentiostaticmethod.TheITOcoatedglassesgrownwithsilverNAsusingasSERSsubstratewereinvestigated.Theresultsshowedthatas-depositedsampleswereidealSERSsubstratesandpre-sentedgoodreproducibility.

2.Experimentaldetails

?Correspondingauthor.Tel.:+8657188276234;fax:+8657187952341.E-mailaddress:zhangxw@http://wendang.chazidian.com(X.-W.Zhang).

SilverNAswereelectrodepositedoncleanITOcoatedglassintheaqueouselectrolytethatconsistedof0.05mMAgNO3,0.2mMsodiumcitrate(C6H5Na3O7)and0.1MKNO3.Theelec-trodepositionwasperformedonanelectrochemicalworkstation(ES550,GaossUnionTechnologyCo.,Ltd.,Wuhan,China).All

0169-4332/$–seefrontmatter© 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.apsusc.2011.10.055

1832J.-C.Bianetal./AppliedSurfaceScience258 (2011) 1831–1835

Fig.1.(a)Linearsweepvoltammogramoftheelectrolyteconsistingof0.05mMAgNO3,0.2mMCitNaand0.1MKNO3from0.2Vto?1.5Vat?0.05V/s,(b)potential–time(?0.6V,?0.8V,?1.0V,?1.2Vand?1.4Vfor100srespectivelyand?0.2Vfor3600s)and(c)thecorrespondingcurrent–timecurvesofthedouble-potentiostaticelectrode-positionprocess.

oftheelectrochemicalexperimentswerecarriedoutatroomtemperature(32±1?C)inastandardthree-electrodesystem.ITOcoatedglasswasusedasworkingelectrodes,Ptplateascounterelectrodeandsaturatedcalomelelectrode(SCE)asref-erenceelectrode.AllthepotentialsinthispaperwereversusSCEscale.

ThesurfacemorphologyofthesilverNAswasstudiedbyHitachiS4800scanningelectronmicroscopy(SEM).Transmissionelectronmicroscopy(TEM)imagewasobtainedonaPhilipsCM200TEMusinganaccelerationvoltageof160kV.TheextinctionspectrawererecordedwithaTU-1901UV–visspectrophotometerbyusingbareITOcoatedglassasthereference.ForSERSspectralassessment,as-preparedsamplesweresoakedina10?6Maqueousrhodamine6G(R6G)solutionfor3h,thentakenoutandrinsedbydeionizedwater.TheRamanscatteringmeasurementswerecarriedoutonaRamansystem(RENISHAWinVia)withconfocalmicroscopy.Thelaser(514.5nm,0.05mW)wasusedandtheacquisitiontimewas10s.

3.Resultsanddiscussion

Fig.1ashowsthelinearsweepvoltammogramfrom+0.2Vto?1.5Vat?0.05V/s.Duringthescanapeakappearsatabout?0.6V,whichcorrespondstoelectrochemicalreductionofsilverdeposit[21].Totestthein?uenceofthenucleationpotentialonthesilverNAs,weselectedthedouble-potentiostaticprogramswherethenucleationpotentialare?0.6V,?0.8V,?1.0V,?1.2Vand?1.4V,separately,holdingfor100stoandthegrowthpoten-tialis?0.2Vholdingfor3600s.Andtheseshortnucleationperiodsandlonggrowthperiodsensurethequicknucleationandslowparticlegrowthprocesses.Thecorrespondingpotential–timeandcurrent–timecurvesweredepictedinFig.1bandc.

Fig.2a–eshowsthetypicalSEMimagesofthesilverNAsdepositedatdifferentnucleationpotentials.Whatoneimmedi-atelynoticesinFig.2a–eistheincreasingparticledensityandthedecreasingparticlesizeasthenucleationpotentialincreases.Thenumberofnucleiincreasessincemoresitesareactivatedbyincreasingthenucleationoverpotential.Andthemoresilverparti-clesaredepositedonthesurfaceoftheelectrode,themore?ercecompetitionforsilverionsamongtheadjacentparticlesareinthegrowthprocess,whichresultsinthedecreaseoftheparti-clesize.Theresultsarewellconsistentwiththepreviouswork[16,22].

Toevaluatetheeffectofnucleationpotentialontheparticlesizeandinterparticledistance,300particleradiusesandinter-particledistancesweremeasuredfromtheSEMimages.FromFig.2,itcanbeseenthatsizeandinterparticledistancedistri-butionarenarrowerandthecorrespondingstandarddeviationsreduceasthenucleationpotentialismorenegative(theoptimumvalue:3.25nminsizestandarddeviationand5.22nmininter-particledistancestandarddeviation),indicatinggooduniformityinsizeandspacialdistributionofsilverNAsonthesubstrates.FromFig.1c,itisfoundthatwhenthenucleationpotentialismorenegativethan?0.8V,thedepositioncurrentdensitiesincreaseinthenucleationstage,indicatingtheaccelerationofgrowthrateofthesilverNAs.However,thesizestandarddeviationdecreases.Weattributethistothedepletionlayersformatedsurround-ingthenucleiunderlowsilverprecursorconcentration,whichrestrainsthenucleigrowingfast[23,24].Hence,thelowconcen-trationsilverprecursorisakeyfactortoensuretheuniformityofthesilverNAsathighnucleationpotential.FromFig.2,itcanbeconcludedthatsizeandspacialdistributionofsilverNAscanbewellcontrolledbyvaryingthenucleationpotential.Fig.3showstheTEMimageofthesilvernanoparticleswhichapproxi-matespheresinshape.TheinsetshowstheSAEDpatternwhichcouldbeindexedtofccsilver.Thediffractionringswithinter-mittentbrightdotsindicatethatthesenanoparticlesarehighlycrystalline.

Theeffectofthenucleationpotentialontheextinctionspec-traofsilverNAswasdepictedinFig.4.Ascanbeseen,therearemainlytwopeaksaround380nmand450nmwhenthenucle-ationpotentialispositivethan?1.0V,whicharecorrespondedtothequadrupoleanddipolemodeofthesilvernanoparticles[25–27],respectively.Asthenucleationpotentialchangesfrom?0.6Vto?1.4V,theresonancepeakataround450nmisobservedto?rstlyblueshift,thenredshiftandanewresonancepeakaround550nmappears,suggestingthetunabilityoftheplasmonsres-onanceofthesilverNAs.Thepeakshiftandtheappearanceofnewresonancepeakareexpectedbecausesmallerparticlesizeandshorterinterparticledistancehavebothbeenobservedtocausethechangesintheplasmonsresonancepeaks[28–30].Ini-tially,theblueshiftismainlyduetothesizeeffect.Althoughtheinterparticledistancedecreases,itsin?uenceontheshiftisnotobviousasthedistanceislargerthan10nm[31].Whenthedis-tanceislessthan10nm,itplaysadominantroleandleadtostronginterparticleplasmonscoupling,inducingtheresonance

J.-C.Bianetal./AppliedSurfaceScience258 (2011) 1831–1835

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Fig.2.SEMimages,sizediagramsandinterparticledistancediagramsofthesilverNAsdepositedatnucleationpotentials(a)?0.6V,(b)?0.8V,(c)?1.0V,(d)?1.2Vand(e)?1.4Vfor100srespectively,and?0.2Vfor3600s.

1834J.-C.Bianetal./AppliedSurfaceScience258 (2011) 1831–1835

Fig.3.TEMimageofAgnanoparticles.TheinsetshowsthecorrespondingSAEDpattern.

peakaround550nmandbroadeningthewidthoftheextinctionspectra.

Fig.5ashowstheSERSspectraofR6Gabsorbedonthesur-faceofthesilverNAsdepositedatdifferentnucleationpotentials.Ascanbeseen,thepeaksaretypicalsignalofR6G,includingtheC–Hout-of-planemodeat774cm?1,C–Hin-planemodeat1129cm?1,C–Cstretchingmodeat1363,1509and1650cm?1[32].Asthepotentialbecomesmorenegative,theSERSsignalsareenhancedastheinterparticledistancedecreases,inducinggiantelectromagnetic?eldsenhancementbythesurfaceplasmonscou-plingbetweentheneighboringnanoparticlesatthegaps(usuallycalled“hotspots”)[33,34].ToassesstheSERSsignalreproducibil-ityofthesilverNAs,sixrandomspotsweremeasuredunderthesameexperimentalconditionssuchaslaserpowerandacquisi-tiontime.Fig.4bshowsthattherelativestandarddeviation(RSD)oftheintensitiesforthe1650cm?1bandislessthan11%whenthenucleationpotentialismorenegativethan?0.6V,whichindi-catesthatthereproducibilityofthesilverNAsontheITOcoatedglassessuitableforhighlysensitiveSERSsubstrate.ItalsoshouldbenotedthattheRSDdecreases,asthenucleationpotentialismorenegative,correspondingtotheimproveduniformityofspacialdistribution.

Additionally,althoughonlysilverNAsarereportedhere,thisdepositiontechniquemightbegeneraltomanyothermetals,suchasAuandPt.Theexperimentparameterssuchasnucleationpoten-tialcanbe

adjusted.

Fig.4.ExtinctionspectraofsilverNAsdepositedatnucleationpotentials?0.6V,?0.8V,?1.0V,?1.2V,?1.4Vfor100s,respectivelyand?0.2Vfor3600

s.

Fig.5.(a)SERSspectraofR6GabsorbedonthesurfaceofthesilverNAsdepositedatnucleationpotentials?0.6V,?0.8V,?1.0V,?1.2V,?1.4Vfor100s,respectivelyand?0.2Vfor3600s.Sixspotsofeverysamplewererandomlychosen,(b)RSDoftheintensitiesforthe1650cm?1bandasafunctionofnucleationpotential.

4.Conclusions

Adouble-potentiostaticmethodwasusedtopreparesilvernanoparticlearraysonITOcoatedglasswithuniformsizeandspacialdistribution.Theresultsshowedthatuniformityofthesil-verNAsimprovedasthesizeandinterparticledistancestandarddeviationofsilvernanoparticlesdecreasedwhenthenucleationpotentialwasmorenegative.Thedecreaseininterparticledis-tanceleadedtotheinterparticlesurfaceplasmonscouplingandsigni?cantSERSeffect.ThelowestrelativestandarddeviationofRamanintensityforthe1650cm?1bandwas2.5%,indicatinggoodreproducibility.Thisdepositiontechniquehaspromisingapplica-tioninothermetals.

Acknowledgments

ThisworkwassupportedbytheNationalBasicResearchPro-gramofChina(973Program)“2007CB613403”andFoundationofthescienti?cresearchbasedevelopment(EngineeringResearchCenteroftheEducationMinistryfortheSurfaceandStructureMod-i?cationofInorganicfunctionalMaterials)“2010KYJD022”.

References

[1]E.Ozbay,Science311(2006)189.

[2]H.A.Atwater,A.Polman,Nat.Mater.9(2010)205.

[3]B.Sepúlvedaa,P.C.Angeloméb,L.M.Lechugaa,L.M.Liz-Marzánb,NanoToday

4(2009)244.

[4]S.Nie,S.R.Emory,Science275(1997)1102.

[5]W.L.Barnes,A.Dereux,T.W.Ebbesen,Nature424(2003)824.[6]C.L.Haynes,R.P.VanDuyne,NanoLett.3(2003)939.

[7]V.Liberman,C.Yilmaz,T.M.Bloomstein,S.Somu,Y.Echegoyen,A.Busnaina,

S.G.Cann,K.E.Krohn,M.F.Marchant,M.Rothschild,Adv.Mater.22(2010)429.

J.-C.Bianetal./AppliedSurfaceScience258 (2011) 1831–1835

1835

[8]X.Zhang,E.M.Hicks,J.Zhao,G.C.Schatz,R.P.VanDuyne,NanoLett.5(2005)

1503.

[9]K.Lee,K.Huang,W.Tseng,T.Chiu,Y.Lin,H.Chang,Langmuir23(2007)1435.[10]A.Sánchez-Iglesias,P.Aldeanueva-Potel,W.Ni,J.Pérez-Juste,I.Pastoriza-Santos,R.A.Alvarez-Puebla,B.N.Mbenkum,L.M.Liz-Marzán,NanoToday5(2010)21.

[11]G.Chang,J.Zhang,M.Oyama,K.Hirao,J.Phys.Chem.B109(2005)1204–1209.[12]S.Kar,T.Ghoshal,S.Chaudhuri,Phys.Lett.419(2006)174.

[13]K.Nielsch,F.Muller,A.P.Li,U.Gosele,Adv.Mater.12(2000)582.

[14]A.Milchev,E.Vassileva,V.Kertov,J.Electroanal.Chem.107(1980)323.[15]G.Sandmann,H.Dietz,W.Plieth,J.Electroanal.Chem.491(2000)78.

[16]M.Ueda,H.Dietz,A.Anders,H.Kneppe,A.Meixner,W.Plieth,Electrochim.

Acta48(2002)377.

[17]X.Dai,http://wendang.chazidian.compton,Anal.Sci.22(2006)567.

[18]L.Wang,W.Mao,D.Ni,J.Di,Y.Wu,Y.Tu,http://wendang.chazidian.commun.10(2008)

673.

[19]A.Radisic,P.M.Vereecken,J.B.Hannon,P.C.Searson,F.M.Ross,NanoLett.6

(2006)238.

[20][21][22][23][24][25][26][27][28]

[29][30][31]

[32][33]

[34]

E.Sheridan,J.Hjelm,R.J.Forster,J.Electroanal.Chem.608(2007)1.

P.Y.Li,R.S.Liu,P.L.She,C.F.Hung,H.C.Shih,Chem.Phys.Lett.420(2006)304.A.Milchev,T.Zapryanova,Electrochim.Acta51(2006)2926.H.Liu,R.M.Penner,J.Phys.Chem.B104(2000)9131.R.M.Penner,J.Phys.Chem.B105(2001)8672.

N.P.W.Pieczonka,P.J.G.Goulet,R.F.Aroca,J.Am.Chem.Soc.128(2006)12626.J.Zhang,X.Li,X.Sun,Y.Li,J.Phys.Chem.B109(2005)12544.Y.Song,H.E.Elsayed-Ali,Appl.Surf.Sci.256(2010)5961–5967.

J.J.Mock,M.Barbic,D.R.Smith,D.A.Schultz,S.Schultz,J.Chem.Phys.116(2002)6755.

S.J.Lee,K.Kim,http://wendang.chazidian.commun.(2003)212.

B.Choi1,H.Lee,S.Jin,S.Chun,S.Kim,Nanotechnology18(2007)075706.

H.Wang,C.Liu,S.Wu,N.Liu,C.Peng,T.Chan,C.Hsu,J.Wang,Y.Wang,Adv.Mater.18(2006)491.

P.Hildebrandt,M.Stockburge,J.Phys.Chem.88(1984)5935.

Z.Huang,G.Meng,Q.Huang,Y.Yang,C.Zhu,C.Tang,Adv.Mater.22(2010)4136.

Y.Lu,G.L.Liu,L.P.Lee,NanoLett.5(2005)5.