银纳米颗粒阵列的表面组分特性

银纳米颗粒阵列的表面组分特性 第17卷第3期 2005年10月 光散射 CHINESEJOURNALOFLIGHTSCATTERING Vo1.17No.3 0ct.2005 文章编号:1004—5929{2005}03.0243.02 SurfaceCompositionalCharacteristicsofAu/AgAlloy Nanoparticles Scat RevealedbySurface._.enhancedRaman teringofAromaticIsocyanides 芳香异腈的SERS光谱所揭示的金/银纳米颗粒阵列 的表面组分特性 HyoungKunPark,KwanKim LaboratoryofIntelligentInterfaces,SchoolofChemistry,SeoulnationalUniversity, Seoul151—742,Korea E—Mail:kwankim@plaza.snu.ac.kr pace:7830 Amajortaskinmolecularelectronicsisthe precisedeterminationofthemolecule—metalinter. facecharacteristics.Thisisparticularlybecause metalsandsinglemoleculeshaveintrinsicallyun. avoidableelectricalmismatchesbutthereisnotyet anestablishedwaytoevaluatethemsystematically. Atpresentthemostattractingmoleculeisdeemed tobearomaticthiolbecauseitcanreadilyformsta. blemetal——sulfurbondtogetherwiththeprovision ofthedelocalizedringorbitals.Consideringthat theelectricaltransportpropertyissusceptibletothe anglemadebythemetalatomandthemolecule, themetal——sulfurbondmaynotbeaseffectiveas themetal—isocyanidebond,however,sincelinear anglesformedinthelatterwillfavorconduction. Ontheotherhand,metalnanoparticlesareattract. inggreatlyinrecentyearssincetheycanbeusedas passivecomponentsinmolecularelectronics.The surfacepropertyofnanoparticlesisquitedifferent fromtheirbulkpropertyduetotheinevitablepres. enceofdanglingbondsatthesurfacesites.Foral. loynanoparticles,surfacechemicalcomposition mayalsobesubstantiallydifferentfromtheirinteri. orcomposition.Evenusingthestate—of—artsur. faceanalyzingtoolssuchasXPSandEDAX,quan. tificationofsuchadifferenceisextremelydifficult duetothefinitepenetrationdepthoftheprobing beams.Inthissymposium,weclearlydemonstrate usingsurface—enhancedRamanscattering(SERS) spectroscopythatAu/Agalloynanoparticles,for instance,areenrichedwithAgatomsatthevery outerpartofthenanoparticles.Thedefinitiveproof isprovidedonthegroundsthat(1)organoiso. cyanidesreadilyadsorbonmetalssuchasAgand AubyformingaM—Cbond,(2)theintrinsiciso— cyanidestretchingfrequency,v(一N三C),observ. ableat2100,2300cm一issubstantiallydifferent fromtheusualgroupfrequenciesoforganiccom— pounds,and(3)theexactisocyanidestretching frequencyisverysusceptibletothekindofmetals attached,therebyaminutemetallicdifferencein compositioncanreadilybedetectedbySERS. Au/Agalloynanoparticleswerepreparedby citratereductionmethodusingHAuC14andAgNO3 asthesourcesofAuandAg,respectively.Topre- parealloynanoparticleswithcomparablepolydis persity,onlyapredeterminednumberofmolesof goldatomsweresubstitutedwiththeequivalent numberofmolesofsilveratoms.AsshowninFig- urel,thepositionofthesurfaceplasmonbandvar. iedlinearlybetween409and525nmasafunction ofmolefractionofAucontent,implyingreadyfor. ? 243? 第3期HyoungRunPar. k:SurfaceCpositionalCharacteristicsofAu/AgAlloyNan0particles2005年 Revealedbysurface—enhancedRamanScatteringofAromaticIsocyanides. marionofAu/Agalloyclusters.TEMimagesalso showedwell—definedalloynanoparticleswithav— eragediameterof35nm.To1mLofAu/Agalloy solsolution.ethanollebenzylisocyanide(BZI)or 2.6一dimethylphenylisocyanide(DMPI)solution wasaddeddropwisetoafinalconcentrationof10一 Mwithamicropipette.Whennecessary.aqueous poly(vinylpyrrolidone)(PVP,Mw360000)was addedintothesolstoafinalconcentrationof,1 wt%asacolloidstabilizer.Ramanspectrawere obtainedusingaRenishawRamansystemModel 2000spectrometerequippedwithanintegralmicro— scope(OlympusBH2一UMA).The632.8一nm linefroma17mWHe/Nelaser(SpectraPhysics Model127)wasusedastheexcitationsource.Ra— manscatteringwasdetectedwith180.geometry withaPeltiercooled(一70?)charged—coupled device(CCD)camera(400×600pixels).Aglass capillary(KIMAX一51)withanouterdiameterof 1.3—1.5mmwasusedasasamplingdevice. Wavelength(nm) Fig.1UV/visspectrumofAu/AgalloyNanoparticles InFigure2(A)areshowntherelativeinten— sitiesandpositionsofv(CN)bandsintheSERS ofBZIdrawnversusthemolefractionofgoldin theAu/Agalloynanoparticles,whiletheSERS spectraofDMPIthemselvesareshowninFigure2 (B).TheseSERSspectraldataclearlysuggest Gddm.Ieon(xJ Fig.2(A)RelativeintensityandpositionforV(NC)mode DMPIinalloysol;eachWRSnormalizedwith(A)VI2 ? 244? thatAgatomsmustbeenrichedattheouterpart ofthealloyclusters.Thesurfacecharacteristicsof Au/Agalloynanoparticlesshouldresemblethatof pureAgnanoparticlesatleastupto50mole%of Au. ofBZISERSspectrum(B)SERSspectrumof10M and(B)v8.modes. 蔼ua量8^ S3sh要oil1 毒尝>糯