北京大學(xué)電分析探針顯微鏡及其應(yīng)用elect8a課件

CollegeofChemistryandMolecularEngineeringPekingUniversityEmail:Phone:62759394ScanningProbingMicroscopy(SPM)

YuanhuaShao掃描探針顯微鏡及其應(yīng)用Outline:1.Introduction

2.Instrumentation 3.Theory

4.Applications

REFERENCES:1.R.M.WightmanandD.O.Wipf,inElectroanalyticalChemistry,Vol:15,(A.J.Bard,Ed.),MarcelDekker,NewYork,1988,p.2672.A.J.Bard,F.Fan,J.KwakandO.Lev,Anal.Chem.,1989,61,1321989,61,1221.3.M.V.Mirkin,Anal.Chem.,1996,68,177A4.M.V.Mirkin,Mikrochim.Acta.,1999,130,1275.A.J.Bard,F.FanandM.V.Mirkin,inElectroanalyticalChemistry,Vol:18(A.J.Bard,Ed.),Marceldekker,NewYork,1993,p.2436.掃描力顯微術(shù)，白春禮，田芳和羅克，科學(xué)出版社，2000Figure.(a)Representationoftunnelingbetweentipandsampleatoms.Shadedportionsdenoteelectrondistributions.(b)TipattachedtothreePiezoelementsusedtopositionthetipandscanitacrossasurfaceSTMitun=(constant)Vexp(-2x)=V/RtunWhereVisthetip-substratebias,xisthedistancebetweentipandsurface,1?-1,AndRtunistheeffectiveresistanceofthetunnelinggap,typically109to1011ohms.Figure.CellforelectrochemicalSTM.Upper:schematicdiagram.Lower:NanoscopeIIIcell,topview.Figure.(a)STMimagesof(A-D)mixedadsorbedlayersOfPPandFePPonHOPG.Takenwithawax-coatedPtTipin0.05MNaBOSolutioncontainingFePPandPPintheratioof(A)0:1(B)1:4(C)4:1and(D)1:0.TheHOPGsubstratepotentialWas–0.41Vvs.SCE;thetip/Substratebiaswas–0.1V;Andthetunnelingcurrentwas30pA.(b)(E-H)TheCorrespondingcyclicVoltammogramsforA-D,Respectively,atasweeprateOf0.2V/s.AFMFigure.ElectrochemicalcellforAFMforNanoscopeIII.2.InstrumentationA.BasicApparatusThebasicSECMapparatusconsistsoffourparts:tippositioncontroller;electrochemicalcell(includingtip,substrate,counterandreferenceelectrodes);bipotentiostatanddataacquisitionsystemB.MicroprobesTheinformationobtainablefromSECMmeasurementsdependsmostlyonthetypeandsizeoftheusedmicroprobe.(1)Amperometrictips:solidUMEs, micro-tonano-meterdiskUMEs(2)Potentiometrictips:Ion-selectivemicroelectrodes(3)Dual-functionaltips:Antimony(Sb),dual-channeltips(4)TipsbasedonCharge-transferacrossliquid/liquidinterface:electrontransfer,iontransferprocesses(Micropipettes)3.TheoryA.ModesofOperationTheSECMcanbeusedinavarietyofways,e.g.,asanelectrochemicaltooltostudyheterogeneousandhomogeneousreactions,asanimagingdevice(microscope),andformicrofabrication.TheseapplicationsmakeuseofdifferentmodesoftheSECMoperation.(1)Amperometricfeedbackmode:(2)Generation/Collectionmodeandpotentiometricmeasurements:(3)PenetrationMode:(4)Iontransferfeedbackmode:ThemasstransferrateinSECMisafunctionofthetip-substratedistance:d>>a,mD/ad<a,mD/dD=1x10-5cm2/s,d=0.1m,m=1cm/s10cm/sHighSpatialResolution:about3050nmlimitforconductingsubstratesand2nmforinsulatingsubstrates3.TheoryoftheSECMTheconsiderablecomplexityofSECMtheoryisduetothecombinationofacylindricaldiffusiontothemicro-tipelectrodewithathin-layerdiffusionspace.Thegeneralsolutionofthediffusionproblemforanuncomplicatedquasi-reversiblenon--steady-stateprocessinSECMwasobtainedasasystemoftwo-dimensionalintegralequations.Twolimitingcases,adiffusion-controlledprocessandonewithtotallyirreversiblekinetics,weretreatednumerically.Theseresultsandthetheoryforcomplexprocesses.Includinghomogeneouschemicalstagesandadsorption-desorptionkinetics,havebeenreviewed.Thetheoryforsteady-state(time-independent)processesissimpler.TheknowledgeoftheshapeoftheiT-L(the"approach")curveforadiffusion-controlledprocessiscriticalforbothimagingandquantitativekineticmeasurementsbecauseitallowsonetoestablishthedistancescale.Thedimensionlesscurrent-distancecurveswereobtainednumericallyforbothinsulatingandconductivesubstratesandseveralvaluesofRG(RG=rg/a,wherergistheradiusoftheglassinsulatorplustheradiusoftheelectrodea),assumingatipheldatthepotentialwherethereactionisdiffusioncontrolled,equalcoefficientsandaninfinitelylargesubstrate.ForRG=10,ananalyticalexpressionforaconductivesubstratecanbefittothenumericalresultstoyieldtheequation:

IT(L)=iT/IT,=0.78377/L+0.3315exp(-1.0672/L)+0.68 (1)4. ApplicationsA.StudyofheterogeneousreactionkineticsB.ImagesC.Micro-fabricationsImageofmicatreatedwithDNA(2.96kbp)specimensonmicatakeninhumidairSingleMoleculedetectionIdealizedschematicillustrationofthetipgeometryandthetip-substrateconfigurationused.SchematicrepresentationoftheprinciplesofSECMwithmicro-ITIESSECMimageobtainedusingamicro-ITIESprobe(5-mtip).Substratewassiliconwithparallelplatinumbands.J.Electroanal.Chem.,1997,439,p137-143PositivefeedbackNegativeFeedbackApproachabigL/LinterfaceApproachasolidsubstrateRG=Rg/aBardetal.havedevelopedthetheoryforRG10cases.However,formicropipettesasthetipsforSECM,theRGsareusually2.UsingsoftwarepackagePDEase(SPDE,Inc.),wehavesolvedthetheoreticali-dcurvesforRG2.J.Phys.ChemB.,1998,102,p9915-9921RG=Rg/a=b/aL=d/aAqueousPhaseOrganicPhaseCurrent-distancecurvesobtainedwithdifferentconcentrationsofTEAClintheaqueousphase.(1)0,(2)0.4,and(3)10mM.TEA+(w)=TEA+(o)RG=1.1ConstantheightmodegrayscaleimagesofporesinpolycarbonatemembraneTCNQ+Fe(CN)64-=TCNQ.-+Fe(CN)63-Fe(CN)63-(w)+e=Fe(CN)64-(w)E1o=0.41VvsSHETCNQ(o)+e=TCNQ.-(o)E2o=0.22VvsSHEow=owo+(RT/nF)ln[ai(o)/ai(w)]

ow<<E2o-E1o(-190mV)owTBA+o=-225mVReverseElectronTransferReactionsApproachcurveforthesystem:H2O,TPAsCl,1mMFe(CN)63-||DCE,1mMTPAsTPB,10mMTCNQ;showingtheelectrontransferdrivenbythephasetransfercatalystTPAs+.Fromtoptobottom,theexperentcurveareshownforKp=10,5,2,1. A:TPAssystem.B:TBAsystem.DependenceoftheeffectiveETrateconstantonconcentrationofTCNQinDCE.Thekvaluewereusedtofittheapproachcurevwitha=10mand.FromtoptobottomtheKpvaluewasshownfor10,5,2. A:TPAssyetem.B:TBAsystem.DependenceoftheeffectiveETrateconstantonpotentialdropacrosstheITIES.

A:TPAs.B:TBA.SECMStudiesofETReactionsacrossIce/LiquidInterfaceFigureExperimentalapproachcurvesofthesystem(line)andthetheoreticalcurves(dot)at-30C.Theicephasecontained5mMK4Fe(CN)6,0.1MKCl,and0.01MTBACl.TheDCEphasecontained1mMFc.Fromtoptobottom,theconcentrationsofTBATPBinDCEphasewere1,5,10,20,40,100and200mM,respectively.Theratesofelectrontransferk/(cm.s-1.M-1)were10.1,3.62,2.45,1.83,1.01,0.65,0.47,Alloftheapproachrateswere1μm/s.CombinationofSECMandpolarizedliquid/liquidinterfacesFc(o)+Fe(CN)63-(w)=Fc+(o)+Fe(CN)64-FigureExperimentalapproachcurves(dot)fittedwiththeoreticalvalues(line).TheDCEphasecontained0.01MTBATPBCland0.2mMferrocene.Theaqueousphasecontained0.1MLiCl+xMK3Fe(CN)6+yMK4Fe(CN)6.(D)x=y=0.2mM.Fromtoptobottom,theexternal-potentialwere-0.10V,-0.05V,0V,0.05V,0.10V,0.20Vand0.30V.Alloftheapproachrateswere1μm/s.InvestigationofModifiedElectrodesSurfacepKaFigure:SchematicdiagramoftheapplicationofSECMtoprobefacilitatediontransferatanexternallypolarizedLiquid/LiquidinterfaceProbingfacilitatediontransferatanexternallypolarizedL/LinterfaceStudyofsimpleion,facilitatedionandelectrontransferacrossaliquid/liquidinterfacebythree-electrodesystemFigure:Cyclicvoltammogramsobtainedforchargetransferreactionsbyuseofathree-electrodesetup(a)PotentialwindowandfacilitatedK+transferreaction,the