北京大学电分析课件探针显微镜及其应用elect8a.ppt

CollegeofChemistryandMolecularEngineeringPekingUniversityEmail yhshao Phone 62759394 ScanningProbingMicroscopy SPM YuanhuaShao 扫描探针显微镜及其应用 Outline 1 Introduction2 Instrumentation3 Theory4 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 扫描力显微术 白春礼 田芳和罗克 科学出版社 2000 STM2 AFM3 SECM Figure a Representationoftunnelingbetweentipandsampleatoms Shadedportionsdenoteelectrondistributions b TipattachedtothreePiezoelementsusedtopositionthetipandscanitacrossasurface STM itun constant Vexp 2 x V Rtun WhereVisthetip substratebias xisthedistancebetweentipandsurface 1 1 AndRtunistheeffectiveresistanceofthetunnelinggap typically109to1011ohms Figure CellforelectrochemicalSTM Upper schematicdiagram Lower NanoscopeIIIcell topview Figure STMimagesofHOPG Gray scaleimagesatlowresolution left andhigherresolutiontopographicplot right 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 AFM Figure ElectrochemicalcellforAFMforNanoscopeIII ScanningElectrochemicalMicroscopy SECM Scanningelectrochemicalmicroscopy SECM wasintroducedin1989byBardandco workersattheUniversityofTexasatAustinwhopublishedaseriesofpapersdescribingtheinstrumentationtheory principlesandapplicationsofthetechnique SECMisanovelin situelectrochemicaltechniquewithitsspatialresolutionbetweenopticalmicroscopyandSTM Sinceitsintroduction ithasprovidedconsiderableinsightsinto andanunderstandingof localizedsurfacereactivityatavarietyofsolid liquidinterfacesrangingfrombiomaterials polymersandmineralstoelectrodesurfaces Ionandelectrontransferprocessesoccurringattheliquid liquidinterfacehavealsobeenstudied 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 iT 4nFDCa 3 TheoryA ModesofOperationTheSECMcanbeusedinavarietyofways e g asanelectrochemicaltooltostudyheterogeneousandhomogeneousreactions asanimagingdevice microscope andformicrofabrication TheseapplicationsmakeuseofdifferentmodesoftheSECMoperation 1 Amperometricfeedbackmode 2 Generation Collectionmodeandpotentiometricmeasurements 3 PenetrationMode 4 Iontransferfeedbackmode B KineticMeasurementsandImagingSurfaceReactivityTherearetwoimportantadvantagesofSECMforheterogeneouskineticmeasurements 1 highmass transferrateallowingonetostudyfastreactionsundersteady stateconditions 2 availabilityofpowerfulmeansforprobingthemechanismandphysicallocalizationofinterfacialreaction HighSpatialresolution ThemasstransferrateinSECMisafunctionofthetip substratedistance d a m D ad a m D dD 1x10 5cm2 s d 0 1 m m 1cm s 10cm sHighSpatialResolution about30 50nmlimitforconductingsubstratesand2nmforinsulatingsubstrates 3 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 WhereL d aisthenormalizeddistancebetweentheconductivesubstrateandthetipofradiusa thisfitstheiT dcurveoveraLintervalfrom0 05to20towithin0 7 Foraninsulatingsubstrate similarequation 2 isslightlylessaccurate towithin1 2 however thelongerexpression equation3 isaccuratetowithin0 5 overthesameLintervalIT L 1 0 292 1 5151 L 0 6553exp 2 4053 L 2 IT L 1 0 15 1 5385 L 0 58exp 1 14 L 0 0908exp L 6 3 1 017L 3 4 ApplicationsA StudyofheterogeneousreactionkineticsB ImagesC Micro fabrications TipSteady statevoltammogramsfortheoxidationof5 8mMFCin0 52MTBABF4inMeCNata1 08 mradiusPttip Solidlinescalculatedwithk0 3 7 0 6cm sand 0 37 0 02 ScanningelectronmicrographofGaAs Crdoped etchedinthreeplacesfor5 6 and20minina0 02MHBrand0 1MHClsolutionwitha25 mPtmicroelectrode ImageofmicatreatedwithDNA 2 96kbp specimensonmicatakeninhumidair SingleMoleculedetection Idealizedschematicillustrationofthetipgeometryandthetip substrateconfigurationused SchematicrepresentationoftheprinciplesofSECMwithmicro ITIES SECMimageobtainedusingamicro ITIESprobe 5 mtip Substratewassiliconwithparallelplatinumbands J Electroanal Chem 1997 439 p137 143 Positivefeedback NegativeFeedback ApproachabigL Linterface Approachasolidsubstrate RG Rg a Bardetal havedevelopedthetheoryforRG 10cases However formicropipettesasthetipsforSECM theRGsareusually 2 UsingsoftwarepackagePDEase SPDE Inc wehavesolvedthetheoreticali dcurvesforRG 2 J Phys ChemB 1998 102 p9915 9921 RG Rg a b a L d a AqueousPhase OrganicPhase Current distancecurvesobtainedwithdifferentconcentrationsofTEAClintheaqueousphase 1 0 2 0 4 and 3 10mM TEA w TEA o RG 1 1 Constantheightmodegrayscaleimagesofporesinpolycarbonatemembrane TCNQ Fe CN 64 TCNQ Fe CN 63 Fe CN 63 w e Fe CN 64 w E1o 0 41VvsSHE TCNQ o e TCNQ o E2o 0 22VvsSHE ow ow o RT nF ln ai o ai w ow E2o E1o 190mV ow TBA o 225mV ReverseElectronTransferReactions Approachcurveforthesystem H2O TPAsCl 1mMFe CN 63 DCE 1mMTPAsTPB 10mMTCNQ showingtheelectrontransferdrivenbythephasetransfercatalystTPAs Fromtoptobottom theexperentcurveareshownforKp 10 5 2 1 A TPAssystem B TBAsystem DependenceoftheeffectiveETrateconstantonconcentrationofTCNQinDCE Thekvaluewereusedtofittheapproachcurevwitha 10 mand FromtoptobottomtheKpvaluewasshownfor10 5 2 A TPAssyetem B TBAsystem DependenceoftheeffectiveETrateconstantonpotentialdropacrosstheITIES A TPAs B TBA SECMStudiesofETReactionsacrossIce LiquidInterface FigureExperimentalapproachcurvesofthesystem 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 Alloftheapproachrateswere1 m s CombinationofSECMandpolarizedliquid liquidinterfaces Fc 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 Alloftheapproachrateswere1 m s InvestigationofModifiedElectrodes SurfacepKa Figure SchematicdiagramoftheapplicationofSECMtoprobefacilitatediontransferatanexternallypolarizedLiquid Liquidinterface ProbingfacilitatediontransferatanexternallypolarizedL Linterface Studyofsimpleion facilitatedionandelectr