近代分析實(shí)驗(yàn)原理：第五課-透射電鏡-1

五、透射電子顯微鏡-1

（TransmissionElectronMicroscope）近代分析實(shí)驗(yàn)原理（Introductionofmodernanalyticalmethods）12透射電子顯微鏡照片：Carbonnanotube31.電鏡的結(jié)構(gòu)（Instrumentation）1.1 光學(xué)顯微鏡（Opticalmicroscope）光的折射（Refraction）：反射定律折射定律n12相對(duì)折射率(refractionindex)n1（n2）絕對(duì)折射率（相對(duì)于真空）法線分界面入射光L折射光反射光4透鏡（Lens）凸透鏡成像圖h0hipp′FF′f′111222333hi/h0=p’/p5RealimageFocallengththedistancebetweentheimageandlens6分辨率（Resolution）Resolutionreferstotheminimumdistancebetweentwopointsatwhichtheycanbevisiblydistinguishedastwopoints.thediffractionoflight艾里斑（Airydisk）refractiveindex折射率half-angleofthecone圓錐體oflightenteringtheobjectivelensnumericalaperture數(shù)值孔徑R~λμ7?沒(méi)有X射線透鏡可以聚焦81.2 電子的波長(zhǎng)（Thewavelengthofelectron）波粒二象性粒子性波動(dòng)性路易·維克多·德布羅意1929年獲諾貝爾物理學(xué)獎(jiǎng)在貝爾實(shí)驗(yàn)室ClintonJosephDavisson和LesterHalbertGermer以低速電子束射向鎳單晶獲得電子經(jīng)單晶衍射，測(cè)得電子的波長(zhǎng)與德布羅意公式一致。在阿伯丁大學(xué)，G.P湯姆孫以高速電子穿過(guò)多晶金屬箔獲得類似X射線在多晶上產(chǎn)生的衍射花紋，確鑿證實(shí)了電子的波動(dòng)性1937年諾貝爾物理學(xué)獎(jiǎng)9電子的波長(zhǎng)（Thewavelengthofelectron）101.3 電子顯微鏡（Transmissionelectronmicroscope）11thermionicsource1.4 電子源（Electronsource）field-emissionsourceYourTEMwilluseathermionicsource(WorLaB6)orafield-emission(W)sourceandthetwocannotbeinterchanged.Field-emissionsourcesgivemoremonochromaticelectrons;thermionicsourcesarelessmonochromaticandgive‘whiter’electrons.currentdensityworkfunctionRefractory(highmeltingpoint)materialsorthosewithanexceptionallylowΦButthereisalimit,becausehighertemperaturesshortenthesourcelifethroughevaporationand/oroxidation.（ThermionicGuns）Fieldemissionguns（FEGs）anelectricfieldEisconsiderablyincreasedatsharppointslowersthework-functionbarrierElectronstotunnelout‘cold’FE.‘thermal’FEultra-highvacuum(UHV)conditions(<10-9Pa)atapoorervacuumbyheatingthetipWLaB612BrightnessBrightnessisthecurrentdensityperunitsolidangleofthesource.TruesourceTemporalCoherencyAmeasureofhowsimilarthewavepacketsare.theenergyspreadofthebeamelectrostaticlensesHowwelltheelectronwavesare‘instep’withoneanother.13SpatialCoherencyPerfectspatialcoherenceimplythattheelectronswereallemanatingfromthesamepointatthesource.smallersourcesbettercoherencytheeffectivesourcesizetheanglesubtendedbythesourceatthespecimenMakethesourcesize,d,smaller,e.g.,byusingaFEsource.Thisexplainswhyresearchintousingnanotubesaselectronsourcesisongoing.Useasmallerilluminationaperture,thusreducing.Ifyoursourcesizeislarge(e.g.,aWhairpin)decreasetheacceleratingvoltageandthusincrease.relatedtothesizeofthesource.14151.5 電子透鏡（Electronlens）magneticlensesnotsusceptible易受影響tohigh-voltagebreakdown16ElectronRayPathsThroughMagneticFields17APERTURESANDDIAPHRAGMS光圈heavymetalsuchasMoorPtand25–50μmthick,butiftheirjobisalsotopreventX-raysfromhittingthespecimen樣品theymaybeseveralmillimetersthick18REALLENSESANDTHEIRPROBLEMSImperfectionsofthelenslimittheresolutionofthemicroscope球差：Thefurtheroffaxistheelectronis,themorestronglyitisbentbacktowardtheaxis.apointobjectadiskoffinitesizeimageMostimportantObjectivelensSphericalAberrationDegrades降級(jí)thedetailthatwecanresolveinTEMimagesThemainlimitationfortheresolutionofTEM.sphericalaberrationcoefficientthemaximumangleofcollectionofthe(objective-lens)apertureManufacturerslike19InmodernTEM,Cscanbecorrected.theCEOSsystemtheNioncorrectorRoseandcolleaguesinGermanyKrivaneketal.20色差：‘colour’frequency,wavelength,orenergyoftheelectronsEnergylostwhentheelectronspassthroughthespecimen.TheobjectivelensbendselectronsoflowerenergymorestronglyandthuselectronsfromapointintheobjectonceagainareblurredtoformadiskintheGaussianimageplane.21像散：Astigmatismoccurswhentheelectronssenseanon-uniformmagneticfieldastheyspiralroundtheopticaxis.Notperfectlycylindricallysymmetricalsoft-ironpolepiecesofobjectivelensMachineerrorMicrostructuralinhomogeneitiesAperturesnotpreciselycenteredaroundtheaxisContaminationonapertureschargesupanddeflectsthebeamthemaximumdifferenceinfocusinducedbytheastigmatism22分辨率：TheoreticalResolution(Diffraction-LimitedResolution)Rayleigh’scriterionThePracticalResolutionDuetoSphericalAberrationTypically,thevalueforrminis0.25–0.3nmandthebesthigh-resolutioninstrumentshavermin0.1–15nm;1-?TEMsareaboutthebestavailablewithoutCscorrectionandabout0.07nmis(atthetimeofwriting)thebestreportedresolutionwithCscorrection.231.6 樣品桿（Samplestage）CuCanhaveamorphousCthinfilmtosupportmuchsmallersample(forexample,Cnanotube)Single-tiltordoubletiltCuThereasonthespecimenholderissoimportantinTEMisthatyourspecimenmustinvariablybelocatedwithintheobjectivelensandtheaberrationsassociatedwiththeobjectivelensdeterminetheresolutionoftheTEM.2.3or3.05mmdiameter241.7 電鏡系統(tǒng)（THETEMIMAGINGSYSTEM）25Diffractionmode:toseetheDP(diffractionpattern)youhavetoadjusttheimaging-systemlensessothattheBFP(back-focalplane)oftheobjectivelensactsastheobjectplanefortheintermediatelens.ThentheDPisprojectedontotheviewingscreen/CCDasshowninA.Imagemode:ifyouwanttolookatanimageinstead,youreadjusttheintermediatelenssothatitsobjectplaneistheimageplaneoftheobjectivelens.Thenanimageisprojectedontotheviewingscreen/CCD,asshowninB.261.8 電鏡樣品的制備（Specimenpreparation）TEMspecimenelectrontransparentrepresentativeofthematerialyouwanttostudy27Powdersample28Pre-ThinningHand-grindingjigforTEMspecimenpreparation.Adisc(S)isgluedtothecenterofthejigandtheguidering(G)controlstheamountofgrinding.reducingthespecimenthicknesstoabout0.1mmbeforefinalthinningto100nmthickness.guardringdiscGrindingBulksample29Dimpling30IonMilling31CROSS-SECTIONSPECIMENSEspeciallyfilm32focused-ionbeam(FIB)thecoatingofPtIonpolishing333435BetterspecimenBetterqualityofthedata361.9 電鏡的局限性（LIMITATIONSOFTHETEM）high-resolutionimagingtechniquesmallpartofyourspecimenThehighertheresolutiontheworsethesamplingabilitiesComplementarytechniques:likeXRD,SEM,et