透射电子显微学课件

电子能量损失谱张庶元ElectronEnergyLossSpectroscopy(EELS)入射高能电子与样品的相互作用3Atomic-scaleviewofelectronenergylossinTEMIncidentbeamelectronE0(100to1000keV)ExcitedspecimenelectronEB+EScatteredbeamelectronE0-EKLZerolossElectronenergyloss(eV)Electronscount01eV290CKInelasticscatteringKLElasticscatteringCarbonatomWhatisanEELSspectrum?电子能量损失谱信息非弹性散射过程:声子激发(0.1eV)等离子激发(30eV)内壳层电子激发(＞13eV)自由电子激发(二次电子)(50eV)(背底)韧致辐射(背底)∙∙∙∙∙∙根据等离子激发能量的大小，即谱峰的位置，可以确定物质的种类和他的组成。Na：5.70ev(一次激发)11.4ev(二次激发)随试样厚度的增加，电子在试样中可能产生二次，甚至多次等离子激发，其峰位出现在第一次激发峰的两倍或多倍能量的位置。Al:14.95ev29.9ev44.35ev59.8ev表中列出了几种物质的等离子激发峰的理论值和实测值SpecimenthicknessmeasurementtlnITIoRoughestimateofλ:λ~0.8Eonmsofor100-keVelectronsλis80-120nmvariousmaterialsλ为电子非弹性散射的平均自由程IT为第一个等离激发峰的强度Io为零损失峰的强度偶极跃迁：Δl=±1内壳层电子激发11CorrelationbetweenEELSandspecimenfeatureMagneticprismspectrometerEELSspectrometer13OpticalconfigurationatentranceDispersionandfocusingsectionProjectionsectionSpectrumplaneIn-columnomega-filterEnergy-filterimagingandelectrondiffraction,CBEDInsertedintheimaginglenssystemPost-columnimagingfilterGatan(Tridiem)imagingfilter(GIF).AttachedtotheTEMcolumnbelowtheviewingchamberEnergy-lossspectroscopy(EELS-lowloss)16SpectrumisenlargedandoptimallycoupledtodetectorFinalEELSreadoutEELSspectrumprojectedontoCCDEnergy-lossspectroscopy(EELS-coreloss)17FinalEELSreadoutOKedgeMnLedgeThespectrumisshiftedBesttodobychangingprismcurrentpreserveprobefocusSpectrumoffsetviaprismcurrentEELSspectrumprojectedontoCCDEFTEM:EnergyFilteredTEM:GIFonly18ProjectionsectionoperatesinimagingmodeSpectrumisprojectedbacktoanimageJustlikeforminganimagefromadiffractionpatterninTEMUnfilteredimageprojectedontoCCDdetectorEnergy-filteredTEMimaging(EFTEM-coreloss)19Core-lossimageprojectedontoCCDdetectorimagemodeSpectrumoffsetviahightensionThespectrumisshiftedrelativetotheslitopeningBesttodobyincreasingbeamenergytopreserveimagefocus20EFTEM-afive-stageprocessSpectrumImaging–EFTEMmode•Collectsdetailedspatialandspectroscopyinformation–Allowsprocessingdecisionsafteracquisition–Spectrumimagingcancreatequantitativeimages/profiles–Canconfidentlylocateartifacts&understandimagecontrast21Dx,DyspatialdimensionsDEenergy-lossdimensionDyDxDEimageatDE1imageatDE2imageatDEi.........spectrumatDxi,DyiSpectrumimaging-STEMEELSmode22Spectrumimaging-STEMEELSmode23ElementalMappingUsingEnergyFilteredImagingSiC/Si3N425AtomicResolvedEELSofGaAsinthebulkHAADFsurveyimage•AnalysiswascarriedoutusingthefacilitiesatFloridaStateUniversity•System:ARM200withcoldFEGequippedwithGIFQuantumheavilyupgraded•SamplewasprovidedbyGlasgowUniversityandSamplewasobservedalongthe[110]direction•Sampleis4yearsoldandshowssomeoxidation26AtomicResolvedEELSofGaAsinthebulkEELSSIEELSspectrumextractedfromtheregionintheredboxintheEELSSIGaL2,3-edgesAsL2,3-edges•Convergenceangle:25mrad•Collectionangle120mrad•EELSdatawasacquiredinsinglerangemode•Exposuretimeperpixel:50ms•Datasetsize:26x25x2048•Totalnumberofpixels:650•Totalacquisitiontime:51seconds27AselementalmapGaelementalmapEELScolorizedelementalmapGa:GreenAs:Red•TheGaAsdumbbellisclearlyresolvedwithhighcontrastAtomicResolvedEELSofGaAsinthebulk28•TheEELSelementalmapforthePdlooksmuchsharperandshowshighercontrastthanthesamemapobtainedusingEDS.ThiscanbedirectlyattributedtothestrongforwardscatteringoftheEELSsignalandthenearly100%collectionefficiencyofdetector.•ThehighsignaltonoiseratiointhedataisevidentfromintensitylineprofilesextractedfromtheregionindicatedintheboxintheEDSandEELSPdelementalmaps.IntensitylineprofilesextractedfromtheregionintheblueinthePdmapsElementalmapsEDSPdEELSPd29MeansignalStd.Dev.SNRAuMEELSMap1446885617:1AuMEDSMap79.910.17.9:1•ThesignalintensitywasanalyzedfromauniformregionofaAuparticle.This16x16pixelregionisshowbytheredboxintheAuelementalmaps•TheSNRfortheEELSdatais~17whilethatfortheEDSdatais~8givingabouta2ximprovementfortheEELSdata.•theEELSsignalismorethantwiceassensitivethantheEDSdataElementalmapsAuEDSAuEELSEDSEELS•Red:Pd•Green:Au•Despitethepresenceofheavyelementsinvolvedintheanalysis,EELSmapsshowbettercontrast•SomedetailsinthemapscanbeobservedonlyintheEELSelementalmapsColorizedElementalMapsStateoftheArtSrTiO3Example–LaMnO3/SrMnO3superlatticegrownonSrTiO3–NIONUltraSTEMwithEnfiniumER•2msec/pixel@250pA•8GBofdata!312008(64x64)Acknowledgements:JuliaMundy,CarolinaAdamo,DarrellSchlom,DavidMuller,CornellUniversity2012(1024x1024)10nmMnLLaMTiLM.S.Varela,etal.,Phy.Rev.Lett.92(2004)095502STEM-EELSAtomic-ResolutionElectronEnergyLossSpectroscopyLa-dopedCaTiO3谢谢!