射线荧光光谱分析学习要点

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SpecimenthicknessmeasurementRoughestimateofλ

:

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)16SpectrumisenlargedandoptimallycoupledtodetectorFinalEELSreadoutEELSspectrumprojectedontoCCDEnergy-lossspectroscopy(EELS-coreloss)17FinalEELSreadoutOKedgeMnLedgeThespectrumisshiftedBesttodobychangingprismcurrentpreserveprobefocusSpectrumoffsetviaprismcurrentEELSspectrumprojectedontoCCDEFTEM:EnergyFilteredTEM:GIFonly18ProjectionsectionoperatesinimagingmodeSpectrumisprojectedbacktoanimageJustlikeforminganimagefromadiffractionpatterninTEMUnfilteredimageprojectedontoCCDdetectorEnergy-filteredTEMimaging(EFTEM-coreloss)

19Core-lossimageprojectedontoCCDdetectorimagemodeSpectrumoffsetviahightensionThespectrumisshiftedrelativetotheslitopeningBesttodobyincreasingbeamenergytopreserveimagefocus20EFTEM-afive-stageprocessSpectrumImaging–EFTEMmodeCollectsdetailedspatialandspectroscopyinformationAllowsprocessingdecisionsafteracquisitionSpectrumimagingcancreatequantitativeimages/profilesCanconfidentlylocateartifacts&understandimagecontrast21Dx,Dy spatialdimensionsDE energy-lossdimensionDyDxDEimageatDE1imageatDE2imageatDEi.........spectrumatDxi,DyiSpectrumimaging-STEMEELSmode22Spectrumimaging-STEMEELSmode23ElementalMappingUsingEnergyFilteredImagingSiC/Si3N425AtomicResolvedEELSofGaAsinthebulkHAADFsurveyimageAnalysiswascarriedoutusingthefacilitiesatFloridaStateUniversitySystem:ARM200withcoldFEGequippedwithGIFQuantumheavilyupgradedSamplewasprovidedbyGlasgowUniversityandSamplewasobservedalongthe[110]directionSampleis4yearsoldandshowssomeoxidation26AtomicResolvedEELSofGaAsinthebulkEELSSIEELSspectrumextractedfromtheregionintheredboxintheEELSSIGaL2,3-edgesAsL2,3-edgesConvergenceangle:25mradCollectionangle120mradEELSdatawasacquiredinsinglerangemodeExposuretimeperpixel:50msDatasetsize:26x25x2048Totalnumberofpixels:650Totalacquisitiontime:51seconds27AselementalmapGaelementalmapEELScolorizedelementalmapGa:GreenAs:RedTheGaAsdumbbellisclearlyresolvedwithhighcontrastAtomicResolvedEELSofGaAsinthebulk28TheEELSelementalmapforthePdlooksmuchsharperandshowshighercontrastthanthesamemapobtainedusingEDS.ThiscanbedirectlyattributedtothestrongforwardscatteringoftheEELSsignalandthenearly100%collectionefficiencyofdetector.ThehighsignaltonoiseratiointhedataisevidentfromintensitylineprofilesextractedfromtheregionindicatedintheboxintheEDSandEELSPdelementalmaps.IntensitylineprofilesextractedfromtheregionintheblueinthePdmapsElementalmapsEDSPdEELSPd29

MeansignalStd.Dev.SNRAuMEELSMap1446885617:1AuMEDSMap79.910.17.9:1ThesignalintensitywasanalyzedfromauniformregionofaAuparticle.This16x16pixelregionisshowbytheredboxintheAuelementalmapsTheSNRfortheEELSdatais~17whilethatfortheEDSdatais~8givingabouta2ximprovementfortheEELSdata.theEELSsignalismorethantwiceassensitivethantheEDSdataElementalmapsAuEDSAuEELSEDSEELSRed:PdGreen:AuDespitethepresenceofheavyelementsinvolvedintheanalysis,EELSmapsshowbettercontrastSomedetailsinthemapscanbeobservedonlyintheEELSelementalmapsColorizedElementalMapsStateoftheArtSrTiO3ExampleLaMnO3/SrMnO3superlatticegrownonSrTiO3NIONUltraSTEMwithEnfiniumER2msec/pixel@250pA8GBofdata!312008(64x64)Ac