射線熒光光譜分析學(xué)習(xí)要點(diǎn)

電子能量損失譜張庶元ElectronEnergyLossSpectroscopy(EELS)入射高能電子與樣品的相互作用3Atomic-scaleviewofelectronenergylossinTEMIncidentbeamelectronE0(100to1000keV)ExcitedspecimenelectronEB+EScatteredbeamelectronE0-EKLZerolossElectronenergyloss(eV)Electronscount01eV290CKInelasticscatteringKLElasticscatteringCarbonatomWhatisanEELSspectrum?電子能量損失譜信息非彈性散射過程:聲子激發(fā)

(<0.1eV)等離子激發(fā)

(<30eV)內(nèi)殼層電子激發(fā)

(＞13eV)自由電子激發(fā)(二次電子)(<50eV)(背底)韌致輻射(背底)??????

根據(jù)等離子激發(fā)能量的大小，即譜峰的位置，可以確定物質(zhì)的種類和他的組成。Na：5.70ev(一次激發(fā))11.4ev(二次激發(fā))

隨試樣厚度的增加，電子在試樣中可能產(chǎn)生二次，甚至多次等離子激發(fā)，其峰位出現(xiàn)在第一次激發(fā)峰的兩倍或多倍能量的位置。Al:14.95ev29.9ev44.35ev59.8ev

表中列出了幾種物質(zhì)的等離子激發(fā)峰的理論值和實測值SpecimenthicknessmeasurementRoughestimateofλ

:

λ~0.8Eonmsofor100-keVelectronsλis80-120nmvariousmaterialsλ

為電子非彈性散射的平均自由程

IT為第一個等離激發(fā)峰的強(qiáng)度

Io為零損失峰的強(qiáng)度偶極躍遷：Δl=±1內(nèi)殼層電子激發(fā)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