电子显微分析 scanning electron microscopy （sem） 课件

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1、电子显微分析ScanningElectronMicroscopy(SEM)6.1InelasticScatteringElectrondiffractionandTEMimagingmainlyuseelasticscatteringelectronsSEMimagingmainlyuseinelasticscatteringelectronsEDS(inTEMandSEM)andEELS(inTEM)alsouseinelasticscatteringelectronsInelasticscatter

2、ingelectronsgenerateCharacteristicX-rayUsedforEDSinTEMandSEMSecondaryelectronSlowsecondaryelectronUsedforSEMimaging(morphology)AugerElectronUsedforsurfaceanalysisOthersEnergy-losstransmittedelectronUsedforEELSinTEMBackscatteredelectronUsedforSEMimaging(c

3、omposition)CharacteristicX-rayIfmorethanacriticalamountofenergyistransferredtoaninnershellelectron,thatelectronisejected.e.g.anKshellelectronisejectedfromtheatombyahigh-energyelectron,leavingaholeintheKshell.WhentheholeintheKshellisfilledbyanelectronfrom

4、Lshell,characteristicKaX-rayemissionoccurs.TheenergyofthecharacteristicX-rayischaracteristicofthedifferenceinenergyofthetwoelectronshellsinvolved.IfwefillaK-shellholefromtheLshellwegetaKaX-ray.IfwefillaK-shellholefromtheMshellwegetaKbX-ray.Inmicroanalysi

5、sweonlyusethemostintenselines,usuallytheKaX-ray.ThecharacteristicX-raywithaspecificenergycanbeusedasanunambiguoussignofthepresenceofanelementinthespecimen.(CuKa8.02keV,FeKa6.40keV)ThecharacteristicX-rayareusedforEDSinTEMandSEM.SecondaryelectronsSecondary

6、electrons(SEs)areelectronsinthespecimenthatareejectedbytheincidentelectron.Theycanbediscussedastwodistinctgroups:SlowsecondaryelectronsFastsecondaryelectronsSlowsecondaryelectrons(SEs)Iftheelectronsareintheconductionorvalencebands,itdoesn’ttakemuchenergy

7、toejectthem.Theyarecalled“slowSEs”energiesofSE:~50eV.SEsarenotassociatedwithaspecificatomandsotheycontainnospecificelementalinformation.BecauseSEsareweaktheycanonlyescapeiftheyarenearthespecimensurface(5-10nm).SoweusetheminSEMsforformingimagesofthespecim

8、ensurface.ThenumberofSEsisdependentontheanglebetweenincidentelectronbeamandsurface.Ifsurfaceisnotflat,itwillgeneratedifferentamountofSEs,resultsinthetopographiccontrast.SEsisusedformorphologyobservationinSEM.Fastsecondarye