电子背散射衍射技术的特点及发展动向

AnalyticswithScanningElectronMicroscopyA.Danilewsky•EnergyDispersiveX-RayAnalysisEDX•ElectronBackScatterDiffractionEBSDDepthofSignalsAuger-elektronsSecondaryelectronsSEBackscatterelectronsBSEX–rays:-CharacteristicX-rays-ContinuumX-raysSamplesurfaceTopographiccontrastElectronbeamElectronbeamManysecondaryelectronsleavethesampleFewsecondaryelectronsleavethesampleCharacteristicX-Rayskα1:LIII→Kkα2:LII→Kkβ:MIII→KkeVRelativeIntensityofCharacteristicX-RaysLshellconsistsof3subshellswithquantumnumbersn,l,jandspinm:lI:2s–orbitaln=2,l=0,j=½,m=±½max.2electrons=forbiddentransitionlII:2p–orbitaln=2,l=1,j=½,m=±½=max.2electrons=kα2–linelII:2p–orbitalsn=2,l=1,j=3/2,m=±½,±3/2max.4electrons=kα1-lineIntensitykα1:kα2=2:1CharacteristicX-RaysCharacteristicX–raysContinuumX-rayskα:L→Kkβ:M→KX–RayDetector•Si–crystaldriftedbyLiwithFET(fieldeffecttransistor)•Be–window•collimator•coolingbyliquidN2(77K)dewarliq.N2Be-windowcollimatorSi-crystalcoldfingerdistanceadjustmentpreamplifiersensorX–RayDetector:Si–crystaldriftedbyLiX-rayphotonsgenerateelectronholepairsSemiconductorX–RayDetector•Valencebandofanintrinsicsemiconductorisfullyoccupied•Conductionbandofanintrinsicsemiconductorislargelyunoccupied•X-raysraiseelectronsfromvalencetoconductionband(photo-andAugerelectrons)•Electron–holepairsmovefreeinthecrystalduringtheirlifetime•Biasvoltageacrossthedetectormoveschargecarrierstooppositeelectrodes=signal/pulse•Thenumberofelectron–holepairsisproportionaltotheenergyofX-rayphotons•Minimumenergyistheenergygapofthesemiconductor(Si:1.1eV)+energyoflatticevibrations+otherphysicaleffects=about3.8eV•Multi-channelanalyser:1024channelssetto10eV/channel=0.5–10keVSemiconductorX–RayDetector:SilicondriftedbyLi•Lowleakagecurrent=highresistivitySi(ultrapure)•Liasadonorcompensatesp-typeconductionofSiatlowtemperature•ListabilisestheSi–structureagainstX-rayradiationdamage•p–n-junctionfromundopedtoLi–dopedarea•Onlyonepulseisisprocessedatatime.TomanyX-rayphotonsduringtheanlyserisbusy:=deadtime:nootherphotonsarecounted!Timescale:nanosecondse.g.30secondscountingtimeat10%deadtimeneeds33secondsrealtimemeasurement•X-raysgeneratedintheSi–detectorcrystalit-self:escapepeakTi–Si=2.77.keVSi=1.74keVTi=4.51keVkeVL-linesKα1Kα2X–RaySpectraEnergyofofphotons:CharacteristicX-raylinesNumberofphotons:ConcentrationofelementM-linesL-linesK–linesat80.8.keVkeVX–Rays:AbsorptionandFluorescencee.g.Fe-MnelectronbeamFekαMnkαSESEZAF–Correction:Z=atomicnumberA=absorptionF=fluorescenceX–Rays:BackgroundCorrectionsContinuumspectrum:•Calculationfromelements•SubtractionEnergydispersiveX-rayanalysis(EDX)Oxford-LinkSystemISISatZeissDSM960Accelerationvoltage:20kVMagnification:x200–x1000Detector:Si:LiQualitativemappingofelements:Al,Si,Ti,Ca,Fe,MnBSEEnergydispersiveX-rayanalysis(EDX)200µm200µmSi200µm200µm200µmAlFeTiGeometrieEBSDBragg:nλ=2dsinθElectronBackscatterDiffractionEBSDOxford-LinkSystemCrystalHomogenous,anisotropicdiscontinuumwiththree-dimensionalperiodicalarrangementoflatticeelementsCrystalLatticebrcr231τrstraightlinethroughthepoints000and231:[231]c1b3a2cwbvaurrrrrrr⋅+⋅+⋅=⋅+⋅+⋅=τar[231]γβα,,Angles,,sBasevectorcbarrrAtomicPlanearbrcrIndicestoWeißreciprocalMillerplaneI111111(111)planeII1221½½(211)ZoneandZoneAxisZoneaxisPlainofthesurfacenormalCrystalStructureGitterBasisLatticeBaseCrystalstructureCrystalSystemsCubicHexagonalTetragonalRhombohedralOrthorhombicMonoclinicTriclinic14BravaisLatticesCubicHexagonalTetragonalOrthorhombicMonoclinicTriclinicUnitCellSmallestassembly,whichexpressesthemetricandincludesallsymmetryelementsz.B.:F43m,ZinkblendestructureSymmetryDeckoperationenimKontinuumDiskontinuumSymmetryelementsintwo-dimensionsMirrorplanemRotationaxis2-fold4-fold3-fold6-foldGlidereflectionTranslationSymmetryTransformations:ContinuumandDiscontinuumPrincipleofSymmetry10SymmetryelementsoftheContinuum:•Rotationaxis1,2,3,4,6•Rotaryinversionaxis3,4,6•Inversion1oderi•Mirrorplanem=32Crystalclasses10SymmetryelementsoftheContinuum+Translation:•Glide-reflectionplanea,b,c,d•Rotaryinversionaxis,z.B.:41,42,43=230SpacegroupsSpaceGroupsTabulatedin:InternationalTablesforCrystallography,VolAAsymmetricunit:Smallestportionofacrystalstructuretowhichcrystallo-graphicsymmetrycanbeappliedtogenerateoneunitcell.Byapplicationofallsymmetryoperationsofthespacegroup,thewholespaceisfilled.11Laue-GroupsDuetothephaseproblem,alldiffractionpatternsincludeaninversioncenter.=Centro-andnoncentrosymmetricgroupscannotbedistinguishedCrystalsystemLaue-GroupAcentricsubgroupstriclinic1monoclinic2/m2,morthorhombicmmm222,mm2tetragonal4/m4/mmm4,44mm,4m2,422trigonalm33m,32hexagonal6/m6/mmm6,66mm,6m2,622cubicmmm2343m,43213333StructureDataSampleOrientationandReferenceSystemtransversedirectionInformationofEBSD-PatternEBSDofGeIndexedEBSDofGeDemonstrationofSampleOrientationProjectionofthesurfacenormalinatwo-dimensionalplainoccursanalog-oustothestereo-graphicprojection:=PoleFigurePoleFigureCorrespondingto~[111]withSlightlyTiltandRotationInversePoleFigurePolycrystallineSampleFewAlignmentofCrystallitesPolycrystallineSampleAlignmentofCrystallites