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1、LightMicroscopesCompoundStereoElectronMicroscopyJinZou(邹进）SchoolofEngineeringandCentreforMicroscopyandMicroanalysisTheUniversityofQueensland,AustraliaEmail:j.zou@uq.edu.au2ComparisonofResolutionWhyElectronsBetterThanLight?&Theresolution(resolvingpower)ofanyOptica

2、limageSEMimagemicroscopeisfundamentallylimitedbythewavelengthoftheilluminationused,accordingtofollowingequationSemiangleofcollectionofthemagnifyinglensδ=0.61λ/µsinβorδ≅λ/2reflectiveindexoftheviewmedium4Forlightinvisiblespectrum,theresolutionisapproximately200nm4I

3、tisdifficulttoworkwithX-rays(problemswith25µmLargedepthoffieldfocusing)4NeedtofindsomethingelseSEMimagehasmuchbetterresolutionthantheopticalimage.34WhyElectrons?Similarity:LightviaElectron&Electronshavewave-likeproperties(deBroglie)withIlluminationwavelengthdepen

4、dentupontheirenergy&A100keVelectronhasλ≅4pm.Condenser&Othereffectslimittheresolution,0.1~0.2nmisSampleachievable,butsufficienttoimageatoms,becausethedistancebetweenthefirstnearestneighborsofatomsImagingisaboutthatrange.Recording&Also,theelectron-specimeninteracti

5、onprovidesmanyusefulsignalsthatcanbeusedtounderstandspecimens561Difference:LightviaElectronElectron-SpecimenInteractionsSource:LightElectronsElasticscatteredInelasticscatteredelectrons-electronsLens:eWhetherelectronsareGlassMagneticreflectedortransparentdependsup

6、on:Medium:•PowerofincidentalAirVacuumSpecimenHeatelectrons(eV)•SpecimenthicknessImportantly:Significantdifference•ChemicalcompositioninresolutionofthespecimenElasticscatteredInelasticscatteredelectronselectrons78ElectronScanningTypesofElectronMicroscopesScanningE

7、lectronMicroscopesourceElectronColumnMicroscopeTVscreenSpecimenchamberthinElectronicsthick910EssentialComponentsinScanningElectronMicroscopesElectronMicroscope&Electrongun:Inordertoextractalotofelectronsfromamaterial,thematerialweusedshouldhavealowwork-function,e

8、.g.tungsten.[Work-function:energy(orwork)requiredtowithdrawanelectroncompletelyfromametalsurface.Thisenergyisameasureofhowtightlyaparticularmetalholdsitselectr