纳米材料和纳米结构第十三讲-2-透射电子显微镜及其能谱.ppt
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纳米材料和纳米结构第十三讲-2-透射电子显微镜及其能谱.ppt
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TransmissionElectronMicroscopyandSpectroscopy透射电子显微镜及其能谱纳米材料和纳米结构第十三讲1IntroductiontoTEM1IntroductiontoTEMNanomaterialsaredominatedbyparticleswithsizesinNanomaterialsaredominatedbyparticleswithsizesinnanometerrange,andthereforetheimagingoftheatomsnanometerrange,andthereforetheimagingoftheatomsandthequantitativeanalysisofthesurfacechemistryareandthequantitativeanalysisofthesurfacechemistryarevitallyimportantfornanomaterialsresearchvitallyimportantfornanomaterialsresearchTransmissionelectronmicroscopy(TEM)isapowerfulTransmissionelectronmicroscopy(TEM)isapowerfulanduniquetechniqueforstructurecharacterization,anduniquetechniqueforstructurecharacterization,whichnotonlycanproviderealspaceimagingatawhichnotonlycanproviderealspaceimagingataresolutionof1-2resolutionof1-2,butalsoananalyticaltoolfor,butalsoananalyticaltoolforquantitativestructureandchemicalanalysisquantitativestructureandchemicalanalysis
(1)IlluminationSystema.ThermionicEmission;b.FieldEmission
(2)SpecimenStage(3)ObjectiveLensSystem(4)MagnificationSystem(5)DataRecodingSystem(6)ChemicalAnalysisSystema.EnergyDispersiveX-raySpectroscopy(EDS)b.ElectronEnergy-LossSpectroscopy(EELS)c.ChargeCoupledDevice(CCD)InstrumentStructureofTEMSchematicstructureofaTEM2AtomicResolutionLatticeImaging2AtomicResolutionLatticeImagingofCrystallineSpecimensofCrystallineSpecimensQualitiesofTEMimagesaredecidedbythreetypesofcontrast:
DiffractionContrastduetoalocaldistortionintheorientationofthecrystal,whichwillperturbthediffractionintensityandleadstocontrastoftheimagePhaseContrastduetothephasemodulationoftheincidentelectronwave,whichissensitivetotheatomdistributioninthespecimenandisthebasisofhigh-resolutionTEMMassthicknessoratomicnumberproducedcontrastduetoatomswithdifferentatomicnumbersexhibitingdifferentpowersofscattering22-1ImageContrast-1ImageContrast2.22.2ImagingTheoryImagingTheory2.3ImagingInterpretationandtheoreticalsimulationTheoreticallysimulatedimagesforadecahedralAuparticalatvariousorientationsandatdifferentfocuses(f=42nmand70nm)33FacetedShapesofNanocrystalsFacetedShapesofNanocrystalsAparticleconstitutingafinitenumberofatomscanhaveaspecificgeometricalshapeSurfaceenergiesassociatedwithdifferentcrystallographicplanesareusuallydifferent,andageneralsequencemayholdforface-centeredcubiccrystal,111100110Forasphericalsinglecrystallineparticle,itssurfacemustcontainhighindexcrystallographyplanes,whichpossiblyresultinalowersurfaceenergyFacetstendtoformontheparticlesurfacetoincreasetheportionofthelowindexplanes3.1PolyhedralShapesofNanocrystalesForparticlessmallerthan10-20nm,thesurfaceispolyhedron.Inthefollowingfigure,agroupofcubo-octahedral(立方八面体)shapesasafunctionoftheratio(R)ofthegrowthrateintothatofthearedemonstratedThefastestgrowthdirectioninacube(R=0.58)is,thelongestdirectionintheoctahedron(R=0.7)isthediagonal,andthelongestdirectioninthecubo-octahedronis(R=0.87)isthedirectionGeometricalshapesofcubo-octahedralnanocrystalsasafunctionoftheratio,R,ofthegrowthratealongtoTheparticleswith0.87R1.73havethe111and100facets,theothergroupofparticleshasafixed(111)basewithexposed111and100facets.Anincreaseinthearearatioof111to100resultsintheevolutionofparticleshapesfromatriangle-basedpyramidtoatetrahedron(四面体).Geometricalshapesofmultiplytwinneddecahedral(十面体)andicosahedral(二十面体)particlesHRTEMimagesofcubicPtnanocrystalsorientedalong(a)001and(b)110,showingsurfacesteps/ledgesandthermodynamicallynonequilibriumshapesHRTEMimagesofPtnanocrystals(a)withatruncated(去顶的)octahedralshapeandorientedalong110,and(b)withaoctahedralshapeandorientedalong110and001.Theinsetin(a)isamodeloftheparticleshapeHRTEMimagesoftruncatedtetrahedralPtnanocrystalsorientedalong110.Thesurfacestepsandledgesatthetruncatedcornersareclearlyresolved3.2TwinningStructureandStackingFaultsTwinningisoneofthemostpopularplanardefectsinnanocrystals,anditisfrequentlyobservedforfccstructuredmetallicnanocrystalsTwinningistheresultoftwosubgrainssharingacommoncrystallographicplane,thus,thestructureofonesubgrainisthemirrorreflectionoftheotherbythetwinplaneStackingfaultsaretypicalplanardefect.TheyareproducedbyadistortiononthestackingsequenceofatomplanesHRTEMimagesof(a)Ptand(b)Aunanocrystalshavingtwin(T)andstackingfault(S)structures,respectively.Thetwinplaneandstackingfaultareparalleltothedirectionoftheelectronbeam3.3DecahedralandIcosahedralParticlesThetwomosttypicalexamplesofmultipletwinnedparticlesarethedecahedral(十面体)十面体)andicosahedral(二十面体)(二十面体),andthecorrespondingparticlesarethemostextensivelystudiedtwinnednanocrystals.Atomicmodelsof(a)decahedral,and(b,c)icosahedralnanocrystalsTEMimagesofdecahedralAunanocrystalswhentheincidentelectronbeamisparallelornearlyparalleltothefive-foldsymmetryaxis.Thestrainfieldintroducedbythefive-foldtwinsisapparentin(a).Afouriertransformoftheimageclearlyrevealsthefive-foldsymmetry3.4NucleationandGrowthofNanoparticlesHRTEMimagesrecordedfromthecentersofcarbonspheres,showingthespiralgrowthnearthecenters2.4ElectronHolography(全息)(全息)Holographyisbasedontheinterferenceanddiffractionpropertiesofwaves,therebyproducingatrueimageofanobject(includingamplitudeandphase)withoutanydistortionofthelenses.(a)Formationofoff-axiselectronholograminTEMusinganelectrostaticbiprism,and(b)Reconstructionofelectronhologramusinglaserdiffraction2.52.5NanodiffractionNanodiffractionHRTEMimageofaCo-SmfilmComparisonofTEM(upperimages)andsimulatednanodiffractionpatterns(bottomimages)of0001zoneaxis(threelayerstackingABCABC),20-21zoneaxis(stackingABACABAC),10-10zoneaxis(fivelayerstackingABCABABCAB.)ComparisonofTEM(upperimages)andsimulatednanodiffractionpatterns(bottomimages)of11-20zoneaxis(threelayerstackingABCABC),11-20zoneaxis(fourlayerstackingABACABAC),11-20zoneaxis(fivelayerstackingABCABABCAB.)Identificationsofpossibleorderingby0001zoneaxispatterns:
(a)Co3Vtypeorderingintheclosepackedplaneand(b)Co3Nitypeorderingintheclosepackedplane.(c,d)arecorrespondingdiffractionpatterns.(e)DiffractionpatternofadisorderedHCPstructure(f)TEMpatternComparisonofnanodiffractionpatterns(a)fromacrystalliteand(b)fromtheamorphousphase2.6InsituTEMandNanomeasurements
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