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with lattice reflections showing as sharp spots•By tilting a crystalline sample to low-index zone axes, SAED patterns can be used to identify crystal structures and measure lattice parameters•SAED is essential for setting up DF-imaging conditions•SAED is used primarily in material science and solid state physics, and is one of the most commonly used experimental techniques in these fieldsSelected Area Electron Diffraction (SAED)
Department of Materials Science & Engineering | UC BerkeleyApril 5, 201646MATERIALSSCIENCE& ENGINEERINGBerkeleyUNIVERSITY OFCALIFORNIAKikuchi Lines•Important feature of diffraction patterns they are frequently used to orient samples precisely•They appear as pairs of parallel light/dark lines in diffraction patterns•Inelasticallyscattered e’s are responsible thus Kikuchi lines are more prominent in thicker samples•e’s scatter inelastically in all directions; much greater probability for scattering in forward direction (only small energy losses)•Some of the inelastically-scattered e’s travel in directions where they can re-scatter elastically through 2θhkl•Geometry dictates that the projection of the (hkl) is mid-way between the lines
Department of Materials Science & Engineering | UC BerkeleyApril 5, 201647MATERIALSSCIENCE& ENGINEERINGBerkeleyUNIVERSITY OFCALIFORNIAConvergent Beam Electron Diffraction (CBED)CBED considerable advantages over SAED; transformed e-crystallographySAED•A spatially-wide (1-10 μm), nearly parallel (very small convergence angle α) beam •Pattern consists of array of sharp maxima in back focal planeCBED•Convergent beam (2α≲2θB) with small area (10-100 nm diameter)•Disks of high-intensity in the back focal plane which can overlap•Thin samples kinematic diffraction rules, no features•Thick samples dynamical diffraction rules, complex contrast arises •The information here is very powerful
Department of Materials Science & Engineering | UC BerkeleyApril 5, 201648MATERIALSSCIENCE& ENGINEERINGBerkeleyUNIVERSITY OFCALIFORNIASample Preparation: ExampleH. Kirmse, Humboldt Univ., Berlin
Department of Materials Science & Engineering | UC BerkeleyApril 5, 201649MATERIALSSCIENCE& ENGINEERINGBerkeleyUNIVERSITY OFCALIFORNIA•Coherent Elastic Scattering Diffraction•Incoherent Inelastic Scattering Spectrometry•Phonon Excitation•Plasmon Excitation•Core Electron Excitationbackscattered electronsIncident electronscharacteristic x-rays (EDX)secondaryelectronsforward-scatteredelectron beamRutherford scattered electrons (z-contrast)-g+gdiffracted beamsInelastically-scattered electrons (EELS)Bremsstrahlung x-raysand visible lightAugerelectrons•Energy is conserved for all of these inelastic processes•The spectrum of energy gained by the sample is mirrored by the spectrum of the energy lost by the incident electron probe•So the usual convention for spectrometries, that is emissive and absorptive, apply here•EDS and EELSInelastic Scattering & Spectroscopy
Department of Materials Science & Engineering | UC BerkeleyApril 5, 201650MATERIALSSCIENCE& ENGINEERING