Electron diffraction (ED)
Electron diffraction comes from the combined scattering from many atoms arranged in a crystal. Bragg’s law and the Ewald sphere explain where the diffraction spots will fall on a detector and when the different reflections will be excited. Phase identification and zone-axis orientation is done from one or a few ED patterns. Determination of the unit-cell dimensions come from three main zone axes, high-order Laue zones (HOLZ) or a tilt series. Precession geometry is explained with ray paths and snap-shots from the collection of precession patterns in the TEM. Digital (by software) and analogue (by hardware) precession are compared. The geometrical factors that influence intensities, i.e. the Lorentz factor are given. The very latest techniques for collecting complete 3D ED data is shown, with the two existing geometries, automated diffraction tomography and the rotation method. Convergent-beam electron diffraction (CBED) is briefly introduced.
Keywords: electron diffraction, Bragg’s law, Ewald sphere, phase identification, Laue zones, indexation, unit-cell determination, precession electron diffraction, 3D electron diffraction, convergent-beam electron diffraction
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