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INTEGRALEED Electrons emitted by the cathode are focused at normal incidence onto the surface of the sample by a series of electrostatic lenses. The first grid of the optics and the last electrode of the electron gun are at the potential of the crystal, so that a field-free space is created. The majority of the electrons back-scattered from the crystal have lost energy in the scattering progcess (inelastic scattering). These electrons contain no diffraction information and have to be separated from the elastically scattered electrons which are back - diffracted from the solid surface. After allowing the scattered electrons to drift radially away from the crystal surface, the separation of the elastic and inelastic components is made by using a retarding potential that repels all electrons that have lost energy in the scattering process. The elastically scattered electrons pass through the retarding field and impinge on the spherical fluorescent screen to create the diffraction pattern. The pattern can be observed visually, reproduced photographically, or recorded by a video system. Applications
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