Electron Scattering

Abstract

The propagation of electrons is governed by the Schrödinger wave equation. Owing to this wave property, the scattering of electrons differs appreciably from that of classical solid particles. In particular, the interference between different partial waves affects the intensity distribution of an electron micrograph and prevents straightforward interpretation in many cases. Without such interference, the formation of an image would not be possible. The description of image formation in an electron microscope must, therefore, account for the possibility of interference, which is determined by the degree of coherence of the electron wave-field. Interference effects must be considered in order to extract correctly the information about the spatial structure of an object from the image. The modulation of the image intensity depends on the partial coherence of the electron wave-field. Partial coherence is caused by the finite energy width and the lateral extent of the effective electron source, by parasitic incoherent perturbations, and by unavoidable inelastic scattering processes within the object. Inelastic scattering generally decreases the degree of coherence. Even for energy-filtered high-resolution imaging, inelastic scattering effects are important because electrons that have suffered a very small energy-loss cannot be separated from the unscattered or elastically scattered electrons by a conventional energy filter [1]. Thermal diffuse scattering, for example, produces this kind of very small energy-losses below 0.1 eV and contributes appreciably to the intensity at high scattering angles [2].