Elastic energy losses due to scattering of fast electrons (20--40 keV) by crystals into large angles (_>_ 45 ~ are experimentally and theoretically investigated. Energy losses up to a few electron volts appear, which depend on the mass of the atoms composing the crystal, of the scattering angle, and of the primary energy of the electrons. These results agree with the assumption of elastic scattering by single atoms and not by the crystal as a whole. The width of the energy losses increases with the energy loss himself, and with the temperature of the crystal. In a first theoretical approximation this effect can be explained by the thermal motion of free atoms.
ProblemstellungElastisch gestreute Elektronen sind per definitionem solche, die keine Anderung des inneren Energiezustandes des Streuers verursachen. Trotzdem erleiden sie Energieverluste. Diese elastischen Energieverluste A E kommen im Laborsystem dutch die mit der Streuung verbundene Impuls/inderung zustande und ergeben sich aus den Erhaltungss/itzen von Energie und Impuls. F/it einen ruhenden Streuer der Masse M, an dem Elektronen der Masse mund der Prirn~irenergie E um den Winkel gestreut werden, wird dann f/Jr m ~ M der elastische Energieverlust: m 0
Inelastic energy losses of free electi~ons (20-100 keV) scattered into crystal reflections are theoretically investigated. By extending the usual dielectric theory of solids to crystals these scattering processes can be explained as an immediate scattering into the reflections. The probability of scattering for an electron with a fixed energy loss is derived. This result agrees in the case of a homogeneous medium with the probability of scattering already known within the frame of the usual dielectric theory.Einleitung
The angular distribution of Li~-ions scattered by rare gas atoms shows at scattering angles in the order of 10 -~ < ~9 < 10 -a tad characteristic maxima of intensity. These maxima cannot be explained by the electron scattering theory applying electrons equienergetie to the Li~-ions. Therefore the interaction potential between the scattered Li~-ions and the rare gas atom is extended in such a way, that the mutual action of the charge distributions of both systems is taken into account. A simple form for this potential gives positions of the maxima which are in good agreement with the experimental values.
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