Temperaturabhängigkeit der Absorptionskoeffizienten für mittelschnelle Elektronen in polykristallinen Aluminium-, Silber- und Goldschichten

The absorption coefficientsμ _el andμ _unel for fast electrons (30–50 keV) due to elastic and inelastic scattering in polycrystalline foils of Al, Ag and Au have been measured at various temperatures between 160 and 600 °K. It is shown that,μ _unel decreases only slightly with temperature. On the other hand, the absorption coefficientμ _el, which is composed ofμ _R for Laue Bragg scattering andμ _TDS for thermal diffuse scattering increases with temperature. Asμ _R andμ _TDS depend on temperature in opposite sense, the resulting increase ofμ _el=μ _R+μ _TDS with temperature depends on the extent, to which the temperature dependence ofμ _R is reduced by dynamical extinction effects. For Al the measured temperature dependence ofμ _el is in good agreement with the theoretical calculation ofμ _TDS on the basis of the Einstein model and ofμ _R according to the two beam approximation of the dynamical theory. For Ag and Au the temperature dependence ofμ _el is much more pronounced than for Al. This is due to the facts that for heavy elements firstly the elastic scattering is stronger and secondly dynamical extinction effects are generally more pronounced. In order to study the influence of dynamical extinction, the crystal size of the foils was varied.