Measurement of absorption of fast electrons in single crystal films of aluminium

Abstract

Measurements of the electron absorption parameters over the voltage range 60 kv to 100 kv for the 111 reflection in aluminium and calculations of the effect of many beams on the relativistic dependence of the mean absorption coefficient on the incident electron velocity are reported. It is shown that the ratio of the mean absorption distance to the extinction distance varies linearly with the incident electron velocity as expected from the relativistic two-beam dynamical theory of electron diffraction. A theoretical investigation shows that when many beams are considered this linearity is not destroyed until an accelerating voltage ∼ 200 kv is reached. It is also shown that the mean absorption distance is independent of the objective aperture size, while the anomalous absorption distance increases with decreasing size of objective aperture.