The variations in background intensity of electron diffraction patterns

Abstract

Very few investigations of the general background of diffusely scattered electrons associated with all electron diffraction patterns have been made, presumably because no direct information about the structure of the crystalline regions can be gained. Nevertheless, such investigations are of interest because they provide a direct test of the theoretical intensity distributions which have been proposed for diffusely scattered electrons. Early results obtained by White (1) and Kirchner (2) did not agree with distributions calculated on the basis of single inelastic scattering by Bethe (3) and Morse (4). This disagreement was undoubtedly due to plural scattering effects in the experiments. More recently Ellis (5) has measured patterns obtained at 50, 100 and 150 kV from aluminium and thallium chloride specimens having a wide range of thicknesses. For the thinnest specimens, the electron intensity f (r) at a distance r from the central spot was almost proportional to r ⁻², but with thicker specimens an enhanced background intensity was discovered in the vicinity of the diffraction rings. This enhancement, which increased with specimen thickness, was attributed to electrons which were scattered after they had been diffracted.