Phase dependence of Kikuchi patterns. I. Theory

Thermal diffuse scattering in high-energy electron diffraction is analysed using the Einstein model of lattice vibrations. An expression for the intensity distribution in the Kikuchi pattern is obtained which includes thickness-dependent terms (i.e. a dependent-Bloch-wave theory is used) and the effects of a general crystal structure. The corresponding two-beam limit is shown to consist of four distinct terms, two of which depend on the phase of the structure factor. One of these is found to be non-zero only for non-centrosymmetric crystals and for relatively thin crystals. It leads to an asymmetric Kikuchi band, even in a symmetrical scattering geometry. This asymmetry may be used to determine the polarity of non-centrosymmetric crystals.