Dynamical calculation of thermal diffuse electron scattering

The theory of Cowley & Pogany (Acta Cryst. (1968). A24, 109) is used for the numerical calculation of thermal diffuse electron scattering from thin monatomic crystals, along the line of a set of systematic reflexions. Dynamical interactions of 15 Bragg and 25 diffuse beams are considered for up to 183 Å of gold (200) systematics, treating the range of coherence of the interaction as a parameter of calculation. A one-phonon Debye model is used. It is found that thermal diffuse scattering will not produce strong thickness fringe contrast, but will yield Kikuchi bands and lines, with little dependence on the range of coherent interaction. The unindexed Kikuchi line at the centre of the bands is predicted. Thermal scattering tends to increase in the region of strong Bragg beams for tilted crystals. Compared to that predicted kinematically, dynamical thermal scattering is greater for thin crystals near principal orientations, but will in general be less for highly tilted and particularly for thick crystals; it is more spread out in the diffraction pattern, and far stronger in the first Brillouin zone. There is an indication that thermal streak patterns from thin crystals should be stronger than expected kinematically.