Model mechanisms in Kikuchi pattern formation from crystals

Abstract

In diffraction experiments on crystals, different types of diffraction patterns can be observed. Depending on various factors like the scattering energy, scattering geometry, sample temperature, or structural disorder, one can observe a combination of discrete diffraction patterns caused by coherent scattering of the incident beam and a structured background formed by patterns which can be explained by emission from internal incoherent sources inside the crystal. For the case of electron diffraction, these patterns from incoherent internal sources are called Kikuchi patterns. It will be shown here that the transition from the discrete coherent electron diffraction patterns to Kikuchi patterns, as well as similar effects in X‐ray and neutron diffraction, can be analyzed qualitatively by a simple model involving a two‐step scattering process. An elementary double‐scattering model is presented extending the kinematic model of X‐ray diffraction. The double‐scattering model outlines the key mechanism that can destroy the coherence between the first scatterers while at the same time some coherence can be preserved in the secondary scattering pathways starting at each of the individual first scatterers, respectively. In this way, the model presented here highlights some non‐trivial experimental effects of coherence loss under conditions of multiple scattering of waves in crystals.