The role of localized recoil in the formation of Kikuchi patterns

In electron scattering from crystals, diffraction spots are replaced by Kikuchi patterns at high momentum transfer. Kikuchi pattern formation is based on the concept of effective incoherent electron sources (or detectors) inside a crystal. The resulting incoherence is a consequence of energy transfer connected with the momentum transfer in large-angle scattering events. We identify atomic recoil as a key incoherent process giving rise to electron Kikuchi patterns in the scope of the “channeling-in and channeling-out” model of electron backscatter diffraction (EBSD) and electron channeling patterns (ECP) in the scanning electron microscope (SEM). Using model calculations, we explore the characteristic role of the localization of the incoherent scattering event at specific places within the unit cell. In this way, we explain why sometimes inelastic losses do cause Kikuchi-type contrast, and sometimes inelastic losses result in the disappearance of this contrast in the SEM.

► We show the role of atomic recoil in Kikuchi pattern formation from crystals.
► The role of the localization of incoherent scattering in the unit cell is explained.
► We use dynamical diffraction simulations to reveal the mechanism of contrast loss.
► The function of recoil in the “channeling-in and channeling-out” model is clarified.