Effects of multiple elastic and inelastic scattering on energy-resolved contrast in Kikuchi diffraction

Abstract

Energy-resolved Kikuchi patterns for silicon crystals were measured for 30 keV electrons in a reflection geometry. The amount of contrast seen depends strongly on both the geometry and the energy loss. For geometries where the outgoing trajectory is glancing with the surface, the contrast is maximum for zero loss, decreases with larger energy losses and for energy losses over 1 keV, a reversal of the contrast is observed. For geometries where the incoming beam is glancing, the contrast first gradually increases with energy loss and decreases slowly for losses larger than 100 eV. Under these conditions contrast reversal was not seen. These observations are modelled using the cross sections of the various elastic and inelastic processes involved.

Inelastic Scattering in Electron Backscatter Diffraction and Electron Channeling Contrast Imaging

“…2h) even the Kikuchi bands are barely visible. This trend of maximum contrast at an energy loss greater than the recoil energy is consistent with experimental results on energy-filtered EBSD (Deal et al, 2008; Vos & Winkelmann, 2019). It should be noted that in the simulation, only the number of plasmon events as the backscattered electron leaves the specimen is recorded, while in experiment what is measured is the absolute energy, which also includes any energy loss prior to the backscattering event.…”

“…This is consistent with the trends expected of a Poisson distribution. Kikuchi band contrast is a result of phonon scattering, which is estimated to have a longer mean free path compared to elastic or plasmon scattering (Vos & Winkelmann, 2019). Since “zero” loss backscatter events are confined to the near-surface region, there is much less phonon scattering that occurs as the electrons escape the solid.…”

“…Therefore, only the plasmon scattering angle, and not the energy loss, was included in the simulations. Other ionization events, such as the Si L- and K-edges, were ignored due to the much smaller cross-sections (Egerton, 1996; Vos & Winkelmann, 2019). Experimentally, it is known that the useful information in an EBSD pattern originates from within the first few nanometers (or tens of nm) of the specimen surface (Zaefferer, 2007; Chen et al, 2011).…”

“…Of these, plasmons typically have the largest scattering cross-section (Egerton, 1996). Energy-filtered EBSD patterns have shown that for the standard experimental geometry of a 70° tilted sample, the Kikuchi band contrast first increases with energy loss, reaching maximum contrast at few tens or hundreds of eV, before slowly decreasing at higher energy losses (Deal et al, 2008; Vos & Winkelmann, 2019). The energy loss at peak contrast is well below that of single electron ionization but greater than the recoil energy for backscattering (Winkelmann & Vos, 2013), which suggests that the contrast mechanism may also involve plasmon and/or interband transitions.…”

“…The energy of backscattered electrons can vary over all energies up to the primary energy of the incident electron beam. However, much of the channeling contrast signal is contained in those electrons with low energy loss (Deal et al, 2008; Vos & Winkelmann, 2019), while the higher energy-loss electrons contribute a background signal with no useful information. While our simulations cannot reproduce the full energy spectrum of the backscattered electrons, it does offer insight into the underlying scattering mechanisms that govern channeling contrast.…”