Dynamical diffraction in electron-energy-loss spectrometry: The independent Bloch-wave model.

Abstract

The double-differential cross section for inner-shell ionization in a crystal by fast electrons is calculated within the theory of dynamical electron diffraction. Bloch waves are used for the incident and the emerging electrons. We show that interference terms are still present in the independent Bloch-wave model. In the two-beam case, the cross section contains but six terms, three of them caused by interference. From the six terms, three are identified as the Kikuchi excess and defect lines and the Kikuchi band. The remaining three terms have not yet been described explicitly. As an example, the Si K-shell ionization cross section is calculated for a (220) two-beam case, in a dipole approximation for the mixed dynamic form factor. It is shown that in electron spectroscopic diffraction the maximum of the fundamental Lorentzian can be significantly shifted with respect to the direction of incidence, and that the interpeak minimum between the fundamental and the Bragg-excited Lorentzians is depressed relative to the kinematical case. \textcopyright{} 1996 The American Physical Society.