Coupled thermal diffuse-atomic inner shell scattering in electron diffraction

In electron diffraction patterns, diffuse scattering at high angles is primarily generated by phonon, or thermal diffuse, scattering (TDS). Techniques were introduced to acquire the electron energy-loss spectra (EELS) of high-angle thermal-diffuse-scattered electrons (TDS-EELS) in a transmission electron microscope (TEM). With regards to the scattering mechanism, the TDS-EELS core ionization edge intensity was believed to be generated primarily by TDS - single electron, double-inelastic electron scattering processes. It was concluded from experimental data that the signal from coupled phonon - atomic inner shell excitations is stronger than that from atomic inner shell excitation alone. A formal dynamical theory is presented in this paper to illustrate the theoretical basis of the experimental observations. The theory can be applied to calculate the diffraction patterns of inelastically double-scattered electrons and the signal intensity observed in TDS-EELS. TDS is actually a statistically averaged, quasi-elastic scattering of the electrons by the crystal lattice of different thermal vibration configurations.