THEORY OF DEEP CORE EXCITATION EELS

In this work we discuss the high-energy electron energy loss spectra from a deep core orbital in a solid based on many-body electron scattering theory developed by Fujikawa and Hedin. Important many-body effects are absorbed into damped one-electron functions and optical potentials. Particular emphasis is placed on the extended electron-energy-loss fine structures (EXELFS) or extended energy-loss fine structures (EELFS), where we have to prepare three different kinds of damping functions and the optical potentials. The first is for the incident fast electron, the second for the scattered electron after the loss, and the third for the secondary excited one from a deep core which behaves like an EXAFS electron. The second optical potential is related to the third one if we use quasi-boson approximation for the valence electrons. Furthermore we explicitly include elastic scatterings of both probe and secondary excited electrons from atoms in the solid. This theory gives us sound theoretical background and practical tools to study EELFS spectra.