Theory of X-ray Absorption Near Edge Structure
Résumé
The purpose of this chapter is to the present the main steps explaining the x-ray absorption phenomenon, specially in the low energy part of the edge spectra. We start from the interaction Hamiltonian between the electromagnetic-field and one electron. We give then the transition rate between two states. From this, the general equations for the absorption process in a material is given. We show that depending on the edge and on the material, different theories can be better to simulate an experiment. Sometimes monoelectronic techniques are sufficient, but a large area around the absorbing atoms must be considered. In the opposite case, multi-electronic phenomena are dominant, but system can be described by some simple parameters. Finally, we present briefly some of the most recent research devoted to situations where both multi-electronic and multi-atomic aspects are important.