Fine structure on inner-shell ionization edges (ELNES/ EXELFS)
The atomic transition matrix governs which subset of the total density of states is probed. Since the inner-shell excitation process is highly localized on a particular atomic site, where two differing coordinations of one element co-exist within the same structure, the individual contributions of the different sites to the observed Electron energy loss near-edge structure (ELNES) is a simple linear sum weighted by the respective site occupancies. Therefore, assuming the existence of distinct ELNES coordination fingerprints, it is often possible to determine semi-quantitatively the relative site occupancies via simple algorithms or fitting routines. In order to extract detailed information from ELNES measurements and to determine bonding effects in a more quantitative fashion, some form of accurate spectral modelling is essential. The valence or oxidation state of the particular atom undergoing excitation influences the ELNES in few distinct ways.