'Self-Absorption' Effects in Grazing-Incidence Total Electron-Yield XAS

Abstract

Uniformly reduced amplitudes of the extended X-ray absorption fine-structure (EXAFS) detected by total electron-yield (TEY) methods have repeatedly been reported in the literature. Some authors ascribed them to the presence of a 'disordered' near-surface layer on the sample, but in situ TEY EXAFS investigations of the annealing behaviour of Ni provide experimental evidence against this hypothesis. It is shown that an amplitude reduction previously observed for metallic Ni can be corrected by taking account of a 'self-absorption' effect which occurs in TEY measurements at grazing X-ray incidence. Furthermore, the TEY also contains contributions excited by fluorescent photons which are another source of distorted EXAFS amplitudes. Using results of Monte-Carlo electron-trajectory simulations, the magnitude of the 'self-absorption' distortions is calculated and compared to the results of TEY measurements of Cr, Ni and ZnO samples as a function of incidence angle.