Surface-sensitive reflection-mode EXAFS from layered sample systems: the influence of surface and interface roughness

The calculation of reflection-mode grazing-incidence X-ray absorption spectra from single surfaces and (multi-)layered systems is studied here. In particular, the influence of the surface and interface roughness was investigated in detail. Simulations of grazing-incidence reflection-mode EXAFS spectra using a simple Fresnel theory neglecting any effect of roughness are compared with the Névot-Croce model and the elaborated distorted-wave Born approximation which both include surface and interface roughness. Data are presented for clean gold surfaces, where the strong influence of the surface roughness on the resulting spectra is demonstrated. Furthermore, in the case of layered systems, the influence of both the outer (air or vacuum side) surface roughness and the inner interface roughness on the reflection-mode EXAFS spectra is evaluated. The practical consequences of the observed correlations are discussed, and a quantitative data analysis of a copper sample that was oxidized in ambient air for several months is shown, including the evaluation of specular reflectivity profiles at fixed energy.