Full correction of the self-absorption in soft-fluorescence extended x-ray-absorption fine structure

TLDR

The amplitude and shape of FLEXAFS spectra depend strongly on detection geometry due to self‑absorption, and conventional EXAFS analysis can yield systematic errors in physical parameters. The study aims to use knowledge of self‑absorption relative to information depth to determine the optimum experimental setup. The authors measured FLEXAFS of a NiO single crystal above the oxygen K edge for various detection geometries and calculated the fluorescence information depth as a function of experimental geometry. Knowing the stoichiometry, the authors fully correct for self‑absorption using a simple theory, yielding geometry‑independent oxygen EXAFS of NiO, and the correction procedure is generally applicable as a first step for concentrated samples.

Abstract

The amplitude of the extended x-ray-absorption fine structure of concentrated samples measured in the fluorescence mode (FLEXAFS) as well as the overall shape of the fluorescence-yield spectra strongly depend on the detection geometry through the self-absorption effect. In these cases, a conventional EXAFS analysis can lead to systematic errors in the determination of physical parameters. We studied the distortions in the FLEXAFS spectra through the self-absorption effect measuring the FLEXAFS of a NiO single crystal above the oxygen K edge for various detection geometries. We show that knowing the stoichiometry of the sample we can fully correct for the self-absorption effect using a simple theory and obtain the correct, geometry-independent oxygen EXAFS of NiO. The correction procedure presented here for the prototype system of NiO is generally applicable and should be the first step in the analysis of FLEXAFS data of concentrated samples. We calculate the information depth of the fluorescence detection as a function of the experimental geometry. The knowledge of the self-absorption in relationship to the information depth allows the determination of the optimum experimental setup.