FULL CORRECTION OF THE SELF-ABSORPTION IN SOFT-FLUORESCENCE EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE

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.