Optimized end station and operating protocols for reflection extended x-ray absorption fine structure (ReflEXAFS) investigations of surface structure at the European Synchrotron Radiation Facility beamline BM29

Setup for optimized grazing incidence x-ray absorption experiments on thin films on substrates

We present a state-of-the-art experimental apparatus and a proper setup to perform x-ray absorption spectroscopy (XAS) experiments in grazing incidence mode. This geometry is appropriate for doped thin films or interfaces buried at moderate depth in a thick matrix, whenever the scattering and/or fluorescence from the matrix has to be strongly attenuated. Both the calculation and the experimental data demonstrate that the specific setup that consists in a grazing incidence and grazing collection geometry is extremely advantageous. In fact, with respect to the standard geometry used to perform XAS experiments in fluorescence mode, the present setup allows an enhancement in the interesting fluorescence signal from the surface layer without a corresponding increase in the elastic scattering contribution from the matrix. The sample holder especially designed for this kind of experiment can work in vacuum and at low temperature. An easy and quick automatic sample alignment procedure is detailed.

A new procedure for the quantitative analysis of extended x-ray absorption fine structure data in total reflection geometry

A novel code for the analysis of extended x-ray absorption fine structure (EXAFS) data collected in total reflection mode (reflEXAFS) is presented. The procedure calculates the theoretical fine structure signals appearing in the reflectivity spectrum starting from the ab initio EXAFS calculations. These signals are then used in complex structural refinement (i.e., also including multiple scattering paths) with usual fitting programs of EXAFS data. A test case consisting in the analysis of a gold film collected at different incidence angles is presented in detail.