Speaker
Description
Today X-ray absorption spectroscopy (XAS) is a versatile and well-established technique for providing electronic and structural information on all kind of materials, whatever the state of the sample, solid, liquid, disordered materials and for atomic concentrations ranging from a few ppm to the pure element [1,2]. The physical process underlying the XAS is the ejection of an electron, called photo-electron, when X-rays are absorbed by the matter. This phenomenon arises when incident X-rays energy is scanned across the range corresponding to that required for the ionization of a core electron from an atom, called absorbing atom, in the sample. The interference between the outgoing wave associated to the photo-electron and the waves originating from the backscattering of this photo-electron by the neighbouring atoms of the absorbing atom gives rise to oscillatory structures on the X-ray absorption spectrum, arbitrarily divided into Extended X-ray Absorption Fine Structures (EXAFS) and X-ray Absorption Near Edge Structures (XANES). On one hand, EXAFS is one of the few structural techniques that provide information over the short-range order (inter-atomic distances, types and number of first and more distant neighbours) around almost any atomic species of the periodic table. On the other hand, complementary information is obtained from the analysis of the XANES spectrum, like the oxidation state and site symmetry of the selected absorbing atom.