Accurate site-selective atomic structure determination by single-energy x-ray holography

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The concept of site-selectivity is of great importance for modern materials science. It entails a full understanding of the atomic scale structure of the functional site in a material, which in turn largely determines its functional properties. New advances in x-ray fluorescence holography (XFH) have the potential to become a universal tool for site-selective investigations in crystals. These methods combine the intrinsic element-selectivity of XFH with the possibility for a chemical characterization of the environment. This is achieved by a resonant approach, i.e. tuning the x-ray energy to an energy that coincides with an x-ray absorption edge in the material. However, the approach is practically limited in the choice of energies, and the reconstruction from single-energy holographic data is still problematic. The proposed project aims to resolve these problems, to practically implement site-selective measurements and to apply them to current research issues in materials science. This approach is useful for, among else, identifying local atomic environments with chemical information and for understanding in detail the chemical disorder. One of the obstacles here is the atomic image cancellation effect, which leads to a large decrease in the signal intensity of certain pairs of distances and incident energies.