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

位置选择性的概念在现代材料科学中具有重要意义。它需要充分了解材料中功能位点的原子尺度结构，这反过来又在很大程度上决定了其功能特性。x射线荧光全息术（XFH）的新进展有可能成为晶体中位点选择性研究的通用工具。这些方法结合了XFH固有的元素选择性和环境化学表征的可能性。这是通过共振方法实现的，即将x射线能量调谐到与材料中的x射线吸收边缘一致的能量。然而，该方法在能量的选择上受到限制，单能量全息数据的重建仍然存在问题。提出的项目旨在解决这些问题，切实实施选址测量，并将其应用于当前材料科学的研究问题。这种方法对于识别具有化学信息的局部原子环境以及详细理解化学紊乱非常有用。其中一个障碍是原子像抵消效应，它会导致某些距离和入射能量对的信号强度大幅下降。

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.