X-ray fluorescence holography as a probe of hyper-ordered structures

X-ray fluorescence holography (XFH) is a powerful local structural analysis technique that can be used to visualize the three-dimensional atomic arrangement around a specific element in materials. This paper reviews XFH studies from the viewpoint of 'hyper-ordered structures' embedded in various materials, such as magnetic, structural, superconducting, thermoelectric, and biological materials. It has been shown that XFH is a useful technique to observe the hyper-ordered structures in crystals, which are closely related to the functions of materials. In addition, potential targets of XFH including the hyper-ordered structures are suggested as a topics in future studies. (author)