X-ray fluorescence holography (XFH) is a method of atomic resolution holography which utilizes fluorescing atoms as a wave source or a monitor of the interference field within a crystal sample. It provides three-dimensional atomic images around a specified element and has a range of up to a few nm in real space. Because of this feature, XFH is expected to be used for medium-range local structural analysis, which cannot be performed by x-ray diffraction or x-ray absorption fine structure analysis. In this article, we explain the theory of XFH including solutions to the twin-image problem, an advanced measuring system, and data processing for the reconstruction of atomic images. Then, we briefly introduce our recent applications of this technique to the analysis of local lattice distortions in mixed crystals and nanometer-size clusters appearing in the low-temperature phase of a shape-memory alloy.

Rare earth oxides are usually widegap insulators like Y2O3 with closed shell trivalent rare earth ions. In this study, solid phase rock salt structure yttrium monoxide, YO, with unusual valence of Y2+ (4d1) was synthesized in a form of epitaxial thin film by pulsed laser deposition method. YO has been recognized as gaseous phase in previous studies. In contrast with Y2O3, YO was dark-brown colored and narrow gap semiconductor. The tunable electrical conductivity ranging from 10−1 to 103 Ω−1 cm−1 was attributed to the presence of oxygen vacancies serving as electron donor. Weak antilocalization behavior observed in magnetoresistance indicated significant role of spin-orbit coupling as a manifestation of 4d electron carrier.

In order to bridge experimental results for the atomic structure in mixed crystals between x-ray diffraction showing a Vegard's law and x-ray absorption fine structure spectroscopy indicating preservations of each Pauling's bond length, an x-ray fluorescence holography ͑XFH͒ experiment was carried out on Zn 0.4 Mn 0.6 Te single crystal for drawing a three-dimensional atomic image around the Zn atom. The XFH image intensities of Te atoms in Zn 0.4 Mn 0.6 Te with respect to the reference ZnTe are almost constant beyond the five chemical bonds from the central Zn atom, while the nearer Te atomic images are much weaker, indicating that the Pauling's bond length interconnects with Vegard's law at about five chemical bonds. The randomness of the atomic positions is well explained by a locomotive wheel atomic configuration model.

Core-level photoemission spectroscopy and anomalous x-ray scattering ͑AXS͒ measurements were performed for the Pd 42.5 Ni 7.5 Cu 30 P 20 ͑PNCP͒ excellent metallic glass to investigate the chemical nature and local atomic structure, and the results were compared to those in Pd 40 Ni 40 P 20 and Pd 40 Cu 40 P 20 . The P 2p core levels clearly separate into two states, indicating that the P atoms have two different chemical sites, which is a strong experimental proof for the existence of an elastic inhomogeneity. From the AXS close to the Pd K edge, a specific Pd-P-Pd atomic configuration was observed, which is related to the stable state in the P 2p core levels. All of the core levels measured in PNCP have the deepest binding energies among these glasses, indicating the most stable electronic states. Local structure around the P atoms is discussed by the AXS data and a metastable crystal appeared in a supercooled metallic alloy close to PNCP.

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