Jens Rüdiger Stellhorn

A valence-selective X-ray fluorescence holography study of an yttrium oxide thin film

The first direct valence-selective structure determination by X-ray fluorescence holography is reported. The method is applied to investigate an epitaxial thin film of the rare earth monoxide YO, which has recently been synthesized by pulsed laser deposition. The surface of the sample is easily oxidized to Y2O3. In order to separate the structural information connected with the two different valence states of Y, the X-ray fluorescence holography measurements were performed close to the Y K absorption edge. Using the shift of the absorption edge for the different valence states, very different relative contributions of YO and Y2O3 are obtained. Thus, it is possible to distinguish the crystal structures of YO and Y2O3 in the thin-film sample.

X-ray Fluorescence Holographic Study on High-Temperature Superconductor FeSe0.4Te0.6

Abstract To observe the difference of atomic heights between the Se and Te layers with respect to the Fe layer in FeSe0.4Te0.6 single crystal, a Fe Kα fluorescence X-ray holography (XFH) experiment was performed at room temperature. The crystal structure of superconductor FeSe0.4Te0.6 obtained by X-ray diffraction (XRD) at a low temperature has distinct z-coordinates of Se and Te, remarkably different from each other. The reconstructed atomic image around central Fe atoms by XFH, however, reveals the different and complex results.

Structural Aspects of the Superionic Conduction Mechanism in Ag-GeSe3 Glasses

Abstract The local and intermediate-range atomic structure in the Ag ion conducting glasses Agx(GeSe3)1−x with x = 0.15 and 0.50 has been investigated by Anomalous X-Ray Scattering experiments at the K absorption edges of each constituent element. This method can provide insight into the structural properties enabling the effect of superionic conductivity for compositions with x > 0.33 in the amorphous phase. The experimental results were analyzed with Reverse Monte Carlo modeling, providing the partial structure factors and the corresponding partial pair-distribution functions. Evidence is found for a high level of intermediate range order for low silver concentrations, whereas the superionic conducting phase formed at high silver concentrations is characterized by cluster-like configurations of Ag atoms on a nanometer scale.

Microscopic Structure Analysis in Disordered Materials using Anomalous X-ray Scattering

Abstract Although X-ray diffraction is still mainly used to determine crystal structures, the demand for an understanding of the atomic arrangement in disordered matter has progressively become more important over the past decades. However, apart from simple model systems, it is still a challenging task to unravel the microscopic ordering of the atoms in amorphous multi-component materials, although this knowledge becomes increasingly important in modern materials science, in which the physical properties are often related to the microscopic ordering of the different chemical species of the substance. This article reports about the combination of Anomalous X-ray Scattering (AXS) with Reverse Monte Carlo Computer simulation (RMC) as a proper tool to precisely determine the microscopic structural characteristics in such systems with high reliability. The basic principles of the method will be illustrated and some examples of modern materials will be given to proof the applicability and the capability of this method.

Anomalous X-ray Scattering on Semiconducting Glasses at ESRF: Review in Recent Fifteen Years

Abstract The most difficult issue for the structural characterizations for non-crystalline multi-component materials is to determine partial structures because n(n + 1)/2 scattering experiments with different scattering cross-sections are necessary for n-component materials. More than three decades have already passed through since anomalous X-ray scattering (AXS) using synchrotron radiation (SR) was expected as a promising tool for investigating partial structures. Compared with a related method, X-ray absorption fine structure, however, AXS is still rarely used owing to difficulties in the experiments and data analyses. We have developed a new detecting system, which can fully utilize intense X-ray fluxes from third-generation SR facilities. Using this detecting system, we have carried out many AXS experiments at the beamline BM02 of the ESRF on several semiconducting glasses. The obtained differential structure factors were analyzed using reverse Monte Carlo modeling to draw three-dimensional atomic configurations. In this article, we review results of semiconducting glasses, and describe the structure-property relations in these glasses.

A combination of anomalous x-ray scattering and neutron diffraction for structural characterizations of Zr63Ni25Al12 metallic glass

Zr63Ni25Al12 bulk metallic glass was investigated using neutron diffraction and anomalous x-ray scattering close to the Zr and Ni K edges. The experimental results were analyzed using reverse Monte Carlo modeling (RMC) to obtain partial structure factors and pair distribution functions. The obtained partial structural results were compared with RMC results when neutron diffraction data are not included in the analysis and the report of Zr60Ni25Al15 by Fukunaga et al. using high-energy x-ray and neutron total scattering data.

A partial structure factor investigation of the bulk metallic glass Zr63Ni25Al12 as studied by using a combination of anomalous x-ray scattering and reverse Monte Carlo modeling

Abstract Anomalous X-ray scattering experiments were performed on Zr63Ni25Al12 bulk metallic glass. The results were analyzed using reverse Monte Carlo modeling to obtain local- and intermediate-range atomic configurations of this good metallic glass former. Although the Al-related partial information is not reliable due to the small values of their weighting factors in X-ray scattering, good partial information could be obtained from a reverse Monte Carlo analysis. The obtained structural information is given by parameters such as bond angle distributions, bond orientation order parameters, the Warren–Cowley order parameters, and Voronoi polyhedra. Results are compared to the previous results from Fukunaga et al. using X-ray and neutron total scattering.