Construction of three-dimensional atomic images of functional materials by x-ray fluorescence holography
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 (XFH) experiment was carried out on Zn_0.4Mn_0.6Te single crystal for drawing a three-dimensional atomic image around the Zn atom. The XFH image intensities of Te atoms in Zn_0.4Mn_0.6Te 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. The feasibility of the XFH technique is also described by reviewing results on other functional materials, such as a mixed crystal In_<1-x>Ga_xSb, a DVD meterial Ge_2Sb_2Te_5, and a shape memorial alloy Ti_<50>Ni_<44>Fe_6.
Departmental Bulletin Paper