Papers by Keyword: XAFS

Abstract: In order to study the evolution of local crystal and electronic structure of Sr₂CuO₂F_2+x, the synchrotron radiation x-ray absorption (XAS) and x-ray absorption fine structure (XAFS) techniques were both performed on different amount of Sr₂CuO₂F_2+x materials. The relationship between high T_c superconductivity and valence state of cooper was mainly discussed. And the effect of by-reproduce SrF₂ in non-superconductive Sr₂CuO₂F_2+x on physical property of this material was considered. The experimental results showed that the valence state of Cu and the amount of SrF₂ was mainly related with high T_c superconductivity of Sr₂CuO₂F_2+x material, indicating a good method for improving T_c.

Abstract: In a process of bioleaching of sulfides, the surface of target mineral is sometimes covered with intermediates and final products to interfere the extraction of metal. Understanding characterization and formation order of secondary minerals, which are responsible for passivation, is a key to resolve the passivation. In the present article, identification of secondary minerals and intermediates in a process of bioleaching of several sulfides by X-ray photoelectron spectroscopy, Raman spectroscopy, identification of jarosite group minerals using Raman spectroscopy, and expectation of formation order of secondary minerals by SEM-EDX and TEM observation are overviewed. Direct observation of a nanodomain by TEM provided a useful information on amorphous secondary minerals. In bioleaching of arsenic-bearing copper sulfides, which are expected to be a new target in the near future, a passivation model was proposed to keep maximizing Cu recovery and minimizing As solubilization, based on combination of solid characterization with aqueous observation.

Abstract: This paper describes structure evaluation of GexSbyTez (GST) film fabricated by chemical vapor deposition (CVD). We successfully established composition controlled GST CVD with smooth surface by applying appropriate deposition conditions. By increasing Ge flow rate or reducing substrate temperature, the average grain size was reduced and the film flatness was improved. As the results, we succeeded to obtain the extremely smooth surface, and also to fill a finite hole with conformal film deposition. All GexSbyTez films showed FCC or amorphous crystalline structures, both are utilized in the proposed phase change random access memory (PRAM), in spite of the wide range of composition control. We believe these CVD-GST films are useful for PRAM applications.

Abstract: X-Rays Absorption Fine Structure Spectroscopy (XAFS) is an analytical technique that can be used as a probe to characterize almost all elements, even if they appear in diluted or non-crystalline systems. This is due to the fact that the absorption probability of X-rays has a unique feature for each element, and is modulated by the chemical and physical state of that element, as well as by its neighborhood. This paper presents a brief description of the X-rays absorption phenomenon and the analytical technique involving this phenomenon, as well as the application of XAFS in biosorption studies. For more details on XAFS theory, refer to [1].

Abstract: Martensitic and magnetic properties of ferromagnetic shape memory alloys are known to depend up on structural modulations and associated changes in the Fermi surface. These modulations although periodic and spanning over multiple unit cells, involve movement of atoms typically of the order of 0.01Å. Therefore X-ray Absorption Fine Structure (XAFS) is an ideal tool to map both, local atomic movements and changes in density of states (DOS) due to changing hybridization as the system transforms from austenitic to martensitic phase. This paper presents a compilation of our XAFS studies on the Ni-Mn based shape memory alloys. A complete description of the changes in local structure around the constituent metal ions in the following alloy compositions: Ni2+xMn1-xGa, Ni2Mn1.4Sn0.6 and Ni2Mn1.4In0.6 in the austenitic and martensitic phases have been obtained. The results give the new experimental evidence for the crucial hybridization component that influences and leads to structural transition in these Ni-Mn based Heusler alloys.

Abstract: Novel low melting glasses in the MoO3-La2O3-Nd2O3 system were obtained at different cooling rates (102 K/s and 104-105 K/s). Characterization of the amorphous samples was made by differential thermal analysis (DTA) and X-ray absorption fine structure (XAFS) method. According to DTA data of the glass samples, the glass transition temperatures are at 325-330 0C, the crystallization started above 410 0C and the melting temperatures are at 660-720 0C. A structural model of glasses was suggested on the basis of XAFS and IR investigations. It was shown that the predominant structural units in the amorphous network of glasses containing 90 -80 mol% MoO3 are MoO6 groups. The appearance of MoO4 groups deteriorates the glass formation ability.

Abstract: TiO2 sol containing nano anatase crystalline grains was prepared using Ti(OC4H9)4 as a precursor in a water-excessive reaction system. The processes of hydrolytic-polymeric reactions and the structures of the products were analyzed. It was found that the -OC4H9 radicals previously linked to Ti atom in Ti (OC4H9) 4 molecular are broken, and there is no organic radicals linked to Ti atoms in the final sol. The structure of particles in the sol changes along with time from tetrahedral [TiO4] to octahedral [TiO6], with the coordination number changing from 3.14 to 5.18, accordingly. Therefore, the structure becomes closer to an anatase, which is octahedral [TiO6] with a coordination number of 6.0. Transmission electron microscope micrograph also reveals the foursquare projection shape of crystalline grains with a size of 200 nm in the sol. As the particles in the sol have a quasi anatase structure, the TiO2 sol can directly photodegrade Rhodamine B under Ultraviolet illumination with a rate of 62.35%.

Abstract: XAFS measurements of the Cu, Ni and Zr K-edges for the melt-quenched Zr67Cu33 and Zr67Ni33 metallic glasses were curried out using synchrotron radiation at 20K. Fitting calculations for the EXAFS results reveal that local structure around Ni and Zr in Zr67Ni33 is well represented by those for the crystalline Zr2Ni, while local structure around Zr in Zr67Cu33 is better fitted by an icosahedron rather than crystalline Zr2Cu. Such differences of the local structure attribute to the differences of the stability of super-cooled liquid state and glass formability between Zr67Cu33 and Zr67Ni33 metallic glasses.

Abstract: Metal particles of silver (Ag) and copper (Cu) have been synthesized in the presence of Aerosol-OT (AOT) or fluorinated surfactants in water-in-scCO2 microemulsions by the chemical reduction of AgClO4 and Cu(ClO4)2. The formation of Ag particles by the photo-reduction using UV-light have been confirmed by in-situ UV-Vis, X-ray absorption fine structure (XAFS), and small angle X-ray scattering (SAXS) measurements. Cu particles have also been prepared by the addition of a reducing reagent sodium borohydride, and the electronic structure of Cu ionic species has been investigated after reduction in the water-in-scCO2 microemulsions. The average size of aggregates of Ag particles in the microemulsions by means of in-situ SAXS measurements also has been estimated.

Abstract: A better efficiency of sensing tera-hertz signals (T-rays) depends on a better crystalline structure which is obtained by replacing a small amount of Cd on Zn sites of ZnTe crystals. Zn1-xCdxTe (ZCT) crystals were fabricated with an advanced vertical Bridgeman method and the structural properties of the ZCT crystals were studied with high resolution x-ray diffraction (HRXRD) and x-ray absorption fine structure (XAFS) measurements. The Rietveld refinement to the HRXRD data showed that the ZCT crystals at x ~ 0.05 were slightly less disordered than the ZnTe crystals. These results were confirmed by the XAFS data analysis. The better structural orderings can be directly related to the sensing and emitting efficiencies of T-ray by the ZCT crystals.