An improved X-ray structural analysis for determining cation distribution in ZnFe2O4 and ZnFe2O4- Fe3O4 solid solutions

The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 has been determined by anomalous X-ray scattering near the Zn K absorption edge. Measured intensity ratio with two energies close to the edge can be quantitatively explained only by assigning all zinc cations to the tetrahedral position in the approximately cubic close packed array of oxygen ions. A similar conclusion has also been reached for ZnxFe3-x04 solid solutions with x = 0.73, 0.54 and 0.35 employing the improved X-ray method. This is consistent with the EXAFS results which indicate an almost unchanged environmental structure around zinc cation in these solid solutions.

Anomalous X-ray scattering study of local structures in the superionic conducting glass (AgBr)0.4 (Ag2O)0.3 (GeO2)0.3

The local structural information in the near-neighbor region of superionic conducting glass (AgBr)0.4(Ag2O)0.3(GeO2)0.3 has been estimated from the anomalous X-ray scattering (AXS) measurements using Ge and Br K absorption edges. The possible atomic arrangements in the near-neighbor region of this glass were obtained by coupling the results with the least-squares variational method so as to reproduce two differential intensity profiles for Ge and Br as well as the ordinary scattering profile. The coordination number of oxygen around Ge is found to be 3.6 at a distance of 0.176 nm, suggesting the GeO4 tetrahedral unit as the probable structural entity in this glass. Moreover, the coordination number of Ag around Br is estimated as 6.3 at a distance of 0.284 nm, suggesting an arrangement similar to that in crystalline AgBr.

Band alignment studies in InN/p-Si(100) heterojunctions by x-ray photoelectron spectroscopy

The band offsets in InN/p-Si heterojunctions are determined by high resolution x-ray photoemission spectroscopy. The valence band of InN is found to be 1.39 eV below that of Si. Given the bandgap of 0.7 eV for InN, a type-III heterojunction with a conduction band offset of 1.81 eV was found. Agreement between the simulated and experimental data obtained from the heterojunction spectra was found to be excellent, establishing that the method of determination was accurate. The charge neutrality level (CNL) model provided a reasonable description of the band alignment of the InN/p-Si interface and a change in the interface dipole by 0.06 eV was observed for InN/p-Si interface.

XPS and x-ray absorption-edge studies of the surface and bulk valence states of cerium in ceco2

XPS and LIII X-ray absorption edge studies regarding the valence state of cerium have been carried out on the intermetallic compounds CeCo2, which becomes superconducting at low temperatures. It is observed from XPS that the surface shows both Ce3+ and Ce4+ valence states, while the X-ray absorption edge studies reveal only Ce4+ in the bulk. Thus valence fluctuation and superconductivity do not coexist in the bulk of this compound.

Band-Structure Lineup at In0.2Ga0.8N/Si Heterostructures by X-ray Photoelectron Spectroscopy

In0.2Ga0.8N layers were directly grown on Si(111) substrate by plasma-assisted molecular beam epitaxy (PAMBE). Structural characteristics of the as-grown InGaN epilayers were evaluated high resolution X-ray diffraction and composition of InGaN was estimated from photoluminescence spectra using the standard Vegard's law. High-resolution X-ray photoemission spectroscopy measurements were used to determine the band offset of wurtzite-In0.2Ga0.8N/Si(111) heterojunctions. The valence band of InGaN is found to be 2.08 +/- 0.04 eV below that of Si. The conduction band offset (CBO) of InGaN/Si heterojunction is found similar to 0.74 eV and a type-II heterojunction. (C) 2012 The Japan Society of Applied Physics

Determination of MBE grown wurtzite GaN/Ge3N4/Ge heterojunctions band offset by X-ray photoelectron spectroscopy

Hexagonal Ge3N4 layer was prepared on Ge surface by in situ direct atomic source nitridation and it is promising buffer layer to grow GaN on Ge (111). The valence band offset (VBO) of GaN/Ge3N4/Ge heterojunctions is determined by X-ray photoemission spectroscopy. The valence band (VB) of Ge3N4 is found to be 0.38?+/-?0.04?eV above the GaN valance band and 1.14?+/-?0.04?eV below the Ge. The GaN/Ge3N4 and Ge3N4/Ge are found type-II and type-I heterojunctions, respectively. The exact measurements of the VBO and conduction band offset (CBO) are important for use of GaN/Ge3N4/Ge (111) heterosystems.

Constraints on axino warm dark matter from X-ray observation at the Chandra telescope and SPI

A sufficiently long lived warm dark matter could be a source of X-rays observed by satellite based X-ray telescopes. We consider axinos and gravitinos with masses between 1 keV and 100 keV in supersymmetric models with sin all R-parity violation. We show that axino dark matter receives significant constraints from X-ray observations of Chandra and SPI, especially for the lower end of the allowed range of the axino decay constant f(a), while the gravitino dark matter remains unconstrained.

Synchrotron Small-Angle X-ray Scattering Studies of Hemoglobin Nonaggregation Confined inside Polymer Capsules

The effect of confinement on the structure of hemoglobin (Hb) within polymer capsules was investigated here. Hemoglobin transformed from an aggregated state in solution to a nonaggregated state when confined inside the polymer capsules. This was directly confirmed using synchrotron small-angle X-ray scattering (SAXS) studies. The radius of gyration (R-g) and polydispersity (p) of the proteins in the confined state were smaller compared to those in solution. In fact, the R-g value is very similar to theoretical values obtained using protein structures generated from the Protein Databank. In the temperature range (25-85 degrees C, Tm 59 degrees C), the R-g values for the confined Hb remained constant. This observation is in contrary to the increasing R-g values obtained for the bare Hb in solution. This suggested higher thermal stability of Hb when confined inside the polymer capsule than when in solution. Changes in protein configuration were also reflected in the protein function. Confinement resulted in a beneficial enhancement of the electroactivity of Hb. While Hb in solution showed dominance of the cathodic process (Fe3+ -> Fe2+), efficient reversible Fe3+/Fe2+ redox response is observed in the case of the confined Hb. This has important protein functional implications. Confinement allows the electroactive heme to take up positions favorable for various biochemical activities such as sensing of analytes of various sizes from small to macromolecules and controlled delivery of drugs.

Equal channel angular pressing processing routes and associated structure modification: a differential scanning calorimetry and X-ray line profile analysis

The effectiveness of different routes of equal channel angular pressing (A, B-c, and C) is studied for commercially pure copper. The stored energy and the activation energy of recrystallization for the deformed samples were quantified using differential scanning calorimetry and X-ray diffraction line profile analysis. Results of the study revealed that the dislocation density and the stored energy are higher in the case of route B-c deformed sample. The activation energy for recrystallization is lower for route B-c. (C) 2012 International Centre for Diffraction Data doi:10.1017/S0885715612000310]

High-pressure synchrotron x-ray diffraction study of RMnO3 (R=Eu, Gd, Tb and Dy) upto 50 GPa

We have carried out synchrotron based high-pressure x-ray diffraction study of orthorhombic EuMnO3, GdMnO3, TbMnO3 and DyMnO3 up to 54.4, 41.6, 47.0 and 50.2 GPa, respectively. The diffraction peaks of all the four manganites shift monotonically to higher diffraction angles and the crystals retain the orthorhombic structure till the highest pressure. We have fitted the observed volume versus pressure data with the Birch-Murnaghan equation of state and determined the bulk modulus to be 185 +/- 6 GPa, 190 +/- 16 GPa, 188 +/- 9 GPa and 192 +/- 8 GPa for EuMnO3, GdMnO3, TbMnO3 and DyMnO3, respectively. The bulk modulus of EuMnO3 is comparable to other manganites, in contrast to theoretical predictions.

Crystallization and preliminary X-ray studies of MutT1 (MSMEG_2390) from Mycobacterium smegmatis

MutT1 (MSMEG_2390) from Mycobacterium smegmatis has been crystallized and the crystals have been characterized using X-ray diffraction. The crystals belonged to space group P2(1)2(1)2(1). The Matthews coefficient suggested the possibility of one protein molecule in the asymmetric unit of the orthorhombic unit cell. Solution of the structure using the known three-dimensional structure of a bacterial MutT1 is anticipated.

Ex Situ X-ray Diffraction, X-ray Absorption Near Edge Structure, Electron Spin Resonance, and Transmission Electron Microscopy Study of the Hydrothermal Crystallization of Vanadium Oxide Nanotubes: An Insight into the Mechanism of Formation

The nucleation and growth of vanadium oxide nanotubes (VOx-NT) have been followed by a combination of numerous ex situ techniques. long the hydrothermal process. Intermediate solid phases extracted at different reaction times have been characterized by powder X-ray diffraction, scanning and transmission electron microscopy, electron spin resonance, and V-K edge :X-ray absorption near-edge structure spectroscopy. The supernatant vanadate solutions extracted during the hydrothermal treatment have been studied by liquid V-51 NMR and flame. spectroscopy. For short durations of the hydrothermal synthesis, the initial V2O5-surfactant intercalate. is progressively transformed into VOx-NT whose crystallization starts to be detected after a hydrothermal treatment of 24 h. Upon heating from 24 h to 7 days, VOx-NT are obtained in larger amount and with an improved crystallinity. The detection of soluble amines and cyclic metavanadate V4O12](4-) in the supernatant solution along the hydrothermal process suggests that VOx-NT result from a dissolution precipitation mechanism. Metavanadate species V4O12](4-) could behave as molecular precursors in the polymerization reactions leading to VOx-NT.

Cloning, expression, purification, crystallization and preliminary X-ray crystallographic study of thymidylate kinase (TTHA1607) from Thermus thermophilus HB8

Nucleotide biosynthesis plays a key role in cell survival and cell proliferation. Thymidylate kinase is an enzyme that catalyses the conversion of dTMP to dTDP using ATP-Mg2+ as a phosphoryl-donor group. This enzyme is present at the junction of the de novo and salvage pathways; thus, any inhibitor designed against it will result in cell death. This highlights the importance of this enzyme as a drug target. Thymidylate kinase from the extremely thermophilic organism Thermus thermophilus HB8 has been expressed, purified and crystallized using the microbatch method. The crystals diffracted to a resolution of 1.83 angstrom and belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 39.50, b = 80.29, c = 122.55 angstrom. Preliminary studies revealed the presence of a dimer in the asymmetric unit with a Matthews coefficient (V-M) of 2.18 angstrom(3) Da(-1).