Galina Yalovega

Photoabsorption of NaCl clusters at the Na K-edge: Development of the bond length with the cluster size

Photoabsorption spectra of free and deposited NaCl clusters at the Na K-edge are presented. The absorption spectra were recorded using the yield of photoelectrons and cluster ions. Above the K-shell ionization limit, multi-scattering-type oscillations could be identified which allow the determination of bond length in the cluster. The variation of the bond length with cluster size is in reasonable agreement with model calculations, assuming a Coulomb interaction and a Born–Meyer type repulsion of the ions.

Geometric structure of (NaCl)4 clusters studied with XANES at the chlorine L-edge and at the sodium K-edge

Abstract X-ray absorption near edge structure (XANES) spectra at the sodium K-edge and chlorine L-edge of Na4Cl4 clusters have been studied. A theoretical ab initio analysis of XANES, based on full multiple scattering theory, is compared to experiment. To study the cluster geometry XANES spectra have been simulated for several different structural models including one obtained here from density functional theory (DFT). The results obtained show a significant dependence on the interatomic Na–Cl distance and also support a Td distortion from a perfect Na4Cl4 cube.

Local atomic and electronic structure of Al90FexCe10‐x alloys: XAFS analysis

X-ray absorption fine structure (XAFS) above the Fe K-edge and the Ce L3-edge in amorphous Al90Fe(x)Ce10-x (x = 3, 5, and 7) alloys have been measured and analyzed. Quantitative analyses of the Fe K-edge and Ce L3-edge EXAFS spectra are limited to local structure parameters of the first coordination sphere. Using a theoretical multiple scattering (MS) approach, we show that the Fe and Ce XANES are sensitive to the structure of coordination spheres, which extend up to nearly 4.5 A. Comparison of experimental XANES spectra with theoretical MS results allows one to determine the local structure around the iron and cerium sites up to at least the third shell of atoms.

X-ray spectroscopic identification of garnet from the placer deposits of the Taman peninsula

Garnet from recent placer deposits of the Taman peninsula has been investigated by energy-dispersive X-ray fluorescence microanalysis and X-ray absorption near-edge structure (XANES) spectroscopy. Energy-dispersive X-ray fluorescence microanalysis showed that the chemical composition of the garnet under study corresponds to pyrope-almandine-spessartine series. The Fe K-edge X-ray absorption spectra of garnet have been recorded using a Rigaku R-XAS laboratory spectrometer. Iron K-edge XANES spectra for two iron-containing garnet minals (components), almandine and andradite, have been calculated using the full multiple-scattering and finite-difference methods. Based on a comparison of the experimental and theoretical Fe K-XANES spectra, it is concluded that recent magnetite-garnet placer deposits of the Taman peninsula contain garnet in the form of almandine.

Synthesis and Characterization of MnCrO4, a New Mixed-Valence Antiferromagnet

A new orthorhombic phase, MnCrO4, isostructural with MCrO4 (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH4)2Cr2O7 + 2 Mn(NO3)2, followed by calcination at 400 °C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO4 phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn(2+)Cr(6+)O4. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at TN ≈ 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above TN. MnCrO4 is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 °C to form first Cr2O3 plus Mn3O4 and then Mn1.5Cr1.5O4 spinel.

Potential antitumor gold drugs: DFT and XANES studies of local atomic and electronic structure

Geometry structure optimization of the potential antitumor agent Au(bipy)(OH)2 was carried out by means of density functional theory simulations. The experimental Au L3-edge X-ray absorption near edge structure (XANES) spectrum of Au(bipy)(OH)2 was obtained. The theoretical Au L3-XANES spectra of the gold(III) complex Au(bipy)(OH)2 were simulated using both the self-consistent real-space full multiple scattering theory within the muffin-tin approximation for the potential shape and the full-potential finite difference method. The comparison of the theoretical spectra with the experimental XANES is discussed. The exact local atomic structure of gold complex Au(bipy)(OH)2 has been defined by two independent ab initio methods.

Nearest surroundings of aluminum atoms and features of the electron structure of Al90FexCe10−x alloys (x=3, 5, 7)

The spectra of x-ray absorption near-edge structure (XANES) were measured at the K-edge of aluminum in Al90FexCe10 −x alloys (x=3, 5, 7). A theoretical XANES analysis at the Al K-edge was performed for Al90Fe5Ce5 by using the multiple scattering algorithm. A comparison of the experimental and theoretical results allowed establishment of the most probable model of local surroundings of aluminum atoms in the alloy system studied. The density of free Al and Fe electron states in the conduction band was determined. It was found that the interaction between Al p states and Fe d states leads to pushing of the former states by the latter ones.

Local geometry and electronic structure of free NaCl clusters

Experimental x-ray spectra of the Cl L2, 3 absorption edge for free NaCl clusters of various sizes are presented. X-ray absorption spectra of the Na4Cl4 cluster have been theoretically calculated by the total multiple scattering method. A distorted cube is determined as the most probable geometric structure of the Na4Cl4 cluster. Curves of the partial densities of states are obtained for the cluster.

Morphology, Atomic and Electronic Structure of Metal Oxide (CuOx, SnOx) Nanocomposites and Thin Films

We investigated the surface morphology , oxidation state , local and electronic structure of a number of metal oxide (CuOx, SnOx) nanoparticles , nanocomposites and thin films based on them, synthesized by electrochemical deposition and sol-gel techniques. Surface morphological studies were carried out using a SEM (scanning electron microscopy). The bonding structure with element sensitivity to Cu and Sn, local environment and electronic structure were studied by the XPS (X-ray photoelectron spectroscopy) and the XANES (X-ray absorption near edge structure ) spectroscopy. The changes in local and electronic structure , oxidation state and the surface morphology of nanocomposites in the interaction of metal oxide nanoparticles with CNT (carbon nanotubes) and SiO2 (silicon oxide) matrices were observed. We discovered that the shape and size of metal oxide nanoparticles depend on metal oxidation state as well as parameters of synthesis and, moreover, kind of matrix affect in direction of the nano-unit nucleation and subsequent organization of metal oxide nanoparticles /microcrystals.

Analysis of the local atomic structure of aluminum nitride nanoparticles

The structure of synthesized AlN nanoparticles was studied based on the theoretical analysis of X-ray absorption spectra near the K-absorption edge of aluminum. The method of full multiple scattering and finite difference method were used for theoretical calculations. The set of phases being present in nanoparticles and concentrations of different phases are determined. It turned out that besides cubic and hexagonal AlN phases the pure Al metal phase is present in synthesized objects.