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[en] X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were used to study the electronic structure of hexagonal h-WO3 and h-WO2.8 nanoparticles. For comparison, nanopowder substoichiometric monoclinic tungsten oxides with close content of oxygen atoms, namely m-WO3 and m-WO2.77 compounds, were also investigated. For the mentioned oxides, XPS valence-band and corelevel spectra, XES O Kα bands and XAS W LIII and O 1s edges were derived. The XPS valence-band spectra and O Kα emission bands in the mentioned hexagonal and monoclinic tungsten oxides were compared on a common energy scale. Both the O Kα bands and XPS valence-band spectra broaden somewhat in the sequences h-WO3 → h-WO2.8 and m-WO3 → m-WO2.77, with the half-widths of the spectra being somewhat higher for the hexagonal oxides as compared with those for the monoclinic compounds. The effective positive charge state of tungsten atoms in h-WO2.8 is very close to that in m-WO2.77, but the negative charge states of oxygen atoms are close to each other for all the tungsten oxides under consideration
[en] Results of studies of the electronic structure of carbon-containing porous materials derived by tolylene-diisocyanate (TDI) carbonization in a matrix of Al2O3 are presented in this paper. It has been established that products of TDI carbonization are fine spherical clusters (with their sizes of about 10 nm) that reveal a strong bonding with the matrix. The shapes of X-ray emission CKα and OKα bands are different for volume and surface parts of the materials. Our study reveals different electronic structures of the materials in volume and surface parts. It has been established that the shape of the X-ray emission CKα band of the volume part of products of carbonization of TDI in the Al2O3 matrix corresponds to that of mixture of the bands of fullerene C60 and graphite, but the shape of the band of the surface part resembles that of the CKα band of graphite. The shape of the X-ray emission OKα band of the volume part of the products of TDI carbonization resembles that of the band of γ-Al2O3, while that of the surface part corresponds to the shape of the OKα band of Al(OH)3.
[en] We report on a facile method of synthesis of Cr2O3 nanoparticles by hydrothermal method. Chromium sulfate was used as a starting material whereas urea was used as a strong reducing agent. Cr2O3 nanoparticles, with rhombohedral crystal structure, have been synthesized, when the reaction solution was treated under hydrothermal condition at high pH (10). At pH = 8 amorphous Cr2O3 powders were obtained. Chromium oxide could not be synthesized in the absence of urea. Two different Raman modes have been detected for the final products synthesized at the high pH value. As-prepared Cr2O3 nanoparticles reveal agglomeration as evidenced from scanning electron microscope (SEM) images. Flake-like Cr2O3 nanoparticles, 20 to 50 nm in size, show clear lattice fringes through the high resolution transmission electron microscope (HRTEM) images. The electronic structure of the Cr2O3 nanoparticles has been studied employing x-ray photoelectron spectroscopy (XPS) and x-ray emission spectroscopy (XES) methods. (paper)
[en] It is shown that narrow band gap semiconductors Tl_1_−_xIn_1_−_xGe_xSe_2 are able effectively to vary the values of the energy gap. DFT simulations of the principal bands during the cationic substitutions is done. Changes of carrier transport features is explored. Relation with the changes of the near the surface states is explored . Comparison on a common energy scale of the x-ray emission Se Kβ _2 bands, representing energy distribution of the Se 4p states, indicates that these states contribute preliminary to the top of the valence band. The temperature dependence of electrical conductivity and spectral dependence photoconductivity for the Tl_1_−_xIn_1_−_xGe_xSe_2 and Tl_1_−_xIn_1_−_xSi_xSe_2 single crystals were explored and compared with previously reported Tl_1_−_xIn_1_−_xSn_xSe_2. Based on our investigations, a model of centre re-charging is proposed. Contrary to other investigated crystals in Tl_1_−_xIn_1_−_xGe_xSe_2 single crystals for x = 0.1 we observe extraordinarily enormous photoresponse, which exceed more than nine times the dark current. X-ray photoelectron core-level and valence-band spectra for pristine and Ar"+-ion irradiated surfaces of Tl_1_−_xIn_1_−_xGe_xSe_2 (x = 0.1 and 0.2) single crystals have been studied. These results indicate that the relatively low hygroscopicity of the studied single crystals is typical for the Tl_1_−_xIn_1_−_xGe_xSe_2 crystals, a property that is very important for handling these quaternary selenides as infrared materials operating at ambient conditions. (paper)
[en] The effect of exchange-correlation potential on InPS4 electronic structure was studied by applying GGA, GGA + U, mBJ, and mBJ + U potentials in the Kohn–Sham framework. The use of mBJ + U in full potential APW + lo method results in reliable K-absorption spectrum, which consists of nearly full experimental peaks of right intensity. The remarkable discrepancy between and occurs at 0 eV, 4 eV, 6 eV, and 9.5 eV, indicating the strong anisotropic optical properties of InPS4 at these energy levels. At 4 eV, is 37% higher than The optical absorption of InPS4 has high order of 105cm−1 magnitude for wide energy range, at least within 4–20 eV. The difference in extinction coefficient and is 30%–50% at 4 eV, 6 eV, 8 eV, and 11 eV. The figure of merit ZT of InPS4 is rather low. At n = 8 × 1018 cm−3, ZT achieves its highest value of about 0.8–1. InPS4 is a p-type semiconductor for chemical potential μ ranging from 0 eV to about 1.6 eV, but it is an n-type semiconductor for μ of about 1.6–2.7 eV. The Poisson’s ratio is equal to 0.26 and B/G 1.75. Indium thiophosphate InPS4 possesses rather low deformation resistance with the Young and shear moduli of 38.47 GPa and 15.27 GPa, respectively. (paper)