I. Ya. Nikiforov

Electronic band structure of In2S3 and CdIn2S4 semiconductor spinels from the data of x-ray spectroscopy and theoretical calculations

The electronic band structure of the chalcogenide spinels In2S3 and CdIn2S4 has been studied using the FEFF8 program. It is shown that the valence band top is formed by the S p states mixed with the In s and In p states for In2S3 or with the Cd s, Cd p, In s, and In p states for CdIn2S4. Compared to In2S3, the presence of Cd atoms in the nearest environment of S atoms in CdIn2S4 does not considerably affect the electronic band structure. In CdIn2S4 the Cd 4d states, as well as the In 4d states, form a narrow localized band shifted deep into the valence band. The theoretical results are in good agreement with the experimental x-ray photoelectron and x-ray spectra.

Electronic energy structure of non-stoichiometric cubic boron nitride

In terms of the multiple-scattering theory using the cluster version of the local coherent-potential approximation the electronic energy structures of both stoichiometric and non-stoichiometric cubic boron nitride have been calculated. It was found that vacancies induced in the sublattice of nitrogen in boron nitride resulted in a marked change in the nitrogen p-band, in a noticeable low-energy shift of the total density of electron states of the valence band and in the appearance of additional acceptor energy levels in the region of forbidden energies. The latter explains the twofold increase in the electrical conductivity of non-stoichiometric boron nitride in comparison with stoichiometric boron nitride found experimentally and calculated in the present work. The calculated partial and total densities of electron states of boron nitride have been used to explain the form of its experimental x-ray emission and x-ray photoelectron spectra.

Electronic structure of metal nanoclusters

The electronic structure and the shape of the K absorption edge for small-sized clusters formed by transition metal atoms (titanium, nickel, and copper) are investigated using the quantum-mechanical multiple scattering method (FEFF8 code) and the molecular mechanics technique. It is shown that the x-ray photoelectron spectra and K x-ray absorption spectra of clusters containing 55 and more atoms are similar to the corresponding experimental spectra of macroscopic samples. The computer simulation of the electronic structure and the shape of the K absorption edge is performed for nanoclusters whose equilibrium geometric shape is determined by the molecular dynamics method.

Electronic energy structure and X-ray spectra of GaN and BxGa1-xN crystals

The electronic energy structures of GaN wurtzite and zinc-blende modifications and BxGa1-xN solid solutions are calculated using the local coherent potential method and the cluster version of the muffin-tin approximation in the framework of the multiple-scattering theory. The electronic structures of binary GaN crystals and ternary BxGa1-xN solid solutions are compared, and their features are interpreted. The boron concentration dependences of the width of the upper subband of the valence band, the band gap, and the bulk modulus of BxGa1-xN solid solutions (x = 0.25, 0.50, 0.75) are studied, and these dependences are shown to be nonlinear.

On the shape of iron K absorption edges for monoferrites with a Me(Mg, Mn, Ni, Zn)Fe2O4 spinel structure

Calculations of the K-edge x-ray absorption near-edge structure (XANES) in a pure metal and in monoferrites of stoichiometric compositions MgFe2O4, MnFe2O4, NiFe2O4, and ZnFe2O4 are carried out using a FEFF8 program. It was confirmed that the Fe K-edge energy shift found experimentally occurs upon the transition from pure iron to monoferrites. It is demonstrated that this shift is identically directed for ferrites with a structure of normal (MnFe2O4, ZnFe2O4) and inverted (MgFe2O4, NiFe2O4) spinels, but numerical values of theoretical Fe K-edge shifts agree well with experimental data only for normal spinels.

Electronic energy structure and x-ray spectra of wide-gap AlN and BN crystals and BxAl1−xN solid solutions

The electronic energy structure of 2H and 3C AlN and BN crystals and BxAl1−xN solid solutions is calculated on the basis of the local coherent potential method using the cluster version of the MT approximation and the theory of multiple scattering. The features of the electronic structure of 2H-AlN crystals are compared with x-ray K and L absorption and emission spectra of aluminum and nitrogen. An interpretation of these features is given. The concentration dependences of the width of the upper subband of the valence band and the band gap in BxAl1−xN solid solutions (x = 0.25, 0.5, 0.75) are investigated. Charge transfer from aluminum to nitrogen atoms is shown to occur and increase with boron doping in both crystallographic modifications.

Electronic Energy Structure of TiCu and Ti2Cu

The electronic energy structure (EES) of the valence band in tetragonal TiCu and Ti2Cu was studied experimentally and theoretically. The experimental study of valence band EES was carried out by X-ray photoelectron spectroscopy (XPS). The calculations were performed in terms of the cluster version of multiple scattering theory in a self-consistent field approximation. The results are compared with X-ray emission spectroscopy data available in the literature. The density of state curves agree well with spectroscopic data. The major contribution to XPS is from the copper d-states. The specifics of chemical bonding in the compounds leading to the observed changes in the shape of the valence band X-ray photoelectron spectra are discussed.

Ab initio calculations of chemical bond parameters and the band structure of a two-dimensional system: Graphene/MnO(001)

The results of the DFT studies of the band structure, Fermi surface, and chemical bond in ultrathin graphene/MnO(001) and MnO(001) films are presented, and the features of the interatomic interactions at the initial stage of the growth of graphene islands on the manganese oxide surface are considered. The features of spin state in the valence band and at the Fermi level in these systems are discussed. The magnetic moment on the Mn atom is estimated, and the effect of spin polarization on oxygen and carbon atoms is found. Their nature is discussedBased on the structural energy calculations of 2D graphene/MnO(001) and 2D MnO(001), the stability of the systems is established, and the chemical bond energy is determined.

ELECTRONIC ENERGY STRUCTURE OF A SERIES OF CHALCOPYRITE-LIKE COMPOUNDS AgGaS2-CdGa2S4-InPS4

AbstractThe effect of pseudovacancies on the density of electronic states of valence electrons in AgGaS2, CdGa2S4, and InPS4 is studied both experimentally, by means of X-ray spectroscopy, and theoretically, by calculating the partial densities of electronic states using the local coherent potential. The compounds under study are the derivatives of the sphalerite structural type (doubled cell) with gradually increasing deficiency of metals from