Yu. M. Yarmoshenko

Electronic structure of VO2 studied by x-ray photoelectron and x-ray emission spectroscopies

A single crystal has been the subject of a combined investigation by high-resolution x-ray photoelectron spectroscopy (XPS), x-ray emission spectroscopy (XES) with both electron and energy-selective x-ray excitation (, and emission) and x-ray absorption spectroscopy (XAS) . We performed first-principles tight-binding LMTO band-structure calculations for in both the monoclinic and tetragonal rutile phases and compared the densities of states (DOS) with the experimental data. From this we conclude that the electronic structure of is more bandlike than correlated.

Electronic structure of Co x TiSe 2 and Cr x TiSe 2

The results of investigations of intercalated compounds Cr_xTiSe_2 and Co_xTiSe_2 by X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES) are presented. The data obtained are compared with theoretical results of spin-polarized band structure calculations. A good agreement between theoretical and experimental data for the electronic structure of the investigated materials has been observed. The interplay between the M3d--Ti3d hybridization (M=Cr, Co) and the magnetic moment at the M site is discussed. A 0.9 eV large splitting of the core Cr2p{3/2} level was observed, which reveals a strong exchange magnetic interaction of 3d-2p electrons of Cr. In the case of a strong localization of the Cr3d electrons (for x<0.25), the broadening of the CrL spectra into the region of the states above the nominal Fermi level was observed and attributed to X-ray re-emission. The measured kinetic properties are in good accordance with spectral investigations and band calculation results.

Valence band spectra of 4d and 5d silicides

A full study of the electronic structure of 4d and 5d silicides (RuSi, RhSi, PdSi, OsSi, IrSi, , PtSi) is undertaken including XPS VB and XES ( and ) measurements and LMTO band structure calculations. It is found that d bands which dominate the density of states are more localized with increasing atomic number Z of the transition metal. A strong hybridization between silicon 3p and transition metal d states occurs over the entire valence band. Si 3s states are found to be not mixed with Si 3p and nd states but Si 3d states participate in bonding and hybridize with transition metal d states. The non-bonding character of the majority of nd states is not confirmed for 4d and 5d silicides.

Electronic structure of titanium dichalcogenides TiX 2 (X = S, Se, Te)

The electronic structure and the chemical bond in titanium dichalcogenides TiX2 (X = S, Se, Te), which are promising electrode materials for lithium batteries, are studied experimentally and theoretically. It is found that the X-ray photoelectron spectra of the valence bands and the core levels of titanium and its X-ray L2, 3 absorption spectra demonstrate a change in the ionic and covalent components of the chemical bond in these compounds. The densities of states in these compounds are calculated by the full-potential augmented-plane-wave method, and multiplet calculations of the X-ray L2, 3 absorption spectra of titanium are performed. It is shown that, in the row TiS2-TiSe2-TiTe2, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

Electronic structure of FeSi

A full set of high-energy spectroscopy measurements including x-ray photoelectron valence band spectra and soft x-ray emission valence band spectra of both components of FeSi (FeKbeta 5, FeLalpha , SiK( beta 1,3) and SiL2,3) are performed and compared with the results of ab initio band structure calculations using the linearized muffin-tin orbital method and the linearized augmented plane wave method.

Analysis of the depth profile of Fe-Si buried layers in Fe+-implanted Si wafer by soft X-ray emission spectroscopy

Abstract The results of an investigation of Fe-implanted (E = 40 keV, D = 1016 cm-2) silicon crystal by the use of soft X-ray emission spectroscopy with a variation of the exciting electron energy are presented. Based on the study of X-ray SiL2,3, Fe Lα and Si Kα spectra obtained at various exciting electron energies, the concentration profile as a function of the depth is constructed. The thickness of a buried FeSi-FeSi2 layer is estimated to be about 2000 A.

Local magnetic moments at X-ray spectra of 3d metals

Abstract The Mn X-ray emission spectra and X-ray photoelectron spectra of Mn-based Heusler alloys Co 2 MnAl, Co 2 MnSb and La 1− x Sm x Mn 2 Si 2 rare-earth compounds ( x =0, 0.8) have been measured and discussed in connection with a value of the local magnetic moment at Mn site. The spectra peculiarities reflect also the localization degree of 3d valence electrons of 3d metals in the considered compounds and could be used as an indicator of the closeness of the density of states to half-metallic character.

X-ray emission spectra of YSr2Cu3O7−δ containing sulphate and phosphate groups

Abstract X-ray emission Kα 1,2 and Kβ 1 spectra of sulphur and phosphorus in [Y 0.89 Sr 0.11 ]Sr 2 Cu 2.78 (SO 4 ) 0.22 O 6.12 and YSr 2 Cu 2.79 (PO 4 ) 0.21 O 6.16 have been investigated. According to an analysis of their fine structure and energy position it is confirmed that the S and P atoms indeed enter superconducting cuprates in the form of oxyanions. It is also found that in YSr 2 Cu 3 O 7−δ containing sulphate groups 0.2 vol.% of CuS is present as an additional phase.

Sulphur-oxygen substitution in YBa2Cu3O6+xSy analyzed by means of X-ray emission spectroscopy

Abstract The analysis of substitution effects upon doping of YBa2Cu3O6+xSy by sulphur is given on the basis of the investigation of S Kα1,2 and S Kβ1 X-ray emission spectra. It is found that sulphur can enter the lattice of YBa2Cu3O7 and substitute oxygen atoms. With increasing sulphur concentration from y > 0.5 to 2.0 S atoms form isolated sulphate groups which do not have a long order but can be detected by X-ray emission spectroscopy.

X-ray spectra and electronic structure of high-Tc superconductors La1.83Sr0.17CuO4 and Bi4Ca3Sr3O16

Abstract X-ray emission, O Kα, Cu Lα, Cu Kβ5 spectra, O 1s total electron yield spectra and Cu K absorption spectra for the high-Tc superconductors La1.83Sr0.17CuO4 and Bi4Ca3Sr3Cu4O16+y have been studied. Spectra of different series and components have been compared in the same energy scale by using Cu 2p and O 1s binding energies and the energies of Cu Kα1 lines. It was found that in given oxides the maximum of O 2p states lies closer to the Fermi level than that of Cu 3d states. Cu 4p states were found to be mixed with the low-energy part of hybridized Cu 3d-O 2p band.