V. R. Galakhov

Electronic structure, x-ray spectra, and magnetic properties of the LiCoO2−δ and NaxCoO2 nonstoichiometric oxides

This paper reports on a study of the magnetic susceptibility, x-ray photoelectron, and x-ray emission spectra of the LiCoO2−δ and NaxCoO2 nonstoichiometric oxides. The valence-band structure of LiCoO2 was analyzed. The hole concentration in the oxygen 2p band of LiNiO2 and LiCoO2 was derived from measurements of the O Kα emission spectra. Measurements of Co 2p and Co 3s photoelectron spectra showed that the Co3+ ions reside in the low-spin state with S=0. The deficiency of oxygen in the LiCoO2−δ reduced oxides gives rise to the formation of divalent cobalt ions. The deficiency of the alkali metal in NaxCoO2 initiates the formation of holes in the oxygen 2p band while not changing the electronic configuration d6 of the cobalt-ion ground state.

Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-ray Absorption, Emission, and Photoelectron Spectroscopies

The electronic structure of nickel nanoparticles encapsulated in carbon was characterized by photoelectron, X-ray absorption, and X-ray emission spectroscopies. Experimental spectra were compared with the density of states calculated in the frame of density functional theory. The carbon shell of Ni nanoparticles has been found to be multilayer graphene with a significant (about 6%) amount of Stone–Wales defects. Results of the experiments evidence protection of the metallic nanoparticles from environmental degradation by providing a barrier against oxidation at least for 2 years. Exposure in air for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles with coverage of functional groups.

Semiconductor-metal transition in defect lithium cobaltite

The magnetic susceptibility, electrical conductivity, and x-ray photoelectron and x-ray absorption spectra of defect lithium cobaltites of the general formula Li1 − xCoO2 are investigated. It is found that, for lithium cobaltites with x > 0.25, the magnetic susceptibility increases abruptly and the conductivity type changes at T ∼ 150 K. The assumption is made that the semiconductor-metal transition in defect lithium cobaltite is caused by the increase in the diffusion mobility of lithium ions with an increase in the temperature when there is a correlation between spatial distributions of lithium vacancies and “electron” holes.

Electronic structure of FeCr2S4 and Fe0.5Cu0.5Cr2S4

A full study of the electronic structures of FeCr2S4 and Fe0.5Cu0.5Cr2S4 is reported based on x-ray photoelectron spectra (valence band and core levels), x-ray emission spectra (Fe Lα, Cu Lα, Cr Lα, S Kβ1,3 and S L2,3) and ab initio TB-LMTO band structure calculations. In the valence band of FeCr2S4, the Fe 3d states are found to be more localized than the Cr 3d states, which dominate at the Fermi level. In Fe0.5Cu0.5Cr2S4, the distribution of Cr 3d (Cr3+) states is unchanged and the Cu ions were found to be in the Cu+ state.

Soft x-ray emission spectra and ferromagnetism in wide-gap doped semiconductors

A study is made of the resonant and nonresonant L x-ray emission spectra of impurities in the semiconducting compounds ZnS:Mn, ZnO:Mn, ZnO:Co, and Co2O:Mn. An analysis of the Mn L2,3 x-ray emission spectra of Zn1−xMnxS (x=0.1–0.3) reveals that the Mn impurities do not form clusters in the ZnS lattice. Studies of the Mn L2,3 spectra and electronic structure of epitaxial films of Zn0.8Mn0.2O annealed at different temperatures show that the cause of the observed suppression of ferromagnetism at T>600°C is segregation of Mn atoms. In this case the Mn atoms occupy both Zn sites and interstitial positions. For Zn1−xCoxO (x=0.02, 0.06, and 0.10) the absence of free carriers that could mediate an exchange interaction between Co ions is established. Mn L2,3 x-ray emission measurements show that in Mn-doped oxides Cu2O synthesized at 650 and 800°C the Mn atoms are found both in interstitial positions and occupy Cu sites, but the configurations of these defects depend on the synthesis temperature. A decrease of the ...

Effect of atomic magnetic moments on the relative intensity of the Lβ and Lα components in x-ray emission spectra of 3d transition metal oxides

The integrated-intensity ratio R of the Lβ and Lα lines in x-ray emission spectra of 3d transition metal oxides was measured. The magnitude of the ratio was found to depend nonmonotonically on the atomic number of the 3d elements, with a sharp rise in the middle of the series. In terms of the theory of one-electron resonant x-ray scattering in a solid, a simple relation was derived connecting this ratio with the spin polarization of occupied and empty d states. The calculated values of R qualitatively reflect the behavior of the measured I(Lβ)/I(Lα) ratio on the atomic number of 3d elements. Thus, the existence of a dependence of the integrated-intensity ratio of Lβ and Lα lines on the atomic magnetic moment has been established. All calculated R curves lie above the I(Lβ)/I(Lα)exp data, because not all factors accompanying the x-ray emission process were included in the calculation.

Electronic structure of highly ordered Sr2FeMoO6: XPS and XES studies

We have investigated the partial densities of states of Sr2FeMoO6 by applying soft x-ray emission spectroscopy (XES) to the Fe?L, the Mo?M and the O?K edges. We discuss the results in the light of complementary measurements of the valence band by means of x-ray photoelectron spectroscopy (XPS) and first-principles generalized gradient approximation (GGA) and LDA +U band structure calculations.

The influence of high-energy electron irradiation and boron implantation on the oxide thickness in the /Si system

The system exposed to irradiation with 11 - 12 MeV electrons was studied by soft-x-ray emission spectroscopy using the variable-exciting-electron-energy, optical ellipsometry, and nuclear reaction techniques. For the system prepared on an n-substrate, oxidation of Si was observed, and the thickness of the layer after electron irradiation was estimated. For the system prepared on a p-Si substrate, irradiation-induced oxidation was not observed. It was found that preliminary boron implantation in the -Si system blocks oxidation of the n-Si substrate exposed to electron irradiation.

Electronic structure and valence-band spectra of Bi4Ti3O12.

The x-ray photoelectron valence band spectrum and x-ray emission valence-band spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented (analyzed in the common energy scale) and interpreted on the basis of a band-structure calculation for an idealized I4/mmm structure of this material.

Electronic structure and resonant X-ray emission spectra of carbon shells of iron nanoparticles

The electronic structure of carbon shells of carbon encapsulated iron nanoparticles carbon encapsulated Fe@C has been studied by X-ray resonant emission and X-ray absorption spectroscopy. The recorded spectra have been compared to the density functional calculations of the electronic structure of graphene. It has been shown that an Fe@C carbon shell can be represented in the form of several graphene layers with Stone-Wales defects. The dispersion of energy bands of Fe@C has been examined using the measured C Kα resonant X-ray emission spectra.