M. V. Yablonskikh

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.

Local electronic structure of Mn dopants in ZnO probed by resonant inelastic x-ray scattering

The electronic structure of Mn dopants in ZnO epitaxial thin films synthesized at different temperatures has been investigated using resonant inelastic x-ray scattering. The resulting Mn L2,3 x-ray emission spectra of Zn0.8Mn0.2O (resonantly excited at L2 and L3 absorption edges) reveal different spectral features depending on the growth temperature of the films. The relative integral intensity ratio of Mn L2 to Mn L3 emission lines is greatly suppressed in the case of nonmagnetic Zn0.8Mn0.2O grown at 700 ◦ C due to L2L3M4,5 Coster‐ Kronig transitions. The ferromagnetic sample grown at 600 ◦ C exhibits a normal oxide structure. The results suggest that a high growth temperature causes direct Mn‐Mn bonds from the segregation of Mn atoms in ZnO. Therefore the disappearance of ferromagnetism in Mn-doped ZnO can be attributed to antiferromagnetic Mn‐Mn exchange interactions due to the inhomogeneous local environment around the Mn impurities.

An X-ray spectrscopy study of the electronic structure of TiS3

X-ray photoemission and absorption spectra of TiS3 are studied. The temperature dependence of the magnetic susceptibility is measured and the electron density of states is calculated. Titanium ions in different oxidation states are found to coexist.

On the bonding situation in TlCo2Se2

The electronic structure of TlCo2Se2 has been investigated by means of band structure calculations and x-ray photoelectron and emission spectroscopy (XPS and XES). The formation of the valence band is described in connection with calculations of partial densities of states of the valence band and Co Lα,β x-ray emission () aligned to the binding energy scale. The experimental results are in agreement with the calculated distribution of Co 3d states, which lie close to the Fermi level. The effect of Co–Se bonding is seen as satellite structures in the XPS Co 2p signals. Thermoelectric and Hall effect data as well as resistivity measurements show that TlCo2Se2 is metallic with electron holes as charge carriers with broadband mobility characteristics. The observed anisotropy of the resistivity in the ab plane and along c remains constant as a function of temperature, i.e. without signs of the magnetic ordering that occurs (TN~85 K). The results of local spin density functional calculations show ferromagnetic coupling within the cobalt plane as a result of direct magnetic interactions between the magnetic moments.

Resonance photoelectron spectroscopy of TiX2 (X = S, Se, Te) titanium dichalcogenides

The photoelectron valence band spectra of TiS2, TiSe2, and TiTe2 dichalcogenides are investigated in the Ti 2p-3d resonance regime. Resonance bands in the vicinity of the Fermi energy are found for TiS2 and TiTe2. The nature of these bands is analyzed based on model calculations of the density of electronic states in TiS2, TiSe2, and TiTe2 compounds intercalated by titanium atoms. Analysis of experimental data and their comparison with model calculations showed that these bands have different origins. It is found that the resonance enhancement of an additional band observed in TiS2 is explained by self-intercalation by titanium during the synthesis of this compound. The resonance enhancement in TiTe2 is caused by occupation of the 3d band in Ti.

Optical XAFS of ZnO Nanowires at the Zn K‐Edge and Related Phenomena

We report x‐ray excited optical luminescence (XEOL) from one‐dimensional nanostructures of ZnO excited with photon energies across the Zn K‐edge. The optical luminescence shows an UV and a green emission band characteristic of near band edge and defect emission, respectively. The optical channels were used in turn to monitor the Zn K‐edge XAFS to high k values. The densities of states of oxygen character in the valence band were also studied with x‐ray emission spectroscopy (XES). The Zn K‐edge decay dynamics was examined with time‐resolved x‐ray excited optical luminescence.

Observing of Ti, Cr and Mn 2p-3d resonance in valence band of titanium dichalcogenides

Ti, Mn, Cr 2p-3d resonant photoemission for compounds with substitution of Ti atoms of host lattice by the Cr atoms CrxTi1-xSe2 and for compounds with intercalation of Mn and Cr atoms MnxTiSe2, CrxTiTe2 is studied. It is shown that the resonant behaviour depends on the geometry of survey, on 3d metal atoms lattice positions and on the magnitude and localization of atomic magnetic moment.