Electronic structures of NiO, CoO, and FeO studied by 2p core-level x-ray photoelectron spectroscopy

Specific features of the electronic structure of CoxTiSe2 according to the resonant photoemission data

The effect of atomic ordering in the Co sublattice on the electronic structure of the Co_xTiSe₂ compounds has been studied using a complex of spectral techniques – XPS, XAS, and ResPES, along with theoretical calculations of the total and partial DOS.

Two-photon photoemission from CoO layers on Ir(1 0 0)

Two-photon photoelectron spectroscopy is used to study the unoccupied electronic states of cobalt oxide layers on Ir(1 0 0). For thicker layers of (1 0 0) orientation the conduction band minimum is found 2 eV above the Fermi level. Layers with (1 1 1) orientation and thickness ≤4 bilayers show a peak around 3.4 eV energy and no evidence for the conduction band minimum. This is attributed to the metallic character of thin CoO(1 1 1) layers.

Strongly correlated electrons in the [Ni(hmp)(ROH)X]4 single molecule magnet: a DFT+U study

The single-molecule magnet [Ni(hmp)(MeOH)Cl]4 (hmp denotes the anion of 2-hydroxymethylpyridine and Me denotes methyl) is studied using both density functional theory (DFT) and the DFT+U method, and the results are compared. By incorporating a Hubbard-U like term for both the nickel and oxygen atoms, the experimentally determined ground state is successfully obtained, and the exchange coupling constants derived from the DFT+U calculation agree with experiment very well. The results show that the nickel 3d and oxygen 2p electrons in this molecule are strongly correlated, and thus the inclusion of on site Coulomb energies is crucial to obtaining the correct results.

Electronic and local structural changes in Li2+xTi3O7ramsdellite compounds upon electrochemical Li-ion insertion reactions by X-ray absorption spectroscopy

Electronic and local structural changes in ramsdellite-type Li(2+x)Ti3O7 compound were investigated by X-ray absorption spectroscopy (XAS) measurements. Upon electrochemical Li-ion insertions, the host lattice with ramsdellite structure is retained, indicated by X-ray powder diffraction. Ti K-edge extended X-ray absorption fine structure (EXAFS) analysis shows, however, slight local structural distortions around Ti ions. The energy shifts and the changes in the peak intensity of Ti K-edge and Ti L-edge XAS reveal the reducing oxidation states of Ti ions as the amount of electrochemically-inserted Li-ion increases. Equally important, oxide ions have a significant effect on the electronic transfer process, suggested by O K-edge XAS. These results on electronic structural changes were interpreted using the Zaanen-Sawatzky-Allen scheme.

Core-level x-ray photoemission satellites in ruthenates: a new mechanism revealing the Mott transition

Core-level x-ray photoemission spectra for the Mott-Hubbard systems are calculated by the dynamical mean-field theory based on the exact diagonalization method. The spectra show a two-peak structure, screened and unscreened peaks. The screened peak is absent in a Mott insulator, but develops into the main peak when the correlation strength becomes weak and the system turns metallic. The calculated spectral behavior is consistent with the experimental Ru 3d core-level spectra of various ruthenates. This new mechanism of the core-level photoemission satellite can be utilized to reveal the Mott transition phenomenon in various strongly correlated electron systems, especially in nanoscale devices and phase-separated materials.

Interplay of intra-atomic and interatomic effects: an investigation of the 2p core level spectra of atomic Fe and molecular FeCl2

The 2p photoabsorption and photoelectron spectra of atomic Fe and molecular FeCl2 were studied by photoion and photoelectron spectroscopy using monochromatized synchrotron radiation and atomic or molecular beam technique. The atomic spectra were analyzed with configuration interaction calculations yielding excellent agreement between experiment and theory. For the analysis of the molecular photoelectron spectrum which shows pronounced interatomic effects, a charge transfer model was used, introducing an additional 3d(7) configuration. The resulting good agreement between the experimental and theoretical spectrum and the remarkable similarity of the molecular with the corresponding spectrum in the solid phase opens a way to a better understanding of the interplay of the interatomic and intra-atomic interactions in the 2p core level spectra of the 3d metal compounds.