Yasuhisa Tezuka

Photoemission and Bremsstrahlung Isochromat Spectroscopy Studies of TiO2 (Rutile) and SrTiO3

Photoemission and bremsstrahlung isochromat spectra have been measured on TiO 2 (rutile) and SrTiO 3 . The magnitudes of the fundamental band gaps estimated from the combined spectra agree well with the results of the photoabsorption and the energy-band calculations. The profiles of the observed spectra do not reveal the fine structure expected to occur in the density-of-states curves obtained by the energy band calculations, suggesting the existence of a mechanism to smear out the fine structure considerably. The combined spectra are used to interpret the charge-transfer-type satellite manifest in the core-level spectra. For 3 s photoemission, satellite features ascribed to the configuration interaction between the 3 s 3 p 6 and 3 s 2 3 p 4 3 d states in the atomic notation are also observed.

Resonant Soft X-ray Emission Study of Rutile (TiO 2)

The Ti2 p and O1 s soft X-ray emission spectra were measured on rutile (TiO 2 ) in the energy region of Ti2 p - and O1 s -excitation threshold. The ordinary fluorescence spectra resolve the valence band into the Ti3 d and O2 p components. On the other hand, a Raman and an elastic scattering peaks were observed in the soft X-ray emission spectra. The Raman scattering peak is resonantly enhanced at excitation energies corresponding to Ti2 p absorption peaks. The Raman scattering is assumed to be caused by the elementary excitation of charge transfer excitation from O2 p valence band to Ti3 d conduction band. The O1 s - and Ti2p-absorption spectra shift to lower energy by about 0.5 and 2.2 eV due to core hole potentials, respectively.

Spectrometer for polarized soft X-ray Raman scattering

An experimental system for polarized soft X-ray Raman scattering spectroscopy has been constructed. The soft X-ray spectrometer is based on the Rowland circle geometry with a holographic spherical grating. Three types of gratings are used to cover the energy range from 18 eV to 1200 eV. According to a ray-trace simulation, the resolution is expected to be 200 meV at 700 eV by using a 10 micro m slit width. The polarized and depolarized soft X-ray Raman scattering spectra can be measured by rotating the soft X-ray spectrometer around the axis of the incident beam. Preliminary measurements of polarized and depolarized spectra were accomplished at undulator beamline BL-2C of the Photon Factory.

Origin of the metallic conductivity in PdCoO2 with delafossite structure

Abstract Valence state, valence band structure and specific heat of metallic oxide PdCoO 2 with the delafossite structure, which has alternative layers of Pd, Co and O ions with a formation of each triangular lattice, are first investigated using polycrystalline samples by means of photoelectron spectroscopy and specific heat measurements. The lowest electrical resistivity in PdCoO 2 among the whole conductive oxides is attributable to a half-filled band formed by s–d hybrid orbitals originated from the monovalent Pd ions and coordinated oxygens.

Ti 2p and Resonant 3d Photoemission Spectra of Ti2O3

We have measured experimentally and analyzed theoretically the Ti 2 p X-ray photoemission spectra (XPS) and the resonant enhancement of valence photoemission at the Ti 2 p threshold for Ti 2 O 3 . A satellite structure of the 2 p XPS is interpreted as the charge transfer (CT) satellite based on the analysis with a cluster model. The behavior of the resonant photoemission is understood in terms of the effect of strong covalency hybridization. It is shown that Ti 2 O 3 is classified as an intermediate-type insulator between the CT insulator and the Mott-Hubbard insulator.

Photoemission Study of the Spectral Function of V2O3 in Relation to the Recent Quantum Monte Carlo Study

Photoelectron energy distribution curves near the Fermi level have been measured on V 2 O 3 above and below the critical temperature of the metal-insulator transition. In insulating phase, the band gap was found to be about 0.2 eV, which is consistent with the other experimental results. A clear Fermi edge, which becomes sharp at lower temperature, is found in the metallic phase. The 3d spectral feature is discussed in relation to the recent quantum-Monte-Carlo calculation. Resonant photoemission shows the hybridization effect is also important for the spectral feature.

Electronic structure of light transition metal compounds studied by photoemission

Abstract The valence band photoemission has been measured on ScF3, TiO2, and V2O5 which have no 3d electron nominally. The charge-transfer satellites are found in the region from 11 eV to 17 eV below the top of the valence band. It is concluded from the resonant photoemission that the charge-transfer-type configuration is manifest to form the valence state in the ground state in addition to the originally filled-up 2p state of ligand.

Electronic structure of a Pt(111)Ge surface alloy and adsorbed CO

Abstract Angle-integrated photoemission spectra are observed for Pt(111) and a Pt(111) Ge surface alloy. The spectra for Pt(111) Ge show d band filling compared with those for Pt(111). Although the chemisorption energy of CO is noticeably reduced by alloy formation, the binding energies of the occupied levels for adsorbed CO are almost the same as those on pure Pt(111). The results are discussed by the d band filling due to s-d hybridization of Ge s electrons and the Pt d band and by two-level hybridization of the 5σ and 2π states with the modified d band.

Photoemission Study on Protonic Conductor CaZrO3: Evidence of the Exchange Mechanism of Proton and Hole

The exchange mechanism of proton and hole in protonic conductor CaZrO3 has been investigated by photoemission spectroscopy. The Fermi level is higher by about 1.0 eV through proton doping, indicating that protons exchange with holes. The defect chemical calculation proves that the change of the number of the protons, holes, and the oxygen vacancies by the proton doping accords with the photoemission process.

Ti 2p-, Ti 3p- and O 1s-resonant photoemission studies of Ti2O3

The Ti 2 p - and Ti 3 p -resonant photoemission studies of Ti 2 O 3 were carried out as well as O 1 s -resonant photoemission. The Ti 3 d band has a broad band width of about 3 eV, but the strong resonance enhancement was observed at Ti 3 d band just below the Fermi level on the Ti 2 p resonance. The enhancement of the doublet Ti 3 p main line was observed mainly at the higher binding energy. The resonant enhancements of the satellite structures in the Ti 3 d and Ti 3 p band regions were also found. The resonance spectra were analyzed by the cluster model calculation with large hybridization energy, where the satellite was elucidated by the charge transfer satellite.