Taichi Okuda

Surface core level shifts of the Au adsorbed Si(111) reconstructed surfaces

Abstract By means of synchrotron radiation we have performed surface sensitive Si 2 p core photoelectron spectroscopy of the Si(111)5x2-Au, α- 3 x 3 - Au , β 3 x 3 Au and 6x6-Au surfaces systematically and determined their surface core level shifts(SCLS) by curve fitting. From the results we discuss about their electronic and geometric structures and compare our results with the so far proposed models for the Si(111) 3 x 3 and 6x6-Au surfaces especially.

Surface electronic structure of ordered alkali- and noble metal-overlayers on Si(111)

Abstract Some progresses of our photoemission studies for ordered metal/Si(111) surfaces are reviewed. The 5-6-7 model having π-bonded chain structure on the alkali metal (AM) induced Si(111)3 × 1 surfaces is strongly suggested from the comparison between our results of angle resolved photoelectron spectroscopy (ARPES) and recently reported theoretical calculations. We also focus on the difference of the Si 2p surface core level shifts (SCLS) between Ag induced- and AM induced-Si(111)3 × 1 surfaces. Finally, we discuss the electronic and geometric structures of the Si(111)5 × 2, α- 3 × 3 , β- 3 × 3 and 6 × 6-Au surfaces from our ARPES and SCLS studies.

Symmetry analysis of the Fermi surface of Bi2Sr2CaCu2O8 by display analyzer

Abstract We have directly observed the Fermi surface of Bi2Sr2CaCu2O8(Bi(2212)) by a display-type angle-resolved photoelectron spectrometer. The experiment was done at room temperature by using linearly-polarized synchrotron radiation (SR). The photon energy was 32 eV and the incident angle of the photon was perpendicular to the sample surface. Photoelectron angular distribution (PEAD) patterns were measured at various azimuthal angles φ from 0° to 135° in steps of 22.5°, where φ is the angle between the direction of the electric vector of the photon and the sample Cu O bond direction. The observed shape of the Fermi surface is consistent with the band calculation by the FLAPW method [S. Massidda et al., Physica C 152 (1998) 251]. We confirmed the symmetry of the atomic orbital constituting the Fermi surface to bedx2−y2 by ‘orbital determination by angular distribution’ (ODAD).

DOMAIN IMAGING OF MESOSCOPIC MAGNETIC STRUCTURES BY PHOTOELECTRON EMISSION MICROSCOPY

We have observed magnetic domains of mesoscopic magnetic structures of Ni by synchrotron radiation photoelectron emission microscopy using circularly polarized soft X-rays from the bending magnet. The mesoscopic magnetic structures of Ni were fabricated by electron beam lithography combined with a chemical liftoff process. The geometries of the Ni mesoscopic samples were square, triangular and hexagonal with the sizes of 5 and 10 μm. The magnetic domains structures were clearly observed by dividing the images measured at the Ni L3-edge by the images measured at the Ni L2-edge. The magnetic domains of the Ni mesoscopic structures are discussed with the results of magnetic force microscopy and micromagnetic simulation.

Two-dimensional band mapping of 2H-TaSe2 using a display-type photoelectron spectrometer

Abstract We have observed the two-dimensional photoelectron angular distribution (PEAD) patterns of the valence band of the 2 H -TaSe 2 using a display type photoelectron spectrometer. The PEAD patterns which correspond to the two-dimensional band map show the various changes with the change of the binding energies, reflecting the complex band structure of 2 H -TaSe 2 . The intensity suppression area of the pattern at the Ta 5d band indicates that the half-filled Ta 5d band consists mainly of d z 2 -like orbitals as predicted by previous band calculation.

Fermi surface of Sr2RuO4 studied by two-dimensional angle resolved photoelectron spectroscopy

Abstract The shape of the Fermi surface of the Sr2RuO4, the first noncuprate superconductor, has been directly observed by two-dimensional angle resolved photoelectron spectroscopy (2D-ARPES) technique using a display-type hemispherical mirror analyzer. The gross shape of the Fermi surface agrees with previous band calculations. The photoelectron angular distribution pattern of the Fermi level shows that the Fermi surface is composed of orbitals withdxy,dyz, anddzx-like symmetries which agree well with those predicted by previous band calculations and are in contrast todx2−y2 symmetry of thehigh-TC superconductors.

Unusual two-dimensional angular distribution of photoelectrons of kish graphite and 1T-TaS2

Abstract Two-dimensional patterns of angle-resolved photoemission are measured on Kish graphite and 1T-TaS 2 for s -polarized synchrotron radiation. Observed symmetry-broken patterns are theoretically discussed. The effect of the dipole selection rules by the s -polarized light is clarified. It is found for the first time that an interference of photoelectron waves from non-equivalent sites provides uneven intensity distribution in different Brillouin zones. The patterns of 1T-TaS 2 measured at 40 eV are remarkably different from those at 22 eV, which is explained by the resonant photoemission in the Ta 5 p core excitation region breaking the dipole selection rule due to the direct recombination type Auger transition.