Hidetoshi Namba

Electronic properties of SO2 adsorbed on Ni(100) studied by UPS and O K-edge NEXAFS

Abstract Surface electronic properties of submonolayer sulfur dioxide SO2 molecularly adsorbed on Ni(100) have been investigated by means of ultraviolet photoelectron spectroscopy (UPS) and O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS has confirmed that the SO2 molecule is lying flat on the surface and significant charge transfer occurs from the substrate to the π ∗ orbital. UPS has directly clarified a partial occupancy of the π ∗ level, and correspondingly the π level was found to shift to a lower binding energy more significantly than other orbitals. It has been clearly elucidated that the SO2 molecule acts as a π acceptor upon adsorption on the Ni(100) surface.

VUV beamline (4–50 eV) with a 1 m Seya–Namioka monochromator for surface studies

Optical and mechanical design of a VUV beamline BL‐7B in PF‐KEK are presented. The optical characteristics are discussed by use of the data of gas absorption spectrum and those of photoelectron spectroscopy.

Photoemission investigation of the room‐temperature adsorption of trimethylgallium on GaAs surface

The adsorption of trimethylgallium (TMG) on GaAsu2009(110) surface at room temperature was studied with ultraviolet photoemission spectroscopy by use of synchrotron radiation. The adsorption was found to saturate for TMG exposure as low as 3 langmuirs (L) resulting in a coverage of less than 0.1 monolayer. It is concluded that TMG molecules are adsorbed on the GaAs surface without decomposition.

Soft x‐ray beamline (10–1000 eV) with a plane grating monochromator for surface studies

The optical design and mechanical solution for a soft x‐ray beamline BL‐7A in PF‐KEK for the energy range 10–1000 eV with a PGM are described. The optical characteristics of the beamline are tested with gas phase absorption and photoelectron spectroscopy.

Photoelectron holography of the si(001) surface.

Three-dimensional images of the near-surface atom arrangement were calculated from two-dimensional photoelectron diffraction data by several imaging algorithms: (i) a basic method with a Fourier transformation at one kinetic energy over k space, considering the phase factor due to the path-length difference; (ii) energy summation of the above results; (iii) Fourier transformation within small k-space windows; and (iv) their combinations. Atomic images produced by these methods from the experimental Si 2p photoelectron diffraction patterns of an Si(001) surface are compared with the crystal geometry. The results show that the energy-summed small-window method, called SWEEP, gives the best images.

One-dimensional electronic states on stepped surfaces of Ni studied by ARUPS

One-dimensional arrays of steps and/or kinks are periodically formed on stepped surfaces of metal single crystals. We found new electronic states induced by step edges on Ni(7 9 11) surfaces by means of angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation. The step electronic states show almost flat dispersions in perpendicular and parallel to steps. The step electronic states are atomic-like and one-dimensionally distributed along steps. We revealed why surface steps are active to adsorption in the point of view of the electronic interaction between the adsorbate and the substrate.

Photon-Stimulated Desorption Mechanism of Cl^+ Ions from Cl/Si(111) Surface

Photon-stimulated desorption (PSD) of Cl+ ions from a Cl/Si(111) surface was studied using synchrotron radiation. The kinetic energy distribution of Cl+ ions in PSD agreed with our previous results of electron-stimulated desorption (ESD). The excitation energy threshold of Cl+ desorption also agreed within the experimental error. Hence, the desorption mechanisms in both PSD and ESD were considered to be the same. We studied the excitation (photon) energy dependence of the Cl+ yield more precisely than ESD to elucidate the excitation mechanism for ion desorption. We found that the lower threshold photon energy was 17eV. Comparison with the ultraviolet photoelectron spectroscopy (UPS) spectrum showed that this energy corresponded to the excitation from the Cl 3s state to the Fermi level. Hence, this PSD process was explained by the KF model, where the Cl 3s core hole was filled by electrons of the Cl-Si bond through the Auger-like process, and then Cl+ ions desorbed by repulsive Coulomb force from the adjacent Si+.

Two-dimensional angular distribution of photoemission spectra from the valence band of 1T-TaS2

Two-dimensional band structures of single-crystalline 1T-TaS2 have been directly observed by using a new version of two-dimensional display-type spherical mirror analyzer. The intensity distribution patterns for linearly-polarized synchrotron radiation normally incident on the cleaved surface have shown unusual angular distributions. The non three-fold symmetry is discussed by considering the angular dependence of the dipole transition probability for the s-polarized synchrotron radiation from each atomic orbital with particular symmetry, as well as the tight-binding initial state and a free electron like final state. In addition, circular dichroism in angular distribution (CDAD) of the photoemission pattern from the valence band is predicted for 1T-TaS2.

High‐temperature diffraction gratings for synchrotron radiation

SiC‐based mechanically ruled master gratings and replicas are developed for synchrotron radiation instruments. An SiC‐based gold replica grating without any thermal deformation due to active cooling is used in a high‐photon‐flux‐soft x‐ray monochromator that is installed in a bending magnet beamline. An SiC‐based gold master grating is used in a vacuum ultraviolet/soft x‐ray monochromator installed in an undulator beamline with slight groove shape deformation. This deformation is caused by the thermal change of the gold film occurring at higher than 250–300u2009°C. A method for cleaning carbon‐contaminated synchrotron radiation optics is tested. The ultraviolet ozone ashing method effectively cleans carbon contamination on the optics and is useful for extending the lifetime of synchrotron radiation optics.

Two-dimensional photoelectron diffraction patterns by display-type spherical mirror analyzer

Abstract Two-dimensional photoelectron diffraction patterns from Si(111), and TaC(111) surfaces have been obtained, The pattern of Si 2p core emissions from Si(111) has a six-fold symmetry and that of Ta 4f emissions from TuC(111) has a three-fold symmetry. They were explained qualitatively by considering the directions of the strong scatterers. The photoelectron diffraction pattern from an ordered adsorbale has been obtained for the first time. The obtained six-fold pattern from Si(111)√3 × √3 -Ga(3d) suggests that the Cia atoms are adsorbed above the first Si layer, and this is in good agreement with the existing model.