Kazutoshi Yagi

Angle-resolved photoemission study of oxygen-induced c(2×4) structure on Pd(110)

Abstract Angle-resolved photoemission spectra have been measured for the oxygen-induced c(2 × 4) structure on Pd(110). Some of the c(2 × 4)-related states are identified in the range of binding energy from -6 eV to E F . In particular, the oxygen 2p Z -derived bonding state and its antibonding counterpart are found to show considerable dispersion of approximately 1 eV with k ‖ in the [110] direction, while there is no measurable dispersion in the [001] direction. This highly anisotropic dispersion suggests the oxygen and surface palladium atoms to form one-dimensional chains along the [110] direction. Surface band structures are calculated for possible structural models using the tight-binding approximation. The zig-zag Pd-O chain model reproduces well the experimental result and is consistent with the coverage dependence of the low energy electron diffraction patterns.

Adsorption and desorption kinetics of oxygen on the Pd(110) surface

Abstract The adsorption and desorption of oxygen on a Pd(110) surface have been investigated by temperature-programmed desorption (TPD). A number of TPD spectra for associative desorption of O 2 from O/Pd(110) were taken at constant heating rate with different initial coverages and at constant initial coverage with different heating rates. The TPD curves were analyzed by the desorption rate isotherm and desorption rate isostere methods. The variations in apparent Arrhenius parameters with coverage were obtained by fitting to the Polanyi–Wigner equation. First-order associative desorption kinetics was found, suggesting the effect of lateral interaction and oxygen-induced added-row reconstruction. Two different processes for associative desorption of oxygen from the O/Pd(110) surface were found. The sticking probability for dissociative adsorption of O 2 on the Pd(110) surface has been measured as a function of surface coverage and surface temperature by using two mass spectrometers. The sticking probability profile suggested a precursor trapping–dissociation mechanism. The initial sticking probability was independent of surface temperature.

Angle-resolved photoemission of the c(2×2) and c(3×1) oxygen overlayers on Fe(110)

Abstract Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the band structure of the c(2×2) and (3×1) oxygen overlayers on Fe(110). The symmetries of the O-2p-derived states at the center of the surface Brillouin zone ( Γ ) were identified using polarized light. At Γ the p x p y - and p z -derived levels are at about 5.5 and 7.0 eV below the Fermi level, respectively, for both ordered overlayers. The p-states of the c(2×2)-O structure show very little dispersion (⪅0.1 eV) with k  . On the other hand, the c(3×1)-O overlayer exhibits considerable dispersion of ∼1.6 eV. The essential features of the measured dispersion are reproduced well by the dispersion predicted in a qualitative way for an isolated c(3×1) oxygen monolayer.

Oxygen adsorption site of Pd(110)c(2×4)-O:: Analysis of ARUPS compared with STM image

Abstract Surface band structures of Pd(110)c(2×4)-O are calculated for all possible models for which the substrate is reconstructed into the (1×2) missing-row structure and the oxygen adatoms are located in three-fold sites. These calculations were compared with the observed energy dispersions by angle-resolved photoemission study (ARUPS) to find out which structure model is the optimum one by means of tight-binding approximation.

Piezoreflectance study of excitons of rubidium iodide in the fundamental absorption region

Abstract Piezoreflectance spectra of RbI were measured in the fundamental absorption region, from 5.5 to 7.5 eV where four reflectivity peaks ( E 1 ≈ E 4 ) are observed. E 1 and E 2 were assigned to the spin-orbit split γ excitons and E 3 to L exciton and E 4 to a composite structure of L and X exciton, and three small peaks locating at slightly higher energy were ascribed to remaining two X and one L excitons.

Angle-resolved photoemission study of Pd(110)

Abstract A clean Pd(110) surface has been studied with angle-resolved photoelectron spectroscopy using polarized synchroton radiation. Valence band dispersions were determined along the ΓKX symmetry line by assuming a free-electron final band with constant inner potential. The symmetries of the initial state valence bands were identified by the polarization selection rule. Normal emission spectra can be interpreted mainly in terms of free-electron primary cone emissions as well as secondary cone emission. Our experimental band plots agree with Christensens calculation. However, there are some features which do not fit the free-electron final band approximation. Some possible interpretations are given for these features.

Pressure Shifts of Valence and Core Exciton Peaks in Potassium Iodide

Hydrostatic pressure shifts of valence and core exciton peaks in KI are measured with a modulation method at about 120 K. The pressure coefficients are determined to be, in units of 10 -3 meV/bar, 17.0 and 4.7 for the valence excitons at 5.73 and 7.22 eV, and 18.8, 17.0 and -38.7 for the core excitons at 19.95, 20.20 and 21.05 eV, respectively. The pressure shifts of the lowest exciton at 5.73 eV and the core excitons are discussed with a simple model of localized transitions. Experimental results for the lowest exciton and the core excitons at 19.95 and 20.20 eV are explained well in this model, but the shift of the core exciton at 21.05 eV does not agree with the theoretical expectation. The exciton-phonon interaction term contributing to thermal shifts of the excitons is deduced from the present pressure coefficients.

Piezoreflectance of potassium iodide in the vacuum ultraviolet region from 5 to 30 eV

Piezoreflectance spectra of potassium iodide were measured from 5 to 30 eV in the fundamental and core excitation region. The deformation potentials cubic, tetragonal and trigonal, were deduced for twenty six structures observed in this energy region and are analyzed in terms of a simple point ion model to identify the electronic origins of these structures.

Polarization characteristics of polarizing undulator radiation installed in the electron storage ring NIJI-II

Abstract An Onuki-type polarizing undulator with fifteen-periods was installed in the electron storage ring NIJI-II in the Electrotechnical Laboratory. The polarization characteristics of the radiation from the undulator were studied in the UV region. It was confirmed that the degree of circular polarization was above 95 %.

Piezoreflectance of Rubidium Chloride in the Vacuum Ultraviolet Region from 6 to 30 eV

Piezoreflectance spectra of rubidium chloride were measured in the photon energy range from 6 to 30 eV at about 120 K. For the structure at 9.01 eV, cubic piezoreflectivity spectrum do not have line shape proportional to that of the logarithmic energy derivative of reflectivity spectrum, and both of tetragonal and trigonal responses on piezoreflectivity were observed. We ascribed it to a composite of the L and X excitons. The piezoreflectance responses of the core excitons located between 15 and 18.5 eV are interpreted well by the localized excitation model by Satoko and Sugano.