Hirohito Fukutani

Optical Spectra of Y2O3 Single Crystals in VUV

Optical absorption in the tail region and reflectivity at room temperature in the VUV region up to 42 eV are measured on Y 2 O 3 single crystals. Various optical constants as functions of photon energy are derived therefrom by use of the Kramers-Kronig relation. The Urbach rule parameters are also determined experimentally for the tail. A tentative interpretation is given on the spectral structures found in the optical constants, referring to the energy levels of Y 2+ and Y 3+ free ions.

Elliptical-polarization analyses of synchrotron radiation in the 5–80-eV region with a reflection polarimeter

Abstract The Stokes parameters, which completely represent the polarization state of light, have been measured in the 5–80-eV energy region for synchrotron-radiation beams on the VUV to soft X-ray beamlines at the Photon Factory. Various states of polarization were produced for the emerging beam by deflecting the incoming beam vertically with respect to the entrance slit of the monochromator with a premirror of the beamline. The resultant beam was polarization-analyzed using a polarimeter comprising two triple-reflection polarizers. Increasing the beam-deflection angle was found to result in a change in the polarization state from predominantly horizontal linear polarization to elliptical polarization. This procedure could be used both to produce and to verify circular polarization with | P c | ≳ 80% in the energy range 60–80 eV, which could be immediately applied to MCD experiments. Unpolarized light could clearly be distinguished from circularly polarized light. The unpolarized component was found to become larger with increasing energy on a soft X-ray beamline; this was shown to be mainly due to scattering by beamline optical elements.

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.

A New Constant Deviation Monochromator for Angle Resolved Photoemission Spectroscopy

A new type of constant deviation monochromator equipped with three interchangeable concave gratings (600, 1200 and 2400 grooves/mm) of 2 m radius of curvature was designed and built specifically for angle resolved photoemission spectroscopy at photon energies ranging from 20 to 160 eV. The exit slit of the monochromator is at a fixed position, whereas the entrance slit moves, simultaneously with grating rotation, along the direction of the incident light so as to minimize the amount of defocusing. A monochromatic light spot of 0.5 mm in diamter was obtained at the fixed sample position with the aid of a toroidal postfocussing mirror. It is found over the energy range concerned that the resolution is bettern than 1700 with 25 µm slits, and the photon flux obtained behind the toroidal mirror for a horizontal acceptance angle 0.5 mrad is 4×1010 photons/s when the width of the slits is 50 µm and the stored current for synchrotron radiation is 100 mA.

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 UPS study of the oxygen-induced 2 × 1 surface of Cu(110)

Abstract The two-dimensional oxygen-induced energy bands of the Cu(110)/2 × 1−O surface were investigated by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). A new finding in the present report is that the oxygen-derived O 2py and O 2pz bands cross and hybridize between λ and Ȳ along the [001] direction. A tight-binding band calculation assuming the missing-row reconstruction model was successfully made to reproduce the dispersion of the oxygen-derived bands, including band crossing as well as symmetry characteristics. An ARUPS study on a surface with a very small amount of adsorbed oxygen of about 0.01 ML was also made. An interesting result is that almost the same dispersion as that of the well-ordered 2 × 1−O surface of 0.5 ML is observed. This result indicates that CuO chains directed along the [001] direction grow long enough to apparently give the same dispersion, even in the initial stage of oxygen adsorption.

Production and direct measurement of circularly polarized vacuum-ultraviolet light with multireflection optics

The conversion of linearly polarized synchrotron radiation to circular polarization has been successfully achieved beyond the LiF transmission cutoff in the vacuum ultraviolet by utilizing a triple‐reflection polarizer as a quarter‐wave retarder. The Stokes parameters of the emerging beam were directly measured at 30 eV with a reflection‐type polarimeter as a function of the rotation angle of the ‘‘circular polarizer’’ around the optical axis. The results show that a degree of circular polarization of up to ∼±82% was attained at ∼±25° rotation angles, respectively, between the incidence plane for the polarizer and the horizontal plane. This result is in good agreement with a calculation which took into account the independently measured Stokes parameters of the incoming beam.

Existence of a stable intermixing phase for monolayer Ge on Si(001)

Abstract A monolayer adsorption of Ge on a single-domain Si(001)2 × 1 surface has been investigated by X-ray excited Auger electron diffraction (AED) and scanning tunneling microscopy. Contrary to the common belief, a significant intermixing of Ge down to at least the fourth layer is identified. This intermixing is found to progress to a stable interface alloy phase that develops fully for annealing at 500–600°C. A possible reason for the alloy phase is discussed to be an elastic interaction from the Si(001) surface.

Optical Properties of CeO2 Crystal in the Photon Energy Range of 2.5–40 eV

Optical reflectance spectra of CeO 2 crystal have been measured in the photon energy range from 2.5 to 40 eV. A Kramers-Kronig analysis of the reflectance data has been performed to obtain the dielectric function and related functions. The observed spectral features can be explained in terms of the charge transfer and interband transitions and the atomic-like excitation of the Ce 5 p core electron. A peak regarded as a candidate for the “4 f 2 ” feature has been observed at an excitation energy of 13 eV.

Anisotropic Optical Spectra of α-Al2O3 Single Crystals in the Vacuum Ultraviolet Region. I. Spectra of Absorption Tail and Reflectivity

The spectra of absorption constant in the intrinsic absorption tail region of α-Al 2 O 3 single crystals at 297 K, 78 K and 10 K are presented for the electric fields of incident light parallel to the optic axis of α-Al 2 O 3 and normal to it. The absorption tail spectra obey the Urbach rule for each polarization, indicating that absorptions in the tail region result from the direct interband transitions. The optical anisotropy characterized by the Urbach rule is interpreted in terms of the bond length O 2- –Al 3+ participating in the absorption processes. The spectra of reflectivity are presented in the range of photon energies from 4.6 eV to 120 eV for electric fields parallel to and normal to it. Spectral positions of main maxima in the reflectivity spectra for each polarization are determined at 297 K and 10 K; the spin-orbit doublet of the Al 3+ L 2,3 is revealed at 78.67 eV and 79.12 eV for the first time in the case of α-Al 2 O 3 .