Hideshi Ishii

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.

Soft X-ray emission spectroscopy of early transition metal compounds

Abstract Soft X-ray emission studies for several early transition metal compounds, such as Sc, Ti and V compounds, have been studied. Raman scattering was found at the 2p→3d excitation in the transition metal compounds. The elementary excitation of the Raman spectrum is mainly elucidated by the d–d transition within the 3d bands, as well as the interband transition from the O 2p valence band to the conduction band, which consists mainly of transition metal 3d states. The charge transfer transition due to the localized electron picture is dominant in the soft X-ray spectra of Sc compounds. Raman scattering is a powerful tool in the study of the electronic structure of transition metal compounds.

Design of a new high angle-resolving electron energy analyzer

Abstract A new angle-resolving input-lens-system for photoelectron diffraction (PED) has been proposed. In this lens system, angle-resolving is accomplished by placing an aperture in the diffraction plane. Using this system, both high angular resolution and high transmission are easily achieved in PED measurements. In this paper, we have designed two electron energy analyzers, which mainly consist of this novel angle-resolving input-lens-system and a hemispherical analyzer. The characteristics of the newly designed analyzers are as follows: (1) high angular resolution (

Two-hole states of the outermost surface layer studied by metastable atom electron spectroscopy: Si(111)−7×7 and Si(100)−2×1

Abstract The He ∗ (2 3 S) metastable atoms were shown to de-excite on the Si(111)−7 × 7 and Si(100)−2 × 1 surfaces through resonance ionization followed by Auger neutralization, producing two holes in the valence states of the outermost surface layer. A comparison between the electron emission spectra of the 7 × 7 and 2 × 1 surfaces exhibits different features which can be interpreted in terms of the surface effect, although such a difference has not been observed in ordinary L 2,3 VV Auger spectra or ion neutralization spectra.

Development of a Novel Instrument for X-Ray Photoelectron Diffraction and Holography

For X-ray photoelectron diffraction (XPED) and holography measurements we developed a novel laboratory instrument with the multienergy high power X-ray source and the high energy and high angular resolution photoelectron spectrometer system. The photon intensities of Al–Kα, Cr–Lα and Cu–Kα were estimated at 4.6 × 1011 cps, 7.5 × 1010 cps and 7.2 × 1010 cps, respectively. Ag3d XPS also revealed that the energy resolutions of Al–Kα and Cr–Lα sources were 0.9 eV and 3.1 eV, respectively. XPS and XPED of h-BN/Ni(111) excited by Al–Kα and Cr–Lα elucidated the potential and the validity of the XPED and holography analysis by using this novel instrument. Cu–Kα excitation XPS and Ti1s XPED measurements of the SrTiO3 (001) surface have also been performed.

Site-specific characteristic of the Kikuch-like bands in high-angular-resolution X-ray photoelectron diffraction

Fine-mesh two-dimensional measurements of Ca2p and F1s X-ray photoelectron diffraction (XPED) patterns from a CaF2(111) surface were performed with high angular resolution. These measurements revealed a great deal of fine structure including many Kikuchi-like bands and circular patterns. On comparing the Ca2p and F1s XPED patterns, an energy dependence of the Kikuchi-like bands and circular patterns was observed. Furthermore, the Kikuchi-like bands associated with the (111) plane differed substantially between the Ca2p and F1s XPED patterns. This is the first report of the site-specific characteristic of the Kikuchi-like bands in XPED.

Surface Structure of Low Coverage Chlorine Adsorbed on a Nickel Stepped Surface

The surface structure of Cl/Ni(7 9 11) was studied by means of SEXAFS. At the initial stage of chemisorption (~0.1 ML), chlorine atoms adsorb mainly on the terrace 3-fold site in contrast to sulfur and phosphorus on Ni(7 9 11), where the adsorption on the step 4-fold site is predominant.

Observation of Auger transitions across the surface states of Si(111)-7×7 by metastable atom electron spectroscopy

Abstract The He∗(23S) metastable atoms incident on the Si(111)-7×7 surface deexcite via the resonance ionization followed by Auger neutralization. In the electron emission spectrum, we found for the first time fine structures assigned to the Auger transitions involving two electrons of the dangling bond surface states. The hole-hole interaction and Auger intensity across the surface states are discussed.

Kikuchi-like effects in X-ray photoelectron diffraction from the CaF2(111) surface

Abstract At relatively high electron energies, the patterns observed in X-ray photoelectron diffraction (XPED) for light solids are dominated by “bands” corresponding to the main crystallographic planes in the crystal. These bands can be termed “Kikuchi-like” and occur for the same reasons that give rise to the well-known Kikuchi bands in electron diffraction. In the present work we examine in detail the fine mesh XPED pattern from the CaF 2 (111) surface by using the single scattering cluster-spherical wave theory (SSC-SW). We find that the theory reproduces well the main Kikuchi-like characteristics of the observed pattern and is sensitive to the size of the diffracting domains.

Site-specific extinction rule for Kikuchi bands in X-ray photoelectron diffraction

The anomalous extinction of specific Kikuchi bands has been recently observed in the X-ray photoelectron diffraction (XPED) pattern for F1s emission from a CaF2(111) surface, even though the corresponding structure factors are not zero. To explain this phenomenon, we have derived a novel extinction rule and have shown that the extinction of Kikuchi bands in XPED depends not only on the structure factors but also on the lattice sites of source atoms. This rule can be used to locate the lattice sites of impurities in single-crystal substrates.