Akito Kakizaki

Surface electronic structure of a single-domain Si(111)4×1-In surface : a synchrotron radiation photoemission study

The electronic structure of a Si(111)4 × 1-In surface has been studied by angle-resolved photoelectron spectroscopy (ARPES). Using a 1.1° off-axis Si(111) wafer as substrate, a single-domain Si(111)4 × 1-In surface has been prepared in order to determine the dispersion of surface state (SS) without the obscurity arising from multi-oriented 4 × 1 domains. Three SSs that cross the Fermi level have been found. Thus, the Si(111)4 × 1-In surface is concluded to be metallic. The dispersions of the metallic SS appeared to be almost one-dimensional, suggesting one-dimensional metallic bonds among In atoms. Completely occupied SSs have been also found. The characteristics of SSs are discussed in relation to the existing structural models for the Si(111)4 × 1-In surface.

A new compact electron spin polarimeter with a high efficiency

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the ΓS line of its surface Brilluoin zone.

A new spin-polarized photoemission spectrometer with very high efficiency and energy resolution

A new spin- and angle-resolved photoemission spectrometer was developed adopting the very-low-energy-electron-diffraction (VLEED)-type spin polarimeter. The Fe(001)p(1x1)-O film grown on MgO(001) crystal for the VLEED target yields significantly high spin-resolving power, the effective Sherman function of 0.40+/-0.02, with long lifetime and stability compared to the conventional Fe(001) target. Under the favor of high resolving power, approximately 100 times higher efficiency than that of conventional Mott-type spin polarimeter, the figure of merit of 1.9+/-0.2x10(-2) was achieved. Owing to this high efficiency, high-energy resolution can be realized with this new spin-polarized photoemission spectrometer. The simplified ways of target preparation and revitalization make the VLEED spin polarimeter much more convenient and feasible for the spin-polarized photoemission spectroscopy.

VARIED LINE-SPACING PLANE GRATING MONOCHROMATOR FOR UNDULATOR BEAMLINE

A varied line‐spacing plane grating monochromator is installed at an undulator beamline BL‐19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line‐spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator.

New soft X-ray beamline BL07LSU at SPring-8

The design and performance of a new soft X-ray beamline BL07LSU at SPring-8 are described. The combination of a novel segmented cross undulator and beamline monochromator has achieved high energy resolution (E/ΔE > 10000) and high photon flux [>1012 photons s−1 (0.01% bandwidth)−1] in the photon energy range 250–2000 eV with fully controllable polarization.

Surface and bulk core level shifts of the Si(111) 3 × 1-Na and Si(111) δ7 × 7-Na surfaces

Abstract By means of surface sensitive photoelectron spectroscopy using synchrotron radiation, we have measured the Si 2p surface and bulk core level shifts for the Si(111)3 × 1-Na and Si(111)δ7 × 7-Na surfaces, and obtained new information about these surface structures. As for the 3 × 1-Na, we found that there are two kinds of surface Si atoms which are differently charged. The number of surface Si atoms is estimated to be about 4 in the surface unit cell. We also estimated the coverage of this surface as ∼ 1 3 ML in contrast to 2 3 ML so far believed from the STM images. This result removes the discrepancy between the semiconductor character and the odd number of electrons in the unit cell of the 3 × 1-Na so far reported in the literature. From these results we have proposed some possible models for the Si(111)3 × 1-Na surface.

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.

XPS and UPS Studies of Valence Fluctuation and Surface States of Yb4As3, Yb4Sb3 and Yb4Bi3

X-ray and vacuum ultraviolet photoemission spectra were measured for valence fluctuating Yb 4 X 3 (X: As, Sb and Bi) by use of Mg K α and synchrotron radiation source. From the line shape analysis of the Yb 4 f spectra, the mean valence is evaluated as 2.32, 2.34 and 2.10 for Yb 4 As 3 ,Yb 4 Sb 3 and Yb 4 Bi 3 . The surface Yb 4 f level shift is estimated as 0.65, 0.63 and 0.59 eV, respectively. The plasmon satellite is confirmed in the Yb 4 f and Yb 4 d core XPS spectra of Yb 4 Bi 3 in contrast to those in Yb 4 As 3 and YbAs. As for the anionic states, the Bi 5 d core UPS spectrum showed a remarkable asymmetry in contrast to the rather symmetric Bi 4 f core XPS spectrum. This result suggests a contribution of the surface Bi 5 d state at larger binding energies of about 0.5 eV.

Mg-induced Si(111)3 × 1 structure studied by photoelectron spectroscopy

Abstract By means of angle resolved photoelectron spectroscopy using synchrotron radiation, we have measured the valence band and surface sensitive Si 2p core-level spectra for the Si(111)3 × 1Mg surface. The dispersion of the valence band shows the fact that this surface has a semiconducting property and two surface states in the projected bulk band gap at the K point. From the fitting results of the Si 2p core-level spectra, we find that the two surface shifted core-level components, S′1 and S′2 stem from the Si atom with single dangling bond and the Si atom bonding to the Mg atom, respectively. From experimental observations we suggest that the Si(111)3 × 1Mg structure is formed by ordering of Mg atoms on the ideal Si(111)1 × 1 surface, not by reconstruction of Si atoms of the substrate.

Initial interface formation study of the Mg/Si(111) system

The initial interface and silicide formation induced by Mg adsorption on the Si(111)7×7 surface have been studied using low‐energy electron diffraction, x‐ray photoelectron spectroscopy, and synchrotron radiation photoelectron spectroscopy. At room temperature, it is found that Mg atoms are preferably adsorbed on top sites of Si adatoms and rest atoms on the Si(111)7×7 surface and with increasing of Mg deposition, a Mg2Si epitaxial layer is formed and the surface structure transforms from the diffuse (1×1) phase into the (2/3√3×2/3√3)R30°. After growing up to a critical thickness, the Mg film grew in a disordered phase on the epitaxial layer. The Fermi level of the Mg2Si film is positioned at 0.51±0.05 eV above the valence band maximum. On the other hand, at 300 °C the Mg2Si epitaxial layer was formed in the (1×1) phase on the Si(111)7×7 and grew up to a critical thickness in the initial stage. For the successive evaporation, the Mg film grew in a disordered phase on the Mg2Si(111)1×1 surface.