Toyohiko Kinoshita

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 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.

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.

Element specific imaging by scanning tunneling microscopy combined with synchrotron radiation light

Microscopic surface images showing a distribution of a designated element was obtained by scanning tunneling microscopy combined with synchrotron radiation light. A tip current induced by photoirradiation is found to increase when the photon energy is just above the absorption edge of a sample element. From the photoinduced current measured during the tip scanning over the surface, element specific images were obtained. An estimated spatial resolution of the chemical imaging is less than 20nm, better than that achieved by photoemission electron microscopy.

Development and trial measurement of synchrotron-radiation-light- illuminated scanning tunneling microscope

Scanning tunneling microscope (STM) study is performed under synchrotron-radiation-light illumination. The equipment is designed so as to achieve atomic resolution even under rather noisy conditions in the synchrotron radiation facility. By measuring photoexcited electron current by the STM tip together with the conventional STM tunneling current, Si 2p soft-x-ray absorption spectra are successfully obtained from a small area of Si(111) surface. The results are a first step toward realizing a new element-specific microscope.

Controls over Structural and Electronic Properties of Epitaxial Graphene on Silicon Using Surface Termination of 3C-SiC(111)/Si

Epitaxial graphene on Si (GOS) using a heteroepitaxy of 3C-SiC/Si has attracted recent attention owing to its capability to fuse graphene with Si-based electronics. We demonstrate that the stacking, interface structure, and hence, electronic properties of GOS can be controlled by tuning the surface termination of 3C-SiC(111)/Si, with a proper choice of Si substrate and SiC growth conditions. On the Si-terminated 3C-SiC(111)/Si(111) surface, GOS is Bernal-stacked with a band splitting, while on the C-terminated 3C-SiC(111)/Si(110) surface, GOS is turbostratically stacked without a band splitting. This work enables us to precisely control the electronic properties of GOS for forthcoming devices.

Photoelectron and inverse photoelectron spectroscopy studies of the Si(111)3 × 3-Sb surface

Abstract Angle-resolved ultraviolet photoelectron spectra and momentum (k)-resolved inverse photo-electron spectra have been measured for the Si (111) 3 × 3 - Sb surface. It has been found that at least two filled-surface-state bands exist on the 3 × 3 - Sb surface and that the 3 × 3 - Sb surface is semiconducting with a large band gap between the filled- and empty-surface-state bands. The absence of dangling bonds in this surface is suggested from results of hydrogen exposure. These results are discussed in connection with the surface electronic structures expected for a recently proposed trimer model.

Comparative study of the Si(111)✓3x✓3-Ga and -Al surfaces by angle-resolved ultraviolet photoelectron spectroscopy

Abstract It has been shown by angle-resolved photoelectron spectroscopy that the surface electronic structures of the Si(111)✓3x✓3-Ga surface are almost identical to those of the Si(111)✓3x✓3-Al surface. This suggests that the two surfaces are very alike. For the ✓3x✓3-Ga surface, we have identified two dispersive surface-state bands and a non-dispersive one. The non-dispersive surface-state band is suggested to be extrinsic to the ✓3x✓3 surfaces. The two dispersive bands are in qualitative agreement with calculated surface-state bands for models in which a metal adatom is placed in every ✓3x✓3 threefold hollow site.

Observation of intracavity Compton backscattering of the UVSOR free electron laser

Abstract High-energy gamma rays produced by intracavity Compton backscattering of a free electron laser (FEL) on the UVSOR storage ring have been observed. In the experiment, the storage ring was operated at an electron energy of 600 MeV. The FEL wavelengths were 466 and 270 nm, and then maximum photon energies were calculated to be 14.6 and 25.2 MeV, respectively. Spectra of the photons measured by using a large NaI scintillation detector were found to be consistent with a theoretical calculation.

Electronic Structure of Al-Li-Cu Quasicrystal: Photoemission and Inverse Photoemission Studies of Icosahedral and Crystalline Phases

Photoemission and inverse photoemission measurements are reported for icosahedral and crystalline phases of Al-Li-Cu with similar compositions. In the photoemission spectra, Al and Li core states of the icosahedral quasicrystal are shifted to larger binding energies from those of the crystalline phase by 0.4 eV, in contrast to negligible shift of Cu states. A gaplike feature of the density of states is observed in the inverse photoemission spectra of the quasicrystal just above the Fermi level. Comparison between the theoretical calculation and the experimental results of the crystalline phase is discussed.