Takasi Sagawa

Study of Ag/Si(111) submonolayer interface: I. Electronic structure by angle-resolved UPS

Abstract Angle-resolved ultraviolet photoelectron spectra have been measured for well defined Ag/Si(111) submonolayer interfaces of (1) Si(111)( 3 × 3 )R30°-Ag , (2) “Si(111)(6 × 1)-Ag”, and (3) Ag/Si(111) as deposited at room temperature. Non-dispersive and very narrow (FWHM ∼ 0.4–0.5 eV) Ag 4d derived peaks are found at 5.6 and 6.5 eV below the Fermi level for surface (1) and at 5.3 and 6.0 eV for surface (2). Dispersions of sp “binding” states in the energy range between E F and Ag 4d states have been precisely determined for surface (1). Electronic structures similar to those of the Ag(111) surface, including the surface state near E F , have been observed for surface (3).

Angle-resolved ultraviolet photoemission study of Si(111) 7 × 7 and 1 × 1 surfaces

Abstract Angle-resolved ultraviolet photoelectron spectra of Si(111) 7 × 7 and 1 × 1 surfaces have been measured as a function of temperature from ambient temperature to ≈ 1120°C. Both the Si(111) 7 × 7 and 1 × 1 surfaces show obvious surface metallic edge at all the temperatures. A middle peak among three surface-state peaks observed for ambient-temperature 7 × 7 surface has been found to disappear for high-temperature 7 × 7 surface. In going from high-T 7 × 7 surface to high-T 1 × 1 surface, no essential changes in the surface-state peaks have been found to occur.

XPS study of rare earth dodecaborides: TmB12, YbB12 and LuB12

Abstract Single phase TmB12, YbB12 and LuB12 were successfully obtained by the arc-melting and floating zone methods. The XPS measurements of these compounds have indicated that (1) only YbB12 is a valence fluctuating compound with the valency of +2.9 at room temperature, (2) the correlation energy between Yb2+ and Yb3+ ions is about 6.0 eV, (3) Tm and Lu ions in the dodecaborides are in a trivalent state, and (4) the binding energy of the 4f level in TmB12 and LuB12 is 5.0 and 7.7 eV, respectively.

Soft X-Ray Absorption Spectra of Metals and Alloys. I. Be, Al, Sb, Bi and Al-Mg Alloys

Soft X-ray absorption spectra of Be, Al, Sb and Bi, and Al-Mg alloys have been obtained by the use of synchrotron radiation emitted from the 750 MeV electron synchrotron at the Institute for Nuclear Study, Tokyo, as a continuous light source. The K-absorption structure of beryllium was found to agree with the density of states calculated by Loucks and Cutler. Some correspondence was found between the maxima in the L 2,3 -absorption spectrum and the K-absorption spectrum of aluminum. A remarkable band was observed in the L 2,3 -absorption spectrum of aluminum at 23 eV above the edge. This band is not attributable to the singularity in the state density of the conduction band. A tentative interpretation based on the delayed onset of transitions 2 p -∞ d is proposed. The L 2,3 -absorption spectrum of aluminum in Al-Mg alloy shows a remarkable degeneration of the edge, while the L 2,3 -absorption edge of magnesium in the same alloy seems relatively unaffected. This behavior is similar to the effect reported b...

Soft X-Ray Absorption Spectra of Some Metal Chlorides

The Cl - L 23 absorption spectra of thin films of CuCl, ZnCl 2 , CdCl 2 , PbCl 2 , MnCl 2 , FeCl 2 , CoCl 2 , NiCl 2 , MgCl 2 , CaCl 2 , SrCl 2 , and BaCl 2 have been measured by the photographic method using synchrotron radiation from a 1.3 Bev electron synchrotron as a soft X-ray source. In all materials studied, other than CaCl 2 , SrCl 2 , and BaCl 2 , the absorption spectra near the threshold show absorption bands probably due to the creation of excitons with holes in the 2 p level of chlorine. The intense and broad absorption continuum beginning around 211 eV is observed in all materials studied. This absorption is assigned to the atomic excitation of Cl - ions. Discussion is given about the profile of each spectrum.

Electronic band structure of graphite studied by highly angle-resolved ultraviolet photoelectron spectroscopy

Abstract The electronic valence band structure of graphite has been experimentally determined with considerable accuracy for the first time by the highly angle-resolved ultraviolet photoelectron spectroscopy. The photoemission measurements were performed on a synthesized single-crystalline graphite (kish graphite) with the He II resonance line as an exciting source. Some high symmetry points in the Brillouin zone have been successfully identified in the experimentally determined band structure. The present experimental result has been compared with early photoemission experiments and some band calculations presented so far.

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.

K Emission Band of Graphite

The K emission band of graphite was observed using a grazing incidence spectrometer, and unfolded with the use of Gaussian window function. The unfolding procedure reveals the intrinsic profile of the state density. The profile consists of four sub-bands. The highest one is π-band and the lower three are σ-bands. The overlapping between them is very small. The height of the Fermi edge is about one fortieth of the peak of the π-band. The width of the π-band is 5.8 5 eV. The ratio of the effective number of electrons per atom for π-and σ-electrons is estimated to be 0.9:3, which suggests a slight mixing between them. It is also estimated that the three σ-electrons are distributed equally into the three parts of the σ-band. The low energy tail is classified as a satellite.

Photoemission (XPS and UPS) study of amorphous Bi2Se3 film

Abstract Photoemission (XPS and UPS) measurements were performed for elemental Se and Bi and, crystalline and amorphous Bi2Se3 films to terminate the long-standing controversy about the charge transfer in Bi-doped chalcogenide glasses. It was elucidated that the Bi atoms in amorphous Bi2Se3 are positively charged owing to an electronic charge transfer from the Bi atoms to the Se atoms. A comparison of the chemical shift of the core levels and the valence band between amorphous and crystalline Bi2Se3 indicates that the bonding is more covalent in amorphous phase than in crystalline phase, suggesting that although the Bi atoms in crystalline Bi2Se3 are six-fold coordinated by Se atoms, the Bi atoms in the amorphous phase are three-fold coordinated like the As and Sb atoms in amorphous chalcogenides.

Ultraviolet Absorption of Transition Metal Halides

The fundamental absorption spectra of the chlorides and the bromides of manganese, iron, cobalt, and nickel have been measured over the range from 2 to 40 eV. Fine structures occurring below 10 eV very as the transition metal changes. Spectral profiles 10 eV are simple and alike among the halides of different transition metals. Peaks located at the absorption edge shift systematically toward high energy from nickel halides to manganese halides, and are ascribed to the charge transfer transition from the outermost p orbitals of halogen to the unoccupied 3d orbitals of the transition metal. Comparison with soft X-ray absorption spectra suggests that the transitions from the outermost p orbitals of halogen to the 4 s orbitals of the transition metals produce peaks around 8 eV. Some of the other structures in the spectra are discussed.