Sung-Te Li

Inelastic Low Energy Electron Diffraction Measurements of Hydrogen Adsorbed Si (001) Surfaces: 2×1:H and 1×1: :2H

We identified the monohydride phase Si(001)2×1:H and the dihydride phase Si(001)1×1: :2H by angle resolved electron energy loss profiles and I–V curves of 00-beam. For the 2×1:H-saturated surfaces, S3 transition from back bond surface state was observed although S1 transition from dangling bond surface state disappeared. For the 1×1: :2H surface, S2 and S3 transitions from back bond surface states completely disappeared but S1 transition was observed. We clearly distinguished hydrogen induced loss peaks for the two surfaces: the peaks were at 8 eV for the 2×1:H surface and at 7 eV for the 1×1: :2H surface.

Diffuse scattering in the high-temperature (1×1) state of Si(111)

Diffuse spots slightly displaced from the (\(\sqrt{3} \times \sqrt{3}\)) positions were observed in the high-temperature (1×1) state of Si (111) by low-energy electron diffraction. The spots showed threefold 3m symmetry and rotated around the \(\sqrt{3}\) positions with changes in primary energy. These are reproduced by kinematic calculations for a surface configuration with adatoms distributed randomly over both the threefold-hollow and threefold atop sites of a (1×1) substrate with the exclusion of forming bonds with a common substrate atoms.

Ag/Si(111)-7×7 systems investigated by angle resolved electron energy loss spectroscopy

Abstract Electronic and crystallographic structures were investigated by using AR-ELS and LEED I - V profile on some different stages of RT deposition of Ag on Si(111): the √3 and the “3 × 1”-Ag surfaces. One of them at 1.2 eV on √3 -Ag was ascribed to the bare silicon dangling bond state. The electronic structure of √3-Ag was consistent with the recent structural model in which Ag atoms are embedded. The results of the RT deposition were explained by a layer by layer growth picture. Dispersions of surface plasmons on the clean, the 2 3 ML-Ag(RT), the √3-Ag and the “3 × 1”-Ag surfaces, and the surface state one-electron transition S 2 of the clean surface were observed.

Effects of adsorption and thermal desorption of atomic hydrogen on electronic and atomic structures of Si(111)(√3×√3)-Al surface

The adsorption and thermal desorption of atomic hydrogen induce electronic and atomic structural changes on the Si(111)(√3×√3)-Al surface. These changes have been studied using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and angle-resolved electron-energy-loss spectroscopy (AR-EELS). Upon exposure to atomic hydrogen, the (√3×√3) surface structure changes into a hydrogen-induced (1×1) in the LEED pattern. Simultaneously, the characteristic loss peaks of the Si(√3×√3)-Al surface completely disappear and a new loss peak appears at 8 eV. We ascribe this new peak to a Si-H bonding state. After thermal desorption of atomic hydrogen, a (√3×√3) LEED pattern reappears and a new loss peak emerges at 1.5 eV. The Al-LVV Auger peak is observed on the Si(√3×√3)-Al surface, but not on this hydrogen-desorbed surface. The new loss peak at 1.5 eV is ascribed to the transition due to the Si-adatom-induced surface state. The reappeared (√3×√3) surface structure is proposed to be induced by the Si adatoms substituting for Al in the T4 adatom geometry.

Si(111)(?3??3)-Al Surface Studied by Angle-Resolved Electron-Energy-Loss Spectroscopy

The surface electronic structures of Si(111)(√3×√3)-Al are investigated with the use of angle-resolved electron-energy-loss spectroscopy. Three new surface one-electron transitions (in specular reflection) are found at 1.8, 7.2, and 13.1 eV. Compared with the surface state band structures calculated by Northrup and STM results by Hamers and Demuth, the loss peak at 1.8 eV is ascribed to the one-electron transition between the occupied and unoccupied surface state bands which originate from the Al adatoms. The other two peaks are considered to be due to the Si-Si strained back bonds.

Initial stages of aluminum epitaxy on the Si(111)√3×√3-Al surface studied by electron-energy-loss spectroscopy

Abstract The initial stages of aluminum epitaxy on the Si(111)√3×√3-Al (√3-Al) surface have been investigated with the use of electron-energy-loss spectroscopy (EELS) and low-energy electron diffraction (LEED). We find that for deposition of 0.6 ML either at room temperature (RT) or at 350°C, the value of the surface plasmon energy (ħωs) decreases to 10.0 eV. With increasing Al coverage at RT, the value of ħωs gradually increases to that on the Al(111) surface. In contrast, by further deposition of 1.1 ML at 350°C, the value of ħωs immediately increases to 10.9 eV and then stays almost constant. The results are explained in terms of the Al overlayer structures.

Ge-derived Si(1 1 1)(7 × 7) structure studied by low-energy electron diffraction and angle-resolved electron-energy-loss spectroscopy

Abstract Using low-energy electron diffraction (LEED) and angle-resolved electron-energy-loss spectroscopy (AR-EELS), we find that a new Ge-derived Si (7 × 7) superstructure is formed as the stable surface phase at a Ge coverage of 1.5 monolayers. A new surface one-electron transition appears at 1.15 eV ( at δk| ( the momentum transfer ) = 0 A −1 ) and the Si dangling bond surface state transition at 1.5 eV ( at δk| = 0 A −1 ) disappears, while loss peaks due to SiSi back-bond surface states still remain. We ascribe the new peak to the Ge dangling-bond surface state transition and propose that the Ge atoms substitute the Si surface atoms which have surface dangling bonds.

(7×7) and (5×5) superstructures of Ge‐covered Si(111) surfaces studied by angle‐resolved electron‐energy‐loss spectroscopy

Using angle‐resolved electron‐energy‐loss spectroscopy (AREELS), (7×7) and (5×5) surface structures of the ultrathin Ge films on Si(111)(7×7) surfaces are investigated. At a coverage of 1.5 monolayers (ML) of Ge, the Si(7×7)–Ge surface appears. On this surface a loss peak due to surface states of Ge dangling bonds appear at 1.15 eV (Δk∥=0 A−1) and the one due to Si dangling bonds disappears, but the loss peaks due to the Si–Si backbonds are still observed. When the (5×5) surface structure develops at a coverage of 2 ML, the remaining loss peaks due to the Si–Si backbonds disappear and loss peaks due to Ge–Ge backbond surface states at 9 and 14 eV. We propose structural models of the Si(7×7)–Ge and Si(5×5)–Ge surfaces based on the structural models on the clean Si(7×7) surface [Takayanagi et al., J. Vac. Sci. Technol. A 3, 1502 (1985)].

Au adsorbed Si(111) surfaces studied by angle-resolved electron-energy-loss spectroscopy

Abstract Electronic structure was investigated by using AR-EELS on some different stages of Au on Si(111): the 5 × 1- and the √3-Au surfaces. The loss peak at 2.2 eV on 5 × 1 was ascribed to the bare Si dangling bond state. The electronic structure of 5 × 1-Au was consistent with the recent structural model in which Au atoms are embedded. Dispersion of surface plasmons on the √3-Au surface was observed.