Tight-binding calculations of surface states of Si(111)

Semi-empirical tight-binding calculations are reported for Si(111) surfaces. The calculations reproduce quantitatively the results obtained both experimentally and by more elaborate theoretical methods.     

On interpretation of intrinsic surface states on Si(111) surface

Extended Hückel theory is applied to the Si9111) ideal and relaxed surfaces. In addition to the results obtained by selfconsistent pseudopotential calculations of Schlütter et al., new surface states gave been found. The results are essentially independent of surface relaxation.     

Electronic states and electron-phonon coupling at the 2×1 reconstructed Si(111) surface

The electronic structure of Si(111)-2x1 is studied selfconsistently for several values of the reconstruction parameters within Haneman's model. The derivatives of the dangling-bond bands with respect to the surface atom displacements are calculated and the surface electron-phonon coupling is estimated.     

Density of states at the Si(111)-(2×1) surface: A study of the clean and H-covered surface

The electronic structure of the Si (111)-(2×1) surface is analyzed by comparing different reconstruction models. The changes of state density induced by chemisorption of hydrogen are investigated for the different surface geometries.     

Laser-induced oxidation of the Si(111) surface

Pulsed laser induced oxidation of clean Si(111) surfaces has been studied by Auger electron spectroscopy and electron energy loss spectroscopy. The short duration time of the pulse has allowed a precise investigation of the first stages of the oxidation. About 1–2 oxide monolayers first grow in less than 10 s. Their stoichiometry evolves from SiO_x towards SiO₂ with increasing beam energy densities. Once this superficial layer has formed, no evolution is seen with further irradiation, suggesting that oxygen diffusion during the pulse duration cannot sustain the oxide growth.     

Ge adsorption on the Si(111) surface

Total energy calculations, performed for one monolayer of Ge adsorbed on Si(111), indicate that 1 × 1 models such as the atop site and hollow site adsorption geometries are unstable with respect to the formation of 2 × 1 Seiwatz chains of Ge adatoms. This result indicates that, for one monolayer coverage, Ge-Ge bonds are likely to form.     

Surface states in Si(111)2×1 and Ge(111)2×1 by optical reflectivity

Surface states in Si(111)2×1 and Ge(111)2×1 are detected by the method of the change of external reflectivity, both at energies below and above the gap. Optical transitions at 2.6 eV in Si and at 1.8 eV and 3.1 eV in Ge, as well as the already known transitions below the gap are observed.     

Study of the Si(111) 7 × 7 surface structure by alkali- metal adsorption

When alkali-metals such as Li, Na, K, Rb and Cs were adsorbed on clean Si(111) 7 × 7 surface at room temperature, the intensity distribution of the original 7 × 7 RHEED pattern changes gradually with the increase of alkali-metal adsorption, and at last a new superstructure with 7 × 7 periodicity, here named δ-7 × 7 structure, has been observed. This change at room temperature can be explained if the 7 × 7 structure is mostly made of displacement. The structure model estimated from the intensity distribution of the δ-7 × 7 pattern is the one that has one vacancy at the corners of the 7 × 7 unit mesh and relaxed surrounding atoms. The change of the 7 × 7 structure by alkali-metal adsorption to this model is naturally understood with our new model (1984). For all alkali metals, by adsorption at high temperature 3 × 1 superstructure has also been observed for the first time.     

Properties of Si nanostructural modification on Si (111) surface

Si nanostructures (Si-NSs) epitaxially grown or adsorbed on Si (111) surface, with various shapes including pit-like, bars, islands, hill-like, diamond-like and double cage, were studied theoretically using density-functional theory (DFT) calculations. The electronic and optical properties of these Si-NSs were calculated, showing that the designed Si-NSs modifications can enhance the optical absorption for Si surface.     

Theoretical study of the Cl-passivated Si(111) surface

The Cl-passivated Si(111) surface is studied using density functional theory, in conjunction with the B3LYP functional and the cluster model. We compute the Si–Cl frequency and the Si–Cl bond energy for R₃SiCl, and the abstraction barrier for the reaction R₃SiCl+H→R₃Si+HCl using the B3LYP approach. We calibrate the B3LYP bond energy and the abstraction barriers using the values obtained using the G2MP2, G2 and CCSD(T) approaches. Our computed B3LYP Si–Cl frequency of 555 cm⁻¹ is in good agreement with the experimental value of 588 cm⁻¹. The shift in the Si–Cl frequency as surface chlorine is added to the cluster agrees with experimental observations.     

Observation of Si(111) and gold-deposited Si(111) surfaces using micro-probe reflection high-energy electron diffraction

Observations of clean Si(111) and gold-deposited Si(111) surfaces have been performed using micro-probe reflection high-energy electron diffraction. It was found that many atomic steps on a Si(111) surface run in nearly the same direction, about 9° off the [1̄1̄2] direction. When gold was deposited on this surface at a substrate temperature of about 800°C, 5 × 1, diffuse √3 × √3R30°, sharp √3 × √3 R30° structures and Au clusters appeared on the surface with continuation of the deposition. During the deposition process, it was found that one kind of Si(111) 5 × 1 Au domain grew selectively along these atomic steps and nearly covered the entire surface. A phenomenon of gold clusters moving during the deposition was also observed. These clusters all moved in nearly the same direction so as to climb the atomic steps.     

First-principle study of Mg adsorption on Si（111） surfaces

We have carried out first-principle calculations of Mg adsorption on Si(111) surfaces. Different adsorption sites and coverage effects have been considered. We found that the threefold hollow adsorption is energy-favoured in each coverage considered, while for the clean Si(111) surface of metallic feature, we found that 0.25 and 0.5 ML Mg adsorption leads to a semiconducting surface. The results for the electronic behaviour suggest a polarized covalent bonding between the Mg adatom and Si(111) surface.