Strain due to nickel diffusion into hydrogen-terminated Si(1 1 1) surface

We studied the affection of thin (i.e., 0.2–0.8 nm) Ni films on hydrogen-terminated Si(1 1 1) substrate surface by using strain-sensitive X-ray diffraction. It was reported that Ni deposition onto hydrogen-terminated Si surface apparently does not cause film growth, but rather diffuses into the Si crystal, creating an “Ni diffusion layer” up to Ni deposition 0.8 nm thick. Measured rocking curves of the Si 1 1 3 reflection and integrated intensities of the rocking curves for the substrate provide information about the evolution of the strain field introduced near the substrate surface during Ni diffusion into the substrate. Comparing the measured and calculated rocking curves indicates that compression of the {1 1 1} spacing of the Si occurs gradually up to an Ni thickness of 0.6 nm, and that above this thickness, strain relaxation occurs.

We found that the slope of the integrated intensity of the rocking curve versus X-ray wavelength correlates to the strain field near the surface, in the same way that the shape of the rocking curves correlate to the strain field near the surface. Dynamical diffraction calculations indicate that measurement of the slope of the integrated intensity of the rocking curve versus X-ray wavelength is useful for strain analysis, because the dependence is not only sensitive to strain fields, but is also insensitive to the effect of absorption by the overlayer, which otherwise would cause deformation of the shape of the rocking curve.     

Adsorption and diffusion of a Si adatom on the H/Si(1 1 1) surface: comparison with the H/Si(0 0 1) surface

Using a first-principles method, we investigate the adsorption and diffusion of a Si adatom on the H-terminated Si(1 1 1) substrate, which would be useful in understanding the initial stages of Si homoepitaxy using a H surfactant. The adatom substitutes H atom(s) to form a monohydride structure or a dihydride structure. In forming the monohydride structure, the energy barrier for H substitution is absent. The adatom migrates on the surface with alternating its chemical state between monohydride and dihydride. These behaviors of the adatom are quite similar to those on the H/Si(0 0 1)2 × 1 surface, despite the significant difference in the substrate structure between both orientations. The resulting diffusion barrier is 1.30 eV, which is also comparable to that on the H/Si(0 0 1)2 × 1 surface.     

New phase and surface melting of Si(111) at high temperature above the (7x7)-(1x1) phase transition

The surface structure of Si(111) at high temperatures (950-1380 degrees C) has been studied with reflection high-energy electron diffraction. We have found three different surface structures: (1) A relaxed bulklike structure with adatoms of 0.25 monolayer (ML) is formed (950-1210 degrees C); (2) there is a new phase where the adatom coverage decreases to 0.20 ML (1250-1270 degrees C); (3) the surface melting occurs over 1290 degrees C. The crystalline structure below the melting layer can be explained by the vacancy model missing all adatoms and 0.45 ML of atoms in the first-double layer.     

One-dimensional Ge nanostructures on Si(001) and Si(1 1 10): Dominant role of surface energy

Ge/Si(001) is a prototypical system for investigating three-dimensional island self-assembly owed to the Stranski–Krastanow growth mode. More than twenty years of research have produced an impressive amount of results, together with various theoretical interpretations. It is commonly believed that lattice-mismatch strain relief is the major driving force leading to the formation of these islands. However, a set of recent results on Si(001) and vicinals point out that, under suitable conditions, this is not the case. Indeed, we here review experimental and theoretical results dealing with nanostructures mainly determined by surface-energy minimization. Results are intriguing, as they reveal the existence of magic sizes, show the presence of very peculiar morphologies, such as micron-long wires, and distinguish among attempts to facet the wetting-layer and true SK islands.     

Structure of the laser annealed Si(1 1 1)-(1 × 1) surface

LEED analysis of the laser annealed Si(1 1 1)-(1 × 1) surface shows that a model with a graphite-like top double layer of atoms with a spacing of 2.95±0.02 Å from the second double layer describes the LEED data as well as the Zehner model, but involves large displacements of the atoms normal to the surface as required by ion scattering results. It is suggested that this model provides a natural interpretation of the low energy He atom scattering data for the Si(1 1 1)-(7 × 7) surface.     

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.     

Metal induced step arrangement on Si(1 1 1) surface observed by LEED

Adsorbed structures of Ba on Si(1 1 1) surfaces have been observed by LEED. In elevating the annealing temperature after a few monolayers (MLs) deposition at room temperature (√3×2√3)R30°, 2×8 and 3×1 patterns were observed as reported by Weitering [H.H. Weitering, Surf. Sci. 355 (1996) L271]. Additionally a one-dimensional 10×1 pattern was observed in the temperature range between the appearance of two-dimensional 2×8 and 3×1 patterns. This pattern is considered to be produced by a combination of the periodical terrace with a width of 10 unit lengths separating each step and a 5×1 reconstruction on the terrace.     

Depth profiling of melting and metallization in Si(111) and Si(001) surfaces

An original approach for measuring the depth profile of melting and metallization of the Si(111) and Si(001) surfaces is proposed and applied. The different probing depths of the Auger electron and electron energy loss (EELS) spectroscopies are exploited to study the number of molten and metallic layers within 5-30 ? from the surface up to about 1650 K. Melting is limited to 3 atomic layers in Si(001) in the range 1400-1650 K while the number of molten layers grows much faster (5 layers at about 1500 K) in Si(111) as also indicated by the L(3)-edge shift observed by EELS. The relationship between melting and metallization is briefly discussed.     

Influence of interface structures on Sn thin film growth on Si(1 1 1) surface

Using coaxial impact collision ion scattering spectroscopy, we have investigated Sn thin film growth on Si(1 1 1)√3×√3-Sn and hydrogen-terminated Si(1 1 1) surfaces at room temperature. Sn formed crystalline film with β-Sn structure on Si(1 1 1)√3×√3-Sn surface, but on the hydrogen-terminated Si(1 1 1) surface, the epitaxial growth of Sn thin film was disrupted, and Sn grew as a polycrystalline film. The growth orientational relationship of the Sn film grown on Si(1 1 1)√3×√3-Sn surface was found to be

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. In the works, we found that interface structure plays a decisive role for the growth mode, crystallinity, and growth orientation of the growth of thin film.     

Highly stable passivation of a Si(1 1 1) surface using bilayer-GaSe

As a stable and ‘epitaxial’ passivation of a Si surface, we propose the bilayer-GaSe termination of a Si(1 1 1) surface. This surface is fabricated by depositing one monolayer of Ga on a clean Si(1 1 1) surface and subsequent annealing in a Se flux at around 520 °C, which results in unreconstructed 1×1 termination of the Si(1 1 1) surface by bilayer-GaSe. We found by scanning tunneling microscopy observation that slow cooling of the clean Si(1 1 1) surface from 850 to 520 °C with simultaneous deposition of a Ga flux results in better termination of the Si(1 1 1) surface. It was also found that this surface is stable against heating around 400 °C in O₂ atmosphere of 3×10⁻³ Pa. By utilizing these properties of the bilayer-GaSe terminated surface, we have succeeded in fabricating ZnO quantum dots on this substrate.     

Optical properties of arrays of Si nanopillars on the (1 0 0) surface of crystalline Si

We studied Si nanopillars arrays interesting for potential applications in both photonics and electronics. Two types of the Si nanopillars arrays were investigated. The first type is a regular array (square lattice with the spacing of 270 nm) made up of nanopillars with diameters of 60–70 nm (non-quantum nanopillars). Polarized reflection spectra displaying photonic band gap features and the corresponding photonic band structures were studied. The second type is a non-regular array made up of nanopillars with diameters of 10–20 nm (quantum nanopillars). Enhancement of the optical phonon Raman band, change of selection rules and a low-frequency shift of 0.5 cm⁻¹ of the band corresponding to the quantum size effect in Si cylinders with average diameter 15 nm were observed for the quantum nanopillars.     

Co-induced nano-structures on Si(1 1 1) surface

The interaction of cobalt atoms with silicon (1 1 1) surface has been investigated by means of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Besides the Co silicide islands, we have successfully distinguished two inequivalent Co-induced reconstructions on Si(1 1 1) surface. Our high-resolution STM images provide some structural properties of the two different derived phases. Both of the two phases seem to form islands with single domain. The new findings will help us to understand the early stage of Co silicide formations.     

Chemisorption of Au on Si（001） surface

The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B_1 site(bridge site), resulting in a Au－Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.