Yukichi Shigeta

Formation of uniform nanoscale Si islands on a Si(111)-7×7 substrate

During epitaxial growth on a substrate with a stable surface structure, rearrangement from a superlattice to a normal 1×1 lattice is essential when the substrate is covered with a growing layer. Since rearrangement needs activation energy, lateral growth is prevented at the boundary of the structure unit. In the growth of Si on a stable 7×7 structure composed of a dimer-adatom-stacking- fault layer, lateral growth of islands is prevented at the dimer row. Such a restriction on the lateral growth leads to a discontinuous size distribution of islands, whose size depends on the size of the 7×7 structure unit. In the initial stage of nucleation and growth, we have observed many rounded Si islands with uniform diameters of 3.8 nm when the substrate temperature has been held at 380 °C for 10 min after deposition of Si. From the change in the island size distribution as a function of annealing time after the deposition, we conclude that the rounded island is constructed of atoms created by the dissociation of un...

STM and SEM studies on the character of triangular Si(111)-7 × 7 domains formed in quenched Si(111) surface☆

Abstract STM and SEM observations have been made on the 7 × 7 ordering process of quenched Si(111)-1 × 1 surface and on quenched metastable atom complexes. All the triangular 7 × 7 domains nucleated in the 1 × 1 region have been found to have character 〈112〉. The rate-controlling process for the growth is the nucleation of a faulted half cell at the outermost edge of the triangular domain. Corner holes, instead of dimer rows play a critical role for the nucleation of the faulted half cell. The contrast of STM filled state images have been examined on the quenched complexes; it is dark for the centered adatoms of 9 × 9 and 11 × 11, and for all the adatoms of 2 × 2, c(2 × 4) and a defected half of unfaulted type which was found for the first time in the present work. In contrast with these complexes, the adatoms of √3 × √3 structure appear bright. These features are interpreted in terms of the charge transfer (between the adatoms and rest atoms) mechanism. Extreme stability has been noted for a triangular defect region of 1 × 1 (with side a ) in quenched Si(111) and has been attributed to the domain boundaries running from the apices of the triangular defect. The stability has been analysed quantitatively in terms of the energy versus a curve derived in this paper.

Surface structure change during solid phase epitaxial growth of an amorphous Si film deposited on Si (111)

Some surface structure change of an amorphous Si film deposited on Si (111) during the solid phase epitaxy was observed by low‐energy electron diffraction (LEED). The LEED intensity profile shows the formation of 7×7 structure whenever a crystallized surface is constructed. The intensity increases with an increase of the annealing temperature Ta, where the increasing rate with Ta becomes small for 590<Ta<700 °C, and for 780<Ta<850 °C. It is discussed that there exists some process inhibiting the growth of the 7×7 structure regions in these two temperature ranges.

Photon Stimulated Desorption of Positive Ions from LiF

Photon stimulated desorption (PSD) of positive ions from LiF is observed in the photon energy region between 30 and 70 eV. The creation of the Li+(1s→2s) core exciton leads to the rapid rise of both Li+ and F+ desorption yields. It is found that PSD of positive ions from LiF is due to the interatomic Auger transition. The yield spectrum of F+ ions is different from that of Li+ ions above 60 eV. The F+ yield spectrum has a deep valley at around 63 eV, while the Li+ spectrum shows a plateau in the same region. However the difference in the yield spectra of Li+ and F+ ions can not be explained at present.

Formation of some hierarchy in amorphous structure during the crystallization of vacuum‐deposited amorphous semiconductor films

A view that some hierarchy in the structure of the amorphous phase surrounding the crystallized phase is formed, is proposed from the investigation of the kinetics in the crystallization process of amorphous semiconductor films. The view is discussed from some results in the study of solid‐phase epitaxial growth of the amorphous Si film deposited on the Si(111) surface by low‐energy electron diffraction. Some comment on the formation of the amorphous structure is also given from a viewpoint of thin‐film growth.

A characteristic feature of crystalline thin-film growth of Si on a 7 × 7 superlattice surface of Si(111)

Abstract A Si film has been grown on a 7 × 7 superlattice surface of a Si(111) substrate at 250 and 380°C. Reflection high-energy electron diffraction patterns of the Si film at 250°C consist of a diffuse 2 × 2 structure and a weak 7 × 7 structure at 380°C. The experimental results indicate that the initial growth of crystalline nuclei is caused by the crystallization of amorphous-like islands at 250°C and by the formation of an island composed of three 5 × 5 structural units with a corner hole at their center at 380°C. The formation of crystalline nuclei is discussed.

Observation of Initial Growth Stage of Amorphous Si Film Deposited on 7×7 Superlattice Surface of Si(111) by Low-Energy Electron Diffraction

The intensities of low-energy electron diffraction (LEED) were measured from Si films with various thicknesses (d) which had been deposited on a 7×7 reconstructed surface of Si(111) substrates maintained at 170°C. The intensity profile from Si films at d>60 A gives a feature showing the formation of an amorphous phase. From ultrathin Si films with 5 A<d<60 A, two peaks were observed clearly at positions which correspond to the (0, 0) and (1, 0) rods in the Si(111) surface. This suggests that the Si film in the vicinity of the Si(111) substrate comprises interface layers with the some ordered structure. Some discussion is given on the interface layers, which are composed of two epitaxially grown grains. A normal stacking sequence of the diamond structure is formed in one grain and the reversed stacking sequence grows at the stacking fault layer on the preserved 7×7 structure in another grain.

Direct observation of Si(111) √7×√7-Co structure and its local electronic structure

The structure of Si(111) √7×√7 R19.1°-Co reconstructed surface have been investigated by scanning tunneling microscopy (STM). Three proposed sites on the reconstructed surface, the Co atom site, the cap-adatom site and the bridge-adatom site have been all visualized by STM. The electric structure at each adatom site was measured by scanning tunneling spectroscopy, exactly. The reason why the bridge site can be visualized under the restricted condition is also explained by the local electric state above the Fermi level.

Surface wave resonance effect in low-energy electron energy-loss spectra from MgO(001)*

Abstract The study the influence of inelastic diffraction on low-energy electron energy-loss spectra (LEELS), the LEELS from an air-cleaved (001) face of MgO were observed for various values of energy and angle of incidence of primary electrons, scattering angle and azimuthai angle. It has been confirmed that the LEELS consist of two kinds of loss peaks: those associated with an energy loss after the elastic diffraction and those associated with an energy loss before the elastic diffraction (Kikuchi line). The latter is observable only when inelastically scattered electrons are diffracted under the surface wave resonance (SWR) conditions. It has also been found that the Kikuchi Une splits into two with an intensity dip at the centre under one of the SWR conditions.

Surfaces of Vacuum-Deposited Silicon Oxide Films Studied by Auger Electron Spectroscopy

Silicon oxide films were deposited at a rate of 10–20 A/min by heating commercial SiO powder in vacuums of 10-5 and 10-7 Torr and were analyzed by Auger electron spectroscopy (AES). To assign the Auger spectra with the energy range 50–100 eV from the film surfaces, AES was carried out on air-fractured and electron-irradiated surfaces of quartz. The spectra are attributed to a three-dimensional network of Si(–O–)4 tetrahedra; no spectra due to networks of Si(–Si–)4 tetrahedra were observed. These results were supported by low-energy electron energy-loss spectra observations. The Auger spectrum associated with oxygen vacancies was also observed, the intensity of this being higher for the films prepared in the higher vacuum. Thus the silicon oxide film surfaces are presumed to consist of a three-dimensional network of Si(–O–)4 tetrahedra with some oxygen vacancies.