Kengo Ishiyama

Homo-epitaxial growth on the Si(111) 7 × 7 surface

Abstract The initial stage of silicon growth on the Si(111)7 × 7 surface is investigated by a field ion scanning tunneling microscope (FI-STM) as a function of substrate temperature. It is found that structures of growth nuclei depend on the substrate temperature and most of the nucleations occur randomly at a faulted half of the unit cell of the dimer-adatom-stacking-fault (DAS) structure. It appears that coalescence between growth nuclei occurs rarely at low temperatures. At the substrate temperature of 300°C, characteristic figures of a cluster structure are found on the surface at submonolayer deposition. Most of the clusters are grown symmetrically with respect to the dimer rows of the DAS structure. The half segment of the symmetric cluster is also formed on the surface. Since crystal nuclei smaller than this cluster are scarcely observed in the STM images, it is concluded that the cluster is the smallest unit of the nuclei of homo-epitaxial growth at about 300°C. From the STM image analysis it is concluded that the structure of the cluster is not made of DAS-type structure, but a structure including dimers and/or pyramidal clusters. Structure analysis of the cluster is underway. At and above 300°C, small islands of 5 × 5 DAS structure are frequently observed on nucleation clusters. In large islands, however, a 5 × 5 structure is rarely observed, and a regular 7 × 7 is observed. This suggests that the transition from 5 × 5 to 7 × 7 structure occurs during the island growth. At temperatures higher than 500°C, step flow growth with 7 x 7 structure is observed as well as a few parts of island growth including 5 × 5 structure.

Thermal decay of silicon islands and craters on silicon surfaces by scanning tunneling microscopy

Thermal decomposition processes of isolated silicon islands and filling-up processes of isolated craters on Si(111)7 X 7 surfaces are observed at various temperatures. By Arrhenius plots of rates of these size charges, activation energies for island decomposition and crater filling-up on the Si(111) surface are determined as (1.5 ± 0.1) and (1.3 ± 0.2) eV, respectively. Pre-exponential factors are 2.1 X 10 11±1 and 2.6 X 10 9±2 s -1 for the islands and craters on the Si(111) respectively. On the Si(111) surface the rates for island decomposition are five times larger than those of craters filling up. We discuss the results with two-dimensional vapor phase processes and the Schwoebel effect.

Ejection angle dependence of electrical properties of ion beam sputtered tantalum oxide films

Ion beam sputtering was used to deposit tantalum oxide films on silicon substrates at different positions surrounding a Ta2O5 target. dc conductance of the films shows dependence on the ejection angle of sputtered particles and primary ion energy. Capacitance‐voltage characteristics also vary by changing the primary ion energy. These variations of electrical properties are discussed by considering the effect of anisotropic ejection of the sputtered energetic particles.

Site conversion path and the kinetics of Ti on Si(001)-2 × 1 observed by scanning tunneling microscopy

Abstract We have used a variable-temperature scanning tunneling microscope to observe the site conversion path and the kinetics of Ti adsorbed on the Si(001)-2 × 1 surface. We have found that the monatomic adsorption of Ti is featured by two metastable precursory states and the final state. A Ti adatom is reversibly converted between the two precursory states, i.e., the pedestal site adsorption and a highly mobile state between the dimer rows. A conversion to the final state at the vacancy site occurs only from the pedestal site adsorption. Rates of two types of the site conversions from the pedestal site were measured by counting individual site conversion events as a function of time. The obtained activation energies and the conversion path are consistently interpreted in terms of the bonding nature of a Ti adatom on the Si dimer configuration.

Adsorption reactions of TiSi(001) by variable-temperature STM

Abstract Monatomic adsorption of Ti on the Si(001)-2 × 1 surface has been observed by variable-temperature scanning tunneling microscopy. A Ti atom is reversibly converted between two precursor states which are pedestal site adsorption and a highly mobile state between the dimer rows. The final state, that is a vacancy site adsorption, is formed only from the pedestal site adsorption inducing ejection of Si dimer atoms. The quantitative and qualitative evaluation of the site conversion reveals that the adsorption behavior is highly affected by the local bonding properties of Ti with the Si 2 × 1 reconstruction.

I. Surface structureAdsorption reactions of TiSi(001) by variable-temperature STM

Abstract Monatomic adsorption of Ti on the Si(001)-2 × 1 surface has been observed by variable-temperature scanning tunneling microscopy. A Ti atom is reversibly converted between two precursor states which are pedestal site adsorption and a highly mobile state between the dimer rows. The final state, that is a vacancy site adsorption, is formed only from the pedestal site adsorption inducing ejection of Si dimer atoms. The quantitative and qualitative evaluation of the site conversion reveals that the adsorption behavior is highly affected by the local bonding properties of Ti with the Si 2 × 1 reconstruction.

Adsorption reactions of by variable-temperature STM

Abstract Monatomic adsorption of Ti on the Si(001)-2 × 1 surface has been observed by variable-temperature scanning tunneling microscopy. A Ti atom is reversibly converted between two precursor states which are pedestal site adsorption and a highly mobile state between the dimer rows. The final state, that is a vacancy site adsorption, is formed only from the pedestal site adsorption inducing ejection of Si dimer atoms. The quantitative and qualitative evaluation of the site conversion reveals that the adsorption behavior is highly affected by the local bonding properties of Ti with the Si 2 × 1 reconstruction.

Observations of Y-Ba-Cu-O Films by Scanning Electron Microscopy and Auger Electron Spectroscopy

Structures of Y-Ba-Cu-O sputter-deposited films were investigated by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES). After heat treatment, the films showed different morphology for different substrates, i.e., A12O3 and MgO, and for different thicknesses of 0.1 μm and 1.2 μm. Only for YBaCuO(P.1μm)/MgO, highly oriented crystal growth is seen, and for other systems, inhomogeneous crystal growths are seen. An interface roughning caused by preferential interdiffusion of Ba into an A12O3 substrate was observed. A surface enrichment of Cu is found for the thick films. These differences in morphology are considered to be due to the differences in the diffusion processes.