Yasunori Tanaka

Surface science lettersAdsorption of H on Si(111) −3 × 3 − Ag: evidence for Ag(111) agglomerates formation

In this low-energy ion scattering study we find that the reaction of H with Si(111) − √3 × √3 − Ag results in an extensive surface modification. Saturated adsorption of H of about 1.5 ML coverage below 100 ° C transforms an uniform Ag monolayer in the √3 × √3 lattice into very small crystallites of Ag(111) grown epitaxially on the Si(111) substrate. The thickness of the Ag(111) crystallites is found to be three atomic layers. When only H is thermally desorbed by moderate heating above 400 ° C, the crystallite disappears and the original √3 × √3 − Ag is recovered.

Low energy ion scattering study of hydrogen-induced reordering of Pb monolayer films on Si(111) surfaces

Abstract The structural change of a Pb monolayer film caused by atomic hydrogen adsorption has been studied by using low-energy ion-scattering spectroscopy. Time-of-flight impact collision ion scattering spectroscopy and LEED are used in ultrahigh vacuum. It has been found that atomic hydrogen adsorption onto a Si(111)-√3 × √3-Pb surface at room temperature transforms a uniform Pb monolayer in the √3 × √3 lattice into very small clusters of Pb(111) grown epitaxially on the Si(111) substrate.

Interfacial structure control of cubic boron nitride films prepared by ion-beam assisted deposition

Abstract Boron nitride films were prepared by ion beam assisted deposition (IBAD). The films were synthesized by depositing boron vapor under simultaneous bombardment with nitrogen ions and nitrogen-argon mixture ions. Cubic boron nitride (c-BN) films with enhanced tribological properties had been explored by inserting a B-rich layer as a controlled buffer at the interface. Tribological characterizations of the buffer layer and the double-layered BN films consisting of the c-BN layer underneath with the B-rich buffer layer have been performed. Successful growth of c-BN layer has been observed on the B-rich layer and the hardness of the films increased almost linearly with increasing fraction of the sp 3 bonded cubic phase in the c-BN layer. The control of the interfacial structure exhibited a significant effect on the improvement of the tribological properties of the films due to the effective relaxation of internal stress of the c-BN films.

Thin-film growth-mode analysis by low energy ion scattering

In this paper we will propose the usefulness of time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) for the investigation of the initial growth mechanism of thin film on the solid surface. By using this technique we can estimate not only the structure of the grown metal crystallites but also the growth mode of the metal thin film on the solid surface and the size of the grown metal crystallites in a real-time measurement.

Ag thin film growth on hydrogen-terminated Si(100) surface studied by TOF-ICISS

Abstract Using time-of-flight (TOF) type low-energy impact-collision ion scattering spectroscopy (ICISS) and elastic recoil detection analysis (ERDA), we have investigated (1) the effect of the saturation of surface dangling bonds of Si(100) surfaces with atomic hydrogen upon Ag thin film growth, and (2) the effect of hydrogen adsorption onto Ag thin films (∼ 1 ML coverage) on the clean surfaces. We find that (1) epitaxial growth of Ag films is promoted by the hydrogen atoms residing at the film/substrate interface and (2) adsorption of hydrogen onto Ag monolayer deposited on Si(100) surfaces transforms the Ag monolayer into very small crystallites of Ag(100) grown epitaxially on the Si(100) substrate.

Hydrogen-induced reconstruction of Si(111)-√3-Ag surface studied by TOF-ICISS

Abstract The structural change of Si(111)-√3 × √3-Ag surfaces caused by atomic hydrogen adsorption has been studied using low-energy ion scattering spectroscopy. Computer simulations of ion scattering spectra have been carried out for various kinds of the morphology of the Ag deposit. Comparison of the simulation results with the observed change of the spectra reveals that the Ag monolayer with the √3 × √3-Ag structure is transformed into small Ag(111) clusters epitaxially grown on Si(111) by hydrogen adsorption at room temperature.

Structural study of SrTiO3(100) surfaces by low energy ion scattering

Abstract We have studied the atomic structure of the SrTiO 3 (100) surface annealed at 600°C in ultrahigh vacuum (UHV) by using time-of-flight impact collision ion scattering spectroscopy (TOF-ICISS) and low energy electron diffraction (LEED). Considering its perovskite structure, the SrTiO 3 (100) surface consists of a SrO-terminated surface, a TiO 2 -terminated surface or a mixture of these surfaces. From the results of TOF-ICISS and LEED experiments, we have found that the SrTiO 3 (100) surface annealed at 600°C is an ordered surface (1 x 1 structure) and consists of a mixture of SrO-terminated and TiO 2 -terminated surfaces.

Ion-beam annealing of diamond using Ar ions up to 400 keV

Abstract Damaged layers in crystalline diamond (1xa00xa00) samples were formed in the depth range of 0–90 nm by irradiation with 40 keV 12C ions to a dose of 1.3×1015 cm−2 at room temperature (RT), and successively annealed with and without 400 keV 40Ar ions with doses up to 3.0×1015 cm−2 at 773 K. Rutherford backscattering spectrometry (RBS)-channeling measurements have revealed that damaged layers were annealed much faster with ion beam assistance than without it. It has been shown that the annealing process using a several hundred keV ion beam as low as 773 K can be applied to the crystallization of diamond. This suggests the promising applicability of an annealing process with ion beams to the introduction of p- and n-type dopants and requisite successive crystallization.

PROPERTIES OF DEPTH-PROFILE CONTROLLED BORON NITRIDE FILMS PREPARED BY ION-BEAM ASSISTED DEPOSITION

Abstract Boron nitride films were prepared by vapor deposition of boron and simultaneous bombardment with mixed gas ions of nitrogen and argon in the energy range of 0.2 to 20 keV. The films were prepared on various kinds of substrates including silicon wafers, tungsten carbide plates and various ceramic plates at a temperature of 400°C. In the synthesis of the BN films, a boron-rich buffer layer between the substrate and the BN film was formed by energetic nitrogen ion beam bombardment, improving tribological properties such as the depth-profile controlled layer. The buffer layer improved film adhesion, and chemical stability, thermal stability at elevated temperature and corrosion resistance of the BN films also gave good results.

A continuous speech recognition expert system—sprex

In the continuously uttered speech, it is often difficult to extract the features of the individual phoneme due to the interaction between phonemes called co-articulation. In such a case, a large amount of empirical knowledge is required for recognition. In the past, efforts have been made to realize the continuous speech recognition system by a procedural language such as FORTRAN, producing problems in the flexibility and expandability of the system. This paper describes the expert system SPREX for continuous speech recognition, which aims at the solution of those problems by introducing knowledge engineering techniques into the speech recognition. The proposed system is an expert system which simulates the behavior of a human expert by the knowledge engineering technique, where the phonemes are recognized by observing the time-course of change of the acoustic feature parameters such as formant frequencies. The system can efficiently manage and utilize the empirical rules inherent to the continuous speech recognition. At present, the system is composed of 114 expert knowledges represented by production rules. The recognition rate of 85 percent is realized for 29-s speech uttered by 3 adult males. Finally, problems left for the studies in this direction are discussed, aiming at the amalgamation of the study of speech and the knowledge engineering.