Yoshio Ishizawa

Quantitative Surface Atomic Geometry and Two-Dimensional Surface Electron Distribution Analysis by a New Technique in Low-Energy Ion Scattering

A new technique for analyzing the quantitative surface atomic geometry and the two-dimensional surface electron distribution is reported. The remarkable effectiveness of this new technique is demonstrated for TiC(111).

NMR Study on the Spin Structure of CeB6

11 B NMR measurement has been made on a typical dense Kondo system CeB 6 mainly in the intermediate temperature phase II by using a single crystal. From the analysis of the angular dependence of the NMR spectra, we propose a quite unusual spin structure in phase II in which the external field induces not only the uniform magnetization but the antiferromagnetic moment which has a triple- q structure.

Preparation of TiCx single crystals with maximum carbon content by a floating zone technique

TiCx single crystals with a maximum carbon content (x = 0.96–0.97) were prepared by controlling the compositions of the initial molten zone and the feed rod (a modified zone leveling method). The homogeneity of the composition was checked along the growth and radial directions. The lattice constants, densities and impurities in the crystal, starting material, feed rod and evaporation product, were measured and reported. All impurities except W, whose carbide has a low vapor pressure, were found to be refined by evaporation. The effect of the helium ambient gas pressure was examined. It was found that good quality crystals could be prepared under relatively low pressure (4–5 atm). The good quality of the crystals was confirmed by X-ray transmission topography.

Interaction Potential between He+ and Ti in a keV Range as Revealed by a Specialized Technique in Ion Scattering Spectroscopy

The interaction potential between He+ and Ti in a keV range has been studied by a specialized technique in low-energy ion scattering spectroscopy. The interaction potential is described well by the Thomas-Fermi-Moliere potential for the interaction between neutral He and Ti with a scaled screening radius.

Superconductivity in Ba2(1−x)Sr2xYCu3O7−y

We report X-ray and chemical properties, phase transition, magnetic susceptibility and superconducting transition temperature of Ba2(1-x)Sr2xYCu3O7-y. Structural instability was detected for sample with x≥0.6. Phase transition occurs at oxygen number of 6.6. Anomalies in magnetization curves at 4.2 K were detected. The Tc decreases linearly from 92 to 80 K with an increase of x. Strontium and oxygen contents are parameters correlated with the depression of Tc.

MnSi and MnSi2−x single crystals growth by Ga flux method and properties

MnSi and MnSi 2- single crystals were grown from high temperature gallium metal fluxes by slowly cooling the melt in argon atmosphere. The growth conditions of MnSi and MnSi 2-x (Mn 15 Si 26 ) crystals with relatively large size, namely MnSi about 0.06 x 0.52 x 2.43 mm 3 and Mn 15 Si 26 about 0.40 × 0.55 x 0.61 mm 3 were established. MnSi crystals were generally obtained in the form of needle-like prisms extending in the direction and with well-developed (111) faces. Mn 15 Si 26 crystals had a nearly spherical polyhedral shape, greyish color and metallic luster. The as-grown MnSi and Mn 15 Si 26 crystals were used for chemical analyses and measurements of unit cell parameters. Vickers microhardness was determined on MnSi and Mn 15 Si 26 crystals, and oxidation at high temperature in air was studied for MnSi and Mn 15 Si 26 crystals.

Preparation of ZrB2 single crystals by the floating zone method

Abstract High quality ZrB2 crystals, free of subgrain boundaries, were prepared in 0.8 MPa of helium ambient gas by the RF heated floating zone method. The optimum growth rate was 2.5−3 cm/h. The composition of the molten zone, which influenced the growth rate, was determined by the difference in vapor pressure between Zr and B elements. Helium ambient gas decreased the inclusions in the grown crystals and consequently increased the optimum growth rate, compared with the growth in argon ambient gas.

Phonon dispersion of monolayer graphite on Pt(111) and NbC surfaces: bond softening and interface structures

Abstract The phonon dispersion relations of monolayer graphite on Pt(111), NbC(111) and NbC(001) were measured by electron energy loss spectroscopy. The monolayer graphite on Ni surfaces has been reported to show large softening, while that on Pt(111) was found to indicate little softening and rather resembled pristine graphite. Similarly, the monolayer graphite on NbC(111) indicated fairly large softening but that on NbC(001) did not. This difference is discussed in relation with the interface structure.

Analysis of the HfC(111) surface structure by impact collision ion scattering spectroscopy (ICISS)

The structure of the HfC(111) clean surface and the O2, D2 adsorption systems at room temperature have been studied by impact collision ion scattering spectroscopy (ICISS). The clean surface exhibits a 1 × 1 low energy electron diffraction (LEED) pattern and no reconstruction occurs. The outermost layer consists of Hf atoms and the space between the first and second layer contracts by 0.18 ± 0.05 A, which is equal to (13.4 ± 3.7)% of the corresponding bulk value. The oxygen-adsorbed surface has a 1 × 1 structure and the O atom is located on the threefold hollow site, under which a Hf atom of third layer exists. By comparing the ICISS spectra with computer simulations, the distance between the O atom and the surface has been determined at 0.90 ± 0.05 A (O-Hf bond length = 2.10 ± 0.07 A). In case of deuterium, D, the atom is adsorbed on the same site as oxygen and the distance from the surface is 1.36 ± 0.07 A (D-Hf bond length = 2.33 ± 0.10 A). Judging from the distance between the Hf atom and the adsorbates, the Hf-O bond seems to be rather ionic and the Hf-D bond seems covalent.

Preparation of Mo2C single crystals by the floating zone method

Abstract Single crystals of Mo2C, 0.7 cm in diameter and 6 cm long, were prepared by the RF heated floating zone method. Argon ambient gas was effective to decrease cracks and subgrain boundaries in the crystals, compared with the case of helium ambient gas.