Yoichiro Uemura

SiO2-sheathed InS nanowires and SiO2 nanotubes

InS nanowires uniformly sheathed with amorphous SiO2 were synthesized via a physical vapor deposition process. InS nanowires were 20–100 nm in diameter, and the SiO2 sheaths were 5–20 nm in thickness. Single-crystalline InS cores displayed orthorhombic structure and their longitudinal directions were preferentially aligned in the [100] orientation. Pure SiO2 nanotubes of typically round cross sections were also obtained by removing InS cores from the prepared nanocables via thermal evaporation. Photoluminescence measurements on these SiO2 nanotubes demonstrated strong visible-light emission peaked at 570 nm.

ZnS–Zn nanocables and ZnS nanotubes

ZnS-Zn nanocables and ZnS nanotubes have been synthesized by a thermochemical process in a simple and safe way. The as-prepared nanocables consist of a single crystal Zn core with a diameter of 20 nm and a polycrystalline ZnS sheath with a thickness of 8 nm. The evaporation of the Zn core leads to the formation of ZnS nanotubes.

Thermoelectric properties of lanthanum sesquisulfide with Ti additive

The electrical resistivity, thermopower, and thermal conductivity have been measured for the lanthanum sesquisulfide (La2S3) of which the crystal phase is controlled by the Ti additive. In all the samples, the thermopower is negative between 300 and 1000 K. The sample with 8 wt % Ti, which consists almost of the cubic γ phase, behaves as a degenerate semiconductor. The thermoelectric figure of merit ZT increases with increasing temperature, reaching a value of 0.21 at 1000 K. In contrast, the sample with 2 wt % Ti consists almost of the tetragonal β phase. The transport mechanism can be well explained by the model of the Anderson localization. The ZT value increases abruptly with increasing temperature. At 1000 K, this ZT value is comparable with that of the sample with 8 wt % Ti.

A SiC bicrystal junction on the (0 0 0 1) plane

A SiC bicrystal junction in which two crystals superpose with a common (0001) plane has been investigated by optical microscopy and X-ray precession camera techniques. The behaviour of such a junction is discussed from the viewpoint of sintering and grain boundaries in SiC using a crystallographic concept of compound tessellation. Six examples of bicrystals are considered with respect to the observed and calculated superposing rotation angles and the densities of the superpositions.