Toshinari Yamazaki

Fabrication and gas sensing properties of In2O3 nanopushpins

The growth of nanopushpin-like In2O3 nanostructures was demonstrated on the silicon substrate by catalyst-free chemical vapor deposition method. Structural analysis revealed single-crystalline nature of the In2O3 nanopushpins with a cubic crystal structure. The hydrogen sensor made from the In2O3 nanopushpins showed swift response and excellent stability. The influence of operation temperature on the hydrogen gas sensing property of In2O3 nanostructures was also investigated. Our results reveal that the sensor response of In2O3 nanopushpins increases with increasing the operation temperature.

Synthesis and Characterization of TeO2 Nanowires

TeO2 nanowires were successfully synthesized by a simple reactive thermal evaporation method using pure Te metal as the source material. The study on synthesis process indicates an optimal synthesis temperature of 400 °C. Structural characterization using X-ray diffraction and transmission electron microscopy shows that the TeO2 nanowires have a single phase tetragonal structure. Scanning electron microscopy observation demonstrates that each TeO2 nanowire starts to grow from a TeO2 nanopartice, which suggests a self-catalytic growth mechanism. The Fourier transform infrared spectrum of TeO2 nanowires shows a blue shift of 20 cm-1 in the axial stretching bands. The gas sensing measurements indicate that TeO2 nanowires have a p-type electrical conduction and can reversibly response to NO2 gas at room temperature.

Electrical Properties of SnO2 Polycrystalline Thin Films and Single Crystals Exposed to O2- and H2-Gases

The electrical conductivity σ and carrier density n have been measured in the range 77–670 K for the SnO2 single crystal and thin films prepared by the vapour deposition technique. It is found that the SnO2 thin film possesses a carrier density of 1019 cm-3, three orders of magnitude larger than that in the as-grown SnO2 single crystal, and exhibits electrical properties characteristic of a degenerate semiconductor. Both single crystals and thin films undergo irreversible changes in electrical properties upon heat treatment in vacuum or exposure to O2- or H2-gases. This occurs as a result of reduction and oxidation of SnO2. However, the oxidation and reduction proceed in thin films at much lower temperatures than in single crystals. The unique gas-sensing character of thin films was interpreted by assuming that the oxidation and reduction preferentially proceed along the grain boundaries in the thin film.

Effect of Angular Distribution of Ejected Atoms from a Target on the Uniformity of Thickness and Composition of MoSix Sputtering Films

The distribution of the thickness and the composition of MoSix films formed by the DC magnetron sputtering method was measured by varying the distance between the target and the substrate and the distribution of the erosion depth of the target. The angular distribution of the ejected atoms from the target is expected to affect the uniformity of the thickness and the composition. A model involving the effect of the angular distribution was considered to calculate the thickness and the composition, and the data were analyzed using the model. The model accounted for the data fairly well, and it was concluded that the angular distribution of the ejected atoms was very important in the determination of the distribution of the thickness and especially of the composition.

Influence of an Electric Field Perpendicular to the Ferroelectric Axis on the Dielectric Properties of Triglycine Sulfate

It is confirmed that value of the spontaneous polarization in triglycine sulfate is reduced by a DC electric field perpendicular to its ferroelectric b axis. The reduction is influenced by temperature and by application time, intensity and direction of the perpendicular electric field. The reduced value is maintained for a long time after removing the perpendicular electric field. Charge injected into the crystal seems to be concerned with the reduction of the spontaneous polarization when considering the characteristics of electric conductivity and (de)polarization current.

Effective Surface Area of SnO2-Sputtered Films Evaluated by Measurement of Physical Adsorption Isotherms

The microstructure of SnO2 sputtered films was investigated by field emission electron microscopy (FE-SEM), and by the measurement of film density and physical adsorption isotherms. FE-SEM shows that the SnO2-sputtered films are composed of columnar grains with thicknesses of about 10–45 nm. The density of the film deposited at a high temperature of 573 K and a low pressure of 0.4 Pa was 6.38×103 kg/m3. On the other hand, the density of the film deposited at room temperature and a high pressure of 12 Pa was 3.82×103 kg/m3. This value is much lower than the bulk density 6.95×103 kg/m3, indicating that the film is very porous. According to the results of the physical adsorption isotherms for Kr gas, the effective surface area of this porous film was 91.0 times larger than the apparent surface area, indicating that the columnar grains are mostly isolated by gaps. Furthermore, the density is discussed in relation to the total pore volume determined from pore size distributions.

Improvement of Bremsstrahlung Counting Method for Measurements of Gaseous Tritium

A thin beryllium disk coated with a gold evaporated film of about 80 nm thickness was fabricated as an effective radiation window of bremsstrahlung X-rays. Its characteristics were examined in detail. The bremsstrahlung counting rate was proportional to the partial pressure of tritium above 0.1 Pa. The specific counting rate was evaluated as 70.8 cps/Pa. On the other hand, it decreased gradually with the total pressure above 2 kPa. This behavior was interpreted in terms of the self-absorption of β-particles in gas phase. It was revealed that the counting rate could be reproduced very well by a simple exponential function. From these results, it was concluded that the beryllium window coated with a thin gold evaporated film is a powerful device for in-situ measurements of tritium concentration in a wide range.

Characteristics of Impurity-Doped GaSe Radiation Detectors

The properties of GaSe radiation detectors doped with Si, Ge and Sn were investigated. It was found that doping with these impurities substantially decreased the leakage current and that most detectors doped with the impurities at about 0.005 to 0.1 at.% showed fairly good energy resolutions from 4 to 15% for 241Am 5.5 MeV alpha particles, while most pure GaSe detectors did not function because of their excessively large leakage current.

Crystal structure of the ferroelectric phase of triglycine sulfate under an electric field

Crystal structure analysis of a triglycine sulfate single crystal under an electric field has been carried out in the ferroelectric phase by X-ray diffraction with anomalous scattering effect. Both crystal structure in positive polarity and that in negative polarity were clarified. The structural change in polarization reversal has been disclosed by indication of flip-flop motion of the hydrogen atoms between oxygen atoms, by rotation of the glycine I group and by changing of the hydrogen bonds connected to nitrogen atoms of the glycines II and III.

Preparation of Ferroelectric Glycine Phosphite Single Crystals

An experimental procedure to prepare single crystals of ferroelectric glycine phosphite (GPI) is presented. Since the solubility of GPI in water increases with temperature, the single crystals are grown from fine seed crystals in a saturated aqueous solution by the gradually-decreasing-temperature method. Full faced, transparent, colorless crystals weighing about 10 g are obtained within 20–30 days. Crystallographic axes and the Miller indices for all faces of the obtained crystals are determined using the lattice parameters as a clue.