Junichi Nishino

Nitrogen-doped titanium dioxide photocatalysts for visible response prepared by using organic compounds

Abstract In order to utilize visible light in photocatalytic reactions, nitrogen atoms were doped in commercially available photocatalytic TiO2 powders by using an organic compound such as urea and guanidine. Analysis by X-ray photoelectron spectroscopy (XPS) indicated that N atoms were incorporated into two different sites of the bulk phase of TiO2. A significant shift of the absorption edge to a lower energy and a higher absorption in the visible light region were observed. These N-doped TiO2 powders exhibited photocatalytic activity for the decomposition of 2-propanol in aqueous solution under visible light irradiation. The photocatalytic activity increased with the decrease of doped N atoms in O site, while decreased with decrease of the other sites. Degradation of photocatalytic activity based on the release of nitrogen atoms was observed for the reaction in the aqueous suspension system.

Conductive indium-doped zinc oxide films prepared by atmospheric-pressure chemical vapour deposition

Abstracts are not published in this journal

Photochemical etching of GaAs using synchrotron radiation

The photochemical etching of gallium arsenide by chlorine was investigated using synchrotron radiation. At the substrate temperatures above 25°C, both the irradiated and nonirradiated regions were uniformly etched. In case of substrate temperatures below -25°C, highly selective etching was observed in the irradiated region. We considered that at low temperatures, etching reaction caused by gas-phase excitation is suppressed and photochemical surface reaction becomes dominant.

Femtosecond Diffuse-Reflectance Spectroscopy of Various Commercially Available TiO2 Powders

ABSTRACT The transient absorption properties of several commercially available TiO2 photocatalysts were investigated by femtosecond diffuse-reflectance spectroscopy. Using femtosecond diffuse-reflectance spectroscopy, the quantities and rates of the initial trapping processes of holes and electrons generated by the photoexcitation of TiO2 photocatalysts were investigated. It was found that the total amounts of trapped electrons for the pure-anatase and pure-rutile TiO2 became smaller with increasing particle size, but increased again when the particles’ diameters were larger than 50 nm. The anatase–rutile mixed TiO2 photocatalysts were found to have smaller amounts of trapped electrons compared with pure-anatase and pure-rutile TiO2 photocatalysts. The lifetimes of trapped holes of various TiO2 photocatalysts were also investigated, and it was found that the lifetimes were proportional to the anatase–rutile mixed ratios.

X-ray Source with Cold Emitter Fabricated Using ZnO Conductive Whiskers

A new structure for the surface illuminant X-ray source system using a low-cost aluminum-doped zinc oxide (ZnO:Al) whisker cold emitter is proposed and a prototype setup is introduced. The X-ray source was fabricated using a cold cathode that consists of an aggregation of conductive ZnO:Al whiskers. The ZnO:Al whiskers were deposited on an n-type single crystalline wafer of silicon by an atmospheric chemical-vapor-deposition method. The electron emission current from the ZnO:Al whiskers varied with the Al concentration of ZnO. The diode and triode X-ray sources generated X-rays from the tungsten target used as an anode. X-ray images of a leaf and a small sardine were taken on medical X-ray films. Clear X-ray images were obtained.

Preparation of Zinc Oxide Films by Low-Pressure Chemical Vapor Deposition Method

ZnO and Al-doped ZnO films prepared using a low-pressure chemical vapor deposition (LP-CVD) method were studied. The films were prepared on fused quartz substrates using bis(2,4-pentanedionato)zinc and tris(2,4-pentanedionato)aluminum which are inexpensive and stable source materials. The highly c-axis oriented ZnO films were grown on the substrates above 500°C. The minimum electrical resistivity of ρ=6.5×10 −5 Ωm was obtained for the ZnO film, and of ρ = 3.5×10 −5 Ωm was obtained for the ZnO:Al film.

An influence of concentration of polyvinylpyrrolidone on the morphology of silver metal formed from AgNO 3 aqueous solution

Metal silver rods having a partly regular direction on the substrate are synthesized from the fine copper particles on acrylic plastic plate immersed in 50 µM-PVP and 0.1M-AgNO3 aqueous solution. An increase of PVP concentration in the AgNO3 aqueous solution inhibits the growth of the string-shaped silver and dendrite-shaped silver as well as polyol method. The absorbance of the plasmon peak around 410 nm immersed in 0.1M-AgNO3 aqueous solution at 25°C for 24 hours increased with an increase of the PVP concentration.

Formation of ZnO films by CO2 laser ablation at atmospheric pressure

Laser ab la t ion has often been used to obtain high-quality thin ceramic films such as A120 3 [1], Si3N 4 [1], TiN [1], CdTe [2], SnO2 [3], BN [4] and high-T0 superconductor films [5, 6]. A laser ablation system usually consists of a clean vacuum chamber in order to rea l i ze a long mean free path of the atoms in the gas phase. However, certain oxide films can be prepared without a vacuum chamber by chemical vapour deposition (CVD). For example, TiO2 films can be prepared by the traditional method of thermal CVD at atmospheric pressure [7]. This observation has led us to an attempt to produce thin ceramic films by a laser ablation method at atmospheric pressure . Zinc oxide (ZnO) provides a wide range of scientific and technological applications because of its semiconducting, photoconducting and piezoelectric characteristics [8]. This letter reports the preparation of ZnO films by CO2 laser ablation at atmospheric pressure . ZnO targets w e r e prepared by pressing 99.99% purity ZnO powder into circular discs (about 1.3 cm in diameter and 1.0 cm thick). A schematic diagram of the experiment is shown in Fig. 1. A glass substrate was heated to 200-600 °C by an infrared lamp. A c.w. CO2 laser was operated at 75 W and focused on the surface of a ZnO target through a ZnSe lens ( f = 30 cm). The ZnO vapour formed by laser i rradiat ion was brought to the surface of the substrate in a stream of nitrogen gas admitted through a nozzle with a slit size of 1 mm × 8 mm. The distance between the nozzle head and the substrate was 2.3 cm. When the snbstrate was not h e a t e d by the lamp, the substrate t e m p e r a t u r e was raised to about 200 °C by the blowing gas containing the high-temperature ZnO vapour formed by the laser irradiation. The growth rate of the ZnO film

Preparation of ZnO by a nearby vaporizing chemical vapor deposition method

Zinc oxide (ZnO) films were prepared by a nearby vaporizing chemical vapor deposition method using bis(2,4-pentanedionato)zinc as a source material. The deposition rate increased exponentially from 0.58 to 147 nm min −1 with increasing substrate temperature ( T s ). The highest preferred orientation to the c axis was obtained under the conditions that the distance between substrate and source surface was 5.0 mm, and the T s was 300 °C. When we used a sapphire (0001) substrate, an epitaxial ZnO film could be deposited on this condition.

Indentation Creep of Nitrogen-Containing Carbon Films

An Indentation creep test has been used to investigate the micro-mechanical properties of nitrogen-containing carbon films. The time-dependent indentation depth of the nitrogen containing carbon films indicates a monotonic increase at the initial stage of creep procedure and remains constant. Using results of the slope of the time-displacement relation at the initial stage of creep procedure, the strain rate sensitivity exponent m and the k value which is equivalent to viscosity are obtained. The m and k values rapidly decrease with increasing deposition temperature, although the nano-indenter hardness test cannot be used to clarify differences in the mechanical properties of the deposited films. We present results that indicate that the nano-indentation creep technique enables clarification of the micro-mechanical properties of nitrogen-containing carbon films.