Jun Tamaki

Copper oxide-loaded tin dioxide thin film for detection of dilute hydrogen sulfide

The H2S sensing characteristics of SnO2 thin films loaded with CuO were found to be much improved by reducing the film thickness. A 40-nm-thick film showed sensitivity as high as 20000 and 2000 to 1.5 and 0.3 ppm H2S in air, respectively, at 200° C, while the rate of response to 0.3 ppm H2S was rather slow.

Improvement of copper oxide–tin oxide sensor for dilute hydrogen sulfide

The influence of the loading and dispersion of CuO on the H2S-sensing properties of CuO–SnO2 sensors has been investigated. The response rates to H2S depend on various factors such as CuO loading, specific surface area (or size) of SnO2 grains, method of loading the SnO2 grains with CuO and the operating temperature. For the CuO–SnO2 sensor prepared by a chemical fixation method, the response rates to dilute H2S (1–10 ppm) increased with decreasing CuO loading, while the sensitivity to H2S decreased monotonically with decreasing amount of CuO dispersed per unit surface area of SnO2. By optimizing these factors, it was possible to obtain a CuO–SnO2 sensor which responded to H2S above 1 ppm at 160 °C with sufficient sensitivity and fairly good response kinetics.

Preparation and catalytic properties of palladium-(boron, phosphorus) thin films using an RF sputtering method

Palladium-(boron, phosphorus) thin films have been prepared by an RF sputtering method. The palladium f c c structure was destroyed by adding boron or phosphorus and the palladium films finally became amorphous in structure. Boron, whose interaction with palladium was very weak, donated electrons to palladium, whereas phosphorus accepted electrons from palladium. The palladium-(boron, phosphorus) films showed high selectivity (above 97%) for the partial hydrogenation of diolefins (cyclopentadiene and 1,3-butadiene) and acetylene. The activity and the selectivity changed with the boron or phosphorus concentration. The changes in the selectivity were explained in terms of the ensemble and the ligand effect in the palladium films. It was found that the palladium-boron films with PdB like structure and the amorphous palladium-phosphorus films were excellent for partial hydrogenation.

Guide Growth of Carbon Nanotube Arrays Using Anodic Porous Alumina with Ni Catalyst

The anodic porous alumina with a cell size of 25 to 40 nm was prepared by applying a voltage of 20 V for 90 s in 20 wt % sulfuric acid at 15°C. The nickel catalyst for the growth of carbon nanotubes (CNTs) was cathodically deposited at the bottom of the porous alumina at a constant current density of 10 mA/cm2. Highly ordered CNT arrays with a diameter of 15 to 20 nm were linearly grown at 625°C for 60 min along the inner wall of the porous alumina by ethanol CVD. On the other hand, the CNT arrays obtained using acetylene had twisted shapes and disordered carbon layers irrespective of the configuration of the porous alumina. This suggests that the alignment of CNTs depends on the crystallinity.

Study of High Functional WO3 Film Sensors for Practical NO2 Detection

Four types of tungsten trioxide (WO3) particles (spherical, disk, cuboid, and hexagonal) were prepared and WO3 thick film sensors were fabricated by dropping suspensions containing the obtained various WO3 powders on Au comb-type microelectrodes. The sensing properties to 0.05-ppm NO2 revealed that a cuboid WO3 film sensor had the best response-recovery characteristics with the 90 % response and 90 % recovery times of 1.3 and 0.9 min at 200 °C, respectively. On the other hand, a hexagonal WO3 film sensor showed extremely high sensor response even to 0.01-ppm NO2 at 200 °C, but the sensor response fluctuated greatly over the operating temperature range from 80 to 300 °C. Practical evaluation of the cuboid WO3 thick film sensor in a roadside atmosphere was carried out and it was demonstrated that the evaluated values for the sensor unit had accuracy and resolution equivalent to CLD (Chemical Luminescence Detection) without any maintenance and calibration for 10 weeks.

Structure dependence in the hydrogenation of diolefins over Ru thin films

Ru thin films were prepared by a radiofrequency (r.f.) sputtering method. The structure of the Ru film changed with film growth. This influenced the activity and the selectivity in the hydrogenation of diolefins. The alterations in the activity and the selectivity were explained in terms of the columnar structure of the Ru film and the Ru (002) intensity in X-ray diffraction patterns. The partial hydrogenation of diolefins proceeded preferably over the (002) face of Ru. Elevating the substrate temperature, the more remarkably (002) orientated Ru film was prepared and showed the higher selectivity for the partial hydrogenation than that on the Ru film prepared at room temperature.