Papers by Author: Toshio Itoh

Abstract: For gas sensors, not only sensitivity and selectivity but also fast response speed is very important. We fabricated a restive type gas sensor using ceria (cerium oxide) porous thick film with a particle size of about 100 nm in order to improve the response speed of the sensor. First, we investigated the sensing properties for the change of oxygen partial pressure. The sensor was able to detect the variation of oxygen partial pressure in the wide range from 10-18 Pa to 105 Pa at 873 K. The response time (t90), which is defined as the time until response changes 90% of the saturated value after a sudden change of oxygen partial pressure, was about 10 ms at 1073 K. Next, we investigated the sensing properties for carbon monoxide. We developed the new sensor having two ceria thick films with and without catalyst layer to give selectivity. The sensor was able to detect carbon monoxide over 330 ppm at 773 K, and t90 was 2 s at 723 K. By using Pt/Al2O3 catalyst, the sensor hardly responded for hydrogen, so it was implied that the sensor had a good selectivity for carbon monoxide.

Abstract: The organic/MoO3 hybrid sensors show a distinct response to aldehyde gases, formaldehyde and acetaldehyde, by changing the electrical resistance, whereas they show almost no response to other VOCs. The organic/MoO3 hybrids have a potential for selective VOC detection because the sensing properties of organic/MoO3 hybrids can be controlled by the kind of interlayer organic components. In this study, we have carried out the detail characterization of the interlayer of the organic/MoO3 hybrids as well as the valence of Mo and evaluation of their sensing properties.

Abstract: Micro-thermoelectric hydrogen sensor (micro-THS) with the combination of the thermoelectric effect of Si0.8Ge0.2 thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation was prepared by microfabrication process. In the viewpoint of high sensitivity of micro-THS, the thermoelectric properties of the Si0.8Ge0.2 thin film could be improved by optimizing carrier concentration using helicon sputtering with an advantage of easy doping control, and sensitivity of the device with this thin film was investigated. As the result, the boron-doped Si0.8Ge0.2 thin film is considered to be the better choice ensuring the reliable monitoring of hydrogen concentration down to ppm level.