Koichi Suematsu

Gas sensing with nanosized oxide materials is attracting much attention because of its promising capability of detecting various toxic gases at very low concentrations. In this study, using clustered SnO2 nanoparticles formed by controlled particle aggregation, we fabricated highly sensitive gas sensing films to detect large gas molecules such as toluene. A hydrothermal method using stanic acid (SnO2·nH2O) gel as a precursor produced monodispersed SnO2 nanoparticles of ca. 5 nm at pH 10.6. Decre

The type and amounts of oxygen adsorption species at various atmospheric humidity levels are important factors in improving the sensitivity to combustible gases and stability to humidity changes of SnO2-based resistive-type gas sensors. We investigated the effect of antimony (Sb) doping of SnO2 nanoparticles on the stability of the sensitivity to humidity changes and oxygen adsorption species under humid atmosphere. No significant degradation of the sensitivity to hydrogen of Sb-SnO2 sensors was

Selectivity is an important parameter of resistive-type gas sensors that use metal oxides. In this study, a highly selective toluene sensor is prepared using highly dispersed gold-nanoparticle-loaded zinc oxide nanoparticles (Au-ZnO NPs). Au-ZnO NPs are synthesized by coprecipitation and calcination at 400 °C with Au loadings of 0.15, 0.5, and 1.5 mol %. The Au NPs on ZnO are about 2-4 nm in size, and exist in a metallic state. Porous gas-sensing layers are fabricated by screen printing. The res

Improvements in the responses of semiconductor gas sensors and reductions in their detection limits toward volatile organic compounds (VOCs) are required in order to facilitate the simple detection of diseases, such as cancer, through human-breath analysis. In this study, we introduce a heater-switching, pulse-driven, micro gas sensor composed of a microheater and a sensor electrode fabricated with Pd-SnO₂-clustered nanoparticles as the sensing material. The sensor was repeatedly heat

Real-time monitoring of specific gas concentrations with a compact and portable gas sensing device is required to sense potential health risk and danger from toxic gases. For such purposes, we developed an ultrasmall gas sensor device, where a micro sensing film was deposited on a micro heater integrated with electrodes fabricated by the microelectromechanical system (MEMS) technology. The developed device was operated in a pulse-heating mode to significantly reduce the heater power consumption

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO₂ particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO₂ resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (<i

Oxygen adsorption plays key roles in resistive-type SnO2 gas sensors that can very sensitively detect combustible gases such as CO and hydrocarbons. Thus, exact evaluation of the electric resistance of SnO2 in response to oxygen is important to understand the oxygen adsorption mechanism. However, infinitesimal impurities contained in even high-grade commercial oxygen cylinders impose great effect on the sensitivity of SnO2. In this study, we designed an experimental system, which composed of gas

Fabrication of a transparent film composed of a barium titanate (BaTiO3) and poly(methyl methacrylate) (PMMA) matrix is reported to expand the application field for composite films such as displays and touch panel screens. BaTiO3 nanoparticles are synthesized by sol–gel route with dispersion carried out in 2-methoxyethanol. The synthesized nanoparticles are 10 nm in size and are highly dispersed in the solvent. The surfaces of the obtained nanoparticles are modified by treatment with titanium is

Improvement of gas selectivity, especially among volatile organic compound (VOC) gases, was attempted by introducing pulse-driven modes in semiconductor gas sensors. The SnO2 microsensor was fabricated on a miniature sensor device constructed with a microheater and electrode. The gas-sensing properties were evaluated under a pulse-driven mode by switching the heater on and off. According to density functional theory calculations and temperature-programmed reaction measurements, toluene molecule,

Aluminium-doped SnO₂ nanoparticles inhibited hydroxyl poisoning and enhanced the sensor response in a humid atmosphere.

To improve the sensing properties toward volatile organic compound gases, a preheating process was introduced in a miniature pulse-driven semiconductor gas sensor, using SnO₂ nanoparticles. The miniature sensor went through a short preheating span at a high temperature before being cooled and then experienced a measurement span under heating; this is the double-pulse-driven mode. This operating profile resulted in the modification of the surface conditions of naked SnO₂ nan

The design of a highly effective isopropanol gas sensor with high response and trace detection capability is extremely important for environmental surveillance and human health. Here, novel flower-like PtO_<i>x</i>@ZnO/In₂O₃ hollow microspheres were prepared by a three-step approach. The hollow structure was composed of an In₂O₃ shell inside and layered ZnO/In₂O₃ nanosheets outside with PtO_<i>x</i> nanoparticl