| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 102 === Tricobalt tetraoxide is a p-type semiconductor oxide with many applications as a functional material. The catalytic ability of Co3O4 toward CO oxidation has been widely reported in the literature, and it is considered as a potential oxide semiconductor for CO gas sensing applications. In this study, we synthesized porous Co3O4 nanoflake thin films on the SiO2/Si substrate by chemical bath deposition using cobalt(II) acetate tetrahydrate and urea as the precursors and deionized water as the solvent, and studied their gas sensing response toward CO. The porous Co3O4 nanoflake thin films has a large surface area and the porous structure can effectively facilitate gas diffusion. The microstructure and morphology of the porous Co3O4 nanoflake thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the surface chemical compositions was analyzed by electron spectroscopy for chemical analysis technique (ESCA). The CO sensing behavior of the Co3O4 thin films was studied under the atmosphere condition. We first performed the gas sensing experiment as a function of the deposition time of the Co3O4 thin film. We found that the sensing response increased with the deposition time, and ascribed the result to the increase in the surface area for CO adsorption. When the gas sensing experiment was conducted as a function of the calcination temperature of the Co3O4 thin film, we found that the sensing response decreased with increasing the calcination temperature as a result of the decrease in the surface to volume ratio of the thin film. For the Co3O4 thin film deposited for 12 hr and later treated by 400oC calcination, the gas sensing behavior of the sensor toward 250 ppm CO at 150oC exhibited a high sensing response, good reproducibility and a high CO/H2 selectivity.
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