| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 98 === Molybdenum trioxide (MoO3), which has phases of α-MoO3, β-MoO3, h-MoO3, is one of the gas sensing materials and a well-known catalyst. Gas sensing properties are influenced by the structure, shape, grain size, morphology. Specially, the resistivity changes occur in the reaction with oxidizing and reducing gases.
In this study, MoO3 thin films were prepared by reactive RF sputtering under O2 flow ratio (35%) and Mo target power (170 W). In order to investigate the phases and morphology of the prepared samples, working pressure, annealing temperature and annealing time were the process parameters. Film structures were analyzed by X-ray powder diffraction (XRD), glancing incident angle X-ray diffraction (GIAXRD), SEM and electron back scattering diffraction (EBSD).
β-MoO3 is formed at annealing temperature 200~300℃ for 1hr in air and α-MoO3 is formed at annealing temperature above 450℃ for 1hr in air. α-MoO3 is stable at annealing temperature 450℃ and shows (0 1 0) preferred orientation. In the gas sensing experiment, β-MoO3 in reaction with ethanol has response time 3~5s and recovery time 85s, and the optimum temperature is 250℃. However, α-MoO3 in reaction with ammonia gas has response time 3~5s and recovery time 200s, and the optimum temperature is 250℃.
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