CO sensing by reactive-sputter-deposited PdO nanoflakes at atmospheric pressure

• Main Authors: Wang, Hung-Shen, 王洪笙
• Other Authors: Pan, Fu-Ming
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/44534695408298281241

碩士 === 國立交通大學 === 工學院半導體材料與製程設備學程 === 102 === This study deposited PdO nanoflake thin films on the SiO2/Si substrates by reactive sputter deposition, and investigated CO sensing properties of the PdO thin film. The thin film has a flake-like nanostructure with a large surface area and, therefore, the film can provide a large amount of adsorption sites for CO molecules. Moreover, because of the ultrathin thickness of the nanoflake, the space charge region induced by O2 or CO adsorption will occupy most volume of the nanoflake, resulting in a very sensitive change in the electrical resistance of the film. According to this study, the PdO thin film exhibits different electrical response behavior toward CO adsorption at different temperature ranges. At low temperatures (≤100oC), CO molecules react with (or replace) anionic oxygen molecules (O2-) and thus change electrical properties of the thin film. Because PdO is a p-type semiconductor, the depletion region in the nanoflake, which is formerly formed due to oxygen ionosorption, is widened upon CO adsorption, leading to the increase in the electrical resistivity of the PdO thin film. At 150oC, the CO molecules can react with surface oxygen atoms, thereby reducing PdO. However, in this temperature range, subsurface oxide can be formed on the reduced Pd surface, and the alternative oxidation-reduction reaction causes oscillatory electrical response during the CO sensing process. At higher sensing temperatures ≥200oC, the change in the sensing current of the PdO thin film upon CO exposure reaches a steady level, suggesting that reactions between adsorbed CO, pre-adsorbed oxygen ion and lattice oxygen are in dynamic equilibrium.