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Oxidation behaviour of carbon monoxide at the photostimulated surface of ZnO nanowires

: Wang, C.Y.; Kinzer, M.; Youn, S.K.; Ramgir, N.; Kunzer, M.; Köhler, K.; Zacharias, M.; Cimalla, V.


Journal of Physics. D. Applied Physics 44 (2011), Nr.30, Art. 305302, 8 S.
ISSN: 0022-3727
ISSN: 1361-6463
Fraunhofer IAF ()

Normally carbon monoxide is considered to be a reducing agent, which can be used for CO detection. However, oxidizing behaviour of CO, to the best of our knowledge, has not been reported. In this work, we find that CO can also act as oxidizing gas at room temperature on photostimulated ZnO nanowires. For photostimulation, the low intensity of light emitting diodes is used to induce a very low photocurrent, which, however, leads to a large resistance change due to the ultraviolet light interaction with the nanowire surface. During CO detection, the oxygen vacancies enhance the CO adsorption on the nanowire surface even at roomtemperature. CO molecules adsorbing on the surface are presumably bound to a zinc-oxygen vacancy complex, causing a reduction in free electron concentration, which leads to an oxidizing effect of CO gas. An adsorption model for CO is proposed to explain the experimental observations. These results shed light on developing room-temperature CO sensor using oxide nanostructures with the help of high energetic photon replacing the high-temperature process normally used in traditional gas sensors.