It was found here that CO could act as an oxidizing gas at room temperature on photostimulated ZnO nanowires. For photostimulation, the low intensity of light emitting diodes was used to induce a very low photocurrent, which, however, led 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 room temperature. CO molecules adsorbing on the surface were 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 was 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.

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, 2011, 44[30], 305302