Mechanistic Model for UV light-enhanced NO2 Sensing utilizing Ordered Mesoporous In2O3

Results on light-enhanced NO2 sensing utilizing ordered mesoporous In2O3 are presented and interpreted by means of a new sensing model for ordered mesoporous indium oxide (In2O3) [1]. This model aims to explain the drop in electronic resistance of n-type semiconducting In2O3 under UV light exposure as well as the light-enhanced sensing properties to oxidizing gases. Compared to the conventional double Schottky model [2] the dominating factor for the resistance change is a change of oxygen vacancy donor states in the bulk phase due to photoreduction [3]. Comparison of conductivity measurements with varying oxygen partial pressure for ordered mesoporous and non-structured material shows an accumulative behavior in the case of the mesoporous material which can be related to faster photoreduction caused by the nanostructure. IR measurements reveal a donor level of 0.18 eV below the conduction band attributed to oxygen vacancies. The unique properties resulting from the structure allow low-temperature sensing of NO2; especially the recovery times are significantly shorter for the mesoporous material.