Room-Temperature NO2 Gas Sensing with Ultra-Sensitivity Activated by Ultraviolet Light Based on SnO2 Monolayer Array Film

Chemiresistive-type gas sensors, which are driven by the thermal activation, have exhibited extraordinary promise for the detection of air pollutions, such as highly toxic gas of nitrogen dioxide (NO2), but are often limited to its high operating temperature, because of the raising explosive risk in inflammable gases. This study reports the construction of a close-packed SnO2 monolayer film, and uses it as the NO2 room-temperature sensing layer induced by ultraviolet (UV)-light irradiation. Such SnO2 monolayer array film shows excellent sensing performances toward NO2 gas with a striking selectivity under the UV-light irradiation even in high humidity. Additionally, by precisely controlling the sensing film thickness, it is observed that the NO2 sensing characteristics can be optimized to provide ultra-selectivity and high gas response. Through the systematic analysis, it reveals that the "clean effect" of UV-light for surface-adsorbed O-2(b-) ions and the competitive adsorption between NO2 and O-2 gas during sensing process are responsible for the possible sensing mechanism. More importantly, this work exhibits the intrinsic relation between sensing performances and the film thickness under the UV-light illumination, which is of vital importance to actual sensing requirements.