Proton-beam engineered surface-point defects for highly sensitive and reliable NO sensing under humid environments.

Cross-interference with humidity is a major limiting factor for the accurate detection of target gases in semiconductor metal-oxide gas sensors. Under humid conditions, the surface-active sites of metal oxides for gas adsorption are easily deactivated by atmospheric water molecules. Thus, development of a new approach that can simultaneously improve the two inversely related features for realizing practical gas sensors is necessary. This paper presents a facile method to engineer surface-point defects based on proton-beam irradiation. The sensor irradiated with a proton beam shows not only an improved NO response but also considerable tolerance toward humidity. Based on surface analyses and DFT calculations, it is found that proton beams induce three types of point defects, which make NO molecules preferentially adsorb on the ZnO surfaces compared to HO molecules, eventually enabling improved NO detection with less humidity interference.