Surface oxygen chemistry of metal oxide semiconductors for gas-sensing applications

With the development of science and technology, the demand for reliable and efficient gas sensors in various applications, ranging from environmental monitoring to industrial safety, is increasing. In particular, metal oxide semiconductor (MOS) based sensors have been extensively studied due to their stability, fast response, and cost-effectiveness. Given this backdrop, the paper reviews the gas-sensing mechanisms of MOS gas sensors, focusing on the role of oxygen participation. The electron depletion layer (EDL)/hole accumulation layer (HAL) theory is discussed, emphasizing the importance of chemisorbed oxygen in gas-sensing reactions. However, recent observations have challenged the conventional oxygen adsorption mechanism, suggesting the involvement of lattice oxygen under certain conditions. This review categorizes the degree of oxygen participation into three levels and analyzes existing theories and methods to enhance sensor performance. The specific scenarios of lattice oxygen participation, current understanding, and characterization methods are presented. The article concludes with future prospects and questions to guide further research in advancing MOS-based gas sensors.