Liquid-tin-printed two-dimensional SnO for optoelectronic NO2 gas sensing at room temperature

High-performance gas sensors have been developed to meet the demand for trace detection of NO2, given the adverse effects of NO2 on the environment and human health. Two-dimensional (2D) metal oxides are considered an emerging class of NO2-sensitive materials. However, their controllable synthesis and poor recovery are two major obstacles to practical NO2 sensing applications. In this study, we prepare tailorable 2D p-type SnO nanosheets with thicknesses between 1.5 and 3 nm by precisely controlling self-limiting oxidation over the liquid Sn surface. At an oxygen concentration of 0.05%, 2D SnO nanosheets exhibit a lateral dimension as large as 100 mu m with a thickness of 1.5 nm, which can be facilely integrated into a field-effect transistor (FET) platform to form 2D devices. The NO2 sensing performance of 2D SnO at room temperature is investigated under excitation of a broad range of UV-Visible light. The optimum response magnitude to 10 ppm NO2 is achieved at similar to 205% at 450 nm excitation with excellent reversibility. In addition, the selectivity for NO2 is also explored, indicating an up to one order enhancement over those of CO2, NH3, H-2, H2S, CO, and CH4. We ascribe this improved performance to the optimum band alignment between 1.5 nm-thick SnO and NO2 gas molecules. This work provides a feasible approach to prepare 2D metal oxide nanosheets and demonstrates that they have great potential for fully reversible gas sensing at room temperature.