Recently a SnS _(2) based NO _(2) gas sensor with a 30 ppb detection limit was demonstrated but this required high operation temperatures. Concurrently, SnS _(2) grown by chemical vapor deposition is known to naturally contain nanoscale defects, which could be exploited. Here, we significantly enhance the performance of a NO _(2) gas sensor based on SnS _(2) with nanoscale defects by photon illumination, and a detection limit of 2.5 ppb is achieved at room temperature. Using a classical Langmuir model and density functional theory simulations, we show S vacancies work as additional adsorption sites with fast adsorption times, higher adsorption energies, and an order of magnitude higher resistance change compared with pristine SnS _(2) . More interestingly, when electron–hole pairs are excited by photon illumination, the average adsorption time first increases and then decreases with NO _(2) concentration, while the average desorption time always decreases with NO _(2) concentration. Our results give a deep understanding of photo-enhanced gas sensing of SnS _(2) with nanoscale defects, and thus open an interesting window for the design of high performance gas sensing devices based on 2D materials.
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