Precise preparation of WO₃@SnO₂ core shell nanosheets for efficient NH₃ gas sensing

Development of high-performance ammonia (NH₃) sensor is imperative for monitoring NH₃ in the living environment. In this work, to obtain a high performance NH₃ gas sensor, structurally well-defined WO₃@SnO₂ core shell nanosheets with a controllable thickness of SnO₂ shell layer have been employed as sensing materials. The prepared core shell nanosheets were used to obtain a miniaturized gas sensor based on micro-electro-mechanical system (MEMS). By tuning the thickness of SnO₂ layer via atomic layer deposition, a series of WO₃@SnO₂ core-shell nanosheets with tunable sensing properties were realized. Particularly, the sensor base on the fabricated WO₃@SnO₂ nanosheets with 20-nm SnO₂ shell layer demonstrated superior gas sensing performance with the highest response (1.55) and selectivity toward 15 ppm NH₃ at 200 °C. This remarkable enhancement of NH₃ sensing ability could be ascribed to the formation of unique WO₃-SnO₂ core-shell heterojunction structure. The detailed mechanism was elucidated by the heterojunction-depletion model with the help of specific band alignment.