Precise preparation of WO@SnO core shell nanosheets for efficient NH gas sensing.

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