WS2 nanoflakes based selective ammonia sensors at room temperature

A selective room-temperature ammonia sensor using WS2 nanoflakes as the sensing materials was successfully developed in this work. The two-dimensional WS2 sharing the same structure with MoS2, has a typical graphene-like 2D microstructure. The WS2 nanoflakes based sensor shows a good sensitivity and an excellent selectivity to ammonia at room temperature. The sensor showed an increased resistance when exposed to ammonia from 1 ppm to 10 ppm indicating a p-type response. The response and recovery time of the sensor to 5 ppm ammonia are ∼120 s and ∼150 s, respectively. The developed ammonia sensor shows excellent selectivity to formaldehyde, ethanol, benzene and acetone at room temperature. The response of the sensor increased as the humidity increase up to 73% possibly due to the sulfides ions-assisted hydroxylation of the co-adsorbed water and the oxidation of the solvated ammonia with adsorbed oxygen ions on the surface of the WS2 nanoflakes.