NO2 gas sensors based on CVD tungsten diselenide monolayer

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising for gas sensors owing to their large surface-to-volume ratios, but the long recovery times stemming from the slow molecular desorption have been an important limitation. In this work, we report on a sensor for nitrogen dioxide (NO2) made with a diselenide (WSe2) monolayer synthesized via chemical vapor deposition, which functions within a range of concentrations from 100 ppb to 5 ppm and at various temperatures, including room temperature. When operated at an optimized temperature of 250 °C, the WSe2 sensor exhibited the fast recovery, with the response (τres) and recovery (τrec) times of 18 s and 38 s, respectively, when exposed to 100 ppb NO2. The sensor also features high selectivity toward NO2 in the presence of other target gases, in addition to reversibility and long-term stability within 60 days. The overall characteristics of the WSe2 sensor make it suitable to monitor indoor/outdoor environments, mainly if further optimization is made with sensor design based on a model for the sensing mechanism we present in this paper.