MoSe₂ Crystalline Nanosheets for Room-Temperature Ammonia Sensing

We report a highly sensitive and selective ammonia (NH3) gas sensor made from liquid exfoliated MoSe2 nanosheets. The powder obtained after exfoliation was used to make a two-terminal sensor on a quartz substrate with predeposited silver contacts. The device so obtained, exhibited excellent sensitivity (5.5%) at an ammonia concentration down to 1 ppm, a fast response and recovery time of 15 and 135 s, respectively, better reproducibility, and impressive selectivity against various gases at room temperature. Moreover, density functional theory (DFT) simulations were used to understand the adsorption kinetic and electronic structure and therefore to shed light on the fundamentals of the sensing mechanism. Bader analysis was performed to understand the charge transfer process between the adsorbed ammonia gas molecule and underlying MoSe2 surface. The resulting analysis confirmed that the electrons transfer from NH3 molecules to MoSe2. The slight shift of the valence band toward the Fermi level which is clear from band structure analysis, along with the experimental fact that after exposure to ammonia the sensor displays an increase in resistance, indicates p-type behavior of the processed MoSe2 crystalline nanosheets. These results imply the potential use of scaled nanosheets of MoSe2 as a promising sensing material for enhanced and selective NH3 gas monitoring at room-temperature.