Highly Enhanced Gas Sensing Performance Using a 1T/2H Heterophase MoS₂ Field-Effect Transistor at Room Temperature

Monolayer MoS₂ (ML-MoS₂) with various polymorphic phases attracts growing interests for device applications in recent years. Herein, a field-effect transistor (FET) gas sensor is developed on the basis of monolayer MoS₂ with a heterophase of a 1T metallic phase and a 2H semiconducting phase. Lithium-exfoliated MoS₂ nanosheets own a monolayer structure with rich active sites for gas adsorption. With thermal annealing from 50 to 300 °C, the initial lithium-exfoliated 1T-phase MoS₂ gradually transforms into the 2H phase, during which the 1T and 2H heterophases can be modulated. The 1T/2H heterophase MoS₂ shows p-type semiconducting properties and prominent adsorption capability for NO₂ molecules. The highest response is observed for 100 °C annealed MoS₂ of a 40% 1T phase and a 60% 2H phase, which shows a sensitivity up to 25% toward 2 ppm NO₂ at room temperature in a very short time (10 s) and a lower limit of detection down to 25 ppb. This study demonstrates that the gas detection capability of ML-MoS₂ could be boosted with the heterophase construction, which brings new insights into transition-metal dichalcogenide gas sensors.