Selective passivation of 2D TMD surface defects by atomic layer deposited Al₂O₃ to enhance recovery properties of gas sensor

The incomplete recovery of Transition Metal Dichalcogenides (TMD) based gas sensors hinders their reliability and scalability. The leading cause of incomplete recovery is the strong chemisorption of gas analytes, such as defects or grain boundaries on the active surface of 2D TMDs. Herein, we demonstrate an improvement in the recovery rate of TMD gas sensors by selectively passivating the TMD surface defects or vacancies with Al₂O₃ via atomic layer deposition. Scanning electron microscopy analysis confirms that the nucleation and growth of atomic-layer-deposited Al₂O₃ occur along the grain boundaries and defects of the 2D MoS₂ and WS₂, not covering the inert basal plane. In addition, the Raman, photoluminescence, and X-ray photoelectron spectroscopy data show lower surface defect densities and a slight n-doping effect of Al₂O₃. This unique selectively defect-passivated TMD gas sensor shows a 400 % response toward 10 ppm of NO₂, along with an increase in the recovery rate from 74 to 96 %, even at room temperature, as the number of atomic layer deposition cycles increases. Also, the recovery rate of NH₃, a reducing gas, shows an increase of more than 30 %. Thus, the method proposed here is a promising strategy for improving the recovery rate of 2D TMD gas sensors.