Identification of Active Sites for Thermal Oxidation-Induced Doping and Etching in CVD-Grown Monolayer Transition Metal Dichalcogenides

Two-dimensional atomically thin transition metal dichalcogenides (TMDs) grown by chemical vapor deposition (CVD) exhibit huge potential as fundamental building blocks for integrated electronics and optoelectronics, but their physical and chemical properties are liable to change with air oxidation. The identification of active sites for the oxidation-induced structural evolution of CVD-grown TMD monolayers is essential for the improvement of their ambient stability and optoelectronic properties. Here, we report thermal-oxidation-induced doping and etching in CVD-grown monolayer TMDs, including MoS 2, MoSe 2, and WS 2 . The chalcogen vacancies are identified as the active sites to capture oxygen atoms or molecules in the initial oxidation process, resulting in enhanced photoluminescence (PL) emission because of defect healing through the incorporation of oxygen dopants. The long-term oxidation induces a transition from oxygen doping to etching in the monolayer TMDs, which is responsible for their structural dissociation and PL quenching. Oxygen etching induces the formation of a series of triangular holes on both TMD basal planes and edges, and the etching rate of CVD-grown TMD monolayers largely follows the trend of MoSe 2 > WS 2 > MoS 2 . This work not only offers deep insights into the oxidation mechanisms of monolayer TMDs but also opens a feasible route to tune the electronic and optical properties of two-dimensional TMDs by the rational control of air oxidation.