Controlled defect creation and removal in graphene and MoS₂ monolayers

It is known that defects strongly influence the properties of two-dimensional (2D) materials. The controlled creation and removal of defects can be utilized to tailor the optical and electronic responses of these 2D materials for optoelectronic and nanoelectronic applications. In this study, we developed an efficient approach to reversibly control the defect states in mechanically exfoliated graphene and molybdenum disulfide (MoS₂) monolayers. The defects were created by aluminium oxide (Al₂O₃) plasmas and removed by moderate thermal annealing at up to 300 °C. We employed Raman and photoluminescence (PL) as well as electrical characterization to monitor the variation of the defect level in graphene and MoS₂. For graphene, Raman spectra indicate that the Al₂O₃ plasma induced sp³-type defects with a controlled concentration, which have been substantially removed after thermal annealing. A similar trend was also observed in monolayer MoS₂, as revealed by the defect-related emission peak (X^b) in the PL spectra. We further showed that the defects induced by the Al₂O₃ plasma in both 2D materials can be restored to any intended level via annealing under well-controlled conditions. Our work presents a new route to the functional design of the optical and electronic properties of graphene and MoS₂-based devices through defect engineering.