Anisotropic point defects in rhenium diselenide monolayers

Point defects in 1T″ anisotropic ReSe(2) offer many possibilities for defect engineering, which could endow this two-dimensional semiconductor with new functionalities, but have so far received limited attention. Here, we systematically investigate a full spectrum of point defects in ReSe(2), including vacancies (V(Se1-4)), isoelectronic substitutions (O(Se1-4) and S(Se1-4)), and antisite defects (Se(Re1-2) and Re(Se1-4)), by atomic-scale electron microscopy imaging and density functional theory (DFT) calculations. Statistical counting reveals a diverse density of various point defects, which are further elaborated by the formation energy calculations. Se vacancy dynamics was unraveled by in-situ electron beam irradiation. DFT calculations reveal that vacancies at Se sites notably introduce in-gap states, which are largely quenched upon isoelectronic substitutions (O and S), whereas antisite defects introduce localized magnetic moments. These results provide atomic-scale insight of atomic defects in 1T″-ReSe(2), paving the way for tuning the electronic structure of anisotropic ReSe(2) via defect engineering.