Low-Energy Photoluminescence Induced by Substitutional Nitrogen in Single-Layer Tungsten Disulfide*

Defect engineering is an important technique to tailor the electronic and optical properties of two-dimensional materials. By creating defects using remote N₂ plasma exposure, distinct low-energy photoluminescence (PL) peak at 1.59 eV is introduced in single-layer WS₂. The N₂ plasma exposure dose has a critical influence over this PL peak intensity, making it strongest at about 2.0% sulfur deficiencies and vanish at 5.6% or higher sulfur deficiencies. First-principles calculations suggest that this PL peak is caused by the sulfur substitutions by nitrogen. The substitutional nitrogen defect can serve as an isolated artificial atom for single-photon emitters and can be used to monitor the nitrogen p-type doping concentrations.