Room-Temperature Photoluminescence Mediated by Sulfur Vacancies in 2D Molybdenum Disulfide.

Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this work, we provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS 2 by annealing at 600 °C in an argon/hydrogen (95%/5%) atmosphere. Synchrotron X-ray photoelectron spectroscopy shows that a Mo 3d 5/2 core peak at 230.1 eV emerges in the annealed MoS 2 associated with nonstoichiometric MoS x (0 < x < 2), and Raman spectroscopy shows an enhancement of the ∼380 cm -1 peak that is attributed to sulfur vacancies. At sulfur vacancy densities of ∼1.8 × 10 14 cm -2 , we observe a defect peak at ∼1.72 eV (referred to as LX D ) at room temperature in the photoluminescence (PL) spectrum. The LX D peak is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LX D emission is longer than that of band edge excitons, both at room and low temperatures (∼2.44 ns at 8 K). The LX D peak can be suppressed by annealing the defective MoS 2 in sulfur vapor, which indicates that it is possible to passivate the vacancies. Our results provide insights into how excitonic and defect-mediated PL emissions in MoS 2 are influenced by sulfur vacancies at room and low temperatures.