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

Atomic defects inmonolayer transition metal dichalcogenides (TMDs)such as chalcogen vacancies significantly affect their properties.In this work, we provide a reproducible and facile strategy to rationallyinduce chalcogen vacancies in monolayer MoS2 by annealingat 600 & DEG;C in an argon/hydrogen (95%/5%) atmosphere. SynchrotronX-ray photoelectron spectroscopy shows that a Mo 3d(5/2) corepeak at 230.1 eV emerges in the annealed MoS2 associatedwith nonstoichiometric MoS x (0 < x < 2), and Raman spectroscopy shows an enhancement ofthe & SIM;380 cm(-1) peak that is attributed tosulfur vacancies. At sulfur vacancy densities of & SIM;1.8 x10(14) cm(-2), we observe a defect peak at & SIM;1.72 eV (referred to as LXD) at room temperaturein the photoluminescence (PL) spectrum. The LXD peak isattributed to excitons trapped at defect-induced in-gap states andis typically observed only at low temperatures (& LE;77 K). Time-resolvedPL measurements reveal that the lifetime of defect-mediated LXD emission is longer than that of band edge excitons, bothat room and low temperatures (& SIM;2.44 ns at 8 K). The LXD peak can be suppressed by annealing the defective MoS2 in sulfur vapor, which indicates that it is possible to passivatethe vacancies. Our results provide insights into how excitonic anddefect-mediated PL emissions in MoS2 are influenced bysulfur vacancies at room and low temperatures.

Automated summary

In this work, a reproducible and facile method of inducing sulfur vacancies in monolayer MoS2 is provided through annealing. The existence of vacancies is confirmed by XPS and Raman spectroscopy. The defect-induced emission peak is observed at room temperature and can be eliminated by annealing in sulfur vapor.