Photoluminescence of Monolayer MoS₂ under Controlled Environment for Optoelectronic Applications

Monolayer MoS₂ has become a very promising two-dimensional materials for photo-related applications. Establishing the impact of individual ambient gas components and chemical dopants on the optical properties of MoS₂ is a necessary step toward application development. By using in situ Raman micro-spectroscopy with an environment-controlled reaction cell, the photoluminescence (PL) intensity of CVD-grown MoS₂ monolayers is monitored at different intralayer locations under ambient and controlled gas environments, such as N₂, O₂, H₂O, and pyridine. Our study demonstrates that photoreactions with the gaseous environment on MoS₂ monolayer flakes should be taken into consideration even upon mild photoirradiation as they strongly impact the flakes’ optical properties. The optical properties of MoS₂ at the edges are strongly affected by photoirradiation induced reactions with O₂ and H₂O. We have also studied the effect of the dopant phase of the same dopants – liquid and gaseous – on the optical properties of ML MoS₂. The gaseous n-type dopant, i.e. pyridine, completely quenches the PL intensity of ML MoS₂, while liquid pyridine preserved 50% of the original PL intensity attributed to its less effective charge transfer to MoS₂ than the gaseous counterpart.