Probing the Effect of Chemical Dopant Phase on Photoluminescence of Monolayer MoS2 Using in Situ Raman Microspectroscopy

Understanding the role of chemical dopants is crucial to modulating the optoelectronic properties of monolayer (ML) MoS2 and realizing its optoelectronic applications such as photodetectors, switching devices, and ultrathin transistors. Here, the effect of the dopant phase of the same dopants—liquid and gaseous—on the optical properties of ML MoS2 has been investigated using in situ Raman microspectroscopy with an environment-controlled reaction cell. The results show that the gaseous n-type dopant, that is, pyridine, completely quenched 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. Photoemission of the quenched MoS2 could not be recovered with mild annealing in nitrogen and only partially recovered upon long-term exposure to air. The results show that the dopant phase strongly impacts the PL properties of ML MoS2.