Nonuniform Chemical Passivation Dynamics in Monolayer MoS₂ from Real-Time Photoluminescence Imaging

Postchemical treatment is a major strategy for improving the optical and electronic performance of two-dimensional transition-metal dichalcogenides (TMDs), where surface defects and unintentional doping limit radiative recombination. Despite its broad application, the passivation dynamics in both time and space remain insufficiently understood. Here, we employ real-time, spatially resolved photoluminescence (PL) imaging to track the evolution of PL emission from monolayer MoS₂ during the Li-TFSI treatment. The PL intensity increases gradually over 4.7 min, indicating reaction-limited passivation kinetics. At the same time, the spatial variation in PL becomes more pronounced, revealing position-dependent reactivity and heterogeneous treatment across the flake. Pixel-level PL statistics compared with noise-based simulations confirm that this broadening originates from the intrinsic spatial heterogeneity of the material. These results demonstrate that chemical treatment enhances radiative recombination while simultaneously amplifying pre-existing spatial differences, establishing real-time PL imaging as a sensitive approach to probing heterogeneous surface reactions in 2D semiconductors.