Ultrafast Nano-Imaging\nof Spatially Modulated Many-Body\nDynamics in CVD-Grown Monolayer WS<sub>2</sub>

Unique optoelectronic properties of monolayer transition\nmetal\ndichalcogenides (TMDs) originate from strong quantum confinement effects\nand reduced dielectric screening. However, their low dimensionality\nalso renders photoinduced dynamics and the resulting properties highly\nsusceptible to defects. Yet, the mechanistic relationship between\nintrinsic defects and non-uniform optoelectronic responses has remained\nelusive, calling for spatially resolved characterization to visualize\nheterogeneous photoinduced dynamics. Here, we apply ultrafast infrared\nscattering scanning near-field optical microscopy (ultrafast IR s-SNOM)\nto investigate WS<sub>2</sub> monolayers grown by chemical vapor deposition.\nWe demonstrate that ultrafast IR s-SNOM, with the relatively high\nexcitation fluence, sensitively probes the dynamics of electron–hole\nplasma induced in local domains of the individual WS<sub>2</sub> monolayers.\nThe transient mid-infrared response is enhanced with extended lifetimes\nnear the edges, indicating local mitigation of many-body interactions.\nWe propose that the spatially modulated many-body dynamics is associated\nwith defect-mediated mechanisms, providing implications for engineering\nTMD-based nanoscale optoelectronics.