Ultrafast Nano-Imaging of Spatially Modulated Many-Body Dynamics in CVD-Grown Monolayer WS2

Unique optoelectronic properties of monolayer transition metal dichalcogenides (TMDs) originate from strong quantum confinement effects and reduced dielectric screening. However, their low dimensionality also renders photoinduced dynamics and the resulting properties highly susceptible to defects. Yet, the mechanistic relationship between intrinsic defects and non-uniform optoelectronic responses has remained elusive, calling for spatially resolved characterization to visualize heterogeneous photoinduced dynamics. Here, we apply ultrafast infrared scattering scanning near-field optical microscopy (ultrafast IR s-SNOM) to investigate WS2 monolayers grown by chemical vapor deposition. We demonstrate that ultrafast IR s-SNOM, with the relatively high excitation fluence, sensitively probes the dynamics of electron-hole plasma induced in local domains of the individual WS2 monolayers. The transient mid-infrared response is enhanced with extended lifetimes near the edges, indicating local mitigation of many-body interactions. We propose that the spatially modulated many-body dynamics is associated with defect-mediated mechanisms, providing implications for engineering TMD-based nanoscale optoelectronics.