Ultrafast Pump-Probe Nano-Imaging of Carrier and Lattice Dynamics of WSe₂/SiO₂ Heterostructures

Carrier and lattice dynamics and coupling across heterointerfaces are at the core of defining device performance and lifetimes in 2D semiconductor heterostructures. However, low spatial resolution, slow speed, or lack of interfacial sensitivity have limited most conventional techniques in addressing the underlying mechanisms. Here we present ultrafast heterodyne pump-probe nano-imaging with pump-modulation as a technique for characterizing the nano-spatial and ps-timescale processes at the interface with full spatial, temporal, and spectral resolutions. We utilize this far-from equilibrium visible-pump, infrared-probe nano-imaging and spectroscopy in the study of monolayer and bulk WSe₂ on SiO₂. We differentiate the few-ps intralayer exciton dynamics from the 100-ps interfacial energy dissipation and transport. We resolve the non-resonant Drude carrier response of WSe₂, revealing layer and boundary dependencies in carrier relaxation times, as well as the resonant substrate surface phonon polariton frequency and its temperature-dependent lattice softening. These results inform the complex interplay and competing relaxation pathways in TMD/substrate heterostructures, whose performance critically depends on exciton lifetimes, hot phonon-bottlenecks, and nanoscale thermal management.