Electronically-coupled ultrafast structural dynamics and interlayer energy transfer of substrate-supported two-dimensional transition metal dichalcogenide heterostructures

Understanding energy flow across layered two-dimensional heterostructures is crucial for controlling carrier and phonon transport as well as thermal management in next-generation optoelectronic devices. By using reflection ultrafast electron diffraction, we directly examine the photoinduced out-of-plane structural dynamics of supported MoS₂/WS₂ heterostructures and their monolayers separately. Experimental evidence reveals surprising early-time impacts of interlayer charge transfer on the photodynamics of van der Waals (vdW) heterojunctions compared to those of the individual monolayers. The enhanced optical absorption observed for heterostructures is also consistent with the notable interlayer electronic coupling. Following carrier–phonon coupling and carrier annihilation, we observe thermalized atomic motions that can be well described by the Debye model and a thermal dissipation picture. A higher thermal boundary conductance (TBC) across MoS₂/WS₂ heterostructures is obtained compared to those at the monolayer–substrate interfaces; however, the similar TBC values suggest comparable phonon scatterings across the vdW contacts. These results further shed light on the optical, phonon, and interfacial thermal properties of vertically-stacked vdW heterostructures.