Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS₂

In this Letter, the ultrafast structural, interfacial, and carrier dynamics of monolayer MoS₂ supported on sapphire are cross-examined by the combination of ultrafast electron diffraction (UED) and transient reflectivity techniques. The out-of-plane motions directly probed by reflection UED suggest a limited anisotropy in the atomic motions of monolayer MoS₂, which is distinct from that of related materials such as graphene and WSe₂. Besides thermal diffusion, the MoS₂-sapphire interface exhibits structural dynamics trailing those of the overlaying MoS₂ and are in stark contrast with the sapphire bulk, which is consistent with the limited thermal boundary conductance. These structural dynamics provide justification for the determination of carriers being trapped by defects in ∼600 fs and releasing energy within a few picoseconds. The rich findings attest to the strength of combining techniques with real-time optical and direct structure probes for a detailed understanding of dynamical processes in functional materials.