Direct Spectroscopic Observation of Cross-Plane Heat Transfer in a Two-Dimensional Van der Waals Heterostructure

Two-dimensional (2D) transition metal chalcogenides (TMDs) have drawn significant attention in recent year s due to their extraordinary optical and electronic properties. As heat transfer plays an important role in device performance, various methods such as optothermal Raman spectroscopy and time-domain thermoreflectance have been developed to measure the thermal conduct i v i t y and interfacial thermal conductance in 2D van der Waals (vdW) heterostructures. Here, we employ the vibrational-pump-visible-probe (VPVP) spectroscopy to directly visualize the heat transfer process in a heterostructure of multilayer h-BN and monolayer WS2. Following an impulsive vibrational excitation of h-BN in the mid-infrared, we probe the heat transfer from h-BN through WS2 and finally to the substrate from the subpicosecond to the submicrosecond timescale. The interfacial thermal conductance of the h-BN/WS2 and WS2/SiO2 interfaces is obtained by corroborating the experiments with heat transfer calculations based on the Fourier's law of heat conduction. Our study demonstrates an alternative, time-resolved optical method to measure cross-plane heat dissipation and opens up a new pathway to investigate the interlayer electron-phonon and phonon-phonon interactions in v d W heterostructures.