Ultimate impedance of coherent heat conduction in van der Waals graphene-MoS2 heterostructures

Abstract

There are growing efforts to control thermal transport via coherent phonons in one-dimensional superlattices. Typically, the difference in intrinsic lattice structures of the constituent materials generates an interface disorder during the fabrication process, limiting the coherent phonon transport manipulation. On the other hand, flexible integration and atomistic interlayer smoothness of a van der Waals (vdW) heterostructure provide an ideal platform for coherent phonon transport manipulations. Toward the ultimate goal of designing small thermal-conductivity materials at room temperature, herein we investigate the controllability of coherent phonon transport in vdW graphene-MoS2 heterostructures with different stacking orders using non-equilibrium molecular dynamics simulations. Using Bayesian optimization–based materials informatics, the optimal stacking order of graphene and MoS2 is efficiently identified from tens of thousands of candidates with varying degrees of phonon localization. The obtained thermal conductivity of the optimized heterostructure (0.026 W/m-K) is significantly lower than that of its building blocks (pristine MoS2 and graphene). Additionally, the optimized heterostructure has a thermal conductivity lower than those of representative low thermal conductivity solid materials (amorphous and disordered crystals), and the amorphous polymers. The underlying physical mechanism of coherent phonon localization is uncovered by calculating the phonon transmission in the optimum heterostructure and analyzing the histogram distribution pattern of the phonon transmissions in different disordered stacking heterostructures. The presence of localization is further validated by a comparative study of the optimum heterostructure to pristine graphene with introduced defects, changed the thickness and temperature of the system. Our work provides insight into the coherent phonons transport behavior in the atomistically smooth vdW structure, which is essential for further development of phononics.