In-plane interfacial phonon transport through multi-layer thin films by theoretical analyses and Monte Carlo simulations

Abstract

This work studies the in-plane phonon transport through double-layer, superlattice, and four-layer thin films by theoretical analyses and Monte Carlo simulations. The spectral diffuse mismatch model and the adiabatic diffuse scattering are taken as the interface and surface boundary conditions respectively. The results indicate that the number of thin-film layers has little impact on the heat flux distribution within each layer and there is a heat flux discontinuity at the interface. Indentical in-plane thermal conductivities are obtained for double-layer, superlattice, and four-layer thin films with a uniform thickness of each layer. This means that the number of thin-film layers has negligible impacts on the in-plane thermal conductivity, which can provide the first explicit explanation to the observation in a recent experiment. Finally, the minimum in-plane thermal conductivity is found in thin films when varying thickness ratios. The extreme points are also analytically obtained. This law is completely different from that for the cross-plane thermal conductivity or that predicted by the Fourier's law of heat conduction for in-plane heat transport which leads to a monotonic relation between the thermal conductivity and the thickness ratio.