Investigation of thermal rectification in bi-layer nanofilm by molecular dynamics

The rectification of the cross-plane thermal conductivity and the interfacial thermal resistance of nanoscale bi-layer films are investigated using the nonequilibrium molecular dynamics method with two different heat baths. The effects of the thickness of the single layer with the total film thickness fixed, the atomic mass ratio and temperature difference across the film on the thermal rectification are considered. The results show that the thermal rectification is dependent on the temperature gradient and the atomic mass ratio. The thermal conductivity is usually larger when the heat flux direction is from the light mass layer to the heavy mass one. It is found, however, that the rectification could be reversed if the heavy layer is thin enough. The phonon density of states is given to explain the mechanism behind the phenomena. The overlap of the phonon density of states of the two layers is almost same even if the rectification of the thermal conductivity is reversed.