Thermal conductivity across transition metal dichalcogenide bilayers

Cross-plane thermal conductivities of transition metal dichalcogenide $$ (M = Mo, W; X = S, Se) bilayers are determined by homogeneous nonequilibrium molecular dynamics. The best insulator is found to be $$ : $$ , closely followed by $$ : $$ and $$ : $$ . Thermal conductivities of heterobilayers are close to the average of the two corresponding homobilayer values, despite the mass and lattice mismatch. To disentangle the effects of atomic mass, lattice constant, and interaction potential, these three parameters are systematically varied. Phonon spectral analysis provides further insight into their roles and reveals the weak influence of spectral overlap between the two layers and the dominance of boundary scattering. The observed trends can be rationalized using Slack's formula in terms of the average atomic mass and the Debye temperature. Accurate interlayer interaction potentials are developed based on experimental elastic constants. Their effect on the bilayer cross-plane thermal conductivities is found to be minor.