Tunable superlattice in-plane thermal conductivity based on asperity sharpness at interfaces: Beyond Ziman’s model of specularity

International audience; We prove that interfacial asperity sharpness allows for tuning superlattice in-plane thermal conductivity below or above the limit of high roughness derived from the Lucas-Ziman (LZ) model. Whereas LZ’s model predicts molecular dynamic (MD) results of Lennard-Jones superlattices for small asperities, it has to be modified with a roughness- and sharpness-dependent layer thickness to remain relevant at higher roughness. For the case of sharpest asperities, the modified LZ model still fails, and ray-tracing computations matching MD data reveal a phonon-trap effect in the asperity valleys. This behavior scales with the Knudsen number and should appear at the micron scale in large mean-free-path crystals, such as silicon.