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At conformal interfaces between dissimilar materials, a finite thermal resistance develops, governed by the transmission behavior of phonons. Understanding the engineering opportunities available for such interfaces thus requires an understanding of phonon transmission behavior. Due to its simplicity, the diffuse mismatch model (DMM) remains a popular description of phonon transmission across solid-solid boundaries. However, it remains unclear in which situations the DMM is good description of the underlying physics. In this talk we present theoretical and experimental observations of interfaces with tailored degrees of disorder. Using a 3-dimensional extension of the frequency domain, perfectly matched layer (FD-PML) method, we probe the validity of the diffuse mismatch model (DMM) on a mode-by-mode basis at the interface between solids with interdiffused atoms. It is found that small levels of disorder at an interface can increase the number of available modes for transmission, and subsequently reduce thermal interface resistance. These general observations are consistent with the DMM, and for submonolayer levels of interdiffusion, similar thermal interface conductance values as the DMM are seen. However, the mode-by-mode predictions of transmission coefficient vary drastically from the DMM. Particularly, (1) contrary to the fundamental assumption of the DMM, not all modes lose memory of their initial polarization and wavevector. (2) Interdiffusion in excess of a monolayer is generally found to make agreement between the DMM and the simulations worse, not better. On the other hand, experimental measurements between epitaxial and non-epitaxial versions of the same material interfaces indicate that the detailed structure of the interfaces are unimportant to the transport properties: a key result of the DMM.
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