Role of the electron-phonon coupling on the thermal boundary conductance of metal/diamond interfaces with nanometric interlayers

Abstract

Thermal boundary conductance (TBC) of the Ag/diamond and Au/diamond interfaces with a nanometer-thick interface layer of either nickel or molybdenum is measured by time domain thermoreflectance and modeled based on a 3-layer two-temperature model (3l-TTM). The rationale for this study is to critically assess the role of the electron-phonon coupling factor of the interlayer along with its thickness on the TBC. It is shown that the TBC of both systems rapidly increases with the interlayer thickness until reaching a stable plateau for thicknesses greater than 1.5 nm. The plateau average value is 15%–25% lower than the intrinsic TBC between the interlayer material and the diamond substrate. This behavior and values of the TBC of both systems are in good agreement with the predictions of the 3l-TTM. The predictability of this model is also analyzed for a Cu interlayer inserted at Au/silicon interfaces with thicknesses ranging from 1.5 to 20 nm. While the room temperature TBC of this system is well described by the 3l-TTM, the values measured at 80 K can only be predicted by the 3l-TTM, provided that the interlayer electron-phonon coupling factor is reduced by a factor of 2, as was experimentally observed for Ag and Au. The obtained experimental results along with the proposed model can thus be useful for tailoring the TBC of metallic interfaces in a wide range of temperatures.