Understanding the thermal transport at metal-dielectric interfaces in the presence of ultrathin metallic interlayers*

Efficient thermal management due to nanoscaling of devices is becoming more critical in numerous technologies such as thermoelectrics, plasmonic devices, etc. In this work, we analyze the role of vibrational properties and electron-phonon coupling constant (EPC) in modifying the thermal conductance at metal-dielectric interfaces by inserting ultrathin metal interlayers. Our results show that for substrates with highly dissimilar debye temperatures, the measured thermal boundary conductance (TBC) between metal/interlayer/substrate remains the same. We suggest that comparing the maximum phonon frequency of the low-energy phonons is a better parameter than the debye temperature to predict the change in the thermal conductance at metal/interlayer/dielectric interfaces. Inserting metallic layers with EPC strength higher than the top layer has been reported to increase the TBC by dragging electrons and phonons into equilibrium quickly. Our results also show that the Ta interlayer with the highest EPC and poorest phonon frequency overlap with the substrate has the lowest measured TBC compared to other interlayers Ni and Cr. Hence, we suggest that the TBC depends on an interplay between the phonon vibrational properties and metal EPC strength in non-trivial ways.