Abstract
The impact of mass and bond energy difference and interface defects on thermal boundary conductance (TBC) is investigated using non-equilibrium molecular dynamics (NEMD) with the Lennard-Jones (L-J) interatomic potential. Results show that the maximum TBC is achieved when the mass and bond energy of two dissimilar materials are matched, although the effective thermal conductivity is not necessarily a maximum due to the contributions of the thermal conductivity of the constituent materials. Mass and bond energy differences result in a mismatch between phonon dispersions, limiting high frequency phonon transport at the interface. This frequency mismatch is defined by a frequency ratio, which is a ratio of the characteristic frequencies of the two materials, presented in the discussion section, and is a reference of the level of phonon dispersion mismatch. Inelastic scattering may result at higher temperatures, especially when there exists a bond energy difference, resulting in strain in the lattice, which would allow phonons outside the allowable frequency range to contribute to transport. TBC decreases abruptly with small mass differences, but at which point larger differences in mass have no impact. In addition, interdiffusion across the interface further reduces the TBC between the frequency ratios of 0.79 and 1.26 while vacancies have negligible impact.
Highlights
As the size of electronic, photonic, and phononic devices becomes smaller there is an increasing need to understand thermal transport across interfaces between two different materials
This temperature discontinuity can be described by the thermal boundary resistance, or Kapitza resistance,[3] which is the inverse of the thermal boundary conductance (TBC)
The TBC from the mass variation is shown in figure 2(a), and the thermal conductivity is shown as an inset
Summary
As the size of electronic, photonic, and phononic devices becomes smaller there is an increasing need to understand thermal transport across interfaces between two different materials. To understand the role of scattering, Duda et al.[6] studied different scattering mechanisms, including complete diffuse scattering, partial diffuse scattering, elastic scattering, and inelastic scattering, and showed the dependency of transmission probability on the principle of detailed balance, and found that one of their specific cases produces the DMM developed by Swartz and Pohl.[5] Hopkins and Norris developed the joint frequency diffuse mismatch model (JFDMM) with the assumption of inelastic scattering at the interface, and found that inelastic scattering can contribute to thermal transport at high temperatures.[7] these models have advanced the understanding of phonon transmission across interfaces by including scattering, a complete and accurate prediction of thermal boundary resistance at higher temperatures and in highly disordered interfaces is still lacking.
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