Thermal conductance of interfaces between highly dissimilar materials

The thermal conductance of interfaces between materials with low Debye temperatures (Pb or Bi) and dielectrics or semiconductors with high Debye temperatures (hydrogen-terminated Si, $\mathrm{Si}{\mathrm{O}}_{2}$, the native oxide of Be, sapphire, or hydrogen-terminated diamond) is measured using time-domain thermoreflectance. The interface thermal conductance $G$ for these combinations of materials falls within a relatively narrow range, $8<G<30\phantom{\rule{0.3em}{0ex}}\mathrm{MW}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, at room temperature. Because the thermal conductance of interfaces with Bi, a semimetal, and interfaces with Pb, a metal, are similar, we conclude that the coupling of electrons in a metal to phonons in a dielectric substrate does not contribute significantly to the thermal transport at interfaces. For Pb or Bi on hydrogen-terminated diamond, the measured conductance greatly exceeds the radiation limit and decreases approximately linearly with decreasing temperature, suggesting that anharmonic processes dominate the transfer of thermal energy across interfaces between materials with highly dissimilar spectra of lattice vibrations.

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