Measurements of the thermal resistivity at interfaces between metal and dielectric thin films and a bulk substrate are reported. The thin-film structures are representative of a variety of superconducting devices with electrically insulated components. Results were obtained for single and multiple layers from 1.5° to 4.2°K. The magnitude of the observed values are within the range of the Little formulation if only longitudinal phonon contribution is considered. The temperature dependence is approximately T−2.5. The thermal resistivities decreased with increasing heat flux and temperature difference. The resistivity of multiple-layered structures was considerably less than the sum of the resistivities of each layer measured separately. This is consistent with wave propagation through layered media. No appreciable effect of film thickness was noted in the 0.2- to 2-micron range.
The radiant heat transfer between two parallel infinite plates was determined. The plates were assumed to be specular, anisotropic reflectors and emitters as characterized by the electromagnetic theory for highly polished electrical conductors.
Numerical results are given for specific metals from 4.2 to 1500° K. Also, the results are expressed in generalized form for obtaining the net radiant heat transfer between any two parallel, infinite metal plates given only the temperatures and electrical resistivities.
Total hemispherical and normal emissivities were determined using the same methods. The results were in very good agreement with empirical equations given in the literature. For a contrasting comparison, Christiansen's equation for the net radiant heat transfer between two parallel, diffuse, gray surfaces of infinite extent was evaluated using these emissivities. The values obtained were less than those computed for the net radiant heat transfer between specular plates.
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