HEAT-TRANSFER BETWEEN 2 METALLIC SURFACES AT SMALL DISTANCES

In scanning thermal microscopy, but also in scanning tunneling microscopy, the thermal contact between tip and sample plays an important role. The heat transfer across the vacuum gap between two parallel metallic surfaces, if the gap width is decreased below several microns, has been investigated. At these distances propagating electromagnetic modes die out but simultaneously a transfer of nonpropagating surface modes across the gap becomes more probable. The heat conductance of the vacuum gap should become distance dependent and larger than that given by the Stefan-Boltzmann law; however, the experimental results and theoretical considerations indicate that the heat transfer, based on the discussed proximity mechanism, is very small, smaller than predicted by the theory of Polder and Van Hove [Phys. Rev. B 4, 3303 (1971)]. © 1994 American Institute of Physics.