Abstract
Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. At large distances the heat transfer can be described by black body radiation, at shorter distances evanescent modes start to contribute, and at separations comparable to inter-atomic spacing the transition to heat conduction should take place. We report on quantitative measurements of the near-field mediated heat flux between a gold coated near-field scanning thermal microscope tip and a planar gold sample at nanometre distances of 0.2–7 nm. We find an extraordinary large heat flux which is more than five orders of magnitude larger than black body radiation and four orders of magnitude larger than the values predicted by conventional theory of fluctuational electrodynamics. Different theories of phonon tunnelling are not able to describe the observations in a satisfactory way. The findings demand modified or even new models of heat transfer across vacuum gaps at nanometre distances.
Highlights
Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum
The heat flux can be enhanced by many orders of magnitude compared with the heat transfer exchanged between two black bodies coupled through the far-field
Commonly used theoretical models of heat transfer are based on Rytov’s theory of macroscopic fluctuational electrodynamics[13], which cannot fully describe heat exchange at distances down to a few nanometres. Such a theory does not account for the cross-over from near field to contact, in which case the objects are separated by atomic distances and heat flux is mediated by conductive transfer
Summary
Heat is transferred by radiation between two well-separated bodies at temperatures of finite difference in vacuum. The heat flux can be enhanced by many orders of magnitude compared with the heat transfer exchanged between two black bodies coupled through the far-field This super-Planckian effect can be attributed to the additional contribution of evanescent waves such as frustrated total internal reflection modes, surface phonon polaritons, surface plasmons, or hyperbolic modes[1,2]. Commonly used theoretical models of heat transfer are based on Rytov’s theory of macroscopic fluctuational electrodynamics[13], which cannot fully describe heat exchange at distances down to a few nanometres Such a theory does not account for the cross-over from near field to contact, in which case the objects are separated by atomic distances and heat flux is mediated by conductive transfer.
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