Phonon transport across a vacuum gap

Abstract

Phonon transport across a silicon/vacuum-gap/silicon structure is modeled using lattice dynamics calculations and Landauer theory. The phonons transmit thermal energy across the vacuum gap via atomic interactions between the leads. Because the incident phonons do not encounter a classically impenetrable potential barrier, this mechanism is not a tunneling phenomenon. While some incident phonons transmit across the vacuum-gap and remain in their original mode, many are annihilated and excite different modes. We show that the heat flux due to phonon transport can be four orders of magnitude larger than that due to photon transport predicted from near-field radiation theory.

Giant heat transfer in the crossover regime between conduction and radiation

“…Given the current lack of appropriate theoretical models that can span this range of distances and geometries, the question of whether the measured heat flux can be explained by phonon or photon tunnelling, or whether there is yet another unknown mechanism at play, remains open. We hope, however, that this work along with previous results on a related experiment 15 , provide the basis and motivation for further theoretical exploration of heat transfer mechanisms in this crossover regime where both radiative and conductive effects can coexist and are greatly affected by geometry.…”

“…In particular, 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. Several recent theoretical works have studied this cross-over by including effects like tunnelling of acoustic phonons 14 15 16 and quantum effects due to the overlap of the electronic wave functions 17 , showing that the radiative heat flux can be further enhanced by several orders of magnitude at distances of a few nanometres or even on the sub-nanometre level. The above-mentioned experiments have confirmed the predictions of the conventional macroscopic theory 3 4 5 6 7 8 9 as they probe the near-field at much larger distances.…”

Scanning thermal microscopy: A review

“…SThM may open new avenues for the investigations of physical phenomena in the quantum regime, at least at low temperatures. In addition, the heat transfer before contact, due to vibrations of both acoustic and optical modes, is also not very well understood on a theoretical basis . Peculiar results may be observed .…”

Phonon-assisted heat transfer between vacuum-separated surfaces

“…It has long been recognized that when two materials are in close proximity in vacuo their exchange of heat is no longer dictated by thermal radiation [5][6][7][8] . For a more complete set of references to earlier work see 7,9 .…”