Study of radiative heat transfer in \xc5ngstr\xf6m- and nanometre-sized gaps

Longji Cui,Juan Carlos Cuevas,Edgar Meyhofer,Pramod Reddy,Johannes Feist,Francisco J García-Vidal,Wonho Jeong,Víctor Fernández-Hurtado

doi:10.1038/ncomms14479

Abstract

Radiative heat transfer in Ångström- and nanometre-sized gaps is of great interest because of both its technological importance and open questions regarding the physics of energy transfer in this regime. Here we report studies of radiative heat transfer in few Å to 5 nm gap sizes, performed under ultrahigh vacuum conditions between a Au-coated probe featuring embedded nanoscale thermocouples and a heated planar Au substrate that were both subjected to various surface-cleaning procedures. By drawing on the apparent tunnelling barrier height as a signature of cleanliness, we found that upon systematically cleaning via a plasma or locally pushing the tip into the substrate by a few nanometres, the observed radiative conductances decreased from unexpectedly large values to extremely small ones—below the detection limit of our probe—as expected from our computational results. Our results show that it is possible to avoid the confounding effects of surface contamination and systematically study thermal radiation in Ångström- and nanometre-sized gaps.

Highlights

Radiative heat transfer in Ångstrom- and nanometre-sized gaps is of great interest because of both its technological importance and open questions regarding the physics of energy transfer in this regime
Our work found excellent agreement with the predictions of fluctuational electrodynamics down to gap sizes of 2–3 nm, it remained unclear whether large discrepancies between theory and experiment, as reported by recent experimental work[30,31,32], arise in gaps of a few Ångstroms
We experimentally studied radiative heat transfer using custom-fabricated scanning thermal microscopy probe (SThM) probes (Fig. 1, see Supplementary Note 1 and Supplementary Fig. 1 for details of probe fabrication)

Summary

Introduction

Radiative heat transfer in Ångstrom- and nanometre-sized gaps is of great interest because of both its technological importance and open questions regarding the physics of energy transfer in this regime. Measurements[30,31,32] for two gold (Au)-coated surfaces with gap size in the range of B0.2–10 nm have suggested an extraordinarily large near-field enhancement—over 3 orders of magnitude larger than the predictions from conventional fluctuational electrodynamics[22,33] These surprising results question the validity of current theories of heat transfer for these small gaps. We show that systematic cleaning of the probe and substrate surfaces increases the apparent barrier height to values as large as 2.5 eV and the measured conductances reduce to considerably small values that are below the detection limit of our probes as expected from our computations

Methods

Results

Conclusion