Radiative transfer of energy at the nanometre length scale is of great importance to a variety of technologies including heat-assisted magnetic recording1, near-field thermophotovoltaics2 and lithography3. Although experimental advances have enabled elucidation of near-field radiative heat transfer in gaps as small as 20–30 nanometres (refs 4, 5, 6), quantitative analysis in the extreme near field (less than 10 nanometres) has been greatly limited by experimental challenges. Moreover, the results of pioneering measurements7,8 differed from theoretical predictions by orders of magnitude. Here we use custom-fabricated scanning probes with embedded thermocouples9,10, in conjunction with new microdevices capable of periodic temperature modulation, to measure radiative heat transfer down to gaps as small as two nanometres. For our experiments we deposited suitably chosen metal or dielectric layers on the scanning probes and microdevices, enabling direct study of extreme near-field radiation between silica–silica, silicon nitride–silicon nitride and gold–gold surfaces to reveal marked, gap-size-dependent enhancements of radiative heat transfer. Furthermore, our state-of-the-art calculations of radiative heat transfer, performed within the theoretical framework of fluctuational electrodynamics, are in excellent agreement with our experimental results, providing unambiguous evidence that confirms the validity of this theory11,12,13 for modelling radiative heat transfer in gaps as small as a few nanometres. This work lays the foundations required for the rational design of novel technologies that leverage nanoscale radiative heat transfer.
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P.R. acknowledges support from US Department of Energy Basic Energy Sciences through a grant from the Scanning Probe Microscopy Division under award no. DE-SC0004871 (fabrication of scanning thermal probes). E.M. and P.R. acknowledge support from the Army Research Office under grant W911NF-12-1-0612 (fabrication of microdevices). P.R. acknowledges support from the Office of Naval Research under grant award no. N00014-13-1-0320 (instrumentation). E.M. and P.R. acknowledge support from the National Science Foundation under grant CBET 1235691 (thermal characterization). J.C.C. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) (contract no. FIS2014-53488-P) and the Comunidad de Madrid (contract no. S2013/MIT-2740) and V.F.-H. from “la Caixa” Foundation. F.J.G.-V. and J.F. acknowledge support from the European Research Council (ERC-2011-AdG Proposal No. 290981), the European Union Seventh Framework Programme (FP7-PEOPLE-2013-CIG-618229), and the Spanish MINECO (MAT2011-28581-C02-01 and MAT2014-53432-C5-5-R). The authors acknowledge the Lurie Nanofabrication Facility for facilitating the nanofabrication of devices.
This file contains Supplementary Text and Data 1-16, Supplementary Figures 1-15 and additional references.
About this article
Scientific Reports (2018)