Abstract
Several experiments have shown a huge enhancement in thermal radiation over the blackbody limit when two objects are separated by nanoscale gaps. Although those measurements only demonstrated enhanced radiation between homogeneous materials, theoretical studies now focus on controlling the near-field radiation by tuning surface polaritons supported in nanomaterials. Here, we experimentally demonstrate near-field thermal radiation between metallo-dielectric multilayers at nanoscale gaps. Significant enhancement in heat transfer is achieved due to the coupling of surface plasmon polaritons (SPPs) supported at multiple metal-dielectric interfaces. This enables the metallo-dielectric multilayers at a 160-nm vacuum gap to have the same heat transfer rate as that between semi-infinite metal surfaces separated by only 75 nm. We also demonstrate that near-field thermal radiation can be readily tuned by modifying the resonance condition of coupled SPPs. This study will provide a new direction for exploiting surface-polariton-mediated near-field thermal radiation between planar structures.
Highlights
Several experiments have shown a huge enhancement in thermal radiation over the blackbody limit when two objects are separated by nanoscale gaps
Recent experimental works have reported that strong enhancements in heat transfer between polar dielectric materials like SiC11 or SiO212,20 separated by vacuum gaps of 25–50 nm resulted from increased spectral heat flux at resonance condition of surface phonon polaritons (SPhPs) corresponding to the characteristic wavelength of thermal radiation at room temperature
Metals have plasma frequencies that are much higher than the characteristic frequencies of thermal radiation at room temperature; no substantial enhancement in near-field thermal radiation due to coupling of surface plasmon polaritons (SPPs) in metals is expected under typical conditions[26]
Summary
Several experiments have shown a huge enhancement in thermal radiation over the blackbody limit when two objects are separated by nanoscale gaps Those measurements only demonstrated enhanced radiation between homogeneous materials, theoretical studies focus on controlling the near-field radiation by tuning surface polaritons supported in nanomaterials. Metallo-dielectric (MD) multilayers have been extensively studied because mutual interactions of surface polaritons at multiple interfaces inside multilayers[24,25,35,36] provide exotic features including tuning of near-field thermal radiation Given that such tuning capability is a pivotal issue in enhancing the performance of electricitygeneration systems[24,25,37,38,39,40] and in thermal management[41,42], an experimental demonstration of the modulation of thermal radiation between MD multilayers is indispensable. Comments on the validity of effective medium theory and the existence of a hyperbolic mode in the MD multilayered structure will be provided
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