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In this Letter we experimentally demonstrate that the radiative heat transfer between metallic planar surfaces exceeds the blackbody limit by employing the near-field and thin-film effects. Nanosized polystyrene particles were used to create a nanometer gap between aluminum thin-films of different thicknesses coated on 5 × 5 mm 2 diced silicon chips while the gap spacing is fitted from the near-field measurement with bare Si chips. The experimental results are validated by theoretical calculation based on fluctuational electrodynamics. The near-field radiative heat flux between 13-nm Al thin-film samples at 215 nm gap distance is measured to be 6.4 times over the blackbody limit and 420 times compared to the far-field radiative heat transfer between metallic surfaces with a temperature difference of 65 K. In addition, the theoretical prediction suggests a near-field enhancement of 122 times relative to the blackbody limit and 8000 times over far-field one at 50-nm vacuum gap between 20-nm Al thin-film samples, under the same temperature difference of 65 K. This work will facilitate the understanding and application of near-field radiation to thermal power conversion, noncontact cooling, heat flow management, and optical storage where metallic materials are involved.

In this work we experimentally demonstrated the near-field thermal radiation enhancement over the blackbody limit by 11 times between highly doped silicon chips with 1×1 cm 2 size at a vacuum gap distance of 190±20 nm under a temperature difference of 74.7 K above room temperature. SU-8 polymer posts, which significantly reduced the conduction less than 6% of the total heat transfer due to its low thermal conductivity, were carefully fabricated with different heights to directly create vacuum gaps from 507±47 nm down to 190±20 nm precisely determined in-situ by capacitance measurement. Experimental results were validated by theoretical calculations based on fluctuational electrodynamics, which revealed the enhancement mechanism mainly as coupled surface plasmon polariton. The experimental method developed here will facilitate the potential applications of near-field radiative devices made of electrically conductive materials like metals, graphene, and transparent conductive oxide besides heavily doped semiconductors for thermal energy conversion, radiative thermal rectification, and radiative heat modulation.

A near-field thermophotovoltaic (TPV) system with a multilayer emitter of alternate tungsten and alumina layer is proposed in this paper. The fluctuational electrodynamics along with the dyadic Green's function for a multilayered structure is applied to calculate the spectral heat flux, and the charge transport equations are solved to get the photocurrent generation and electrical power output. The spectral heat flux is much enhanced when plain tungsten emitter is replaced with multilayer emitter. The mechanism of surface plasmon polariton coupling in the tungsten thin film, which is responsible for the heat flux enhancement, is analyzed. In addition, the invalidity of effective medium theory to predict the optical properties of multilayer structure in near-field radiation is discussed. The tungsten and alumina layer thicknesses are optimized to match the spectral heat flux with the bandgap of TPV cell. Practically, with a gold reflector placed on the back of TPV cell, which also acts as the back electrode, and a 5-nm-thick indium tin oxide (ITO) layer as the front contact, when the emitter and receiver temperature are respectively set as 2000 K and 300 K, the conversion efficiency and electrical power output can be achieved to 23.7% and 0.31 MW/m 2 at a vacuum gap distance of 100 nm.

In this work, the effect of magnetic polaritons (MP) inside the SiC grating microstructures on both near-and far-field radiative transport is theoretically studied. Fluctuational electrodynamics that incorporates scattering matrix theory with rigorous coupled-wave analysis is employed to calculate the spectral heat flux between two SiC deep gratings. The results are compared with effective medium theory and proximity approximation method. Besides the well-known coupled surface phonon polaritons (SPhP), MP excited in the grating groove can also cause enhanced spectral heat flux. Confined magnetic field inside the groove of SiC grating, contour plot of transmission coefficient and the prediction by an inductor-capacitor circuit model are used to elucidate the effect of MP. It shows that, compared to the total heat flux between two SiC plates, the one between SiC gratings can be enhanced in far field, while suppressed in near field with small vacuum gap distance. The effects of misalignments, geometrical parameters and vacuum gap distances on both SPhP and MP are investigated as well.