  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 5x5 mm2 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.
