  Recently, many works have experimentally demonstrated near-field radiative
heat transfer (NFRHT) exceeding the far-field blackbody limit between planar
surfaces. Due to the difficulties associated with maintaining the nanosize gaps
required for measuring a near-field enhancement, these demonstrations have been
limited to experiments that cannot be implemented into actual applications.
This poses a significant bottleneck to the advancement of NFRHT research. Here,
we describe devices bridging laboratory-scale measurements and potential NFRHT
engineering applications in energy conversion and thermal management. We report
a maximum NFRHT enhancement of ~ 28.5 over the blackbody limit with devices
made of millimeter-sized doped silicon (Si) surfaces separated by vacuum gap
spacings down to ~ 110 nm. The devices capitalize on micropillars, separating
the high-temperature emitter and low-temperature receiver, manufactured within
micrometer-deep pits. These micropillars, which are ~ 4.5 to 45 times longer
than the nanosize vacuum spacing where radiation transfer takes place, minimize
parasitic heat conduction without sacrificing device structural integrity. The
robustness of our devices enables gap spacing visualization via scanning
electron microscopy (SEM) prior to performing NFRHT measurements. Direct gap
spacing characterization is critical for transitioning NFRHT research from
laboratory-scale experiments to applications.
