Enhanced Near-Field Radiative Heat Transfer Between Planar Membranes Thinner Than the Vacuum Gap Spacing—Experiment

Several experiments have demonstrated that near-field radiative heat transfer (NFRHT) between two flat surfaces can exceed Planck’s blackbody limit (e.g., Song et al., <i>Nature Nanotechnology</i> 11, 509-514, 2016; DeSutter et al., <i>Nature Nanotechnology</i> 14, 751-755, 2019; Tang et al., <i>ACS Photonics</i> 7, 1304-1311, 2020). Recent simulations based on the discrete system Green’s function (DSGF) method (Walter et al., arXiv:2204.05399, 2022) used for modeling NFRHT in arbitrary 3D geometries suggest that the radiative heat transfer coefficient can be further enhanced when the two surfaces facing laterally are thinner than their separation gap. To date there has been no experimental work in this regime, which here we address by measuring NFRHT between the edges of two planar silicon carbide (SiC) membranes thinner than their vacuum gap spacing. More specifically we measured the NFRHT between a series of suspended microdevices consisting of pairs of coplanar SiC membranes with thickness and gap spacing respectively smaller than 100 nm and 500 nm. The measured radiative heat transfer coefficients are large and exceed predictions for two infinite surfaces at the same gap. For instance, at a fixed separation gap of an estimated ~ 100 nm, the measured near-room-temperature radiative heat transfer coefficient for 50-nm-thick SiC membranes is 470 W/m²-K, which is around 3.1 times larger than calculations for two infinite surfaces of SiC at the same gap, ~ 30 times larger than the far-field results of Thompson et al. for 270-nm-thick SiN membranes (<i>Nature</i> 561, 216-221, 2018), and ~ 320 times higher than predicted from a classical blackbody heat transfer calculation for the same geometry. The measurements also agree reasonably well with simulations using the DSGF method. These findings may help inform various applications such as energy conversion, radiative cooling, and thermal rectification.