| Description |
A photonic thermal diode is a two-terminal device in which the magnitude of the heat transfer is significantly different depending on the direction of the temperature bias. Near-field radiation-mediated photonic thermal diodes not only allow the direction of heat transfer to be rectified, but also make radiation to exceed the blackbody limit. This thesis is separated into two main parts: discussing and investigating photonic thermal diodes via numerical and experimental approaches. In the first part of the thesis, a simple photonic thermal diode with terminals made of the same material but with dissimilar structures is designed and analyzed theoretically using fluctuational electrodynamics. Specifically, the two terminals of the proposed diode, separated by a nanosize vacuum gap, are made of a thin film and a bulk of 3C silicon carbide (SiC). Thermal rectification induced from such diode design capitalizes on the temperature dependence of coupled surface phonon-polaritons in nanostructures. The antisymmetric resonant mode of the thin film, resulting from surface phonon-polariton coupling, is tuned on- and off-resonance with the resonant mode of the bulk by switching the direction of the temperature bias. Due to dissimilar resonances in the different directions of the temperature bias, high thermal rectification efficiencies ranging from 80% to 87% are obtained for a wide temperature band (~700 K to 1000 K). In the second part of the thesis, near-field radiation measurements between two 5 × 5 mm2 6H-SiC surfaces separated by a 100-nm-thick vacuum gap are performed and iv verified against fluctuational electrodynamics predictions. This experimental investigation is a prerequisite step to implement thermal rectification based on the proposed diode design. The gap separating the surfaces is maintained by 100-nm-diameter polystyrene particles. The measured heat transfer rates are dominated by thermal radiation between two 6H-SiC surfaces rather than conduction through polystyrene particles. The results obtained are in relatively good agreement with theoretical predictions based on fluctuational electrodynamics and the largest measured heat flux exceeds the blackbody limit by a factor of more than 20. This high enhancement factor is due to thermal excitation of surface phonon-polaritons supported by 6H-SiC, which contribute to more than half of the total heat flux. These results pave the way to the experimental demonstration of a photonic thermal diode capitalizing on surface phonon-polaritons. |
