Radiation-based near-field thermal rectification with phase transition materials

The capability of manipulating heat flow has promising applications in thermal management and thermal circuits. In this Letter, we report strong thermal rectification effect based on the near-field thermal radiation between silicon dioxide (SiO₂) and a phase transition material, vanadium dioxide (VO₂), separated by nanometer vacuum gaps under the framework of fluctuational electrodynamics. Strong coupling of surface phonon polaritons between SiO₂ and insulating VO₂ leads to enhanced near-field radiative transfer, which on the other hand is suppressed when VO₂ becomes metallic, resulting in thermal rectification. The rectification factor is close to 1 when vacuum gap is at 1 μm and it increases to almost 2 at sub-20-nm gaps when emitter and receiver temperatures are set to 400 and 300 K, respectively. Replacing bulk SiO₂ with a thin film of several nanometers, rectification factor of 3 can be achieved when the vacuum gap is around 100 nm.