Gate-Tunable Near-Field Heat Transfer ACS Photonics, Article, 2019
Thermal management is fundamental for novel energy-harvesting technologies, enabling control and conversion of energy from heat to electricity. Among heat exchange processes, near-field heat transfer is of particular importance as it enables exchange rates beyond the Stefan-Boltzmann limit between objects separated by submicron distances, promising improved power throughput in high-temperature solid-state energy conversion. Controlling the flow of heat also allows electricity-free radiative cooling, the temperature reduction of hot objects passively, through emission of electromagnetic radiation.
Precise nanophotonic design can dramatically increase the degrees of freedom for controlling the flow of heat. Both near-field heat transfer and radiative cooling pertain to engineering the electromagnetic response of layered heterostructures, constituting the emitter (hot body) or the receiver (e.g. a thermophotovoltaic cell) in solid-state devices. Previous approaches focused on schemes that support the excitation of surface plasmon- or surface phonon-polaritons, which, however, are polarization-dependent. This polarization dependence limits the performance of near-field heat transfer schemes by 50%, and originates from an asymmetry in the palette of naturally available materials, providing a wide range of dielectric properties, while the magnetic properties vanish at infrared and visible frequencies. Georgia’s previous research showed that excitations similar to plasmons can occur in heterostructure metamaterials engineered to respond simultaneously to electric and magnetic fields. This concept will be explored for increasing the efficiency of near-field heat transfer and radiative cooling modules. Georgia will explore and identify technologically relevant materials, particularly polar dielectrics, wide- (Si) and low- (III-V) bandgap semiconductors and plasmonic materials, and their combinations in heterostructures, for achieving record-high rates of near-field heat transfer and for improving absorption and emissivity for radiative cooling.