The potential of hyperbolic films for radiative heat transfer in micro/nanoscale

Thin films exhibit substantial potential in energy management and utilization as the development of micro- and nanofabrication technologies. It is well known that thermal radiation is one of the fundamental ways of energy transfer. However, the potential of hyperbolic films for radiative heat transfer is always ignored. Whether the radiative heat flux between hyperbolic films surpasses that of the bulk materials remains insufficiently explored. In this work, we theoretically investigate the radiative heat transfer between hexagonal boron nitride (hBN) at a separation from 20 nm to 2 μm. The results show that when the optical axis of hBN is oriented in-plane, the near-field radiative heat flux of hBN with a thickness of 10 nm exceeds that of hBN bulk by 47% and exceeds the blackbody limit by two orders of magnitude at a gap distance of 20 nm. The physical mechanism is attributed to the volume-confined hyperbolic polaritons can be excited in a higher wavevector space. Conversely, when the gap distance is 600 nm, the heat flux between films is considerably lower than that of bulk material. This work opens up potential avenues for developing hyperbolic film-dependent thermal devices and strategies for thermal management.