Radiative heat transfer between biaxial hyperbolic film in the far-field and near-field

Thin films demonstrate considerable potential in the realms of radiative heat transfer and play a major role in thermal rectification and energy conversion. Hyperbolic materials can effectively promote radiative heat transfer due to the ability to excite hyperbolic polaritons in a wide range of hyperbolic bands. However, the potential of biaxial hyperbolic film in radiative heat transfer remains insufficiently explored. In this work, the radiative heat transfer between alpha-phase molybdenum trioxide (alpha-MoO3) is theoretically investigated, considering separations ranging from 20 nm to 2 mu m. When considering radiative heat flux along the [010] direction, the near-field radiative heat flux of alpha-MoO3 with a thickness of 10 nm is only 8 % less than that of the bulk material and exceeds the blackbody limit by approximately three orders of magnitude at a separation of 20 nm. This phenomenon is attributed to the excitation of hyperbolic polaritons. Conversely, when the gap distance is 1000 nm, the heat flux between films is an order of magnitude lower than that between bulk materials. These findings help study radiative heat transfer between thin films at micro- and nano-scale.