Enhanced Near-Field Thermal Radiation Based on Multilayer Graphene-hBN Heterostructures

Graphene-covered hexagonal boron nitride (hBN) can exceed blackbody thermal radiation in near-field due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). As previous research found that the thickness of hBN in a graphene-hBN cell can be very thin while still presenting strong radiation enhancement, multilayer graphene-hBN heterostructures are proposed in this paper to further enhance the near-field thermal radiation. We found that a heterostructure consisting of five or more graphene-hBN cells performs better than all existing graphene-hBN configurations, and the infinite cell limit exhibits 1.87- and 2.94-fold larger heat flux at 10 nm separation than sandwich and monocell structures do, respectively, due to the continuously and perfectly coupled modes. The heat flux is found to be 4 orders of magnitude larger than that of the blackbody. The effective tunability of the thermal radiation of the multicell structure is also observed by adjusting the chemical potentials of graphene with an optimized thickness of 20 nm on each hBN, which is instructive for both experimental design and fabrication of thermal radiation devices.