Enhanced energy transfer by near-field coupling of a nanostructured metamaterial with a graphene-covered plate

• Near-field radiative transfer between a metamaterial and a graphene-covered plate is studied.
• Effective medium theory with uniaxial optics is employed to model nanohole metamaterials.
• Enhancement by 2 orders is found between dissimilar materials with graphene coating.
• Extraordinary coupling of the nanostructured emitter with graphene is elucidated.
• Effects of doping level of silicon and graphene chemical potential are investigated.

Coupled surface plasmon/phonon polaritons and hyperbolic modes are known to enhance radiative transfer across nanometer vacuum gaps but usually require identical materials. It becomes crucial to achieve strong near-field energy transfer between dissimilar materials for applications like near-field thermophotovoltaic and thermal rectification. In this work, we theoretically demonstrate enhanced near-field radiative transfer between a nanostructured metamaterial emitter and a graphene-covered planar receiver. Strong near-field coupling with two orders of magnitude enhancement in the spectral heat flux is achieved at the gap distance of 20 nm. By carefully selecting the graphene chemical potential and doping levels of silicon nanohole emitter and silicon plate receiver, the total near-field radiative heat flux can reach about 500 times higher than the far-field blackbody limit between 400 K and 300 K. The physical mechanism is elucidated by the near-field surface plasmon coupling with fluctuational electrodynamics and dispersion relations. The effects of graphene chemical potential, emitter and receiver doping levels, and vacuum gap distance on the near-field coupling and radiative energy transfer are analyzed in detail.