Super-planckian thermal radiation in borophene sheets

Abstract Recently, borophene, a pioneering two-dimensional metal, has been attracting broad interest due to the in-plane anisotropic polaritons and large electrical tunability. Its attractive electronic and optical properties imply that borophene can find novel applications in electronics, thermionics, and photonics. Here, we study the near-field thermal radiation (NFTR) of monolayer borophene sheets; the results show that the NFTR of monolayer borophene is three-orders of magnitude larger than the black-body limit, even significantly exceeding the NFTR from traditional metals and metallic oxides with metallic behavior. An analysis of the photon tunneling coefficient and plasmon dispersion indicates that the coupling of quasi-elliptic surface plasmon polaritons (SPPs) of the borophene system extends robustly to the near- and mid-infrared frequencies, producing a broadband near-field emission from borophene. We also analyze the possibility of using the electrochemical method (that is, tuning the electron density) to modulate the NFTR between borophene sheets. The results reveal since the suppression on the wave-vector range and the anisotropy of SPPs by electron density, the switching coefficient of such electrochemical method can exceed up to 95%. Finally, the modulate effect of the mechanical decoupling on the NFTR is explored. We clarify the influence of decoupling effect at different frequencies on the mechanical thermal modulation of borophene. All in all, we explore the NFTR of the 2D borophene thoroughly for the first time, opening potential possibility for novel borophene-dependent thermal devices and thermal management.