Broadband and Omni-directional Enhancement of Emissivity Enabled by Thermal Excitation of Mie Resonances

Abstract

Enhancing the emissivity of materials in a broadband and omni-directional manner is crucial for thermal management applications. The emissivity of dielectric media is commonly enhanced by utilizing thermal excitation of surface phonon polaritons (SPhPs) and localized surface phonons (LSPhs) supported by these materials. The SPhPs and LSPhs resonantly enhance emissivity at selective wavelengths inside the Reststrahlen band of the material, which usually spans a limited spectral range and can be distant from the wavelength of the peak thermal radiation. Dielectric media can also support Mie resonances, which are not limited to a spectral range and thus can potentially be used for broadband enhancement of emissivity. In this study, we analyze thermal excitation of Mie resonances in individual and arrays of microcuboids of 6H-SiC. Based on this analysis, we design a periodic array of microcuboids for broadband and omni-directional emissivity enhancement. The designed array increases thermal radiation from a flat, unpatterned 6H-SiC substrate at the normal direction from 67 to 91% of a blackbody while demonstrating enhanced emissivity in a wide angular range. The designed array is fabricated using e-beam lithography and reactive ion etching, and the broadband and omni-directional enhancement of emissivity by capitalizing on Mie resonances is experimentally demonstrated. This study shows the potential of Mie resonances for thermal management applications and provides a guide for the design of efficient thermal emitters.