Plasmonically Enhanced Thermal Radiation by Means of Surface Phonon Polaritons

Radiative heat transfer at the nanoscale has the potential to produce thermal emission with both spectral feature and intensity different from the bulk materials. Specifically, the idea of coupling the energy states of photons and phonons using surface phonon polaritons (SPhPs) blurs the boundary between light and heat, opening a path to the manipulation of heat transfer through photonic engineering and breaking the classical limit established by Planck's law. SPhPs can generate a strong energy confinement effect near the surface; however, this effect is only valid within a narrow spectral regime, the so-called reststrahlen band. In this study, we employ a hybrid structure to broaden the effective energy regime for thermal emission by coupling SPhPs and surface plasmon polaritons (SPPs). We report remarkably enhanced thermal emission of a hybrid structure made of a SiO2 nanoribbon decorated with Au nanoparticles by a factor of 4 over that of a bare SiO2 nanoribbon. We introduce an experimental technique to quantify the emissivity from the complex nanostructured surface using frequency-dependent heat-transfer measurement. Not only does it enable us to detect feeble emission from a single nanoemitter, but it also differentiates two distinct heat conducting processes of conduction and radiation, simultaneously. Our work may offer insights to engineer far-field thermal emission using hybrid structures combining the surface plasma and phonon polaritons.