Enhancement of near-field thermal radiation between composite materials with gradient plasmonic nanoparticles.

Near-field radiative heat transfer (NFRHT) with composite materials is of significant technological interest for practical applications. In this study, we investigate the NFRHT occurring between two composite materials composed of gradient plasmonic nanoparticles (GPNs). We delve into the physical mechanism underlying NFRHT, highlighting the strong coupling and enhancement effect from surface plasmon polaritons (SPPs) at the composite/air interface or the localized SPPs (LSPPs) on the surface of nanoparticles. Furthermore, leveraging the red-shift effect caused by the gradient profile, the intensity of NFRHT can be controlled by adjusting the gradient function and volume fraction of GPNs. Notably, we observe the enhancement of NFRHT from composite materials to bulk materials, with the enhancement ratio exhibiting a notable increase at large spacing. This research establishes a theoretical foundation for the development of near-field thermal devices utilizing composite materials containing GPNs.