Low‐Loss Hybrid High‐Index Dielectric Particles on a Mirror for Extreme Light Confinement

Abstract The quest for enhancing light–matter interactions at the nanoscale has led scientists to nanophotonic systems that support the smallest possible modes, which are currently realized via particle‐on‐mirror (PoM) geometries using plasmonic particles. The drawback of metallic PoM systems is the large absorption/scattering ratio due to the significant Ohmic losses inherent to plasmonics. Here, an alternative dielectric PoM composed of a high‐index dielectric nanodisk on top of a metallic mirror is realized. Custom‐shaped high‐quality dielectric colloidal nanoparticles are fabricated and dispersed on a mirror to fully unlock the potential of PoM systems. This hybrid device combines the large field enhancement and extreme localization of plasmonic systems with the low absorption of dielectric nanoresonators. By means of far‐field scattering and near‐field cathodoluminescence spectroscopy, the nature of the modes supported by the hybrid PoM are revealed. Utilizing enhanced spectroscopies, such as Raman and fluorescence, these hybrid‐PoM systems are used in proof‐of‐principle applications. A comparison with Au antennas indicates that the hybrid PoM system presents efficiencies and optical characteristics comparable or superior to those of more conventional purely plasmonic systems, opening new avenues for low‐loss light control at the deep nanoscale level.