Broadband Raman scattering enhancement with reduced heat generation in a dielectric-metal hybrid nanocavity

Abstract

The strongly localized electric field achieved in metallic nanoparticles (NPs) and nanostructures are commonly employed to realize surface-enhanced Raman scattering. However, the heat originating from the Ohmic loss of metals may lead to the damage of the analyzed molecules, which severely limits the practical applications of pure-metallic nanostructures. Here, we propose a dielectric-metallic hybrid nanocavity placing silicon (Si) NPs onto a gold (Au) film to realize broadband Raman scattering enhancement with significantly reduced heat generation. Our results reveal that the heat generation is dramatically reduced in the hybrid nanocavity as compared with its pure-metallic counterpart while a significantly enhanced electric field is maintained. We demonstrate numerically and experimentally that the optical resonances, which arise from the coherent coupling of the electric and magnetic dipoles excited inside the Si NP with their mirror images arisen from the Au film, can be employed to enhance the excitation and radiation of Raman signals, respectively. We find that the enhancement in the radiation of Raman signals plays a crucial role in enhancing the total Raman scattering. We also show that the hybrid nanocavity acts as a nano-antenna which effectively radiates Raman signals into the far-field. These findings indicate the advantages of such hybrid nanocavities in temperature-sensitive Raman scattering characterization and supply new strategies for designing nanoscale photonic devices of other functionalities with hybrid nanocavities.