Accessing Plasmonic Hotspots Using Nanoparticle-on-Foil Constructs

Metal–insulator–metal (MIM) nanogaps in the canonical nanoparticle-on-mirror geometry (NPoM) provide deep-subwavelength confinement of light with mode volumes smaller than V/Vλ < 10–6. However, access to these hotspots is limited by impendence mismatch between high in-plane k∥ trapped and free-space plane-waves, making in- out-coupling difficult. Here, constructing a nanoparticle-on-foil (NPoF) system thin metal films, we show mixing insulator–metal–insulator (IMI) modes MIM gap results MIMI modes. This provides multichannel plasmonic nanocavity through incident from both sides film. The red-tuning near-field strength for thinner foils measured experimentally white-light scattering surface-enhanced Raman individual NPoFs. We discuss further utility NPoF systems, since allows tightly confined be accessed simply different ports.