Plasmonic particle-on-film nanocavities: a versatile platform for plasmon-enhanced spectroscopy and photochemistry

Metallic nanostructures with nanometer gaps support hybrid plasmonic modes with an extremely small mode volume and strong local field intensity, which constitutes an attractive plasmonic platform for exploring novel light-matter interaction phenomena at the nanoscale. Particularly, the plasmonic nanocavity formed by a metal nanoparticle closely separated from a thin metal film has received intensive attention in the nanophotonics community, largely attributed to its ease of fabrication, tunable optical properties over a wide spectral range, and the ultrastrong confinement of light at the small gap region scaled down to sub-nanometer. In this article, we review the recent exciting progress in exploring the plasmonic properties of such metal particle-on-film nanocavities (MPoFNs), as well as their fascinating applications in the area of plasmon-enhanced imaging and spectroscopies. We focus our discussion on the experimental fabrication and optical characterization of MPoFNs and the theoretical interpretation of their hybridized plasmon modes, with particular interest on the nanocavity-enhanced photoluminescence and Raman spectroscopies, as well as photocatalysis and molecular nanochemistry.