Highly tunable optical response in dielectric-embedded plasmonic nanocavities

Developing approaches for precise engineering of the optical response of plasmonic nanocavities at the post-fabrication stage is important for achieving enhanced and tunable light-matter interactions. In this work, we demonstrate selective enhancement/suppression of specific plasmonic modes by embedding nanocube-on-mirror plasmonic nanocavities into a poly(methyl methacrylate) (PMMA) layer with a controllable thickness. With the increase of the PMMA thickness from 0 to approximately 100 nm, the dominating out-of-plane plasmonic modes are significantly suppressed in the scattering spectra, while the in-plane plasmonic modes are greatly enhanced with a factor reaching 102±20. This enhancement is related to the variation of momentum matching between the plasmonic modes and the radiative fields, affecting both mode excitation and emission properties. In addition, the spectral positions of the in-plane and out-of-plane plasmonic modes shift up to 52±5 and 81±2 nm, respectively. These properties are important for matching and enhancing plasmonic and molecular resonances in a variety of applications.