Dispersion control in plasmonic open nanocavities.

We experimentally demonstrate the dependence of plasmonic resonant properties on cavity height in open circular cylinder nanocavities as a result of a strong three-dimensional confinement of the electromagnetic field, which shows a new way to tailor the dispersion of surface plasmon polaritons in cavities. The azimuthal and the axial symmetric plasmonic mode patterns are directly observed at resonant wavelengths using cathodoluminescence spectroscopy. Plasmonic modes and optical vertical cavity modes can be simultaneously excited and can coexist in a nanocavity with sufficient height. The highest quality factor, which is up to 73, is obtained in a 500 nm high cavity. The smallest mode volume is only 0.031 λ(SPP)(3), and the corresponding Purcell factor is 71. Open nanocavities provide space for the interaction between an optical emitter and a confined electromagnetic field. Many applications can be expected, such as plasmonic light-emitting devices and nanolasers.