Extreme Sub-Wavelength Light Confinement in Plasmonic Film-Coupled Nanostar Resonators

TL;DR

This paper demonstrates that gold nanostars coupled with a gold film can confine light in sub-10 nm volumes, revealing complex resonant behaviors and polarization effects, with potential applications in sensing and light-matter interaction enhancement.

Contribution

It introduces a novel plasmonic nanostar-film system that achieves extreme subwavelength light confinement and analyzes its spectral and polarization properties through experiments and simulations.

Findings

Strong light confinement in sub-10 nm volumes at nanostar tips.

Resonant spectra vary with nanostar symmetry and orientation.

Resonant peaks are highly polarized under white light.

Abstract

Confining light in extreme subwavelength scales is a tantalizing task. In this work, we report a study of individual plasmonic film-coupled nanostar resonators where plasmonic optical modes are trapped in ultrasmall volumes. Individual gold nanostars, separated from a flat gold film by a thin dielectric spacer layer, exhibit a strong light confinement within the sub-10 nm volume of the nanostar's tips and the film. Through dark field scattering measurements of many individual nanostars, a statistical observation of the scattered spectra is obtained and compared with extensive simulation data to reveal the origins of the resonant peaks. We observe that an individual nanostar on a flat gold film can result in a resonant spectrum with single, double or multiple peaks. Further, these resonant peaks are strongly polarized under white light illumination. Our simulation data revealed that the resonant spectrum of an individual film-coupled nanostar resonator is related to the symmetry of the nanostar, as well as the orientation of the nanostar relative to its placement on the gold substrate. Our results demonstrate a simple method to create an ultrasmall mode volume plasmonic platform which could be useful for applications in sensing or enhanced light-matter interactions.