Annular nanoplasmonic void arrays as tunable surface enhanced Raman spectroscopy substrates

We report the use of annular nano-voids in a metallic thin-film as programmable molecular sensors for surface-enhanced Raman spectroscopy (SERS). To date, research into these structures has focused on the exploration of their extraordinary optical transmission attributes. We now show that by using advanced lithography and simulation tools, we can generate a porous SERS material for molecular interrogation. Using ultra-thin annular structures, rather than simple circular holes, allows us to reduce both the volume and cross-sectional area of the void, maximizing the electric-field confinement, while, importantly for SERS, producing resonant conditions in the visible region of the spectrum. By comparing our annular films with conventional circular films with the same resonant frequency, we show a significant improvement in the efficiency of Raman scatter, creating stronger signals that also contain more spectral information