Controlling optical field enhancement of a nanoring dimer for plasmon-based applications

Control of resonance dynamics and gap plasmons of coupled nanostructures beyond commonly used parameters such as the dimer gap has a paramount importance in practical applications where a fixed feed-gap is needed. In this report, we show control of resonance peak shift and gap plasmon intensity of a closely spaced nanoring dimer through polarization and illumination angle of incident light, geometry of the constituent nanorings and refractive index of the substrate underneath. For fixed outer radii and constant dimer gap, the resonance peak of the nanodimer shows universal redshift as the inner radii of nanorings increase and polarization of the incident light approaches the dimer axis. Furthermore, we show that increasing inner dimer radii and introducing a small split gap to the nanodimer results in highly enhanced gap plasmon intensity. Finally, at optimized dimer geometry and illumination of the incident light, 682 nm RIU-1 refractive index sensitivity of the nanodimer was obtained and its implication for surface-based sensing is discussed in detail.