Plasmon hybridization and strong near-field enhancements in opposing nanocrescent dimers with tunable resonances.

A novel dimer nanostructure architecture featuring two symmetrically arranged crescents with opposing, nanometer-sized tips in close proximity is fabricated by colloidal lithography. This structure exhibits a strong and highly localized electrical near-field in the gap region between the tips. The close proximity of the tips in the nanocrescent dimers leads to a strong coupling process which generates new hybrid plasmon modes with different optical resonances. The optical properties of both single crescents and dimeric double crescent arrangements are investigated in detail, and correlations between resonance wavelengths and geometrical parameters are established. We apply plasmon hybridization theory to explain the spectral shifts between coupled and uncoupled crescent nanostructures based on simple geometric arguments for all polarization-dependent resonances. Computer simulations support the hybridization model and were further used to examine and compare the near-field enhancement of single and opposing double crescents. For close proximities of the two opposing crescents, a strong near-field with an enhancement factor of approximately 53 was detected. Compared to the near-field enhancement of approximately 20 for single crescents, the proximity of the second crescents further increases the near-field to more than seven times the initial value.