Local-field confinement in three-pair arrays of metallic nanocylinders

Confinement of light in nano-scale region of three silver nanocylinder pairs is studied by finite-difference time-domain simulations. Light is confined in gaps between nanocylinders due to localized plasmon excitation and the strongest local-field enhancement exhibits in the gap of the second pair. The surface plasmon resonance has red-shift for nanocylinders of larger radius. The resonance wavelength and local-field enhancement are nearly proportional to the radius of nanocylinders in visible light region, i.e., the plasmon resonance of nanocylinder pairs is predictable and controllable. An open cavity model is proposed to understand the linear relation between the resonant wavelength and the radius of nanocylinders.