A Simulation Study for Field Enhancement due to Multiresonant Localized Surface Plasmon Excitation in the truncated Octahedral Gold Nanoparticle Arrays

We theoretically demonstrates large field enhancement at the close-packed, truncated octahedral gold nanoparticle array by using a finite difference time domain method. A multiple peak at the visible and near infrared frequency implies the multiple resonance in the nanostructures, corresponding to the dipolar and quadrupolar mode excitation of electric field at the single octahedral particles. The splitting of two adjacent resonant peak as a function of the distance of the particles implies the existence of the significant coupling between the resonant modes of the individual nanoparticles. The electric field profile at the gap between the particles shows the field enhancement due to such mode couplings, where dipolar and quadrupolar mode are simultaneously involved. Such evolution of mode coupling with increasing gap distance confirms the resonant modes excitation and their coupling is the origin of the strong field enhancement. Simulation with different polarization of the incident light denotes the dominant coupling mode is governed by the size of the interaction area. Importantly, electric field at the gap is hugely enhanced up to 17 at the optimal gap distance of 4 nm.