Broad range electric field enhancement of a plasmonic nanosphere heterodimer

Abstract

Interaction between metallic nanoparticles has been widely investigated due to the rise of the enhanced local electric field inside the gap. We numerically present the broadband near- and far-field spectra from the near-ultraviolet (UV) through the visible wavelength range using plasmonic heterodimers. Both near- and far-field resonances can be manipulated by the composition of heterodimers. They show strong dependencies on gap width and particle size. Compared with Al-Au and Al-Ag heterodimers, the dipole-mode resonant peak has a redshift for the Au-Ag heterodimer. In the near-UV range, the Al-Ag heterodimer gains the strongest optical enhancement. This is due to the robust optical resonance of Al and Ag particles in the near-UV range. On the other hand, the heterodimers with Au particles exhibit a better field enhancement at longer wavelengths. The physical origin of plasmonic resonances of the bonding dipole modes and higher-order modes are revealed by the simulated mappings of local electric fields and 3D surface charge distributions. Moreover, our simulations also reveal the suitability of the plasmon ruler equation and the power law enhancement equation to quantify the optical response of heterodimers.