Plasmon Coupling in Silver Nanosphere Pairs

In this work we study the optical properties of silver metal nanosphere pairs by means of rigorous electrodynamics calculations based on the generalized multiparticle Mie theory. By correlating the dipole longitudinal plasmon wavelength with its corresponding value of the real part of the dielectric constant, and based on the dipole quasi-electrostatic approximation, we were able to derive a new plasmon ruler equation for the longitudinal dipole plasmon resonance of Ag dimers, suitable for a wide range of interparticle distances and radii. The new resonance condition equation, at variance with previous work on noble metal nanoparticle pairs, takes into account empirically retardation effects and multipole interactions, being a novel, accurate, and potentially useful tool for future applications in plasmonic nanometrology or sensor devices.