Finite-Difference Time-Domain Modeling of the Optical Properties of Nanoparticles near Dielectric Substrates

We show how the finite-difference time-domain method can be used to model the plasmonic interactions between nanoparticles and adjacent dielectric substrates. The image screening introduced by the dielectric substrate can result in significant polarization dependent red-shifts and hybridization of the nanoparticle plasmon resonances. For small nanoparticle-substrate separations and substrates with large dielectric permittivities, the hybridized quadrupolar nanoparticle plasmon resonances also appear in the scattering spectrum. Different numerical approaches for calculating the scattering spectrum in typical dark-field scattering geometries are discussed, and it is shown that the scattering spectra can be calculated using finite substrate slab models.