Unified Model for Plasmon Coupling in Metal Nanoparticles and Effect of the Polymer Shell

Abstract

Plasmon resonance and its coupling in metal nanoparticles enable the modulation of the resonance spectrum with particle size, shape, and near/far-field interactions. The plasmon coupling of the resonance spectrum is blue-shifted when the nanoparticles are separated by a distance in the range of lattice spacings but is red-shifted for larger separations (much more greater than the lattice spacing). The spectral behavior in these two regimes is driven by charge transfer and plasmon hybridization and has not been explained simultaneously for an assembly of nanoparticles with existing models. Herein, we developed a model by considering a virtual nanobridge for lattice parameter spacing to account for the charge transfer between nanoparticles in the dimer, trimer, tetramer, and pentamer assemblies, while for larger separations, the coupling adheres to hybridization. The interparticle separation-dependent spectral shift in both regimes was established well with the proposed unified plasmon coupling model, which is consistent with previous experiments and theories and is applicable to assemblies of any number of nanoparticles. We also showed the effect of the polymer shell on monomer/dimer plasmons and examined the polarization-dependent plasmon coupling in multinanoparticle assemblies, providing insight on tunable plasmon enhancement toward advanced quantum devices.