Localized surface plasmon based on coupled metallic nanoaggregates has been extensively studied in enhancing light scattering and optical force, which depends on the geometry/symmetry of plasmonic oligomers and the refractive index of surrounding medium. As the interparticle gap distance between nanoparticles becomes smaller than several nanometers, quantum effects can change the plasmon coupling in classical predictions. However, most of the research on plasmonic scattering and optical force has been done based on local calculations even for the gap below ~3 nm, in which the nonlocal screening plays a vital role. Here, we theoretically investigate the nonlocal effect on the evolution of plasmon resonance modes in strongly coupled nanoparticle dimer antennas with the gap down to 1 nm. Then, the refractive index sensing and optical force in this nonlocal system is evaluated and compared with the results in classical calculations. We find that in the nonlocal regime, both refractive index sensibility factor and optical force are actually smaller than their classical counterparts mainly due to the saturation of both plasmon-shifts and near-field enhancement. These results would be beneficial for the understanding of interaction between light and nonlocal plasmonic nanostructures and the development of plasmonic devices such as nanoantennas, nanosensors, and photonic manipulation.
Recently, plasmonic quantum effects have become appreciated for its significant influence on surface plasmons coupling
as the gapwidths down to sub-nanometer scale. In this paper, we assemble gold dimer structures with the gapwidths
ranging from tens of to sub-nanometer scale by capillary force during solvent evaporation. It is found that surface
plasmons coupling has translated from classical to quantum regime as the gapwidths down to sub-nanometer range.
Emitting-polarization resolved scattering on these gold dimers is also performed. Different from the incident-polarization
dependence, these emitting-polarization spectra can unveil the intrinsic antenna interactions between unpolarized
illumination and surface plasmons modes. Furthermore, the polarization-resolved scattering spectra show that the
quantum effects can influence the polarizability of antenna emission. These findings would be beneficial for the
development of quantum plasmonic antenna and sensor designs, etc.