Plasmonic Lightning-Rod Effect

The plasmonic lightning-rod effect refers to the formation of a strong electric near field of localized surface plasmons at the sharp features of plasmonic antennas. Although this effect is intuitively utilized in the design and optimization of plasmonic antennas, the relation between the magnitude of the electric field and the local curvature of the plasmonic antenna has not yet been rigorously established. Here, we provide such a study. We design sets of plasmonic antennas that allow us to isolate the role of the local curvature from other effects influencing the field. The electric near field is inspected by electron energy-loss spectroscopy and electrodynamic simulations. We confirm the existence of the plasmonic lightning-rod effect, demonstrate its decoupling from concurrent effects influencing the field, and establish its quantitative description, showing that its strength can be interpreted as comparable to that of the electrostatic lightning-rod effect. We also provide a simple empirical formula for the spatial dependence of the field, which includes the effective radius of curvature significantly smaller than the geometrical radius.