  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. While 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 been
yet rigorously established. Here, we provide such a study. We design sets of
plasmonic antennas that allow to isolate the role of the local curvature from
other effects influencing the field. The near electric field is inspected by
electron energy loss spectroscopy and electrodynamic simulations. We
demonstrate the existence of the plasmonic lightning-rod effect and establish
its quantitative description, showing that its strength is comparable to the
electrostatic lightning-rod effect. We also provide a simple phenomenological
formula for the spatial dependence of the field. Finally, we introduce the
effective radius of curvature related to the spatial distribution of induced
charge in plasmonic antennas, significantly smaller than their geometrical
radius.
