Fig. 1. Electron-near-field interaction.

BEM calculation of swift electron excitation of a conical Au nanotip attached to a spherical core (tip length 30 nm, cone aperture angle 22° tip apex radius-of-curvature 2.5 nm, core diameter 50 nm). At an incident energy of 20 keV, the electron passes 3 nm away from the tip apex along the dashed line perpendicular to the symmetry axis of the tip (z direction). a Frozen-time snapshot at a minimum electron-apex distance (t = 0) of the z component of the electric field induced upon excitation of the tip resonance at $ħ{\omega }_0=$1.73 eV. b Dashed-gray curve: field profile along the electron trajectory in a, with z = 0 corresponding to the tip symmetry axis. Solid-blue curve: time evolution of the field as effectively experienced by the electron. c Time evolution of the optical phase of the induced field oscillating at the plasmon resonance frequency ${\omega }_0$