Tunneling field emission from nano-optics under electron irradiation.

While field emission, which is crucial for sub-angstrom resolution imaging and nanofabrication, has been extensively investigated in high-voltage and laser-driven systems, its realization through plasmonics under electron irradiation remains unexplored. Here, we demonstrate a proof of concept for electron beam-driven field emission from plasmonic emitter arrays with nanoscale hotspots acting as highly efficient emission sites, which also exhibit strong surface-enhanced Raman scattering activity. The electron beam-induced field distributions and electrical polarization switching are visualized by four-dimensional scanning transmission electron microscopy. Classical and quantum-corrected electromagnetic simulations combined with experimental field maps identify the highest field intensities at the apex of emitter tips. Optical excitation experiments confirm the giant field enhancement at these locations. In situ electrical measurements in a transmission electron microscope reveal a distinct tunneling field emission signature that surpasses secondary electron emission. The demonstrated field emission mechanism opens unexplored possibilities for realizing spatially confined electron sources with ultrafast temporal switching capabilities.