Nanoscale probing of resonant photonic modes in dielectric nanoparticles with focused electron beams

Engineering dielectric nanoparticles to select and manipulate light at specific resonance energies has great potential in fields such as solar energy conversion and optical communication. To accomplish this challenging task, it is necessary to develop tools to probe the optical resonance behavior of nanostructure locally. This work shows that focused electron beams and monochromated electron energy-loss spectroscopy provide a unique way for studying the optical resonance properties of dielectric structures with nanometer-scale spatial resolution. Resonant optical-frequency geometric modes excited by fast electrons show up as a series of pronounced peaks within the band gap of the spectra, where absorption is negligible.