Interaction of fast electrons with sub-10 nm silver spheres: recent results

The interaction of fast electrons with metallic nanoparticles has been of great scientific and technological interest due to the possibility to explore the optical properties of metallic nanoparticles with sub-nanometric spatial resolution and spectral resolution in the order of few meV. This combination of spatial-spectral information is possible thanks to scanning transmission electron microscopy (STEM) together with an electron energy loss spectrometer (EELS). Recently, different articles have shown EELS studies in silver nanospheres of sizes less than 10 nm, where quantum size effects are expected, reporting contradictory results compared to those obtained in the past decades by the well-known optical absorbance technique. This EELS-optics discrepancy has been the subject of debate in recent years and in this review article we will show how this problem has been clarified considering the influence of the electron beam on the particle-medium interface.