Atomistic Characterization of Confined Bulk and Bennett Plasmons in Metallic Nanoparticles as Probed by Penetrating Electrons.

Despite the experimental observation of confined bulk plasmons (CBPs) in metallic nanostructures using electron energy-loss spectroscopy (EELS), there is still a limited theoretical understanding of their resonance structure when they are excited by penetrating electron beams. In this work, we use atomistic time-dependent density functional theory (TDDFT) to perform a first-principles study of the excitation of CBPs induced by swift electrons. Our quantum approach offers a parameter-free framework for the calculation of the EEL spectra of metallic nanoparticles with atomistic resolution, while jellium TDDFT and classical hydrodynamic calculations allow us to unravel the rich spectral pattern associated with CBPs. Additionally, the excitation of high-energy surface resonances characterized by an induced dipole moment across the nanoparticle surface, known as Bennett modes, is also explored. This study represents a significant step forward in the exploration of plasmonic signatures in the EELS of metallic nanoparticles.