Electron- and photon-induced plasmonic excitations in two-dimensional silver nanostructures

Plasmons are the quasi particles of collective oscillations of electrons and form the basis of plasmonics and optical metamaterials. We combined electron spectroscopy and optical spectroscopy techniques to study plasmons in atomically smooth Ag films and in epitaxial Ag nanodisks to map the momentum-energy dispersion curves of the two-dimensional (2D) sheet plasmon and the quasi-2D plasmons to clarify the essential differences between them. Our experimental results combined with the results of numerical electromagnetic simulations showed that the bulk-like nature of the silver plasmon starts in layers that are only two atoms thick.