Plasmonic Modes Confined in Nanoscale Thin Silver Films Deposited onto Metallic Substrates

Collective electronic excitations in nanoscale thin Ag layers adsorbed on Cu(1 1 1) and Ni(1 1 1) at room temperature have been investigated by high-resolution electron energy loss spectroscopy. Surface plasmon was found to be confined within grains on Ag thin films on Cu(1 1 1) nanostructured in islands. Annealing removed surface plasmon confinement and induced a negative linear term of the dispersion relation. On the other hand, on flat thin films on Ni(1 1 1) the dispersion of Ag surface plasmon is fully quadratic. Landau damping processes of the plasmonic excitation were found to be dependent on the growth mode. Ag multipole surface plasmon at 7.7 eV was observed only under stringent kinematic conditions enhancing surface sensitivity.