Damping of the surface plasmon in clean and K-modified Ag thin films

The damping processes of electronic collective excitations of Ag/Ni(1 1 1) were studied by high-resolution electron energy spectroscopy. The FMHM of the Ag surface plasmon was reported as a function of Ag thickness, primary electron beam energy, Ag surface plasmon energy, and parallel momentum transfer. The broadening of the Ag surface plasmon was found to be related to 5sp-5sp transitions, for which a critical wave vector of 0.2 Å−1 exists. Moreover, we provide a direct evidence of the occurrence of chemical interface damping in thin films, upon doping the Ag/Ni(1 1 1) system with K adatoms. The enhanced plasmon broadening in K/Ag/Ni(1 1 1) was ascribed to the existence of additional electron-hole decay channels at the K/Ag interface.