Dispersion and damping of surface plasmon in Ag thin films grown on Cu(111) and Ni(111)

We present high-resolution energy loss spectroscopy measurements on the dispersion and damping of collective electronic excitations in ultrathin Ag films grown on Cu(111) and Ni(111). For Ag/Cu(111) the surface plasmon was found to be confined within grains but confinement was removed by annealing. On the other hand, a purely quadratic dispersion was observed for the layer-by-layer Ag film deposited onto the Ni(111) surface.