Plasmon confinement in ultrathin continuous Ag films

We investigate the effect of film thickness and granularity on the collecti ve excitation of nanostructured ultrathin Ag films deposited on Si(111)7 x 7 by energy loss spectroscopy and low energy electron diffraction to obtain structural and spectroscopic information. For continuous thin films we fin d that the plasmon frequency at a vanishing wave vector scales with the sur face-to-volume ratio of the grains, i.e., as the Mie resonance of separated clusters, instead of with inverse thickness. This indicates a confinement of the plasmon into single domains, in spite of metallic conductivity.