F. Moresco et al., EVIDENCE FOR THE PRESENCE OF THE MULTIPOLE PLASMON MODE ON AG SURFACES, Physical review. B, Condensed matter, 54(20), 1996, pp. 14333-14336
Collective surface electronic excitations on Ag(111) and Ag(110) have
been studied by energy-loss-spectroscopy LEED. The data allow separati
on of the contribution to the loss intensity due to monopole and to mu
ltipole surface plasmons, thus demonstrating the existence of the latt
er mode also on noble-metal surfaces. Multipole plasmons are therefore
a general property of the optical response of metal surfaces whenever
the charge-density profile at the interface is not too abrupt.