Figure 2.

Left: an example of angle-resolved electron energy loss spectra of the clean Ag(001) surface. The incident electron energy is 10.5 eV. The energy of the surface plasmon is minimum at zero momentum and disperses to higher values as momentum q increases. (Reproduced from [36]) Right: comparison of surface-plasmon dispersion curves for the clean Ag(111) and chlorine-adsorbed Ag (111) surfaces obtained at low (<20 eV; open symbols) and high (>75 eV; shaded symbols) impact energies. Error bars are indicated for representative q vectors. (Reproduced from [38].)