Identification of plasmons on small metallic particles

The surface and bulk plasmons on potassium spheres are studied on the basis of the hydrodynamic dispersive model of electron gas. This model gives a finite number of surface plasmons on a sphere, this number being a function of the sphere size, the electron number density, and the host-matrix dielectric constant. A potassium sphere of 20-Å radius supports precisely ten surface plasmons. The calculated dispersion of surface plasmons and the inelastic-scattering cross section are in good agreement with recent electron-energy-loss-spectroscopy results of vom Felde, Fink, and Ekardt.