SURFACE EFFECTS ON BULK PLASMONS

We discuss the effects of surfaces on bulk plasma oscillations in a me tallic film of thickness L. The leading corrections to the plasma freq uencies due to the surfaces are proportional to L-1. The frequencies o f low-lying long-wavelength modes are given by the dispersion relation of bulk modes, omega = omega(p)[1 + alpha(q2/k(F)2)], where the allow ed q values are q(n) = (npi/LBAR), LBAR = L - 2d(b), and d(b) is a com plex length characteristic of the surface (reminiscent of, but differe nt from, Feibelman's d(perpendicular-to)). An explicit expression for d(b) is derived. Resonant excitation by an external field E0e(-iwt) is calculated.