The dispersion of plasmons at the surface of a metal and at the interface between two metals is derived by a proper combination of electrodynamics with the hydrodynamic approximation. With a two-step model we discuss the effect of a transition region at the surface of a metal and we so explain recent measurements by Krane and Raether for aluminum.

• Received 22 June 1977

DOI:https://doi.org/10.1103/PhysRevB.17.1489