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Surface Electromagnetic Fields in the "Semi-Classical Infinite Barrier" Model: Collective and Single-Particle Response

The electromagnetic field near a metal surface is calculated within the "SCIB" model, which replaces the surface by a specular reflection condition on a homogeneous system and assumes the conduction electrons to respond according to Lindhard's dielectric function. The longitudinal fields included in the model are separated into contributions from a collective plasmon mode and from non-collective particle-hole excitations producing Friedel-type oscillations. The analytical properties of Lindhard's function in the complex k-plane are exploited to prove that these contributions sum in such a manner that, in contrast to previous erroneous statements, the normal component of the total electric field is continuous and no singular surface charges occur. Numerical results are presented which show that in a large frequency regime most of the electronic response is carried by the plasmon mode. These results, which refute earlier speculations about the physical implications of the SCIB model, are compared with other model calculations of surface fields.