Retardation effects in the interaction of charged particle beams with bounded condensed media

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Abstract
The interaction of a relativistic electron beam, travelling parallel to the surface of a semi-infinite medium, is analysed. The specific energy loss of the beam and the probability of excitation of surface and bulk modes in the medium are calculated. Beams both external and internal with the medium are considered, and the predictions are compared with well known non-retarded limits. A detailed analysis of the expressions derived is provided for electron beams interacting with specific dielectric materials. The effects of retardation are seen to be large, particularly for beam energy losses in regions where the real part of the dielectric constant is large. The retarded excitation probability is typically about 10-30% larger than the non-retarded result, for electron energies greater than about 100 keV. The image force is calculated for an external beam, and the radiative de-excitation of the medium is also analysed.