Recent experimental data on electron-energy-loss spectrometry of the interaction between small crystallites and beams traveling at a fixed beam-solid surface distance are analyzed in terms of the surface and bulk excitation modes of parabolically shaped wedges. The probability of excitation of the surface modes is calculated, in the nonretarded limit, for an electron traveling parallel to the wedge surface, either outside or inside the dielectric wedge. The main features of available experimental data for MgO crystallites can be explained by the theory.

• Received 23 May 1984

DOI:https://doi.org/10.1103/PhysRevB.31.121