Surface-plasmon excitation on oxide-covered spherical particles

We have investigated the inelastic scattering of fast electrons (50–100 keV) by oxide-covered spherical metallic particles, considering losses due to the excitation of bulk and surface plasmons. Whereas the electrons may be treated classically, the plasmons are described by a second-quantization formalism. After the establishment of the electron-plasmon interaction Hamiltonian, we derive the loss probability as a function of the electron impact parameter D. Numerical results are given for oxidized Al particles with inner radii a=105 and 255 Å covered by a 45-Å-thick ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ layer described by a static dielectric function ${\epsilon }_0$=3.73. As compared to oxide-free Al particles, the addition of an oxide layer not only produces a shift of the surface-plasmon frequencies, but also leads to a significant modification of the loss probability. Discussion of our results is made in comparison with experimental results of Batson and Treacy.