Angle-resolved electron-energy-loss spectroscopy of two-dimensional plasmons

Angle-resolved electron-energy-loss spectroscopy from solid-state surfaces is studied both theoretically and experimentally, with particular emphasis on the ZnO surface. The plasmonlike loss peak is found to shift as a function of detector angle. This is due to the highly dispersive nature of the plasmon mode. There is also evidence for a phononlike model which remains unshifted as a function of detector angle. The role of both collective and single-particle excitations are considered, and the theory is found to be in good agreement with the experiment.