Spatially resolved electron energy-loss spectroscopy of the surface excitations on the insulating fine particle of aluminum oxide

Spatially resolved electron energy-loss spectra were measured from aluminum oxide fine particles of 10 and 55 nm radius. The impact parameter dependence of the surface plasmon generated between the surface of the particle and vacuum were revealed. The spectra due to the surface plasmon excitation of the fine particle of 10 nm radius are well explained by the local dielectric theory but those of 55 nm radius are not. This difference can be attributed to the relativistic effect applied for large size fine particles, which has been predicted by [Abajo: Phys. Rev. B 59 (1999) 3095].