Electron-energy-loss spectroscopy of plasmon excitations in concentric-shell fullerenes

We report evidence for surface plasmon excitations in concentric-shell fullerenes. A film of these concentric-shell fullerenes with radii around 5--7 nm was produced by carbon bombardment of a silver polycrystalline target and measured by electron-energy-loss spectroscopy (EELS) in reflection geometry. These data were analyzed with the help of a dielectric theory developed for EELS in transmission geometry. Taking into account the concentric-shell--substrate interaction, the spectral shape can be explained as a combination of contributions from σ-π* interband transitions (around 13.5 eV), from the surface radial (σ-π*) and tangential (σ-σ*) plasmons (around 14.5 eV and 16.7 eV, respectively), and from the volume plasmon (24.5 eV).