Understanding of electronic excitations of C₆₀ on graphite

Electron energy loss spectroscopy has been used to probe the coverage-dependent electronic excitations from a C-60 covered graphite surface. In the energy region corresponding to the optical band-gap of the bulk C-60 solid, the dipole-scattering contribution to the loss features is simulated by a double dielectric layer model. We find that a good agreement between the simulated spectra and the experimental results can be achieved for a C-60 multilayer. However, an additional energy loss channel is required in order to describe the electronic excitations for a C-60 monolayer. The possible significances of this finding are discussed.