SCATTERING OF ELECTRONS ON METAL-CLUSTERS AND FULLERENES

It is shown that the main contribution to the elastic cross section of fast electrons on metal clusters and fullerenes results from scatteri ng on the frozen cluster potential, which is determined by the electro n density distribution of the ground state of the target cluster. The specific shape of the electron distribution in fullerenes and metal cl usters manifests itself in the diffraction behaviour of the elastic di fferential cross section. The analysis of the total elastic cross sect ion dependence upon projectile velocity, the number of atoms in the cl uster and its size is provided. The cross section of elastic scatterin g on a cluster surpasses the sum of the individual scattering cross se ctions on the equivalent number of isolated atoms. This occurs because of the coherent interaction of the projectile electron with electrons delocalized in the cluster volume. We have demonstrated that collecti ve electron excitations sensitive to the many-electron correlations do minate inelastic scattering. The surface plasmon resonances can be obs erved in the differential cross section for inelastic scattering. We f ound a condition for the quadrupole and higher multipole plasmon excit ations to contribute relatively little to the electron energy loss spe ctrum. The results obtained have been compared with experimental data for the electron-fullerene C-60 collision. Reasonable agreement betwee n theoretical and experimental results is reported. We have also demon strated that plasmon excitations provide the main contribution to the total inelastic cross section over a wide energy range. We have calcul ated the dependence of the total inelastic;cross section on collision energy and compared the result obtained with the experimental data ava ilable, giving an interpretation for the plateau region in the cross s ection as caused by plasmon excitations rather than the cluster fragme ntation process. We have shown that the single-particle jellium approx imation fails to describe this experiment. Our analysis is performed f or metal clusters and fullerenes, However, it can also be applied to o ther polarizable systems, possessing plasmon or giant collective reson ances.