Electron emission from a clean gold surface bombarded by slow multiply charged fullerenes

Total electron emission yields have been measured for impact of carbon cluster ions C(i)(q+) on atomically clean polycrystalline gold as a function of projectile size (i less than or equal to 60), charge (q less than or equal to 5) and kinetic energy (E less than or equal to 165 keV). Electron emission arises already far below the classical threshold for common kinetic emission, probably because of quasi-molecular autoionization in close collisions of projectile constituents with individual target particles at the surface. At a given impact energy, there is a linear dependence of electron yield on carbon cluster size. However, there is no influence of the projectile charge and, thus, apparently no potential electron emission, in striking contrast to the impact of slow multi-charged atomic ions on solid surfaces. We accredit this suppression of potential emission to a rapid transfer of the fullerene electronic excitation being gained during surface neutralization into projectile vibrational degrees of freedom and subsequent fast fragmentation. Molecular dynamics calculations show that this fragmentation takes place within picoseconds after surface impact, which is much faster than the established rates for thermionic electron emission from collisionally heated fullerenes. (C) 1998 Elsevier Science B.V.