Electron emission for impact of slow fullerene ions on clean gold

Abstract

Electron emission for impact of singly and multiply charged fullerene ions Cnq+ (15 ⩽ n ⩽ 60; 1 ⩽ q ⩽ 5) on atomically clean polycrystalline gold has been studied at impact energies far from below threshold up to 250 eV/amu by measuring the number statistics of emitted electrons, from which accurate absolute total electron yields have been determined. In contrast to impact of atomic ions the fullerene charge q apparently has no influence on the total electron yield, i.e. no potential emission takes place. There is also no clear threshold for the electron emission which becomes measurable already around 10 eV/amu, above which it rises faster than linear with the ion impact velocity. Isotachic Cnq+ ions cause electron yields in direct proportion to their size n, with 250 eV/amu C60q+ producing on average more than 25 electrons. These results are tentatively explained by assuming that either the fullerene ions are completey shattered at the gold surface and individual carbon atoms produce kinetic emission, or electrons originate from thermionic emission of projectiles and their fragments heated up in the surface collision.