SURFACE IMPACT-INDUCED SHATTERING OF C-60 - DETECTION OF SMALL C-M FRAGMENTS BY NEGATIVE SURFACE-IONIZATION

The efficient formation of small C-m(-) cluster anions (m = 2-28) is d etected when mass selected C-60(+) cations collide with room temperatu re graphite, passivated silicon or tantalum surfaces at kinetic energi es ranging from 300 to 1800 eV. Experimental evidence indicates that t hese anions are generated by negative surface ionization of small C-m fragments resulting from prompt impact induced fragmentation of the in cident C-60(+) at the surface (shattering). This high energy process a ppears to be distinct from the slower metastable decay of surface scat tered C-60(+) which leads to even numbered fullerene fragment distribu tions C-58(+), C-56(+) ..., observed at impact energies below 300 eV. A bond percolation model for C-60 combined with an exponential depende nce of the electron attachment efficiency on the electron affinity of the neutral C-m fragments qualitatively reproduces the observed C-m(-) fragment distributions for the shattering process.