Sputtering of C-60 fullerenes physisorbed on Ar, Xe, H2O, O-2, and C8F18 matrix films studied with time-of-flight secondary ion mass spectrometry

摘要

The ionization and fragmentation of C-60 fullerenes were investigated using matrix films covered with C-60 molecules and bombarded with 1.5-KeV He+ ions. C+, C-60(+), and C-60(++) ions were sputtered from the C-60 molecules that were physisorbed on Ar and Xe matrix films, whereas the sputtering of C-60 on the O-2 and C8F18 matrix films induced an additional emission of ion adducts, such as (OC60)(+) and (FC60)(+), as well as the fragment ions, C-(60-2n)(+) (n = 1-10). Very few ions were sputtered from the C-60 molecules that were adsorbed on the H2O matrix film and the Ni(111) substrate. The ions are thought to be created at the surface when C (C-60) collides with the Ar, Xe, O, and F species via the electron-promotion mechanism, and the formation of quasi-molecules is manifested from the emission of the ion adducts. The fragmentation occurs during the interaction with the reactive species at the surface, and the delayed ionization/fragmentation of the internally excited C-60 molecules in the gas phase has negligible contribution in the present experiment. The matrix effect arises from the suppressed neutralization of the C-60(+) ion because of the localization of a valence hole. The C-60(+) ion undergoes neutralization on the H2O film because the hydrogen bond has some covalent character.