Ion-beam-induced modification of fullerene films as studied by electron-energy-loss spectroscopy

The ion-beam (2 keV Ar) -induced amorphization of thin fullerene films has been studied by in situ electron-energy-loss spectroscopy (EELS). With due care to the electron-beam current, the EELS spectrum may be measured without degradation during the electron bombardment to provide an EELS fingerprint of ${\mathrm{C}}_{60}$ films. The diminution of the intensity of characteristic peaks in the EELS spectrum upon ion impact was used to deduce a cross section for the destruction of the ${\mathrm{C}}_{60}$ molecules of (0.85±0.2)×${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$. This value corresponds closely to the geometric size of one ${\mathrm{C}}_{60}$ molecule, suggesting that each incident Ar ion destroys one ${\mathrm{C}}_{60}$ molecule upon ion impact. This cross section is somewhat smaller than that expected using scaling arguments from the results of more energetic ion bombardment (100-300 keV). The difference may be due to surface processes, which become important for low-energy ion-beam irradiation.