PROTON IRRADIATION OF THIN-FILMS OF C-60 MOLECULES

Vaccum-sublimed films of C60 molecules with thicknesses of 180–300 nm were irradiated with 100- or 200-keV protons at room temperature. The effects of fluences of 3.3 × 10±4;>to 6.1 × 10±6; H/cm²have been examined in detail using Fourier transform infrared (FTIR) spectrometry, glancing-angle X-ray diffraction (GXRD) and low-energy X-ray fluorescence (LXRF). All three techniques indicated that the major changes occurred for fluences greater than 1 × 10µ H/cm². Intensities of the C60 FTIR peaks decreased exponentially with fluence without significant peak shifts or peak width changes. This suggests that each C60 molecule was destroyed in a catastrophic event, rather than a gradual process. Because essentially all the energy deposited in the films by the protons was in the form of electronic excitation and because solid CR60 is an electrically insulating material, a Coulombic, or ionic, explosion at each C60 molecule is proposed to explain the observations. For the larger fluences, the presence of broad FTIR bands near 740 and 1420 cm·-1;and the absence of sharp diffraction peaks in GXRD were taken as evidence that the C60 films were transformed into a form of amorphous carbon. © 1991, Taylor & Francis Group, LLC. All rights reserved.