Polymerization of C60 fullerene thin films by UV pulsed laser irradiation

Fullerene C60 thin films were grown by physical vapor deposition (PVD) onto Si (1 0 0) substrates at room temperature in a vacuum chamber kept at 10−6 Torr. Photopolymerization of C60 was performed by irradiation with a pulsed Kr-F laser. The films obtained at a fluence of 25 mJ/cm2 were no longer soluble in toluene, indicating the conversion of C60 into a different solid phase. IR spectra of the irradiated films exhibit several new intense modes indicating the lowering of fullerene molecule symmetry. At the same time, the characteristic modes of pristine C60 had reduced intensities or disappeared, indicating the contribution of sp3-bonding. Raman spectra of the modified C60 films showed the lowering of C60 symmetry as well, along with the increasing disorder due to sp3 carbon atoms. The highest applied irradiation of above 30 mJ/cm2 resulted in the broadening of G and D-bands related to the amorphous carbon phase. The optimal experimental conditions for fullerene photopolymerization for areas larger than 1 cm2, reducing the undesirable formation of other carbon phases, were found.