On the mechanism of carbon clusters formation under laser irradiation. : The case of diamond grains and solid C60 fullerene

It is shown by FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry that carbon clusters considered to be the superior homologues of C-60 fullerene are formed by laser irradiation of both synthetic diamond grains or from pure C-60 fullerene crystals. The surfaces of the laser irradiated diamond or C-60 have been examined by Raman spectroscopy. In the case of diamond the Raman spectrum suggests the superficial formation of mixed carbon nanostructures consisting of disordered graphite, fullerenic nanostructures, onion-like carbon nanostructures and diamond-like carbon. Based on the Raman spectra of the surface and on data taken from the phase diagram of carbon, it is shown that the graphitization is needed in order to produce fullerenes from diamond under laser ablation conditions. In the case of C-60 fullerene, it is shown by Raman spectroscopy that the laser irradiation of the crystals causes initially their photopolymerization and after further irradiation their transformation into disordered graphite. Based on these results and on a literature survey on the formation of fullerenes from more than 15 completely different substrates, it is concluded that fullerenes are formed always when laser ablation leads to a graphitization of the laser-irradiated substrate. Some astrochemical implications of the conclusions have been discussed.