Laser-ablation fourier-transform mass spectrometry of films based on amorphous hydrogenated carbon

Mass spectrometry of laser-desorbed hydrocarbon fragments from amorphous hydrogenated carbon (a-C:H) and stainless steel/a-C:H films show a distribution over a m/z range of 100-400 with an envelope resembling that for other polymeric carbonaceous materials. The distribution is centred at 300 amu, which corresponds to the average aggregate mass in the film. Increasing the laser power leads to increasing fragmentation and the distribution shifts to be centred at m/z = 190 with a range of 70-400. Photodissociation of hydrocarbon fragments in "as-prepared" and thermally annealed films also led to the gas-phase formation of carbon clusters up to C⁺ ₁₃ and C^- ₂₀, together with higher molecular weight including fullerenes. The absence of metal-hydrocarbon peaks in the low-power spectra indicate weak binding of metal atoms to the hydrocarbon matrix in these films. For benzene-treated samples, there was no evidence of direct laser desorption of hydrocarbon-benzene complexes. However, metal-benzene complexes were formed in the gas phase by the association of metal ions with free benzene, both of which were released on ablation.