LASER-ABLATION FOURIER-TRANSFORM MASS-SPECTROMETRY OF FILMS BASED ON AMORPHOUS HYDROGENATED CARBON

Mass spectrometry of laser-desorbed hydrocarbon fragments from amorpho us 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 t hat for other polymeric carbonaceous materials. The distribution is ce ntred at 300 amu, which corresponds to the average aggregate mass in t he film. Increasing the laser power lends to increasing fragmentation and the distribution shifts to be centred at m/z=190 with a range of 7 0-400. Photodissociation of hydrocarbon fragments in ''as-prepared'' a nd thermally annealed films also led to the gas-phase formation of car bon clusters up to C-13(+) and C-20(-) together with higher molecular weight including fullerenes. The absence. of metal-hydrocarbon peaks i n the low-power spectra indicate weak binding of metal atoms to the hy drocarbon matrix in these films. For benzene-treated samples, there wa s no evidence of direct laser desorption of hydrocarbon-benzene comple xes. However, metal-benzene complexes were formed in the gas phase by the association of metal ions with fret benzene, both of which were re leased on ablation. (C) 1997 Elsevier Science S.A.