Gas exposure and thermal stability of linear carbon chains in nanostructured carbon films investigated by in situ Raman spectroscopy

In situ Raman spectroscopy from nanostructured carbon films, produced by supersonic cluster beam deposition, has revealed a high fraction of sp1 linear carbon chains (also known as carbynoid structures) embedded in a sp2 amorphous matrix. The presence of sp1 linear carbon chains is revealed by a large structured band with a main peak at nearly 2100 cm-1 and a shoulder at 1980 cm-1, assigned to polyyne (alternating single–triple bonds) and polycumulene (double bonds) moietes respectively. The stability of these species has been analysed following the temporal evolution of the characteristic sp1 Raman band intensity under exposure to several gases (He, N2, H2 and dry air). The carbynoid species appear to be very reactive to oxygen-rich environment, whereas the effects of other gases are less destructive. Actually, exposure to oxygen reveals different decay mechanisms with respect to other gases. The thermal stability in ultra high vacuum has been also studied up to 200 °C. We observe different decay kinetics as a function of annealing temperature, showing thresholds in the chain stability.