Probing the tribochemical degradation of hydrogenated amorphous carbon using mechanically stimulated gas emission spectroscopy

Mechanically Stimulated Gas Emission (MSGE) spectroscopy was used for investigation into tribochemical reactions and gas emission for four types of amorphous hydrogenated carbon (a-C:H) coatings, which were obtained by either ion beam deposition (IBD) or plasma enhanced chemical vapour deposition (PECVD). The results of statistical analysis, which was employed to identify the components of the emitted gases from the mass-spectrometry data, argue against the hypothesis that considerable amount of CH3 could be present in the emitted gases. For the IBD coatings the main components of the emitted gases were methane and/or argon, whereas for the PECVD coatings they were mainly methane and hydrogen. Noticeable emission of ethane, propane, carbon mono- and dioxides was also detected under sliding of PECVD coatings deposited with the lowest ion energy. While frictional heating has been definitely ruled out as the driving mechanism for MSGE, there are experimental evidences that MSGE has to be associated with structural degradation of the coating.