In situ analysis of the tribochemical reactions of diamond-like carbon by internal reflection spectroscopy

An apparatus has been constructed to characterize the chemical intermediates and products of tribochemical reactions in situ by means of internal reflection spectroscopy. Diamond-like carbon (DLC) films were deposited by plasma chemical vapor deposition on rubbing substrates and on a germanium internal reflectance element. Spectra were taken in situ while rubbing the surfaces together under moderate loads (approximately 7.8 kPa pressure). The surface of the DLC was found to contain carbonyl groups immediately after deposition. Rubbing the surfaces in air and in water removed these groups. Rubbing also oxidized the surface, forming carbon-oxygen single bonds. A sporadic tribochemical reaction involved the formation of tertiary vinyl groups at the surface.