Chemical erosion behavior of graphite due to energetic oxygen impact

Pyrolytic graphite, fine grain graphite and amorphous a-C:H films were irradiated with energetic oxygen in the energy range 1-5 keV between room temperature and 1800 K. CO and CO2 molecules released during implantation were analyzed by residual and line-of-sight mass spectroscopy and their velocity distributions were determined by time-of-flight measurements. The retained oxygen was determined by thermal desorption spectroscopy after irradiation. The impact of energetic oxygen (E > 1 keV) on these materials results in the formation of CO and CO2 with an erosion yield close to unity. The observed CO release behavior can be described by a local saturation model. Special experiments indicate that the underlying release mechanism is driven by ion-induced collision processes at the end of the ion trajectory of the impinging oxygen. Time-of-flight measurements have shown that released CO molecules have two different energy distributions with a thermal component corresponding to the target temperature and an overthermal component at a maximum energy of about 0.12 eV, whereas the CO2 molecules are exclusively released with thermal energies. (C) 1997 Elsevier Science B.V.