Chemical erosion of graphite under simultaneous O+ and H+ irradiation

Our present investigation of the chemical erosion of graphite during simultaneous O+ and H+ irradiation was undertaken to gain an understanding of the reaction mechanisms, by varying the implantation depth and the incident flux ratio (Phi(O)/Phi(H)) Of the two ion species. The results indicate that the yields of CO and CO2 are reduced when H+ is added to Of irradiation whereas the yield of CH4 is reduced when O+ is added to H+ irradiation. Furthermore, these reductions are accompanied by the formation of H2O. We found that the relative ion range has negligible effect on the H2O yield, as well as on the reduction of CO, CO2 and CH4 formation during O-H-C reactions as compared to O-C reactions (CO and CO2) and H-C reaction (CH4). The relative changes of CO, CO2, and CH4 yields, as well as H2O production, however, do depend on flux ratio. The reductions of CO/O+ and CO2/O+ yields during H+ and O+ cobombardment are highest for 'small' Phi(O)/Phi(H) flux ratios; the corresponding water production is also highest for Phi(O)/Phi(H) flux ratios. On the other hand, the reductions of CH4/H+ yields during H+ and Of co-bombardment, as compared to H-C reactions, are highest for 'large' Phi(O)/Phi(H) flux ratios. A plausible mechanism is proposed to explain the observed synergistic effects. (C) 1999 Elsevier Science B.V. All rights reserved.