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

Our present investigation of the chemical erosion of graphite during simult aneous O+ and H+ irradiation was undertaken to gain an understanding of the reaction mechanisms, by varying the implantation depth and the incident fl ux 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 whe reas the yield of CH4 is reduced when O+ is added to H+ irradiation. Furthe rmore, these reductions are accompanied by the formation of H2O. We found t hat 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 Hand 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 rati os. 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)/P hi(H) flux ratios. A plausible mechanism is proposed to explain the observe d synergistic effects. (C) 1999 Elsevier Science B.V. All rights reserved.