SYNERGISTIC EROSION OF GRAPHITE DUE TO SIMULTANEOUS BOMBARDMENT BY C+ AND H+

The chemical sputtering of pyrolytic graphite due to simultaneous bombardment by C+ and H+ ions has been studied as a function of ion energies, relative fluxes and sample temperature. Combined bombardment by C+ ions (1 and 3 keV) and 300 eV H+ does not result in a significant increase in the hydrocarbon yield (i.e., SIGMAC(i)H(j)/H+) over the H+-only case. On the other hand, for 100 eV H+ ions, an increase of up to about approximately 50% in the hydrocarbon yield was observed, as the phi(C+)/phi(H+) flux ratio was varied from about 0.01 to 0.05. Above this flux ratio, the surface damage caused by the energetic ions appears to saturate, and there is no further increase in hydrocarbon production. The effect of near-surface damage on hydrocarbon formation was also seen for He+ + H+ cobombardment.