ENERGY, FLUX AND FLUENCE DEPENDENCE OF METHANE BREAKUP IN GRAPHITE DURING IRRADIATION

Simulataneous H+/He+ bombardment of graphite has conclusively shown that methane molecules formed during the irradiation are being broken up by the incident ions. Evidence for the breakup process is contained in the transient behavior of the methane emission signal at the termination of irradiation. The observed transient (or ''spike'') effect is dependent on the energy, flux, fluence and mass of the incident hydrogenic species, indicating that the methane breakup process occurs most likely throughout the whole implantation zone as methane molecules diffuse from the end of ion range, where they are formed, to the front surface.