Sputtering and ion-induced electron emission of graphite under high-dose nitrogen bombardment

The dependence of the sputtering yield Y and the electron emission coefficient γ of isotropic graphites (POCO-AXF-5Q and Russian MPG-LT) on ion fluence and ion incidence angle θ at near room temperatures and the dependence of γ on target temperature under high dose 30 keV N2+ ion irradiation were measured. It was found that Y and γ are stabilized at fluences F⩾1×1019 N/cm2. A specific target surface topography develops. At steady-state conditions, the N concentration in MPG-LT is 19 at.% and in POCO16 at.%. In the angular range θ=0–80°, Y and γ increase and the angular dependence of Y is slightly stronger than that of γ. Sputtering yields of POCO are 1.5 times higher than those of MPG-LT. The reasons of the difference between the experimental and calculated sputtering yields using the TRIM.SP code are discussed. The dependence of γ on the target temperature manifests a step-like increase at ≃250 °C which may be due to radiation induced structure transformation in the modified surface layer.