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 gamma of isotropic graphites (POCO-AXF-5Q and Russian MPG-LT) on ion fluence and ion incidence angle 0 at near room temperatures and the dependence of gamma on target temperature under high dose 30 keV N-2(+) ion irradiation were measured. It was found that Y and gamma are stabilized at fluences F greater than or equal to 1 x 10(19) N/cm(2). 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 0 = 0-80degrees, Y and gamma increase and the angular dependence of Y is slightly stronger than that of gamma. 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 gamma on the target temperature manifests a step-like increase at similar or equal to250 degreesC which may be due to radiation induced structure transformation in the modified surface layer. (C) 2002 Published by Elsevier Science B.V.