Low-energy helium bombardment of copper and niobium: gas depth profiles measurements

The operation of fusion reactors will result in the implantation of many isotopes of H, He, Li (Be) in various components. To study their effects on materials, in particular, possible cooperative effects, the method of Elastic Recoil Detection for non-destructive simultaneous depth-profiling of all light atoms was developped. Firstly the depth profiles of He implanted in Cu at 1, 5, 10, 15, 20 and 25 keV, room temperature, and low dose (<=0.01 C/cm2), undisturbed by sputtering or blistering were measured. The average depths are larger by a fairly constant 150-200 A than the theoretical values of Oen and Robinson (O.-R). The doses retained are consistent with a picture where the reflection coefficient is in agreement with O.-R. and re-emission is nil at 10 keV and above, small at 5 keV (approximately 5%) and imporant (43%) at 1 keV, at the dose studied (4x10-3C/cm2). Secondly the re-emission and profile shapes of He in Nb at 10 keV, room temperature were measured for doses of 0.01 C/cm2 (no surface change), 0.16 C/cm2 (abundant blistering), and 0.98 C/cm2 (micro-relief).. Again, profile appear to be deeper than theory. Strong re-emission takes place at the middle and higher doses with near saturation of the He concentration