Surface roughness as a means of suppressing helium ion induced blister formation in metals

There is considerable interest in devising methods of blister suppression. Roth et al. have done two experiments. In their first niobium had been injected with 9 keV helium ions at doses up to 1000 times the critical dose for blister formation. Initially they find that blisters are formed but these are eroded away by sputtering; further blisters do not appear. In their second experiment they demonstrate that blistering in 6 or 9 keV helium-injected niobium can be suppressed by pre-injecting with doses of lower energy ions. In the 9 keV case, for example, they pre-injected with 0.5, 1, 2, 4 and 6 keV ions. Their explanation of the results of both experiments was in terms of the irradiation damage creating pores and cracks through which helium subsequent escaped. As discussed later it seems difficult to accept this explanation completely. This letter discusses the alternative possibility that the results could be due to surface roughness effects. (Auth.)