Blistering of molybdenum under helium ion bombardment

Polished molybdenum targets have been bombarded with helium ions of energy from 7 to 80 keV in ultra-high vacuum. During bombardment the release of gas was continuously monitored and after bombardment the targets were examined in a scanning electron microscope. Blister formation was observed to occur after a critical dose of ∼ 5 × 1017 ions/cm2, and the appearance of blisters coincides with gas release from the surface. The average size of the blisters increases with energy but not with ion dose. In addition to room temperature observations, blisters have also been examined following high temperature bombardment of molybdenum, and room temperature bombardments of W, Pt, Ni, Cu and Zr targets.