The shape of bubbles in He-implanted Cu and Au

Bubble evolution under thermal annealing has been studied in He-implanted Cu and Au by in situ transmission electron microscopy. We show that, under the minimum energy requirement of system, the bubble developed into an octahedron (or truncated octahedron) shape consisting of {1 1 1} planes in the manner predicted by the Wulff construction. The non-spherical shape of the bubbles and the existence of sessile dislocations along the edges of octahedron provide a barrier to Ostwald ripening and migration of bubbles, leading to low bubble mobility under thermal annealing.