Evolution of He bubbles at HAGBs. Atoms are colored according to magnitude of displacement in panels (a), (d), and (g) as indicated by color bar. Arrows represent displacement direction. In panels (a)–(i), the Bule atom are W, and dark red atoms are He. In panels (j) and (k), potential energy of atomic layer without He bubble at GB plane is shown. Atoms are colored according to potential energy as indicated by color bar. View is along [110] direction.