To further evaluate the diffusion of oxygen in the Cu shell case, the simulations for the model in Figure were ran for at least 300 ns for 400-800 K (with 100K intervals). Below 500K, no oxygen appears on the surface even after 300ns. Already at 600 K, at most 4 oxygen atoms appear in the run and the last oxygen atom first emerges at 235.7 ns (diffusion distance ~ 6Å), while at 900 K this happens even below ns scale, Table .