Figure 5. Barrier effect of defects on structural stability of nanoparticles.

(a) Schematic of an atom located with a distance of x to the center of a slit defect of width w in graphene and the evolution of potential energy as the function of x, clearly showing an energy barrier as the atom approaches the defect. (b) On defect-free graphene, two neighbouring 3-nm Al nanoparticles are initially apart from each other by 5 nm, then migrate by Brownian random walk at 2,200 K and eventually aggregate and coalesce into a single particle, driven by surface energy minimization. (c) On graphene with slit defects, two 3 nm Al nanoparticles with the same initial dispersion distance are shown to be effectively confined within the domain demarcated by the slit defects, owing to the barrier effect. The two nanoparticles remain dispersed without coalescence at 2,200 K. (d) On graphene with grain boundaries (as outlined by dotted lines in left panel, mainly made of pentagon-heptagon paired defects), the two nanoparticles also remain dispersed without coalescence at 2,200 K.