Island adsorption and adatom diffusion on 3D non-crystalline silver nanoclusters

We report a systematic study of island adsorption and single-adatom diffusion on free silver nanoclusters, and discuss the consequences on the growth. In our calculations, silver is modelled by semiempirical many-body potentials. We consider magic non-crystallographic structures at different sizes: icosahedra (Ih) at 55, 147 and 309 atoms; Marks-truncated decahedra (m-Dh) at 75, 146 and 192 atoms. We calculate the map of adsorption sites and the energy barriers for the different diffusion processes. We find that, due to purely geometrical reasons, medium-size (from 6-8 to 30-40 atoms depending on the cluster) islands on the cluster (1 1 1) facets prefer the hcp stacking on both Ih and Dh structures, while both smaller and larger islands are better placed on fcc stacking. Interfacet diffusion is easy on both Dh and Ih, indicating that large islands are easily grown; in particular, there are multi-atom diffusion processes which allow fast diffusion among the two caps of Dh clusters. For Dh clusters, island s on hcp stacking may lead to the appearance of new fivefold symmetry points, and to the transformation of the cluster into an icosahedron.