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

We report a systematic study of island adsorption and single-adatom diffusi on on free silver nanoclusters, and discuss the consequences on the growth. In our calculations, silver is modelled by semiempirical many-body potenti als. We consider magic non-crystallographic structures at different sizes: icosahedra (Ih) at 55, 147 and 309 atoms; Markstruncated decahedra (m-Dh) a t 75, 146 and 192 atoms. We calculate the map of adsorption sites and the e nergy 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 stacki ng 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 ar e multi-atom diffusion processes which allow fast diffusion among the two c aps of Dh clusters. For Dh clusters, islands on hcp stacking may lead to th e appearance of new fivefold symmetry points, and to the transformation of the cluster into an icosahedron. (C) 2001 Elsevier Science B.V. All rights reserved.