Epitaxial matching of small metallic nanoclusters in large-misfit systems

The deposition at low energies of Cu and Au nanoclusters, respectively, on Au(0 0 1) and Cu(0 0 1) substrates is studied by constant-temperature molecular-dynamics simulations. Initially, clusters had icosahedral or Wulff shapes and their number of atoms ranged between 13 and 1289. The deposition energy and the temperature were, respectively, 17 meV/atom and 300 K. Atomic interactions are mimicked by a many-body potential based on the tight-binding model. A different behaviour of the clusters has been found as a function of the number of atoms and of the material. Below 100 atoms, Cu clusters align all their {2 0 0} planes with the substrate but do not achieve epitaxy since either their lattice structure becomes bcc or stacking faults arise. On the contrary, Au clusters with similar number of atoms grow epitaxially but hardly change the distances parallel and perpendicular to the interface in their unit cell. Cu clusters, for their part, fit the parallel distances to the Au lattice parameter. For larger clusters, in general, the alignment or epitaxy is not complete even in the cases of more favourable landing.