Eur. Phys. J. D 29, 33-38 (2004)
https://doi.org/10.1140/epjd/e2004-00007-5

Atomic scale models of Co-Ag mixed nanoclusters at thermodynamic equilibrium

Physique des Solides Irradiés et des Nanostructures, CP 234, Université Libre de Bruxelles, boulevard du Triomphe, 1050 Brussels, Belgium

Corresponding author: ^a mhou@ulb.ac.be

Received: 1 October 2003
Published online: 27 January 2004

Abstract

The configurations at thermodynamic equilibrium of Co_xAg nanoparticles are explored for 0<x<201 by means of Metropolis Monte Carlo simulations with a semi-empirical embedded atom potential at temperatures from 100 K to 1000 K. Remarkable configurations are predicted in this temperature range. As a consequence of a competition between strain and Co binding at low temperature, for x<20, Co is distributed just below the cluster surface layer into groups of no more than 5 atoms, favouring well-defined positions, and the cluster central area is avoided. To increase the temperature favours the clustering of these small groups. Their dissolution is predicted at temperatures higher than the melting temperature of the cluster. For x>50, Co regroups at the centre of the cluster and intersects -facets when Ag atoms are not numerous enough to form an entire surface shell. At these stoechiometries, temperature is not sufficient to mix Ag and Co, even above the melting point. At still smaller Ag concentrations, the Ag atoms are distributed at lowest coordination sites, along the edges of the cluster, avoiding the cluster facets as well as inner sites. At intermediate stoechiometries (20<x<50), either oblate Co groups below the surface or a compact group at the centre of the cluster are possible.