Could you explain the significance of your article to the non-specialist?

Bimetallic nanoclusters are small aggregates of metal atoms. They are some nanometers large, and are used in applications as diverse as catalysis, optics and magnetism, nanomedicine. Their properties depend on their size, geometrical structure, chemical composition and chemical order. A key questions about clusters regards their formation process - what is the mechanism by which clusters are formed? This paper investigates the growth process of small clusters made out of gold and copper atoms. Atom by atom the formation of the cluster is simulated, trying to predict the influence of any kinetic factor onto the structure and the chemical order of the cluster.

The main motivation to study the formation dynamics of gold-copper clusters is just to understand how the energetic and kinetic driving forces compete to determine the structure and the chemical order of the cluster during its growth process. Such an investigation can indeed help to predict what is likely to be produced in real experiments, how thermodynamic parameters as temperature and pressure can influence the structure of the cluster and, as a consequence, all its physical and chemical properties.

Two major outcomes can be singled out and deserve attention for future investigation. The first regards cluster structure. During the cluster growth it has been indeed observed a transition from the decahedral geometrical shape, to the icosahedral shape. The dynamic of this transition is not clear yet at the atomic scale, and this could be investigated trying to get quantitative information about the possible transition patterns and the associated diffusion barriers. The second important outcome concerns the chemical order of gold and copper at the cluster scale. These metals present alloy ordering in the bulk, and at the nanometer scale the tendency to form ordered compounds compete with the tendency of gold to segregate at the surface of the clusters. Future studies will be devoted to study the segregation of gold on copper surface, both in free and matrix-embedded clusters.

The main challenge in this area is probably to achieve a complete control on the structural and chemical characteristics of the clusters at the production stage. This will allow to shape clusters at will, opening lots of prospectives in many science fields, ranging from medicine to biology, physics, chemistry.