Size-Dependent Icosahedral-to-fcc Structure Change Confirmed in Unsupported Nanometer-Sized Copper Clusters

Unsupported nanometer-sized copper particles in a molecular beam of inert carrier gas have been studied using electron diffraction. A distinct separation in the size distributions of fcc and icosahedral particles is observed: Icosahedra occur at sizes well below a diameter limit of 3.8 nm predicted for copper by molecular dynamics simulations, while fcc particles occur close to this limit or above. Molecular dynamics simulations have also provided information about particle temperature via thermal expansion and atomic dynamics.