Unsupported nanometer-sized copper clusters studied by electron diffraction and molecular dynamics

An electron diffraction study on unsupported nanometer-sized copper clusters has been combined with molecular-dynamics calculations to investigate size-related structural effects. The experimental conditions allow slow cluster growth, close to thermodynamic equilibrium, in an inert-gas-aggregation source. A distinct structural change is observed, which is correlated with cluster size: there is a predominance of icosahedra below 3.8 nm in diameter, and a clear separation of size distributions for icosahedra and fcc particles, which are larger. These results confirm the predictions of an earlier molecular-dynamics study. Further molecular-dynamics simulations have provided information on atomic dynamics and thermal expansion of interatomic distances and are compared with experimental data.