CLUSTER-SIZE DEPENDENCE OF ALLOYING BEHAVIOR IN GOLD CLUSTERS

Cluster-size dependence of alloying behavior in nm-sized atom clusters has been studied by transmission electron microscopy, using clusters in the Au-Cu system. It was revealed that occurrence of rapid spontane ous alloying becomes more difficult with increasing cluster size. In g old clusters of approximately 4 nm in the mean size, a rapid dissoluti on of copper atoms took place and homogeneously mixed Au-Cu alloy clus ters were formed. In gold clusters of approximately 10 nm in the mean size, rapid alloying of copper took place only at a shell-shaped regio n beneath the free surface of individual clusters and pure gold was re tained at the central region of clusters. In gold clusters of approxim ately 30 nm in the mean size, no rapid alloying of copper was induced. The ease with which spontaneous alloying takes place is discussed in terms of the lattice softening in atom clusters.