Observation by TEM of spontaneous alloying in nanometre‐sized atom clusters in the Au‐Al system

SUMMARY Cluster‐size dependence of alloying behaviour in nanometre‐sized atom clusters has been studied by transmission electron microscopy, using clusters in the Au‐Al system, which forms several intermetallic compounds in the phase diagram. In gold clusters of approximately 6–12 nm mean size, rapid dissolution of aluminium atoms took place and Au2Al or AuAl2 clusters were formed. When the size of gold clusters was increased to approximately 40 nm, no such rapid spontaneous alloying occurred. These observations suggest that there exists a critical size of initial gold clusters below which aluminide clusters are successfully formed by spontaneous alloying.