EFFECT OF CLUSTER-SIZE ON THE CHEMICAL ORDERING IN NANOMETER-SIZED AU-75AT-PERCENT-CU ALLOY CLUSTERS

The effect of cluster size on the chemical ordering in nanometer(nm)-s ized Au-75at%Cu alloy clusters has been studied by means of transmissi on electron microscopy (TEM). It was found that the chemically disorde red high-temperature phase, i.e. solid solution, becomes more stable t han the ordered (L1(2)) low-temperature phase even at room temperature when the cluster diameter is reduced below approximately 5 nm. Simula tion has revealed that when the lattice of these nm-sized Au-75at%Cu c lusters is so soft that the Debye temperature of the clusters is depre ssed, the order-disorder transition temperature, T-c of nm-sized clust ers falls below room temperature.