Metastable alloy layers produced by implantation of Ag and Ta + ions into Cu crystals

Transmission electron microscopy and MeV 4 He + ion channelling have been used to study alloy layers formed by Ag + and Ta + ion implantation into Cu. The Ag-Cu layers, for concentrations up to 17 at.%, are metastable solid solutions similar to those produced by conventional rapid quenching techniques. However, the Ta-Cu layers undergo a transition from metastable solid solutions to essentially non-crystalline alloys for increasing Ta concentration, this occurring at about 10 at. % Ta. The formation of such metastable layers is attributed to rapid quenching during thermal spike decay. The structure difference between the high concentration Ta-Cu and Ag-Cu alloys is correlated with concepts of equilibrium solubility and impurity interactions. Thermal annealing of the Ag-Cu alloys gives rise to aligned Ag precipitates for temperatures below 400°C, whereas the Ta-Cu non-crystalline layers are relatively stable at temperatures up to ∼ 600°C.