Ion-induced mixing and demixing in the immiscible Ni-Ag system

By molecular-dynamics simulation, we study the effect of 10 keV primary knock-on atoms (PKA’s) on a Ni-Ag interface, and a homogeneous random Ni_0.5Ag_0.5 alloy. The interface roughens; compact islands of 1 ML thickness are created. Only a few isolated impurity atoms are formed. Effects in the random alloy are stronger. It decomposes, creating Ag- and Ni-rich regions. Due to the different lattice constants of the elements, both the interface and in particular the random alloy amorphize. The thermal spike created by the PKA persists longer in the random alloy, due to heating by the large positive heat of mixing of the Ni-Ag system. Comparison with simulation of Cu-Ag demonstrates that the demixing in Ni-Ag derives from its immiscibility in the liquid phase.