Atomistic simulation of surface segregation processes in unstrained and strained Ag-Cu nanowires

Molecular dynamics simulations have been used to investigate the thermal stability of Ag50Cu50 nanowires with square and circular cross sections under different stress conditions. Being Ag and Cu immiscible in the solid state, the systems tend to decompose as temperature is raised both in the absence and in the presence of stress. At zero stress and relatively low temperatures, nanowires undergo a segregation of Ag atoms at the surface. Only individual displacements of surface atoms are observed at the lower temperatures, whereas extensive collective rearrangements occur at the higher temperatures. These were characterized in detail at constant temperature on relatively long times. It is also shown that the application of a stress along the nanowire axis determines a rate enhancement of the Ag surface segregation process. At the same time the number of Ag atoms segregating at the surface decreases. This correlates with a corresponding decrease of the difference between the surface energies of the Ag and Ag50Cu50 phases as the uniaxial strain increases.