Numerical Investigation Of The Stability Of Ag-Cu Nanorods And Nanowires

Molecular dynamics simulations have been employed to investigate thermally-induced phase separation processes in nanometer-sized Ag50Cu50 rods and wires. In the absence of concentration gradients, the mechanism underlying the system decomposition consists of two stages. Roughly below 260 K, the thermal response is governed by the displacement of individual surface atoms. Above such temperature, phase separation proceeds via cooperative rearrangements involving also bulklike atomic species. The result is the formation of systems with an Ag-rich phase segregated at the surface. Significantly different thermal responses are obtained in the presence of concentration gradients perpendicular or parallel to the wire axis. First, the phase separation process is favored and takes place at lower temperatures. Second, an almost complete decomposition of the system in Ag- and Cu-rich domains is obtained and not the surface segregation of the Ag-rich phase. The decomposition is also accompanied by a considerable distortion of the originally regular nanowire shape.