Abstract:
The structural stability of Au−Ag, Au−Cu and Ag−Cu alloy monoatomic chains have been systematically investigated via first−principles calculations. We used the string tensioncriterion, rather than the energycriterion, to measure and identify the stability of tip−suspendedand finite alloy chains. We have found that the tip−suspended Ag−Au and Cu−Au alloy monoatomic chains are of stable zigzag structures due to the existence of local minima in the string tensions variation with their z−projected interatomic distance. However, a tip−suspended Ag−Cualloy monoatomic chain would be difficult to form in future experiments due to the nonexistent of local minima in the string tensions. We have also found that both the relativistic effect of elemental gold and the string tension applied by the tip contacts play important roles in suppressing effectively the self-purification effect, leading to the formation of the Au−Ag and Au−Cu alloy monoatomic chains.