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Species Fractionation in Atomic Chains from Mechanically Stretched Alloys

Bettini et al. [Nature Nanotech 1, 182 (2006)] reported the first experimental realization of linear atomic chains (LACs) composed of different atoms (Au and Ag). Different contents of Au and Ag were observed in the chains from what found in the bulk alloys, which rises the question of what is the wire composition if in equilibrium with a bulk alloy. In this work we address the thermodynamic driving force for species fractionation in LACs under tension, and we present density-functional theory results for Ag-Au chain alloys. A pronounced stabilization of wires with an alternating Ag-Au sequence is observed, which could be behind the experimentally observed Au enrichment in LACs from alloys of high Ag content.