Surface segregation of Au-Ag bimetallic nanowires

Monte Carlo simulation has been performed to study the size, shape, composition and temperature dependent surface segregation behaviors and atomic-scale structure of Au-Ag nanowires (NWs). Segregation of Ag to the surface is observed in all the NWs considered. The surface segregation of prism-like nanowires with tetragonal cross-section (T-NWs) is enhanced by the increasing of the particle sizes (or Ag compositions) and the decreasing of temperatures. For Au3Ag T-NWs, variation range of surface Ag fraction is smaller than that of truncated octahedron nanoparticles (TO-NPs) with the same diameter, however, AuAg and AuAg3 T-NWs show the opposite character. The surface Ag fraction of T-NWs is higher than that of cylindrical nanowires (C-NWs) and hexagonal cross-section nanowires (H-NWs) due to T-NWs' owning more low-coordination sites while surface Ag fraction of C-NWs and H-NWs are close to each other under every composition, size and temperature. It is found that the most stable mixing configuration of NWs is Ag-rich-surface, Au-rich-subsurface and alloyed-core structures. Accordingly, the calculated alloying extents for NWs are consistent with those of Au-Ag NPs. The possible effects of size and shape distribution of surface Au atoms on tuning the catalytic activity and selectivity of bimetallic NWs are also discussed. (C) 2012 Elsevier B.V. All rights reserved.