(376c) Relating Segregation Behavior in Metal Alloy Nano-Particles of Different Shapes and Sizes

Surface segregation in metal alloy nano particles (NP), i.e., preferential enrichment of one of constituent metal species at the top few surface layers, is important to adsorption, catalysis, separation and optoelectronic applications. Among the large number of factors that influence segregation are NP shape and size, which can be experimentally hard to control. Therefore, an efficient computational strategy is required to estimate the segregation profiles in nano particles of a given size and shape distribution. The talk focuses on a nano-thermodynamic model based on distribution coefficient Δ, which we have developed recently. While Δ helps to determine the preference of metal species to be at surface facets, edges, vertices and bulk regions, the nano-thermodynamic model includes the number of sites in each region so that the segregation profiles in nano particles of different shapes and size can be predicted. Δ, which is a function of the alloy composition in each region, is determined for a NP of a given size and shape, and directly employed with NPs of other sizes and shapes. Different NP shapes like cube, truncated-octahedron and icosahedron are explored. Using Au-Pt, Ni-Pt and Ag-Au as prototype systems, we demonstrate that a wide range of alloying behavior from complete mixing to complete segregation can be captured in bimetallic nano particles of different shape and size using the nano-thermodynamic model.