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Step Decoration for Improving Enantioselectivity of Chiral Metal Surfaces

Jeong Woo Han and David S. Sholl. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, GA 30332-0100

There is a strong industrial need for enantiopure chiral molecules. Highly stepped metal surfaces can define intrinsically chiral structures. Using the chiral environments created by these chiral surfaces, we can potentially separate chiral molecules. In order to improve the enantioselectivity of those surfaces, step decoration of the stepped metal surfaces by a second metal species can be considered. For successful step decoration, the second metal species on the surface should ideally remain on the kinked step sites. This kind of step decoration may also have interesting implications in creating tailored bimetallic nanoparticles for heterogeneous catalysis applications. Because carrying out experiments on surface segregation is difficult, we performed Density Functional Theory (DFT) calculations to make theoretical predictions about these phenomena. Our DFT calculations have identified multiple stable examples of step decoration. Simultaneously, a strong coordination dependency of surface segregation for each surface/impurity pair was observed. Combining these calculated data and coordination dependency with other possible factors of surface segregation such as bond strength and d-band properties, we developed a model to predict surface segregation on stepped surfaces. With this model, we have estimated the stability of step decoration without further DFT calculations for surface segregation for a very large number of bimetallic pairs.