The structural and electronic properties of Au(n) clusters on the α-Al2O3(0001) surface: a first principles study.

We report the structural and electronic properties of Aun (n = 1-7 and 10) clusters supported on a clean α-Al2O3(0001) surface using the spin-polarized version of the plane wave based pseudo-potential method. To underscore the effect of support interaction, the geometries of the deposited Au clusters are compared with the gas-phase structures. In general, the trend in the growth pattern shows that all deposited Au clusters favor planar configurations, similar to that in the isolated case. However, due to the roughness of the Al2O3(0001) surface the deposited Au atoms are arranged in a zig-zag pattern. The binding energy of an Au atom on the Al2O3 surface is 0.79 eV and it binds to the surface Al atom. Two Au atoms prefer to form a dimer on the alumina surface rather than adsorbing as a monomer at a long distance. As the size of the cluster increases the adsorption energy shows a decreasing trend. The nature of chemical bonding at the interface is established by the charge distribution analysis, which suggests an overall charge transfer from the surface to the Au cluster. The additional negative charge on the deposited Au cluster corroborates the red shift of the energy levels of the Au-Al2O3 composite in comparison to the isolated Aun clusters. Further investigations were carried out by analyzing the interaction between the oxygen molecule and the Aun@Al2O3 system, a prototype to study the oxidation mechanism. The results reveal that the interaction of O2 with Aun@Al2O3 follows a dissociative chemisorption route and ruptures the O-O bond.