Adsorption of Small Palladium Clusters on the α-Al2O3(0001) Surface: A First Principles Study

In this work, we report the growth behavior of small Pdn clusters (n = 1–7) on the α–Al2O3 (0001) surface using a first principle approach based on the plane wave-pseudopotential method. The results reveal that in general the interaction of Pdn clusters with Al2O3 surface deforms the equilibrium geometry of the isolated clusters. For Pd atom, the most preferred adsorption site is found to be on top of the oxygen atom with an interaction energy of 1.40 eV. For the dimer, binding between two Pd atoms is more favorable than atomic adsorption at a distance. The competition between Pd–Pd and Pd–surface interactions further governs the growth motif of larger clusters. As the size of the Pd cluster increases, it prefers an open structure to maximize the Pd–surface interaction. In case of Pd7, the compact pentagonal bipyramidal structure of the isolated cluster reorganizes into a hexagon with one central atom. Further, a comparison of chemical bonding analysis through electronic density of state (EDOS) between the gas phase and deposited clusters shows that the EDOS of the deposited Pdn cluster is significantly broader, which has been ascribed to the enhanced spd hybridization.