The Effect of the Size of Ni Clusters Deposited on Alumina α-AlO(0001) upon the Adsorption Character of Nitric Oxide Molecules NO

With the aid of combination of surface analysis techniques and theoretical calculations by density functional theory it is shown that the electronic and NO-adsorption properties of Ni nanoclusters deposited onto alumina α-AlO(0001) are notably dependent upon the cluster size. The properties of Ni clusters with a mean size lower than 2 nm are primarily determined by chemisorption bond polarized towards the oxide Ni–AlO. As a result, the Ni clusters acquire a net positive charge. The latter is manifested in that that the intramolecular bond of adsorbed NO strengthens compared to that of NO on the bulk Ni. As the size of the cluster grows, the chemisorption bond depolarizes due to the charge redistribution from the Ni–AlO interface to the Ni-Ni lateral bonds. When the equivalent coverage of Ni exceeds 0.25 equivalent monoatomic layers, their NO-adsorption properties resemble those characteristic for bulk Ni. Such a size-dependence opens an opportunity for controlled tuning of electronic and adsorption properties of the oxide supported metal clusters, as well as the metal/oxide system as a whole.