Size Dependence of the Adsorption Properties of Nickel Clusters on the Surface of Aluminum Oxide

Despite the recent activity in the field of studying the properties of systems formed during the adsorption of metal atoms on the surface of oxides, many questions of a fundamental nature remain open. Elucidation of the fundamental features of the behavior of systems of the type under consideration will improve the technological basis for the practical development and application of existing materials. In this regard, in the present work, the system Ni/Al2O3/Mo(110) is studied in ultrahigh vacuum using surface-diagnostic methods. Investigations using X-ray photoelectron and Auger electron spectroscopy, low-energy-ion backscattering spectroscopy, and Fourier-transform infrared spectroscopy show that the electronic and adsorption properties of nickel nanoclusters on the surface of aluminum oxide depend significantly on the cluster size. The properties of clusters no larger than 2 nm are determined by the formation of a bond polarized toward the oxide substrate at the Ni/Al2O3 interface. With growth of the cluster, depolarization of this bond occurs with redistribution of the electron density to lateral bonds between Ni atoms. Such a size dependence makes it possible to tune the properties of metal clusters and the metal-oxide system as a whole, for example, to achieve the required electronic and adsorption-reaction parameters.