Angle resolved X-ray photoelectron spectroscopy study of Pd/NbOx/Nb interfaces

The thermal stability of ultrathin palladium overlayers deposited at room temperature onto oxidized niobium has been studied by high resolution angle-resolved X-ray photoelectron spectroscopy. The Pd overlayers were almost not influenced by heating up to temperatures ∼550 K. Heating above this temperature leads to reduction of Nb2O5 oxide accompanied by dissolution of oxygen into the bulk Nb. Inward diffusion of Pd followed by formation of intermetallic phase at NbOx/Nb interface occurs at temperatures above 600 K. This finding explains the observation of a large decrease of adsorption capacity of Pd/NbOx/Nb samples towards carbon monoxide caused by their annealing.