THE PREPARATION OF AND WATER-ADSORPTION ON THIN-FILMS OF NIOBIUM OXIDE ON PT(111)

Three types of thin films of niobium oxide on Pt(111): NbOx, Nb2O5 and Ar+-bombarded Nb2O5 were studied. The thin films were made up of a hi gh density of small crystallites on an epitaxial monolayer. AES, ILS a nd UPS showed that the NbOx thin film had an electronic structure that is a composite of those of NbO, NbO2 and Nb2O5, while the Nb2O5 thin film had an electronic structure similar to Nb2O5. LEED and HREELS sho wed that the surface periodicities and crystal structures differ from those of the bulk oxides. HREELS indicates a structural similarity wit h some supported two-dimensional Nb oxide monolayers with Nb=O surface sites of highly distorted NbO6 octahedra. Ar+ bombardment decreased t he proportion of surface oxygen. Water adsorption at room temperature, studied by HREELS and UPS, was associative on Nb2O5 and dissociative on Ar+-bombarded Nb2O5. It was associative on NbOx but dissociates on heating.