Characterization of uranium oxide thin films grown from solution onto Fe surfaces

Abstract

A novel method has been discovered for growing uranium oxide films onto iron substrates from solution. The films were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, and near-edge X-ray absorption fine structure. The as-grown films appear to be iridescent. They are composed of an amorphous uranium(VI) oxide with water incorporated, and are most likely a partially dehydrated schoepite. Topographic images reveal that the surfaces of the films are basically flat, but contain some small hills and valleys. Small cracks are distributed randomly across the surfaces. Upon heating in vacuum, the films crystallize and reduce to a uranium(IV) oxide, and the cracks enlarge. When a heated sample is exposed to air, the surface re-oxidizes to uranium(VI) while the bulk remains as crystalline uranium(IV) oxide.