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

A novel method has been discovered for growing uranium oxide films onto iro n substrates from solution. The films were characterized by X-ray photoelec tron spectroscopy, X-ray diffraction, scanning electron microscopy, Rutherf ord backscattering spectrometry, and near-edge X-ray absorption fine struct ure. The as-grown films appear to be iridescent. They are composed of an am orphous uranium(Vl) oxide with water incorporated, and are most likely a pa rtially dehydrated schoepite. Topographic images reveal that the surfaces o f the films are basically flat, but contain some small hills and valleys. S mall cracks are distributed randomly across the surfaces. Upon heating in v acuum, the films crystallize and reduce to a uranium(IV) oxide, and the cra cks enlarge. When a heated sample is exposed to air, the surface re-oxidize s to uranium(VI) while the bulk remains as crystalline uranium(IV) oxide. ( C) 2001 Elsevier Science BY. All rights reserved.