X-ray photoelectron spectroscopy on uranium oxides: a comparison between bulk and thin layers

The use of sputter deposited thin layers of UO2 as a model system for the i nvestigation of fuel-fission product interactions is presented. The represe ntativity of the layers for the bulk system will be validated and it will b e shown, both on theoretical and experimental grounds, that layers of stoic hiometric UO2 can be produced by this method. A comparison will be made bet ween X-ray photoelectron spectroscopic (XPS) results on bulk UO2 and on the deposited layers. The films deposited can easily be doped with other eleme nts, such as fission products, by codepositing these elements with the UO2. This codeposition technique has subsequently been used to produce layers o f UO2 containing cesium. It will be demonstrated that the codeposition with cesium produces uranium in higher valence states (up to U-V1). while witho ut cesium, no higher uranium valencies can be obtained. (C) 2001 Elsevier S cience B.V. All rights reserved.