Ice on UO2 and UO3 Oxide Films

Goal: study the reaction of H2O ice overlayers with UO2+x under light and in the dark. Implementation: Deposit thin films of UO2 on Si(111) substrates. Deposition is done by reactive sputtering of a U targets by an Ar plasma in presence of oxygen (O2). Films are then oxidized to UO3 by exposure to atomic oxygen. Films are cooled by liquid nitrogen (passing through the sample holder, onto which the substrate is fixed)) and exposed to a water (introduced through a capillary directly to the sample surface (distance: about 20 mm)). This allows enhancing the ocal pressures on the sample surface (by a factor about 20) and keep the water load of the preparation chamber as low as possible. The reaction of the surface during ice warming/desorption is studied with/without UV light, and at different heating rates. Stability of the surface oxidation state in UV light was tested (to see if UV along can induce reduction) The machine used for this study was the cold machine.