UO2 (111) Single Crystal: Comparison of Stoichiometric and Defective Surfaces by XPS

This work undertakes a photoelectron study of the surface of a uranium dioxide (111) single crystal. The formation of a defected surface with argon ions sputtering can be identified as an n-type semiconductor, UO2-x phase. Annealing to high temperatures under an oxygen pressure of similar to 5 x 10(-6) Torr for 30 min or more yielded the hyper-stoichiometric p-type semiconductor, UO2+x phase. A shift in the core level line of U4+ ions is observed and attributed to a shift in the Fermi level from hyper-stoichiometric UO2+x to sub-stoichiometric UO2-x. (C) 2007 American Vacuum Society.