Oxidation of a depleted uranium-5 wt% molybdenum (U-5Mo) alloy in UHV by AES and XPS

Early stage oxidation of a dilute-depleted uranium-molybdenum alloy was analysed in situ under ultra-high vacuum conditions by AES and XPS. At the equivalent of less than 300ns at 1-atm O-2, U-5Mo oxidizes to form stoichiometric UO2. No molybdenum oxidation is observed. After an oxygen dose of approximately 39L, the oxide layer approached a limiting thickness of approximately 2.4nm. The oxidation kinetics followed a logarithmic rate law, with the best fit to the experimental data for the oxide thickness, d, being given by d=1.26 log(0.12t+0.56). Changes in oxygen KLL and 1s peak positions associated with transformation from chemisorbed oxygen to metal oxide were observed at similar oxygen doses of 2.3 and 2.6 L O-2 by AES and XPS, respectively, which opens up the possibility of using well-characterized XPS chemical information to inform Auger peak shifts.