Surface oxidation on U₂N_3+xO_y films in oxygen atmosphere by XPS

Highlights: • The U₂N_3+xO_y films were deposited by magnetic sputtering deposition method. • The initial oxidation behaviors of U₂N_3+xO_y films were analyzed by XPS in detail. • Effective information is extracted from the spectra variations during oxidation and depth profile, and a cascade mechanism is proposed and discussed. - Abstract: U₂N_3+xO_y films were deposited on Si substrate by magnetic sputtering deposition method, and the oxidation behavior of U₂N_3+xO_y films in air and oxygen atmosphere were investigated by X-ray photoelectron spectroscopy (XPS) at room temperature. During oxidation, U4f peaks gradually shift to higher binding energy accompanied with variations of satellites at 386.6 eV and 397.7 eV in U4f region. And similar satellites variations are observed on U₂N_3+xO_y surface during oxidation and depth profile, which is attributed to the N-enriched intermediate product. The final product of U₂N_3+xO_y is UO₃, and oxidized nitrogen is also observed after a several-week exposure in air. A cascade mechanism is discussed and applied to explain the oxidation process, in which more than three series reactions are included.