Composition of natural oxide films on polycrystalline tantalum using XPS electron take-off angle experiments

A model is presented to interpret the results of XPS electron take‐off experiments obtained for natural oxide films on polycrystalline tantalum. The high‐resolution spectrum of Ta 4f shows signals from Ta, TaO and Ta2O5. The angle variations of the intensity ratios Ta2O5/Ta and TaO/Ta show that the emitted signals came from three successive layers: Ta bulk, TaO at the interface and Ta2O5. The stoichiometry and thickness of the derived layers agree with the intensity ratio calculation obtained using a modelization where the interface is not homogeneous but made by large clusters of TaO (height 20 ± 4 Å, fractional coverage 0.56 ± 0.07). The surface is covered by 30 Å of Ta2O5, a value nearly equal to the sputtering result of Mathieu and Landolt.