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Ion scattering spectroscopy (ISS) was used to study the adsorption of O(2) on UNi(5) at room temperature. The main goal was to follow the changes of the stoichiometry of the surface with O(2) exposure exploiting the topmost surface layer sensitivity of ISS. Simultaneous ultraviolet photoemission spectroscopy (UPS/He II, 40.81 eV) analysis allowed the determination of related changes of the valence electrons which are responsible for the chemical reactivity of the surface. The ISS/He(+) data show that at an exposure of L about 3 Langmuir of O(2), no Ni atoms are detected in the topmost surface layer. However, the less surface-sensitive UPS spectra still reveal the presence of Ni in the surface. Submitting the sample to higher exposure ISS shows a He(+)/O contribution, which increases with the exposure, but a constant He(+)/U peak intensity. The UPS spectra confirm the previous results: the U metal derived 5f peak at the Fermi-edge disappears, the U dioxide derived 5f(2) peak increases and the O 2p line is no longer symmetric and develops a shoulder at higher binding energy. At high exposure values the surface will be composed of UO(2) with Ni metal below the topmost layer. The ISS data suggest that an exponential will describe the evolution of the U concentration. The UPS data suggest that the evolution of the O 2p intensity can also be described by a different exponential.

Additional information

Authors: PRAXEDES A J F, JRC Karlsruhe (DE);NAEGELE J R, JRC Karlsruhe (DE)
Bibliographic Reference: Article: Surface Science, Vol. 251/252 (1991) pp. 916-920
Record Number: 199210136 / Last updated on: 1994-12-02
Original language: en
Available languages: en