| Abstract
| - The interaction of oxygen with nickel deposited on polycrystalline aluminum surfaces has been investigatedusing Auger electron spectroscopy, X-ray photoelectron spectroscopy, and angle-resolved X-ray photoelectronspectroscopy. The growth of the nickel on the aluminum surfaces occurs in two stages: formation of NiAlx(x≈ 0.45) islands 10 monolayers (ML) thick up to a coverage of θNiAlx≈ 0.7, followed by the formation ofmetallic nickel islands 8 ML thick that grow over the intermetallic islands previously formed. For surfacescontaining NiAlx islands alone, the chemical information obtained by the analytical techniques shows thatoxygen exposure causes the formation of aluminum intermediate oxidation states Al+ and Al2+, in additionto Al3+, which are attributed to the formation of Al−O−Ni cross-linking bonds at the interface. The analysisof the Ni 2p peak shape shows that no nickel oxide is formed, the small changes observed in this bandbeing attributed to Ni atoms in an aluminum-depleted layer at the interface. In contrast, nickel oxide isformed during the oxidation of surfaces containing nickel islands. In such a case, the oxide film is composedof a mixture of intermediate aluminum oxidation states that grow over a NiO oxide layer. At the interfacebetween Al and Ni oxides, a NiAl2O4-like mixed oxide or Ni3+ defects are formed.
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