Influence of X Cation Covalence in the Formation of Ni-O-X Mixed Oxides by Reactive Ion Beam Mixing of Ni/X Interfaces

The reaction of the Ni/X interfaces (X = Si or Cr) with O2+ ions at low energy (3 keV) was studied using X-ray photoelectron spectroscopy (XPS) and factor analysis (FA). It was found that low ion doses lead to the formation of a NiO thin film on the surface that was progressively transformed into a Ni-O-X mixed oxide with increasing the ion dose. The degree of transformation of NiO into Ni-O-X depended on the covalence of the X cation, indicating that the reaction was influenced by chemical driving forces. For strong covalent cations (Si and Al), NiO was completely transformed into Ni-O-X at ion doses above 1.8 × 1017 ions/cm2, whereas for ionic cations (Cr) the transformation was incomplete. The ionicity of Ni atoms in the Ni-O-X mixed oxide increased with the increase in the covalence of X cation, and the features of the Ni 2p core level, characteristic of bulk NiO which were attributed to non-local screening, disappeared.