EXAFS study of mixed nickel molybdenum oxide thin films at the Ni and Mo K-edges

Mixed nickel molybdenum oxide thin films were produced by DC magnetron co-sputtering technique with the nickel content about 8, 16 and 25 at%. X-ray absorption spectroscopy at the Ni and Mo K-edges was used to study the local atomic structure in the films. The best-fit analysis of the EXAFS signals suggests that (i) the films are amorphous, except for the highest nickel content (25 at%), at which a segregation of NiO phase was observed; (ii) nickel and molybdenum atoms are octahedrally coordinated by oxygen atoms. Opposite to the NiO6 octahedra, the MoO6 octahedra are strongly distorted, that results in an existence of two groups of oxygen atoms—four nearest at ∼1.76 Å and two distant at ∼2.2 Å. It was also found that the MoO6 octahedra are joined by edges, with the Mo–Mo distance about 3.26–3.31 Å.