Difference in charge transport properties of Ni-Nb thin films with native and artificial oxide

Here, we report on the properties of native and artificial oxide amorphous thin film on a surface of an amorphous Ni-Nb sample. Careful measurements of local current-voltage characteristics of the system Ni-Nb / NiNb oxide/Pt, were carried out in contact mode of an atomic force microscope. Native oxide showed n-type conductivity, while in the artificial one exhibited p-type one. The shape of current-voltage characteristic curves is unique in both cases and no analogical behavior is found in the literature. X-ray photoelectron spectroscopy (XPS) measurements were used to detect chemical composition of the oxide films and the oxidation state of the alloy components. Detailed analysis of the XPS data revealed that the structure of natural Ni-Nb oxide film consists of Ni-NbOx top layer and nickel enriched bottom layer which provides n-type conductivity. In contrast, in the artificial oxide film Nb is oxidized completely to Nb2O5, Ni atoms migrate into bulk Ni-Nb matrix. Electron depletion layer is formed at the Ni-Nb/Nb2O5 interface providing ptype conductivity