Nanoscale imaging of the electronic conductivity of the native oxide film on titanium using conducting atomic force microscopy

Conducting atomic force microscopy (C-AFM) is used to visualize the heterogeneous electronic conductivity of the native oxide film (nominally a 2.9 nm thick TiO2 layer) on polycrystalline Ti electrodes (hereafter referred to as Ti/TiO2 electrodes). Ex situ C-AFM images of Ti/TiO2 electrodes recorded in air demonstrate that the electronic conductivity of the oxide film in contact with the underlying Ti grain boundaries is at least 200x higher than the conductivity of the oxide film on grain faces. The width of the conductive zone in the oxide film over grain boundaries is estimated to be less than 50 nm (resolution limited by the C-AFM tip size). Small islands of oxide exhibiting high electronic conductivity are also observed on topographically featureless regions of grain faces. The observed spatial variations in conductivity are tentatively attributed to the presence of defects (e.g., Ti3+ sites) and lower valence oxides (e.g., Ti2O3) in the native oxide film.