Formation of Hierarchical NiO Coatings on the Surface of Al 2 O 3 Substrates under Hydrothermal Conditions

A hierarchical nickel oxide film was grown on the surface of a polycrystalline Al 2 O 3 substrate by hydrothermal synthesis. The microstructure of the obtained coating was studied by scanning electron microscopy and atomic force microscopy, which showed that this coating comprises porous nanosheets (about 7 nm thick) arranged at various angles to each other and to the surface of the substrate. The lateral sizes of these nanosheets were in the range 3–5 μm. The local electrophysical characteristics of the obtained oxide coating were investigated by scanning capacitance microscopy and Kelvin probe force microscopy; using the obtained results, the maps of the distributions of the surface potential and capacitance contrast over the surface of the NiO film were constructed, and the work function of the surface of this film was calculated.