Study on growth mechanisms and electronic structures of polar NiO(1 1 1) ultrathin films using iron oxide buffer layers

• Polar NiO(1 1 1) films were grown on FeO(1 1 1), Fe3O4(1 1 1), Fe2O3(0 0 0 1) buffer layers.
• Iron oxide buffer layers reduced the lattice mismatch between NiO(1 1 1) and Mo(1 1 0).
• Interfacial reaction between NiO and iron oxides decreased the interfacial energy.

Polar surfaces of metal oxides have attracted considerable attention in fundamental science and technological applications because of their peculiar stabilization mechanisms and unusual adsorption and catalytic properties. In this study, various ordered iron oxide films, including FeO(1 1 1), Fe3O4(1 1 1) and Fe2O3(0 0 0 1), were successfully used as the buffer layers for the growth of polar NiO(1 1 1) films with several nanometer thickness. The results indicated that the iron oxide buffer layers reduced the lattice mismatch between NiO(1 1 1) and Mo(1 1 0) substrate, and also decreased the interfacial energy by means of the interfacial reaction between NiO and iron oxide surfaces, benefiting the initial nucleation and the growth of polar NiO(1 1 1) films. This study will be essential for understanding the physical and chemical properties of polar surfaces.