Fig. 1: Structure characteristics of NiO on different substrates.

a, b The X-ray diffraction patterns of the NiO(20 nm) film on the MgO(001) and STO(001) substrates, respectively. The pentacle marks out the peak of NiO(001). c Cross-sectional TEM image of the structure of MgO(001)/NiO(20)/Pt. d HRTEM image of the MgO(001)/NiO(20) interface.