Formation of artificial superlattice composed of ultrathin layers of CoO and NiO by reactive evaporation

Abstract

Films composed of alternating ultrathin layers of CoO and NiO have been prepared by reactive evaporation. The structure was investigated by x-ray diffraction and transmission electron microscopy (TEM). The CoO-NiO multilayered films deposited on the (100) plane of NaCl at 250 °C were single crystal, having the NaCl structure with lattice constants intermediate between the ones of CoO and NiO when each layer was ultrathin (<5 nm). The stacking sequence could be directly observed by the cross-sectional TEM method. The artificial periodicity in the films was also confirmed by the low angle Bragg diffraction and the satellite peaks appearing around the (200) peak. It was found that the films had an artificial superlattice consisting of coherently stacked CoO and NiO single-crystal layers. This structure resulted from alternate epitaxial deposition of these oxides. An artificial superlattice formed also on glass substrates although they were polycrystal films.