Effects of substrate temperature and oxygen pressure on crystallographic orientations of sputtered nickel oxide films

Nickel oxide (NiO) films with NaCl-type structure were deposited onto Corning glass substrates at different substrate temperatures by radio-frequency (RF) magnetron sputtering under an RF power of 200W. The resulting films were analyzed by grazing-incidence X-ray diffraction, ultrahigh resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). The relationships among the gas ratio of O-2, substrate temperature, preferred orientation and microstructure of the NiO films were investigated. Those films deposited at a substrate temperatures of 303 or 473 K with the ratio of oxygen varying from 0 to 100% displayed a (111) preferred orientation. At the substrate temperature of 673 K, while the (111)-orientated film was obtained under a low ratio of oxygen (< 50%n O-2), a (200) preferred orientation was developed under 100% oxygen. All the films have a columnar structure with the growth direction perpendicular to the surface. The origin of the preferred orientations is also discussed.