The effect of the oxygen ratio control of DC reactive magnetron sputtering on as-deposited non stoichiometric NiO thin films

Abstract

Non-stoichiometric Ni1-xO thin films were prepared on glass substrate by direct current reactive magnetron sputtering in a large range of oxygen partial pressure (0≤pO2≤1Pa). The dependence of the deposited film structure and properties on oxygen stoichiometry were systematically analyzed by X-ray diffraction, X-ray reflectivity, X-ray photoemission spectroscopy, Raman spectroscopy, atomic force microscopy, UV–vis measurements and electrical transport properties measurements. The deposition rates, surface morphology and opto-electrical properties are very sensitive to the oxygen partial pressure lower than 0.05Pa due to the presence of metallic nickel cluster phase determined by X-ray diffraction, X-ray reflectivity and XPS spectroscopy. Presence of nanocrystallized NiO phase was highlighted even for pO2=0Pa. For pO2>0.05Pa, only the NiO phase was detected. Progressive appearance of Ni3+ species is characterized by a fine increase of the lattice parameter and (111) preferred orientation determined by grazing angle X-ray diffraction, fine increase of the X-ray reflectivity critical angle, displacement of the Ni 2p3/2 signal towards lower energy, significant increase of the electrical conductivity and decrease of the total transmittance. Quantification of Ni3+ by XPS method is discussed. We also showed that the use of Raman spectroscopy was relevant for demonstrating the presence of Ni3+ in the Ni1-xO thin films.