Abstract
This study investigated nonstoichiometric nickel oxide thin films prepared via the DC-sputtering technique at different film thicknesses. The prepared films were characterized by a surface profiler for thickness measurement, X-ray diffraction (XRD) for film nature, atomic force microscopy (AFM) for film morphology and roughness, UV-visible-near infrared (UV-vis.-NIR) spectroscopy for optical transmittance spectra of the films, and the photoluminescence (PL) spectra of the prepared films were obtained. The measured film thickness increased from 150 to 503 nm as the deposition time increased. XRD detected the trigonal crystal system of NiO0.96. The crystallite sizes were mainly grown through (101) and (110) characteristic planes. NiO0.96 films have a spherical particle shape and their sizes decreases as the film thickness increased. The optical band gap values decrease from 3.817 to 3.663 eV when the film thickness increases. The refractive index was estimated from the Moss relation, while the high-frequency dielectric constant and the static dielectric constant were deduced from the empirical Adachi formula. The photoluminescence behavior of the studied films confirmed the photogeneration of an electron-hole in nickel and oxygen vacancies. Hence, this study confirms the presence of nickel oxide lattice in the hexagonal structure containing the defects originated from the nickel vacancies or the excess of oxygen.
Highlights
Three-dimensional transition metal oxide materials such as nickel oxide are mostly antiferromagnetic materials as a result of their partially filled 3d orbitals [1,2]
Passerini and Scrosati [5] investigated non-stoichiometric nickel oxide thin films prepared by the DC-sputtering technique
The films are synthesized at an operating pressure of 5 mTorr and a substrate cycle of 15 rpm, and the Ni base targets to the substrate distance are fixed at 140 mm
Summary
Three-dimensional transition metal oxide materials such as nickel oxide are mostly antiferromagnetic materials as a result of their partially filled 3d orbitals [1,2]. Nickel oxide crystals are predominately deficient due to the excess of oxygen atoms and the deficiency in the nickel structure. This causes nickel oxide crystals non-stoichiometries to show p-type semiconductor behavior [3,4]. Passerini and Scrosati [5] investigated non-stoichiometric nickel oxide thin films prepared by the DC-sputtering technique. They found that these films could be used as intercalation electrodes, and could be applied to the improvement of electrochromic displays [5].
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