Growth and Correlation of the Physical and Structural Properties of Hexagonal Nanocrystalline Nickel Oxide Thin Films with Film Thickness

• Main Authors: Ahmed H. Hammad, Mohamed Sh. Abdel-wahab, Sajith Vattamkandathil, Akhalakur Rahman Ansari
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Coatings
• Subjects: sputtered nickel oxide; x-ray diffraction; morphology; optical band gap; refractive index; dielectric constant
• Online Access: https://www.mdpi.com/2079-6412/9/10/615

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 NiO_0.96. The crystallite sizes were mainly grown through (101) and (110) characteristic planes. NiO_0.96 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.