Structural and optical evaluations of deposited nanocrystalline NiO thin films via a Ni(II)–8-hydroxyquinolate complex by the static step-by-step soft surface reaction technique for optoelectronic applications

摘要

The static step-by-step soft surface reaction (SS-b-SSR) technique was implemented as an efficient soft chemical methodology for the synthesis of nanocrystalline NiO thin films. The target nanocrystalline NiO was produced upon thermal annealing of deposited thin films of the Ni(II)–8-hydroxyquinolate complex, Ni(II)–(8HQ)_2. The (SS-b-SSR) technique was also used to initially produce the Ni(II)–(8HQ)_2 complex with a first step deposition of 8HQ on a glass substrate, followed by a second soft reaction step with the Ni(II) ion. The assembled thin films of nanocrystalline Ni(II)–(8HQ)_2 and NiO were characterized by elemental analysis, FT-IR, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The results of XRD revealed that the diffraction peaks of NiO are well crystalline and corresponding to a face centered cubic crystal structure. The mean crystallite size (D) and dislocation density (d) were found to be 25 nm and 1.60 × 10~(-3) nm~(-2), respectively. The photoluminescence (PL) spectrum indicated a single broad peak, a near-band-edge emission in the ultraviolet region, and a relatively weak blue-green light (visible) emission at ~458.5 nm. The refractive index (n) and the absorption index (k) were calculated using spectrophotometric measurements of T(λ) and R(λ). The analysis of the spectral behavior of the absorption coefficient (α), in the absorption region revealed direct transitions and the energy gap was calculated as 3.47 eV. The temperature dependence of the resistivity ρ(T) and thermoelectric power S(T) were investigated. The photocurrent properties of the device under various illuminations were also explored and it was found that the reverse bias voltage was increased by increasing the photo-illumination intensity. The transient photocurrent results indicated that the photocurrent under illumination is higher than the dark current.