Structural and optoelectrical properties of nanostructured LiNiO2 thin films grown by spray pyrolysis technique

摘要

LiNiO2 thin films of different thicknesses (200-354 nm) have been synthesized using conventional pyrolysis technique. Systematic investigations of the structure, morphology, optical, and optoelectrical properties have been made using X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, High-resolution scanning electron microscopy (HR-SEM), and spectrophotometric analysis. XRD patterns of the as-synthesized LiNiO2 films have revealed the polycrystalline nature of films under study with the rhombohedral crystal structure. HR-SEM micrographs have shown an evolution in films morphology from a rugged to a smooth surface with the increase in the film thickness. The change in morphology has been interpreted to the orientation and/or crystalline phase. Remarkable changes in the crystalline and surface properties of the films have been noticed with increasing film thickness. The optical constants of the studied films have been extracted from both transmittance and reflectance spectra. The films band gap was found to decrease with the increase of film thickness. The dispersion of the refractive index has been analyzed in the view of Wemple-DiDomenico model which enable the determination of linear and nonlinear optical parameters. Among the investigated films, the 354 nm film demonstrated the highest nonlinear optical parameters. This finding could shed lights of the possibility of using LiNiO2 in nonlinear devices. In addition, the real and imaginary parts of the dielectric constants have been utilized to determine various optoelectrical parameters such as the dissipation factor tan delta, relaxation time tau, the optical carrier concentration N-opt, optical mobility mu(opt), optical resistivity rho(opt), plasma frequency omega(p), and damping frequency omega(d). Good correlations have been established between the optical and optoelectrical parameters of the investigated films. (C) 2017 Elsevier B. V. All rights reserved.