Hydrothermally derived co, Ni co-doped ZnO nanorods; structural, optical, and morphological study

Thin films of ZnO and Co, Ni co-doped ZnO nanorods were successfully synthesized on the silicon substrate (100) by the hydrothermal method. The grown thin films were annealed at 105 degrees C for 4.5 h and characterized by employing different analytical techniques to investigate the effects of co-doping on structural, morphological, and optical properties of ZnO nanorods. X-ray diffraction (XRD) analysis confirmed the successful substitution of dopants (Co and Ni) without altering the hexagonal wurtzite structure of ZnO. The crystallite size and microstrain of grown films were calculated by employing Scherer, W-H, and SSP methods. The unit cell volume and lattice parameters were increased for Co doping, moreover by increasing Ni concentration as a co-dopant these parameters were decreased. Crystallite size of ZnO, ZnCo, ZnCoNi3, ZnCoNi6 and ZnCoNi9 grown thin films were 73 nm, 42 nm, 71 nm, 60 nm, and 52 nm respectively. The Fourier transform infrared spectroscopy (FTIR) has shown the existence of characteristic vibrational bonds of Zn-O in all co-doped samples at 499.35 cm(-1), 561.25 cm(-1), 570.89 cm(-1), 565.10 cm(-1), and 553.53 cm(-1), respectively. SEM images show the surface morphology of grown thin films, which indicates that the diameter of nanorods is increased by increasing Ni contents. The UV-visible spectroscopy was employed to measure the energy bandgap (E-g) using Tauc's plot. The optical energy band gap was decreased (3.37-3.16) eV for all co-doped samples. The redshift in energy bandgap by Co and Ni co-doping is mainly due to the strong orbital coupling and generation of new energy states between the VB and CB. The other optical parameters including optical absorption coefficient (a), transmittance (T), skin depth, optical density (OD), extinction coefficient (k), refractive index (n), optical conductivity (sigma(opt)), and dielectric constants (epsilon(r), epsilon(i)) of the grown thin films were also discussed.