Structural and optical characterizations of Ni (II) tetraphenyl porphyrin thin films

Abstract

Thermal evaporation technique was used to prepare thin films of 5,10,15,20-tetraphenyl-21H,23H-porphine nickel (II), NiTPP, onto glass and quartz substrates. The crystal structures and morphologies of all prepared NiTTP thin films were investigated at 298, 423 and 573 K by using X-ray diffraction, XRD, and scan electron microscopy, SEM, respectively. The lattice of all prepared NiTPP films was investigated as a monoclinic with space group P2/M. The surface topography of the prepared films showed granular particles of sizes 49.7, 64.7 and 107 nm. The annealed NiTPP films at 423 K have a spatial configuration of well-defined grains boundary with nanoporous nature and all annealed films at 573 K have higher aggregates and the porosity of the films was increased. Optical constants namely refractive index, n , and the absorption index, k , of NiTPP films have been estimated by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500 nm. The absorption spectra in the UV-vis spectrum were analyzed in terms of both molecular orbital and band theories. The obtained data of n and k were used to estimate the type of transitions and were found to be indirect transition for all films. The optical and fundamental gaps were decreased as the annealing temperature was increased. Some optical parameters namely molar extinction coefficient, e molar, oscillator strength, f , and electric dipole strength, q 2 , have been evaluated. According to the single oscillator model and Drude model, some related parameters such as oscillation energy, E o , the dispersion energy, E d , the optical dielectric constant, e ∞ , the lattice dielectric constant, e L , and the ratio of free carrier concentration to its effective mass, N/m ∗ , the third-order nonlinear susceptibility, χ (3) , and molar polarizability, α p , were estimated before and after annealing.