Structural, optical and dispersion energy parameters of nickel oxide nanocrystalline thin films prepared by electron beam deposition technique

Abstract

In the present paper, we report on the structure and optical properties of non-annealed nickel oxides (NiO) nanocrystalline semiconductor thin films synthesized by electron beam deposition technique. The structure parameters of the as-deposited NiO nanocrystalline thin films are extracted from the X-ray powder diffraction (XRD) spectra and shows that the as-deposited films crystallize in the form of cubic NaCl structure with average lattice constant equal to 4.1797 Å and average lattice volume 73.018 (Å)3. In addition, the crystallite size (D) is found to increase from 15 nm to 24 nm with increasing film thickness from 151 nm to 343 nm. In a wide wavelength range, the optical parameters (absorption coefficient, refractive index and refractive index dispersion) of the nanocrystalline NiO thin films have been calculated from transmission and reflection spectra. The variation of the factors (αhν)2 and (αhν)0.5 as a function of photon energy identifying the optical transitions as direct transition with energy Egdir≈ 3.849 eV and indirect transition with energy Egindir≈ 2.924 eV and phonon energy of order 212 meV, respectively. In the same wavelength range, the variation of the refractive index show normal dispersion behavior with single oscillator model Eo and Ed parameters obtained as 3.082 eV and 10.47 eV, respectively. The coordination number of the NiO nanocrystalline thin film is identified as 3.36. In addition, the lattice oscillator strength El, lattice dielectric constant εl, ratio of free carrier density to free carrier effective mass (N/m∗) and plasma frequency (ωp) are extracted as 0.31 eV, 5.408, 1.043 × 1047 g−1 cm−3, 5.492 × 10+14 s−1, respectively. Also, the molar and volume refractions Rm, Vm and molar polarizability αm, are also calculated and found to be 3.082 cm3/mol, 11.20 cm3/mol, 2.49(A∘)3, respectively. Finally, the Urbach energy Eu is also calculated and found to be 0.38 eV.