Characterization of thorium dioxide thin films prepared by the spray pyrolysis technique

摘要

Thorium dioxide (ThO_2) thin films were deposited by the spray pyrolysis technique onto a glass substrate maintained in the temperature range 100-350 deg C by using thorium nitrate as a starting solution. Structural, morphological, optical and electrical properties have been investigated. The results of FTIR showed that thorium nitrate is completely decomposed to ThO_2 at 350 deg C, via two unstable intermediates. XRD patterns showed that the films deposited at T_s < 350 deg C were amorphous, whereas those deposited at higher temperatures crystallized in the cubic structure with a preferential orientation along the (111) direction. The film growth was investigated experimentally by atomic force microscopy (AFM). The dark resistivity was of the order of l0~6 OMEGA cm. The activation energy was found to be 0.81 eV. The optical parameters such as refractive index, absorption coefficient, energy gap width have also been determined. The energy of the effective dispersion oscillator and the dispersion energy which measures the average strength of interband optical transitions were found to be 6.62 and 3.04 eV, respectively, and the dielectric constant, epsilon_alpha, was found to be 3.17. The free-carrier concentration N_(opt) have also been determined.