Morphological and optical properties induced by ultraviolet radiation of a thiadiazole derivative

Abstract

CThB amorphous thin films were synthesized by thermal evaporation technique. The amorphous structure of thin films was investigated by X-ray diffraction technique (XRD). The surface morphology of CThB thin films were analyzed by atomic force microscopy (AFM). The optical constants such as refractive index, n, the absorption index, k, and the absorption coefficient, α for as-deposited and UV—irradiated thin films were determined by spectrophotometric measurements of transmittance (T) and reflectance (R) at normal light incidence of wavelength in range (200–2500) nm. The absorption spectrum of CThB shows two absorption bands in UV region of spectra ascribed to n → π^* orbital molecular transition. The results denote that UV—irradiation has no effect on the type of electron transition. Optical measurement of CThB as—deposited and UV- irradiated thin films showed normal dispersion of refractive index, n at λ > 750 nm and anomalous dispersion at λ < 750 nm. Some of dispersion parameters such as the high-frequency dielectric constant (ε_∞), the lattice dielectric constant (ε_L), the dispersion energy (E_d), the oscillator energy (E_o) and ratio of the free charge carrier concentrate to effective mass (N/m*) were calculated. The optical functions as the real (ε₁), imaginary (ε₂) parts of the dielectric constant were estimated and their response to UV—irradiation was discussed. The effect of UV—irradiation on optical energy gap ${E}_{g}^{\text{ind}}$ with respect of exposure time was estimated. The value of the band gap was found to be 2.5 eV. The width of the localized states was found to be 0.3 eV and was increased upon irradiation.