Influence of heat treatment and gamma-rays irradiation on the structural and optical characterizations of nano-crystalline cobalt phthalocyanine thin films

Thin films of nano-crystalline cobalt phthalocyanine (CoPc) were prepared by thermal evaporation technique under high vacuum at room temperature and were identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The prepared films were divided into three groups for study: the first was the as deposited films, the second was heat treated under vacuum for I h at 630 K, and the third group was irradiated in gamma cell type Co-60 source in air at room temperature with total absorbed dose of 150 kGy. The optical properties for the three groups were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 200 to 2500 nm. The optical constants, refractive index, n, and absorption index, k, were calculated and found to be independent of film thickness in the measured film thickness range. The dispersion energy, E-d the oscillator energy. E-o and the high frequency dielectric constant, epsilon(infinity) of the three groups were obtained. The energy band model was applied and the types of the optical transitions responsible for optical absorption were found to be indirect allowed transition. The onset and optical energy gaps were calculated. Discussion of the obtained results and their comparison with the previously published data were also given. (C) 2008 Elsevier B.V. All rights reserved.