Structural and optical studies of thermally evaporated CoPc thin films

Abstract

The structure of the thermally evaporated cobalt phthalocyanine (CoPc) thin film in the β-form is investigated, and shows a single strong peak indicating preferential orientation in the (1 0 0) direction. Some structural parameters such as crystallite grain size, dislocation density and the number of crystallites per unit surface area are determined. The spectral parameters are determined by applying the electronic orbital transitions. But the optical parameters are deduced using band-model consideration for thin films of Pc. The spectral and optical parameters have also been investigated by using the spectrophotometric measurements of transmittance and reflectance in the wavelength range 200– 2500 nm . The absorption spectra recorded in the UV–VIS region show two absorption bands of phthalocyanine (Pc) molecule, namely the Soret band (B) and the Q-band. The Q-band shows its characteristic splitting (Davydov splitting) with ΔQ=0.23 eV . Some of the important spectral parameters, namely optical absorption coefficient ( α), molar extinction coefficient ( ε molar), oscillator strength ( f), electric dipole strength ( q 2) and absorption half bandwidth (Δ λ) of the principle optical transitions have been evaluated. The fundamental and the onset indirect energy gaps could be estimated as 2.90 + or − 0.05 and 1.51 eV , respectively. The refractive index showed an anomalous dispersion in the absorption region as well as normal dispersion in the transparent region. From analysis of dispersion curves, the dielectric constants, the dispersion parameters and the molar polarizability were obtained. All the above parameters were obtained for films as deposited and as annealed. No remarkable annealing effect on many parameters was observed.