Structural, absorption and dispersion characteristics of nanocrystalline copper tetraphenyl porphyrin thin films

Abstract

Thin films of tetraphenyl porphyrin (CuTPP) were prepared by thermal evaporation technique under vacuum. The surface morphology and crystalline structural characteristics of CuTPP were achieved by atomic force microscopy (AFM). The crystalline structure of CuTPP thin films was investigated by using X-ray diffraction. The average crystallite size, D, was calculated using the modified Scherrer's equation. Optical constants (refractive index, n, and absorption index, k) of CuTPP films were estimated by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500nm.The optical constants of CuTPP are independent of film thickness in the thickness range 400–1270nm. The dependence of absorption coefficient on the photon energy was determined and the analysis of the result showed that the optical transition in CuTPP films is allowed and indirect. The onset and optical energy gap for are 1.80 and 2.30eV, respectively. The UV–vis absorption spectrum was analyzed in terms of both molecular orbital and band theories. The optical dispersion parameters of CuTPP thin films such as oscillator energy, Eo, dispersion energy, Ed, the lattice dielectric constant, ɛL, the high frequency dielectric constant, ɛ∞, and the ratio of the free charge carrier concentration to the effective mass, N/m* were investigated. Moreover, third order nonlinear susceptibility, χ(3) of CuTPP films was also considered.