Structural, optical and dispersion properties of 5,10,15,20-tetraphenyl-21H,23H-porphyrin zinc thin films

The thin films of 5,10,15,20-tetraphenyl-21H,23H-porphyrin zinc, ZnTPP, were successfully prepared by the thermal evaporation technique. The structure formation and optical properties of ZnTPP thin films were studied. The surface morphology and structural characteristics of ZnTPP thin films were analyzed by atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques, respectively. The optical constants of ZnTPP films were measured by spectrophotometer measurements of the transmittance and reflectance at a normal incidence of light in the spectral wavelength range from 200 to 2500 nm. The absorption spectrum of ZnTPP films showed four absorption bands, namely, the Q, B, N, and M bands. Anomalous dispersion was observed in the absorption region and normal dispersion occurred in the transparent region of the spectrum. We adopted the multi-oscillator and the single-oscillator models to interpret the results of anomalous and normal dispersion characteristics, respectively. The energy band gap of ZnTPP films was measured and the type of electron transition was determined to be the indirect allowed transition. The annealing process had an obvious effect on the morphology, structure, optical constants, and spectral dispersion parameters of ZnTPP thin films.