Optical constants of the as-prepared and annealed (Se80Te20)94Ag6/PMMA thin films

Thin films of (Se80Te20)94Ag6/PMMA have been deposited on glass substrate by thermal co-evaporation technique. Melt quenching approach has been adopted to prepared bulk (Se80Te20)94Ag6 chalcogenide glass. Glass transition temperature of bulk (Se80Te20)94Ag6 glass and poly (methyl methacrylate) (PMMA) polymer have been found out by differential scanning calorimetry (DSC) at a heating rate of 10 K/min. Thin films were annealed above glass transition temperatures of glass (332 K) and polymer (340 K) at two different temperatures 343 K and 365 K. The presence of different phases in annealed film was confirmed by X-ray diffraction studies. Transmission spectra of as-deposited and annealed films were obtained by Uv-Vis spectroscopy in the wavelength range of 350-900 nm. To analyze refractive index dispersion Wemple-Didomenico model have been used. Optical parameters viz refractive index (n), extinction coefficient (k), real and imaginary dielectric constants (ε′ and ε′′) and optical band gap (Eg) are calculated by using optical transmittance. The increasing behavior of the optical band gap with increase in annealing temperature is explained on the basis of density of state model.