Absorption edge and the refractive index dispersion of carbon-nickel composite films at different annealing temperatures

In this paper, the optical properties of carbon-nickel films annealed at different temperatures 300, 500, 800 and 1000 degrees C, with a special emphasis on the absorption edge, were investigated. The optical transmittance spectra in the wavelength range 300-1000 nm were used to compute the absorption coefficient. The optical dispersion parameters were calculated according to Wemple and DiDomenico (WDD) single-oscillator model. Photoluminescence (PL) measurements of carbon-nickel films exhibit two main peaks at about 2.5 and 3.3 eV which correspond to the fundamental indirect and direct gap, respectively. The field emission scanning electron microscopy (FESEM) showed that the absorption edge in the films was controlled by the nanoparticle size. The films annealed at 500 degrees C have minimum indirect optical band gap and maximum disorder.