Nonmetal–metal transition in carbon films embedded by nickel nanoparticles: absorption coefficients studies and Wemple–Didomenico dispersion parameters

Abstract

In this paper, the optical properties of carbon films embedded by Ni nanoparticles under four deposition processing using mosaic targets made of graphite and nickel with Ni surface areas from 1.78 to 4.64% with a special emphasis on the absorption edge were investigated. Resulting films with Ni surface areas 1.78, 3.21, 3.92 and 4.64% have approximately Ni atomic ratio of about 59.7, 86.5, 90 and 92.9 wt%, respectively. The optical reflectance and transmittance spectra in the wavelength range 300–2500 nm were used to compute the absorption coefficient. The optical dispersion parameters were calculated according to Wemple and Didomenico single oscillator model (WDD). The variation of complex optical conductivity σ with energy of films exhibit values for optical gaps from about 0.8 to 4 eV which correspod to the fundamental indirect and direct gap which are about 0.3 to 3.7 eV. It can be seen that at Ni surface areas 3.92% the films have minimum indirect optical band gap about 0.2 eV. Due to high Ni content of films at 4.64%, they have maximum disordered. It can be seen that these optical properties were in consistent with room temperature electrical resistivity of films.