Effect of non-equilibrium synthesis conditions on structure and optical properties of amorphous carbon films

Amorphous carbon (a-C) thin films were synthesized by non-equilibrium method of ion-plasma sputtering of graphite target in Ar atmosphere at constant value of plasma current. Studies of the local structure of the carbon films were carried out using Raman spectroscopy method. Using normal distribution for Raman spectra decomposition it was revealed that at synthesis temperatures below 150 C a peak at about 1260 cm$^{-1}$ occurred, which is characteristic for phonon density of states with $sp^{3}$-hybridized bonds. In addition, it was shown the dependence of the optical bandgap on the sizes of $sp^{2}$-site nanostructures and correlation of it with the results of X-ray photoelectron spectroscopy (XPS) in the a-C films.