Optical properties of hydrogenated amorphous carbon thin films prepared by dc saddle field plasma-enhanced chemical vapor deposition

Hydrogenated amorphous carbon thin films were grown through dc saddle field plasma-enhanced chemical vapor deposition. All samples were grown in similar conditions, except that the chamber pressure and the substrate bias parameters were varied. The sample films were analyzed using Ultraviolet–Visible, Fourier Transform Infrared, and Raman spectroscopies. The Ultraviolet–Visible analysis was used in order to obtain the wavelength dependence of the index of refraction, the extinction coefficient, and the optical absorption coefficient. The index of refraction was found to increase as a function of the substrate bias voltage. Fourier Transform Infrared spectroscopic and Raman analyses were used in order to obtain the concentration of the sp2 carbon bonds in the films. This measurement helped us interpret the relation between the sp2 bond concentration and the optical absorption in the a-C:H thin films.