Studying the effects of plasma produced species on the optical characteristics and bonding structure of diamond-like carbon films deposited by direct current unbalanced magnetron sputtering

In the present study, the influence of target power and plasma produced species on optical, structural and morphological properties of diamond-like carbon thin films deposited by direct current unbalanced magnetron sputtering is investigated. Raman spectroscopy and spectroscopic ellipsometry are used to study the structural properties and optical characteristics, respectively. Additionally, optical spectroscopy is used to measure the optical band gap of the films and investigate the produced active species in the plasma. Optical emission spectroscopy of the plasma shows that increasing the target power from 60 W to 120 W, increases the hydrogen containing species in the plasma which was due to the water vapor remained in the vacuum chamber. Surface topography of the films illustrates that the surface roughness of the films decreases slightly which leads to the smoother surfaces. Raman spectroscopy shows that I D /I G ratio decreases and the G peak position shifts toward lower wavenumber. Indirect optical band gap also increases from 1.77 eV to 2.18 eV. Results of spectroscopic ellipsometry measurements illustrate that the refractive index decreases from 2.01 to 1.67 at 550 nm and the spectrum of the extinction coefficient decreases as well. These results indicate that increasing the sputtering power, increases the sp 3 C–]H bonding more than C–]C bonding in the matrix of the film