Argon flow effect on the properties and composition of diamond-like carbon films grown by plasma-enhanced chemical vapor deposition

Abstract

Diamond-like carbon (DLC) films were synthesized on single-crystal silicon and glass substrates by plasma-enhanced chemical vapor deposition at varying argon flow in the methane/argon plasma-forming mixture. The resulting DLC films were studied by energy-dispersive spectroscopy, scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, spectroscopic ellipsometry, Raman and ultraviolet-visible spectroscopy. It was found that the thickness of the DLC films decreases with increasing argon flow while the argon content increases throughout the entire volume of the films. The synthesized films were characterized by a refractive index of 2.16 and an extinction coefficient of 0.195 over the entire studied range of argon flow. At the same time, increasing the argon flow resulted in a decrease in the band gap from 1.19 to 1.14 eV and a decrease in the hydrogen concentration from 28.5 to 28 at. % in the coating material. The synthesized films were classified as amorphous hydrogenated diamond-like carbon films. Furthermore, calculations revealed that the increase in argon flow was accompanied by a decrease in the proportion of sp³-hybridized carbon atoms from 46.4 to 45.5 % and an increase of sp² cluster size from 0.79 to 0.81 nm. The most probable reason for this could be the introduction of high-energy argon ions into the coating material, facilitating the transition of subsurface sp³-hybridized carbon atoms to sp²-hybridized ones during the relaxation process.