Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C2H2 gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C2H2 ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C2H2 = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm−1 related with sp3 CH2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C2H2 = 8:1 and 0.06 m has the highest sp3 C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.