Synthesis of carbon coatings employing a plasma torch from an argon–acetylene gas mixture at reduced pressure

Amorphous hydrogenated carbon films (a-C:H) were formed on Si (1 1 1) wafers from an argon–acetylene gas mixture at a reduced pressure of 1000 Pa using a direct current (DC) plasma torch discharge. The Ar/C2H2 gas volume ratio varied from 1:1 to 8:1, the distance between plasma torch exit and the samples 0.04–0.095 m. The DC plasma torch technique allows the production of thick (∼90 μm) coatings at 0.3 μm/s growth rates. Raman spectra shape, D and G peak positions and the intensity ratio (ID/IG) show an increase of sp3 bond fraction with decreasing acetylene flow in argon plasma. Reflectance of the coatings deposited at Ar/C2H2=8:1 is high (∼97%) and slightly increases with increasing distance between samples and plasma torch exit.