Influence of hydrogen gas flow ratio on the properties of silicon- and nitrogen-doped diamond-like carbon films by plasma-enhanced chemical vapor deposition

Abstract

We deposited silicon- and nitrogen-doped diamond-like carbon (Si–N–DLC) films by radio frequency (RF) plasma-enhanced chemical vapor deposition using H2 and Ar as dilution gases. We investigated the influence of the H2 flow ratio [H₂/(H₂ + Ar)] on the structure; chemical bonding; and mechanical, tribological, optical, and surface properties of the Si–N–DLC films. The optical bandgap increased from 1.88 eV to 2.06 eV with the H2 flow ratio, and it had a negative correlation with the sp2 CC bonding fraction in the films. When the H2 flow ratio increased from 0% to 100%, the critical load of the Si–N–DLC films increased by ~14% due to a reduction of ~26% in the internal stress of the films. As the H2 flow ratio increased, the friction coefficient and specific wear rate decreased by ~11% and ~35%, respectively, whereas the pure water contact angles of the film surfaces increased from 74.7° to 86.5°. The film surfaces had root mean square roughnesses (RMS) less than 0.2 nm. Therefore, the improvement in their tribological properties and the increase in their contact angles were probably due to the hydrogen termination of dangling bonds. The friction coefficient and wear rate of the Si–N–DLC film deposited at a H2 flow ratio of 0% (100%) changed little (increased) after annealing at 773 K.