Tailoring durability and tribological stability of PECVD-derived diamond-like carbon films through nitrogen doping .

Abstract

Structural integrity (SI), durability, and tribological stability (TS) of diamond-like carbon (DLC) films deposited on silicon substrates were tailored through nitrogen doping during deposition via radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). This approach specifically addresses the challenges of poor adhesion, short lifetime, surface irregularities, and limited wear resistance encountered by DLC coatings in dry sliding environments. Nitrogen flow rates ranging from 0 to 10 sccm were introduced during deposition to modulate bonding structure and surface morphology. At 10 sccm, the nitrogen-doped DLC (N-DLC) films exhibited a uniform, droplet-free surface and suppressed voids achieving 42 % reduction in maximum surface height (Sz), reaching 27 nm and stable average roughness (Ra) of 1 nm. The deposition rate increased significantly from 0.5 to 13 nm/min, resulting in film thicknesses up to 2.3 μm due to enhanced adatom surface mobility. XPS analysis indicated a reduction in sp3 content from 43 % to 28 %, along with an increase in the ID/IG ratio, reflecting a shift toward graphitic sp2 bonding associated with improved self-lubricating behaviour. Although hardness decreased from 28 to 21 GPa, the adhesion strength improved by 73 % from 30 N to 52 N due to interfacial stress relaxation and formation of a silicon carbide interlayer. Under dry sliding conditions, the N-DLC coatings demonstrated negligible wear and ultra-low friction performance with ultra-low coefficient of friction of 0.05. These results demonstrate that N-doping effectively tailors bonding structures and interfacial properties, enhancing N-DLC coatings for MEMS and dry-contact applications