Is 2 nm DLC coating enough to resist the nanowear of silicon

The ultrathin DLC coatings with thickness of 2 nm and 5 nm were deposited onto Si(100) substrate by the filtered cathodic arc technique. The nanowear tests were performed on DLC coatings and Si(100) substrate by diamond tip and SiO2 microspheric tips. The results indicated that the coatings could support an indentation with a peak contact pressure of 7 GPa. During scratch tests, the critical load corresponding to the generation of grooves on silicon substrate could be raised by 75%/125% after the deposition of DLC coating of 2 nm/5 nm in thickness. When the nanowear tests were conducted by a diamond tip, DLC coatings could effectively resist the mechanical wear and prevent the formation of hillock on silicon substrate. Moreover, since two DLC coatings present a close coverage on silicon substrate, they can largely resist the tribochemical wear of silicon substrate by SiO2 tip in humid air. Under a contact pressure of 1.3 GPa, the wear depth on 2 nm/5 nm DLC coating was only 0.42 nm/0.28 nm, which was less than 5% of that on silicon substrate. Finally, either in humid air or in vacuum, 2 nm DLC coating presented the excellent durability to protect the silicon substrate from wear damage. Therefore, although thicker DLC coating to some extent reveals better wear resistance, 2 nm DLC coating is enough to protect its substrate against nanowear.