Understanding The Effects Of Nano-scale Surface Texture And Environment On Diamond-like Carbon

Open Access
Author:
Al-azizi, Ala' Ahmad
Graduate Program:
Chemical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 15, 2013
Committee Members:
  • Seong Han Kim, Thesis Advisor
Keywords:
  • DLC
  • surface
  • friction
  • texture
  • water
  • nano
Abstract:
The effects of nano-scale surface texture and the environment on the tribological and mechanical properties of diamond-like carbon (DLC) are investigated. Nano-textured DLC was produced by coating DLC film on a textured silicon substrate. In this study it was found that the nano-texture has a different lubrication mechanism than micro-scale texture. The nano-confinement-induced solidification of a liquid lubricant plays a critical role in reducing the friction coefficient when the nano-texture deforms under the contact pressure. The lubricant molecules sandwiched between the high points of the textured DLC and the counter-surface show long-range structuring and solidification upon confinement. However, the lubricant molecules entrapped in the depressed regions of the nano-textured DLC would not solidify, which can contribute to the reduction of the interfacial friction. The nano-texture effect is not limited to macro-scale friction tests; it was also observed in nanoindentation measurements where the probe depth is only about 10% of the DLC film thickness. The presence of sub-surface polystyrene spheres seems to change the DLC deformation pattern under pressure which reduces plastic deformation and residual indent size. The contact geometry and the presence of the polystyrene spheres both significantly affect the measured local hardness and elastic modulus of DLC, as well as the residual indents dimensions in single-asperity indentation measurements. The presence of water in the environment also has a profound effect on the friction and wear behavior of DLC. The effects of bulk liquid water were quite different from those of the water layers adsorbed from the vapor phase. Moreover, the structure and the amount of transfer film that forms on the counter surface depends on the amount of adsorbed water vapor present on the DLC surface, which is governed by the relative humidity.