Numerical Analysis of Surface Force of Diamond-Like Carbon Surface Coated with Monolayer Lubricant Film

Abstract

Diamond-like carbon (DLC) is widely used as a hard, protective layer with a relatively low surface energy. In the head‒disk interface in magnetic disk drives, however, the DLC layer is coated with a monolayer perfluoropolyether lubricant with a high bond ratio to avoid DLC‒DLC contact and to secure head/disk wear reliability. In this study, we theoretically analyzed the effect of lubricant thickness and bond ratio on the adhesion force between the head‒disk interface (HDI) in a mono/submono-layer thickness regime. It was found that the adhesion force had the lowest sensitivity to lubricant thickness variations at a 0.85 bond ratio. In addition, the maximum adhesion force was minimized when the lubricant thickness was ~0.6 nm for the measured parameter values of the HDI. This suggests that the current lubricant thickness of 1.0–1.2 nm can be reduced to 0.6 nm, accompanied by a slight decrease in the adhesion force and a slight increase in the resistance against any variation in its thickness. This tribo-surface-modification concept can be applied to surface-modification coatings in other fields such as micro/nano-electromechanical systems. The compatibility of the theoretical surface energy function with experimental data indicates the validity and consistency of this theory.

Keywords

• surface force analysis
• rough surface adhesive contact
• asperity meniscus pressure
• van der waals pressure
• head-disk interface
• diamond-like carbon
• molecularly thin lubricant film
• bond ratio
• surface-modification coating