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

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 similar to 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.