Coupled Effects of Surface Roughness and Accommodation Coefficient for Ultra-Thin Gas Film Lubrication

For modern magnetic disk drives, as the minimum flying height in the head-disk interface (HDI) is continuously reduced to about 1-2 nm, the surface roughness and the accommodation coefficient (AC) effects should be considered in addition to the gaseous rarefaction effect. However, only a few published papers had studied both the effects of these two parameters simultaneously. Based on the modified molecular gas film lubrication equation proposed for ultra-thin gas film lubrication, the coupled effects of the surface roughness, the AC, and the gaseous rarefaction in the HDIs are investigated for various groups of the surface roughness and the AC. Numerical results are presented and discussed to show the coupled effects on the pressure and the load carrying capacity of the film. Both the symmetrical and asymmetrical molecular interactions are studied and rational interpretations are given for the phenomena observed.