Roughness of Thin Perfluoropolyether Lubricant Films: Influence on Disk Drive Technology

In disk drive technology, lubricant thickness and roughness are important, but often overlooked, contributors to slider–disk spacing. In this paper, we use X-ray reflectivity to measure the thickness and lubricant–air roughness of a perfluoropolyether lubricant (Fomblin Zdol) on silicon wafers and carbon overcoats. For Zdol on smooth silicon, the roughness increases with increasing lubricant thickness consistent with capillary wave roughening. For Zdol on the rougher surface of amorphous hydrogenated carbon, the lubricant smoothes to a value limited by the capillary wave roughening. We show that the lubricant density above the surface does not reach the density of air until approximately 3 away from the average lubricant thickness. This lubricant–air interface width contributes substantially to current and future slider–disk spacings.