Lubricant distribution on hard disk surfaces: Effect of humidity and terminal group reactivity

We report studies of the effect of humidity and the chemical nature of the molecular end groups on the structure and spatial distribution of perfluorinated lubricants on hard carbon substrates. The studies are performed with a noncontact atomic force microscopy (AFM) technique that is capable of providing nanometer scale images of soft and liquid surfaces. Our results indicate that reactive end groups enhance the wear resistivity of the lubricants. ZDOL and ZDLAC. which have CH2OH and COOH end groups, respectively, could not be displaced by a sharp tip (approximate to 500 Angstrom radius) under a load of 1 x 10(-8) N while, under the same conditions, Z03, which has CF3 groups at both ends, and Demnum SA, which has a CF3 group and a CH2OH group at each end, could be easily displaced. We found that humidity enhances the mobility of the lubricants. Humidity also causes dramatic changes in the state of aggregation of ZDIAC and Demnum SA. The binding of these lubricants to the surface becomes unstable, and upon contact with the tip, they dewet the surface to form solid-like or liquid-like agglomerates.