Adsorption Properties of an Ultrathin PFPE Lubricant With Ionic End-Groups for DLC Surfaces

Abstract

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules; the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.