Structure of Molecularly -Thin Perfluoropolyether Films on Amorphous Carbon Surfaces
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ABSTRACT Surface energies of molecularly-thin, perfluoropolyether (PFPE)-lubricated, amorphous carbon surfaces are presented as a function of the applied PFPE structure and thickness. A framework is developed to aid in the interpretation of the surface energy data. Information regarding the structure of these PFPE films adsorbed on CHx at the monolayer thickness levels is elucidated. Evidence for ordering in these polymer films is presented and interpreted to result from a combination of both, lateral cohesive interactions within the plane of the monolayer, and adhesive interactions between the PFPE monolayer and the underlying substrate.
INTRODUCTION The hard-disk drive industry is a highly competitive $50B/year industry. Timely introduction of new products with ever-increasing magnetic recording densities is required of successful companies in this industry sector. The historic 60% compound yearly growth rate in storage densities has placed unprecedented demand on many of the materials used in the drive. In the past few years, a number of advances have been made in the magnetic films employed in both the magnetic recording heads and the magnetic recording disks. In the case of the magnetic recording head, the substituition of magneto-resitstive (MR) heads for thin-film inductive heads, and more recently the replacement of MR heads with giant magneto-resistive (GMR) heads have dramatically increased the detection sensitivity of the sensor, and hence have led to subtantial increases in the storage density. In the case of the magnetic recording media (disk), grain size reduction requirements coupled with media noise considerations, have led to the development of quartenary alloys to replace the traditional temary alloys. In addition to advances in the magnetic films, increased recording densities can be achieved via decreasing the physical separation between the active elements. Decreasing the fly height of the magnetic recording head relative to the magnetic recording disk however, induces more frequent mechanical contact between these two surfaces, which places more stringent demands on the tribological properties of the protective, wear-resistent films employed at the head-disk interface (HDI). Future increases in magnetic recording densities will therefore require an increased focus on the materials employed at the HDI in addition to continued advancement in the magnetic materials. The magnetic recording industry universally employs a hard, amorphous-carbon overcoat to protect the magnetic film of the disk. A similar carbon overcoat is typically used on the magnetic recording head. Perfluoropolyether (PFPE) films are then topically applied to the carbon overcoat of the disk to provide lubrication during head-disk contacts. In current hard-disk drives, nominally 100M of amorphous carbon is used on both the head and the disk, and sub-monolayer PFPE films are used as lubricants. The materials utilized at the HDI are typically evaluated mechanically either on a component test stand or within the disk-drive environm
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