Tribochemistry in contact recording

Abstract

Even though the flying height is approaching molecular dimensions, it is expected to decrease as the areal recording density is increased. This study employs a new low-velocity test to obtain ultralow flying height with sustained intermittent asperity contacts and random seek accessing in a region near the middle diameter of the disk. Sensitive surface analytical tools are employed to follow tribochemical changes. Profiles are periodically measured across the disk surface using Fourier transform infrared spectroscopy for lubricant thickness and scanning-imaging micro-ellipsometry. Zdol lubricant is removed from the tested region through evaporation of low molecular weight scission fragments. The removal rate increased with increasing chemisorbed fraction and decreasing relative humidity. The increased removal rate is attributed to increases in the Zdol relaxation time. A longer relaxation time allows more time for bond dissociation following asperity contacts. Chemisorption sites in the tested region were occupied by chemisorbed scission fragments with a carboxylic acid end group. Amine and sodium salts of the carboxylic acid were detected on the tested regions of Zdol lubricated, and unlubricated, overcoats. The presence of tribochemically generated carboxylic acid groups on Zdol and overcoat carbon explain the increased water adsorption measured on the tested regions.