Formation of lubricant "moguls" at the head/disk interface

In a typical head/disk interface of a rigid disk drive, the motion and redistribution of a 14 Angstrom thick lubricant film on the disk under a flying slider is analyzed with an optical surface analyzer. At short times (similar to seconds to a few minutes), the film is rearranged in an isotropic manner, creating a pattern of "moguls"(1) of similar to 100 mum in lateral size and a few angstroms in height. A strong correlation is demonstrated between the resulting distribution of the lubricant film and the underlying substrate topography. Surprisingly, lubricant becomes thicker on the peaks of the micro-waviness, and thinner in the valleys. Possible mechanisms for this unexpected behavior will be discussed, as well as its tribological implications. At longer times, the lubricant film is pushed away from underneath the slider, creating the previously reported circumferentially depleted tracks beneath the slider rails. In the timeframe of our experiment, no significant net lubricant loss was observed.