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Lubricant reflow for 10 Å Z-Tetraol film is characterized for heat-assisted magnetic recording by numerical simulation using the experimentally determined thickness-dependent diffusion equation. The competition between laser-induced lubricant depletion (troughs) and subsequent healing by reflow is investigated as a function of lubricant depletion rate, trough width, trough depth, and duty cycle (reflow time between successive laser exposures). The simulations include 1, 5, 9 and 13 adjacent troughs. Trough width of 50 nm with an edge-to-edge separation distance of 50 nm and laser depletion rates of 1.0, 0.1 and 0.001 Å/cycle are simulated. Reflow kinetics on 13 troughs with a trough width of 20 nm and an edge-to-edge separation distance of 20 nm is also included to probe the effects in the limit of very small laser spots. Duty cycles of 10 and 100 millisec are used in the simulations. The results of the numerical simulations indicate that trough recovery by reflow increases with increasing duty cycle or decreasing number of adjacent troughs, trough separation distance and laser depletion rate. Conclusions based upon single trough studies are misleading for HAMR interfaces.

Lubricant reflow for Z-Tetraol is characterized for heat-assisted magnetic recording (HAMR). The thickness-dependent diffusion constant, D(h), is determined from flow experiments for submonolayer Z-Tetraol films between 2.5 and 13 Å. Fickian diffusion using experimental D(h) values are used to numerically simulate lubricant reflow into HAMR laser-depleted troughs as a function of trough number, trough depth, trough distance and trough width. Reflow is computed to be slower for multiple, wider and deeper troughs. Reflow kinetics as a function of trough separation distance is complicated by adjacent trough interactions. Two major kinetic regimes are identified. Multiple troughs that have not coalesced recover more quickly. Once multiple troughs coalesce into a single larger trough, reflow kinetics is drastically slowed. The crossover time between the two kinetic regimes is computed to be approximately 400 millisec for the system under investigation here, but will be a strong function of trough number, width, depth and separation distances. The simulation of multiple troughs provides significant insight into HAMR conditions. Single trough lubricant studies may be misleading for HAMR systems.

Z-dol and Z-tetraol represent most often used disk lubricants. So that we would be better able to design lubricants of higher thermal stability (for Heat-Assisted-Magnetic-Recording application), detailed analysis of thermally induced oxidation processes of Z-dol and Z-tetraol were performed. Samples were heated in a thin-film configuration where facile infusion of oxygen occurred and were examined by F-19 and C-13 NMR. Z-dol was found to be stable in the 150 ∼ 200 °C temperature range. In the same temperature range Z-tetraol was found to undergo either (1) the well known step-wise oxidation of primary alcohol (alcohol → aldehyde → acid) or (2) direct conversion to Z-dol. The latter process is initiated by a base-catalyzed step whereby the end-group Z-O-CF2-CH2-O-CH2-CH(-OH)-CH2-OH converts to an aldehyde, Z-O-CF2-CH2-O-CH2-CH( = O), and CH3OH. Z-dol results upon oxidation of the aldehyde yielding Z-O-CF2-CH2-OH, CH2 = O and CO2. It was found that substitution of the terminal OH with a phenoxy unit suppressed these decomposition processes. Z-tetraol lubricant molecular chains that became bound to the carbon overcoat at their termini are also protected from these oxidation processes. Thus for HAMR application, a combination of lubricants bonded to the carbon overcoat at their termini and mobile lubricants possessing phenoxy groups at their termini may be the best possible system based on perfluoropolyether lubricants.

High temperature (hot) and high humidity (wet) effects on perfluoropolyether lubricants, Z-dol and Z-tetraol, were investigated using the high speed spin-tester. The study has shown that: (1) higher humidity accelerates the lubricant spin-off on the disk surface, (2) in the case of Z-tetraol, oxidative reaction occurs under the hot-dry condition, but not under the hot-wet condition, (3) aforementioned phenomenon occurs only when the mobile fraction is present, and (4) the oxidation occurs the more strongly, the closer the location is to the spindle shaft. An NMR analysis of bulk materials heated in 150 oC revealed that the oxidative chemical changes are confined within the end-groups of Z-tetraol. No change was observed from bulk Z-dol heated similarly.