AVS2001 Session MR+MI+AS+SE-WeM: Magnetic Recording: Tribology & Integration

Wednesday, October 31, 2001 8:20 AM in Room 110

Wednesday Morning

Start	Invited?	Item
8:20 AM	Invited	MR+MI+AS+SE-WeM-1 Nanotribology of Simple and Complex Fluids at Aqueous Interfaces¹ S. Granick (University of Illinois, Urbana) Oil and lubrication are so synonymous that it is easy to discount the importance of aqueous-based lubrication -- not least in our own bodies, wich are full of surfaces in sliding contact. This talk will present recent studies of (a) the hydrophobic effect when surfaces are in relative motion, (b) modifying the boundary conditions of fluid flow, from no-slip to slip, and (c) ongoing attempts to watch single molecules under confinement. These issues of water in intimate contact with solid surfaces point the way to possible new strategies for energy-saving during fluid transport and have relevance to filtration, colloidal dynamics, and microfluidic devices.² ¹Work performed with Yingxi Zhu, John Jiang Zhao, Ashish Mukhopadhyay, and Hyungjung Lee ²Work supported by the National Science Foundation and by the U.S. Dept. of Energy, Division of Materials Sciences under Award Number DEFG9645439 through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign.
9:00 AM	Invited	MR+MI+AS+SE-WeM-3 The Ever Changing Disk Drive Environment: Can Filter Technology Keep Pace? A.J. Dallas, J. Joriman, L. Ding, D. Arends, S.B. Miller, III (Donaldson Co., Inc.) The cleanliness of the internal environment of a disk drive is critical to its reliability, performance, and longevity. As a result, we have seen particulate and chemical filters become commonplace in the design of disk drives of all types and sizes. The incorporation of chemical filters into the disk drive environment has proven to be an effective means of controlling the humidity and contamination level. Generally, silica gel is used to control the humidity level, whereas carbon and chemically-treated activated carbon are used to minimize organic and acid gas contamination levels. As disk drive technology moves into the future, chemical filtration is expected to play an ever-increasing role in the overall drive’s performance. How will filter technology change to meet these requirements? This presentation will provide an overview of chemical filtration, filter design, and the current technology. In addition, we intend to focus on: 1) test methods designed to evaluate and identify internal drive contamination; 2) test methods to evaluate materials used in chemical filters; 3) chemical filter performance; 4) extending test methods and chemical filters to low contaminant concentrations; 5) targeting specific chemical species with chemical filters; 6) humidity control; and 7) the future of chemical filtration.
9:40 AM		MR+MI+AS+SE-WeM-5 Effect of Humidity on Lubricated Carbon Overcoats N. Shukla (Seagate Technology); A.J. Gellman (Carnegie Mellon University); R. Veerdonk, X. Ma, J. Gui (Seagate Technology) A quartz crystal microbalance has been used to measure contaminant adsorption on magnetic data storage media under controlled conditions. This apparatus has been developed to make measurements of contaminant adsorption at the level of 0.1 ng/cm2 with a time resolution on the order of seconds. Initially we have measured humidity uptake on amorphous carbon overcoats coated with lubricants. We have been able to estimate the amount of water adsorbed on lubricated carbon overcoats at room temperature and at moderate humidity levels (~ 25% RH ). Adsorption and desorption is fast indicating that equilibrium with ambient humidity is reached on timescales of minutes, much faster than the timescales for fluctuations in ambient humidity. We have also studied water adsorption on different types of lubricants deposited at different thicknesses. Interestingly, the amount of water adsorbed on lubricated and unlubricated carbon overcoats is similar suggesting that water adsorption is primarily dependent on the properties of the carbon. We have studied the bonding of water on carbon overcoats and also studied bonding of lubricants on carbon overcoats.
10:00 AM	Invited	MR+MI+AS+SE-WeM-6 Tribological Implications of the Confinement in PFPE Boundary Lubricant Films G.W. Tyndall (IBM Almaden Research Center) Perfluoropolyether (PFPE) films of nominally 1.0 - 2.5 nm are commonly utilized by the magnetic recording industry to lubricate the head/disk interface in hard-disk drives. In this film thickness regime, the surface of the magnetic recording disk will "energetically confine" the lubricant. This confinement is manifested in physical and mechanical properties of the PFPE lubricant that differ substantially from those of the bulk fluid. In the current talk, the experimental evidence for confinement in the PFPE/carbon system will be reviewed, and the implications to the tribology of the head-disk interface discussed.
10:40 AM		MR+MI+AS+SE-WeM-8 Pushing Perfluoropolyether Molecules Across Surfaces Using Air Shear M.A. Scarpulla, C.M. Mate (IBM Almaden Research Center) We have investigated the surface mobility of thin films (<5 nm thick)of linear chain perfluoropolyether polymers on silicon and CN_x surfaces while subjecting them to air shear stresses. These experiments are elucidating the nature of viscosity in molecularly thin films of lubricants important for magnetic recording. For polymer chains with neutral CF₃ end groups, we find that the effective viscosity is close to the bulk viscosity even at sub-monolayer coverage. The addition of alcohol end groups to the polymer chains acts to anchor the first layer of molecules to a surface, greatly increasing the effective viscosity relative to the bulk. For the second layer, the alcohol-terminated polymers exhibit effective viscosities near their bulk viscosity, while dewetting is observed in thicker films.
11:00 AM		MR+MI+AS+SE-WeM-9 Kinetics and Energetics of the Desorption of Polyether Lubricants K.R. Paserba, N. Prashanth, A.J. Gellman (Carnegie Mellon University) Desorption or evaporation is one of the mechanisms for loss of perfluoropolyalkylether (PFPE) lubricants from the surfaces of data storage media. One approach to minimizing PFPE loss by desorption is the use of lubricants with increasing molecular weight or increasing average chain length. In order to understand the effects of chain length on the lubricant evaporation kinetics we have studied the desorption kinetics of monolayer films of oligomeric ethers with varying chain length adsorbed on the surface of graphite. This study has used monodispersed samples of oligomeric ethyleneglycol dimethylethers, CH3O(CH2CH2O)mCH3, and oligomeric ethyleneglycols, HO(CH2CH2O)mH, as models for the perfluoropolyalkylether lubricants Fomblin Z and Fomblin Zdol. Their adsorption and desorption from the surface of graphite has been measured as a function of chain length, M = 3m+3, or molecular weight by using thermally programmed desorption methods in ultra-high vacuum. The results of these measurements show the surprising result that the desorption energies, ΔE_des, are non-linear in the chain length. What is most interesting is that the desorption energies can be expressed by the power law expression ΔE_des = a + b Mγ with γ ~ 0.5. A model has been proposed for the desorption mechanism of such oligomeric lubricants from surfaces which can quantitatively reproduce the dependence of the desorption energies on chain length. The origin of the non-linearity is the conformational isomerism of the oligomers as they desorb from the surface. We will discuss the implications of these results on the desorption of oligomeric PFPE lubricants from the surfaces of magnetic data storage media.
11:20 AM	Invited	MR+MI+AS+SE-WeM-10 Ramp Materials Challenges with Load/Unload Technology B. Hiller (Maxtor Corporation) Dynamic ramp load/unload technology (or short: ramp load) is replacing contact start/stop technology in hard disk drives. Key reasons are superior shock performance and improved reliability. Ramp load adds a new part to the drive (the ramp) and a new interface (between ramp and suspension lift tab). Proper selection of the ramp material and specification of the ramp/tab interface are key to drive reliability. This talk will address the important issues and will present state-of-the art solutions, as well as an outlook on future developments. As with all in-drive materials, minimal chemical outgassing is required. After that, the most important criteria for the ramp material are low friction and wear, and adequate mechanical stability. Out of a large number of candidate materials, only two materials are primarily used in today's products: Teflon-filled liquid crystal polymer (LCP) and acetal homopolymer (POM). These two materials optimize the materials issues in different ways and have their unique application range. LCP excels at mechanical stability, while POM exhibits superior tribology. Surface roughness affects friction and wear and needs to be controlled for both sliding partners, but control is more crucial for the much harder stainless steel suspension lift tab. Current products employ both spherical and cylindrical lift tab shapes. The relative merits of both approaches will be discussed. Tribological and mechanical properties are so multi-faceted that a large portion of this talk will be devoted to presenting measurement techniques and key results. Other important properties such as electrostatic charging and cost will also be addressed.