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ABSTRACT: SUMMARYA (001) surface of molybdenum, covered by one monolayer of sulphur was prepared in UHV and characterized by LEED, Auger and XPS. This surface was found to be stable in air for periods of several days. STM images of the surface, obtained in air in the topographic and local barrier height modes, revealed the atomic arrangement of sulphur atoms in domains with 1×2 and 2×1 periodicities. Boundaries between domains, adsorbate and substrate defect structures and crystallites formed during the initial oxidation of the Mo substrate were observed.
Journal of Microscopy 08/2011; 152(2):427 - 439. · 1.63 Impact Factor
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ABSTRACT: This paper demonstrates that electrochemical impedance spectroscopy combined with atomic force microscopy analysis can successfully characterize the coverage ability of an overcoat on perpendicular magnetic recording media. Rougher media, brought about by lower surface energy oxide segregants, can adversely impact the overcoat integrity. The role of the capping layer, and its ability to somewhat planarize the overall structure, is also discussed.
IEEE Transactions on Magnetics 02/2010; · 1.36 Impact Factor
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ABSTRACT: In a modern disk drive, the total slider-to-disk distance, or magnetic spacing, needs to scale with the size of the recorded bit, and nowadays, it amounts to a mere 10 nm or less. As disk lubricant often transfers to some extent to the slider surface, it can potentially increase the magnetic spacing. Therefore, it is important to quantify the thickness and flow dynamics of these molecularly thin films on the slider surface. In this paper, modeling, as well as experimental data, is shown that demonstrate the effect on recording performance of a subnanometer thin lubricant layer on the slider. Cleanup by air shear can be predicted reasonably well using the shear map calculated from an air-bearing solver, and reflow by surface diffusion highlights the importance of controlling lubricant transfer from the disk to the slider.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
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ABSTRACT: This paper reviews the present state of understanding of lubricant-slider interactions in a rigid disk drive. As slider flying heights are rapidly approaching the intrinsic limit of a disk topography (1-3 nm), it has become apparent that disk-slider clearance of less than a nanometer can be achieved, at least on a laboratory setup. We will discuss the implication of such low spacing on the lubricant film behavior, and provide general physical arguments that attempt to highlight lubricant attributes that are relevant under those clearance conditions.
IEEE Transactions on Magnetics 10/2007; · 1.36 Impact Factor
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ABSTRACT: As the hard disk drive industry is transitioning from longitudinal (LMR) to perpendicular (PMR) recording, a new set of reliability
challenges had to be overcome. In particular, the magnetic media structure, which relies on well-segregated grains of 6–10nm
diameter, can exhibit a rough structure, with peak-to-mean amplitude of 3–6nm. In this paper, we will discuss how this topography
could affect the overall reliability of the head–disk interface. In the first part, we will illustrate the loss of adequate
coverage from the overcoat on PMR media, compared to the smoother LMR media, and we will attempt to quantify the topography
in terms of its deviation from a Gaussian height distribution. Particular emphasis will be given to surface outliers and their
removal during the burnishing process. The second part will be devoted to the lubricant preferential migration to the grain
boundaries, driven by surface tension. It will be shown by an EELS line scan that the lubricant film is indeed thicker in
the valleys between the grains, in agreement with surface tension driven redistribution. Finally, we will demonstrate that
the Touchdown Height (TDH) of a PMR disk is ∼0.5nm higher than its LMR counterpart, owing to its enhanced nano-roughness.
Once recognized, these challenges can be overcome through a careful and thorough optimization of the various processing parameters,
eventually leading to an overall reliability level equal or better than LMR media.
Tribology Letters 03/2007; 26(1):1-9. · 1.58 Impact Factor
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ABSTRACT: The spreading behavior of non-polar polymers in the nanometer thickness range is revisited. By incorporating a distance of closest approach d0 corresponding to the unbonded atom-atom distance, to the classical London slab-slab interaction energy, we demonstrate that the spreading profiles of a non-polar perfluoropolyether molecule perfectly obeys a Poiseuille flow driven by a disjoining pressure gradient. The dynamics of the thin film is entirely defined by d0, the polymer bulk viscosity, and the composite Hamaker constant of the polymer/surface system.
EPL (Europhysics Letters) 01/2007; 74(2):294. · 2.17 Impact Factor
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ABSTRACT: Needle-like crystalline nanostructures were formed on the surface of a lubricated experimental thin-film media during exposure to elevated temperature and humidity. Clusters of nodules were formed on unlubricated media during the same exposure. Both the needles and nodules were identified as cobalt oxalate by Micro-Raman spectroscopy. A chemical mechanism is proposed to explain how cobalt hydroxide corrosion product and atmospheric oxalic acid combine to form cobalt oxalate in the presence of moisture
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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ABSTRACT: This paper discusses a new class of lubricants for disk application, designed for ultra-low magnetic spacing. By tying down the middle of the long perfluoropolyether (PFPE) Fomblin chain to the overcoat surface with additional functional groups, one can achieve the very low clearance needed for the future, sub-5 nm flying height head-disk interface. Bulk synthesis and characterization are described, and tribological performance is investigated. Benefits of this novel lubricant family can be attributed not only to its shorter free chain length, but also to disjoining pressure attributes
IEEE Transactions on Magnetics 11/2006; · 1.36 Impact Factor
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M. Xiao,
H. Do,
W. Weresin,
Q. Dai,
Y. Ikeda,
K. Takano,
A. Moser,
B. Lengsfield,
A. Berger,
M. Schabes,
V. Nayak,
N. Supper,
H. Rosen, B. Marchon,
M. Minardi,
B. Heinz
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ABSTRACT: Two media, A and B, are discussed to illustrate the media requirements and properties for the 230 Gb/in2 demonstration. A and B had similar layer structures except that the recording layers had different oxide compositions and that the exchange break layer thicknesses were 21 and 13 nm, respectively. They had similar coercivity and intrinsic switching field but showed large difference in writability. Consequently, even though they achieved similar performance for heads down to a track width of 150 nm, medium A could not be saturated adequately for heads with a track width of 120 nm. On the other hand, medium B possessed the desirable properties for high density recording and formed the base for the media that were used in the 230 Gb/in2 demonstration.
Journal of Applied Physics 04/2006; 99(8):08E712-08E712-3. · 2.17 Impact Factor
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ABSTRACT: Circumferential texture grooves polished into NiP plated AlMg substrates promote magnetic crystal anisotropy in longitudinal recording media. Freshly textured or washed NiP is a chemically reactive surface, and combines with atmospheric moisture and carbon dioxide to form Ni carbonates. These adventitious products alter the surface morphology and interfere with magnetic domain growth.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: This paper presents studies designed toward understanding media defect corrosion. Focused ion beam technology is used to create well-defined defects exposing alloys of interest. Temperature and humidity stressing is employed to facilitate defect corrosion. Atomic force microscopy is used to characterize the defects before and after environmental stressing. It is found that corrosion growth is largely affected by the exposed alloy corrosion sensitivity. Interaction with overcoat type and lubricant is also discussed.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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ABSTRACT: Humidity effects in magnetic recording are reviewed. We highlight the progress made toward quantifying water adsorption on lubricated overcoats, leading up to the present understanding of humidity effects on magnetic recording tribology. Recently, it was found that moisture is also absorbed by hygroscopic atmospheric contaminants to form liquid nanodroplets on the overcoat. Rheological and dielectric measurements were performed to investigate the properties of the nanodroplets. Solutions of 1 wt% to 10 wt% water in Ztetraol are gel like and highly viscous. Dissolved water increases the low-frequency permittivity and conductivity, and shortens the dielectric relaxation time, relative to dry lubricant.
IEEE Transactions on Magnetics 03/2005; · 1.36 Impact Factor
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ABSTRACT: Molecular dynamics simulation would be well suited to predict the physics of molecularly-thick lubricants on magnetic disk surfaces. The difficulty in defining suitable interatomic potentials, as well as the requirement for large computing power, makes this type of study difficult. Treating the lubricant film in the framework of fluid dynamics has proven a much better way to model its behavior. This paper describes a full numerical model of lubricant moguls and ripples formation using finite difference analysis. We demonstrate that both moguls and ripples result from slider-induced air shear. Ripples tend to form at higher disk speed and narrower slider width, whereas moguls are seen at lower speed and larger slider width. Both moguls and ripples are enhanced for thicker lubricants, higher waviness, and lower flying heights. Ripple instabilities that were predicted earlier using a stability analysis are also quantitatively confirmed using this numerical model.
IEEE Transactions on Magnetics 03/2005; · 1.36 Impact Factor
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ABSTRACT: This paper presents experimental investigations of the lubricant ripple formation when the slider flies on the track. We quantified the impact of ripple amplitude on slider flying height modulation (FHM). Comparisons were made between experimental observations and a previous modeling study where rippling was shown to be caused by slider-induced air shear modulation. We confirmed our model predictions and demonstrated conditions under which ripple formation is enhanced or reduced.
IEEE Transactions on Magnetics 08/2004; · 1.36 Impact Factor
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ABSTRACT: This paper presents time evolution studies of slider dynamics as a result of lubricant-slider interaction. Lubricant moguls and ripples are observed to form and they change in frequency and amplitude, following the slider dynamics. The slider motion and lubricant thickness modulation appear to build on each other. Eventually when enough lubricant is lost, mogul and ripple amplitudes decrease and the slider dynamics stabilizes.
IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
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ABSTRACT: This paper presents detailed electrochemical investigations on the role of overcoat and lubricant in head and media corrosion protection. Depending on the types of metal to be protected, some types of overcoat materials can actually accelerate corrosion due to galvanic coupling effect. To eliminate such coupling, a true dielectric film needs to be used instead of the conventional hydrogenated carbon films. On the other hand, galvanic coupling is not always detrimental depending on the types of materials to be protected.
IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
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ABSTRACT: A model is presented that calculates the equilibrium lubricant thickness on a slider, resulting from a steady state where net inflow from disk evaporation equals net outflow from evaporation back to the disk, and flow to the slider back end from air shear. Based on experimental vapor pressure and viscosity data, and using surface viscosity enhancement factor and disjoining pressure values available in the literature, this model predicts a transition from a flooded regime for molecular weight M<sub>n</sub> below 1.5 kDaltons to a starved regime where slider lubricant thickness drops to a value close to zero. At the same time, lubricant accumulation to the slider back end is expected to decrease exponentially.
IEEE Transactions on Magnetics 10/2003; · 1.36 Impact Factor
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ABSTRACT: A simple method is introduced to contaminate either the slider or the disk with a small amount of lubricant, with the intent of studying the interaction between the slider and the lubricant layer on hard disks at low mechanical fly heights. Lubricant ripples at a frequency of 220-280 kHz, corresponding to the second pitch mode of the sliders used, were observed on the disk with an optical surface analyzer. Using laser Doppler velocimetry, a corresponding fly height modulation of up to 20 nm was measured on the slider body. It is hypothesized that this is due to a sustained stick-slip mechanism involving lubricant bridging.
IEEE Transactions on Magnetics 04/2003; · 1.36 Impact Factor
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ABSTRACT: Presents studies on lubricant mogul formation when a slider flies over a disk surface. In the range of parameters used in this study, moguls form and reach a steady-state pattern within 100 revolutions. During this period, no significant net lubricant loss is observed in the track. The completion of the full mogul pattern is followed by an asymptotic lubricant loss from the track. The loss was not compensated by an increase in thickness outside the track. It is speculated that this lubricant loss from the disk is initiated when the peak thickness of the moguls exceeds the critical dewetting thickness, therefore allowing an energetically favored process. Theoretical modeling based on Van der Waal's interactions is presented.
IEEE Transactions on Magnetics 10/2002; · 1.36 Impact Factor
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