Qing Dai
IBM
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Publication
Featured researches published by Qing Dai.
IEEE Transactions on Magnetics | 2003
Bruno Marchon; Tom Karis; Qing Dai; Remmelt Pit
As head/media magnetic spacing in disk drives is fast approaching the 10 nm mark, the need to understand the spacing contribution of the disk lubricant becomes more pressing. In this paper, a model of lubricant transfer between disk and slider surface is presented that takes into account evaporation/condensation driven by thin film vapour pressure, as well as shear of the film towards the back of the slider.
IEEE Transactions on Magnetics | 2003
Remmelt Pit; Qinghua Zeng; Qing Dai; Bruno Marchon
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 | 2005
Bruno Marchon; Qing Dai; Vasant Nayak; Remmelt Pit
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 | 2002
Qing Dai; Celine Saint-Olive; Remmelt Pit; Bruno Marchon
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 Waals interactions is presented.
Journal of Vacuum Science and Technology | 2003
Bing K. Yen; Richard L. White; Robert J. Waltman; Qing Dai; Dolores C. Miller; A. J. Kellock; Bruno Marchon; Paul H. Kasai; Michael F. Toney; Brian R. York; Hong Deng; Qi-Fan Xiao; Vedantham Raman
The effect of N content on the structure and properties of rf reactively sputtered amorphous silicon nitride (a-SiNx) has been studied by Rutherford backscattering spectrometry, x-ray reflectivity, ellipsometry, and nano-indentation. The N content in the film increased with the N2 concentration in the sputtering gas until the Si3N4 stoichiometry was reached. The hardness of a-SiNx increased with density, which in turn increased with the N content. The maximum hardness of 25 GPa and density of 3.2 g/cm3 were attained at the stoichiometric Si3N4 composition. With the application of a protective overcoat for magnetic disks in mind, thin a-SiNx films were deposited on CoPtCr media to examine their coverage, pinhole density, and wear resistance. According to x-ray photoelectron spectroscopy, the minimum thickness of a-SiNx required to protect the CoPtCr alloy from oxidation was 10 A, which was 10 A thinner than that of the reference amorphous nitrogenated carbon (a-CNx). A statistic model showed this lower thi...
ieee international magnetics conference | 2006
Bruno Marchon; Xing-Cai Guo; Thomas E. Karis; Hong Deng; Qing Dai; John Burns; Robert Waltman
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 | 2004
Qing Dai; Ferdinand Hendriks; Bruno Marchon
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 | 2003
Qing Dai; Bernhard E. Knigge; Robert J. Waltman; Bruno Marchon
In this paper, we report slider dynamics changes as a result of lube-slider interactions. Lubricant moguls as well as ripples are observed, and they change in amplitude and in frequency, following the slider dynamics.
asia-pacific magnetic recording conference | 2006
Bruno Marchon; Qing Dai; Bernhard E. Knigge; Remmelt Pit
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 set-up. 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
ASME/STLE 2002 International Joint Tribology Conference | 2002
Bernhard E. Knigge; C. Mathew Mate; Qing Dai; Francis Chee-Shuen Lee; Robert N. Payne; Oscar Jaime Ruiz
Contact recording is fast becoming an attractive alternative to conventional flying recording heads. For contact recording, a new design philosophy has to be developed based on good understanding of contact dynamics of the head-disk interface. We have developed an integrated approach to understanding these interfaces, where experimental results from friction and laser doppler interferometer measurements are modeled using modified air bearing codes. Important insights gained: 1) smaller contact pad size reduces friction and bounce, 2) rougher disk surfaces have lower friction and contact stiffness, and 3) pitch angle and lubricant lube thickness strongly influence damping of slider motions.Copyright