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TECHNICAL PAPERS

Stiffness and Damping of Thin PFPE Lubricant Bridging Between Magnetic Disk and Diamond Probe Tip

[+] Author and Article Information
Yasunaga Mitsuya

Department of Micro-Nano Systems Engineering,  Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japanmitsuya@nuem.nagoya-u.ac.jp

Yasuji Ohshima

Liberal Arts Department, Aichi Konan College, Ohmatsubara 172, Takaya-cho, Konan 483-8086, Japanohshima@konan.ac.jp

Hedong Zhang

Department of Complex Systems Science,  Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japanzhang@nuem.nagoya-u.ac.jp

Kei Aoyama

 Space Communication Corporation, 60, Industrial Park, Hitachiomiya 319-2134, Japanaoyama.kei@superbird.co.jp

Toshiyuki Kawai

Department of Electronic Mechanical Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japant_kawai@nuem.nagoya-u.ac.jp

Kenji Fukuzawa

Department of Micro-Nano Systems Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japanfukuzawa@nuem.nagoya-u.ac.jp

J. Tribol 129(4), 720-728 (May 16, 2007) (9 pages) doi:10.1115/1.2768070 History: Received June 13, 2006; Revised May 16, 2007

Spring constants and damping coefficients of a thin lubricant bridge of a perfluoropolyether (PFPE) lubricant intervening between a diamond probe tip and a diamond-like carbon (DLC) surface of a magnetic disk are identified through regression analysis of tip damping vibration. PFPE lubricants with functional end groups were used to form a lubricant bridge between the DLC surface and a probe tip with a notably small curvature radius of 0.1μm. The tip was both retracted from and extended toward the disk surface at four different progressive distances to attain varied elongation of the bridge. It was also vibrated at each step to provide damping waveforms. By applying regression analysis to the observed waveforms, the spring constant and the damping coefficient of the lubricant bridge were identified within an elongation range from 50nm to 800nm. Spring constant of the lubricant bridge kb had a negative value varying from 0.15Nm to 0.1Nm. The damping value expressed in the form of frequency-multiplied damping cb×ω ranged from 0.02Nm to 0.06Nm. Note that both the absolute value of spring constant kb and frequency-multiplied damping cb×ω exhibited U-shaped variation with lubricant bridge elongation; that is, those values decrease with bridge elongation and they begin to increase after reaching the minimum. The variation in the spring constant was found to be in good accordance with the quasi-static stiffness of the lubricant bridge, and variation in the damping coefficient was explained by energy loss arising in the vibrating lubricant bridge.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of experimental apparatus

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Figure 2

Image of probe tip taken by scanning electron microscope

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Figure 3

Stepwise of cantilever movement

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Figure 4

Vibration system model

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Figure 5

Typical waveforms for Zdol2000 with film thickness of 22nm: (a) upward (while tip retracting) and (b) downward (while tip approaching)

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Figure 11

Mechanism of damping action induced by meniscus motion: (a) shorter elongation and (b) longer elongation

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Figure 6

Identified spring constant relative to bridge elongation for Zdol2000: (a) film thickness h=24μm and (b) film thickness h=49μm

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Figure 7

Identified spring constant relative to bridge elongation for Zdol4000: (a) film thickness h=24μm and (b) film thickness h=44μm

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Figure 8

Lubricant bridge elongation and lubricant bridging force for constant speed retraction motion: (a) elongation of lubricant bridge for different retracting speeds for h=29nm and (b) lubricant bridging force versus elongation of lubricant

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Figure 9

Identified frequency-multiplied damping coefficient relative to bridge elongation for Zdol2000: (a) film thickness h=22μm and (b) film thickness h=49μm

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Figure 10

Identified frequency-multiplied damping coefficient relative to bridge elongation for Zdol4000: (a) film thickness h=24μm and (b) film thickness h=46μm

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