Proceedings of the ASME Information Storage and Processing Systems Conference 2016 ASME-ISPS 2016 June 20-22, 2016, San Jose, California, USA ISPS2016-9610
Experimental Investigation of the Effect of Hydrocarbon Oil Contamination on a Disk Surface Young Woo Seo University of California, San Diego Center for Memory and Recording Research 9500 Gilman Drive, MC 0401, La Jolla, CA 92093 Email:
[email protected] Yongqi Yan University of California, San Diego Center for Memory and Recording Research 9500 Gilman Drive, MC 0401, La Jolla, CA 92093 ABSTRACT Hydrocarbon oil is used to lubricate the spindle motor as well as the pivot actuator arm in current hard disk drives. Previous investigations using molecular dynamics have shown that hydrocarbon oil can contaminate the head-disk interface. In this paper, an experimental study is conducted to investigate the mechanism of hydrocarbon oil contamination on the disk surface using contact angle measurements, atomic force microscopy (AFM), ellipsometry, and gas chromatography mass spectrometry (GC-MS). INTRODUCTION In recent years, the head-disk flying height has decreased to the 1-nm regime. At this spacing, contacts between slider and disk may lead to failure of a hard disk drive. Current hard disk drives use a thin layer of diamond-like carbon (DLC) together with a topically applied perfluoropolyether (PFPE) lubricant for wear protection of the head-disk interface. Organic compounds, specifically hydrocarbon (alkane) oils, can contaminate the head-disk interface and cause failure. Fowler and Geiss [1] observed that alkane hydrocarbons can contaminate the head-disk interface by forming droplets on the slider surface, leading to stiction at the head-disk interface. Lei et al. [2] used thermally programmed desorption (TPD) spectroscopy to experimentally investigate the effect of hydrocarbons on PFPE lubricant bonding with an aCHx over-coated surface. They observed that hydrocarbon molecules weaken the interaction between the lubricant and the carbon overcoat, thereby making the lubricant ineffective for wear protection of the head-disk interface. Li, et al. [3] numerically simulated contact between a slider surface and a droplet of lubricant on the disk surface. They concluded that contact-induced vibrations can cause flying instability, leading to read/write errors. Sonoda [4] observed that large slider vibrations can be induced by slider contact with a hydrocarbon droplet. Kasai
Andrey Ovcharenko Western Digital Corporation 5863 Rue Ferrari, San Jose, CA 95138 Frank E. Talke University of California, San Diego Center for Memory and Recording Research 9500 Gilman Drive, MC 0401, La Jolla, CA 92093 and Raman [5] suggested that hydrocarbon molecules first condense on pinholes in the carbon overcoat before being picked up by the slider at close proximity to the disk surface. Seo et al. [6] used molecular dynamics to investigate the transfer mechanism of hydrocarbon molecules at the head-disk interface. In this paper, we study hydrocarbon contamination of a disk surface coated with a nanometer-thick lubricant layer of per-fluorinated polyether (PFPE) and investigate the adsorption behavior of both linear hydrocarbons (C24H50 and C36H74) and branched hydrocarbons on the disk surface. We first use contact angle measurements to determine the surface energy of hydrocarbon oils on the lubricated disk surface. We then use atomic force microscopy (AFM) to investigate the crystal morphology of linear hydrocarbon chains deposited on the disk surface. Finally, we apply ellipsometry to study the changes in the PFPE lubricant layer due to hydrocarbon contamination. Then, we use gas chromatography mass spectrometry (GC-MS) to quantify the amount of
Micro-controller Syringe LabVIEW
Droplet CCD Camera Disk
Figure 1. Schematic of contact angle analyzer. LabVIEW is used to control a micro-controller (Arduino Uno) to dispense hydrocarbon oil on the disk surface and to acquire droplet images from the CCD camera
Proceedings of the ASME Information Storage and Processing Systems Conference 2016 ASME-ISPS 2016 June 20-22, 2016, San Jose, California, USA hydrocarbon oils deposited on the disk surface as a energy γS and the liquid surface energy γL must be function of temperature and time. measured separately. In order to acquire the solid surface energy γ S of a EXPERIMENT Intermolecular interactions between hydrocarbon commercially available disk, we used the “Owens, contaminants and the lubricant film on a disk surface Wendt, Rabel, and Kaelble” (OWRK) method [7]. In play an important role in the contamination of disk this approach, pure hexadecane (C16H34) and distilled surfaces. One of the most important parameters in the water [8-9] were used to acquire the surface free contamination process is the surface energy between energy of a solid by measuring the dispersive (𝛾𝑆𝑑 ) and 𝑝 the oil and the lubricated surface. polar (𝛾𝑆 ) terms. Since the liquid surface energy γL for p In Fig. 1, a schematic is shown for measuring the hexadecane ( γdL = 27.5 dynes/cm; γL = 0 ) [9] and surface energy between hydrocarbon oil and a disk p water (γdL = 51.0 dynes/cm; γL = 21.8 dynes/cm) [9] surface. The set-up consists of a micro-controller, a are known, the surface energy γ S of the disk can be syringe for dispensing hydrocarbon oil, and a CCD calculated. camera to acquire the images of a hydrocarbon droplet After determining the surface energy of the solid, placed on the disk surface. the remaining unknown in Eq. (1) is the surface energy The surface energy γSL between a liquid oil droplet γL of the hydrocarbon oil. In order to acquire the liquid and a solid disk surface can be calculated using surface energy of the oil, we have used the so-called Young’s equation: “pendant drop technique” [10-12], which consists of γSL = 𝛾𝑆 − 𝛾𝐿 cos(𝜃𝐶𝐴 ) (1) analyzing the shape of a “hanging” droplet (Fig. 3) and where γSL is the surface energy at the solid-liquid correlating this shape with γL, i.e., interface, γL is the surface energy of the liquid droplet, Δ𝜌𝑔𝑅2⁄ γL = (2) and γS is the surface energy of the solid surface (Fig. 𝛽 2). where Δρ is the density difference between the liquid drop and the surrounding air, g is the gravitational acceleration, R is the radius of curvature of the γL “hanging” liquid drop, and β is a shape parameter θCA estimated numerically [12]. The contact angles θCA for each hydrocarbon oil γS was measured using the setup shown in Fig. 1. With γS, γL, and θCA known, the solid-liquid surface energy γSL γSL between the disk surface and hydrocarbon droplets was calculated. Figure 2. Schematic of liquid droplet on a solid After characterizing the solid-liquid interfacial surface showing the surface energy and contact surface energy, we deposited linear and branched angle parameters from Young's equation hydrocarbon oils onto the disk surface as shown in Fig. As can be seen from Fig. 2, the contact angle θCA 3 in order to experimentally analyze the disk surface can be measured experimentally. To determine the after contamination. The following procedure was solid-liquid surface energy γSL, the solid surface used.
Disk Hydrocarbon Oil Fixture
(a)
Aluminum Foil
Glass Container
Thermal Chamber
Fixture
Fixture
(b)
(c)
Figure 3. A schematic of hydrocarbon oil deposition procedure. (a) Prepare hydrocarbon oil and a clean disk, (b) seal it in a glass container wrapped with aluminum foil, and (c) place it in a thermal chamber to deposit hydrocarbon on the disk surface at high temperature
Proceedings of the ASME Information Storage and Processing Systems Conference 2016 ASME-ISPS 2016 June 20-22, 2016, San Jose, California, USA Lubricant Bonding to a-CH x Overcoats."Langmuir 17.20 First, a fixed volume, 20µL, of hydrocarbon oil was (2001): 6240-6247. applied on the horizontal fixture surface shown in Fig [3] Li, Jianhua, Junguo Xu, and Yuichi Aoki. "Simulation on 3(a). Using a cleanroom wipe, we spread the oil contact between the droplet and the slider at head-disk uniformly on the surface. Thereafter, we positioned a interface based on water-hammer pressure model." Microsystem technologies 16.1-2 (2010): 57-65. clean disk about 2 mm above the horizontal fixture [4] Sonoda, Koji. "Flying Instability due to Organic surface containing the hydrocarbon oil. As shown in Compounds in Hard Disk Drive." Advances in Fig. 3(b), the sample was then placed in a glass Tribology 2012 (2012). container, and wrapped with several sheets of [5] Kasai, Paul H., and Vedantham Raman. "Hydrocarbon Transfer in Disk Drives."ASME 2014 Conference on aluminum foil to seal the test sample from Information Storage and Processing Systems. American environmental contaminants. Then, as shown in Fig. Society of Mechanical Engineers, 2014. 3(c), the sample was placed in an environmental [6] Seo, Young W., Andrey Ovcharenko, and Frank E. Talke, chamber and heated up to a temperature of 80°C for “Simulation of Hydrocarbon Oil Contamination at the Head-Disk Interface using Molecular Dynamics.” several hours. This procedure caused hydrocarbon oil Submitted to Tribology Letters, 2016 to transfer from the fixture surface to the disk surface, [7] Owens, Daniel K., and R. C. Wendt. "Estimation of the contaminating the disk surface with hydrocarbon oil. surface free energy of polymers." Journal of applied polymer [8]
[9]
(a) Before HC Deposition (b) After HC Deposition
Figure 4. Optical surface analysis (Candela 6100) images of a disk surface (a) before HC deposition and (b) after HC deposition Fig. 4(a) shows the image of a clean disk surface without contaminants, while Fig. 4(b) shows a contaminated surface, measured with an optical surface analyzer (Candela 6100). Clearly, a large number of contaminant particles is observed in Fig. 4(b), while almost none are present on the uncontaminated surface. To study the height, width, and morphological features of the hydrocarbon contaminants, we have used atomic force microscopy (AFM) and ellipsometry [13]. In addition, we have used gas chromatography mass spectrometry (GC-MS) to quantify the amount of hydrocarbon oil on the disk surface after contamination [14]. In the full paper, we will analyze the contamination characteristics of linear and branched hydrocarbons as a function of temperature, “baking time”, disk lubricant type, and molecular weight. ACKNOWLEDGEMENT We would like thank Prof. Lubarda for helpful comments. We would also like to acknowledge constructive discussions with Benjamin Suen concerning the experimental setup. REFERENCES [1]
[2]
Fowler, David E., and Roy H. Geiss. "Chemical contamination at the head-disk interface in a disk drive." Magnetics, IEEE Transactions on 36.1 (2000): 133139. Lei, Ryan Z., Andrew J. Gellman, and Christopher F. McFadden. "Alkane Contamination Effects on PFPE
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