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The kinetic friction and wear at high sliding speeds is investigated using the head-disk interface of hard disk drives, wherein, the head and the disk are less than 10 nm apart and move at sliding speeds of 5-10 m/s relative to each other. While the spacing between the sliding surfaces is of the same order of magnitude as various AFM based fundamental studies on friction, the sliding speed is nearly six orders of magnitude larger, allowing a unique set-up for a systematic study of nanoscale wear at high sliding speeds. In a hard disk drive, the physical contact between the head and the disk leads to friction, wear and degradation of the head overcoat material (typically diamond like carbon). In this work, strain gauge based friction measurements are performed; the friction coefficient as well as the adhering shear strength at the head-disk interface are extracted;and an experimental set-up for studying friction between high speed sliding surfaces is exemplified.

Contact hysteresis between sliding interfaces is a widely observed phenomenon from macro-to nano-scale sliding interfaces. Most of such studies are done using an atomic force microscope (AFM) where the sliding speed is a few µm/s. Here, we present a unique study on stiction between the head-disk interface of commercially available hard disk drives, wherein vertical clearance between the head and the disk is of the same order as in various AFM based fundamental studies, but with a sliding speed that is nearly six orders of magnitude higher. We demonstrate that although the electrostatic force (DC or AC voltage) is an attractive force, the AC voltage induced out-of-plane oscillation of the head with respect to disk is able to suppress completely the contact hysteresis.The ability to reduce stiction in sliding surfaces is extremely important for a variety of applications ranging from very-high-density data storage (> 1 Tb/inch 2 ) [1-3] to nanoscale manufacturing in micro or nano mechanical systems (M/NEMS) [4][5][6]. Our research focuses on data storage in hard disk drives, in which the recording heads fly at sub-nanometer spacing from the disk and move at relative sliding speeds of 5-40 m/s. Maintaining good tribological properties such as low wear and stiction of such a high speed sliding interface at low clearance is critical for the long term reliability of hard disk drives [7]. Any contact between the head and the disk leads to friction and wear of the head overcoat layer, adversely impacting the disk drive performance [8][9][10][11].A unique way of reducing the friction during contact is through externally imposed oscillations of small amplitude and energy. Previous experimental and theoretical work to reduce the friction at a sliding interface explored the use of external excitation with either surface acoustic waves or electrostatic forces to modulate the out-of-plane or in-plane motion [12][13][14][15]. The out-of-plane vibrations reduce the friction by momentarily separating the interfering surfaces such that the friction is zero during this time. Consequently, the time averaged friction is reduced below the value that occurs in the absence of oscillation. In this letter, we describe an experimental study of contact events at the head-disk interface, focusing on hysteresis in contact cycle. We show that although the electrostatic force (DC or AC voltage) at the interface is an attractive force, the AC voltage induced oscillation can significantly reduce the contact hysteresis. We provide a fully quantitative analysis of the hysteresis in such a high sliding speed system which shows that the AC voltage induced oscillation has a dominant influence on suppressing the contact hysteresis.