AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Monday Sessions
       Session NS1-MoA

Paper NS1-MoA6
Combined Nanoindenter and Quartz Microbalance Studies of Realistic Tribological Contacts and Ultrathin Lubricant Films

Monday, October 31, 2005, 3:40 pm, Room 204

Session: Nanotribology
Presenter: B. Borovsky, Grinnell College
Authors: B. Borovsky, Grinnell College
A. Booth, Grinnell College
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For emerging technologies such as micromachined devices, it is increasingly important to understand high-speed, multi-asperity, microscale contacts lubricated with films as thin as a single molecule, and to control the effects of humidity. Most theoretical and experimental studies of small contacts do not directly access this physical regime. We have therefore used a combined nanoindenter and quartz crystal microbalance (QCM) to study the contact between a sapphire sphere and a polycrystalline gold electrode undergoing transverse shear at speeds on the order of 1 m/s. For the first time, we have used this combined system to study both dry and lubricated contacts, by applying monolayer octadecanethiol films. We have extended previous work@footnote 1@ by adding continuous monitoring of the QCM resonance bandwidth during indentations. We find that both the frequency and bandwidth of the QCM track changes in the contact area, as derived from the contact stiffness. Depending on the roughness of the gold electrode, variations in the frequency with contact area follow either the single-asperity or multi-asperity limits of the elastic no-slip model of the interface. However, this model fails to account for the large levels of dissipation observed during indentations and the dependence of the bandwidth on contact area. We attribute this to dissipation in outer portions of the contact subject to interfacial slip. We also report a reversible humidity effect whereby the levels of dissipation in lubricated contacts increase and decrease reproducibly with the amount of water incorporated into the octadecanethiol film. We will discuss refinements of the interaction model to account for frictional processes and the response of the polymer film to humidity, confinement, and high-frequency shear. Research supported by NSF, Research Corporation, and Hysitron, Inc. @FootnoteText@ @footnote 1@B. Borovsky, J. Krim, S.A. Syed Asif, and K. J. Wahl, J. Appl. Phys. 90, 6391 (2001).