AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Monday Sessions
       Session NS1-MoA

Paper NS1-MoA3
Energy Dissipation in Defective Alkanethiol Monolayers

Monday, October 25, 1999, 2:40 pm, Room 612

Session: Nanoscale Tribology and Adhesion
Presenter: N.D. Shinn, Sandia National Laboratories
Authors: N.D. Shinn, Sandia National Laboratories
J.D. Kiely, Sandia National Laboratories
J.E. Houston, Sandia National Laboratories
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Although highly ordered, alkanethiol self assembled monolayers (SAMs) have a hierarchy of structural defects that lead to dynamic energy dissipation.@footnote 1@ Counter-intuitive friction results on nominally isomorphic monolayers suggest surprising sensitivity to subtle structural differences or demonstrate that extrinsic probe/monolayer interactions dominate friction.@footnote 2@ We separate intrinsic and extrinsic contributions to friction by using a Quartz Crystal Microbalance to inertially shear and simultaneously measure the intrinsic energy dissipation in pure, mixed and damaged alkanethiol SAMs chemisorbed on Au(111)-textured QCM electrodes. For complete monolayers, domain boundaries are the major symmetry-breaking defects that enable dissipation. Point defects created by electron or UV irradiation only incrementally increase the intrinsic dissipation. Residual fluid phases, most notably in sub-monolayer films, lead to the highest dissipative losses. Oxidation by ozone decouples the SAM from the Au(111) substrate and dramatically increases the intrinsic dissipation. Interfacial Force Microscope experiments demonstrate how the structure-dependent SAM viscoelasticity is manifested in controlled friction measurements.@footnote 3@ Research supported by DOE-BES Materials Sciences. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000. @FootnoteText@@footnote 1@N. D. Shinn, T. M. Mayer and T. A. Michalske, Tribology Letts. (in press). @footnote 2@ H. I. Kim, T. Koini, T. R. Lee and S. S. Perry, Langmuir 13, 7192 (1997). @footnote 3@J. E. Kiely, N. D. Shinn and J. E. Houston, Langmuir (submitted).