AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS2+NS-ThA

Paper SS2+NS-ThA4
Chemical and Mechanical Contributions to the Friction In Self-Assembled Monolayers on Au Surfaces

Thursday, October 5, 2000, 3:00 pm, Room 209

Session: Tribology and Adhesion
Presenter: H.I. Kim, Sandia National Laboratories
Authors: H.I. Kim, Sandia National Laboratories
J.E. Houston, Sandia National Laboratories
Correspondent: Click to Email
By studying various combinations of chemically distinct end groups on alkanethiol molecules self-assembled on Au probe/substrate surfaces, and by varying the odd-even length of the chains, we are able to delineate the contributions of chemical and mechani cal effects to interfacial friction. Because it is stable and quantitative throughout the entire range of the interfacial interactions (including the attractive load regime), we use the interfacial force microscope (IFM) to measure the friction force as a function of applied load. For even-length molecular chains, the friction forces progressively increase in the order CH3-CH3, CH3-COOH, COOH-COOH, while the interfacial adhesive force remains virtually identical. In contrast, for odd chain lengths, fricti on and adhesion are low for both CH3-CH3 and CH3-COOH combinations, but much higher for COOH-COOH. By systematically correlating the interfacial adhesion and friction, we conclude that energy dissipation giving rise to sliding friction has distinct chemic al and mechanical components. The making and breaking of hydrogen bonds, due to either intra- or inter-film interactions, gives rise to the "chemical" dissipation while simply disturbing the structure of the film under interfacial sliding invokes the "mechanical" component. This work was supported by the US Department of Energy under Contract DE-AC04-94AL85000. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the US Department of Energy.