IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Tribology Wednesday Sessions
       Session TR+SS-WeM

Paper TR+SS-WeM6
Molecular Layer Effects on Friction Between Single Crystalline Metal Surfaces

Wednesday, October 31, 2001, 10:00 am, Room 132

Session: Fundamentals of Tribology & Adhesion
Presenter: A.J. Gellman, Carnegie Mellon University
Authors: A.J. Gellman, Carnegie Mellon University
J.S. Ko, Merck & Co.
Correspondent: Click to Email
The combined use of an ultrahigh vacuum tribometer and a variety of surface science techniques has enabled us to explore the tribological properties of interfaces between Ni(100) surfaces and to observe phenomena attributable to molecular layering. Friction measurements have been made between a pair of clean Ni(100) surfaces, modified by the presence of adsorbed atomic sulfur with and without adsorbed ethanol. Friction measurements made with ethanol coverages ranging from 0 – 10 monolayers on each Ni(100) surface reveal that the friction coefficient is discontinuous in coverage and can be correlated to the coverage dependence of the ethanol desorption energy. During shearing sliding never commences between clean Ni(100) surfaces or sulfided Ni(100) surfaces without adsorbed ethanol. In the submonolayer coverage regime of either atomic sulfur or adsorbed ethanol the behavior is characterized by a high friction coefficient (µ@sub s@ > 5.5) accompanied by high adhesive forces (µ@sub ad@ = 1.5 ± 0.7). An abrupt decrease in both the friction coefficient and adhesion coefficient occurs at a coverage of one monolayer of ethanol on each surface. The friction coefficient drops to (µ@sub s@ = 3.1 ± 1. while the adhesion coefficient is lowered to µ@sub ad@ ~ 0.25. At coverages between 1.0 and 2.5 monolayers of ethanol on each Ni(100) surface the static friction coefficient decreases in a step-wise manner that is correlated with discontinuities in the ethanol desorption energy. This step-wise decrease in both the friction coefficient and the desorption energy may be due to molecular layering of the ethanol.