AVS 57th International Symposium & Exhibition
    Tribology Focus Topic Wednesday Sessions
       Session TR+MN+NS+SS-WeM

Paper TR+MN+NS+SS-WeM11
In-Situ Scanning Auger Analysis of a Tribological Wear Scar in UHV Conditions

Wednesday, October 20, 2010, 11:20 am, Room Tesuque

Session: Influence of Atmosphere, Temperature, and Materials on Friction
Presenter: B.P. Miller, University of Wisconsin-Milwaukee
Authors: B.P. Miller, University of Wisconsin-Milwaukee
O.J. Furlong, University of Wisconsin-Milwaukee
W.T. Tysoe, University of Wisconsin-Milwaukee
Correspondent: Click to Email
Lubrication of sliding copper-copper interfaces for use in brushes in electrical motors provides a particular challenge. Not only is a reduction in friction and wear required, but also allowing for high conductivity through the contact. Therefore, a self-limiting tribofilm is essential. The following explores the surface chemistry and tribology of dimethyl disulfide (DMDS) on copper surfaces to establish whether it is sufficiently reactive to potentially form a tribofilm near room temperature as required for lubrication of the sliding copper-copper contact in an electric motor. The surface chemistry and decomposition pathways of DMDS on copper surfaces are analyzed using temperature-programmed desorption (TPD), reflection-absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). It is shown that DMDS reacts to form methyl thiolate species on the copper surface at room temperature. After heating to about 430K, methane and C2 hydrocarbons desorb leaving molecular sulfur adsorbed onto the surface. A UHV tribometer chamber was equipped with a scanning electron gun having a ~100 micron diameter spot size. DMDS was dosed in the gas phase while performing friction measurements so that in-situ elemental analysis of the wear scar could be made. An increase in the sulfur signal is witnessed inside compared to outside of the tribological wear scar. A depth profile Auger analysis of the sample showed selective diffusion of sulfur into the bulk only inside the wear scar attributed to tribologically induced effects. This novel method of analysis can give important insights into the fundamentals of tribological systems.