Investigation of Tribochemical Reactions Using the Model System of Methyl Thiolate on Copper Foil in Ultrahigh Vacuum and Ab-Initio Calculations

Abstract

Advancement in the understanding of tribochemical systems suffers from several obstacles that hinder the progress in advancing an understanding of the fundamental processes involved in the evolution of friction and wear. Characterizing ephemeral chemical states within a buried interface is an experimental challenge and work in this dissertation uses a model system, methyl thiolate on copper foil, that undergoes tribo-activated decomposition to investigate the rate of change of the chemical components in the interface. The elementary steps in the tribochemical reaction were identified and consist of a shear-induced decomposition of methyl thiolate species to produce gas-phase hydrocarbons and form surface sulfur, which is mechanochemically transported into the sub-surface copper region resulting in changes in the friction coefficient. A method has been developed to analyze the changes in sliding-induced gas-phase product formation and friction coefficient as a function of the number of passes over the surface with a tribopin. Finally, the Vienna Ab-Initio Simulation Package (VASP) is used to calculate the methyl thiolate decomposition energies on Cu(100) as a function of load and the results are compared to the extended-Bell model.