Tribochemical and thermochemical reactions of stearic acid on copper surfaces in air as measured by ultra-soft X-ray absorption spectroscopy

For copper, steel, and gold surfaces the chemisorption of stearic acid was found to adsorb via the acid head group, displacing adsorbed contaminants on the surfaces. Tribochemical and thermochemical reactions of stearic acid adsorbed (in air) on a copper surface, were studied by ultra-soft X-ray absorption spectroscopy above the carbon and oxygen K edges. Chemisorbed stearic acid was found to adsorb in both monodentate and bidentate sites. The bidentate surface configuration was increased after the occurrence of the tribochemical reactions induced by surface rubbing. When the surface was subjected to a vacuum thermal annealing process, a reduction in bidentate configuration was observed. Carbon-K-edge X-ray absorption measurements were used to determine the tilt of the alkyl molecular chain from the surface normal, before and after the tribochemical or thermal annealing surface treatments. A stable chemically bonded molecular adsorbed layer persists on the surface even after these surface treatments. The molecular orientation of the molecules is also generally preserved after rubbing.