Chemical modification of the interfacial frictional properties of vanadium carbide through ethanol adsorption

The frictional properties of the (1 0 0) face of vanadium carbide have been measured with atomic force microscopy (AFM) as a function of ethanol exposure under ultrahigh vacuum conditions. Although exhibiting a small sticking coefficient, ethanol reacts upon adsorption at room temperature producing a thin chemisorbed layer. This reaction has been characterized through high resolution electron energy loss spectroscopy and temperature programmed desorption. These studies demonstrate the formation of a partially dehydrated species involving bonds to the surface through both oxygen and carbon atoms. The growth of this reaction layer film has been followed with X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and scanning tunneling microscopy. The results of these surface analytical measurements have been correlated with the frictional and adhesion properties measured with AFM. An approximate 40% reduction in frictional forces is observed upon the formation of a complete monolayer of a hydrocarbon reaction layer. Little change in the interfacial friction was detected at higher or lower exposures of ethanol. The origin of the friction reduction, which cannot be directly related to changes in interfacial adhesion, is assigned to a change in interfacial shear strength as a result of the growth of the ethanol decomposition species.