Chemical modification of the interfacial frictional properties of vanadiumcarbide 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 expos ure 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 de sorption. These studies demonstrate the formation of a partially dehydrated species involving bonds to the surface through both oxygen and carbon atom s. The growth of this reaction layer film has been followed with X-ray phot oelectron spectroscopy, ultraviolet photoelectron spectroscopy. and scannin g tunneling microscopy. The results of these surface analytical measurement s have been correlated with the frictional and adhesion properties measured with AFM. An approximate 40% reduction in frictional forces is observed up on the formation of a complete monolayer of a hydrocarbon reaction layer. L ittle change in the interfacial friction was detected at higher or lower ex posures of ethanol. The origin of the friction reduction, which cannot be d irectly related to changes in interfacial adhesion, is assigned to a change in interfacial shear strength as a result of the growth of the ethanol dec omposition species. (C) 2001 Elsevier Science B.V. All rights reserved.