Carbon-Sulfur Bond Cleavage During Adsorption of Octadecane Thiol to Copper in Ethanol

The effect of the solvent on the formation ofthiol self-assembled monolayers (SAMs) on oxide-covered,reactive metals is more involved than in the well-studied gold−thiol system. In this work, copper covered with a native oxidewas modified with 1-octadecanethiol (ODT) in eithertetrahydrofuran or ethanol. Infrared spectroscopy indicatedthe formation of crystalline chain packing of alkyl chains fromboth solvents. Surface coverage was approximately equal inboth systems, with differences in tilt angles of the chains. Adetailed analysis by X-ray photoelectron spectroscopy showedthe formation of Cu2S and copper-bound carbon when theadsorption was carried out in ethanol. This observation can beexplained by the cleavage of the C−S bond in ODT duringadsorption. Based on the analogy of preparations, we reasonthat the solvation of ODT in ethanol must be such that it weakens the C−S bond in ODT, thus enabling the cleavage of thisbond. Based on the evidence presented here, it is not possible to distinguish between surface solvation and bulk solvation.Electrochemical linear sweep voltammetry shows that SAMs from both solvents have an enhancing protective effect comparedto the native oxide layer. The results from this work show interesting possibilities for the preparation of adsorbed monolayerswith chemical interaction to reactive metals, with some similarities to carbene-based SAMs