Monolayer Films Prepared by the Spontaneous Self-Assembly of Symmetrical and Unsymmetrical Dialkyl Sulfides from Solution onto Gold Substrates: Structure, Properties, and Reactivity of Constituent Functional Groups

Exposure of evaporated gold films supported on silicon wafers to solutions of dialkyl sulfides or alkanethiols in methanol or ethanol results in rapid formation of a monolayer of the organosulfur compound adsorbed onto the gold. The resulting films have been characterized by using a number of techniques, including X-ray photoelectron spectroscopy, infrared spectroscopy, ellipsometry, and wetting. These self-assembled, supported organic monolayer films are systems that can be used to study problems in the physical-organic chemistry and materials science of organic surfaces, especially the relation between the molecular-level structure of the film constituents and the macroscopic properties of the assembled monolayers. The films are relatively robust: examples formed from both dialkyl sulfides and alkanethiols withstand washing and prolonged soaking in neutral water, but films containing dialkyl sulfides are destroyed by contact with aqueous base at pH 8-13.