Modification of Alkanethiolate Self-Assembled Monolayers by Atomic Hydrogen: Influence of Alkyl Chain Length

Abstract

The interaction of atomic hydrogen with four alkanethiolate self-assembled monolayers (SAMs), octadecanethiolate, hexadecanethiolate, dodecanethiolate, and nonanethiolate, has been studied in situ, using X-ray photoelectron spectroscopy. Atomic hydrogen reactions with gold−sulfur bonds result in sulfur desorption and the formation of new sulfur species within the film. The loss of sulfur from each SAM exhibits first-order kinetics with a rate constant that decreases with increasing alkyl chain length. This supports the idea that sulfur desorption is controlled by the diffusion of atomic hydrogen through the alkyl chains to the film/substrate interface. In the two shorter chain SAMs, sulfur and carbon desorption is rapid and concerted. This indicates that the modification of dodecanethiolate and nonanethiolate SAMs is dominated by desorption of intact adsorbate chains and alkyl sulfur fragments formed by atomic hydrogen reactions at the film/substrate interface. For octadecanethiolate and hexadecanethiolat...