Self-assembly of methanethiol on the reconstructed Au(111) surface

We present a combined experimental and theoretical study of molecular methanethiol (CH3SH) adsorption on the reconstructed Au(111) surface in the temperature range between 90 and 300 K in UHV. We find that the simplest thiol molecules form two stable self-assembled monolayer (SAM) structures that are created by distinct processes. Below 120 K, a solid rectangular phase, preserving the herringbone reconstruction, emerges from individual chains of spontaneously formed dimers. At higher adsorption temperatures below 170 K, a close-packed phase forms via dissociative CH3SH adsorption and the formation of Au adatoms that are not incorporated into the SAM. We show that the combination of a strong substrate-mediated interaction with nondissociative dimerization and temperature activated removal of the Au(111) reconstruction drives the large-scale assembly of molecular CH3SH into two distinct phases.