Theoretical study of thiol-induced reconstructions on the Au(1 1 1) surface

A new suggestion for the structure of the Au substrate underlying self-assembled monolayers (SAM) made of thiols is presented on the basis of density functional theory results for methylthiolate (–SCH3) adsorption on Au(1 1 1). It is found that by introducing vacancy defects on the substrate, the adsorption of SCH3 is stabilized by about 0.8 eV with respect to the perfect Au(1 1 1) surface. As this overcomes the vacancy formation energy (≈0.6 eV), a net driving force exists leading to an adsorbate-induced reconstruction, that enhances adsorption at defected Au(1 1 1). A comparison of results at high and low SCH3 coverage provides further insight into which specific gold vacancy sites enhance the adsorption energy of the SCH3 molecule.