A novel model for the (√3 × √3)R30° alkanethiolate–Au(111) phase based on alkanethiolate–Au adatom complexes

Abstract

Self-assembled monolayers of thiols on Au(111) have attracted considerable interest from the theoretical and experimental points of view as model systems for understanding the organization of molecules on metallic surfaces, and also as key elements in nanoscience and nanotechnology. Today, there is strong theoretical and experimental evidence indicating that the surface chemistry of these monolayers at high coverage involves dithiolate–adatom (RS–Au_ad–SR) species, showing the existence of the (3 × 4) and c(4 × 2) lattices usually observed by scanning tunneling microscopy. However, concealing the existence of dithiolate–Au adatom species with the presence of the paradigmatic (√3 × √3)R30° lattice, which dominates the structure of long alkanethiols, still remains a challenge. Here, we propose a novel (3√3 × 3√3)R30° structural model containing RS–Au_ad–SR moieties based on DFT calculations which reconciles most of the experimental data observed for the (√3 × √3)R30° lattice. Our results provide a unified picture of the surface chemistry of the thiol–Au(111) system.