Sulfur adsorbed (Q = 1=2) on gold (111) substrate

Abstract

The adsorption of Q = 1=2 monolayer (ML) of S on Au(111) is calculated. The evolution of the positions of adatoms for 800 K, 500 K, 300 K, 150 K and 1 K is evaluated by using a density functional theory (DFT)-tight binding approach combined with classical molecular dynamics. For this coverage there is a controversy about the existence of superficial composite AuS or molecular aggregates. We find a configuration in which sulfur atoms form quasi-S2 superficial molecules with total energy very close to the monoatomic phase suggesting the coexistence of both configurations at room temperature. We find that the stability of the dimeric phase is due to the increase of the binding energies between sulfurs. In the other phase, the stabilization occur due to a formation of AuS dimers. At high temperatures (T> 300 K) sulfurs have high mobility which allows the migration among different adsorption sites. At low temperatures the mobility decreases and a thermal activation barrier of 25 30 meV can be estimated.