From the Terrace Contraction to the Hexameric Sulfur Phase in the Au(100) Surface: A Combined Density Functional Theory and Scanning Tunneling Microscopy Study

The lifting of the Au(100) quasi-hexagonal reconstruction by atoms or molecules leaves a rough surface with islands, terraces, and vacancies where different patterns of adsorbates can appear. Although the roughness of the (1 X 1)-Au(100) surface has been well characterized, to our knowledge, there are no theoretical studies considering its effect on the formation of adsorbate patterns, for instance, in the case of sulfur adsorption. In this study, we have combined DFT calculations and STM measurements to explore the structural effects induced on the terrace when the sulfur adsorption takes place on the island and vacancy. Models predict a decrease of the Au-Au bond length in the terrace if the terrace has an appropriate size when the simultaneous adsorption of the sulfur structure (root 2 x root 2) occurs on the island and vacancy. According to our predictions, this process of gold bond length contraction on the terrace can affect the formation of the sulfur structure on it. STM images reveal regions where the (root 2 x root 2) structure is observed on the island and vacancy, while a different structure, denoted as a hexamer, appears on the terrace. Results from our calculations considering the roughness of the (1 X 1)-Au(100) surface and the gold bond contraction agree well with these experimental observations.