Silicene on Ag(111) : domains and local defects of the observed superstructures

On Ag(111) substrate, the growth of a silicene layer (the equivalent of graphene for silicon) gives rise to four main superstructures due to the epitaxy between the silicene layer (honeycomb structure) and the Ag(111) substrate. Depending on both the substrate temperature and the deposition rate, the following superstructures were observed: (4×4), (× )R13.9°, (2× 2)R30° and (× )R19.1°. Each one corresponds to a specific rotation of the silicene layer with respect to the silver substrate. In this paper we show and discuss for each superstructure all the expected equivalent domains due to the symmetry properties of both the silicene honeycomb structure and the trigonal silver surface. Finally, we show, from STM images of the (2× 2)R30° superstructure, the role played by periodic local defects on the average direction of the superstructures.