Silicene phases on Ag(111)

Silicene, an atom-thin two-dimensional sheet of silicon atoms arranged in a honeycomb lattice, recently synthesized on Ag(111), has attracted considerable interest as a potential alternative to graphene. For single layer silicene, two main phases have been identified among a few possible ones. They correspond to differently buckled silicene sheets, in coincidence either with 4×4 or Root13×Root13R(13.9°) silver (111) supercells. Instead, we demonstrate via surface crystallography considerations and Density Functional Theory calculations that a previously claimed, 2Root3×2Root3R(30°) Ag(111) superstructure cannot accommodate a true honeycomb silicon sheet.