Determination of atomic positions in silicene on Ag(111) by low-energy electron diffraction

We have investigated the structure of silicene forming into the (4 × 4) superstructure on Ag(111) by using the low-energy electron diffraction. We found that Si atoms form a buckled honeycomb structure on Ag(111), which fully matches with the structure optimized with the density functional theory calculations. The SiSi bond lengths range from 2.29 to 2.31 Å, which are close to the upper limit of SiSi double bond and shorter than the bond length in the bulk diamond structure. The buckling in the silicene layer causes the displacement of Ag atoms in the first substrate layer with 0.3 Å perpendicular to the surface, which is a compelling evidence of the strong couplings at the interface between the silicene and the substrate.