Combined AFM and STM measurements of a silicene sheet grown on Ag(111) surface

In this Letter, we present the first non-contact atomic force microscopy (nc-AFM) of a silicene on silver (Ag) surface, obtained by combining non-contact atomic force microscopy (nc-AFM) and scanning tunneling microscopy (STM). STM images over large areas of silicene grown on Ag(111) surface show both (sqrt13xsqrt13)R13.9{\deg} and (4x4) superstructures. For the widely observed (4x4) structure, the nc-AFM topography shows an atomic-scale contrast inversion as the tip-surface distance is decreased. At the shortest tip-surface distance, the nc-AFM topography is very similar to the STM one. The observed structure in the nc-AFM topography is compatible with only one out of two silicon atoms being visible. This indicates unambiguously a strong buckling of the silicene honeycomb layer.