High-resolution imaging of silicene on an Ag(111) surface by atomic force microscopy

Abstract

Silicene, a two-dimensional (2D) honeycomb arrangement of Si atoms, is expected to have better electronic properties than graphene and has been mostly synthesized on Ag surfaces. Although scanning tunneling microscopy (STM) has been used for visualizing its atomic structure in real space, the interpretation of STM contrast is not straightforward and only the topmost Si atoms were observed on the $(4\ifmmode\times\else\texttimes\fi{}4)$ silicene/Ag(111) surface. Here, we demonstrate that high-resolution atomic force microscopy (AFM) can resolve all constituent Si atoms in the buckled honeycomb arrangement of the $(4\ifmmode\times\else\texttimes\fi{}4)$ silicene. Site-specific force spectroscopy attributes the origin of the high-resolution AFM images to chemical bonds between the AFM probe apex and the individual Si atoms on the $(4\ifmmode\times\else\texttimes\fi{}4)$ silicene. A detailed analysis of the geometric parameters suggests that the pulling up of lower-buckled Si atoms by the AFM tip could be a key for high-resolution AFM, implying a weakening of the Si-Ag interactions at the interface. We expect that high-resolution AFM will also unveil atomic structures of edges and defects of silicene, or other emerging 2D materials.