Silicene, a silicon analog of graphene, has the potential to become a candidate next-generation material by virtue of its novel physical and chemical properties. Although a rich variety of rotationally nonequivalent silicene structures have been observed with silicene grown on Ag(111) surfaces, the $T$ phase, which has been considered a precursor phase, has a less-ordered structure, and thus, it is difficult to clarify its atomic structure. In this paper, we report the atomic structures of the $T$ phase observed by high-resolution atomic force microscopy (AFM). While scanning tunneling microscopy images of the $T$ phase show characteristic round dots, AFM reveals that the $T$ phase has a continuous Si honeycomb arrangement, thus forming silicene. We identify two types of $T$ phases with different silicene rotation angles with respect to the Ag substrate: the ($\sqrt{13}\times \sqrt{13}$) type-I $T$ phase and the tiling-pattern $T$ phase. The former has a unit cell corresponding to the conventionally proposed ($\sqrt{13}\times \sqrt{13}$) type I with less periodicity of Si buckling, while the latter is identified by the tessellation with four different rhombuses. We also investigate the $T$ phase by site-specific force spectroscopy and find that some Si atoms at the $T$ phase have slightly different chemical reactivities.

• Received 8 August 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.104002