Crystal phase engineering of silicene by Sn-modified Ag(111)

The synthesis of silicene by direct growth on silver is characterized by the formation of multiple phases and domains, posing severe constraints on the spatial charge conduction towards a technological transfer of silicene to electronic transport devices. Here we engineer the silicene/silver interface by two schemes, namely, either through decoration by Sn atoms, forming an Ag2Sn surface alloy, or by buffering the interface with a stanene layer. Whereas in both cases Raman spectra confirm the typical features as expected from silicene, by electron diffraction we observe that a very well-ordered single-phase 4 x 4 monolayer silicene is stabilized by the decorated surface, while the buffered interface exhibits a sharp root 3 x root 3 phase at all silicon coverages. Both interfaces also stabilize the ordered growth of a root 3 x root 3 phase in the multilayer range, featuring a single rotational domain. Theoretical ab initio models are used to investigate low-buckled silicene phases (4 x 4 and a competing root 13 x root 13 one) and various root 3 x root 3 structures, supporting the experimental findings. This study provides new and promising technology routes to manipulate the silicene structure by controlled phase selection and single-crystal silicene growth on a wafer-scale.