Monolayer-to-bilayer transformation of silicenes and their structural analysis

Abstract

Silicene, a two-dimensional honeycomb network of silicon atoms like graphene, holds great potential as a key material in the next generation of electronics; however, its use in more demanding applications is prevented because of its instability under ambient conditions. Here we report three types of bilayer silicenes that form after treating calcium-intercalated monolayer silicene (CaSi 2) with a BF 4 '-based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF 2 and/or CaSi 2, with one of the bilayer silicenes being a new allotrope of silicon, containing four-, five-and six-membered sp 3 silicon rings. The number of unsaturated silicon bonds in the structure is reduced compared with monolayer silicene. Additionally, the bandgap opens to 1.08 eV and is indirect; this is in contrast to monolayer silicene which is a zero-gap semiconductor.