title: 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 (CaSi2) with a BF4(-) -based ionic liquid. The bilayer silicenes that are obtained are sandwiched between planar crystals of CaF2 and/or CaSi2, 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.
authors: TOYOTA Central R&D Labs, Inc., 41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan.
authors: Ritsuko
authors: R
authors: Yaokawa
authors: TOYOTA Central R&D Labs, Inc., 41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan.
authors: Tetsu
authors: T
authors: Ohsuna
authors: CD-FMat, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors: Tetsuya
authors: T
authors: Morishita
authors: The Electron Microscopy Center, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
authors: Yuichiro
authors: Y
authors: Hayasaka
authors: School of Science, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.
authors: Michelle J S
authors: MJ
authors: Spencer
authors: TOYOTA Central R&D Labs, Inc., 41-1, Yokomichi, Nagakute, Aichi 480-1192, Japan.|JST Presto, Kawaguchi 332-0012, Japan.
authors: Hideyuki
authors: H
authors: Nakano