Silicene: experimental evidence and properties of the graphene-like form of silicon
A Fleurence, Japan Advanced Institute of Science and Technology (JAIST), Japan

Due to their flexibility, their smoothness and their ultimate thinness, two-dimensional materials are expected to improve the efficiencies of electronic devices. Silicene, as an analogue of graphene made of Si atoms is an appealing candidate. This atom-thick honeycomb lattice is predicted to be stable, in the free-standing form, in a slightly-buckled conformation whose computed band structure is similar to that of graphene since it features Dirac cones at the K points of its Brillouin zone.

So far, silicene only exists in epitaxial forms on conductive substrates like (0001)-oriented zirconium diboride (ZrB2) thin films grown on Si(111). We experimentally demonstrated that a single layer of silicon atoms segregating spontaneously on the diboride surface crystallises in the form of a honeycomb structure. The silicene nature of this silicon monolayer was found in the existence of a π-electronic band centered on the K points of the Brillouin zone. The observed gap opening is a result of the specific buckling of epitaxial silicene and evidences that the flexibility of its internal structure allows the tuning of the electronic properties of silicene.

Major challenges such as the oxidation of silicene in air, are still facing the development of silicene-based devices. The demonstration of the existence of this new allotrope of silicon opens the way to the search of other 2D materials.