Silicene

Silicene is a two-dimensional allotrope of silicon consisting of a single layer of silicon atoms arranged in a hexagonal honeycomb lattice. Unlike planar graphene, silicene adopts a low-buckled geometry in which the two sublattices are vertically displaced. This buckling reflects silicon’s preference for sp3 bonding and affects its electronic structure, yielding Dirac-like states near the K points in theory.

Because free-standing silicene is not stable in air, most realizations have been grown epitaxially on substrates, notably metallic surfaces such as Ag(111). Other substrates, including zirconium diboride, have been explored. The strong interaction with substrates, together with oxidation sensitivity, means that the intrinsic properties of silicene can be altered in practical samples, so measurements are often performed in situ or with protective capping layers.

Electronic properties: Theoretical work predicts Dirac cones and high carrier mobility in silicene, analogous to graphene but influenced by silicon’s heavier atomic mass and buckled structure. The intrinsic spin-orbit coupling in silicene is larger than in graphene, opening the possibility of a quantum spin Hall insulator phase under suitable conditions. A perpendicular electric field or substrate-induced symmetry breaking can induce a tunable band gap, though observed gaps in experiments are frequently limited by the substrate environment. The Fermi velocity is typically discussed in the same broad range as graphene, reflecting similar linear dispersion near the Dirac points.

Applications and status: Silicene holds potential for silicon-compatible nanoelectronics and spintronics, with prospects for a controllable band gap and topological states. Realizing scalable, stable devices remains challenging due to air sensitivity and strong substrate effects. Research continues on protective encapsulation, synthesis on diverse substrates, and the development of silicene-based nanostructures such as nanoribbons.