Silicene

Silicene is a two-dimensional allotrope of silicon, with a hexagonal honeycomb structure similar to that of graphene. Contrary to graphene, silicene is not flat, but has a periodically buckled topology; the coupling between layers in silicene is much stronger than in multilayered graphene; and the oxidized form of silicene, 2D silica, has a very different chemical structure from graphene oxide. Although theorists had speculated about the existence and possible properties of free-standing silicene, researchers first observed silicon structures that were suggestive of silicene in 2010. Using a scanning tunneling microscope they studied self-assembled silicene nanoribbons and silicene sheets deposited onto a silver crystal, Ag(110) and Ag(111), with atomic resolution. The images revealed hexagons in a honeycomb structure similar to that of graphene, which, however, were shown to originate from the silver surface mimicking the hexagons. Density functional theory (DFT) calculations showed that silicon atoms tend to form such honeycomb structures on silver, and adopt a slight curvature that makes the graphene-like configuration more likely. However, such a model has been invalidated for Si/Ag(110): the Ag surface displays a missing-row reconstruction upon Si adsorption and the honeycomb structures observed are tip artifacts. This was followed in 2013 by the discovery of dumbbell reconstruction in silicene that explains the formation mechanisms of layered silicene and silicene on Ag. In 2015, a silicene field-effect transistor was tested. that opens up opportunities for two-dimensional silicon for fundamental science studies and electronic applications. In 2022, it was found that silicene/Ag(111) growth on top of a Si/Ag(111) surface alloy, functions as a foundation and scaffold for the two-dimensional layer. This, however, raises questions of whether silicene can be truly regarded as two-dimensional material at all, due to its strong chemical bonds to the surface alloy. Silicon and carbon are similar atoms.