(Invited) Is the Silicene a 2D Dirac Material?

Silicene, a 2D honeycomb layer of Si, has attracted much attention, since a Dirac fermion character like graphene was predicted.  Furthermore the silicene has a 2D topological insulator due to the 1000 times stronger spin-orbit coupling than graphene. The hypothetical silicene is a free standing layer, but in practice, experimentally fabricated silicenes so far are 2D layers of silicon epitaxially grown on substrates. We will discuss, on the basis of the structure determination on an atomic scale by using quantitative LEED analysis, the nature of the epitaxial silicenes on Ag(111) surface; the influence of the silicene-substrate interaction for the single layer silicene and if the multi-layer silicene fabricated on the substrate has the features expected for the free-standing silicene.