Silicene and germanene: Silicon and germanium in the “flatland”

• Free-standing buckled silicene and germanene are predicted to be stable.
• 4 × 4 Silicene/Ag(1 1 1): evidence for a 2D hybrid surface metallic band, as in graphene.
• Evidence of Dirac bands in multilayer silicene with (3×3)R30° superstructure.
• Promising progress in the growth of stable epitaxial germanene.
• 2D hexagonal AlN is a non-metallic candidate substrate for silicene and germanene.

Atomically thin two dimensional (2D) materials offer ultimate thickness scaling of nanoelectronic devices which could substantially improve the electrostatic control and enable a number of low power versatile applications. Silicene and germanene, the silicon and germanium equivalents of graphene have attracted an immense interest. The progress in the growth and physical characterization of these materials will be reviewed. Emphasis will be given on the most stable phases of silicene focusing on the electronic bandstructure attempting to answer the question about the existence of Dirac Fermions. The stability and the challenges for field effect device processing are discussed and the new trends towards multilayer silicene and growth on non-metallic/insulating substrates are reviewed.

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