Flat Building Blocks for Flat Silicene

Silicene is the silicon equivalent of graphene, which is composed of a honeycomb carbon structure with one atom thickness and has attractive characteristics of a perfect two-dimensional p-conjugated sheet. However, unlike flat and highly stable graphene, silicene is sticky and thus unstable due to its crinkled structure. Flatness is important for stability, and to obtain perfect p-conjugation, electron-donating atoms and molecules should not interact with the p electrons. The structural differences between silicene and graphene result from the differences in their building blocks, flat benzene and chair-form hexasilabenzene. It is crucial to design flat building blocks for silicene with no interactions between the electron donor and p-orbitals. I report here our recent successful design of such building blocks with density functional theory calculations [M. Takahashi, Sci. Rep. 2017, 7, 10855]. Our fundamental concept is to attach substituents that have sp-hybrid orbitals and act as electron donors in a manner that it does not interact with the p orbitals. The honeycomb silicon molecule with BeH at the edge designed according to our concept, clearly shows the same structural, charge distribution, and molecular orbital characteristics as the corresponding carbon-based molecule.