Exploration of Structures of Two-Dimensional Boron-Silicon Compounds with sp(2) Silicon.

The most stable structures of two-dimensional (2D) boron-silicon (B-Si) compounds containing planar sp(2)-bonding silicon (sp(2)-Si) are explored using the first-principles calculation-based particle-swarm optimization method. Among 10 B-Si compounds considered, we find that for BSi4, BSi3, BSi, B2Si, B3Si, B5Si, and B6Si, each Si atom is bonded with three B or Si atoms within the same plane, representing a preference of planar sp(2)-Si structure in B-Si compounds. For BSi2 and B4Si, the predicted lowest-energy structures entail a small out-of-plane buckling. Furthermore, a planar-tetracoordinated Si (ptSi) atom bonded with four B atoms within the same plane is observed in the lowest-energy structure of B7Si compound. Dynamical stabilities of the predicted 10 2D B-Si compounds are confirmed via phonon-spectrum calculation. The lowest-energy 2D B-Si compounds are all metals, regardless of the B-Si stoichiometry considered in this study.