Exploration of Structures of Two-Dimensional Boron–Silicon Compounds with sp² Silicon

The most stable structures of two-dimensional (2D) boron–silicon (B–Si) compounds containing planar sp²-bonding silicon (sp²-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 sp²-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.