Feasibility study of dative bond formation for bilayer silicon growth under excessive strain

Energy bandgap opening has been found in low-buckle bilayer silicene under tensile in-plane strain. Practically such substantial in-plane strain could be provided from the substrates. The intense interfacial covalent bonds ensure an in-plane lattice-matching expitaxial growth, but at the same time impose a challenge in forming low-buckle two-dimensional films. We performed a theoretical study using density function theory to investigate the feasibility of growing bilayer silicon under excessive in-plane strain on various substrates. By the insertion of an air gap, dative bonds have been found at the interface on the substrates with the preferred polarized surface. The interactions of the transferred electrons from the surface-terminating metallic atoms of the substrates and the electron sea in the bilayer silicon was observed. The strength of the dative bond is reduced to about ∼0.05% of the Ga-Si covalent bond in the absence of the air gap. Preservation of substantial in-plane strain has been obtained in the bilayer silicon, resulting in a low-buckle bilayer silicon with opened energy bandgap up to ∼75 meV.