A Novel Two-Dimensional Allotrope of Silicon Grown on Al(111): A Case Study of the Interface Effect

Based on density functional calculations, a novel planar allotrope of silicon on Al(111) is rationally designed by using the lowest energy principle, which is also predicted to be stable above room temperature to suggest the possibility for its fabrication. The corresponding free-standing sheet would be buckled though the structural characteristics still remain, whose stability has also been evaluated in detail. It has been found to have strong anisotropic properties to be as hard as silicene in a specific direction and to be very soft in the perpendicular direction. Surprisingly, a peculiar negative Poisson's ratio showing unusual mechanical properties is also found. The indirect bandgap of 0.14 eV of the free-standing sheet could be closed by applying tensile strain. Interestingly, the Dirac cone of the orthogonal lattice allotrope sheet can be obtained by applying biaxial strain, for which the velocity of the charge carriers could reach 5.97 × 105 m/s. In addition, the hydrogenated sheet is also quite stable and may find usage for sunlight absorption, field-effect transistor, etc., which may be decorated with Ti, Fe, or Co adsorptions to have half-metallic conducting properties for spin filtering.