Tailoring topological states in silicene using different halogen-passivated Si(111) substrates

Abstract

We investigate the band structure and topological phases of silicene embedded on halogenated Si(111) surface, by virtue of density functional theory calculations. Our results show that the Dirac character of low energy excitations in silicene is almost preserved in the presence of silicon substrate passivated by various halogens. Nevertheless, the combined effects of symmetry breaking due to both direct and van der Waals interactions between silicene and the substrate, charge transfer from suspended silicene into the substrate, and finally the hybridization which leads to the charge redistribution, result in a gap in the spectrum of the embedded silicene. We further take the spin-orbit interaction into account and obtain the resulting modification in the gap. The energy gaps with and without spin-orbit coupling, vary significantly when different halogen atoms are used for the passivation of the Si surface and for the case of iodine, they become on the order of 100 meV. To examine the topological properties, we calculate the projected band structure of silicene from which the Berry curvature and Z 2 -invariant based on the evolution of Wannier charge centers are obtained. As a key finding, it is shown that silicene on halogenated Si substrates has a topological insulating state which can survive even at room temperature for the substrates with iodine and bromine at the surface. Therefore, these results suggest that we can have a reliable, stable and robust silicene-based two-dimensional topological insulator using the considered substrates.

Halide-Induced Self-Limited Growth of Ultrathin Nonlayered Ge Flakes for High-Performance Phototransistors

“…Because of the relatively weak van der Waals interaction between contiguous layers, 2D layered materials with ultrathin thickness can be effortlessly realized through mechanical exfoliation or chemical vapor deposition (CVD). However, there are also many nonlayered materials such as group IVA, 22 II−VI, 23 and III− VA 24 semiconductors with excellent electronic and optoelectronic properties. 25 Ge is famed for the high carrier mobilities (electron: μ e = 3900 cm 2 V −1 s −1 , hole: μ h = 1900 cm 2 V −1 s −1 ), a narrow bandgap of 0.67 eV in the bulk phase at 300 K, and large absorption coefficient of 2 × 10 5 cm −1 , rendering it an excellent candidate for near-infrared (NIR) photodetection.…”