Two-dimensional hexagonal tin: ab initio geometry, stability, electronic structure and functionalization

Abstract

We study the structural, mechanical and electronic properties of the two-dimensional (2D) allotrope of tin: tinene/stanene using first-principles calculation within density functional theory, implemented in a set of computer codes. Continuing the trend of the group-IV 2D materials graphene, silicene and germanene; tinene is predicted to have a honeycomb lattice with lattice parameter of a0 = 4.62 Å and a buckling of d0 = 0.92 Å. The electronic dispersion shows a Dirac cone with zero gap at the Fermi energy and a Fermi velocity of m s−1; including spin–orbit coupling yields a bandgap of 0.10 eV. The monolayer is thermally stable up to 700 K, as indicated by first-principles molecular dynamics, and has a phonon dispersion without imaginary frequencies. We explore applied electric field and applied strain as functionalization mechanisms. Combining these two mechanisms allows for an induced bandgap up to 0.21 eV, whilst retaining the linear dispersion, albeit with degraded electronic transport parameters.

Stability and electronic structure of two-dimensional allotropes of group-IV materials

“…Naturally, the other group-IV elements have been considered as candidates to have a graphenelike hexagonal, honeycomb structure with similar exceptional properties. Indeed, corresponding 2D structures for other group-IV elements have been predicted and studied theoretically, namely, silicene (Si-based), germanene (Gebased), and stanene (or tinene) (Sn-based) [12][13][14][15][16][17][18]. Different from graphene, in the sheet the silicon atoms are buckled, which makes an electronic system with a partial sp 3 hybridization.…”

Tension-induced mechanical properties of stanene

“…In a form of 2D stannum, stanene is first proposed by Zhang et al and has drawn broad attention. [11][12][13][14][15][16][17] It is believed that stanene is a 2D topological insulator (TI). TIs are a class of novel condensed matter with insulating band gap in the bulk while conducting states at the edges (for 2D TIs) resulted from strong SOC effect and protected by time reversal symmetry.…”

Emerging Applications of Elemental 2D Materials

“…While all elements in Group IV share electronic features similar to its lightest element, C, the favorable hybridization state for Si, Ge, and Sn is somewhere between sp 2 and sp 3 . This leads to buckled crystal lattice structures rather than planar as observed in graphene, although a planar polymorph of 2D Sn has also been experimentally synthesized on silver substrates . In a recent study, Matusalem et al suggested the MoS 2 ‐like symmetry to be most stable for stanene, while large honeycomb dumb‐bell (LHD) geometry (Figure ) was reported to be more stable for silicene and germanene .…”

“…While silicene and germanene also possess nonzero Z 2 invariants and therefore the possibility for the QSHE, their small spin–orbit splitting makes it only possible at low temperature . Stanene, however, has been predicted to possess an appreciable spin–orbit gap of around 70 meV …”

“…Strain : In semimetallic germanene, tensile strain of up to 16% was predicted to shift the Dirac point above the Fermi level, inducing p‐type behavior due to decreased sp hybridization and increased Ge–Ge bond length . Broek et al suggested that applying lateral strain on stanene under out‐of‐plane electric field can open up the bandgap up to 0.21 eV, while Modarresi and co‐workers suggested that the SOC bandgap of ≈0.07 eV in stanene closes under applied strain . Fu et al studied stanene and predicted a metal–insulator transition under critical biaxial strain .…”