Single and bilayer bismuthene: Stability at high temperature and mechanical and electronic properties

Abstract

Based on first-principles phonon and finite temperature molecular dynamics calculations including spinorbit coupling, we showed that free-standing single-layer phases of bismuth, namely buckled honeycomb and asymmetric washboard structures named as bismuthene, are stable at high temperature. We studied the atomic structure, mechanical, and electronic properties of these single-layer bismuthene phases and their bilayers. The spin-orbit coupling is found to be crucial in determining lattice constants, phonon frequencies, band gaps, and cohesion. In particular, phonons of 3D hexagonal crystal, as well as those of single-layer bismuthene phases, are softened with spin orbit coupling. By going from 3D hexagonal crystal to free-standing single-layer structures, 2D hexagonal lattice is compressed and semimetal is transformed to semiconductor as a result of confinement effect. On the contrary, by going from single-layer to bilayer bismuthenes, the lattice is slightly expanded and fundamental band gaps are narrowed. Our results reveals that interlayer coupling in multilayer and 3D Bi crystal is crucial for topologically trivial to nontrivial and semimetal to semiconductor transitions.

Stable single-layer structure of group-V elements

“…Entries are square-lattice constants a = b, bond lengths d i (i = 1,2), selected bond angles α i (i = 1,2,3) and β, buckling parameter z, in-plane stiffness C x , C y ; Poisson's ratios ν xy , ν yx . [43] aw-X (X = P, As, Sb, and Bi) structures. Notably, the lattice constants a = b, bond lengths d 1,2 , and the buckling z increase with increasing the row number of the X atom.…”

“…After the synthesis of very thin films of phosphorus [27] researchers started to seek similar structures in other group-V elements or pnictogens. Recent theoretical studies have predicted that nitrogen [28], phosphorus [29][30][31], arsenic [32][33][34][35], antimony [36][37][38][39], bismuth [40][41][42][43], and compounds of group-V elements [44] can form stable freestanding SL, planar as well as buckled honeycomb (b) structures similar to that of silicene and germanene and also other manifolds, such as SL symmetric (w) and asymmetric (aw) washboard structures, among others. These SL phases are named, respectively, nitrogene, phosphorene, arsenene, antimonene, and bismuthene.…”

“…Earlier, we studied SL pnictogen phases consisting of planar and buckled honeycomb and symmetric and asymmetric washboard structures, whereby their dynamical and thermal stability, mechanical, electronic, magnetic, and optical properties were revealed and also their functionalization with selected single atoms and molecules was investigated [21,[34][35][36]43]. In those studies crucial effects of the structures on physical properties were revealed.…”

Optical properties of single-layer and bilayer arsenene phases

“…The layered black and blue phosphorus with band gaps suitable for 2D electronics have initiated the search for similar structures in other group V elements or pnictogens. In general, the recent theoretical works have predicted that nitrogen [13], phosphorus [14], arsenic [15], antimony [16,17], and bismuth [18] can form similar single-layer, buckled honeycomb or washboard structures.…”

Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects

“…Most recently, based on extensive dynamical and thermal stability analysis, stable, free-standing, 2D SL phases of bismuth, namely buckled honeycomb or hexagonal (h-Bi), symmetric washboard (w-Bi), asymmetric washboard (aw-Bi), and square-octagon (so-Bi) structures identified as bismuthene, were unveiled, with aw-Bi being more energetic than w-Bi [21,22]. Once the stability of free-standing bismuthenes has been demonstrated, whether they are topologically trivial remains to be examined.…”