Semiconducting defect-free polymorph of borophene: Peierls distortion in two dimensions

Abstract

In contrast to the well-defined lattices of various two-dimensional (2D) systems, the atomic structure of borophene is sensitive to growth conditions and type of the substrate which results in rich polymorphism. By employing ab initio methods, we reveal a thermodynamically stable borophene polymorph without vacancies which is a semiconductor unlike the other known boron sheets, in the form of an asymmetric centered-washboard structure. Our results indicate that asymmetric distortion is induced due to Peierls instability which transforms a symmetric metallic system into a semiconductor. We also show that applying uniaxial or biaxial strain gradually lowers the obtained band gap and the symmetric configuration is restored following the closure of the band gap. Furthermore, while the Poisson's ratio is calculated to be high and positive in the semiconducting regime, it switches to negative once the metallicity is retrieved. The realization of semiconducting borophene polymorphs without defects and tunability of its electronic and mechanical response can extend the usage of boron sheets in a variety of nanoelectronic applications.

Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table

“…In the search for other defect-free polymorphs of borophene, a thermodynamically stable puckered phase with an asymmetric centered-washboard (acw) structure of orthorhombic symmetry has been discovered that, unlike other boron sheets, is a semiconductor (centered because there is another atom at the center of the hexagons). 27 According to MD simulations, this semiconducting polymorph is dynamically and thermodynamically stable up to about 800 K. Interestingly, the application of uniaxial or biaxial tensile strain closes the gap and transforms the system back to the metallic state, and the positive Poisson ratio becomes negative. 27 For aluminene, besides the planar honeycomb structure of aluminium, 28,29 a graphene-like buckled, 30 triangular, 29 and four-layer 8-Pmmn structure 31 have been proposed (see Table 1).…”

“…27 According to MD simulations, this semiconducting polymorph is dynamically and thermodynamically stable up to about 800 K. Interestingly, the application of uniaxial or biaxial tensile strain closes the gap and transforms the system back to the metallic state, and the positive Poisson ratio becomes negative. 27 For aluminene, besides the planar honeycomb structure of aluminium, 28,29 a graphene-like buckled, 30 triangular, 29 and four-layer 8-Pmmn structure 31 have been proposed (see Table 1). Note that some of these phases have not yet been fully characterized and confirmed by other authors and some allotropic modifications may only be stable if the phonon dynamics is stabilized by the strain exerted by monolayer-substrate interaction.…”

Formation of stable polonium monolayers with tunable semiconducting properties driven by strong quantum size effects

“…The process of phase transition of the Po film with N = 6 can be viewed as layered Peierls-like distortion. 51–53 The occupation of electronic states near the E F of Po films with N = 4 and 5 is almost unchanged after relaxation, showing that the stability of these films were not improved, as demonstrated in the calculated phonon spectra in Fig. 3f and g.…”

The Diffusion and Clustering Formation of Gold Atoms on Alpha-Graphyne

“…The discovery of graphene (Novoselov, 2004) has led to emerge a new era in material science due to its various remarkable mechanical and electronic properties including zero-gap semiconductor nature, ultrahigh carrier mobility, and unusual high intrinsic thermal conductiovity (Novoselov et al, 2005;Zhang et al, 2005;Yan et al, 2008). Since then, the list of 2D materials (graphyne (Baughman et al, 1987), silicene (Okamoto et al, 2010), and many more (Kilic et al, 2016;Ipek et al, 2018;Pekoz et al, 2018;) is fast expanding.…”