Versatile two-dimensional boron monosulfide polymorphs with tunable bandgaps and superconducting properties

Abstract

The typical two-dimensional semiconductors, group IIIA chalcogenides, have garnered tremendous interest for their outstanding electronic, mechanical, and chemical properties. However, so far, there have been rare reports on boron monosulfides (BS) binary material. Here, four two-dimensional BS sheets, namely, the α-, β-, γ-, and δ-BS sheets, are proposed and discussed from first principles calculations. State-of-the-art calculations reveal all these structures are thermally and dynamically stable, indicating the potential for experimental synthesis. Specifically, for α-BS, it has a calculated exfoliation energy of 0.96 J m−2, suggesting that the preparation of α-BS is feasible by the exfoliation of bulk rhombohedral-BS. Our results show that α-, β-, and γ-BS are semiconductors, whereas δ-BS is a metallic system. Remarkably, our calculations indicate that δ-BS is a superconductor with a large electron-phonon coupling (λ ≈ 1.51), leading to a high superconducting critical temperature (Tc ≈ 21.56 K), which is the interesting property with intrinsic superconducting among all two-dimensional group IIIA chalcogenides. The potential of semiconducting BS monolayers as the gas-sensor or thermoelectric materials is also demonstrated.

Two-Dimensional Direct Semiconductor Boron Monochalcogenide γ-BTe: Room-Temperature Single-Bound Exciton and Novel Donor Material in Excitonic Solar Cells

“…Each B atom connects three X atoms and a B atom, and each X atom connects three B atoms. For monolayer γ-BS, the PBE-obtained lattice constant a is 7.38 Å and b is 3.06 Å, which is in well agreement with the previous result . The corresponding lattice parameter of monolayer γ-BSe and γ-BTe is shown in Table .…”

Crystalline boron monosulfide nanosheets with tunable bandgaps

“…1d and S3), which is consistent with the theoretical prediction that r-BS is easily exfoliated to form nanosheets. 14 Crucially, our TEM observations suggest that the 2D BS nanosheets formed by the exfoliation of r-BS preserve the original crystal structure.…”

“…Reliability factors based on weighted profiles, Rwp, and Bragg Intensities, RI, were 5.9% and 2.7%, respectively. Lattice constants determined by refinement are a = 3.05065(1) and c = 20.38458 (14).…”

“…Among these 2D materials, boronrelated materials are of particular interest because of their polymorphism 7,8,9 and ability to easily form multi-center bonds. 10 Theoretically, boron exhibits a wide variety of stable 2D phases, including borophene, 7,11,12,13 hydrogenated 2D boron (borophane or hydrogen boride), 9 2D boron monosulfide (BS), 14 2D boron oxide, 15 and 2D boron phosphide. 16 Hence, several building blocks can be obtained by tuning the bonding configurations of 2D boron nanomaterial.…”

“…However, to date, only borophene, 17,18,19 borophane, 20,21,22,23 and boron nitride have been realized experimentally, and, to the best of our knowledge, no other 2D boron compounds have been reported. Nevertheless, a recent theoretical study predicted that 2D BS exists in several stable phases with unique electronic structures, 24 including superconducting, 14 thermoelectric, 25 and hydrogen storage properties. 26 In this paper, we report the preparation of 2D BS nanosheets by physically exfoliating bulk rhombohedral boron monosulfide (r-BS).…”