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.