Band engineering of B2H2 nanoribbons**Project supported by the National Natural Science Foundation of China (Grant Nos. 61888102, 61390501, and 51872284), the CAS Pioneer Hundred Talents Program, the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB28000000), the Beijing Nova Program, China (Grant No. Z181100006218023), and the University of Chinese Academy of Sciences.

Abstract

Freestanding honeycomb borophene is unstable due to the electron-deficiency of boron atoms. B2H2 monolayer, a typical borophene hydride, has been predicted to be structurally stable and attracts great attention. Here, we investigate the electronic structures of B2H2 nanoribbons. Based on first-principles calculations, we have found that all narrow armchair nanoribbons with and without mirror symmetry (ANR-s and ANR-as, respectively) are semiconducting. The energy gap has a relation with the width of the ribbon. When the ribbon is getting wider, the gap disappears. The zigzag ribbons without mirror symmetry (ZNR-as) have the same trend. But the zigzag ribbons with mirror symmetry (ZNR-s) are always metallic. We have also found that the metallic ANR-as and ZNR-s can be switched to semiconducting by applying a tensile strain along the nanoribbon. A gap of 1.10 eV is opened under 16% strain for the 11.0-Å ANR-as. Structural stability under such a large strain has also been confirmed. The flexible band tunability of B2H2 nanoribbon increases its possibility of potential applications in nanodevices.