5. Chemically Modified Borophene

Two-dimensional (2D) materials have great potential in several applications such as batteries, catalysts, and electronic devices because of their unique properties, such as large surface area and novel electronic states (Butler et al. ACS Nano. 7(4):2898–926 (2013); Osada and Sasaki. Adv Mater. 24(2):210–28 (2012); Deng et al. Nat Nanotechnol. 11(3):218–30 (2016)). Among these 2D materials, boron-related materials exhibit polymorphisms (Zhang et al. Chem Soc Rev. 46(22):6746–63 (2017); Kondo. Sci Technol Adv Mater. 18(1):780–804 (2017); Jiao et al. Angew Chemie Int Ed. 55(35):10292–5 (2016)), which are unique characteristics differentiating them from 2D materials—that is, there are a wide variety of stable 2D phases owing to the ability to form multicenter bonding configurations of boron (Oganov et al. J Superhard Mater. 31(5):285–291 (2009)). Single monoatomic 2D boron (borophene) layers have been fabricated on solid surfaces with several different stable structures (Mannix et al. Nat Rev Chem. 1:0014 (2017); Xie et al. Adv Mater. 1900392:1–13 (2019)), which is consistent with theoretical predictions regarding polymorphs of borophene (Boustani. Surf Sci. 370(2–3):355–63 (1997); Penev et al. Nano Lett. 12(5):2441–5 (2012); Wu. ACS Nano. 6(8):7443–53 (2012)). Chemically modified borophene should also exhibit polymorphisms owing to these characteristics. Several stable structures are predicted for hydrogenated borophene (borophane) (Jiao et al. Angew Chemie Int Ed. 55(35):10292–5 (2016)). Chemically modified borophene can thus be regarded as a material with potential to exhibit several intriguing functionalities, physical properties, and chemical properties in a wide variety of applications. We note that a wide variety of chemically modified borophenes could also be used as building blocks from the viewpoint of large-scale material production. Indeed, combining 2D materials through layer stacking in a controlled manner has already been focused on and is reported to produce several novel functionalities including superconductivity in the form of new three-dimensional (3D) layered materials (van der Waals heterostructures) (Geim and Grigorieva. Nature. 499(7459):419–25 (2013)). In this paper, both theoretically predicted results and experimentally realized results of chemically modified borophene are reviewed.