How is Honeycomb Borophene Stabilized on Al(111)?

Because of the electron deficiency, freestanding honeycomb borophene (HB) is predicted to be kinetically unstable. Very recently, the honeycomb phase of two-dimensional boron, nevertheless, has been surprisingly synthesized via a molecular beam epitaxy method on Al(111) (Sci. Bull. 2018, 63, 282-286). The mechanism underlying the enhanced stability of the supported HB remains unclear. Here, we comprehensively investigate the structural, energetic, electronic, and lattice dynamic properties of HB supported on Al(111) via ab initio calculations. Our calculations reveal a strong adhesion energy between the HB and the Al(111) substrate similar to 1.05 eV/atom, which is significantly stronger than the interaction between graphene and any transition-metal surfaces that have been studied before. The strong interaction can be elucidated by the charge donation/back donation as well as the strong covalent bonding interactions between the HB and the substrate. Such a strong adhesive interaction stabilizes the supported HB, whose kinetic stability is further validated by the direct calculation of phonon dispersion.