  We report a successful preparation of a purely honeycomb, graphene-like
borophene, by using an Al(111) surface as the substrate and molecular beam
epitaxy (MBE) growth in ultrahigh vacuum. Our scanning tunneling microscopy
(STM) reveals perfect monolayer borophene with planar, non-buckled honeycomb
lattice similar as graphene. Theoretical calculations show that the honeycomb
borophene on Al(111) is energetically stable. Remarkably, nearly one electron
charge is transferred to each boron atom from the Al(111) substrate and
stabilizes the honeycomb borophene structure, in contrast to the little charge
transfer in borophene/Ag(111) case. This work demonstrates that the borophene
lattice can be manipulated by controlling the charge transfer between the
substrate and the borophene film.
