Fullerphene: A double covalently bonded two-dimensional fullerene semiconducting crystal with preserved Dirac states and emergent flat bands

The discovery of each new allotropic manifestation of carbon has substantially propelled contemporary scientific research and applications, as vividly exemplified by the explosive progressions within the realms of fullerene, carbon nanotube, graphene, and diamond sciences over recent decades. Here, using state-of-the-art first-principles calculations, we predict a new type of two- dimensional carbon network, dubbed fullerphene, by replacing each C atom in graphene with a fullerene (C[in60}). Its high energetic stability is tied to the symmetric cycloaddition of the double bonds between each C[in60} superatom with each of its three neighbors. A kinetic pathway is also proposed for the selective fabrication of fullerphene on Cu(111) or Rh(111), upon exploiting its en- hanced stability over other competing C[in60} assemblies and significantly lowered kinetic barrier in seed growing, as strategically supported by a recent experimental advance. Further investigations on fullerphene reveal an array of desirable characteristics, including a substantial band gap of ~2 eV, Dirac states for the conduction electrons, and flat bands for the valence electrons. These findings represent a distinctly new and significant advance in both fullerene and graphene sciences.