Modulating the bandgap of Cr-intercalated bilayer graphene combining the 18-electron rule and the 2D superatomic-molecule theory.

Bandgap engineering of graphene is of great significance for its potential applications in electronic devices. Herein, we used a sandwich compound Cr(CH) as the building block to construct Cr-intercalated bilayer graphene (BLG), namely a CCr monolayer. Chemical bonding analysis reveals that strong d-π interaction ensures π electrons of the graphene layers and d orbitals of the Cr atoms localized in CCrC units to achieve the favored 18-electron rule, thus leading to a bandgap of 0.24 eV. Subsequently, a CCr monolayer with lower proportion of Cr is further designed using Cr(CH) as building units, where a newly developed two-dimensional (2D) superatomic-molecule theory is introduced to rationalize its electronic structure. The CCr monolayer not only satisfies the 18-electron rule, but also localizes extra π electrons to form two layers of 2D superatomic crystals composed of 2D superatoms (O and N), resulting in a wider bandgap of 0.74 eV. This work opens an effective avenue to modulate the bandgap of BLG combining the 18-electron rule and the 2D superatomic-molecule theory.