The Tunable Bandgap of AB-Stacked Bilayer Graphene on SiO₂ with H₂O Molecule Adsorption

The atomic and electronic structures of AB-stacking bilayer graphene (BLG) in the presence of H₂O molecules are investigated by density functional theory calculations. For free−standing BLG, the bandgap is opened to 0.101 eV with a single H₂O molecule adsorbed on its surface. The perfectly suspended BLG is sensitive to H₂O adsorbates, which break the BLG lattice symmetry and open an energy gap. While a single H₂O molecule is adsorbed on the BLG surface with a SiO₂ substrate, the bandgap widens to 0.363 eV. Both the H₂O molecule adsorption and the oxide substrate contribute to the BLG bandgap opening. The phenomenon is interpreted with the charge transfer process in 2D carbon nanostructures.