Superlattices of Fluorinated Interlayer-Bonded Domains in Twisted Bilayer Graphene

We report results based on first-principles density functional theory calculations for the structural and electronic properties of fluorinated carbon nanostructures formed by interlayer covalent C-C bonding in twisted bilayer graphene (TBG). These hybrid sp(2)/sp(3) carbon nanostructures consist of superlattices of diamond-like or fullerene-like nanodomains embedded within the graphene layers of TBG. The symmetry and periodicity of these superstructures are determined by the Moire pattern formed by the twisting of the graphene planes of the bilayer and is responsible for the character of the superstructures, which may range from semimetallic to semiconducting or insulating depending on the tuning of specific parameters, such as the twist angle and the density of interlayer C-C bonds. We demonstrate that fluorine chemisorption generates more stable structures than those formed by hydrogen chemisorption, suggesting that functionalizing TBG by controlled patterned fluorination is a better strategy than hydrogenation for synthesis of nanostructures that are stable over a broader temperature range consistently with what has been observed for single-layer graphene. Significant differences found between fluorinated and hydrogenated configurations in their structural parameters, surface properties, and electronic structures suggest that the choice of functionalizing agent can be used for precise tuning of the properties of the resulting nanostructures.