Twist Angle-Dependent Chemical Reactivity of Bilayer Graphene.

Bilayer graphene (BLG) exhibits unique physical properties that strongly depend on the twist angle, such as superconductivity at magic angles, moiré superlattices, and quasicrystal structures. However, the influence of the twist angle on the chemical properties remains unclear. Here, we investigated the chemical reactivity of twist-angle-controlled BLG toward ultraviolet (UV)/ozone oxidation. For the systematic study of the angle dependence, two sheets of monolayer graphene were stacked with controlled stacking angles from 0° to 30° with 5° intervals. Raman spectroscopy revealed that the degree of oxidation is strongly dependent on the twist angle and it increases with the twist angle, indicating a strong influence of the interlayer coupling on the reactivity. Scanning transmission electron microscopy and X-ray photoelectron spectroscopy revealed that the oxidation proceeds through the formation of localized oxygen functional groups in the graphene lattice. Density functional theory calculations suggested that functionalization becomes energetically more favorable at higher twist angles. Layer-specific 12C/13C isotope labeling demonstrated that the oxidation occurs mostly at the top graphene layer, while the bottom layer remains almost intact. Furthermore, the generality of the twist-angle-dependent reactivity was confirmed via molecular functionalization with 4-nitrobenzenediazonium molecules. Our work highlights the importance of twist angle in the chemistry of graphene, paving a way to tune its electronic structure and carrier transport properties.