Interlayer Coulomb interaction in twisted bilayer graphene nanofragments characterized by the vibrational mode of Gr+ band

Tip enhanced Raman spectra of AB-stacked bilayer graphene (BLG) and twisted bilayer graphene (TwBLG) nanofragments have been studied by using density functional theory. Different from a normal Raman spectrum of BLG, a unique Raman band Gr+ is observed in its tip enhanced Raman spectrum and assigned as a split of the G band. We attribute this split to the nonuniformity distribution of the charge on carbon atoms. Compared with BLG, the Gr+ band intensity of TwBLG is dramatically enhanced at a small twist angle and decreases with the angle increasing. Interlayer Coulomb interaction represented in the Gr+ mode of TwBLG matches well with the atom vibration strength distribution of the Gr+ band at different twist angles, and thereby the properties of the Gr+ band can be tuned by the twisted angle. The results may help to further understand the Raman spectra of TwBLG and provide deep insights for exploring vibrational modes of two-dimensional nanomaterials.