Electronic and vibrational signatures of Stone-Wales defects in graphene: First-principles analysis

We identify electronic and vibrational signatures of Stone-Wales (SW) defects in graphene as a function of their concentration using first-principles calculations. We show that an array of SW defects leads to (a) a defect band in the electronic structure about 0.5 eV above the Fermi level, and (b) a shift in the Dirac cone from K to K +/- delta k in the Brillouin zone (BZ), with anisotropic dependence on the orientation and concentration of SW defects. These shifts in the Dirac cone are explained with a simple theoretical analysis based on BZ folding and electron-phonon coupling. Structural changes accompanying a SW defect induce long-wavelength rippling instabilities in graphene, which are shown within a quasicontinuum analysis to originate from the coupling between the G band and strain (acoustic modes). Formation of a rather short and stiff C-C bond at the center of a SW defect leads to (a) softening of the G band, which is scattered away from the defect, and (b) hardening of the D band, which gets localized at the defect. Our work will facilitate interpretation of experimentally observed changes in the morphology and Raman spectra of graphene associated with SW defects.