Investigation of spatial disorder in graphite by Raman lineshape analysis

Disorder in graphite is studied as a function of phonon softening of Raman active modes. A comprehensive analysis of disorder is discussed here using the G and D modes of the graphite. Two-dimensional disorder is manifested in the correlation length of the sp² hybridization in the graphitic plane. It is characterized here by lineshape analysis of Raman activated G and D modes. Phonon softening of the G mode is almost insensitive to disorder. It is more asymmetric on the lower energy side with increasing disorder. Phonon softening and line broadening of the D mode have high sensitivity to disorder in polycrystalline graphite. Electron-phonon coupling is responsible for phonon softening and line broadening of the D mode, which is double-resonant Raman scattering involving disorder, electron, and TO (transverse optical) phonon. Increasing disorder allows TO phonons of higher wavevector and lower energy during double-resonant Raman scattering. (author)