Vacancy induced phonon properties of hydrogen passivated graphene

The phonon properties of hydrogen passivated graphene with vacancy defects are studied using the forced vibrational method. The phonon density of states (PDOS) and typical mode patterns are calculated over a broad range of vacancies. We find that phonon properties of graphene strongly depend on the system size. We observe a broadening and softening of the PDOS peaks with the increase of vacancy concentrations. We find an increasing C-H stretching mode with the increase of defect density. Our numerical experiments reveal that the typical mode pattern for K point in-plane TO modes phonon show the spatial localized vibrations persuaded by vacancy defects, which are in conceptually good agreement with the experimental results of the large D band peak of the Raman spectra comes from the imperfections of crystal. The typical displacement pattern for C-H stretching mode shows a random displacement of H atoms in contrast to C atoms. Our simulation results show the significant impact of vacancy defects on the vibrational properties of graphene.