Raman study on defective graphene: Effect of the excitation energy, type, and amount of defects

We present a detailed Raman study of defective graphene samples containing specific types of defects. In particular, we compared sp^3 sites, vacancies, and substitutional Boron atoms. We find that the ratio between the D and G peak intensities, I (D) /I (G), does not depend on the geometry of the defect (within the Raman spectrometer resolution). In contrast, in the limit of low defect concentration, the ratio between the D^' and G peak intensities is higher for vacancies than sp^3 sites. By using the local activation model, we attribute this difference to the term Cₒ, ₗ, representing the Raman cross section of I (x) /I (G) associated with the distortion of the crystal lattice after defect introduction per unit of damaged area, where x = D or D^'. We observed that Cₒ, ₃=0 for all the defects analyzed, while Cₒ, ₃^{'} of vacancies is 2. 5 times larger than Cₒ, ₃^{'} of sp^3 sites. This makes I (D) /I (D^') strongly sensitive to the nature of the defect. We also show that the exact dependence of I (D) /I (D^') on the excitation energy may be affected by the nature of the defect. These results can be used to obtain further insights into the Raman scattering process (in particular for the D^' peak) in order to improve our understanding and modeling of defects in graphene.