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 sp³ 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 sp³ sites. By using the local activation model, we attribute this difference to the term C{}S,x$, 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 ${C}S,D=0$ for all the defects analyzed, while ${C}_{S,{D}^{{'}}}$ of vacancies is 2.5 times larger than ${C}_{S,{D}^{{'}}}$ 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.