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

Abstract

We present a detailed Raman study of defective graphene samples containing specific types of defects. In particular, we compared ${\mathit{sp}}^{3}$ 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 ${D}^{\ensuremath{'}}$ and $G$ peak intensities is higher for vacancies than ${\mathit{sp}}^{3}$ 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 ${D}^{\ensuremath{'}}$. We observed that ${C}_{S,D}=0$ for all the defects analyzed, while ${C}_{S,{D}^{\ensuremath{'}}}$ of vacancies is 2.5 times larger than ${C}_{S,{D}^{\ensuremath{'}}}$ of ${\mathit{sp}}^{3}$ sites. This makes $I$($D$)/$I$(${D}^{\ensuremath{'}}$) strongly sensitive to the nature of the defect. We also show that the exact dependence of $I$($D$)/$I$(${D}^{\ensuremath{'}}$) 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 ${D}^{\ensuremath{'}}$ peak) in order to improve our understanding and modeling of defects in graphene.