Probing Edge defects in \textit{n} (\textit{n}=1,2..) Graphene Layer system via Raman Scattering

Results of a microRaman study (spot size $\sim $0.7 microns; 514.5 nm excitation) of an edge (or boundary) of n- layer graphene films is presented. Graphene (n=1 layer) exhibits a very narrow Lorentzian D-band at $\sim $1344 cm$^{-1}$ with FWHM $\sim $15 cm$^{-1}$. For 2$<$n$<$5, this narrow peak is found to split into four bands. Interestingly, the D band intensity of the edge is quite strong (1/4 of the G-band) If te defects are truly localized on the edge, this implies a better resonance than found for defects at the interior, or, on the other hand, the range of the defects may extend a long distance into the interior of the films and involve many sites. Polarized Raman studies on this D band were made with the incident field at an angle $\theta $ with the respect to the average direction of the edge. The scattered light was collected either parallel (H) or perpendicular (V) to the edge. The polar intensity plots I$_{V}(\theta )$ and I$_{H}(\theta )$ were found to exhibit a quadrupolar and dipolar pattern, respectively.