# Structural Modifications in Epitaxial Graphene on SiC Following 10 keV Nitrogen Ion Implantation
## 3 Results
### Raman Spectroscopy  
Raman spectroscopy provides structural fingerprints of the molecules in a material and is a nondestructive method. Figure 2 presents spectra obtained from Raman spectroscopy of pristine and 10 keV N\({}^{+}\) ion-implanted EG at varying fluences. The Raman spectra of graphene are characterized by the G peak located around \(\sim\)1580 cm\({}^{-1}\) and a 2D peak present at 2730 cm\({}^{-1}\) wavenumbers. The G peak is the only first order peak and is a result of bond stretching both by aromatic ring atoms and chain atoms [33]. The 2D peak indicates defect free graphene and is related to a two phonons process. D peak which occurs at \(\sim\)1350 cm\({}^{-1}\) wavenumber is related to defects in graphene and is not observed for pristine graphene [34]. Additionally, the presence of D+D\({}^{\prime}\) at 2950 cm\({}^{-1}\) and D\({}^{\prime}\) at 1620 cm\({}^{-1}\), also demonstrate defects in EG [35]. Figure 2 shows the absence of the D peak in pristine graphene, thus showing as grown graphene is of high quality. Figure 2 shows the presence of the D peak in all ion-implanted samples. The D\({}^{\prime}\) peak is clearly visible up to \(5\times 10^{13}\) ions/cm\({}^{2}\) fluence, however, at the highest fluence (\(1\times 10^{14}\) ions/cm\({}^{2}\)) the D\({}^{\prime}\) peak is not visible as it merged with the G peak. The D+D\({}^{\prime}\) peak appeared in all ion-implanted samples, reflecting a significant amount of defects [35]. The intensity ratio of D peak and G peak is represented as I(D)/I(G) and the intensity ratio of 2D peak and G peak is represented as I(2D)/I(G). They were calculated using Figure 2 for all ion-implanted samples. Defects are generated following ion implantation which resulted in the decrease in I(2D)/I(G) and an increase I(D)/I(G) which was also evident from a previous study [36]. Figure 2 also shows the flu  
Figure 2: Raman spectra of pristine and N\({}^{+}\) ion-implanted EG on SiC obtained at different fluences. intensity of D peak and fall in the intensity of the 2D peak. This signifying increase in defects with the increase in fluence. This is similar to a previous study following ion implantation on graphene sheets. The graphene sheets were prepared by the direct liquid exfoliation of graphite layers which then were deposited on a Si-substrate [37]. There is an increment in the full width half maxima (FWHM) of the 2D peak with increasing fluence. In graphene, the sp\({}^{3}\) defects dominate when I(2D)/I(G) \(>\) 1 and I(D)/I(G) \(<\) 1, while domination by vacancy defects is observed when I(2D)/I(G) \(<\) 1 and I(D)/I(G) \(>\) 1 [38]. Another study reported domination of sp\({}^{3}\) defects when I(D)/I(D\({}^{\prime}\)) is in the range of 7 to 13, and domination of vacancy defects when I(D)/I(D\({}^{\prime}\)) is in the range of 3.5 to 7 [35]. The authors referred to sp\({}^{3}\) defects as \"hopping defects\". These defects distort the bonds between the carbon atoms, retaining the general sp\({}^{2}\) configuration, while vacancy defects arise due to missing of atoms from its lattice site. At a fluence of 1 \(\times\) 10\({}^{12}\) ions/cm\({}^{2}\), sp\({}^{3}\) defects dominate as I(2D)/I(G) \(>\) 1, I(D)/I(G) \(<\) 1 and I(D)/I(D\({}^{\prime}\)) is higher than 7 and at a fluence 5 \(\times\) 10\({}^{12}\) ions/cm\({}^{2}\) and higher, vacancy defects dominate as I(2D)/I(G) \(<\) 1 and I(D)/I(G) \(>\) 1, and I(D)/I(D\({}^{\prime}\)) is in the range of 3.5 to 7. [PERSON] et al., based on the intensity ratio between D peak and G peak, classified graphene defect generation into two stages, stage I and stage II. In Stage I, there is a rise in the I(D)/I(G) ratio, but in stage II there is a fall in the I(D)/I(G) ratio. The stage II is also marked by a broadening of FWHM of D and 2D peaks [36]. The two stages are discussed in detail by [PERSON] et al. for ion implantation using Ag\({}^{-}\) ion in epitaxial graphene [17]. Figure 2 shows an increase of the FWHM of the 2D peak in N\({}^{+}\) ion-implanted EG at varying fluences.