## 3 Results
### Raman Spectroscopy  
A typical Raman spectrum is displayed in Figure 7, collected on the center of a TLG fragment. As expected, the Raman spectrum exhibits a D band at 1358 cm\({}^{-1}\), a G band at 1581 cm\({}^{-1}\) and a 2D band around 2700 cm\({}^{-1}\). The G band is the one-mode Raman vibration characteristic of graphitic carbon [27]. The 2D band is a multiple step mode of carbon vibration in which intensity, shape, and wave number are sensitive to many parameters, such as the interaction with the substrate, the thickness of the graphene layers, the ordering within the graphene layers in the direction c normal to the graphene plan, and the presence of either impurities, doping atoms, vacancies, or functionalized molecules [23; 28; 29; 30; 31]. Finally, as soon as a graphitic domain displays either structural defects or size-limited dimensions, a D band will appear [32]. Figure 6: TLG size distribution of the Ni/Si sample after \({}^{13}\)C implantation at 600 \({}^{\circ}\)C.  
Figure 7: Typical Raman spectrum obtained on a dark fragment on the Ni/Si sample annealed at 900 \({}^{\circ}\)C and implanted with 20 keV \({}^{12}\)C at 600 \({}^{\circ}\)C with 4 EGM. Figure 8b-d displays the corresponding mappings of the G, 2D, and D bands, respectively, obtained on the domain imaged in Figure 5a, speckled with dark TLG fragments. Pixel size is around \(0.3\times 0.3~{}\upmu\mathrm{m}^{2}\). **Figure 8. (a)** Optical micrograph on the Ni/Si sample implanted at 600 \({}^{\circ}\)C \({}^{12}\)C at 20 keV; Raman mapping of the (**b**) G, (**c**) 2D, and (**d**) D bands. Note that the intensity scale of I\({}_{\mathrm{2D}}\) is half the ones of I\({}_{\mathrm{G}}\) and I\({}_{\mathrm{D}}\). We can note the close correlation between the intensity of the G and D bands, whereas the 2D band is much less intense as the intensity scale of the former images are almost twice that of the latter. The appearance of this band is a clear indication that graphenization occurs at 600 \({}^{\circ}\)C, in contrast with lower temperatures (not shown). The weak intensity of the 2D is due to the poor ordering of the graphene plans in the c direction. Moreover, in order to investigate the effect of isotopic labeling on the Raman spectra, a couple of samples were prepared with either \({}^{12}\)C or \({}^{13}\)C ions at an implantation energy of 20 keV, at 450 \({}^{\circ}\)C, 525 \({}^{\circ}\)C, and 600 \({}^{\circ}\)C, respectively. In Figure 9 we report in a panel the main features obtained on the sample implanted at 600 \({}^{\circ}\)C.  
In Figure 9b typical Raman spectra are reported for the \({}^{12}\)C (blue) and \({}^{13}\)C (red) implanted samples on the dark fragments noted 1 in Figure 9a, respectively. In addition, a Raman spectrum of pure \({}^{13}\)C is reported (green), according to the wavenumber calculated with further Equation (2), in good agreement with those reported in [33] for a (\({}^{12}\)C\(-^{13}\)C) bilayer graphene. As expected, on the dark fragments, all the Raman bands (D, G, and 2D) exhibit a wavenumber downshift for the \({}^{13}\)C implanted sample. This downshift can be explained by phonon localization, due to elastic scattering of phonons by the \({}^{13}\)C atoms [34]. Single, but widened, contributions are observed for each band with the \({}^{13}\)C implanted Ni/Si samples, which can be explained by some mixing of \({}^{12}\)C and \({}^{13}\)C in the TLG [35]. In contrast, we never observed distinct contributions like those observed in a distinct (\({}^{12}\)C\(-^{13}\)C) bilayer graphene [33]. For the \({}^{13}\)C implanted sample, the following contributions of the Raman red spectrum in Figure 9b are: a D peak at 1338 cm\({}^{-1}\), a G peak at 1555 cm\({}^{-1}\), and, finally, a 2D band at 2653 cm\({}^{-1}\), to be compared with the D, G, and 2D contributions of the \({}^{12}\)C implanted sample (bluespectrum in Figure 9b) at 1358 cm\({}^{-1}\), 1581 cm\({}^{-1}\), and 2700 cm\({}^{-1}\), respectively.