## 3 Results and Discussion
### Raman Spectroscopy  
In the Raman spectra from the laser ablation products (Figure 5), the D and G bands that are known to characterize the presence of defects in graphitic structures (structural (lattice) defects) and graphitic order appear at \(\sim\)1360 and 1582 cm\({}^{-1}\); 1364 and 1582 cm\({}^{-1}\)  
Figure 4: TEM images of the ablation products ((**a**) 98 \(\upmu\)J/1 kHz, 33 + 33 min; (**c**) and (**d**) 80 \(\upmu\)J/6 kHz, 33 min). The plot in (**b**) shows the large versus the small diameter of NPs in (**a**) (measured from the TEM images). Figure 3: XRD patterns of the ablation products after drying the produced solutions on a substrate. and 1372 and 1582 cm\({}^{-1}\) for the 800 nm ablation with pulse energies of 40, 110, and 200 uJ, respectively (-1356 and 1581 cm\({}^{-1}\); 1383 and 1580 cm\({}^{-1}\) for the 343 nm ablation with 80 uJ/6 kHz and 98 uJ/1 kHz, respectively). The shapes, relative intensities, and FWHM of the two bands in the spectra are typical of the presence of carbon systems with an sp\({}^{2}\) hybridization [29]. The G band is narrower and higher in intensity by a factor of almost two compared with the D band. In the case of a single crystal graphite or monolayer graphene, only a sharp G band is present in the spectrum [29; 30]. This indicates that the ablation products are disordered, but not too much when compared with the graphite target. The narrower G band for the products from the 343 nm ablation compared with that from the 800 nm ablation indicates that they contain a higher percentage of graphene-like structures (a lower percentage of disordered (amorphous) carbon), most probably corresponding to the small NPs and sheet-like structures of Figure 4c,d. The intensity of the D band is inversely proportional to the graphite crystal size [29]. The ratio of the intensities of the D and G bands [I\({}_{\textrm{D}}\)/I\({}_{\textrm{G}}\)], which is usually a measure of the degree of structural disorder in graphitic materials, was determined to be \(\approx\) 0.70, 0.71, and 0.71 for the products produced at a 40, 110, and 200 uJ pulse energy with the 800 nm laser beam; and \(\approx\) 0.36 and 0.63 for those produced with the 343 nm laser beam (80 uJ/6 kHz and 98 uJ/1 kHz, respectively). Furthermore, the integrated area ratio of the D and G bands [I\({}^{\textrm{\tau}}_{\textrm{D}}\)A/I\({}^{\textrm{\tau}}_{\textrm{G}}\)A] can be calculated by fitting Voigt (Gaussian-Lorentzian) shape components to the spectra in the region of 1200-1800 cm\({}^{-1}\) and is derived to be \(\approx\) 1.46, 1.11, and 1.14 for the products produced at a 40, 110, and 200 uJ pulse energy with the 800 nm laser beam; and \(\approx\) 1.24 and 2.03 for those produced with the 343 nm laser beam (80 uJ/6 kHz and 98 uJ/1 kHz, respectively). The larger ratio for the products compared with that for the bulk material indicates that they have a smaller degree of graphitization (contain more disordered carbon) compared with graphite. This indicates that the synthesized C-NMs have a graphitic structure but also have a high percentage of a less ordered crystalline phase. The intensity ratios of the two bands in the region of 0.149-0.032 were determined for NPs (mean diameter \(\approx\) 100-400 nm) produced by ns laser ablation (1.5 ns/532 nm) of a graphite target in water using different pulse repetition rates in the region ranging from 1 to 100 Hz and fluences ranging from 0.21 to 0.004 J/cm\({}^{2}\)[31]. In the case of a ps laser ablation of graphite, the I\({}_{\textrm{D}}\)/I\({}_{\textrm{G}}\) ratio was determined to be equal to 0.90, and it was concluded that the synthesized CNPs had a similar graphitic-like structure [12]; in the case of a 200 ns laser ablation of graphite, the synthesized CNPs were found to also contain fullerenes (C60) in addition to having a graphitic structure with a high content of disordered graphite [32].