## 3 Results and Discussion  
The morphologies and structures of the pyrolyzed carbon powders were determined using HR-field emission scanning electron microscopy equipped with selected area electron energy dispersive X-ray spectroscopy. The SEM images at 53.54 \(\times\) 66.33 \(\upmu\)m\({}^{2}\) and that of the overlapped false color table from EDS total yield spectra, taken with the Zeiss system FEG-SEM, LEO 1530 operating at an accelerating high voltage (HV) of 20.0 KV, are reported in Figure 1a,b. At this magnification, the C powders display the coexistence of structures at various scales, from large flakes a few \(\upmu\)m across to small spheres of some nanometres. They are inconsistently arranged, even if somehow, they keep the memory of their original shape attributed to the bio-waste, [40], _Allium cepa_, L., [41] (onion vulgaris) peels from which they derive. On the other hand, Figure 1b evidences the different chemical composition, Na, O, Ca, Cl, K, Si, Al, and Mg, in addition to the predominant carbon, in close agreement with what reported in [40] and to the fact that the red onion vulgaris already contains these elements as precursors and, probably, in a conjugate form. The false color EDS images of C (red), Ca (light blue), K (green), O (dark blue), Mg (magenta), and S (yellow) and their corresponding K\(\alpha_{1}\) and K\(\alpha_{2}\) shells are shown in Figure 1c-h, whereas Figure 1i shows the intensity of the L\(\alpha_{1}\), L\(\alpha_{2}\) and K\(\alpha_{1}\), K\(\alpha_{2}\) emission lines as a function of increasing energy for these elements. We can easily note, from the inset, that the presence of chemical species different from carbon can mainly be assigned to impurities, including the Cu L\(\alpha_{1}\), L\(\alpha_{2}\) emission lines that are clearly visible at around (0.93-0.95) KeV of energy, as well as the others K\(\alpha_{1}\), K\(\alpha_{2}\), and K\(\alpha_{3}\) less intense around (8.0-8.9) KeV, proving C to be over 80%. The Si peak originated from the substrate. A typical HR-SEM image, (58.56 \(\times\) 77.91) \(\upmu\)m\({}^{2}\), from C nanopowders supported on the gold substrate at magnifications of 3.54 K\(\times\) and an electron acceleration HV of 2.0 KV, collected by using the Zeiss FE-SEM, is shown in Figure 2a. At first sight, we observe very defined and large C flakes (from 5 to 50 \(\upmu\)m in length) randomly oriented and occupying most of the image area. Smaller structures scattered over the entire surface of these C flakes are clearly visible. Among these, three vaguely spherical objects (indicated with blue arrows) can be seen, the largest (red arrow) having a diameter of \(\sim\)7 \(\upmu\)m and the other smaller two of approximately 0.5 \(\upmu\)m (yellow arrows). These particles were studied in a detailed morphological and chemical analysis, described hereafter. Figure 2b-d show the SEM images at a higher resolution (17.92, 46.64, 169.32) K\(\times\) of the largest spherical structure located at the center of the image of Figure 2a. We can interestingly remark the presence of rolled-up structures like nano-roses, distributed in a fractal like pseudo-morphism. The red dashed circle in Figure 2b with the diameter B = 2.63 \(\upmu\)m indicates one of the composite structures that in a mathematical similarity forms the entire larger sphere of diameter A = 7.54 \(\upmu\)m marked with a dashed light-blue circle. The yellow dashed circle with a diameter C = 0.92 \(\upmu\)m emphasizes a single small rounded structure that builds-up the entire larger object in the dashed red circle. Although in our bi-dimensional SEM images (consider for example the dotted light-blue area), we collapsed the three-dimensional reality of the rounded nano-roses on two-dimensional projections, we could extract some geometrical relations of the similarity among the spheres. One should also bear in mind that the circles drawn in Figure 2b must be considered as an average. In particular, with the dotted light-blue circle we tried to enclose the maximum possible nanostructures.