## 3 Results and Discussion
### HIP-Treated Fullerite C\({}_{60}\) Study
The absence of the A\({}_{\rm g}\)(2) \"pentagonal pinch\" mode, as well as the appearance of the \"graphitic\" G-band and disorder-induced D-band in the Raman spectrum, on the one hand, indicates the complete destruction of pentagonal rings, and on the other hand, the formation of nanoscale structures consisting of hexagonal rings. Figure 3: Raman spectra of the HOPG, MWCNTs, pristine and HIP-treated at different temperatures fullerite C\({}_{60}\) over a wide spectral range (**a**) and in the region of 1100–1700 cm\({}^{-1}\) (**b**). Figure 3 shows that the spectra of the modified fullerite have significantly widened G, D and 2D bands. A comparison of the Raman spectrum of the fullerite C\({}_{60}\) with those of HOPG and MWCNTs (Figure 3b) shows that the energy position of the D band of C\({}_{60}\) is consistent with its position in the HOPG and MWCNTs spectra, while the position of the G band (1597 cm\({}^{-1}\)) undergoes a low energy shift of 11 cm\({}^{-1}\) for MWCNTs (1586 cm\({}^{-1}\)) and 15 cm\({}^{-1}\) for HOPG (1582 cm\({}^{-1}\)). An essential point is the absence of narrow 2D peaks in the range of 2300-3200 cm\({}^{-1}\) in the spectrum of the HIP-treated C\({}_{60}\), and only a weakly modulated very wide band is present. The absence of peaks in the 2300-3200 cm\({}^{-1}\) region of Raman spectra in the three-stage model of classification of the graphite disorderliness degree during the transition from graphite to amorphous carbon [49] suggests that fullerite C\({}_{60}\) after HIP treatment is an intermediate material between the first (nanocrystalline graphite) and the second (mainly sp\({}^{2}\) or low sp\({}^{3}\) amorphous carbon) stages. The dimensions of this material structural elements can be estimated using an empirical relation between the intensity (area) ratios of the G and D bands and the average sizes of crystallites or large molecules \(L_{a}\)[49; 79] as \(I(\text{D})/I(\text{G})=C(\lambda)/L_{a}\), where \(C(\lambda)\) is a constant that depends on the laser radiation wavelength \(\lambda\) and is equal to 4.4 nm for \(\lambda=488\) nm. In our case, \(L_{a}\approx 2.5\) nm, which is quite comparable to the fullerene C\({}_{60}\) molecule diameter (\(\sim\)1 nm) and is consistent with the X-ray phase analysis data (\(\sim\)2-4 nm). It is known that with a certain orientation of two neighboring C\({}_{60}\) molecules, when the double bonds are parallel to each other, polymerization processes of C\({}_{60}\) fullerene molecules by the [2+2]-cycloaddition reaction are possible [4; 5; 80; 81]. In the work [81], it was shown that by 23 consecutive turns of bonds, or the so-called generalized Stone-Wales (GSW) transformations, it is possible to describe the fusion of two fullerene C\({}_{60}\) molecules into a C\({}_{120}\) nanocapsule (a short nanotube 2-3 nm long) with the surface consisting mainly of hexagons. It should be noted that in the solid state, a fullerene C\({}_{60}\) molecule can interact by the [2+2]-cycloaddition reaction with at least four neighboring molecules. Given the size of the fullerene molecule, it is possible that two competing transformation processes occur simultaneously. This can lead to a sharp increase of the GSW transformation activation energy barrier and to the fusion process termination. Studies on modeling the molecular transformation of two fullerene C\({}_{60}\) molecules into a C\({}_{120}\) nanocapsule were carried out in the work [4]. Authors found that, depending on the initial orientation of the molecules, C\({}_{120}\) nanocapsules of different chirality with diameters in the range of 0.68-0.98 nm can be formed. The fusion of fullerene molecules into a cylindrical structure during heating to temperatures above 1370 K in a vacuum was observed experimentally by transmission electron microscopy [6]. In this study, fullerene molecules located inside single-walled nanotubes were used.