## 3 Results and Discussion
### HIP-Treated Fullerite C\({}_{60}\) Study
In the works [7; 82], high-resolution transmission electron microscopy (HRTEM) was used to study HIP-treated fullerite C\({}_{60}\) at a pressure of 0.15 GPa and temperature of 1300 K in nitrogen [7], and at 0.22 GPa an 1670 K in argon [82]. In these studies, it was shown that the structure of the fullerite C\({}_{60}\) after HIP treatment is a disoriented sequence of curved fragments with a size of \(\sim\)1-5 nm. In the work [8], a similar picture of HRTEM images of randomly oriented graphite-type clusters with sizes of 1.5-3 nm, synthesized from fullerite C\({}_{60}\) at a temperature of 1270 K and a pressure in the range of 1.5-8 GPa were obtained. In order to clarify the symmetry and composition of the carbon atom's nearest environment in the HIP-modified fullerite C\({}_{60}\) samples, the NEXAFS spectroscopy was used. Figure 4 shows the C 1s NEXAFS spectra of the pristine and HIP-treated fullerite C\({}_{60}\), obtained after subtracting the contribution to the absorption of the overlying shells and normalized to the absorption level at the photon energy of 320 eV. The spectrum of C\({}_{60}\) HIP-treated at a temperature of 920 K contains all the peaks characteristic of the pristine fullerite. However, there is a significant decrease in the intensity of the first peak and a change in the relative intensities of the first three absorption bands, which correspond to transitions to the unoccupied antibonding \(\pi^{\ast}\)-orbitals of the C\({}_{60}\) molecule. This is in good agreement with the XRD and Raman spectroscopy data and demonstrates that fullerene molecules retain their structure. In the work [83], similar changes in C 1s NEXAFS spectrum of C\({}_{60}\) powder after treatment at a pressure of 1.1-1.2 GPa and a temperature of 580-585 K were observed and interpreted as the evidence of the formation of covalent C\(-\)C bonds and changes in the distances between C\({}_{60}\) molecules. With an increase in temperature to 1170 K and further to 1270 K, C 1s NEXAFS spectrum is dramatically changed, as in the cases of the XRD patterns and Raman spectra. In particular, all the peaks present in the C 1s NEXAFS spectrum of the pristine C\({}_{60}\) disappear, with the exception of the first intense peak, which is transformed into a shoulder on the low-energy side of the new absorption band at photon energy of 285.4 eV. In addition, new absorption structures appeared in the spectrum: a broad band at an energy of 291.7 eV, and two low-intensity bands at 287.2 eV and 288.9 eV, corresponding to C1s \(\rightarrow\)\(\pi^{\pm}\) transitions in the C\(-\)O and C=O groups [43]. At a temperature of 1270 K, the absorption structure characteristic of the C 1s NEXAFS spectrum of the C\({}_{60}\) fullerene molecule disappears, thus indicating the complete destruction of the C\({}_{60}\) molecule and the formation of a new material. The absorption bands of the C 1s NEXAFS spectrum of this new material correlate well with the ones in the corresponding spectra of HOPG and MWCNTs. This means that the nearest environment of the carbon atom corresponds to a hexagonal graphene network of a high degree of perfection. In the case of nanoparticles with a size of 2-5 nm, the occurrence of such an atomic environment is possible if these particles have closed graphene surfaces. The formation of such structures during HIP treatment is predicted theoretically from C\({}_{60}\) dimers and confirmed experimentally [4; 5; 20; 81]. In our case, the C\({}_{60}\) dimer formation is confirmed by the Raman spectra analysis. In the NEXAFS spectrum of C\({}_{60}\) powder after HIP treatment at 1120 K (Figure 4), there are two bands associated with carbon-oxygen groups, the intensities of which are enhanced with the treatment temperature increasing. The reason for the appearance of these bands is the interaction with molecular water, which was adsorbed on the pristine C\({}_{60}\) powder surface.