## 4 Conclusions  
The C\({}_{60}\) powder samples subjected to HIP treatment were studied by a complementary set of methods (XRD, XPS, NEXAFS and Raman spectroscopy). The obtained results were analyzed using a literature data on electron microscopy [7; 8; 82] and various theoretical approaches [4; 50; 81; 80]. The conducted study clearly shows the advantages of combining different complementary theoretical and experimental methods for the most complete characterization of such complex samples. A strong bonding of the water molecules with the C\({}_{60}\) powder, MWCNTs and the surface of the HOPG was found. Using the XPS method, the presence of a residual surface layer of water molecules on all samples even under ultrahigh vacuum was detected and the concentration of oxygen atoms was determined as equal to 4-8%. Thus, the presence of adsorbed water on the surface of fullerite and MWCNTs leads to the formation of carbon oxides during HIP treatment, with the concentration of carbon atoms bonded with oxygen atoms equals to \(\sim\)3%. The analysis of the data obtained by a complementary set of methods showed the following scenario of the pristine fullerite C\({}_{60}\) powder transformation into closed graphene  
Figure 6: Survey XPS spectra of the fullerite C\({}_{60}\) subjected to HIP treatment at 1270 K and subsequently exposed to air for a long time. The insets show C 1s and O 1s core-level XPS spectra. shells of 2-5 nm in size, connected by covalent bonds. At the first stage of HIP treatment, when heated to a temperature of 920 K, fullerite retains its crystalline fcc structure, but the process of forming bonds between molecules and the formation of C\({}_{60}\) dimers begins. This is expressed in a decrease and change in the relative intensity of the first four bands in the C 1s NEXAFS spectrum. With an increase in temperature to 1120 K, the process of bond formation becomes more intense, which is evident from the presence of peaks characteristic of C\({}_{60}\) dimers in the Raman spectra and the preservation of the fcc structure reflexes on the diffractogram. However, at the same time, the process of merging neighboring molecules begins, which ends at 1270 K with the transformation of fullerene molecules into capsules of 2-5 nm in size. These capsules are completely disoriented, which is clearly seen by the appearance of diffuse bands on diffractograms and Raman spectra, and is confirmed by HRTEM data [7; 8; 82]. The mechanism of such capsule formation through the fusion of C\({}_{60}\) fullerene molecules during HIP treatment is predicted theoretically and described in detail in the work [81], but has no experimental confirmation. To solve this problem, it is necessary to show the formation of a closed graphene surface during fullerite HIP treatment. The proof can be the formation of the carbon atom environment after HIP treatment, similar to one in the case of HOPG or pure MWCNTs. The best method for solving this problem is NEXAFS spectroscopy. In the modern publications, there is no data on the study of HIP-treated fullerite C\({}_{60}\) by spectroscopy methods. In the paper, for the first time, systematic studies of HIP-treated fullerite C\({}_{60}\) with a sequential step-by-step increase in temperature were carried out by a complementary set of methods, including XPS and NEXAFS spectroscopy using synchrotron radiation. Successive changes in the C\({}_{60}\) powder subjected to HIP treatment at temperatures equal to 920, 1120, 1170 and 1270 K clearly demonstrate the formation of a structure in the form of \(\pi^{\star}\) and \(\sigma^{\star}\) absorption bands in the C\({}_{60}\) powder C 1s NEXAFS spectrum, also presented in the C 1s NEXAFS spectra of HOPG, MWCNTs and MWCNTs HIP-treated at a temperature of 1270 K. Nanoparticles of 2-5 nm in size stacked in several graphene-like layers cannot be characterized by an ideal arrangement of carbon atoms, as in the case of HOPG and MWCNTs, except for the case when they form a closed surface consisting of hexagons.