## 3 Results and Discussion
### HIP-Treated Fullerite C\({}_{60}\) Study
As discussed earlier in Section 3.1, the formation of carbon oxides [35] occurs already at 570 K, but the corresponding peaks in the sample C 1s NEXAFS spectrum of the sample at 920 K are not observed. Figure 4: C 1s NEXAFS spectra of the HOPG, MWCNTs, pristine and HIP-treated at different temperatures fullerite C\({}_{60}\). The arrow indicates the position of the fullerite C\({}_{60}\) C 1s absorption edge (289.60 eV) [42]. The HOPG spectrum was obtained at the 40\({}^{\circ}\) grazing incidence angle of a linearly polarized SR beam on the sample surface. The comparison between the C 1s NEXAFS spectra of pristine HOPG and MWCNTs, and C\({}_{60}\) powder HIP treated at a temperature of 1270 K (Figure 5a) clearly demonstrates the sequential broadening of the first \(\pi^{\bullet}\) peak during going from the HOPG spectrum to the MWCNTs one and then to the HIP-treated sample spectrum. The main reason of these spectral changes is an increase in distortions, which is clearly visible from the changes in the width and intensity of the D band in the Raman spectra presented in Figure 3. This band broadening may occur due to the formation of carbon oxides during HIP treatment. To find this out the C 1s NEXAFS spectral studies of MWCNTs after HIP treatment under the same conditions were conducted. In this study the atomic oxygen content in the initial sample was about 4%, the same as one on the surface of the pristine C\({}_{60}\) powder. Figure 5b shows the C 1s NEXAFS spectrum of the pristine MWCNTs, and HIP-treated C\({}_{60}\) powder and MWCNTs. The treatment was performed in an argon atmosphere at pressure of 0.1 GPa and temperature of 1270 K for 3 hours. The figure demonstrates the broadening of the \(\pi^{\bullet}\) and \(\sigma^{\bullet}\) absorption bands and the appearance of the peaks characteristic of the C\(-\)O, C\(-\)O\(-\)C, O\(=\)C\(-\)O and C\(=\)O functional groups in the HIP-treated MWCNTs C 1s NEXAFS spectrum. This confirms that the broadening of the absorption bands is caused by the formation of carbon oxides during the C\({}_{60}\) HIP treatment. Taking into account the impossibility of the complete removal of adsorbed water even in a high vacuum, it is very likely to expect the appearance of the absorption bands associated with the presence of carbon oxides in the C 1s NEXAFS spectrum of the carbon material subjected to HIP treatment in inert media. The high sensitivity of the C 1s NEXAFS spectrum of the new carbon material to the presence of the C\(-\)O, C\(-\)O\(-\)C, O\(=\)C\(-\)O and C\(=\)O functional groups is due to the high oscillator strengths of C1s \(\rightarrow\pi^{\bullet}\) transitions in such linear atomic groups. Therefore, even at small oxide concentrations, their presence is manifested in C 1s NEXAFS spectra. To determine the quantitative atomic concentration of oxygen in the fullerite C\({}_{60}\) powder after HIP treatment at 1270 K, its C 1s XPS spectra were measured. The overview XPS spectrum of the C\({}_{60}\) powder after HIP treatment at 1270 K (Figure 6) contains a C 1s peak at 284.7 eV (FWHM is 1.4) and a broad O 1s line at 532.7 eV (FWHM is 2.6). The XPS measurements allow the determination of the relative atomic concentration of oxygen on the HIP-treated powder C\({}_{60}\) surface equal to 4%. The O 1s peak in the XPS spectra indicates the presence of oxygen-containing compounds on the sample surface (carbon oxides as well as water and oxygen molecules physically adsorbed from the atmosphere). Figure 5: C 1s NEXAFS spectra of HOPG, MWCNTs and fullerite C\({}_{60}\) HIP-treated at 1270 K, (**a**) normalized the \(\pi^{\bullet}\) peak maximum and (**b**) normalized to the photoabsorption cross section at the photon energy of 320 eV. As can be seen from the C 1s core-level PE spectrum (left inset in Figure 6) the main C 1s peak is asymmetric and splits into four components at the BE of 284.7 eV (C-C), 286.5 eV (C-O), 287.6 eV (C=O) and \(\sim\)290 eV (O=C-O).