## 3 Results
These changes occur as a result of exposure to the ion beam, which causes the formation of point and extended structural defects inside nanotube walls due to the incorporation of nitrogen ions. The interplanar distances before and after irradiation were determined using the Bragg's formula (\(d_{(002)}=\lambda/2\) sin(\(\theta\)), where \(d_{(002)}\) is the interplanar spacing, \(\lambda\) is the wavelength of Cu K\(\alpha\) radiation (0.15406 nm), and \(\theta\) is the Bragg angle). The \(d_{(002)}\) parameter was found to increase from 3.46 A (untreated MWCNTs) to 3.51 A (N-MWCNTs), which correlated with the TEM data (Figure 5). It is important to note that the (002) peak in the X-ray diffraction spectrum of irradiated MWCNTs remains, although it becomes wider and less intense. Combining these analyzed data and TEM data, we can conclude that, in general, the nanotubes retain their crystalline structure after irradiation, and the greatest damages occur mainly in the near-surface region of the MWCNT. The evaluation of the chemical composition and charge state of atoms within the nanotubes, as well as the determination of the configurations of nitrogen inclusions formed subsequent to irradiation with N\({}^{+}\) ions, was carried out using XPS techniques. Examination of the survey PE spectra (Figure 7) obtained in the binding energy range of 1300 to \(-\)5 eV for MWCNTs revealed the presence of only the following elements: oxygen (O1s PE line \(\sim\)532 eV) and carbon (C1s PE line \(\sim\)285 eV). In the case of N-MWCNTs, the N1s PE line (\(\sim\)400 eV) is additionally observed in the survey spectrum. Thus, we can conclude that after irradiation with a beam of nitrogen ions, there are no extraneous inclusions in the sample. For the quantification of element concentrations, the elemental sensitivity factors method [54] was employed. As depicted in Table 1, the total nitrogen concentration (Ntot) within the irradiated sample is approximately \(\sim\)1.3 at.%. In addition, an increase in oxygen concentration by approximately \(\sim\)5 at.% is observed. Figure 5: TEM images of nanotubes before (**a**) and after (**b**) irradiation with nitrogen. The insets show HRTEM images of a selected section of MWCNTs. Figure 6: XRD patterns for nanotubes before and after irradiation with nitrogen ions. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**[C]**} & \multicolumn{4}{c}{**[N]**} & \multirow{2}{*}{**[O]**} \\ \cline{2-2} \cline{5-6}  & & \(\mathbf{N_{tot}}\) & \(\mathbf{N}\)**-Q** & \(\mathbf{N}\)**-pyrr** & \(\mathbf{N}\)**-pyrr** & \\ \hline MWCNTs & 99.16 & - & - & - & - & 0.84 \\ N-MWCNTs & 92.98 & 1.33 & 0.27 & 0.81 & 0.25 & 5.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concentration of elements in at.% by XPS. Figure 7: Survey PE spectra of carbon nanotubes before and after irradiation with nitrogen ions (\(h\
u=1487\) eV). The study of the chemical state of carbon atoms was carried out using the C1s PE spectra presented in Figure 8. The C1s PE spectrum of the pristine MWCNTs (Figure 8, bottom panel) is well fitted by six components. This is evidenced by the complete coincidence of the envelope curve, designated in brown, with the experimental signal (black curve). The C=C component at an energy of 284.7 eV (red curve) corresponds to sp\({}^{2}\) hybridized carbon atoms in the walls of MWCNTs. The next C-C component at an energy of 285.2 eV (green curve) is associated with structural defects (mainly topologic pentagon-heptagon (5-7) Stow-Wales defects and point: mono- and di-vacancy), as well as the presence of amorphous carbon on the surface or near-surface region of MWCNTs, which are formed during the synthesis of nanotubes [13; 14; 55; 56]. The remaining components at 286.3, 287.4, and 288.7 eV correspond to carbon atoms in the hydroxyl (C-OH), carbonyl (C=O), and carboxyl (COOH) oxygen-containing functional groups (OCFG) present on the surface of MWCNTs near structural defects [13; 14; 55; 56].