## 3 Results  
The experimental studies carried out showed that for one cycle of nitrogen ion irradiation of a layer of deposited MWCNTs with a thickness of about 650-700 nm on a round titanium disk with an area of 30 cm\({}^{2}\), approximately 1 mg of N-MWCNT powder is obtained. At the same time, the dimensions of the accelerator chamber and the design features of the ion source, due to the possibility of supplying a potential to the sample, make it possible to irradiate round samples with an area of up to 8000 cm\({}^{2}\), which theoretically corresponds to about 100 mg of N-MWCNT powder per irradiation cycle. Next, we characterize nitrogen-modified carbon nanotubes in detail in comparison with the pristine MWCNTs using SEM, TEM, XRD, and XPS techniques. The SEM images in Figure 4 show that the untreated MWCNTs are compared with those subjected to irradiation with a nitrogen ion beam. Examination of these SEM images did not disclose substantial alterations in the morphology of individual nanotubes prior toand following exposure to N\({}^{+}\) ions. However, for the N-MWCNTs sample, a slight increase in the average outer diameter (\(d\)) of individual nanotubes was observed from approximately 16-18 nm to about 22-25 nm. The observed change in parameter \(d\) subsequent to irradiation can be attributed to the partial sputtering of outer nanotube layers, along with the fusion of individual nanotubes at specific locations. Previously, we observed a similar effect when MWCNTs were irradiated with argon ions [13; 14; 27; 47]. This fusion may be associated with the creation of point and extended structural defects as a result of carbon atom removal from nanotube walls. Such removal elevates the free energy of the surface of individual nanotubes. Figure 5 shows TEM images of nanotubes without and after modification. The untreated MWCNTs are cylindrical in shape and contain a hollow part (cavity) in the middle. The outer diameter of the three MWCNTs presented is 12, 13, and 16 nm, and the total number of layers observed is 12, 12, and 15 layers, respectively. The cavity diameter is approximately 5.4-6.4 nm depending on the MWCNT structure. The inset (enlarged area shown in Figure 5a) clearly shows that the untreated MWCNTs have highly ordered layers with an interplanar spacing of 0.34 nm, characteristic of carbon nanotubes [53]. However, on individual MWCNTs, the presence of the first or second layer of the outer layer with signs of disorder is observed. This is also observed for the last inner layers near the MWCNT cavity. In the TEM image of irradiated MWCNTs (Figure 5b), the outer diameter of the MWCNT ranges from 9 to 24 nm, and the inner diameter of the cavity lies between 2.1 and 5.4 nm. It can be seen that thicker MWCNTs are less damaged, while thinner ones are much more damaged. The inset in Figure 5b shows that for thick MWCNTs, damages are observed mainly in the first near-surface layers. It is clear that the interplanar distance in the near-surface region increases from approximately 0.34 to 0.35 nm. In the case of thin MWCNTs, due to the small number of internal layers, the changes are more significant. In  
Figure 4: SEM images of nanotubes before and after irradiation with nitrogen. general, we can conclude that the internal graphene structure of MWCNTs is preserved after irradiation, although some distortions are observed. Figure 6 presents the X-ray diffraction patterns of the examined samples. Evidently, for MWCNTs, pronounced peaks manifest at 20 = 25.7\({}^{\circ}\) and 43.1\({}^{\circ}\), 44.6\({}^{\circ}\), corresponding to reflections from the (002) and (100), (101) graphene planes, respectively [10]. On the other hand, in the case of N-MWCNTs, a general decrease in the intensity of the (002) and (100), (101) peaks is noticeable, accompanied by a shift in the most prominent (002) reflection toward smaller angles by 0.3\({}^{\circ}\).