## 1 Introduction
An alternative approach, post-treatment, is favored due to the availability of commercial undoped CNTs with specific physicochemical or physico-mechanical traits. In post-treatment, nitrogen doping is typically achieved using gaseous ammonia or by pyrolyzing nitrogen precursors such as acetonitrile, pyridine, melamine, and polyvinylpyridine [33; 34; 35; 36; 37; 38]. However, post-treatment necessitates high temperatures (800-1200 \({}^{\circ}\)C) and often employs  
Figure 1: Types of nitrogen inclusions in the nanotube wall: pyridinic (N-pyr), pyrrolic (N-pyrr), graphitic/quaternary (N-Q) forms. toxic nitrogen precursors (acetonitrile, NH\({}_{3}\), pyridine), limiting its practical utility. Additionally, the multi-step nature of the post-treatment procedure contributes to the elevated production costs of N-CNTs. To address these challenges, ion and plasma treatment methods are promising, offering precise control over nitrogen doping parameters [39; 40; 41; 42; 43; 44; 45]. Studies have demonstrated that plasma treatment, influenced by parameters like plasma power, pressure, and exposure time, can lead to N-CNTs with varying nitrogen content (up to 8-20 at.%) embedded into their wall structure [43; 44]. Notably, the nitrogen inclusions in the side walls of N-CNTs predominantly assume pyridinic and graphitic configurations, while the tips of nanotubes exhibit a pyrrolic configuration during plasma treatment [44]. In comparison, treatment with N\({}^{+}\) ions, akin to plasma but distinct in its capability to modify both the outer surface layers and inner bulk layers of nanotubes by adjusting the average ion beam energy, offers a compelling avenue [44; 46; 47; 48]. This method involves implanting nitrogen within both wall structures (graphitic/quaternary and pyridinic forms) and tip regions (primarily pyrrolic and graphitic/quaternary forms), resembling the outcomes of plasma treatment [44; 48]. Despite recent advancements in nitrogen doping of carbon nanomaterials, challenges persist in achieving N-CNTs with a predetermined nitrogen content and specific configurations in targeted locations on nanotube walls, necessitating innovative approaches. Earlier, our team carried out ion doping with nitrogen atoms of CNTs to improve their electrochemical activity [49]. At the same time, irradiation was carried out on pressed CNT powder, as well as prepared electrodes, and a comparison was made with nitrogen-doped CNTs at the stage of CVD synthesis. Such an energy impact led to local destruction of the electrodes and to a decrease in the stability of such materials during cyclic charge-discharge processes. The primary goal of this study is to develop an ion-beam doping technique for nitrogen incorporation in multi-walled CNTs (MWCNTs). This approach aims to produce N-MWCNT powder (about 100 mg per irradiation cycle) with a predominant presence of pyridinic and pyrrolic nitrogen forms, aligning with their potential applications in electro-catalysis and the oxygen reduction reaction (ORR). The proposed methodology involves depositing a 650-700 nm thick layer of MWCNTs on a titanium substrate using the spray method, followed by irradiation with N\({}^{+}\) ions using a high-dose ion implanter. A comprehensive set of experimental techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) is used to elucidate the resulting morphology, structure, and chemical states of carbon and nitrogen atoms.