## 3 Results and Discussion
### XPS Research of the Nanocomposites and Initial MWCNTs
Figure 9b shows the results of the composite O1-line fitting with four components O (530.4 eV), B\({}^{\prime}\) (531.2 eV), O\({}^{\prime}\) (532.1 eV) and O\({}^{\prime\prime}\) (537.2 eV). When comparing the XPS O1 spectra of the initial nanotubes and the WC\({}_{1\text{-}\text{x}}\)/MWCNT composite shown in Figure 9b, the additional intense O peak (530.4 eV) is observed. The energy position of this peak is in good agreement with the main peak in the WO\({}_{3}\) spectra [85; 86]. This suggests that, in addition to the WC\({}_{1\text{-}\text{x}}\) bulk layer, a tungsten oxide layer forms on the composite surface. It can be seen from the figure that the peaks B\({}^{\prime}\) (531.2 eV) and O\({}^{\prime}\) (532.1 eV) are shifted toward lower energies relative to the peaks B and C positions in the nanotube spectrum by 0.4 eV and 1.3 eV, respectively. The observed \"red\" shift of the binding energies indicates a change in the state of oxygen atoms on the MWCNT surface and the formation of new compounds. According to X-ray diffractometry, tungsten carbide coatings are nanosized crystallites of the nonstoichiometric WC\({}_{1\text{-}\text{x}}\) phase. Taking this into account, it is also reasonable to expect the tungsten oxide formation in the nonstoichiometric WO\({}_{3\text{-}\text{x}}\) phase. In [87], it was shown that the XPS O1 spectra of the nonstoichiometric crystalline WO\({}_{3\text{-}\text{x}}\) contain two peaks. The low-energy peak with the energy 530.5 eV corresponds to the O\({}^{2-}\) ion of WO\({}_{3}\), and the high-energy peak--532.6 eV, identical to the O1 peak of the O\({}^{2-}\) ion of WO\({}_{3\text{-}\text{x}}\) other combination states. It was shown in [85; 88; 89] that free  
Figure 9: The C1 (**a**), O1 (**b**) XPS spectra of the WC\({}_{1\text{-}\text{x}}\)/MWCNTs sample 2 (black) and initial MWCNTs (red). The inset in (**a**) shows the composite XPS C1 spectrum. (**c**) the W4f XPS spectra (black) fitting (colored) of the sample 2.  
oxide surfaces contacting with the atmosphere are always hydrated, i.e., contain water molecules and hydroxyl groups. Component O\({}^{\prime}\) and O\({}^{\prime\prime}\) located at 532.1 eV and 537.2 eV illustrates the water bound at the samples surface, proving the existence of WO\({}_{3}\)(H\({}_{2}\)O)n phases at the surface. Therefore, the peaks O\({}^{\prime}\) and O\({}^{\prime\prime}\) in the O1 spectrum of the nanocomposite should be identified as excitations in the tungsten oxide layer. In this case, the peak B\({}^{\prime}\) energy position is in good agreement with the oxygen atom binding energy in the C=O group (531.6 eV) [90], which confirms the presence of an oxygen-carbon double bond in the nanocomposite and is consistent with the WC\({}_{1\text{-}\text{x}}\)/MWCNT NEXAFS and XPS C1 spectra, indicating the C=O group presence. From the comparison of the peak B\({}^{\prime}\) areas of the nanocomposite XPS C1 and O1 spectra, the ratio of carbon and oxygen atoms participating in the oxides formation on the nanotube surface was found to be 2.3. This means that carbon forms not only the C=O bond but also compounds with higher oxygen coordination, for example, such as the epoxy O-C-O bond and the [CO\({}_{3}\)]\({}^{2-}\) anion. This is consistent with NEXAFS spectroscopy data (Figure 7a). Figure 9c shows the W4f line deconvolution in five components M\({}_{1}\) (32.13 eV), M\({}_{2}\) (34.20 eV), O\({}_{1}\) (35.53 eV), O\({}_{2}\) (37.67 eV and O\({}_{3}\) (40.95 eV). The binding energies of the peaks M\({}_{1}\) and M\({}_{2}\) are close to the binding energies of the W4f\({}_{7/2,5/2}\) levels of crystalline WC (31.8 eV and 33.96 eV) [80]. According to [64; 91], binding energies of 32.0 and 34.1 eV are associated with the presence of WC\({}_{1\text{-}\text{x}}\). The XRD analysis results are in good agreement with the fact that the non-stoichiometric WC\({}_{1\text{-}\text{x}}\) phase predominates in the coatings. M and M\({}_{1}\) bands in the carbon and tungsten spectra are responsible for the W-C chemical bond formation.