## 3 Results and Discussion
### Raman Spectra of the Nanocomposites and Initial MWCNTs  
In order to obtain information about the coatings and to test the structure of nanotubes, the samples were analyzed by Raman spectroscopy. The Raman scattering spectrum was studied by using 488 nm laser light. The corresponding experimental curves are shown in Figure 5. In the MWCNT spectrum, in addition to the main peak G (1586 cm\({}^{-1}\)), peak D (1361 cm\({}^{-1}\)), characteristic of non-crystalline materials, appears. The degree of sample graphitization can be determined through the \(I_{D}/I_{G}\) (peak intensities ratio). This value depends on number of impurities and defects in the composition of MWCNT graphene layers. The lower the ratio, the higher the graphitization and the less the amount of impurities and defects. For the MWCNTs under study, the value \(I_{D}/I_{G}=0.45\), which indicates the high purity of the samples [47].  
Figure 4: The TEM images of (**a**) WC1-x/ MWCNTs, (**b**) WC1-x/MWCNT with the HRTEM insert, and (**c**) the HRTEM image of WC1-x nanoparticles with the fast Fourier transform (FFT) insert (sample 1).  
Figure 5: The Raman spectra in wide (**a**) and narrow (**b**) energy range of the initial MWCNTs (red), (pyrolytic tungsten)/MWCNT nanocomposite sample 2 (black) and sample 3 (blue).  
Figure 5 shows the Raman spectra of the initial MWCNTs and nanocomposites (samples 2 and 3). The WC/MWCNT spectra in Figure 5 contain all the characteristic peaks of the initial nanotube. Since their ratios \(I_{\text{D}}\)/\(I_{\text{G}}\) are close to 0.5, one can make the conclusion that the metal deposition does not destroy the nanotube structure. The intensities of D and G peaks in the Raman spectrum are greatly reduced for sample 2 and become very small for sample 3 compared with those for the initial MWCNTs. These noticeable changes are due to the strong absorption of the incident, scattered by the nanotube laser radiation by a pyrolytic tungsten carbide coating layer and the uncoated nanotube surface area decrease. The penetration depth of the exciting laser light into the WC and WC\({}_{\text{1-x}}\) coating could roughly be estimated to a 30-80 nm [48; 49; 50]. In doing so, the penetration depth into the amorphous and crystalline WO\({}_{3}\) films is very high, because all the films are transparent above \(\lambda=400\) nm [51]. Therefore, the strong suppression of the MWCNT surface Raman modes is caused only in the pyrolytic tungsten carbide layer. From previously published works [52; 53; 54; 55; 56; 57; 58; 59; 60; 61; 62], it is known that crystalline WO\({}_{3}\) corresponds to the Raman peaks at 275, 880 and 945 cm\({}^{-1}\). However, this structure is not observed in the Raman spectra of the studied samples. It can be seen from Figure 5 that in the region 600-1000 cm\({}^{-1}\), some broad peaks are visible and can be created by tungsten carbide or oxide phases. The strong broadening of this band suggests that the formed compounds present a high structural disorder, indicating low crystallinity [60; 61; 62]. The presence of the band in the Raman spectra is characteristic of WC\({}_{\text{1-x}}\) nanoscale crystallites and its appearance in the spectra of samples 2 and 3 is probably associated with a nanocomposite structure formed by WC\({}_{\text{1-x}}\) nanocrystals [63; 64; 55; 60], which is consistent with diffraction analysis.