## 3 Results
First of all, FTIR reflectance (Figure 10) was found to depend on metallic content; in fact, cermet 700 W had the higher FTIR reflectance and cermet 300 W the lower FTIR reflectance. After annealing, there was a decrease in FTIR reflectance for the 500 W and 700 W films, while the 300 W cermet was revealed to be stable (Figure 11). This indicates that matrix protects metallic W\({}_{2}\)N particles. Moreover, the NH stretching band at 3225 cm\({}^{-1}\) disappeared in relation to the proceeding of nitridation process. It is possible that for 700 W cermet film, inside the ceramic AlN matrix, W produced by dismutation was newly exposed to \"activated\" nitrogen and then newly nitridated. Wetting experiments were performed to examine the role of electrostatic interactions on annealed WN\({}_{\mathrm{x}}\)-based thin films. In particular, by using the contact angle made by a droplet of two liquids, polar and nonpolar (water and di-iodomethane), on the solid surface of the samples' basal plane, surface tension was measured, separating the London dispersion (D) and electrostatic components (P). In Figure 12, the water contact angles (WCA\({}^{\circ}\)) of the three annealed WN\({}_{\mathrm{x}}\) samples are reported. Figure 10: Comparison of FTIR reflectance of cermet samples. In Table 3, the WCA\({}^{\circ}\) of various WN\({}_{\rm x}\) samples and AlN-based cermets are given, including those after annealing. Surface energies, along with dispersive and electrostatic contributes, are reported in Table 4. Moreover, a further comparison was useful for analyzing wetting behavior: the cermet 500 W before (C500-pre) and after (C500-post) annealing (for estimating the effect of thermal treatment). From the overall set of measurements, it can be outlined that:  
* All annealed tungsten nitrides display a similar mild hydrophobic behavior, with a WCA\({}^{\circ}\) of around 70\({}^{\circ}\), surface energies around 35 mN/m and a prevalent dispersive force but non-negligible polar contribution to wettability. * AlN-based cermets containing tungsten nitride nanoparticles are much more hydrophobic with respect to single WN films in terms of the matrix behavior (AlN WCA\({}^{\circ}\) > 100\({}^{\circ}\)) with surficial energies due to prevalently dispersive forces. A full and detailed analysis can be devoted in a future study to elucidate the frictional properties of tungsten nitrides' basal plane for samples selected as potential electro-catalysts, as an alternative to platinum in HER water-splitting reactions. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **WN300** & **WN500** & **WN700** & **C500-pre** & **C50-post** & **C300** \\ \hline Surface energy (mN/m) & 34.27 \(\pm\) 1.7 & 37 \(\pm\) 2 & 35 \(\pm\) 2 & 39 \(\pm\) 2 & 37 \(\pm\) 1 & 36.6 \(\pm\) 1.9 \\ D (mN/m) & 22 \(\pm\) 2 & 23.9 \(\pm\) 0.5 & 24.0 \(\pm\) 0.9 & 36 & 35.3 \(\pm\) 0.5 & 35.2 \(\pm\) 1.2 \\ P (mN/m) & 12.8 \(\pm\) 0.7 & 13.0 \(\pm\) 1.7 & 11.0 \(\pm\) 1.3 & 2.7 & 1.42 \(\pm\) 0.8 & 1.42 \(\pm\) 0.8 \\ \hline \end{tabular}
\end{table} 
Table 4: Surface energy contributes. Figure 11: FTIR reflectance of cermet AlN–WN produced at 300 W, 500 W and 700 W. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **WN300** & **WN500** & **WN700** & **AlN** & **C300** & **C500** \\ \hline WCA (\({}^{\circ}\)) & 73.1 \(\pm\) 0.9 & 70 \(\pm\) 3 & 74 \(\pm\) 2 & 101 \(\pm\) 2 & 90.3 \(\pm\) 4 & 89.2 \(\pm\) 2 \\ \hline \end{tabular}
\end{table} 
Table 3: Water contact angle measurements.