## 3 Results
For the 500 W and 700 W films, the prevalent modification occurred around 1000 nm but the overall reflectance diminished after annealing, which can be explained by the nitridation and/or oxidation of metallic tungsten by means of gases entrapped in the lattice or at grain boundaries and their subsequent release. The X-ray diffraction peaks of reactively sputtered tungsten nitride, WN\({}_{\mathrm{x}}\) produced at different deposition powers are shown in Figure 3. Phases of the WN\({}_{\mathrm{x}}\) films before and after annealing at 470 \({}^{\circ}\)C and 580 \({}^{\circ}\)C were analyzed. The \"as grown\" film produced at the lowest deposition power (300 W) exhibited a single fcc W\({}_{2}\)N phase whose crystallinity increased with annealing. At 500 W, a poorly ordered W\({}_{2}\)N phase mixed with an amorphous phase (identified by the deconvolution procedure as a broad peak around 20 37.7\({}^{\circ}\) and with a full width at half height (FWHM) at maximum of 5.2\({}^{\circ}\)) was observed, whereas at 700 W only a prevalent amorphous phase was present. The cubic \(\beta\)-W\({}_{2}\)N phase had a (111) preferred orientation. The material deposited at 300 W, having a high nitridation level, exhibited the highest 20 shift in the diffraction peaks with regards to the ICDD database position, which may be due to the release of stresses. When the deposition power increases, this phenomenon is less noticeable. Related lattice parameters (see Figure 4) were higher than the corresponding bulk value of the W\({}_{2}\)N phase (4.126 A). The increase in the lattice constant can be attributed to the incorporation of excess nitrogen atoms that can occupy the vacant octahedral sites, resulting in the W\({}_{2}\)N lattice's expansion [16]. The film deposited at lower deposition power consisted of small grains, whereas at higher deposition powers larger grains were present. Annealing of the deposited films resulted in an improved crystallinity of the W\({}_{2}\)N grains and in a crystallization of the amorphous phase. The larger annealing effects on the crystallization could already observed at 470 \({}^{\circ}\)C; raising the temperature to 580 \({}^{\circ}\)C produced only a slight improvement in crystallinity. At deposition powers of 300 and 500 W, only \(\beta\)-W\({}_{2}\)N was present after annealing, whereas for the material obtained at 700 W, a two-phase structure of W\({}_{2}\)N and bbc \(\alpha\)-W appeared and the diffracted intensities increased at the higher annealing temperature. The modification seems to be progressive. For the films obtained at a low deposition power (300 W), the preferential (111) orientation of the W\({}_{2}\)N phase persisted after annealing, whereas when the deposition power was increased, the annealing produced not only large grains with a (111) preferential orientation, but also a further growth of grains with a (200) orientation. At a deposition power of 700 W, this effect was more pronounced. Interchanges from the preferred (111) direction to (200) have also been reported for thin niobium nitride films subjected to annealing [17]. Nitrogen readily chemisorbs on the (200) planes but not on the N-terminated (111) planes, which reduces the flux of cations in the (200) compared to the (111) planes, resulting in the orientation of growth in the (200) direction. Figure 3: XRD patterns of different WN\({}_{\mathrm{x}}\) films before and after annealing. Moreover, a shift of the diffraction lines towards a higher 20 was observed after the annealing treatment for all the examined films. The shift in XRD diffraction lines, as well as the variation in intensity, could be due to the release of stresses. The lattice constant decreased with increasing annealing temperature, indicating a relaxation of the structure due to the diffusion out of excess nitrogen atoms by means of a recrystallization process.