## 3 Results
After annealing at 580 \({}^{\circ}\)C, the a-lattice constant values changed from 4.273 \(\AA\) to 4.223 \(\AA\), from 4.231 \(\AA\) to 4.181 \(\AA\) and from 4.204 \(\AA\) to 4.129 \(\AA\) for the films deposited at 300 W, 500 W and 700 W, respectively. Only a slight change of crystallite size was observed when the annealing temperature was increased for each analyzed deposition power. The surface morphology of the film deposited at 500 W after annealing at 580 \({}^{\circ}\)C is shown in Figure 5. The surface appears smooth and consisted of rounded small grains, as expected for sputtered films, which generally tended to have a columnar microstructure. Figure 6 shows the surface topography of the film deposited at 700 W before and after annealing treatments. After annealing at 580 \({}^{\circ}\)C, the amorphous film was fully crystallized and a segregation of coarse grains was evident. These grains were presumed to be \(\alpha\)-W as it results from the X-ray diffraction shown in Figure 3.  
Figure 4: (**a**) Lattice constant vs. annealing T. (**b**) Crystalline size of \(\mathrm{WN_{x}}\) films obtained at different deposition powers before and after annealing. Figure 5: AFM image of 500 W sample after annealing at 580 \({}^{\circ}\)C.  
For metal nitrides that crystallize in cubic structures and ideal \"perfect\" crystals, first-order Raman scattering is forbidden because there is translational symmetry, q = 0, and all atoms are in centrosymmetric octahedral sites [18]. Nevertheless, sputtered coatings are known to have vacancies that induce distortion in the structure and, as a consequence of this, the Raman spectrum is composed of broadened bands due to disorder and second-order processes. In analyzed samples there was Raman activity, so no stoichiometric cubic nitrides were present. Lattices were expanded by the effect of nitrogen adsorption. The Raman spectra of the as-grown films reported in Figure 7 had three main regions:  
* 150-350 cm\({}^{-1}\) acoustic bands
* 450-650 cm\({}^{-1}\) optic bands
* 850-1150 cm\({}^{-1}\) two phonons contributes. With regard to the acoustic modes, their intensity is proportional to the dimensions of the crystallites. These bands should have two maxima; in Mo\({}_{2}\)N they are reported to be 145 cm\({}^{-1}\) and 205 cm\({}^{-1}\)[19] Acoustic bands of tungsten nitrides split after annealing into two maxima, as reported in Table 2. In all the as-grown films, there was a unique broad band of low intensity. This behavior can be associated with an increase in crystallite size. In the 700 W film, after annealing the splitting was less accentuated with respect to the other films and a contribute at 187 cm\({}^{-1}\) was also present, testifying to the contribution of an amorphous phase. Figure 6: AFM pictures of 700 W WNs films, (**a**) as deposited and (**b**) annealed at 580 \({}^{\circ}\)C.  
Figure 7: Micro-Raman before (red line) and after (blue line) annealing at 580 \({}^{\circ}\)C for 300 W (**a**), 500 W (**b**), 700 W (**c**). The optical band located at 482 cm\({}^{-1}\) in the 300 W film, at 487 cm\({}^{-1}\) in the 500 W film and at 492 cm\({}^{-1}\) in the 700 W film is due to the stretching of the W-N bond. A film with a higher compressive stress shows a higher frequency shift of this band [20]. The absence of sharp and well-defined peaks could be attributed to local disorder. With the increase in metallic character there Raman activity progressively decreases. Consistently with resistivity measurements, in the 300 W film, after annealing Raman activity increased, the film in fact became more resistive. The 500 W and 700 W films, acoustic bands aside, had an overall comparable Raman activity before and after annealing, consistent with having a similar metallic character. As can be seen from the 700 W spectrum, after annealing there was a band at 270-280 cm\({}^{-1}\) RS that can be attributed to W-O bending, and a band at 780 cm\({}^{-1}\) that can be attributed to the W-O-W bonds stretching [21].