**7. Mechanical properties**

*Silicon Materials*

**6. Optical properties**

are shown in **Figure 8**.

**32**

**Figure 8.**

**Figure 7.**

*optical of the films also increase.*

*Reflectance spectra of ZrN and ZrN + 1Si films from 300 to 2500 nm. As Si content increases, the transmittance* 

The optical properties were investigated using a UV–Vis–NIR spectrophotometer. Reflectance and transmittance measurement were carried out from 300 to 2500 nm. The reflectance spectra of ZrN (black line) and ZrN + 1Si (red line) films are shown in **Figure 7**. In this figure, the typical reflectance of ZrN is observed [85]. It exhibits a maximum reflectance in the infrared region, which decreases as wavelengths decrease, and for wavelengths <500 nm, the reflectance slightly increases again. The ZrN films exhibit a similar Drude-like behavior [53, 85]. At longer wavelengths, the high electromagnetic absorption in this optical region is due to the conduction electrons and to the absorption at shorter wavelengths is due to the inter-band transitions of the bounded electron [85]. However, with the addition of silicon, the reflectance decreases drastically. At longer wavelengths, the film without silicon has a reflectance <80%, but the film with a Si content of 8 at.% has a reflectance <20%. Therefore, transmittance measurements were done to investigate the effect of silicon in the ZrN films. The transmittance spectra of ZrN + 1Si and ZrN + 2Si films

*Transmittance spectra of ZrN*▬*Si films with different Si contents and of the bare substrate (common glass).* 

*As the silicon content increases, the transmittance of the deposited films increases.*

The nanohardness (H) values as a function of Si content for the deposited films are shown in **Figure 9** and **Table 6**. The H for the ZrN film is 29.55 ± 3.70 GPa, which decreases with the addition of silicon to 18.12 ± 2.65 and 15.92 ± 1.23 GPa at 8 and 15 at.% of Si, respectively. The value obtained for ZrN was similar to the reports from other authors [99, 100]. The decrease of the nanohardness with the Si addition is related with the increase amorphous phase of SiNx and decreasing of the crystalline size of ZrN [101].

The mechanical properties of nanocomposite films depend on the chemical composition of each one of the phases present, of the crystallite size, crystallographic orientation, lattice structure, and the thickness grain boundary phase [94, 101]. Different works have reported that the main mechanisms that allow to explain the hardness enhancement in the nanocomposites are three: (i) the dislocation-induced plastic deformation when the crystalline size is >10 nm, (ii) the nanostructure of materials when the crystalline size is ≤10 nm, and (iii) cohesive force between atoms when the crystalline size is <10 nm. However, when the thickness of amorphous phase is larger than the crystalline size, the nanohardness of the films decreases due to a deformation mechanism reported as grain boundary sliding [24, 94].

According to the XPS and electrical resistivity value results, the Si addition generated the formation of an amorphous phase of SiNx, which increases its thickness with the silicon content in the film. It has been reported that when

**Figure 9.**

*Nanohardness of the films as a function of silicon content. As Si content increases, the nanohardness of films decreases.*


**Table 6.**

*Results from nanohardness tests.*

the SiNx phase thickness is larger than the crystallite size of the ZrN phase, the nanohardness of the films decreases due to an increase of the volume fraction of the amorphous soft phase. The deformation mechanism, in this case, is grain boundary sliding [24].
