## 3 Results and Discussion
### Interfaces Characterization  
Using the formerly described targets, four films were deposited on silicon substrate, two from each target, changing the temperature at which the substrate was maintained during the experiment. Their appearance, together with the visualization of the bare substrate, is available in Figure 2. On one hand, the silicon plate exhibits a clean and smooth surface, without defects even at high magnification (Figure 2a), while on the other hand, all grown interfaces are composed of grains with dimensions below 50 nm and covered by a family of droplets of a maximum of 3 \(\upmu\)m (Figure 2b-e). An obvious difference can be noticed between the two approached compositions, especially at low magnification, namely a surface more crowded with droplets, but also pieces of material of irregular shape for Sr-including coatings (Figure 2d,e). Additionally, the elevations seem to be more flattened in the case of Mg-containing layers, for which the SEM images show a smaller number of bright areas, namely, fewer heights for electron accumulation (Figure 2b,c). This ascertainment can be translated into a higher roughness for PLD-Sr-1 and PLD-Sr-2, which can be further considered as a matter of low-quality deposition from a target that does not fully meet the requirements of densification. However, this morphology could have positive implications on cells adhesion, as usually they are much more compatible with those materials of suited roughness. For example, [PERSON] et al. (2015) deposited bioactive glass-ceramic films by nanosecond PLD and obtained the typical morphology: a surface sprinkled with droplets, which supposes an inherent roughness, suitable for cell attachment. [PERSON] et al. (2016) also employed PLD to obtain bioactive glass films; the increase in the laser pulse energy was correlated with better surface properties and cellular behaviour. The next two samples were prepared through the chemical route (SC) on silicon substrate with different features. Since very thin films are expected, a rougher substrate was necessary in order to ensure an adherence that will last during the immersion in physiological fluids or subjection to mechanical stresses. Figure 3 comparatively presents the aspect of the bare silicon plate, as well as coated ones. If the first one is crossed by mixed hills and valleys with sharp edges and corners, in other words, a coarse and faceted roughness (Figure 3a), the next two display surfaces within which the primary irregularities were partially alleviated by the deposited interfaces, proving their reduced thickness, but also their homogeneity and continuity (Figure 3b,c). Moreover, at high magnification, a visible nanostructuring (grains with dimensions below 20 nm) can be seen, interrupted by branched cracks prevalently for SC-Mg, likely a consequence of the drying and calcining processes, when the solvents and thermally degradable components are removed, leaving behind a discontinuous layer due to the high dilution of the precursor solution and subsequently insufficient amount of solid material. However, the covering degree is quite high, exceeding 95%; the value was estimated by relating the area covered by cracks to the total investigated area. Figure 2: _Cont._Figure 2: SEM images at different magnifications of: (**a**) bare substrate and (**b**) PLD-Mg-1, (**c**) PLD-Mg-2, (**d**) PLD-Sr-1 and (**e**) PCL-Sr-2 interfaces. The EDX spectra corresponding to the grown coatings are illustrated in Figure 4a in comparison with those of the substrates used for each set of samples. To the signals of Si, mainly identified for the bare silicon plates, supplementary maxima assigned to the elements considered in the primary compositions (Ca, P, Zn, Mg/Sr) emerge, similar to the targets. Due to the higher thickness of PLD-derived interfaces, the Sr maximum placed at high energy is entirely discernible, while its existence in the spectrum of SC-Sr is ambiguous, even though the associated quantitative estimation proposes a value of several percent.