## 3 Results and Discussions
### Surface Morphology and Chemical Composition  
To distinguish between n-type and p-type conductivity of the deposited ZnO thin films, a simple method developed by [PERSON] et al. was employed [30]. Hot-point probe measurements have been successfully utilized to determine the conductivity type of materials as an alternative for the time-consuming Hall-effect measurements. Using simple laboratory equipment, mainly a soldering iron station, a multimeter, and a pair of probes, it is possible to measure the nature of the thin films and the conductivity of the films by evaluating whether the voltage between hot and cold probes is positive or negative. The n-type nature of the ZnO is usually given by the point's defects present in its lattice [31]. The hot probe is obtained by heating up the positive probe that thermally excites the carries, electrons in the case of n-type ZnO, that diffuse from a high carrier concentration region to a low carrier concentration region in all directions. When a positive voltage is generated between a hot and cold probe, the thin films are of n-type conduction. The method is employed only to depict the fact that the thin ZnO films exhibits n-type conductivity and does not give absolute values. Figure 3 shows the surface of the thin films obtained for different substrate temperatures. It is clearly seen that this is a crucial factor that dictates the morphology, as found for other deposition methods as well such as sputtering--the ratio between the temperature of the substrate and the melting temperature of the deposited material influences the porosity of the deposited films [32]. The porosity of the films is important in applications such as the fabrication of dye-synthesized solar cells and lithium cells but also in designing p-type doped ZnO structures [33]. The obtained films seem to have a wall-like structure for 200 and 350 \({}^{\circ}\)C, due to the substrate temperature that dictates the nucleation process, and determines a two-dimensional growth. At low temperature, it was shown that the atoms remain in the place where they land without too much diffusion in the surface, the process being considered as a quench growth. Figure 3 shows that for room temperature and 100 \({}^{\circ}\)C, the substrates seem to be covered by clusters of nanoparticles that develop in a dense film [17; 34]. It seems that, starting from a specific temperature, the porous structure would be initially composed of small grains that would promote the growth of fine particles, limiting the preferential growth along specific directions and affecting the crystallinity of the thin films. For temperatures higher than 350 \({}^{\circ}\)C, we found that the films have a more grain-like structure, with large exposure of the substrate that makes them unsuitable for the applications we envisioned. This fact corresponds with other reports and was the reason why we have chosen the studied temperatures [25; 35; 36]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**T (\({}^{\circ}\)C)**} & **Peak** & **Peak** & \multirow{2}{*}{**FWHM \(\beta\)**} & **Lattice** & \multirow{2}{*}{**Grain Size**} & \multirow{2}{*}{**Strain \(\varepsilon\)**} \\  & **Position** & **Intensity** & & **(deg)** & & **(nm)** & \\ \hline RT & 33.53 & 10,602 & 0.46 & 0.5342 & 18.65 & 0.0260 \\ \hline
100 & 33.81 & 36,494 & 0.39 & 0.5299 & 21.99 & 0.0178 \\ \hline
200 & 34.21 & 94,816 & 0.21 & 0.5239 & 40.44 & 0.0062 \\ \hline
350 & 34.18 & 196,246 & 0.21 & 0.5244 & 40.43 & 0.00 EDS spectra of the ZnO thin films are presented in Figure 4. For each of the samples, Zn and O are the main constituents, with no trace of impurities (within the detection limit of EDS) with respect to substrate temperature used during PLD deposition. For the samples deposited at 350 \({}^{\circ}\)C, the EDS spectrum also shows an increase in the Si signal related with the substrate.