## 3 Results and Discussion
Due to long-range wetting transparency, the water contact angle of the MgF\({}_{2}\) layer, thinner than 100 nm, becomes highly insensitive of its chemical composition and its value approaches the value of the CA of the underlying materials: glass, Au and Au/MgF\({}_{2}\) metamaterial [30]. Therefore, it could be assumed that very thin (<100 nm) layers of metal-oxides did not contribute to the water CA value. Due to the similarity in the experiments [28], the change in the components was small and due to the forming of LIPSS by fs ablation (energy invested in ablation, not in heating), not many of the oxides were produced and their contribution to the CA value was not significant. The CA changed mostly due to the corrugations and not the presence of oxides. In this view, all the samples should have a similar increase in the CA after the interaction. However, there is a small difference which would mean that slightly different amounts of Zr and Ti components are removed by laser treatment depending on the initial order of the layers. Here, a significant mixture of the materials did not take place and spatial distribution retained a layered structure, which resulted in a similar increase in the CA angle. From the SEM images (Figure 1), the Gwyddion program was used to graphically extract the profiles along the selected lines perpendicular to the direction of the LIPSS, and from them to estimate the filling factors--the ratio between the ripple width and the spatial period. For 15\(\times\)(Ti/Zr), it is \(\sim\)0.6, while for 8\(\times\)(Zr/Cr/Ti), it is \(\sim\)0.72. It is possible to assume that greater filling factor leads to greater Casimir pressure for the same distance between the surfaces, while the corrugation height does not play a significant role [23]. The topmost surface is covered with a very thin oxide layer, because the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & \begin{tabular}{c} **LIPSS** \\ **Period (nm)** \\ \end{tabular} & **CA (\({}^{\circ}\))** & & \
\begin{tabular}{c} **\(\Delta\)CA** \\ **(\({}^{\circ}\))** \\ \end{tabular} &
\begin{tabular}{c} **CA Increase** \\ **(\%)** \\ \end{tabular} \\ \hline  & & untreated & corrugated & & \\  & & surface & surface & & \\ \hline
15\(\times\)(Ti/Zr) & 740 & 72.11 \(\pm\) 3.32 & 137.15 \(\pm\) 11.63 & 65.04 & 90 \\ \hline
15\(\times\)(Zr/Ti) & 740 & 77.29 \(\pm\) 1.71 & 144.49 \(\pm\) 14.97 & 67.20 & 87 \\ \hline
8\(\times\)(Zr/Cr/Ti) & 790 & 68.10 \(\pm\) 6.41 & 123.45 \(\pm\) 25.26 & 55.35 & 81 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The LIPSS period of the sample materials and the CA values. ambience is open air. Laser interaction will enforce the oxidation, but only to the saturation level [35]. However, the results presented in Table 1 show that whichever film structure we have at the beginning, after the interaction with the laser, the creation of the nanoscale corrugation causes an increase in CA. The higher filling factor for the samples with Zr as the topmost layer should cause the CA values' relatively more significant change than for those with Ti on top. This was observed for 15\(\times\)(Zr/Ti), but in the case of 15\(\times\)(Zr/Cr/Ti), the long-range wetting transparency [30] means that CA is also affected by the presence of a thin Cr layer. While LIPSS are anisotropic, the isotropy of the contact angles was not investigated. The direction of LIPSS (sample orientation) relative to the direction of recording (camera orientation) was arbitrary for each sample and undetermined. No significant difference in the left and right contact angles can be seen in Figure 3b,d,f, meaning either LIPSS and recording directions were set parallel by chance for each sample or the droplets were not significantly anisotropic. To match the directions of LIPSS and camera recording to be parallel by chance is less likely, indicating that the droplets are not significantly anisotropic.