# Enhancing the Photocatalytic Activity of Immobilized TiO2 Using Laser-Micropatterned Surfaces
## 3 Results and Discussion
### Morphological, Optical, and Structural Properties of Photocatalytic Surfaces
A higher concentration of titanium and oxygen is observed in the valleys between the microcones, as more material flows towards these areas during spin coating. The presence of silicon in both mapping distributions is attributed to the substrates on which the TiO\({}_{2}\) films are deposited. Importantly, no contamination of carbon or other elements has been detected in either case, confirming the high purity of the samples. Figure 5a,b depicts the UV-visible transmittance spectra of TiO\({}_{2}\) and TiO\({}_{2}\) + Degussa P25 films on glass substrates within the spectral range of 300-800 nm. Notably, both spectra exhibit a distinct absorption edge at 320 nm, and the films demonstrate high transparency within the visible range (400-700 nm). In the transmittance spectrum of TiO\({}_{2}\), interference fringes are evident, attributed to the nanometric thickness of the film (135 nm) and reflections occurring from the back and front sides [13]. Conversely, this \begin{table}
\begin{tabular}{c c c} \hline
**Half-Height Diameter** & **Height** & **Distance between Neighboring Microcones** \\
[\(\mu\)m] & [\(\mu\)m] & [\(\mu\)m] \\ \hline
6.8 \(\pm\) 0.2 & 29.0 \(\pm\) 0.7 & 9.0 \(\pm\) 0.4 \\ \hline \end{tabular}
\end{table} 
Table 1: Geometrical characteristics of silicon microcones. Figure 2: SEM images of (**a,b**) silicon microcones and (**c,d**) rippled silicon surfaces. All images are taken at a side (45\({}^{\circ}\)) view. interference behavior is not observed in TiO\({}_{2}\) + Degussa P25 films, owing to their one-order-of-magnitude-greater thickness (2 \(\upmu\)m). From the Tauc plot presented in the inset of Figure 5a, the optical band gap (\(E_{g}\)) of TiO\({}_{2}\) was calculated using the following equation: \(\left(\mathit{ahv}\right)^{n}=K\left(\mathit{hv}-E_{g}\right)\), where \(\mathit{h}\) is the Plank constant, \(\mathit{v}\) is frequency of radiation, \(\mathit{a}\) is the absorption coefficient of the film, \(K\) is an experimental parameter depending on the photon energy, and \(\mathit{n}\) is a constant related to the nature of electronic transitions (TiO\({}_{2}\) is an indirect semiconductor, \(\mathit{n}=0.5\)) [50]. The \(E_{g}\) for TiO\({}_{2}\), estimated by extrapolating the linear portion of \(\left(\mathit{ahv}\right)^{n}\) versus \(\mathit{hv}\), is determined to be 3.4 eV, consistent with the literature values [13; 59]. The previously measured \(E_{g}\) for Degussa P25 is 3.15 eV [60]. Figure 6a presents the Raman spectrum of F-Si-P25-solgel, revealing five active modes of TiO\({}_{2}\) + Degussa P25 on silicon. The distinct peaks at 144 cm\({}^{-1}\), 196 cm\({}^{-1}\), 397 cm\({}^{-1}\), 517 cm\({}^{-1}\), and 639 cm\({}^{-1}\) correspond to the active modes E\({}_{g}\)(1), E\({}_{g}\)(2), B\({}_{1g}\)(1), A\({}_{1g}\)(1) + B\({}_{1g}\)(2), and E\({}_{g}\)(3), respectively. According to research studies, these values are associated with the anatase phase of TiO\({}_{2}\)[61]. No active mode of silicon is detected in this sample, attributed to the micrometric thickness of the film. Conversely, for F-Si-solgel and M-Si-solgel (Figure 6b,c), the A\({}_{1g}\)(1) + B\({}_{1g}\)(2) active mode is not detected due to the nanometric thickness of the sample and the coexistence of a strong Raman peak of silicon at the same Raman shift. Two Raman modes observed at 303 cm\({}^{-1}\) and 520 cm\({}^{-1}\) in these spectra correspond to the single crystal silicon substrate [62; 63]. All other detected peaks are associated with the anatase phase of TiO\({}_{2}\). Slight shifts in anatase Raman peaks (-2-3 cm\({}^{-1}\)) between the different samples may arise from differences in laboratory temperatures during measurements [13]. These observations collectively confirm that the developed TiO\({}_{2}\) is in the anatase phase, with no signs of bro  
Figure 3: SEM images of (**a**,**b**) TiO\({}_{2}\) and (**c**,**d**) TiO\({}_{2}\) + Degussa P25 thin films on flat silicon substrates.