# Enhancing the Photocatalytic Activity of Immobilized TiO2 Using Laser-Micropatterned Surfaces
## 3 Results and Discussion
### Morphological, Optical, and Structural Properties of Photocatalytic Surfaces  
The XRD pattern of F-Si-solgel is depicted in Figure 1. This pattern confirms that only the (400) reflection of the flat silicon substrate is observed, consistent with its single crystal texture. None of the other red lines, representing the literature Bragg peaks of different silicon orientations, align with any experimental peak. Regarding TiO\({}_{2}\), the experimental peaks align with the green lines, corresponding to the Bragg peaks of the anatase phase [53]. Notably, there are no indications of rutile or brookite, consistent with the findings from the Raman spectra. Both XRD and Raman analysis confirm that the TiO\({}_{2}\) thin films are exclusively in the anatase phase. Figure 2a,b show representative scanning electron microscope (SEM) images of laser-microstructured silicon substrates. The entire surface exhibits a semi-periodic array of conical microstructures. The geometric characteristics of these conical microstructures were quantified using image analysis software (ImageJ, 1.53v), with measurements conducted on at least 40 microcones on the SEM images (Table 1). Laser microstructuring is a cost-effective method, eliminating the need for cleanroom facilities and the use of masks [54]. The creation of this distinctive micromorphology relies on melting and interference phenomena, occurring on the nanosecond timescale, during laser irradiation of silicon wafers in an etching SF\({}_{6}\) gas environment [32; 55]. The tuning of experimental parameters, such as laser pulse duration, repetition rate, wavelength, gas pressure, and laser fluence, can significantly influence surface morphology [30; 56]. For example, reducing the laser fluence results in the formation of rippled silicon surfaces, as depicted in Figure 2c,d. These ripples exhibit a semi-periodic structure, with an average peak height of 9.1 \(\pm\) 0.2 \(\upmu\)m. Notably, these structures represent the early stages of silicon microcone formation. The morphology of F-Si-solgel is shown in the SEM images in Figure 3a,b. The TiO\({}_{2}\) film exhibits notable uniformity, with nanometric cracks distributed across the surface. In the case of the reference F-Si-P25-solgel (Figure 3c,d), the surface displays both micro- and nanoscale roughness. The former stems from the porous structure and the latter from nanoparticle aggregations on the surface. The morphological characteristics shown in Figure 3 are in agreement with typical features observed in TiO\({}_{2}\) thin films and commercial Degussa P25 films [13; 57; 58]. Figure 3c,d indicates that the composite TiO\({}_{2}\) + Degussa P25 film predominantly adopts the morphology associated with Degussa P25. Thickness measurements for the TiO\({}_{2}\) and TiO\({}_{2}\) + Degussa films on flat silicon substrates indicate average values of 135 \(\pm\) 15 nm and 2.0 \(\pm\) 0.2 \(\upmu\)m, respectively. The thickness of the films was measured by profilometry on partially coated substrates, where part of the substrate was covered by copper tape during spin coating. Figure 1: XRD pattern of TiO\({}_{2}\) film on flat silicon (red and green lines correspond to the literature Bragg peaks of silicon and anatase phase of TiO\({}_{2}\), respectively). The chemical composition of the samples was determined through EDX analysis. Figure 4a,b presents layered EDX images of F-Si-slogel. These images indicate the successful deposition of TiO\({}_{2}\) coating on the flat silicon substrate, as evidenced by the uniformly distributed presence of oxygen and titanium throughout the film. Figure 4c,d maps the M-Si-slogel surface. From these figures, it is evident that the spin-coating method has successfully resulted in the coverage of the entire silicon structure by the TiO\({}_{2}\) film. Therefore, the TiO\({}_{2}\) film adopts the 3D microstructured silicon morphology and increased surface area.