## 3 Results  
### Morphological and Topography Characterization  
Figure 1 shows the cross-section morphology of the four TiO\({}_{2}\) nanostructures prepared by electrochemical anodization. TiO\({}_{2}\)-nt can be observed in Figure 1a; their good organization was achieved thanks to the three steps of anodization which resulted in a homogeneous wall thickness with an inner diameter of approximately 65 nm and a length of 1.67 \(\upmu\)m. At the bottom of these nanotubes, Ti nanobowls (Ti-nb), known as \"the dimples\" can be seen, which help to enhance the organization of nanotubes as a template [17]. Meanwhile, Figure 1b shows the morphology of TiO\({}_{2}\)-nc, their length and inner diameter were 250 \(\pm\) 50 nm and 29 \(\pm\) 3 nm, respectively. The roughness caused by the organic electrolyte can be seen in the upper part of the nanocavities [18]. While in their template of Ti-nb, in the lower part, a hexagonal geometric mesh can be observed in contrast to the template of TiO\({}_{2}\)-nt (Figure 1a) whose arrangement is made of circular mesh. Figure 1c displays the cross-section of TiO\({}_{2}\)-ns/TiO\({}_{2}\)-nc. In this case, the length of the nanocavities was 362 nm and their inner diameter 22 nm, whereas the thickness and outer diameter of nanosheets were 35 nm and 85 nm, respectively. The nanosheets were grown selectively between the upper ends of two or three nanocavities. This unique morphology was achieved by controlling the time of the second step anodization, resulting in a homogeneous length of nanocavities and a thickness of nanosheets [16]. Different structural forms were noticed in Figure 1d for TiO\({}_{2}\)-nb/TiO\({}_{2}\)-nc; in the upper part TiO\({}_{2}\)-nb; in the middle part TiO\({}_{2}\)-nc; and in the lower part Ti-nb. The shape of TiO\({}_{2}\)-nb was obtained  
due to the control over the anodization time, they were selectively grown among the tops of the nanocavities acquiring a hexagonal organization [16]. The length and inner diameter of nanocavities were 96 nm, and 30 nm, respectively, while the thickness and outer diameter of nanobowls were 40 nm and 75 nm, respectively. A summary of these geometric parameters is shown in Table 1.  
Figure 2 shows the surface morphology of the four nanostructures. The surface morphology of TiO\({}_{2}\)-nt is displayed in Figure 2a, as mentioned above, nanotubes had a highly organized morphology because of the three-step anodization process. This organization clearly consists of six nanotubes surrounding a central nanotube because the template of the Ti-nb operates as a mask of \"dimples\" [17; 19]. Here, the inner and outer diameters were about 65 nm and 98 nm, respectively. A different morphology for TiO\({}_{2}\)-nc is shown in Figure 2b. As can be seen, the morphology resembles a porous membrane whose surface is an oxide film that presents significant roughness caused by organic electrolyte solutions, this film is known as \"the entire surface layer\" [20]. The inner diameter of the nanocavities was about 29 nm. A more complex morphology for TiO\({}_{2}\)-ns/TiO\({}_{2}\)-nc is noticed in Figure 2c. As can be seen, the nanosheets were selectively grown among the tops of the nanocavities acquiring a highly ordered morphology, such organization is a periodicity function of the template of the Ti foil. The outer diameter of nanosheets was about 85 nm, which is notably larger than the inner diameter of the nanocavities (22 nm), shown as black circles. Figure 2d shows the surface morphology of TiO\({}_{2}\)-nb/TiO\({}_{2}\)-nc. The nanobowls were assembled on top of a set of several nanocavities forming an arrangement similar to a six-petals flower. The diameter of the nanocavities, in gray color, was about 30 nm, and the outer diameter of nanobowls was 75 nm being more homogeneous than the outer diameter of the nanosheets of 85 nm.