**2. Structural characterization of 1D titania coatings**

Titania is well known to exist mainly in three crystalline modifications: tetragonal rutile, tetragonal anatase, and orthorhombic brookite [82]. The structure of the titania lattice is determined by the way in which TiO<sup>6</sup> octahedra are linked [83]. These polymorphic forms of TiO<sup>2</sup> characterize different structural stability, different photo- and bioactivity, as well as different electrical and optical properties [84–86]. This fact causes that the determination of the structure of materials basing on TiO<sup>2</sup> is especially important for their further, for example, biomedical, applications.

In order to determine the titania structure, X-ray diffraction studies are often carried out. Characteristic set of 2Θ [°] signals: 25.33 (101), 37.80 (004), 48.08 (200), 55.12 (211) indicates the presence of anatase form, whereas the signals: 27.50 (110), 36.17 (101), 41.50 (111), 54.46 (211) prove that rutile form is our studied sample [87–90].

Raman spectroscopy is another very useful method to recognize and characterize the titania structures. Basing on the group analysis, there are six active Raman modes (A1g, 2B1g, 3Eg ) for anatase D4h (I4<sup>1</sup> /amd) and four active Raman modes (A1g, B1g, B2g, and Eg ) for rutile D4h (P4<sup>2</sup> / mnm) [91, 92]. According to previous reports, the set of bands, which appear in Raman spectra at 197, 339, 519 and 639 cm−1, indicates the formation of TiO<sup>2</sup> anatase form. For TiO<sup>2</sup> rutile form, the base of identification is the detection of bands at 447 and 612 cm−1 [91–94]. It should be pointed out that very often the fabrication of materials based on TiO<sup>2</sup> on nanoscale causes the formation of amorphic systems or amorphic systems containing small amount of crystalline phases [95, 96]. In such cases, Raman mapping of whole sample surface can help in the detailed determination of the structure.

The structure of thin titania films can be determined by the use of transmission electron microscopy studies, on the base of selective area electron diffraction (SAED) and the determination of *d*-spacing from HRTEM images of nano-TiO<sup>2</sup> -sample [97, 98].

The use of mentioned in this subsection instrumental methods led to state about the structure of 1D-titania nanostructures. Even if they are not perfectly crystalline just like in case of amorphous samples possessing some crystalline islands in the structure.
