**2. Experimental procedure**

The growth of TiO2 thin films was realized by metalorganic chemical vapor deposition (MOCVD) in a conventional horizontal reactor at 400°C under a pressure of 50 mbar. Titanium(IV) isopropoxide (*Sigma-Aldrich*, 99.999%) was used as precursor of titanium and oxygen. Nitrogen (flow rate of 0.5 mL min−1) was used as carrier and purge gas. The borosilicate substrates (25 × 76 × 1 mm) were previously cleaned in a 5% H2 SO4 aqueous solution, rinsed in deionized water, dried in nitrogen, and immediately inserted into the reactor. **Figure 4** shows schematically the MOCVD equipment [45]. The main components are the reaction chamber, which consists of a quartz tube heated by an infrared oven containing the sample holder, and a vacuum pump that keeps the reaction chamber under a pressure below the atmospheric. The TTiP is maintained in a bubbler heated to 39°C. The gas conduction lines are made of stainless steel and are kept heated to prevent condensation and premature pyrolysis of the precursor.
