Raman spectra of all TiO2 layers were recorded using a LabRam micro-Raman spectrometer (Horiba Jobin-Yvon HR800 UV) equipped with an optical microscope and a 5x objective lens. A green laser (532 nm) or a red laser (650 nm) was used for laser excitation of the Raman signal. The laser power at the sample was 1%. Slit width of the spectrometer was normally set to 650 cm. A holographic grating with 1800 grooves/mm was used to acquire all Raman spectra.