“…From the Raman spectrum of TiO 2 many different information can be obtained: titanium oxide phase fraction [22,23], crystallinity, crystallite size [24] and residual stresses [25] down to a minimum coating thickness of about 100 to 250 nm, depending on the substrate chemistry [26]. Crystallographic alterations caused by small amounts of dopants into the TiO 2 structure can also be easily discriminated by the appearance of their associated Raman bands [27], thus making Raman spectroscopy adequate for the characterization of functionalized titanium oxide layers [28][29][30]. The presence of a characteristic Raman spectrum associated with sodium titanate and clearly discernible A C C E P T E D M A N U S C R I P T…”