The phase evolution and photocatalytic properties of a ti-tio₂ bilayer thin film prepared using thermal oxidation

Ti-TiO₂ bilayer thin films were successfully prepared onto a glass substrate using magnetron sputtering with different TiO₂ bottom layer conditions. These represent a lack of (as-deposited) and full oxygen content (annealed). Single-layer Ti was additionally used as a control. The influence of oxygen diffusion phenomena of the bottom layer of TiO₂ to the upper layer of Ti thin films at different oxidation temperatures on structural, optical, and photocatalytic performance was investigated. X-ray diffraction (XRD) results confirmed that the crystalline phases coexisting on thin-film samples oxidized at 450^◦C were TiO, TiO_1.4, (bilayer, as-deposited TiO₂ ), anatase (bilayer, annealed TiO₂ ), and rutile (single and bilayer). This finding showed that the film’s phase structure evolution is significantly affected by oxygen diffusion from the bottom layer. Further increasing the thermal oxidation temperature caused a notable decline in the amorphous zone in bilayer thin films based on TEM analysis. Bilayer thin films lead to higher degradation of methylene blue under UV light radiation (63%) than single-layer films (45%) oxidized at 450^◦C. High photocatalytic activity performance was found in the bilayer annealed TiO₂-Ti thin-film sample. This study demonstrates that the bilayer modification strategy promotes the oxygen-induced bottom layer of TiO₂ bilayer thin films.