Effect of Na diffusion from glass substrate on the microstructural and photocatalytic properties of post-annealed TiO2 films synthesised by reactive sputtering

►Columnar TiO2 films were synthesised by sputtering on glass substrates containing Na. ►After crystallisation treatment, XPS analyses reveal the presence of metallic Na. ►The Na diffusion leads to a crystallisation delay and grains coalescence. ►A photocatalytic activity deterioration is observed with the Na content increase. ►A comparison is made with Na-free TiO2/SiNx/glass films.