Phase transformation of TiO 2 nanoparticles by femtosecond laser ablation in aqueous solutions and deposition on conductive substrates

Titanium dioxide (TiO₂) is a wide bandgap semiconductor that is chemically stable, non-toxic, and economical compared to other semiconductors and has been implemented in a wide range of applications such as photocatalysis, photovoltaics, and memristors. In this work we studied the femtosecond laser ablation of titanium dioxide powders (P25) dispersed either in water or deposited onto a fluoride-doped tin oxide (FTO) substrate. The process was used as a route to induce the phase-transformation of TiO₂ nanoparticles which was governed by laser parameters such as ablation time and power. It was observed that upon increase of the ablation time of TiO₂ dispersion in water a bandgap widening occurred, leading to the possibility of bandgap engineering of TiO₂ using controlled laser parameter profiles.