Phase transformation from rutile to anatase with oxygen ion dose in the TiO₂ layer formed on a Ti substrate

The oxygen plasma immersion ion implantation (O-PIII) method was used to form a TiO₂ layer on a Ti substrate. The content of the anatase polycrystalline phase increased from 5.1% to 22.3% of the total TiO₂ amount with a higher O⁺ ion dose. The oxygen ion doses were 3.6 × 10¹⁶ ions, 8.1 × 10¹⁶ ions, 1.26 × 10¹⁷ ions, for 1, 2, and 3 h, respectively, with ion energies of E ≈ 0.8 keV. The polycrystalline phases and morphology of the obtained films were characterized by XRD, FESEM, AFM, and Raman spectroscopy. The chemical bond analysis and layer-by-layer measurements for TiO₂ layer thickness evaluation were performed by XPS. The photocatalytic decomposition reaction constants of a methylene blue solution increased from 3.2 × 10⁻³ min⁻¹ to 4.2 × 10⁻³ min⁻¹ under UV-A irradiation and the liquid free surface energy increased from 39.0 mJ/m² to 49.5 mJ/m² with a higher O-PIII treatment doses. These results were explained by the partial phase transition of the TiO₂ layer from rutile to anatase. Thus, the increase in the O⁺ ions implantation dose into the Ti substrate invoked the reduction of material density from Ti (ρ = 4.506 g/cm³) through TiO₂ rutile (4.23 g/cm³) to TiO₂ anatase (3.78 g/cm³) phase.