Heat Treatment Optical Properties Of Titanium Dioxide Thin Films Prepared By Ion Implantation

TiO₂ has application in the filed of environmental science, e.g., wastewater treatment, air purification and antibacterial aspect, due to its excellent photocatalytic performance in UV light. In this paper, ion implantation and subsequent annealing in N₂ have been used to prepare TiO₂ films in order to obtain TiO₂ with catalysis in visible light. Ti ion-implantated fused silica andα-Al₂O₃ single crystals have been annealed in N₂ ambience. In this way, N-doped TiO₂ films are successfully prepared.In this work, optical absorption spectroscopy, Rutherford backscattering spectrometry (RBS) , transmission electron microscopy (TEM) , X-ray photoelectron spectroscopy ( XPS ) and SRIM 2006 calculation code have been utilized to characterize the optical and structural properties of samples. The results are listed as follows:1. 80 keV Ti ion implantation was performed at room temperature up at a fluence of 1×10¹⁷ cm^-2 in both fused silica andα-Al₂O₃ single crystals (sapphire) . The implantation of Ti ions has introduced many defects in substrates. Therefore, the absorption of UV waveband increased, however, there is no clear absorption peak appeared. According to XPS results, metallic Ti⁰ and TiO₂ film coexisted in the as-implanted samples.2. The as-implanted samples have been annealed in N₂ and O₂ ambience, respectively. The optical absorption edge of TiO₂ appeared in fused silica matrix at 500℃and in sapphire at 600℃, respectively, after annealing in N₂ ambience. After annealing at 900 C in N₂ ambience, a red shift of the optical absorption edge of TiO₂ was observed from 3.98 eV (500℃) to 3.30 eV (900℃) in fused silica while 3.90 eV(600℃) to 3.45 eV (900℃) in sapphire, due to the formation of O-Ti-N compound. The tail of the absorption edge extends to the visible waveband and the absorption intensity of TiO₂ increases in the visible waveband. After annealing in O₂ ambience at 500℃, the optical absorption edge of TiO₂ in both fused silica and sapphire appeared. But the red shift is not so clear as that in N₂ ambient with the increasing temperature.3. The results show that the optical properties of TiO₂ film in fused silica and α-Al₂O₃ single crystals are similar. However, the annealing ambience plays a very important role in the optical properties of TiO₂ film. For the samples annealed in the N₂ ambience at 900℃, a new compound of O-Ti-N formed because a small amount of O atoms are substituted by N atoms in the lattice of TiO₂. The formation of O-Ti- N makes the tail of the absorption edge extend to the visible waveband and the absorption intensity of TiO₂ increase in the visible waveband. This result shows that nitrogen-doped TiO₂ has catalysis in the visible light.