Paper SE-WeM1
High Rate Deposition of Photocatalytic TiO₂ Films by dc Magnetron Sputtering using a TiO_2-x Target

Wednesday, October 17, 2007, 8:00 am, Room 617

Sputter deposition should be the most promising technique for the uniform coatings in large area with very high durability and strong adhesion. However, the deposition rate of TiO₂ films by conventional reactive sputtering using a Ti metal target is very low, because the target surface should be fully oxidized (in "oxide mode") in order to deposit stoichiometric TiO₂ films. Recently, a slightly reduced TiO_2-x target (2-x = 1.986, Resistivity: 0.27 Ωcm) has been developed. Using this TiO_2-x target TiO₂ film deposition by dc sputtering with rater high rate and high durability should be possible. TiO₂ films were deposited on alkali-free glass substrate at RT-400°C by dc magnetron sputtering using the TiO_2-x target under 3.0 Pa. O₂ flow ratio during deposition was controlled from 0 to 100%. The variation in the deposition as a function of O₂ flow ratio did not show hysteresis curve at "transition region" as can be seen in the case of using Ti metal target, indicating that the TiO_2-x target surface was gradually oxidized with increasing O₂ flow ratio. The deposition rate using TiO_2-x target under 100% Ar gas was about 5 times higher than that using Ti metal target in "oxide mode". XRD patterns of the films deposited at O₂ flow at 0-5% showed entirely amorphous structure. After postannealing in air at higher than 200°C for 1 hour, these films changed to polycrystalline anatase TiO₂ and showed excellent photocatalytic activities such as photo-decomposition of acetaldehyde (CH₃CHO) or photo-induced hydrophilicity. Furthermore, we carried out in-situ analyses on the sputtering processes using the different sputtering target. A quadrupole mass spectrometer (QMS, AQ-360, ANELVA) combined with a specially designed energy analyzer revealed that high-energy O^- ion flux was detected clearly even in the sputtering with 100% Ar gas in the case of using the TiO_2-x target. Whereas in the case of using Ti metal target the O^- ion flux was detected only in the "oxide mode". The sputtered fragments mass analyses showed that Ti⁺ and TiO⁺ existed as sputtered particles in case of using the TiO_2-x target under O₂ flow ratio from 0 to 100 %, which was the same result as in the case of using the Ti metal target in the "oxide mode".