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Ultra high-rate deposition of photocatalytic TiO2 films by reactive magnetron sputtering with unipolar pulsing and plasma emission control systems

: Takasawa, N.; Ohno, S.; Sato, D.; Song, P.K.; Yoshikawa, M.; Suzuki, K.; Frach, P.; Shigesato, Y.

Puetz, J. ; Leibniz-Institut für Neue Materialien gGmbH -INM-, Saarbrücken:
Advanced coatings on glass & plastics for large-area or high-volume products : Proceedings of the 5th International Conference on Coatings on Glass, ICCG 5, July 4 - 8, 2004, Congress Hall, Saarbruecken, Germany
Saarbrücken: INM, 2004
International Conference on Coatings on Glass (ICCG) <5, 2004, Saarbrücken>
Fraunhofer FEP ()
titanium oxide; photocatalyse; reactive sputtering; unipolar pulsing; plasma control units (PCU); plasma emission monitor; high deposition rate

Titanium dioxide (TiO2) has been well-known as a photocatalyst, which has been synthesized mainly by sol-gel wet processes. With the comparison of the conventional wet processes, sputter depositions should be one of the most promising techniques for the window-size uniform coatings with high packing density and strong adhesion. Furthermore, high deposition rate could be excepted for the reactive sputtering processes using unipolar pulsing technique and plasma control units (PCU) with the feed back system of plasma emission intensity. These techniques enable us to operate the arc free and reliable plasma process in the "transition region".
In this study, TiO2 films with the thickness of about 500nm were deposited on unheated non-alkali glass substrates by reactive magnetron sputtering using one Ti metal target with unipolar pulsed powering and PCU. In order to keep the very high deposition rate, the depositions were carried out in the "transition region". Stable deposition was successfully carried out in the whole transition region at total gas pressure of 3.0 Pa. All the as-deposited films deposited in the "transition region" showed amorphous structure, which performed very low photocatalitic activity. On the other hand, the films deposited in the "oxide mode" performed clear photocatalytic activities in spite of that the films still showed amorphous structure. In this case, however, the deposition rate was very small of 8nm/min because the oxidized Ti surface have a very small sputtering yield. After the post-annealing in air at higher than 300?, all the films deposited in the "transition region" crystallized to anatase polycrystalline structure. They performed both photo-induced decomposition of acetaldehyde and photo-induced hydrophilicity under UV light illumination (black light, 0.4mW/cm2). The highest deposition rate in this study to deposit the photocatalytic TiO2 films in the transition region was 90nm/min, which was over twenty times higher than that for conventional sputter deposition processes.