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G. Schmid, M. Quirchmair, C. Eisenmenger-Sittner:
"TiO2 FILMS DEPOSITED ON PLANAR AND GRANAULAR SUBSTRATES BY PULSED DC MAGNETRON SPUTTERING";
Vortrag: Joint Vacuum Conference 14 (JVC-14), Dubrovnik, Kroatien; 04.06.2012 - 08.06.2012.

This work deals with TiO2 thin films deposited by bipolar pulsed DC magnetron sputtering and also addresses the coating of powder shaped substrates (diameter 5-70 µm), in special hollow glass microspheres that shall be used to store hydrogen at high pressure.
Hydrogen is released out of the hollow glass microspheres when they are heated up to a temperature of about 120 °C. To reach this temperature is the main challenge of this storage system. For that an exothermal chemical reaction can be used, in this case a NaBH4-water (Venpure^TM) reaction, which produces hydrogen as a most welcome by-product. This chemical reaction has to be initialized by a catalyst deposited on the hollow glass microspheres. Therefore, it is necessary that every single sphere is coated with the catalyst, which was done by magnetron sputtering. To generate uniform coatings on the microspheres an apparatus was designed with coating vessels of special shape rotating beneath the sputtering target.
Catalyst performance strongly depends on the morphological structure not only of the catalyst but also of the support material of the catalyst. For this application the catalyst support of choice was TiO2. The TiO2 films were deposited with a bipolar pulsed DC power supply on plain glass substrates at different deposition pressures (Ar, O2), reverse time and frequency. Anatase, one crystalline phase of TiO2, is preferred over the TiO2 rutile phase for this catalytic application.
It was concluded that higher frequencies and higher pressure lead to more amorphous structures in TiO2. With the coating apparatus for granular substrates it was possible to coat each hollow glass microsphere of a batch of approx. 10 cm³ volume as it is indicated by comparison of optical micrographs of uncoated and coated spheres.

This work was supported by the Austrian Science Fund (FWF), project "CatSphere", grant number P-22718.