Among the semiconductors, TiO2 (Eg = 3.2eV) has proven to be the most suitable for widespread environmental applications, since it is biologically and chemically inert; it is stable with respect to photocorrosion and chemical corrosion; and it is inexpensive. The most active field of TiO2 photocatalysis is the photodegeneration of organic compounds. TiO2 can be prepared in the form of powder, crystals, or thin films. While powders are frequently utilized, thin films prepared by different methods, as magnetron sputter deposition, plasma immersion ion implantation and metal arc deposition, are also under investigation. Metal Plasma Immersion Ion Implantation and Deposition (MEPIIID) is a relatively new method for surface modification of materials. Using this method, a pulsed regime is employed with accelerated, energetic ions arriving on the substrate during the high voltage pulses and low energy, respective hypersonic ions from the cathodic arc used to generate the Ti ions, between the pulses. Compared to continuous bombardment with 500-1500 eV ions, in this pulsed mode the total sputter rate of the growing film by the impinging ions is reduced. Oxygen gas backfill leads to a partial transfer of the kinetic energy from Ti ions to oxygen molecules during the transit from the cathode towards the substrate, thus partially ionizing the oxygen molecules. Furthermore, neutral oxygen atoms are preferentially adsorbed on the reactive TiO2 surface and included in the film growth.
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