Nitrogen incorporation during PVD deposition of TiO2:N thin films

TiO2:N is known for its photoactivity upon illumination with visible light. Using filtered arc with energetic particle fluxes, deposition near room temperature on sensitive substrates, e.g. polymers should be possible. However, addition of nitrogen gas flux during deposition results in very small nitrogen contents. Incorporation of nitrogen up to 5-7.5 at.% for either cathodic arc deposition or plasma based ion implantation and deposition leads to a reduction of the band gap down to 2.7 eV before the films become semimetallic. However, only deposition at a temperature of 200 °C allows avoiding the early formation of defects within the band gap. The nitrogen content was determined using secondary ion mass spectroscopy (SIMS) and calibrated with nitrogen implanted TiO2 samples using conventional beamline implantation. The results show that the nitrogen/oxygen flow ratio in two completely different deposition systems is a reliable indicator of the physical properties.