Structures and photocatalytic behavior of tantalum-oxynitride thin films

Tantalum oxynitride films were created by direct nitridation/oxidation during rapid thermal annealing at temperatures 450-700 °C. Instead of during deposition, this post process may be proved to be an alternative way to make transition metallic oxynitride films. With sufficient supply of oxygen flow (≥ 30 sccm), TaO_xN_y was formed as examined from X-ray diffraction (XRD) analysis. This oxynitride film has a broad optical absorption over the range of visible light and sufficient photocatalytic function. For optical absorption, the films' transmittance and reflectance were measured by a UV-VIS-NIR spectrophotometer with wavelengths ranging from 300 to 900 nm. The broad visible light absorption is associated with the formation of band gap in TaO_xN_y film, which was examined by the theoretical calculations combining the Beer-Lambert law and Tauc formula. Lastly, the photocatalysis of TaO_xN_y was gauged by the photodegradation test which measured the reduction of light absorbance affected by the decomposition of methylene blue (C₁₆H₁₈N ₃SCl.3H₂O) on TaO_xN_y under visible light irradiation.