Deposition of TiOx and N-TiOx by dielectric barrier discharge at atmospheric pressure

Over the past years, atmospheric pressure deposition assisted by plasma has attracted interest due to its low cost. Among other materials deposited by this technology, titanium dioxide (TiO2) is very popular, mostly due to its good photocatalytic properties. However, due to intrinsic drawbacks of the process, the control of the deposition parameters needs to be fine-tuned to obtain a thin film presenting the expected properties. Here we report the deposition of TiOx and N-doped TiOx thin films by dielectric barrier discharge at atmospheric pressure (AP-DBD) plasma with titanium (IV) isopropoxide and oxygen as reactants, and argon as a working gas during 10 min. In the first part, we highlight the advantages of heating the substrate at 400 °C during the deposition. Then, the influence of the oxygen content and power on the morphology and composition is reported. In the second part, we demonstrate the successful doping of the structure with nitrogen by adding ammonia (NH3) to the working gas. Through a screening over deposition parameters (i.e. oxygen content and power), the lowest bandgap reachable was 3.22 eV for a working gas composed of 1.8 vol% of NH3, 5, and 10 vol% of O2, and a power of 75 W during the film deposition. Evaluating the formation of oxygen vacancies in the TiOx films and the N doping, we were able to tentatively explain the observed evolution of the bandgap.