Colour control of titanium nitride coatings produced by reactive magnetron sputtering at temperature less than 100°C

Abstract

Decorative dry coatings are extensively used nowadays to replace the current pollutant wet coating processes, but the links between the coating appearance and the physical properties are usually not fully understood. This paper presents the results obtained by optical measurements in order to investigate the import of titanium nitride physical properties such as stoichiometry and structure on the coating visual appearance for TiNx thin films deposited by DC reactive magnetron sputtering at temperature lower than 100°C onto grounded substrate. It was shown that colours going from metallic grey to gold and finally brownish red have been obtained when the N2 flow is raised. These TiNx layer colour variations can be resolved in terms of the Drude model. As titanium metallic bonds decrease in the film, the absorbed part of the spectra moves towards lower energies, and when the minimum titanium content in the deposited films is reached (N2 mass flow>4 sccm), defects also reduce the amortised spectra towards slightly more reddish energies, but are difficult to control. In conclusion, as the N2 content in the gas discharge guides the nitrogen composition, it is the key parameter in colour control for TiNx sputtered films, especially when N2 mass flow is less than 4 sccm.