Variation of color in titanium and zirconium nitride decorative thin films

Abstract

The color variation in zirconium and titanium nitrides was investigated with respect to the atomic ratio between nitrogen and transition metals and with oxygen as the contaminant. The nitride thin films were deposited using cathodic arc evaporation. The stoichiometry of the films was varied through changes in nitrogen gas flow rate and total pressure in the deposition chamber. Thickness of all nitride films was controlled at 0.5 μm. Oxygen content in the thin films was correlated to their color. The reflectivity spectra of ZrN and TiN thin films were measured in the visible region of the spectrum and their color was quantified in the L*a*b* color system. Increasing the atomic ratio of nitrogen to transition metals causes the overall reflectivity of the gold-like color to decrease and the yellowness to increase. A change of the stoichiometry without a noticeable change of thin film color is wider for TiN than ZrN. The variation in oxygen contents results in the color change in the same direction as that of the variation of nitrogen content. Therefore, oxygen found in the nitride thin films behaves as nitrogen; it consumes free electrons from transition metal.