Effect of ytterbium on hardness and color of titanium nitride thin films

Abstract

Yb mononitride (YbN) has a B1 (NaCl-type) structure similar to the structure of titanium nitride (TiN), which makes it a candidate for use in new hard coating materials via solid-solution hardening. Ternary system (Ti–Yb–N) thin films with various Yb contents were prepared on Si substrates by pulsed laser deposition, and compositional analysis confirmed that the resultant films contained the expected elements. Phase identification revealed that the ternary nitride (Ti1−x Yb x )N thin films were all single-phase thin films that comprised YbN in TiN as a solid solution in the form of a B1- (Ti1−x Yb x )N phase. Although the hardness of the Ti–Yb–N thin films could be increased to a certain degree compared with that of a pure TiN thin film, the improvement was not significant. A change in the optical properties of the (Ti1−x Yb x )N thin films was indicated by a change in their color from gold to copper to silver with increasing x. This effect could make such thin films suitable for use as decorative coatings that are resistant to oxidation.