Optical properties and color of hard quaternary nanocomposite TiCxNy/SiCN coatings prepared by plasma enhanced chemical vapor deposition

In this work we investigate the optical properties and color effects of superhard TiCxNy/SiCN nanocomposite (nc) coatings deposited by plasma enhanced chemical vapor deposition (PECVD) from TiCl4/CH4/SiH4/N2 gas mixtures at an intermediate substrate temperature of 500 °C. Combining individual hard materials such as TiN, TiC and SiCN, and the control of the microstructure allows one to optimize the materialʹs mechanical as well as optical properties. The optical characteristics and electronic structure of the quaternary TiCxNy/SiCN nanocomposite, such as dispersion relations, electrical resistivity, reflectance, and colors are systematically investigated using spectroscopic ellipsometry, four-point probe, and spectrophotometry. By increasing the carbon content up to 23 at.% we were able to vary the properties from their metallic to their dielectric character. As a result, the refractive index and extinction coefficient changed from 1.2 to 1.7 and from 2.0 to 1.2 at 550 nm, respectively, while the resistivity increased from 70 to 334 μΩ cm. Shift of the plasma energy from 2.53 to 1.78 eV caused reflectance and color variations. At the same time, the coatings exhibited very interesting mechanical properties documented by a hardness and Youngʹs modulus exceeding 55 and 300 GPa, respectively.