Optical characteristics and color of TiN/SiN1.3 nanocomposite coatings

Abstract

Decorative and protective coatings deposited by dry methods are very attractive due to the environmental restrictions on traditional wet chemical techniques. In this context, nanocomposite hard coatings were fabricated by plasma enhanced chemical vapor deposition from TiCl4/SiH4/N2/H2/Ar gas mixtures at substrate temperatures of 300 and 500 °C. Their optical characteristics such as refractive index, extinction coefficient, luminosity, and colors were quantitatively determined by spectroscopic ellipsometry and spectrophotometry. Pure TiN exhibited a metal-like behavior, and its optical properties were modeled by the Drude (free carrier) approach. Nanocomposite films consisting of about 5–10 nm size TiN grains incorporated in an amorphous SiN1.3 matrix were modeled by a sum of Drude and Lorentz (interband) transitions. Optical properties of the films were explained by their morphology and chemical structure, investigated by a multitechnique approach using scanning electron microscopy, transmission electron microscopy, elastic recoil detection in the time-of-flight regime, Auger electron spectroscopy, x-ray photoelectron spectroscopy, and Raman spectroscopy. Subsequent addition of Si to TiN caused a complex transformation from a polycrystalline to nanocomposite microstructure, which adopted a predominantly amorphous character. This was accompanied by a transition from a metallic to a dielectric behavior in terms of the optical response and electronic properties.