Chromium titanium nitride films with different content of Cr and Ti were deposited on a silicon substrate by ion beam assisted deposition and characterised by Rutherford Backscattering Spectroscopy, X-ray Diffraction, X-ray Photoelectron Spectroscopy (XPS), Cross-sectional Transmission Electron Microscopy and nanoindentation testing. All of the samples except for the pure Cr2N coating have a structure similar to the fee form of TiN (111). XPS data showed that the films contained a small amount of oxygen. The dependence of hardness on film composition was observed. Maximum hardness at about 30 GPa was for coatings containing 15 at.% Ti and 35 at.% Cr. The high hardness in the ternary compound is thought to be attributed to high energy of dislocation propagation. It has been shown that chromium nitride formed in the absence of atomic nitrogen always grows as Cr2N. The addition of atomic nitrogen using an ion assisting beam promotes growth of CrN. The presence of a relatively low amount of Ti in the Ti-Cr-N film was seen to promote a significant increase in the number of Cr-N bonds. Preferential sputtering of nitrogen from the film during Ar ion cleaning for XPS analysis shows that composition analysis by XPS can be unreliable and should be done with great care. (c) 2005 Elsevier B.V. All rights reserved.