Titanium oxynitride (TiO xN y) thin films are of great interest for the fabrication of protective optical coatings. By varying the oxygen and nitrogen content in the films, the electrical, optical and mechanical properties of these coatings can be tailored properly. In this work, we fabricated TiN and TiO xN y films by dual ion beam sputtering technique. TiO xN y films were ion-assisted by a low energy oxygen and nitrogen mixed ion beam of variable O/N flux ratio. We observe that the incorporation of oxygen greatly improves the adhesion of the film on the glass substrate. Further, the optical extinction coefficient drastically decreases for increasing oxygen content, suggesting new applications of TiO xN y films as protective coatings on transparent substrates. The film composition by XPS analyses is in agreement with the results obtained by a simple model to describe the ion assistance phenomena. The crystallographic structure of the deposited films was characterized by using Θ - 2Θ x-ray diffraction and grazing incidence x-ray diffraction measurements. In the range up to 14 percent of the oxygen to nitrogen flux ratio, a TiN f.c.c. phase structure with preferred (111) growth-orientation of the grains is observed. For higher oxygen concentrations the absence of diffraction peaks suggests a more amorphous-like structure of the deposited film. Specular x-ray reflectivity measurements provide important and accurate information about the film-air and film-substrate interface roughness. The Kiessig fringes are caused by multiple internal interference of the x-ray beam and can be observed up to 3 degrees, which is a clear indication of the high homogeneity of the film thickness and of sharp interfaces.