The influence of structure changes in the properties of TiCxOy decorative thin films

Abstract

The main purpose of this work consists in the preparation of titanium oxycarbide, TiCxOy, thin films, in which the presence of oxygen changed the film properties between those of titanium carbide and those of titanium oxide. Varying the oxide/carbide ratio allowed to tune the structure of the films between titanium oxide and carbide and consequently electronic, mechanical and optical properties of the films. The depositions were carried out from a TiC target by direct current, dc, reactive magnetron sputtering, varying the oxygen flow rate. The obtained results showed that the film's properties can be divided into 3 different regimes -- i) carbide, ii) a transition zone and iii) an oxide one. X-ray diffraction results revealed the occurrence of a face-centered cubic phase (TiC-type) for low oxygen content, also obtained in the TiC1.6(O) film, with a clear tendency towards amorphization with the increase of the oxygen flow rate. For the highest oxygen contents, the results revealed the development of a mixture of poorly crystallized TiO2 phases. The colour results indicated a strong dependence on the O/Ti ratio. A progressive reduction of hardness and residual stresses with the increase of the O/Ti ratio was also observed. The residual stresses, as well as the film structure, seem to play an important role on the adhesion of the coatings. The static friction coefficient revealed also some correlation with the mechanical properties, but mainly with the surface roughness.