Formation of anatase and srilankite mixture as a result of the thermally induced transformation of the a-C:H:TiOx coating

Abstract The a-C:H:TiOx coating deposited by radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD) method, using methane and titanium (IV) isopropoxide mixture atmosphere, was post-deposition annealed at 400 °C in the atmosphere of air. Phase composition and coating structure were studied in detail by Raman spectroscopy, X-ray diffraction and transmission electron microscopy. Depending on the duration of the annealing process, two stages of transformation were identified. In the first stage, during the first 30 min of annealing, processes related to the degradation of a carbon matrix occurred. Characteristic bands attributed to carbon coatings disappeared in Raman spectra and hardness decreased from 10 GPa measured for the as-deposited coating to 2.7 GPa. In the second stage, after additional 10 min of annealing, the coating transformed into a crystalline TiO2 in which two polymorphs (anatase and srilankite) coexisted.