Effect of carbon and oxygen on phase transformation of titania films during annealing

Pure and carbon-doped amorphous titania films were prepared in an argon–oxygen plasma by reactive sputtering of a titanium metal target and co-sputtering of a Ti and a graphite target, respectively. The as-deposited films were subsequently annealed in vacuum and in air. The influence of the annealing atmosphere and temperature on the composition, phase transformation and crystallinity of the films was systematically studied. The results indicate that carbon incorporated in titania and an oxygen deficient environment both facilitate the formation of oxygen vacancies in titania which favors the phase transformation to rutile during annealing at low temperatures. A mechanism is proposed to explain why carbon incorporation and oxygen defects in titania favors the formation of rutile during annealing.