Phase transformation and structures of pure and carbon containing titania thin films annealed in air and in hydrogen

Pure titania (TiO2) and carbon containing titania(C-TiO2) thin films were prepared by reactive sputtering in argon–oxygen plasma at 100 °C. The as-deposited thin films were amorphous and subsequently annealed at various temperatures of 280–800 °C in air and H2 atmosphere. The effects of annealing on the films were systematically studied in terms of phase transformation, activation energy, crystallinity, oxygen vacancies and their photocatalytic properties. The as-deposited TiO2 transforms to anatase at a much lower temperature than the C-TiO2. At the same temperature, the H2-annealed films achieve better crystallinity than the air-annealed films. The activation energies of phase transformation from amorphous to anatase are 180 and 168 kJ/mol for the air- and the H2-annealed pure TiO2 films, respectively. The result also shows that the C-TiO2 requires higher temperature or more energy for phase transformation than the pure TiO2.

► Oxygen vacancies created in TiO2 annealed in H2 accelerate phase transformation.
► Carbon atoms in C-TiO2 act as a diffusion barrier and retard phase transformation.
► Activation energies from amorphous TiO2 and C-TiO2 to anatase are obtained.