Structural and mechanical properties of annealed thin films of pure and carbon doped titania.

This study investigated the annealing effects on structural and mechanical properties of pure (pure TiO 2 ) and carbon doped titania (C-TiO 2 ) thin films. The amorphous films of pure TiO 2 and C-TiO 2 were deposited on the substrates of Si wafer (100) at 100 °C by reactive magnetron sputtering. Through annealing at different temperatures, times and atmospheres, the crystallinity and defect density of the films could be varied. Under H 2 annealing, oxygen vacancies are generated in the films which facilitate the phase transformation from amorphous to anatase at a lower onset temperature than those under air annealing. The onset temperature of crystallization for C-TiO 2 is higher than that for pureTiO 2 due to the existence of carbon atoms which impairs the diffusion of Ti and O atoms for crystallization. The hardness of the films by nano-indentation test ranges from ~ 7 GPa for the amorphous to ~ 12 GPa for the crystallized films and is affected by the phase, degree of crystallinity, grain size and defect density. When the amorphous titania film fully transforms to a crystalline phase of small grains at temperatures ranging from 300 to 500 °C, its hardness will reach a maximum. However, at temperatures over 400 to 500 °C, the film hardness declines conversely with increasing temperatures or extending annealing time due to increase in grain size and change in defect density. [ABSTRACT FROM AUTHOR]