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RESEARCH PRODUCT

Influence of the crystallization process on the photoelectrochemical behaviour of anodic TiO2 films

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On the basis of kinetic and photoelectrochemical studies we show that the formation of amorphous or strongly disordered TiO2 films on electropolished titanium rods can occur upon anodization in 0.5 M H2SO4 solution in a range of thickness which depends on the anodization rate. This finding is confirmed both by the changes in the shape of the photocurrent vs. potential curves with the energy of the incident photons, and by the impedance behaviour of the junction. Our data indicate that TiO2 films having different degree of disorder are formed depending on the anodization rate and oxide thickness. Crystalline films are formed at very low growth rates since very low thicknesses. Amorphous or strongly disordered films can be grown at high oxidation rates (≥ 100 mV/s) before the onset of a crystallization process. At higher thicknesses a gradual crystallization process takes place, as revealed both by the decrease of the anodizing current during the tensiodynamic growth and by the changes in the shape of the photocurrent vs. potential curves. The onset of the crystallization process of the film occurs at higher thicknesses with increasing the growth rate.