Sol-gel titanium dioxide thin films on platinum substrates: preparation and characterization

Titanium dioxide was prepared by hydrolysis and polycondensation of titanium tetraisopropoxide. TiO2 films were obtained by spin-coating platinum substrates with the precursor solution. Infrared reflection-absorption spectroscopy, Raman spectroscopy and X-ray diffractrometry showed that films prepared at 100 degreesC were amorphous, films dried at 400 and 600 degreesC were composed of anatase and those prepared at 800 degreesC were rutile. Independent of the drying temperature, field emission scanning electron microscopy of the electrode surface showed that films have a cracked morphology. Cyclic voltammetry carried out at different scan rates showed that in films dried from 100 to 600 degreesC, the mass transport occurs by a semi-infinite linear diffusion. For rutile, however, the cyclic voltammetry results were better fitted considering a linear peak current, I-p, dependence on scan rate, i.e., the mass transport can be characterized by a surface reaction where the diffusion occurs only on the electrode I film interface (thin layer diffusion). Films were also characterized by electrochemical impedance spectroscopy. For an ac frequency equal to 10,000 Hz, the flatband potentials shifted toward more positive potentials as the drying temperature increased. The S800 sample showed lower donor densities (1.2 x 10(18) cm(-3) at 10,000 Hz) compared with the other samples. The electrochemical behavior of the films was discussed in the light of structural differences. (C) 2003 Elsevier Science B.V. All rights reserved.544475