Impedance spectroscopy studies on SnO2 films prepared by the sol-gel process

The stannic chloride was used as the starting material to prepare undoped SnO2 films. Films with different thickness were made by multiple applications of the precursor solutions using a dip coating apparatus. The as-prepared and heat treated, in air, films were analyzed using impedance spectroscopy as a function of the thickness or number of layers constituting the films. The impedance spectra of the films represented in the complex plane showed two well-defined but partially convoluted semicircles. The impedance spectra were analyzed using the brick layer model, generally employed for polycrystalline materials. X-ray diffraction, optical transmission and reflection as well as atomic force microscopy measurements were also used in the characterization of the films. The results show that the as-deposited SnO2 films are amorphous and that the annealing treatments produce their crystallization and densification. The impedance spectra provided quantitative information about the densification process, which is in agreement with the qualitative information obtained by the atomic force microscopy measurements. (C) 2003 Elsevier Science Ltd. All rights reserved.