SnO2 thin films prepared by ion beam induced CVD:: preparation and characterization by X-ray absorption spectroscopy

Tin dioxide thin films have been prepared by ion beam induced chemical vapour deposition (IBICVD). The films, with a SnO2 stoichiometry as determined by X-ray photoelectron spectroscopy (XPS), are compact and homogeneous as revealed by SEM/TEM. Preparation was carried out on different substrates at 300 K (i.e. room temperature) and 673 K. Small differences were detected in the granular structure at these two temperatures. In the two cases the films were partially crystalline and depicted the cassiterite structure of SnO2. Small crystallographic domains between 30 and 50 Angstrom and a preferential growth of certain planes are deduced from the analysis of the X-ray diagrams. The UV-vis spectra are characterised by a oscillatory absorption behaviour typical of a transparent film with a refractive index of 1.9 deposited on a transparent substrate with a different refraction index. This is fairly close to the value of bulk SnO2. A selective deposition of the SnO2 films has been also carried out by using a mask between the accelerated ion beam used for IBICVD and the substrate. The paper also presents a structural characterisation of the SnO2 thin films and of their crystallisation behaviour by annealing at increasing temperatures. The original films were annealed in air and their structure studied by X-ray absorption spectroscopy (XAS) at different stages of the annealing treatment. XAS provides a description of the structure of the films even if they are partially or completely amorphous. The procedure involves the factor analysis (FA) of the X-ray absorption near edge structure (XANES) spectra after the different treatments and the study by Fourier transformation, fitting and FEFF simulation of the extended X-ray absorption fine structure (EXAFS) zone. The results have shown that the original films are partially amorphous and that their amorphisation degree decreases with the annealing temperature. Approximate quantification of the amorphisation degree, progression of the crystallisation upon annealing and description of the crystal domains in the original samples are some of the information obtained by the proposed method of analysis. (C) 1999 Elsevier Science S.A. All rights reserved.