GROWTH AND STRUCTURE OF TIN DIOXIDE THIN-FILMS OBTAINED BY AN IMPROVED SPRAY PYROHYDROLYSIS TECHNIQUE

Undoped and doped tin dioxide thin films have been prepared by an improved method of spray pyrohydrolytic decomposition of SnCl4.5H2O onto a glass substrate. We show that, with this overhead hot-plate and counter flux spray, the gravitational force plays an important role in distinguishing droplets with a radius greater than 26 mum. X-ray diffraction spectra show that the structure is polycrystalline, with a grain size in the range 24-100 nm and a preferred orientation that is thickness dependent. It is shown by observations of the film microstructure by transmission electron microscopy that there is first an amorphous layer with embedded crystallites over which many crystals grow. This microstructure suggests that the films start to grow in an amorphous manner, then film growth continues with the nucleation of many small crystallites and finally some of them grow until a closely packed microstructure of crystallites is formed. Scanning electron microscopy of film surfaces indicates that surface roughness could be responsible for the large decrease in optical transmission of some films. Rutherford backscattering spectroscopy shows that film stoichiometry is close to the SnO2 phase and no significant chlorine contamination is present in the films.