The Diffusion of Sodium Ions into Tin Oxide Thin Films from Glass Substrates

Electrical resistance and X-ray photoelectron depth profile analysis are studied for antimony doped tin oxide films developed on silica, alkali-free and sodalime slide glass substrates. The sodium ions diffused from the substrates to the films prevented the crystal growth of rutile type tin oxide in the film, resulting in the high electrical resistance. A diffusion layer has been detected for each film with diffuse profiles of multi valent cations (Sn, Si or Ca) at the interface of the tin oxide film and substrate. A greater amount of sodium atoms have been detected in the film developed on the soda-lime glass while almost no sodium atoms have been found in those on the other substrates. This can be explained by the diffusion of the sodium ions in the substrate due to a drastic hydronium-sodium exchange mechanism under highly acidic conditions during the dipping and drying processes.