The migration of alkali ions from glass substrates coated with sol-gel barrier films

Abstract The migration characteristics of alkali ions from glass substrates coated with SiO 2 or other films were studied. Soda-lime-silica glasses were coated with SiO 2 , TiO 2 , SiO 2 TiO 2 , SiO 2 ZrO 2 , SiO 2 ZrO 2 , SiO 2 B 2 O 3 and SiO 2 P 2 O 5 films using the sol-gel dipping process and then an indium-tin-oxide film (ITO film) was deposited onto the samples of rf sputtering. After heat treatment at different temperatures, the diffusion of alkali ions into the ITO film was measured by means of atomic absorption spectroscopy. The characteristics of the different films in hindering alkali ion diffusion were compared. In our experiments the SiO 2 film was very effective in hindering the migration of alkali ions from the substrate into the ITO films. An SiO 2 film which has a thickness of about 700 A reduced the concentration of sodium ions in the ITO film from 1 μg/cm 2 without barrier coating to 0.2 μg/cm 2 . The effect of the SiO 2 barrier coating was more marked when the film thickness was increased or when the substrate was treated at a higher temperature. The effect of the other kinds of film on the migration of alkali ions was dependent on the density and thickness of the film, the former being the more important.