Suppression of Grain Growth in Sol–Gel‐Derived Tin Dioxide Ultrathin Films

Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO 2 (particle size 3 nm) by a spin‐coating method and subjected to calcination at different temperatures up to 800°C for 30 min. The grain size of SnO 2 was found to be far smaller than those obtained from the SnO 2 sol‐derived powder under the same calcination conditions. The suppression of grain growth of SnO 2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO 2 grain size remained as small as 6 nm after calcination at 800°C. It is suggested that the SnO 2 grains in the ultrathin film deposited on the substrate are restrained from moving and coalescing with each other, resulting in the suppression of grain growth.