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

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Abstract
Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (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 SnO2 was found to be far smaller than those obtained from the SnO2 sol‐derived powder under the same calcination conditions. The suppression of grain growth of SnO2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO2 grain size remained as small as 6 nm after calcination at 800°C. It is suggested that the SnO2 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.