Microstructural control of SnO₂ thin films by using polyethylene glycol-mixed sols

Microstructural control of SnO₂ thin films was attempted by introducing various amounts of polyethylene glycol (PEG) into an aqueous sol of SnO₂ to be spin-coated. As measured for the powder samples derived from the sols, the addition of PEG cut the specific surface area of SnO ₂ almost in half, while keeping the crystallite size almost unchanged. Pore size distribution analysis revealed that the average pore diameter was about 6 nm for the powder derived from the neat SnO₂ sol, while it was enlarged to about 20 nm by the addition of PEG1000 by 18 wt%. SEM observation of spin-coated thin films revealed that morphology changed from a dense packing of very fine particles to a more porous packing of larger particles with the addition of PEG1000 or PEG6000. The thickness of spin-coated film could be increased by increasing amount of PEG1000 or PEG6000 added. The sensor response of these films to H₂ gas increased with increasing film thickness. This tendency is considered to result because the porous structure of the film becomes better developed as the amount of PEG increases.