Effect of the Added Polyethylene Glycol Molecular Weight and Calcination Heating Rate on the Morphology of TiO₂ Films Formed by Sol-Gel

抄録

This research investigated the changing morphology of silicon (Si)-supported titanium dioxide (TiO₂) thin films with different heating rates and molecular weights (M_W) of the added polyethylene glycol (PEG). The TiO₂ films were deposited on a Si wafer (100) by sol-gel spin coating with PEG (M_W = 6,000 or 35,000 g·mol⁻¹) as pore generating agents. Calcination at 450℃ completely decomposed all the organic residues in the TiO₂ sol, and the resultant films were in the anatase phase. The combustion nature of PEG was found to be the main factor controlling the film's morphology, where the exothermic heat of PEG combustion tended to be higher with increased heating rates and dependent on the type of PEG (extended and folded chain crystal). At heating rates of 10℃·min⁻¹ or higher, the exothermic heat led to localized grain coalescence in the TiO₂ films, which decreased the film porosity. However, this exothermic heat also simultaneously induced pore agglomeration. Hence, the average pore size of PEG-containing films were larger than in films without PEG. In contrast, the heating rate did not significantly affect the morphology films without PEG.