Solution deposition of micropatterned TiO2, ZrO2, SnO2, and In2O3 thin films through metal-loaded hydrogels

High-quality micropatterned SnO2, In2O3, ZrO2 and TiO2 thin films were prepared by a simple soft-lithographic process, based on the use of metal-loaded poly(ethylene glycol)-based hydrogels. The hydrogels liquid precursors have been embossed using polydimethylsiloxane molds, then rapidly photopolymerized and thermally degraded producing, despite the large volume contraction, crack-free and highly transparent ceramic patterns, with a thickness tunable between 40 nm and 1 μm. The films were characterized by a very fine nanostructure, presenting uniform, well-sintered and crystallized nanoparticles with a grain size in the range of 5-30 nm. The influence of both annealing temperature and heating rate on the thermal degradation of the precursor has been investigated: in the case of ZrO2 and TiO2, size-induced stabilization of tetragonal and anatase structures, respectively, was obtained and maintained also after annealing at temperatures up to 700 °C. The typical drawbacks associated to other soft-lithographic approaches (such as the limited thickness to avoid crack formation, the uncontrolled reactivity or the need for thermal solidification with the mold in place) were overcome, thanks to the intimate hybridization between the polymer and the inorganic salts, coupled with the improved reliable solidification achieved by the photopolymerization.