Abstract
AbstractAs a crucial material in the field of energy storage, SnO2 thin films are widely applied in daily life and have been in the focus of scientific research. Compared to the planar counterpart, mesoporous SnO2 thin films with high specific surface area possess more attractive physical and chemical properties. In the present work, a novel amphiphilic block copolymer‐assisted sol–gel chemistry is utilized for the synthesis of porous tin oxide (SnO2). Two key factors for the sol–gel stock solution preparation, the solvent category and the catalyst content, are systematically varied to tune the thin film morphologies. A calcination process is performed to remove the polymer template at 500 °C in ambient conditions. The surface morphology and the buried inner structure are probed with scanning electron microscope and grazing‐incidence small‐angle X‐ray scattering. Crystallinity is characterized by X‐ray diffraction. The multi‐dimensional characterization results suggest that cassiterite SnO2 with spherical, cylindrical, and vesicular pore structures are obtained. The variation of the film morphology is governed by the preferential affinity of the utilized solvent mixture and the hydrogen bond interaction between the employed cycloether and H2O molecules in the solution.
Highlights
Nanostructured SnO2 thin films were widely investigated during the past decades because of its wide band gap
Due to the existence of large vesicles within the thin film prepared with 200 μL hydrochloric acid, an additional large structure with center-to-center distance of (300 ± 80) nm and a radius of (22 ± 2) nm is used for modeling, which results in a calculated pore size of (256 ± 84) nm
Since the water comprised in the hydrochloric acid is a significant factor affecting the preferential affinity of the solvent to the different polymer blocks, the morphology variation of the SnO2 thin films is discussed in detail with respect to the water content in the sol–gel solution
Summary
Nanostructured SnO2 thin films were widely investigated during the past decades because of its wide band gap. In order to integrate the functional inorganic part into the micro-phase-separated block polymer network, a hydrogen bond interaction between the precursor molecules and a specific segment of the block copolymer template is expected.[48] According to previous studies, the factors that affect the microstructure of the block copolymer-templated metal oxide thin films include the reaction time,[49] the component content,[50,51,52] the surface conditions of the substrate,[53] the operational environment,[54] and the way of removing the polymer template.[55]. A morphology control of the SnO2 thin films is realized by changing two key factors in the sol–gel stock solution: the content of hydrochloric acid catalyst and the category of the organic solvent (tetrahydrofuran (THF) or 1,4-dioxane). By correlating different characterization results with the thin film preparation method, the thin film morphology evolution is understood to originate from the preferential affinity of the utilized solvent mixture and the hydrogen bond interaction between the cycloether and H2O molecules
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