Formation and Stabilization of Mesostructured Vanadium-Oxo-Based Hybrid Thin Films

Mesostructured vanadium-oxo-based hybrid thin films have been prepared by evaporation-induced self-assembly. Anhydrous metal chlorides (VOCl<INF>3</INF> or VCl<INF>4</INF>) were used as the vanadium source, and the nonionic surfactant Brij 56 or 58 was used as the structure-directing agent in ethanol/water solutions. Mesostructured films were obtained from solutions having V(IV)/V<INF>total</INF> ratios higher than 0.7, evidencing the role of V(IV) in the formation of a curved inorganic VO<INF>x</INF><INF></INF>-based (2 ≤ x ≤ 2.15) framework. The hybrids obtained are fragile and water-sensitive, so that deposition and all of the processing leading to stabilization of the mesostructure must be performed at low relative humidity. A combination of synchrotron-SAXS and interferometry was applied to evaluate the structural evolution related to the evaporation process during dip-coating. The SAXS data clearly showed a 2D hexagonal structure (P6m space group, a = 65−80 Å) that is converted to a 2D centered rectangular (C2m space group) through preferential contraction in the direction normal to the substrate. The structure of the hybrid films is stable up to 250 °C in inert atmosphere.