This work is focalized on the definition of a low-cost, low-impact, surfactant-based sol-gel route suitable to fabricate nanostructured thin films of tungsten oxide, in view of the development of electrochemical and sensing devices. Besides its low cost and ease of application to wide areas, the sol-gel process offers an effective possibility to direct the structure of the products. To gain major control over both the kinetics of crystallization and the architecture of the metal oxide networks, various templating agents (Brij^®76, Triton X-100, Tween-60 and CTAB) were added to the sols. Their effect on the final structure has been evaluated by XRD, SEM, and micro-Raman spectroscopy.

The films were deposited by spin-coating on ITO-coated glass substrates to enable future electrochemical analyses, being ITO a transparent conducting oxide. The structure-tailoring effects of surfactants were then made evident, justifying the chosen approach.

At low temperatures (100-200 °C), the presence of a medium range ordered phase (mesophase) of hybrid organic/inorganic nature is found by XRD. During the annealing, the short and medium range ordering in the oxide network at intermediate temperatures (250-300 °C), as revealed by Raman analysis, takes place even in presence of residual surfactant and before complete crystallization (XRD). Around 300-350 °C the monoclinic γ-WO₃ phase crystallizes and evolves under thermal treatment at higher temperatures. The sintering process, however, keeps memory of the organic-template-induced mesophase.

Being tungsten oxide characterized by an isotropic perovskite-related structure, in absence of specific anisotropic growth requirements, spherical particles are formed, condensing into an interconnected fractal-like network. The formation of spherical particles takes place in the initial steps of the spin-coating/evaporation process, while the random arrangement of particles appears before the complete solvent removal.

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1. Micro-Raman and XAS study of V₂O₅ and WO₃ nanostructured thin films for electrochromic applications
2. Surfactant-based synthesis and characterization of nanostructured V₂O₅ thin films