Synthesis of mesostructured thin films by ionic wind assisted electrostatic spray deposition

Thin films produced by electrostatic spray deposition (ESD) have nanometer-sized structures despite the initial sprayed droplets being typically a few tens of microns in diameter. The size and morphology of the resulting structures is not only affected by the solvent properties and drying kinetics, but also by Coulomb fission owing to the high surface charge density that the droplets build up upon evaporation. In this work we modulate the charge density of the droplets by inducing ionic wind along the spray, and produce mesoscopic structures. Using WO₃ as an example, we show that the technique provides a practical way to control the morphology of thin films produced by ESD.