Effect of thermo-physical properties of Zn precursors on ZnO thin films grown by ultrasonic spray

In the present work we have investigated temperature and precursor solution concentration influences on the density, viscosity and surface tension of zinc aqueous solutions. Three zinc salt solution sources, namely acetate, nitrate and chloride, have been investigated. The study was carried out at different concentrations ranged from 0.02 to 0.20 mol/l and solution temperatures varied from 20 to 60 °C. The measurements results show, for the whole studied salt sources, a linear increase in density, surface tension and viscosity with salt concentration. While an inverse behavior of these properties is observed with increasing solution temperature. Zinc acetate has the lower surface tension and viscosity, while zinc chloride has the largest ones. Droplets Weber, Reynolds numbers and surface enthalpy formation have been estimated from solution properties measurements. Ultimately a correlation between the used salts, concentrations and the obtained ZnO thin films morphologies and structures is addressed. Solution viscosity and surface tension are key parameters controlling the films growth and morphology. At fixed substrate temperature, films with smooth surface can be produced by reducing the surface tension and the viscosity of the starting solution.