Etude de l’influence d’un spray pyrolytique sur les caracteristiques de couches minces de ZnO

Abstract

This work of thesis aims to study the dynamics and thermal properties of ultrasonic spray pyrolysis technique (USP) applied in the field of zinc oxides thin films deposition (ZnO). It covers the principal stages of spray method: (i) starting precursor solution, (ii) intermediate phase of transport and evaporation of droplets, (iii) the thin film formation and its characterizations. The investigation covers three different chemical sources of Zinc (acetate, nitrate and chloride). In the first part of work, we studied experimentally, the influences of the zinc precursor natural, the concentration of salt and the temperature on the thermophysical properties, namely density, viscosity and surface tension. The measurements showed, for all the solutions, a linear increasing of all the properties with the concentration and a reverse behavior with the temperature. Zinc acetate has been characterized compared to other sources of salts, with significant values of two Reynolds and Weber numbers with a low enthalpy of formation. In the second part, we modeled the transport and evaporation of a typical droplet of each zinc solution under conventional deposit conditions. Similar trends in the evaporation of droplets formed from different salts with different times and distances were obtained. The evaporation of droplet based on zinc nitrate is important. The presence of solvent in the droplet made delay the crust formation. The hottest medium accelerates the evaporation rate and reduces the displacement distance of the droplet to transforming to powder. In the last part, ZnO thin films were elaborated by varying the same experimental parameters. Films with a smooth surface can be produced by reducing the viscosity and the surface tension of the starting solution. The film prepared by using zinc acetate has an aspect continuous and smooth, where, the impact of the droplets is broader with 50 µm compared to the zinc nitrate and chloride which was equalizes to 32 and 25 μm respectively. An aspect continuous and smooth of the thin film morphology is obtained by using the 0.05mol/l of concentration and 300°C and 350°C of temperatures.