Inexpensive tin oxide films obtained at several substrate temperatures: A High Resolution Electron Microscopy study

Abstract

Obtention of inexpensive thin films for practical uses is currently a challenge for any research group working in this field. Spray pyrolysis, electrodeposition and screen printing are some of the low-cost non vacuum deposition techniques commonly used for the above purposes In this work we present some results on tin oxide fi1ms-SnO2 - grown using the spray pyrolysis method which consists of spraying a finely atomised solution onto a suitable hot substrate. During the thermal decomposition, the chemicals in the spray solution provide the complexes that will undergo a thermallly activated reaction to yield a thin tin oxide film. Deposition was achieved in this work by keeping the substrate at 350°C, 400°C and 450°C respectively. The initial suspension had a composition of Sn Cl4 5H2O, at 0.2 molar concentration in ethyl alcohol. A solution flux of 3.2 ml/min and air flux of 4 lt/min were used in the process. A deposition rate of 20 A/sec was impinging the hot substrate and a 30 nm average thickness was obtained for the films in all the cases. At this point we recall that droplets size variations and temperature changes in the substrate will give rise to different deposition processes: for large and medium droplet sizes not all the solvent vaporise before reaching the hot surface and many defective zones are obtained. For very small droplet size the precipitated particles melt, grow and diffuse with the consequent nucleation and layer growth.