Nanostructured ZnO Thin Films for Sensor Applications

Fabrication of sensitive and selective ZnO thin film gas sensors depends on the ability to control the composition and microstructure of the film. In this work, ZnO thin films were prepared by the sol-gel process using a Zn(CH3COO)2 2H2O precursor in a solution of isopropanol and ethanolamine. Transparent and stable films, ~25-250 nm in thickness, were deposited by spin-coating precursor solutions onto glass substrates, followed by heat treatment at temperatures through 500oC. For comparison, bulk ZnO xerogel powders were made by evaporation of the solvent from the sol-gel. Microstructure and composition were studied by X-ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Scanning electron microcopy (SEM) was used to examine the surface morphology of the films. Both precursor concentration and heat-treatment conditions were found to strongly affect the crystallographic orientation and morphology of the ZnO films.