Structural properties and stress in ZnO films obtained from a nanocolloidal sol

This paper deals with stress analysis of ZnO films, via substrate curvature measurements. The films were prepared from a nanocolloidal sol by dip-coating and annealed from 150 to 400degreesC under pure or ozone-enriched oxygen. The chemical film evolution is followed by FT-IR spectroscopy, and the structural properties by X-ray diffraction and optical absorption spectroscopy. It is shown that the films annealed under pure oxygen are in a compressive stress state due to a stuffing effect during grain growth, whereas the films annealed under ozone-enriched oxygen are in a tensile stress state due to pore collapsing. This astonishing difference has been attributed to the skeleton, thinner in the latter than in the former films. Indeed, the acidifying action of ozone on alcohols is believed to be responsible for slowing down the grain growth during annealing.