The dependence of structural and mechanical properties on film thickness in sol-gel zirconia films

Abstract

The structure, morphology, and mechanical properties of sol-gel zirconia films have been examined using XRD, AES depth profiling, AFM, and ultramicro indentation. There is a systematic variation in the structure and morphology of the zirconia films with increasing thickness. These changes include increases in the amount of monoclinic phase, substrate oxides, and a decrease in grain size. Ultramicro indentation measurements indicate measured hardness increases with film thickness. The highest hardness value was 6.12 GPa for a 900 nm thick film. However, these values may be influenced by the substrate oxide layer at the film/substrate interface which increases with film thickness. The modulus of the films appears to be thickness independent. As the films are made up of a number of separately fired layers, it appears that the property changes observed are also related to the number of thermal cycles experienced by the sample.