Mechanical properties of xerogel silica films derived from stress versus temperature and cracking experiments

The biaxial modulus, coefficient of thermal expansion, and crack energy rel ease rate of sol-gel derived silica, xerogel, films are presented. Using st ress versus temperature measurements for xerogel on Si and quartz substrate s, the biaxial modulus and linear thermal expansion coefficient of the film were determined. The film thickness at the onset of cracking and the corre sponding stress were also found. For the critical thickness sample, the cra cks initiated in the xerogel film and propagated into the Si substrate. The depth of the cracks in the substrate was roughly equal to the thickness of the film. From these data, the crack energy release rate for steady state channeling in the film was estimated; it was found to be roughly five times 2 gamma(s), where gamma(s) is the reported surface energy of the film. Thi s is an indication of a plastic zone at the crack tip. (C) 2000 American In stitute of Physics. [S0021-8979(00)03209-6].