Dependence of cracking behavior of sol-gel films on symmetries of substrates

The cracking of sol-gel derived films on Si(100), Si(111), and glass substrates has been studied experimentally using optical microscopy, scanning electron microscopy and optical scattering method, as well as theoretically using the static method and the dynamic method. The experimental observations show that the primary cracking directions of the sol-gel derived film depend strongly on the symmetry of the substrate. As all the studied substrates have a uniform biaxial elastic modulus, the static method cannot explain such cracking behavior. However, the most probable directions of the primary cracks can be determined by considering the anisotropy of the longitudinal and the transversal elastic waves, and these directions are in good agreement with the experimental observations.