Mathematical modeling methods were used to estimate the stress response of oxide coatings to wet cleaning at elevated temperature. Results indicate that substrate thickness strongly affects the thermal stress response of the thin film material. An oxide coating on a thin substrate generally exhibits either tensile or compressive stresses during elevated temperature processing, depending on the mismatch in coefficient of thermal expansion between substrate and coating. In the case of a thick substrate, however, the thin film coating is likely to exhibit both compressive and tensile stresses during its processing history. These results suggest that special consideration be paid to geometry in the selection of small-scale witness/test material to model the response of large optics to thermal processing.
© 2012 OSAPDF Article