Temperature-Induced Curvature Control in X-Ray Optics

by Prof. Alex A. Volinsky, University of South Florida, USA

Friday 25 Jul 2008, 14:15 → 15:00 Europe/Berlin

Bldg. 25b, room 109

Alex A. Volinsky, Grygoriy Kravchenko, Dirk Meyer Solids tend to expand when heated. Temperature gradient along the beam thickness causes its bending in two planes perpendicular to the beam surface. This effect is observed in several systems, including X-Ray optics heated by the beam, and in laminated flooring exposed to direct Sun radiation. For example, only 25 C gradient over the 0.5 mm thick (001) Si wafer causes 10 m radius of curvature, which is comparable to the curvature required for X-Ray optics applications. While temperature gradients are unavoidable, the beam curvature could be managed by design. Thin films of dissimilar materials cause substrate curvature when heated due to the difference in thermal expansion coefficient. This results in film stress and consequent substrate curvature change, an effect utilized in thin film technology to calculate the film biaxial stress. It may be also possible to make a tunable X-Ray mirror, where the film deposited on the opposite side of the mirror will cause its curvature just due to heating, or by using additional localized heating-cooling sources. Other aspects of thin film mechanics and fracture will be discussed.