Under synchrotron radiation white beam exposure, strong mechanical stress can build up in multilayer optics, caused by the thermal mismatch between layer material and substrate material. To study the stability and performance of multilayer optics under heat load, Pd, Cr, and B₄C single layers of thicknesses in the nanometer range and [Pd/B₄C] multilayers were prepared in the sputter-depositing facility of the ESRF Multilayer Laboratory. Curvature changes versus temperature were measured using a Shack-Hartmann wave front sensor. Films coated on 200 μm thin Si wafers induced significant curvature changes over a temperature range from 60°C to 200°C. A combined parameter K including Young’s modulus and thermal expansion coefficient (CTE) was defined to describe the thermal deformation properties of the thin-film layer. The investigation shows that all three materials in thin film cause less thermal expansion than expected from material properties for bulk material in the literature. In particular, the thermal expansion of B₄C films appears to be close to that of the Si substrate.

Date Published: 5 September 2014
PDF: 12 pages
Proc. SPIE 9207, Advances in X-Ray/EUV Optics and Components IX, 920709 (5 September 2014);

Published in SPIE Proceedings Vol. 9207:
Advances in X-Ray/EUV Optics and Components IX
Christian Morawe; Ali M. Khounsary; Shunji Goto, Editor(s)