Structural modifications in Pd/B4C multilayers for X-ray optical applications

Sputtered Pd/B4C multilayer coatings for X-ray optical applications were investigated with respect to their long term stability. The samples were studied using X-ray reflectivity and diffraction, in-situ stress monitoring, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Low d-spacing Pd/B4C multilayers grow with excessive compressive stress and form defects. The presence of oxygen triggers boron depletion and oxidation leading to a significant reduction of the d-spacing and to considerable damage of the layered structure within a few days. Protecting cap layers can slow down the degradation process by orders of magnitude.