Structure, stress, and optical property correlations in nano-structured Mo/Si and W/B4C multilayer mirrors for hard x-ray applications

The comprehensive structure, stress, and optical property correlation of high performance x-ray multilayer (ML) mirrors based on Mo/Si and W/B4C material systems is systematically investigated for hard x-ray applications in the 10–20 keV range. All MLs are deposited by magnetron sputtering with carefully tuned periodicities and number of layer pairs to optimize for either high photon flux or high spectral resolution. Structural properties are probed using x-ray reflectivity and diffuse scattering, while residual stress and crystallite characteristics of metallic layer are analyzed by grazing incidence x-ray diffraction. The Mo/Si MLs, with relatively large periods (∼6.53 and 9.43 nm), exhibit interlayer formation and demonstrate high reflectivity up to ∼92% along with very high integrated reflectivity, making them suitable for high-flux applications. In contrast, short and ultra-short period (∼3.74 and 1.85 nm) W/B4C MLs show sharp interfaces, supporting their use in high-resolution optics with relative energy resolution down to ∼1.2%.