High-reflectance magnetron-sputtered scandium-based x-ray multilayer mirrors for the water window

Area of Science:

• Materials Science
• Optics
• X-ray Physics

Background:

• Multilayer mirrors are crucial for applications requiring high reflectivity in specific wavelength ranges, such as the water window (284-500 eV).
• Scandium-based multilayers offer promising properties for soft X-ray optics, but their performance is sensitive to interface quality and material stability.

Purpose of the Study:

• To experimentally compare the performance of various Sc-based short-period multilayer mirrors.
• To identify optimal material combinations and deposition strategies for enhanced reflectance in the water window domain.
• To propose a new multilayer structure with potential for significantly higher reflectance.

Main Methods:

• Fabrication of multilayer samples with period thickness between 1.5-1.7 nm using magnetron sputtering.
• Characterization via X-ray reflectometry (XRR) using a Cu-Kα source.
• Synchrotron radiation-based XRR near the Sc-L2,3 edge for detailed analysis of multilayer structures.

Main Results:

• Experimental comparison of Cr/Sc with B4C barrier layers and CrNx/Sc multilayer mirrors.
• Achieved a near normal incidence reflectance of 23% at 397 eV using optimized CrNx/Sc mirrors with B4C barrier layers.
• Demonstrated that combining Cr layer nitridation and B4C barrier layers significantly improves mirror performance.

Conclusions:

• Nitridation of Cr layers and incorporation of B4C barrier layers are effective strategies for enhancing Sc-based multilayer mirrors.
• The developed CrNx/B4C/Sc multilayer mirrors show high potential for applications in the water window.
• A simulation model predicts that CrNx/B4C/Sc mirrors could achieve reflectance exceeding 32%, highlighting future design possibilities.