Impact of B4C co-sputtering on structure and optical performance of Cr/Sc multilayer X-ray mirrors

• Published in: Optics express Vol. 25; no. 15; pp. 18274 - 18287
• Main Authors: Ghafoor, Naureen, Eriksson, Fredrik, Aquila, Andrew, Gullikson, Eric, Schäfers, Franz, Greczynski, Grezgorz, Birch, Jens
• Format: Journal Article
• Language: English
• Published: United States Optical Society of America (OSA) 24.07.2017
• Subjects: CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; MATERIALS SCIENCE
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.25.018274

The influence of B4C incorporation during magnetron sputter deposition of Cr/Sc multilayers intended for soft X-ray reflective optics is investigated. Chemical analysis suggests formation of metal: boride and carbide bonds which stabilize an amorphous layer structure, resulting in smoother interfaces and an increased reflectivity. A near-normal incidence reflectivity of 11.7%, corresponding to a 67% increase, is achieved at λ = 3.11 nm upon adding 23 at.% (B + C). The advantage is significant for the multilayer periods larger than 1.8 nm, where amorphization results in smaller interface widths, for example, giving 36% reflectance and 99.89% degree of polarization near Brewster angle for a multilayer polarizer. The modulated ion-energy-assistance during the growth is considered vital to avoid intermixing during the interface formation even when B + C are added.