Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics.

Area of Science:

• Materials Science
• Optics
• Surface Science

Background:

• Soft x-ray mirrors and polarizers are crucial for various scientific applications.
• Achieving high performance requires precise control over multilayer interfaces.
• Existing methods often struggle with roughness and intermixing at the atomic scale.

Purpose of the Study:

• To synthesize Cr/Sc and Ni/V multilayers for soft x-ray applications.
• To engineer atomic-scale interfaces using modulated ion assistance.
• To evaluate the performance of these multilayers as normal incidence mirrors and Brewster angle polarizers.

Main Methods:

• Magnetron sputter deposition with novel modulated low-energy, high-flux ion assistance.
• Ion energy modulation within each subnanometer layer to reduce roughness and intermixing.
• Characterization using transmission electron microscopy (TEM) and elastic recoil detection analysis (ERDA).

Main Results:

• Achieved flat and abrupt interfaces, yielding soft x-ray mirrors with reflectances of 20.7% (Cr/Sc) and 2.7% (Ni/V) at specific absorption edges.
• Optimized multilayers demonstrated high extinction ratios for Brewster angle polarizers: 5450 (Cr/Sc) and 4190 (Ni/V).
• Identified nitrogen as the major impurity (15 at.% in Cr/Sc, 9 at.% in Ni/V), impacting performance.

Conclusions:

• Modulated ion assistance is effective for engineering atomic-scale interfaces in multilayers.
• Cr/Sc and Ni/V multilayers show promise for soft x-ray optics, with potential for >31% and 5.8% reflectivity respectively.
• Improved impurity control and deposition process optimization are key for achieving theoretical performance limits.