Multilayer on-chip stacked Fresnel zone plates: Hard x-ray fabrication and soft x-ray simulations

TLDR: In this article, a two-step writing process was used to produce 50nm finest zone width at a zone thickness of 1.14μm for possible hard x-ray applications, and simulations were carried out using a multislice propagation method employing Hankel transforms.

Abstract: Fresnel zone plates are widely used as x-ray nanofocusing optics. To achieve high spatial resolution combined with good focusing efficiency, high aspect ratio nanolithography is required, and one way to achieve that is through multiple e-beam lithography writing steps to achieve on-chip stacking. A two-step writing process producing 50 nm finest zone width at a zone thickness of 1.14 μm for possible hard x-ray applications is shown here. The authors also consider in simulations the case of soft x-ray focusing where the zone thickness might exceed the depth of focus. In this case, the authors compare on-chip stacking with, and without, adjustment of zone positions and show that the offset zones lead to improved focusing efficiency. The simulations were carried out using a multislice propagation method employing Hankel transforms.