Multilayer Laue lens (MLL) is a new class of x-ray optics that offer great promise for achieving nanometre-level spatial resolution by focusing hard x-rays. Fabricating an MLL via thin-film deposition provides the means to achieve a linear Fresnel-zone plate structure with zone widths below 1?nm, while retaining a virtually limitless aspect ratio. Despite its similarity to the Fresnel-zone plate, MLL exhibits categorically distinctive focusing properties and their fabrication comes with a wide array of challenges. This article provides a comprehensive review of advances in MLLs, and includes extensive theoretical modelling on focusing performance, discussion on fabrication challenges, their current capabilities and notable results from x-ray focusing experiments.

https://iopscience.iop.org/article/10.1088/0022-3727/47/26/263001/pdf

Hard x-ray nanofocusing by multilayer Laue lenses

Principles and Applications of Zone Plate X-Ray Microscopes

Fresnel zone plates are the key optical elements for nanoscale focusing of X-ray beams with high spatial resolution Conventional zone plates manufactured by planar nanotechnology processes are limited by the achievable aspect ratios of their zone structures Additionally, ultra-high resolution X-ray optics with high efficiency requires three-dimensional (3-D) shaped tilted zones The combination of high spatial resolution and high diffraction efficiency is a fundamental problem in X-ray optics Based on electrodynamical simulations, we find that the optimized zone plate profile for volume diffraction is given by zone structures with radially increasing tilt angles and decreasing zone heights On-chip stacking permits the realization of such advanced 3-D profiles without significant loss of the maximum theoretical efficiency We developed triple layer on-chip stacked zone plates with an overlay accuracy of sub-2 nm which fulfills the nanofabrication requirements Efficiency measurements of on-chip stacked zone plates show significantly increased values compared to conventional zone plates

Three-dimensional structured on-chip stacked zone plates for nanoscale X-ray imaging with high efficiency

Fresnel zone plates produced by electron beam lithography and planar etching techniques provide a resolving power of about 10 nm. An alternative zone plate fabrication approach is based on alternately coating a micro-wire with two different materials. With this process, very thin zone layers with very high aspect ratios can be deposited. However, depending on the fabrication method, random zone positioning errors may introduce strong aberrations. We simulate the effect of positioning errors using different random fluctuations and study their influence on zone plate resolution. We find that random errors significantly decrease the contrast transfer of X-ray microscopes. Additionally, we derive an upper bound for the mean acceptable variance of the deposition rate.

Influence of random zone positioning errors on the resolving power of Fresnel zone plates

https://iopscience.iop.org/article/10.3367/UFNe.2016.06.037830/pdf

X-ray microscopy

Phase zone plates for multi-kilovolt X-rays with an outermost zone width of 169-30 nm and aspect ratios up to 177 were generated by a sputtered-sliced technology The generated lenses of alternating Ni80Cr20 and SiO2 consist of 188–365 layers on borosilicate glass wires and were polished by mechanical and ion processes to a thickness of 3–4 μm without carrier foil The groove efficiency was measured at the ESRF beamline ID 21 up to 38% in first order But small parts of a zone plate show an efficiency of about 10–15%

G. Schmahl

Papers

Fabrication of thick zone plates for multi-kilovolt X-rays