X-ray ptychography with multiple beams

QC 2025-02-27

Abstract

The future of X-ray ptychography, a coherent diffraction imaging method, promises unprecedented resolution and experimental efficiency while probing features on samples that are increasingly more complicated. This is enabled by sophisticated imaging methods, combining highly optimized hardware, software and procedure.

In this thesis, several aspects of an X-ray ptychography experiment are addressed, emphasizing the enhanced versatility and effectiveness achieved through the use of multiple beams.

Starting with a comprehensive understanding of nanofabrication, the production of focusing X-ray optics is discussed. Specifically, a direct-write lithographic process was developed and its details are described, with particular emphasis on electron-beam lithography at 50 kV acceleration voltage on chemically semi-amplified resist. This process is both versatile and precise, ultimately facilitating the fabrication of Fresnel zone plates (FZPs).

The thesis thus reports on the application of several FZPs in parallel, used to generate multiple X-ray beams to perform ptychography. In particular, novel extensions to the standard ptychographic approach are investigated.

Research on multi-beam X-ray ptychography began with closely spaced FZPs, arranged in a linear array on the same chip, emulating and advancing previous research on the topic and demonstrating the readiness of the self-made hardware for more sophisticated implementations. Most notably, the FZPs wereas close as 48 μm from one another, and up to three beams were used contemporarily, extending the imaged field of view (FOV) by a factor of three.

Next, a novel setup was introduced, promoting the concept of adaptivity within the context of multi-beam X-ray ptychography thanks to FZPs that are stacked and motorized. The possibility of moving the focusing optics in between measurements conferred a status of unprecedented versatility to said setup. The optics did not have to be redesigned for every new iteration of the experiment, sample change, or detecting conditions. It was enough to use the respective motors and adapt the setup to the new measurements. Gold nanocrystal clusters were imaged with a variety of beam spacings, enabling imaging over equally spaced regions on the sample and extending the FOV by a factor of two.

The success of this setup led to its implementation in more complicated measurements, ultimately resulting in the demonstration of simultaneous multi-beam and multi-slice ptychography—these two had never been put together before.

Two-layered samples were imaged, with a layer-to-layer separation ranging from 1400 μm down to 100 μm, with no compromise in resolution as compared to single beam ptychographic measurements.

Finally, the focusing action of FZPs was combined with reflection by curated mirrors to provide an angled perspective on samples in a novel X-ray stereo vision experiment. Here, the depth resolution on a multi-layered sample could be improved from several μm down to 300 nm, again, with no compromise on resolution as compared to single beam ptychography.

For all of these approaches to X-ray ptychography there is one major implication: samples that are larger in all three dimensions can be more readily addressed. In fact, optimized multi-beam X-ray ptychography makes use of more coherent flux from the X-ray source, distributing more photons on the sample and collecting more data across a larger field of view during the same experiment time. Furthermore, thanks to multi-slicing and stereo vision, the depth resolution aspect can be addressed simultaneously.

urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-360505