Off-axis multilayer zone plate with 16†nm × 28†nm focus for high-resolution X-ray beam induced current imaging.

Using multilayer zone plates (MZPs) as two-dimensional optics, focal spot sizes of less than 10 nm can be achieved, as we show here with a focus of 8.4 nm × 9.6 nm, but the need for order-sorting apertures prohibits practical working distances. To overcome this issue, here an off-axis illumination of a circular MZP is introduced to trade off between working distance and focal spot size. By this, the working distance between order-sorting aperture and sample can be more than doubled. Exploiting a 2D focus of 16 nm × 28 nm, real-space 2D mapping of local electric fields and charge carrier recombination using X-ray beam induced current in a single InP nanowire is demonstrated. Simulations show that a dedicated off-axis MZP can reach sub-10 nm focusing combined with reasonable working distances and low background, which could be used for in operando imaging of composition, carrier collection and strain in nanostructured devices.

Planar refractive lenses made of SiC for high intensity nanofocusing.

We report on the manufacturing and testing of the first nanofocusing refractive lenses made of single-crystal silicon carbide. We introduce the fabrication process based on lithography, followed by deep isotropic etching. The lenses were characterized at the energy of 12 keV at the beamline P06 of the synchrotron radiation source PETRA III. A focal spot of 186 nm×275 nm has been achieved with a lens working distance of 29 mm.

Hard X-ray wavefront correction via refractive phase plates made by additive and subtractive fabrication techniques.

Modern subtractive and additive manufacturing techniques present new avenues for X-ray optics with complex shapes and patterns. Refractive phase plates acting as glasses for X-ray optics have been fabricated, and spherical aberration in refractive X-ray lenses made from beryllium has been successfully corrected. A diamond phase plate made by femtosecond laser ablation was found to improve the Strehl ratio of a lens stack with a numerical aperture (NA) of 0.88 × 10-3 at 8.2 keV from 0.1 to 0.7. A polymer phase plate made by additive printing achieved an increase in the Strehl ratio of a lens stack at 35 keV with NA of 0.18 × 10-3 from 0.15 to 0.89, demonstrating diffraction-limited nanofocusing at high X-ray energies.

Diamond nanofocusing refractive X-ray lenses made by planar etching technology.

The manufacturing steps and first tests of a refractive lens made of polycrystalline diamond are described. A fabrication process based on electron-beam lithography and deep reactive ion etching is introduced. Experimental tests on beamline ID13 at the ESRF have been performed. A spot size of 360 nm (FWHM) at an energy E = 24.3 keV is observed.

Refractive hard x-ray vortex phase plates.

In this Letter, we report on the creation of hard x-ray beams carrying orbital angular momentum of topological charge -ℏ and -3ℏ at a photon energy of 8.2 keV via spiral phase plates made out of fused silica by ultrashort-pulsed laser ablation. The phase plates feature a smooth phase ramp with a 0.5 µm nominal step height and a surface roughness of 0.5 µm. The measured vortex beams show submicrometer-sized donut rings and agree well with numerical modeling. Fused silica phase plates are potentially suited to manipulate the electromagnetic field in highly intense x-ray beams at x-ray free-electron laser sources.

30-Lens interferometer for high-energy X-rays.

A novel high-energy multi-lens interferometer consisting of 30 arrays of planar compound refractive lenses is reported. Under coherent illumination each lens array creates a diffraction-limited secondary source. Overlapping such coherent beams produces an interference pattern demonstrating strong longitudinal functional dependence. The proposed multi-lens interferometer was tested experimentally at the 100 m-long ID11 ESRF beamline in the X-ray energy range from 30 to 65 keV. The interference pattern generated by the interferometer was recorded at fundamental and fractional Talbot distances. An effective source size (FWHM) of the order of 15 µm was determined from the first Talbot image, proving the concept that the multi-lens interferometer can be used as a high-resolution tool for beam diagnostics.

Lens coupled tunable Young's double pinhole system for hard X-ray spatial coherence characterization.

We have implemented a modified Young's double slit experiment using pinholes with tunable separation distance coupled with compound refractive lens for hard X-ray spatial coherence characterization. Varying distance between the apertures provides a high sensitivity to the determination of spatial coherence across a wide range of experimental parameters. The use of refractive lenses as a Fourier transformer ensures far field registration conditions and allows the realization of a very compact experimental setup in comparison with the classical Young technique and its derivatives. The tunable double aperture interferometer was experimentally tested at the ESRF ID06 beamline in the energy range from 8 to 25 keV. The spatial coherence and the source size were measured by evaluating the visibility of the interference fringes at various separation distances between the apertures and this value agrees very well with the data obtained by other techniques. The proposed scheme can be used for comprehensive characterization of the coherence properties of the source on low emittance synchrotrons in the hard X-ray region.

X-Ray Multibeam Ptychography at up to 20 keV: Nano-Lithography Enhances X-Ray Nano-Imaging.

Hard X-rays are needed for non-destructive nano-imaging of solid matter. Synchrotron radiation facilities (SRF) provide the highest-quality images with single-digit nm resolution using advanced techniques such as X-ray ptychography. However, the resolution or field of view is ultimately constrained by the available coherent flux. To address this, the beam's incoherent fraction can be exploited using multiple parallel beams in an X-ray multibeam ptychography (MBP) approach. This expands the domain of X-ray ptychography to larger samples or more rapid measurements. Both qualities favor the study of complex composite or functional samples, such as catalysts, energy materials, or electronic devices. The challenge of performing ptychography at high energy and with many parallel beams must be overcome to extract the full advantages for extended samples while minimizing beam attenuation. Here, that challenge is overcome by creating a lens array using cutting-edge laser printing technology and applying it to perform scanning with MBP with up to 12 beams and at photon energies of 13 and 20 keV. This exceeds the measurement limits of conventional hard X-ray ptychography without compromising image quality for various samples: Siemens star test pattern, Ni/Al2O3 catalyst, microchip, and gold nano-crystal clusters.

Multimodal imaging of cubic Cu2O@Au nanocage formation via galvanic replacement using X-ray ptychography and nano diffraction.

Being able to observe the formation of multi-material nanostructures in situ, simultaneously from a morphological and crystallographic perspective, is a challenging task. Yet, this is essential for the fabrication of nanomaterials with well-controlled composition exposing the most active crystallographic surfaces, as required for highly active catalysts in energy applications. To demonstrate how X-ray ptychography can be combined with scanning nanoprobe diffraction to realize multimodal imaging, we study growing Cu2O nanocubes and their transformation into Au nanocages. During the growth of nanocubes at a temperature of 138 °C, we measure the crystal structure of an individual nanoparticle and determine the presence of (100) crystallographic facets at its surface. We subsequently visualize the transformation of Cu2O into Au nanocages by galvanic replacement. The nanocubes interior homogeneously dissolves while smaller Au particles grow on their surface and later coalesce to form porous nanocages. We finally determine the amount of radiation damage making use of the quantitative phase images. We find that both the total surface dose as well as the dose rate imparted by the X-ray beam trigger additional deposition of Au onto the nanocages. Our multimodal approach can benefit in-solution imaging of multi-material nanostructures in many related fields.

Multi-beam X-ray ptychography using coded probes for rapid non-destructive high resolution imaging of extended samples.

Imaging large areas of a sample non-destructively and with high resolution is of great interest for both science and industry. For scanning coherent X-ray diffraction microscopy, i. e., ptychography, the achievable scan area at a given spatial resolution is limited by the coherent photon flux of modern X-ray sources. Multibeam X-ray ptychography can improve the scanning speed by scanning the sample with several parallel mutually incoherent beams, e. g., generated by illuminating multiple focusing optics in parallel by a partially coherent beam. The main difficulty with this scheme is the robust separation of the superimposed signals from the different beams, especially when the beams and the illuminated sample areas are quite similar. We overcome this difficulty by encoding each of the probing beams with its own X-ray phase plate. This helps the algorithm to robustly reconstruct the multibeam data. We compare the coded multibeam scans to uncoded multibeam and single beam scans, demonstrating the enhanced performance on a microchip sample with regular and repeating structures.

Evolution of Hierarchically Porous Nickel Alumina Catalysts Studied by X-Ray Ptychography.

The synthesis of hierarchically porous materials usually requires complex experimental procedures, often based around extensive trial and error approaches. One common synthesis strategy is the sol-gel method, although the relation between synthesis parameters, material structure and function has not been widely explored. Here, in situ 2D hard X-ray ptychography (XRP) and 3D ptychographic X-ray computed tomography (PXCT) are applied to monitor the development of hierarchical porosity in Ni/Al2 O3 and Al2 O3 catalysts with connected meso- and macropore networks. In situ XRP allows to follow textural changes of a dried gel Ni/Al2 O3 sample as a function of temperature during calcination, activation and CO2 methanation reaction. Complementary PXCT studies on dried gel particles of Ni/Al2 O3 and Al2 O3 provide quantitative information on pore structure, size distribution, and shape with 3D spatial resolution approaching 50 nm, while identical particles are imaged ex situ before and after calcination. The X-ray imaging results are correlated with N2 -sorption, Hg porosimetry and He pycnometry pore characterization. Hard X-ray nanotomography is highlighted to derive fine structural details including tortuosity, branching nodes, and closed pores, which are relevant in understanding transport phenomena during chemical reactions. XRP and PXCT are enabling technologies to understand complex synthesis pathways of porous materials.

PtyNAMi: ptychographic nano-analytical microscope.

Ptychographic X-ray imaging at the highest spatial resolution requires an optimal experimental environment, providing a high coherent flux, excellent mechanical stability and a low background in the measured data. This requires, for example, a stable performance of all optical components along the entire beam path, high temperature stability, a robust sample and optics tracking system, and a scatter-free environment. This contribution summarizes the efforts along these lines to transform the nanoprobe station on beamline P06 (PETRA III) into the ptychographic nano-analytical microscope (PtyNAMi).