Symposium CT03—Imaging Materials with X-Rays—Recent Advances with Synchrotron and Laboratory Sources

In order to develop shear-based solid phase processing methods, we aim to better understand the fundamental atomic scale mechanisms of mass and energy transfer in materials under shear deformation. To achieve this aim, we developed a first of its kind synchrotron-based in situ high-energy x-ray diffraction capability using a high-speed rotational diamond anvil cell (HSRDAC). HSRDAC provided time resolved synchrotron-based XRD results on lattice strain evolution and change in spatial variation of shear deformation induced alloying in Cu-Ni alloys. These in situ results were correlated with detailed microstructural characterization before and after shear deformation using transmission electron microscopy and atom probe tomography. This HSRDAC capability can provide new insights into the unique role of shear deformation in formation of metastable states, as well as in modifying the phase transformation pathways in a wide variety of alloy systems.

Understanding structural changes in the atomic scale during the catalytic reaction process is crucial for revealing underlying mechanisms. However, it remains challenging to characterize the strain and defect evolution for a single nanocrystal catalyst in situ. Bragg coherent diffraction imaging (BCDI) is a powerful tool for investigating structural changes inside the nanoparticle in-situ in a non-destructive way. In my talk, I show how the atomic level of interaction of reactants affects the nanoparticles as strain-induced and the defect dynamics during the catalytic process by exploiting the merits of BCDI.
This work was supported by the National Research Foundation of Korea (NRF-2015R1A5A1009962 and NRF-2019R1A6B2A02100883) and Samsung Electronics..

Characterising the structural properties (strain gradients, chemical composition, crystal orientation and defects) inside nanostructures is a grand challenge in materials science. Bragg coherent diffraction imaging (Bragg CDI) can be utilised to address this challenge for crystalline nanostructures. A resolution of the structural properties of less than 10 nm is achieved up-to-date [1,2]. The capabilities of the Bragg CDI technique will be demonstrated on single nanoparticles for enhanced catalysis.

As an example, the Bragg CDI technique [3,4] allows understanding the interplay between shape, size, strain, faceting [5], composition and defects at the nanoscale. We will demonstrate that Bragg CDI on a single particle model catalyst makes it possible to map its local strain/defect field and directly image strain build-up close to the facets. We will also show results obtained during in situ [6,7] and operando Bragg CDI measurements: it was possible to track a single particle in gas or liquid phase environments to monitor its facet changes and to measure its strain/defect response to reaction.

This technique opens pathways to determine and control the internal structure of nanoparticles to tune and optimise them during catalytic and other chemical reactions. This technique should benefit from a unique opportunity: the ESRF EBS Upgrade. This should revolutionise imaging by making it possible to map evolving physico-chemical processes in a slow-motion movie.


[1] S. Labat, M.-I. Richard, M. Dupraz, M. Gailhanou, G. Beutier, M. Verdier, F. Mastropietro, T. W. Cornelius, T. U. Schülli, J. Eymery, and O. Thomas, Inversion Domain Boundaries in GaN Wires Revealed by Coherent Bragg Imaging, ACS Nano 9, 9210 (2015).
[2] N. Li, S. Labat, S. J. Leake, M. Dupraz, J. Carnis, T. W. Cornelius, G. Beutier, M. Verdier, V. Favre-Nicolin, T. U. Schülli, O. Thomas, J. Eymery, and M.-I. Richard, Mapping Inversion Domain Boundaries along Single GaN Wires with Bragg Coherent X-Ray Imaging, ACS Nano 14, 10305 (2020).
[3] J. Carnis, L. Gao, S. Labat, Y. Y. Kim, J. P. Hofmann, S. J. Leake, T. U. Schülli, E. J. M. Hensen, O. Thomas, and M.-I. Richard, Towards a Quantitative Determination of Strain in Bragg Coherent X-Ray Diffraction Imaging: Artefacts and Sign Convention in Reconstructions, Sci Rep 9, 1 (2019).
[4] N. Li, M. Dupraz, L. Wu, S. J. Leake, A. Resta, J. Carnis, S. Labat, E. Almog, E. Rabkin, V. Favre-Nicolin, F.-E. Picca, F. Berenguer, R. van de Poll, J. P. Hofmann, A. Vlad, O. Thomas, Y. Garreau, A. Coati, and M.-I. Richard, Continuous Scanning for Bragg Coherent X-Ray Imaging, Sci Rep 10, 12760 (2020).
[5] M.-I. Richard, S. Fernández, J. Eymery, J. P. Hofmann, L. Gao, J. Carnis, S. Labat, V. Favre-Nicolin, E. J. M. Hensen, O. Thomas, T. U. Schülli, and S. J. Leake, Crystallographic Orientation of Facets and Planar Defects in Functional Nanostructures Elucidated by Nano-Focused Coherent Diffractive X-Ray Imaging, Nanoscale 10, 4833 (2018).
[6] M.-I. Richard, S. Fernández, J. P. Hofmann, L. Gao, G. A. Chahine, S. J. Leake, H. Djazouli, Y. De Bortoli, L. Petit, P. Boesecke, S. Labat, E. J. M. Hensen, O. Thomas, and T. Schülli, Reactor for Nano-Focused x-Ray Diffraction and Imaging under Catalytic in Situ Conditions, Review of Scientific Instruments 88, 093902 (2017).
[7] S. Fernández, L. Gao, J. P. Hofmann, J. Carnis, S. Labat, G. A. Chahine, A. J. F. van Hoof, M. W. G. M. (Tiny) Verhoeven, T. U. Schülli, E. J. M. Hensen, O. Thomas, and M.-I. Richard, In Situ Structural Evolution of Single Particle Model Catalysts under Ambient Pressure Reaction Conditions, Nanoscale 11, 331 (2019).

Halide perovskites attract significant interest due to their remarkable performance in solar cells. However, the gap in understanding of the relationship between their nanoscale structure and properties limits their application towards novel devices. Here we present a direct 3D imaging of twinned ferroelastic domains in single 500-nm CsPbBr₃ particles using Bragg Coherent X-ray Diffractive Imaging (BCDI) at sub-60 nm resolution. A preferential double-domain structure is revealed in several identical particles, with one (110)-oriented and one (002)-oriented domain and a similar domain volume ratio of 1:2.5. The domains exhibit a difference in lattice tilt of 0.59 degrees, in excellent agreement with calculations based on the lattice mismatch. The results in this work provide important insights both for the fundamental understanding of these materials and for the performance improvement of perovskite-based devices.

Measurement of Bragg coherent diffraction imaging (BCDI) data relies on finding a Bragg diffraction signal from a single nanoscale crystal object. Often the object of interest can have unknown orientation in the sample or be one of many crystallites in a polycrystalline sample. In addition, even when a single Bragg reflection is found, the full crystallographic orientation remains unknown, and thus finding other Bragg reflections from the identical crystal becomes time-consuming or impossible.
In this talk, the commissioning of a movable double-bounce Si (111) monochromator at the 34-ID-C end station of the Advanced Photon Source will be described. The resulting capability aims at delivering multi-reflection BCDI as a standard tool in a single beamline instrument. The upgraded instrument enables, through rapid switching from monochromatic to broadband (pink) beam, the use of Laue diffraction to determine crystal orientation. With a proper orientation matrix determined for the lattice of a specific crystal, one can measure coherent diffraction patterns near multiple Bragg reflections, thus providing enough information to image the full strain tensor in 3D at the nanoscale. The design, concept of operation, the developed procedures for indexing Laue patterns, as well as automated measurement of Bragg coherent diffraction data from multiple reflections of the same nanocrystal will be presented. In addition, recent advances in identifying single grains of interest in a polycrystalline sample will be described.

Ptychography, a powerful scanning coherent diffractive imaging technique, has attracted significant attention for its general applicability. Here we experimentally demonstrate x-ray linear dichroic ptychography for the first time and map the c-axis orientations of the aragonite (CaCO₃) crystal. Linear dichroic phase imaging at the oxygen K-edge energy shows strong polarization-dependent contrast and reveals the presence of both narrow (<35°) and wide (>35°) c-axis angular spread in the coral samples. These x-ray ptychography results are corroborated by 4D scanning transmission electron microscopy (STEM) on the same samples. Evidence of co-oriented but disconnected corallite sub-domains indicates jagged crystal boundaries consistent with formation by amorphous nanoparticle attachment. We expect that the combination of x-ray linear dichroic ptychography and 4D STEM could be an important multimodal tool to study nano-crystallites, interfaces, nucleation and mineral growth of optically anisotropic materials at multiple length scales.

Understanding the structure and dynamics of spin textures in magnetic materials on the scale of the magnetic exchange interaction is both a question of fundamental physics and at the forefront of developing quantum technologies. Topologically stabilized magnetic textures such as skyrmions and the direct light-induced manipulation of spins hold promise for spintronics, low-energy data transport, and memory. However, because of their small size and low contrast, intricate nanoscale magnetic textures have proven difficult to image directly in 3D without prior knowledge of the sample.

Correlative multi-modal spectro-microscopy using complementary nanoscale imaging techniques and extreme ultraviolet and x-ray spectroscopies at both tabletop and facility scale provides access to a more complete range of elemental, chemical, electronic, magnetic, and structural and dynamic properties of complex samples. Resonant x-ray magnetic circular dichroism (XMCD) provides element-specific magnetic sensitivity; ptychography yields diffraction-limited images with phase contrast, ideal for low-contrast materials; time-resolved extreme UV (EUV) spectroscopies can capture new light-induced spin excitations; and x-ray reflectometry can image buried layers with sub-nm depth resolution. By combining these techniques, we are able to uncover new materials function and comprehensively characterize complex nanostructured, layered, and heterogeneous samples.

X-ray Absorption Spectroscopy (XAS) is among the techniques widely employed to characterize materials providing atomic selective information on the materials structure and chemical speciation. Since the advent of 3^rd generation synchrotron radiation facilities, a high photon flux is achieved at XAS beamlines which permits fast measurements and thus time-resolved monitoring of evolutionary processes. A wide range of materials science topics has taken advantage of this breakthrough (e.g. catalysis, energy storage, materials synthesis) through in situ and operando approaches. In order to access to a deeper and more accurate temporal description of the processes, multivariate data analysis is now commonly employed and provides spectra of the pure chemical species together with their concentration profiles.
Nevertheless, time-resolved XAS data are generally collected as macroscopic information related to the fraction of sample exposed to X-rays. At specialized beamlines, spatial resolution can be achieved using micro- or nano-focused beam while scanning the sample but with increased collection times. Alternatively, full-field sample illumination collected by a 2D detector can provide both spatial and time resolutions. Recent developments have been conducted at the ROCK beamline of SOLEIL synchrotron to allow time-resolved hyperspectral full-field X-ray imaging with XAS information.
ROCK is a XAS beamline tailored for in situ and operando investigations in the 4 to 40 keV energy range using Quick-EXAFS monochromators to achieve sub-second time resolution for macroscopic measurements. Hyperspectral full-field X-ray imaging experiments are operated at the beamline in transmission by collecting the visible light emitted from a thin scintillator imaging the sample absorption by a pixelated detector (ORCA Flash 4.0 V3 CMOS camera, Hamamatsu). Depending on the objective mounted on the camera, the pixel size and field of view (FoV) range from 0.65 µm to 1.625 µm and 1.3 mm to 3.3 mm, respectively, with a resolution of ca. 5 µm. Images at different energies of the XAS spectrum (typically ∼ 600 images) are collected with an exposure time of 5 ms during the Quick-EXAFS monochromator energy scan yielding to one complete hyperspectral dataset every 10 s. XAS spectra can then be reconstructed on individual or binned pixels to improve the signal-to-noise (S/N) ratio when necessary. A specificity of ROCK is its versatile beam size from 0.4 to ∼ 4 mm while keeping constant the flux delivered by the optics. Thus the beam size on the sample can be optimized considering the nature and size of the sample, the FoV and the S/N ratio of reconstructed spectra.
Selected examples of studies using the methodology implemented at ROCK beamline will be presented in the field of pressure-induced spin transition, regeneration of heterogeneous catalysis, and cycling of Li-ion batteries. These examples illustrate the great potential of time-resolved XAS hyperspectral imaging and the gain obtained in comparison with macroscopic information for identifying potential dynamic heterogeneous behavior of materials.

Acknowledgment: The ROCK beamline construction and operation (2011-2019) were supported by a public grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” program (ref: ANR-10-EQPX-45).

Global concerns over the consistent consumption of finite fossil fuel stores have called for a transition to renewable energy sources. A significant stepping stone in completing this movement relies on the safety and reliability of energy storage technologies. Revolutionizing the industry John Goodenough, Stan Wittingham, and Akira Yoshinos were all critical of the development in current Lithium-Ion battery energy storage. However, their efforts are not without need of improvements. Sub-optimal reliability is caused by prevalent capacity fade at moderate working potentials. For global adoption in heavy uses cases (EV, power grid storage, etc.) this must be remedied. Degradation of the cathode material is narrowed down to three main categories; structural/chemical strain, electrolyte decomposition, and increase of surface-electrolyte interfaces. Narrowing these options, my focus is on cathode material strain characterization, both structural and chemical, at the nano-scale through the use of multiple techniques.

Well characterized, relevant LiNi0.33Mn0.33Co0.33O2 (LiNMC) material was chosen as an agent for nano-characterization. Ptychographic analysis methods with a resolution of 5 nm has been implemented in mapping transition metal oxidation states of a single particle for various states of charge. Further, lattice strain analysis has been carried out through the application of Scanning X-Ray Diffraction Microscopy. With a resolution of 30 nm, spatially resolving crystallographic spacing's for Pristine, Charged (to 4.75V), Discharged (to 2.7V) material was achieved. It was determined most point defect upon cycling effect primarily the chi regime of the diffraction patterns. Heterogeneities in both regards have given insight into degradation pathways for the LiNMC material.

The diffusion of chemicals and inorganic ions through wood cell walls is a critical process in nearly all woody biomass applications, including biorefineries, wood-based building materials, green electronics, and even as bioinspiration for new smart materials. Despite the near ubiquitous importance of intra-cell wall diffusion, the poorly understood diffusion mechanisms and rates are hindering progress. In this work, a new experimental methodology utilizing synchrotron-based X-ray fluorescence microscopy (XFM) was developed to study inorganic ion diffusion at submicron length scales in individual wood cell wall layers. Using a custom-built in situ relative humidity (RH) chamber, it was discovered that deposited K, Cu, Zn, and Cl ions only diffuse when the humidity is above 60% RH. Additionally, time-lapse XFM imaging was used to measure the time-dependent concentration profiles of implanted K, Cu, and Cl ions diffusing through cell wall layers. Time-lapse XFM imaging was performed at 70, 75, or 80% RH. Diffusion constants were calculated from the time-dependent concentration profiles using an analytical model developed based on Fick’s second law for diffusion. Results revealed that diffusion rates increased with RH, the larger Cu ion diffused slower than the K ion, and the Cl ion diffusion constant was the same as the counter cation, indicating ions diffused together to maintain charge neutrality. The results also improve the understanding of the diffusion mechanisms. It is now understood that diffusion occurs via interconnecting pathways of rubbery amorphous polysaccharides, which contrasts the nearly century-old assumption of intra-cell wall transport occurring through interconnecting water pathways. With these new insights, researchers can now utilize polymer science approaches to engineer the molecular architecture of lignocellulosic biomass to optimize properties for specific end uses.

The development and integration of next-generation nano and quantum devices is approaching a significant metrology hurdle. This is because nanoscale functional properties are no longer well-described by macroscopic models and can become almost entirely geometry- or interface-dominated. Moreover, the transport across interfaces (i.e. charge, spin and heat transport) impact various device properties, such as the switching energy of magnetic memory or the coherence time of quantum devices. This transport is difficult to measure and its in-situ measurement in working devices will be critical to further understanding and optimizing their synthesis and integration. Thus, there is a great need for non-destructive, non-contact imaging techniques applicable to general samples.
There exist many techniques for nano-characterization; however, most are destructive to the sample or insensitive to depth or composition. Milling techniques like secondary-ion mass spectroscopy (SIMS) and auger electron spectroscopy (AES) can determine the chemical composition through the sample’s depth, but have a spatial resolution limited by the spot size of the milling beam, and destroy the sample in order to measure it. On the other hand, techniques based on transmission electron microscope (TEM) — such as energy-dispersive x-ray spectroscopy (EDS) or high-angle annular dark-field imaging (HAADF) — can measure composition or structure with atomic resolution, but require the sample to be extremely thin, and often require complex and destructive sample preparation (e.g. FIB-excavation). Non-destructive techniques like atomic-force microscopy (AFM) and scanning-electron microscopy (SEM) can do high-resolution imaging, but lack quantitative depth- or chemical-sensitivity.
Photon-based techniques such as x-ray reflectivity (XRR) and x-ray diffraction (XRD) perform non-destructive measurements that are sensitive to composition, layer thicknesses, and interface quality by measuring the reflectivity as a function of incidence angle (aka reflectometry). However, since XRR and XRD use hard x-rays, they must operate within 1deg of grazing-incidence to get sufficient reflectivity, and the resulting on-sample focus size limits their resolution to >1μm.
Extreme ultraviolet light (EUV, wavelength ~10-100nm) has many unique advantages for sample characterization. Many absorption edges lie in this region of the spectrum, providing excellent composition-sensitivity. Unlike x-rays, EUV absorption depths are 10nm-1μm, enhancing the depth-sensitivity of reflectometry. This work combines EUV reflectometry with ptychographic coherent diffractive imaging (CDI) to demonstrate a unique non-destructive microscopy whose resolution approaches the diffraction limit. Furthermore, the quantitative phase information also given by ptychography, which traditional XRR cannot measure, is extremely sensitive to the sample’s composition and structure.
We use this technique to investigate a sample fabricated by imec. The sample consists of Si₃N₄ structures on an As-doped Si substrate (5x10²⁰ atoms/cm³). We investigated our technique’s sensitivity to composition, layer thickness, interface quality and dopant level and found, for several, it approached or exceeded other techniques, while remaining non-destructive and high-resolution.
This work demonstrates a general nanoimaging technique that promises to fill a current gap in sample metrology. Our technique combines the unique advantages of coherent EUV light with the composition- and interface sensitivity of XRR and XRD and the resolution-enhancement and quantitative phase information of ptychography. This technique enables non-destructive, large-area, quantitative, 3D imaging of nanostructures and their chemical makeup, layer thicknesses, interface quality and dopant levels, without special sample preparation.
This work was financially supported by NSF STROBE STC (DMR-1548924); DARPA STTR (W31P4Q-17-C-0104); DARPA PULSE (W31P4Q-13-1-0015).

Liquid-Liquid extraction can be a complex chemical purification process involving many thermodynamic and kinetic parameters. For instance, the recycling industry has an incoming waste stream with high variability. Thus, they need to constantly adjust their processes to match the variation in chemical composition. There is a need for fast process development tools to study liquid-liquid extraction. In this regard, downscaling an extraction system in microfluidics can be more accurate, faster and safer due to fluids being more stable and controlled.
We report on newly developed microfluidic devices integrated with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray fluorescence (XRF) [1, 2]. These tools are primarily aimed at studying liquid/liquid extraction processes. First, using FTIR characterization of the vapor pressure, we study the chemical activity of the solvents [3]. Second, we perform, for the first time, on-line XRF quantification of metals to monitor liquid-liquid extraction in microfluidics[4]. The measurement is automated and performed for both aqueous and organic phase. This approach allowed us to quickly study the variation of free energies of transfer for the extraction and reverse-extraction of three rare-earth elements at different temperatures. Overall, thanks to a fully automated approach, we show that thermodynamics and kinetics of extraction can be obtained in less than 12 hours with a resulting liquid waste of less than 20mL.

1. Maurice, A., J. Theisen, and J.-C.P. Gabriel, Microfluidic lab-on-chip advances for liquid–liquid extraction process studies. Current Opinion in Colloid & Interface Science, 2020. 46: p. 20-35.

2. Theisen, J., et al., Effects of porous media on extraction kinetics: Is the membrane really a limiting factor? Journal of Membrane Science, 2019. 586: p. 318-325.

3. Kokoric, V., et al., Determining the Partial Pressure of Volatile Components via Substrate-Integrated Hollow Waveguide Infrared Spectroscopy with Integrated Microfluidics. Analytical chemistry, 2018. 90(7): p. 4445-4451.

4. Unpublished results

The NSLS-II has outstanding nanoscale x-ray imaging capabilities in the hard x-ray regime, enabling a broad range of scientific research. The transmission x-ray microscopy (TXM) method, offered at the Full-field X-ray Imaging (FXI) Beamline, has the world-leading morphological and spectroscopic imaging capabilities with spatial resolutions from 20-50 nm. This full-field imaging capability with unprecedented imaging throughput finds excellent application in visualizing 3D chemical transformation in complex materials under in-situ controls [1-2].
With the focus size down to 12 nm, the Hard X-ray Nanoprobe (HXN) offers simultaneous multimodal imaging capabilities, which are ideal for visualizing material heterogeneity or defects with outstanding detection sensitivities. Some of the recent scientific applications include fluorescence tomography [3], high-sensitivity oxidation-state imaging [4], and strain imaging [5]. Significant efforts are directed toward achieving sub-10 nm 3D imaging using ptychography and performing more comprehensive material analysis by utilizing both full-field and scanning imaging modalities. The presentation will describe the latest technical capabilities and their applications for solving scientific problems.

References
[1] Zhengrui Xu et. al., “Charge distribution guided by grain crystallographic orientations in polycrystalline battery materials,” Nat. Commun. 11 (1), ID(83) (2020). 10.1038/s41467-019-13884-x
[2] Cheng-Hung Lin et. al., “Systems-level investigation of aqueous batteries for understanding the benefit of water-in-salt electrolyte by synchrotron nanoimaging.” Sci. Adv. 6 (10), eaay7129 (2020). 10.1126/sciadv.aay7129
[3] Tiffany W. Victor et. al., “Lanthanide-Binding Tags for 3D X-ray Imaging of Proteins in Cells at Nanoscale Resolution,” J. Am. Chem. Soc. 142 (5), 2145-2149 (2020). 10.1021/jacs.9b11571
[4] Ajith Pattammattel et. al, “High-sensitivity nanoscale chemical imaging with hard x-ray nano-XANES”. Sci. Adv., 6(37), eabb3615 (2020). 10.1126/sciadv.abb3615
[5] Yue Cao et. al., “Complete Strain Mapping of Nanosheets of Tantalum Disulfide,” ACS Appl. Mater. Interfaces 12 (38), 43173-43179 (2020). https://dx.doi.org/10.1021/acsami.0c06517

Core–shell nanowires (NWs) with asymmetric shells allow for strain engineering of NW properties because of the bending resulting from the lattice mismatch between core and shell material. For this study GaAs core NWs were grown by molecular beam epitaxy (MBE) onto an
Si(111) substrate and In_xAl_(1-�x)As shells were preferentially grown onto one side of the core only, for example onto the
(1�-10) plane. Besides electron microscopy the bending of NWs has been observed by X-ray diffraction analysis using a micro- and nanofocused beam. Respective measurements have been performed at beamlines ID1 of ESRF and P23 of PETRA III, respectively. A new scheme of data recording has been developed in order to determine bending radii and strains of NWs with different nominal bending radius. For data analysis a kinematical diffraction theory for highly bent crystals was developed and applied. The homogeneity of the bending and strain was studied along the growth axis of the NWs, and it was found that the lower parts, i.e. close to the substrate/wire interface, are bent less than the parts further up. Extreme bending radii down to about 3 micron did result in strain variation of about 5% in the NW core.

Strongly correlated materials exhibit interesting emergent behavior, such as high temperature superconductivity, colossal magnetoresistance and metal-insulator transitions (MIT) [1-3]. For perovskites, these exotic functional properties can be tuned via strain engineering [4,5] due to the strong coupling between the charge, spin, and lattice degrees of freedom. It is still not fully understood how these degrees of freedom interrelate to produce exotic states, and part of the complexity comes from spatial inhomogeneities on the nanometer scale [1]. Moreover, real material systems contain defects that can greatly influence their behavior, such as phase transitions being pinned to and nucleated at point defects. It is thus critical to characterize the electronic and structural evolutions of correlated materials at the nanoscale, through their relevant phase transitions. As part of this effort, we use nano x-ray diffraction (nano-XRD) to image strain and structural changes in La_1/3Sr_2/3FeO₃ (LSFO) across its MIT. LSFO has a concurrent metal-insulator phase transition involving the spin and charge orders, along with a structural component, according to past work [6]. We synthesize LSFO films on SrTiO₃ (001) and (111) substrates, where both samples exhibit a MIT, but with onset temperatures that differ by 20 K. Whether these LSFO films are identical to the bulk LSFO, the nature of the MIT, and the role of the lattice strain are not fully understood. Utilizing the 30 nm spatial resolution and 10^-5 strain sensitivity of nano-XRD, we image the evolution of strain with temperature for LSFO on the (111) substrate. We find that LSFO on STO (111) has a smooth structural response through the MIT, in contrast with the relatively sharp onset of the charge order. This differs from the sample on the (001) substrate, where the exact same charge order parameter cannot be found. Moreover, using nano-XRD, we see evidence of structural heterogeneity and domain formation in the (111) sample that becomes more pronounced 50K below the MIT, without a corresponding change in the charge order. Our results on the strain and lattice changes across the MIT will directly inform first principles calculations of correlated behavior in LSFO on STO. Clarifying the complicated energy balance between the lattice and electronic degrees of freedom in strain-engineered LSFO will have further implications for other MIT materials being investigated for next-generation memory devices. Time permitting, I will also discuss how simple machine learning techniques can enhance nano-XRD data analysis, independently extracting information on the film’s local surface normal tilt and lattice plane spacing, in a single measurement.

The sample processing, experimental design, data collection, and development of new analysis methods were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. Work at the 26-ID-C and 33-ID-D beamlines of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE- AC02-06CH11357.

[1] Dagotto, E. Complexity in Strongly Correlated Electronic Systems. Science 309, 257–262 (2005).
[2] Millis, A. J. Lattice effects in magnetoresistive manganese perovskites. Nature 392, 147–150 (1998).
[3] Imada, M., Fujimori, A. & Tokura, Y. Metal-insulator transitions. Rev. Mod. Phys. 70, 1039–1263 (1998).
[4] Wang, J. et al. Epitaxial BiFeO₃ Multiferroic Thin Film Heterostructures. Science 299, 1719–1722 (2003).
[5] May, S. J. et al. Quantifying octahedral rotations in strained perovskite oxide films. Phys. Rev. B 82, 014110 (2010).
[6] Zhu, Y. et al. Unconventional slowing down of electronic recovery in photoexcited charge-ordered La_1/3Sr_2/3FeO₃. Nat. Commun. 9, 1799 (2018).

Unprecedented tools to image crystalline structure distributions in materials have been made possible by recent advances in X-ray sources, X-ray optics and X-ray methods. Nanobeams combined with diffraction have made it possible to image parameters that were traditionally only addressed as ensemble averages. This enables the study of highly heterogeneous materials such as microelectronic devices and opens a new field of material science on the mesoscale. Furthermore, coherent nanobeams offer the opportunity to image nanomaterials in three dimensions with a resolution far smaller than the focused beam size. This has opened up new fields in X-ray diffraction in general and has become one of the main drivers for the enhancement of existing, and the construction of new, large scale scientific infrastructure projects around the world.
As one example, the ID01 beamline has been built to combine Bragg diffraction with imaging techniques to produce a strain and mosaicity microscope for materials in their native or operando state. A scanning probe with nano-focused beams, objective lens-based full-field microscopy and coherent diffraction imaging provide a suite of tools which deliver micrometre to few nanometre spatial resolution combined with the unrivalled strain resolution supplied by X-ray diffraction.
With worldwide efforts in the upgrading or new conception of synchrotron sources, improvements of several orders of magnitude in the throughput of these methods are expected in the next years. Our first results show the relevance of such new tools in complex experimental environments as encountered in nanotechnology and chemistry.
Although many basic principles and processes in what is in a wider sense called nanotechnology are known and exploited since more than a century, their development and improvement is still very much based on a trial and error approach. In the sector of energy materials such as batteries or electrochemical systems for energy conversion, the physiochemical complexity has prevented over decades a clear-cut understanding of processes and reactions at the nanoscale, essentially due to the absence of suited characterization tools. Looking at the example of batteries, and the worldwide implication of research groups on only a few prominent material systems, it becomes clear that rarely any progress in a technology depended so much on characterization and understanding of the complete reaction system. On the other hand, many common characterization techniques cannot assess such electrochemical systems under reaction but rather their constituents once isolated or extracted from the reactive system. Lab and synchrotron based powder X-ray diffraction has been a tool of choice for investigating nanomaterials in complex systems and under reaction. But only very recent developments permit to overcome the absence of spatial resolution of this method. We have developed several diffraction based microscopes that have proven their usefulness in microelectronic samples where high strain resolution needs to be combined with large fields of view and sub micrometer resolution. For typical nanostructures as present in catalytic reactions or batteries, coherent X-ray diffraction imaging tools will allow to zoom into single nanocrystallites with the potential of 3D nanometric imaging. While most published examples of the recent past aimed at high spatial resolution in static samples, current efforts are aiming at the operando assessment at a time resolution of relevance in chemical engineering, while preserving a 3D spatial resolution well below 10 nm. These tools that are today mainly limited to a small expert community are prone to quickly develop into one of the most powerful operando assessment methods; We will present the current state of the art of X-ray diffraction based microscopy with examples for imaging of individual nanostructures.
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Due to novel functionalities recently discovered at domain walls, thin-film ferroelectrics with dense ferroelastic domain structures represent promising candidates for a new generation of nanoelectronic devices [1]. Ferroelastic domain structures form to minimize epitaxial strain in the film, which can be tailored by selecting an appropriate combination of thin film and substrate material [2]. Certain combinations give rise to peculiar hierarchical organizations, whereby ferroelastic domains arrange in distinct “superdomain” bundles [3,4]. Recent studies have demonstrated that interconversion between superdomain states can be induced by the application of an external electric field [5] or stress [6], making these systems attractive for potential applications in reconfigurable electronics.

Little is still known about the superdomain arrangement locally, as well as the exact nature of its response to applied fields in device-like conditions. Studies to date have been confined to surface-limited Piezoresponse Force Microscopy (PFM) imaging or large area X-ray diffraction.

Here we attempt to fill this gap by employing synchrotron Scanning X-ray NanoDiffraction (SXND) [7]. An X-ray beam focused down to 50nm is swept across a ferroelectric thin film displaying a superdomain arrangement, giving local and spatially resolved access to its crystallography – with beam-size resolution. We use PbTiO3 (PTO) // KTaO3 (KTO) thin films as a prototype system for this study due to the rich mixture of both in-plane and out-of-plane domain bundles (the so-called “a₁a₂ / c” structure) that PTO exhibits as a result of the moderate epitaxial tensile strain exerted by the KTO substrate.

The superdomain structure revealed by SXND displays a peculiar distribution of PTO tilt and tetragonality gradients [8], especially evident at the boundaries between a₁a₂ and ac bundles. We subsequently track changes in this spatial distribution of tilts as a function of in-plane electric field applied via interdigitated electrodes, observing 90 degree domain wall rotations to accommodate 180 degree switching of the in-plane polarization component as the applied field polarity is inverted. PFM data collected on the same regions corroborates our interpretation, and suggests that the peculiar nature of the superdomain boundaries plays a major role in the switching mechanism.

References

[1] Sharma, P., et al. Materials 12, 2927 (2019)
[2] Damodaran A. R., et al. J Phys Condens Matter, 28(26), p. 263001. (2016)
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The Submicron Resolution X-ray (SRX) Spectroscopy beamline at the National Synchrotron Light Source II (NSLS-II) is a hard X-ray scanning-probe imaging and spectroscopy beamline. A focused X-ray beam is rastered over the sample to collect X-ray fluorescence (XRF) maps and spatially-resolved X-ray absorption spectroscopy (XAS) measurements from the sample. These techniques support a wide range of scientific fields including environmental and biological sciences, earth sciences, and material and energy sciences. Recently, a new nano-endstation was commissioned to provide users with an increased spatial resolution and higher photon flux onto the sample. This nano-endstation is the result of a multiyear program coordinated by an in-house team of scientists and engineers to replace the existing micro-endstation at SRX by filling a gap in imaging spatial resolution at the NSLS-II and providing users with additional imaging capabilities.

The nano-endstation at the SRX was built downstream of the existing micro-endstation and utilizes all new equipment. A pair of fixed-curvature Kirkpatrick-Baez (KB) mirrors focus the incident beam onto the sample. These mirrors are installed in a vacuum chamber designed to provide high stability with a newly designed alignment mechanism and interferometer feedback. The KB mirrors were manufactured with tight tolerances to provide a sub-250 nm focus and have demonstrated a 225 nm focus from a knife-edge scan on a test pattern. The sample is mounted on a new piezo stage stack which uses coarse and fine stages to raster the sample through the focused beam. Additionally, a rotation stage is mounted to allow for tomographic measurements. The rotation stage with slip-ring connectors can be run with continuous rotation for advanced scan strategies. This is also important for operando measurements where an electrical connection is necessary, e.g. electrochemical cycling. An interferometer system is installed to monitor the sample position and correct for any potential run out. These enhancements and added capabilities at SRX enable our user community to collect the high-quality elemental maps and spectroscopy for their experiments, as well as collecting more information on their samples by extending from 2D images to 3D volumes.

Nanostructured materials can exhibit exotic properties and behaviors that enrich the landscape of bulk materials, due to the increased influence of dopants, surfaces, geometry, and interfaces. Moreover, at the nanometer length scale, conventional macroscopic models of materials fail to accurately describe their physical behavior. In addition, traditional metrology tools struggle to precisely measure their functional properties. Specifically, heat transport in dielectric and semiconductor materials—which is dominated by phonons—is traditionally considered to follow Fourier’s law of diffusion. However, when the relevant length scales of the system approach the scale of the phonon mean free paths, past experiments observed [1] and theories predicted [2] a breakdown of Fourier’s law. To date, experimentally probing thermal transport at the nanoscale for general geometries is an outstanding challenge, precluding the development of comprehensive models of heat flow in complex systems. These challenges are a current roadblock for nano- and quantum technologies, including the development of advanced nanoelectronics and efficient thermoelectric devices.
Fortunately, tabletop sources of ultrafast, coherent extreme ultraviolet (EUV) pulses, produced via high harmonic generation, have nanometer wavelengths and femtosecond pulse durations which are well-matched to the intrinsic length- and timescales of energy transport at the nanoscale [3]. Here, we demonstrate that a dynamic scatterometry technique—based on these coherent EUV beams—is a versatile route for uncovering non-diffusive thermal transport behavior in nanostructured systems, from nanostructures on single crystal silicon to complex metalattices.
Using this new metrology capability, we map non-diffusive thermal transport away from 1D- and 2D-confined nanoscale heat sources on bulk substrates. This allows us to validate the counter-intuitive behavior that heat source periodicity (reduced spacing) can increase thermal dissipation efficiency [4,5]. We probe the full thermal transport landscape by studying varying heat source geometries on a variety of materials with drastically different phonon properties: silicon, silica, and diamond. Moreover, these EUV scatterometry results made it possible to develop and benchmark advanced mesoscopic and microscopic models to form a more general picture of phonon transport. We demonstrate that the kinetic-collective model, a mesosopic model using a hydrodynamic-like transport equation, predicts the full thermomechanical response observed in the experiment—including non-diffusive transport behavior—over a wide range of length- and timescales. We also perform microscopic atomistic calculations to model experimentally relevant geometries and uncover the fundamental physics responsible for the observed counter-intuitive behavior.
Furthermore, we advance this EUV-based technique to probe transport in nanoengineered metalattices [6]. Metalattices are a powerful bottom-up approach to tuning the propagation of high frequency phonons—highly ordered nanoscale opal templates allow for precise control over structure, into which different materials can be infiltrated. Specifically, we explore the interplay between heat source geometry and the nanoscale structure of the metalattices. We observe that metalattices are capable of significantly reducing the thermal conductivity below the prediction of continuum models and support these findings with atomistic calculations. In conclusion, we highlight extensions of this scatterometry technique to novel modalities based on coherent EUV beams to probe behavior in general devices [7].

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Many mechanical systems are submitted to deformations repeated for a very large number of cycles during their service (e.g. several billion cycles, in what is called the gigacycle fatigue domain or very high cycle fatigue – VHCF - domain) and can break under stress lower than their ultimate tensile stress. This phenomenon, called fatigue of materials, can be encountered in many industrial sectors. Fatigue design is thus crucial in engineering and it requires the accurate characterization of material behavior under cyclic loadings to ensure the safety and reliability of structures throughout their life. The characterization of the fatigue behavior of materials has been largely investigated with fatigue tests requiring long testing time in standard laboratory. To overcome this inconvenient new approaches based on ultrasonic fatigue machines have been developed during the last decades. In particular, the present research focuses on a new method for the fast determination of fatigue behavior by interpreting diffraction patterns with a temporal resolution of ∼ 1μs during an ultrasonic fatigue test at loading frequency of about 20kHz.
The present study points the estimation of the XRD peak broadening evolution during sample deformation due to ultrasonic fatigue cyclic loadings. This is a crucial parameter as it is strictly related to the microstructure of a material in term of mean elastic strain distribution and its fluctuation, intragranular strain heterogeneity and dislocation density.
A fully perlitic steel specimen was loaded using a 20kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. Since we are interested to investigate the VHCF domain, the amplitudes of the cyclic stresses ranges from 78 to 262 MPa. The diffraction patterns were acquired with a 2D hybrid pixel X-ray detector (XPAD3.2) with a temporal resolution of 1μs.
From the XRD patterns, peaks position and their respective broadening can be estimated. In particular, the evolution of diffraction peak broadening of ferrite (110) and (220) reflections is calculated by fitting the experimental data with an asymmetric Pearson-7 function. The results highlight an increase of the peak broadening with the amplitude of applied stresses. The micromechanical interpretation of these experimental data, based on a homogenization scheme capturing the strain heterogeneity inside the material, will be presented.

Piezotransducers, based on piezoelectric materials, that convert electrical into mechanical energy (and vice-versa) are widely used in several communication, sensing and energy harvesting applications. Piezoelectric materials are thus used in various devices, including resonators, actuators and sensors, recently as thin films to facilitate their integration into microelectronic devices and for miniaturization purposes (at lowest energy consumption). Among piezoelectric materials it is well established that the piezoelectric coupling coefficients are very large in crystalline materials which are also ferroelectric, i.e. which exhibit a remanent electrical polarization, switchable by applying an external electric field.
Besides the intrinsic piezoelectric effect, extrinsic mechanisms related to the presence of domains contribute to the piezoelectric effect in ferroelectrics. The domains are regions in which the orientations of the polarization vector and the spontaneous strain tensor are uniform. They are separated by domain walls, within which polarization and strain change direction upon passing to an adjacent domain having different orientations of the polarization vector and spontaneous strain. When external fields are applied to the ferroelectric, the domain walls move to minimize the energy of the unfavourably oriented domains, thus contributing to the field-induced changes in polarization and strain. The intinsic and extrinsic mechanisms are interdependent and, consequently, the total macroscopic response of a piezoelectric ceramic emerges from complex interactions of intrinsic and extrinsic mechanisms.
To investigate the physical properties of ferroelectric thin films various techniques, e.g. piezoelectric force microscopy (PFM), interferometry etc. are typically used. We use in situ synchrotron X-ray diffraction combined with the application of an electric field during measurements, which provides useful and precise information beyond the usual applications for structural studies [1-5]. It grants strain resolutions of the piezoelectrically-induced strain of better than 10^-4. In addition, time-resolved X-ray diffraction gives access to the structural dynamics during electrical loading [6]. We present the electric field-dependence of structural dynamics in lead zirconate titanate (PZT) and lanthanum-modified lead zirconate titanate (PLZT) thin films with various La concentrations using in-situ and time-resolved X-ray diffraction with temporal resolutions down to few tens of nanoseconds. The build-in electric field effects on butterfly curves asymmetry in PZT films and the La-doping effects on the coexistence of nanodomains and coarse domains evolution in PLZT films is shown and discussed.

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[5] T.W Cornelius, C. Mocuta, S. Escoubas, L.R.M. Lima, E.B. Araújo, A.L. Kholkin, O. Thomas, Materials 13, 3338 (2020)
[6] C. Kwamen, M. Rössle, W. Leitenberger, M. Alexe, M. Bargheer, Appl. Phys. Lett. 114, 162907 (2019)

CuInSe₂ nanocrystals offer promise for optoelectronics including thin-film photovoltaics and printed electronics. Additive manufacturing methods such as photonic curing controllably sinter particles into quasi-continuous films and offer improved device performance. To gain understanding of nanocrystal response under such processing conditions, we investigate impacts of photoexcitation on colloidal nanocrystal lattices via time-resolved X-ray diffraction. We probe three sizes of particles and two capping ligands (oleylamine and inorganic S^2–) to evaluate resultant crystal lattice temperature, phase stability, and thermal dissipation. Elevated fluences produce heating and loss of crystallinity, the onset of which exhibits particle size dependence. We find size-dependent recrystallization and cooling lifetimes ranging from 90 to 200 ps with additional slower cooling on the nanosecond time scale. Sulfide-capped nanocrystals show faster recrystallization and cooling compared to oleylamine-capped nanocrystals. Using these lifetimes, we find interfacial thermal conductivities from 3 to 28 MW/(m² K), demonstrating that ligand identity strongly influences thermal dissipation.

Transmission X-ray microscopy (TXM) is a full-field imaging technique. By taking advantage of using a synchrotron light source, TXM provides unique capabilities in fast 2D/3D imaging with nano-scale resolution. At the Full-field X-ray Imaging (FXI) Beamline at NSLS-II, we can routine perform 3D x-ray imaging with 1k x 1k x 1k voxels at a sub-50 nm resolution in less than one minute¹. While morphology characterization is the primary mode of the TXM application for vast samples, quantitative analysis in terms of material composition and oxidation states can be achieved through a TXM XANES method, where the imaging data are collected at multiple x-ray energies across one or more elemental absorption edges allowing spatially-resolved XANES analysis². The high-imaging rate at the FXI Beamline makes it possible to perform three-dimensional TXM XANES imaging under in-situ sample environment. In the presentation, we will report our recent instrument and data analysis development with few examples to describe the quantitative analysis using the data analysis tools we developed in-house³.

References:
1 Ge, M. Y. et al. One-minute nano-tomography using hard X-ray full-field transmission microscope. Appl Phys Lett 113 (2018).
2 Wang, J. J., Chen-Wiegart, Y. C. K. & Wang, J. In operando tracking phase transformation evolution of lithium iron phosphate with hard X-ray microscopy. Nat Commun 5 (2014).
3 Ge, M. Y. & Lee, W. K. PyXAS - an open-source package for 2D X-ray near-edge spectroscopy analysis. J Synchrotron Radiat 27, 567-575 (2020).

Nature is not only a constant source of inspiration and knowledge for modern engineering but also most of all the source of materials with unique complex structures and properties. The structure optimized by millennial evolution can be used as a base for the preparation of advanced engineering materials. An essential requirement for this is the full understanding of the laws endowing the nature-built materials with superb properties. To this end, high resolution imaging techniques are essential for understanding the hierarchical structures formed in self-assembly processes.
Examples of inspirational organisms are diatoms. The particularly extensively studied diatom characteristic is their intricate cell wall structure, called frustule, mainly made of silicon dioxide (opal). These silica shells exhibit large variation in morphology as well as hierarchical architecture (from nano- to micro-metres).
In recent years, scientists have bridged the gap between biology and material science of diatoms by developing techniques for imaging diatom frustule cross-sections, using scanning electron microscopy (SEM) [1,2]. It enables imaging the fine details of the structure. However, an intrinsic limitation of this technique is the need of cross-sectioning of the studied species, e.g. applying Focus Ion Beam (FIB) milling. Recently, a new insight into the structure of diatoms has been provided by non-destructive visualization of interior structures using nano X-ray computed tomography (nano-XCT) [1,3-4].
The advantage of nano-XCT is demonstrated based on high-resolution 3D data sets describing the structure of diatoms non-destructively. These data sets are of particular importance and were complemented by high resolution three-dimensional structure information using soft X-ray nano-tomography (available at Helmholtz Zentrum Berlin HZB) combined with high-resolution transmission electron microscopy.
The associated imaging and composition analysis results from SEM/FIB, nano-XCT and TEM allow to describe the microstructure of frustules on multiple length scale. Those datasets are used to describe complex structure of diatoms frustules and to derive models in aim of fabrication of a self-similar, bio-inspired structure by applying 3D Selective Laser Melting (SLM) [3] as well as simulation to determinate mechanical properties of such shells [4].

Bibliography
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[2] Witkowski A., Plocinski T., Grzonka J., Zglobicka I., Bak M., Dabek P., Gomes A.I., Kurzydlowski K.J. (2019): Application of Focused Ion Beam Technique in Taxonomy-Oriented Research on Ultrastructure of Diatoms in J. Seckbach and R. Gordon (Eds.) Diatoms: Fundamentals and Applications, (113–126) © 2019 Scrivener Publishing LLC
[3] Zglobicka I., Chmielewska A., Topal E., Kutukova K., Gluch J., Krüger P., Kilroy C., Swieszkowski W., Kurzydlowski K.J., Zschech E. (2019): 3D Diatom–Designed and Selective Laser Melting (SLM) Manufactured Metallic Structures. Scientific Reports, 9:19777. DOI: 10.1038/s41598-019-56434-7
[4] Topal E., Rajendran H., Zglobicka I., Gluch J., Liao Z., Clausner A., Kurzydlowski K.J., Zschech E. (2020): Numerical and Experimental Study of the Mechanical Response of Diatom Frustules. Nanomaterials, 10, 959. doi:10.3390/nano10050959

Lead-based rechargeable batteries are promising candidates for stationary grid storage due to their low cost, high stability, and fast discharge capabilities compared to other electrochemical energy storage chemistries. However, current lead-based batteries are unable to fully utilize the theoretical storage capacity, and are limited in their charging rates. Changes in particle size and porosity impact ion and electron transport dynamics between the electrolyte, active material, and current collector grid, ultimately affecting charge acceptance and cyclability. During cycling, large volume changes are encountered that strongly influence electrode morphology and hence battery performance. An improved understanding of this relationship is necessary in order to design more efficient batteries capable of meeting future energy storage needs. The strong attenuation of lead presents several challenges for conventional X-ray imaging. This work presents new techniques and tools developed to overcome these challenges including experimental design, instrumentation, and data analysis; then uses these tools to track the evolution of electrode morphology during initial formation and subsequent cycling of lead-acid batteries.

The combination of high-resolution X-ray imaging with in-situ mechanical testing, particularly the application of specially designed test setups in a transmission X-ray microscope, allows the study of the fracture behaviour in heterogeneous materials, composites and micropatterned devices. A miniaturised micro double-cantilever beam test (micro-DCB) setup is integrated into a laboratory transmission X-ray microscope (TXM) to guide microcracks to the mechanically weakest region of a material, which is determined by the materials-dependent fracture toughness, the size and the shape of defects as well as the local stress, and to achieve stable crack propagation in a controlled way [1]. In-situ mechanical studies in a nano X-ray computed tomography (nano-XCT) system allow a 3D visualization of the micro-crack evolution in materials or in microchips with a spatial resolution of about 100 nm. During the micro-DCB experiment, the load is applied perpendicular to the optical axis of the X-ray microscope while images are collected. A force sensor allows to determine the mechanical load at certain stages of crack propagation. The local energy release rate can be determined quantitatively. The in-situ micro-DCB technique offers several benefits over existing methods and is applicable across a range of disciplines, including materials science (e.g. composites), microelectronics (e.g. interconnect stacks), and life sciences (e.g. tissue, bones).
High-resolution 3D image sequences based on nano-XCT are used to visualize crack opening and propagation in fully integrated multilevel on-chip interconnect structures of integrated circuits. The nondestructive study of the propagation of sub-micron cracks during the in-situ micro-DCB test allows to image cohesive failures in organosilicate glass (so-called low-k materials) or adhesive failure, i.e. delamination along Cu/dielectrics interfaces. Weakest layers and interfaces in the interconnect stack can be identified [2]. The quantitative determination of the energy release rate allows to judge the robustness of Cu/low-k interconnect stacks against process-induced thermomechanical stress and the effectiveness of so-called guard-ring structures. These data provide important input for the guard-ring design and for the selection of materials, particularly the insulating dielectrics. Eventually, the risk of failure of the patterned metal/dielectrics structures can be reduced.

[1] K. Kutukova, S. Niese, J. Gelb, R. Dauskardt, E. Zschech, "A Novel Micro-Double Cantilever Beam (micro-DCB) Test in an X-ray Microscope to Study Crack Propagation in Materials and Structures", Mater. Today Comm. 16, 293–299 (2018)
[2] K. Kutukova, S. Niese, C. Sander, Y. Standke, J. Gluch, M. Gall, E. Zschech, "A Laboratory X-ray Microscopy Study of Cracks in on-chip Interconnect Stacks of Integrated Circuits", Appl. Phys. Lett. 113, 091901 (2018)

Characterizing the polycrystalline grain microstructure of metals, alloys, ceramics or minerals in three dimensions nondestructively is paramount to better understanding the material properties. Often, such samples demand a larger representative volume/quantity to be statistically relevant or possess characteristic geometry (e.g. high aspect ratio rolling geometry) that is essential to interpret grain structure anisotropy.

Recent advances of Laboratory Diffraction Contrast Tomography (LabDCT) allow to record and reconstruct larger representative volumes seamlessly. We will present and discuss different approaches of data acquisition strategies attacking acquisition problems inherent to a given sample. Combining the 3D grain microstructure, i.e. grain morphology and crystallographic orientation, with traditional absorption contrast tomography gives unprecedented insights on the laboratory scale. Time resolved studies of the response of the material under investigation to external stimuli in- or ex-situ can be conducted.

Advanced x-ray beam facilities support a wide range of scientific and technological development of materials. To maximize the value of these experiments, the x-ray beam itself needs to be well understood, with fine control over its position. As x-ray sources become more advanced, they will benefit from better beam monitoring and measurements. Most of the monitoring methods currently in use can only position the beam or measure beam flux before or after experiments; any drift in the beam position or intensity fluctuations that occur during the experiment would go unnoticed. Therefore, there is a need for real-time, direct beam monitoring which can be integrated with beam controls to quickly set up and control beam parameters, and image the beam. Recent advances demonstrate that thin diamond detectors are a viable technology for minimally invasive imaging of x-ray beams. The choice of diamond brings a number of advantages due to diamond’s remarkable physical properties, such as large bandgap, semi-transparency to x-rays, extreme thermal properties, and fast electron and hole mobilities. In this work, we will describe our advances in producing a pixelated, thin, transparent x-ray beam monitor based on doped diamond, with a p-type/intrinsic/n-type (PIN) design, and preliminary results of testing the detector and readout system at the National Synchrotron Light Source II at Brookhaven National Lab.

X-ray Computed Tomography has proven to be a crucial method to properly characterize and understand a huge variety of materials applications. Due to the non-destructive 3D imaging capabilities, this imaging methodology provides unique insight into material properties with comparatively minimal sample processing. One limitation however has been resolution capabilities. Previously, X-ray tomography imaging has utilized the principle of geometric magnification to obtain resolution. This has several limitations, the main impact being the realistic resolution achievable. Recently, the application of using a photon-converting scintillator and objective lenses has enabled much higher resolution imaging. A unique ability of this system architecture is to enable non-destructive, multi-length scale visualization; with an imaging field of view range from tens of millimeters down to tens of micrometers, and resolution capabilities reaching 500 nm in instruments such as the ZEISS Xradia Versa. Alternatively, another X-ray imaging method is to use X-ray lenses such as Fresnel Zone Plates that can achieve resolutions down to 50 nm and less, utilizing a quasi-monochromatic lab-based X-ray source in instruments such as the ZEISS Xradia Ultra. This system also employs an inline phase ring that enables Zernike phase contrast imaging which can greatly improve imaging contrast.
Due to the restrictions of lab-based equipment, each imaging solution requires its own imaging system. Often, this results in non-correlative imaging workflows – where a similar but different sample or region is imaged in each system to the maximum system resolution capabilities. This poses a number of inherent limitations in obtaining the full understanding of the sample in question: What does the sample look like as a whole and how representative is this region to another? Are there microscale properties that correlate to macroscale features? Additionally, knowing the exact resolution limit required to properly characterize a sample is an important question that can be difficult to answer without observing enhanced resolution of the exact same feature. Combining systems that can achieve different resolutions in a correlative workflow of the same sample also allows for advanced analysis, such as applying properties obtained from high resolution imaging to a large volume obtained from lower resolution imaging. For example, intra- and inter-particle porosity that is not resolved could inherently change simulation results without proper characterization.
We present here results combining two X-ray tomography systems, the Zeiss Xradia Versa and Zeiss Xradia Ultra instruments, into a correlative, multi-length scale analysis workflow through the use of specifically designed hardware and software tools. We demonstrate several applications using this combined approach to enable non-destructive, massively multiscale 3D imaging. Specific examples include combined quantitative studies in nuclear graphite material to facilitate a multiscale porosity and microstructural analysis, battery anode particles with combined machine learning upscaling as well as polymer electrolyte fuel cell device layers.

A refined systematic method for imaging and analyzing the structural characteristics of dot-core GaN substrates using X-ray topography is presented. Currently, fundamental understanding of the defect nature of dot-core GaN substrates and the impact on device performance is still in its infancy. Work by Raghothamachar et al.,¹ have previously used X-ray topography to catalogue various dislocations in dot-core GaN substrates. However, only rocked images were generated in that study, which are integrated images recorded by exposing a single film along different angular positions along an X-ray diffraction rocking curve. Our method involves generating single exposure images instead – images exposed at various points along the rocking curve with each image recorded on separate pieces of film. Rocked images were also generated for comparison. The measurements were performed at the 1-BM beamline of the Advanced Photon Source, Argonne National Laboratory using an X-ray energy of 8.05000 ± 0.00015 keV and a (111) Si beam expander to measure the (1124) GaN reflection in the glancing incidence geometry. Unlike the rocked images, the single exposure images unequivocally preserve all the structural information pertaining to lattice tilt and distortion – both the magnitude of tilts and the spatial locations of tilt boundaries for example. The importance of preserving this structural information is that it enables us to describe quantitatively the distortion of the defects present. In fact, the single exposure images allow us to calculate the lattice curvature on two different scales: (1) globally across the entire dot-core GaN substrate (~tens of mm) and (2) locally across each highly distorted core (~500 μm). One of the dot-core substrates measured had a radius of curvature of ~15 m across the entire substrate, while locally across individual cores the radius was on the order of ~0.2 m to ~0.4 m. This information is lost in rocked image measurements because the integration of images along different parts of the rocking curve loses angular information. Furthermore, the single exposure image method has the freedom of generating a ‘rocked image’ by superimposing each of these single exposure images together. Measured rocked images cannot be accurately deconvoluted into its image components. We demonstrate that a contour tilt map can be generated when superimposing many of these images together – an impossible task to accomplish from a measured rocked image. Lastly, many instances were found where dislocations that appeared in the single exposure image measurements were not present in the rocked image measurements. This is due to spatial overlapping of diffraction areas from recording images from different parts along the rocking curve on the same film when measuring rocked images.

References
1. B. Raghothamachar, et al., J. Crys. Growth, 544, 125709 (2020).

The authors would like to acknowledge supported through the ARPA-E PNDIODES program under contract DE-AR0001116 at UCLA. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The synchrotron X-ray topography measurements were carried out at 1-BM Beamline of the Advanced Photon Source, Argonne National Laboratory.

In this work, we demonstrate how machine learning and its related optimization tools can be used to replace conventional phase retrieval methods in X-ray transmission and Bragg ptychography. X-ray transmission ptychography has become a well-established technique for high resolution imaging and phase retrieval. We present PtychoNN, a novel approach to solve the ptychography problem based on deep convolutional neural networks. Once trained, PtychoNN is capable of generating high quality reconstructions up to hundreds of times faster compared to conventional iterative methods, essential for implementing real time phase retrieval. Moreover, by surpassing the numerical constraints of iterative methods, the sampling condition can also be significantly relaxed. The counterpart of transmission ptychography in diffraction condition is known as Bragg ptychography. The technique itself is less mature, as limited by the more complex diffraction geometry and data quality. Here we describe the forward propagation in Bragg ptychography using the Takagi-Taupin Equations (TTE). We show that, when combined with Automatic Differentiation (AD), TTE can be used as a general formalism for 3D phase retrieval, applicable to both Bragg ptychography and Bragg Coherent Diffraction Imaging. Compared to conventional Fourier Transform based methods, our approach accounts for additionally refraction, absorption, interference, dynamical effects, and is applicable to any kind of weakly strained material system. [1] M. J. Cherukara, T. Zhou, Y. Nashed, P. Enfedaque, A. Hexemer, R. J. Harder, M. V. Holt, Appl. Phys. Lett. 2020, 117, 044103. [2] T. Zhou, M.J. Cherukara, S.O. Hruszkewycz, M. Allain, N. Hua, O. Shpyrko, Y. Takamura and M.V. Holt, in submission.

Artificial intelligence methods attract significant interest nowadays due to the general tendency of automating analysis procedures. Computer-based techniques are not only much faster and less demanding for expert knowledge of operators than manual techniques, but also provide reliability and reproducibility of the analysis results due to much lesser vulnerability to accidental errors. In this contribution, we focus on those two aspects of X-ray diffraction experiments: namely, we demonstrate how artificial intelligence can help in choosing the optimal measurement configuration and in data interpretation (both in powder and high-resolution X-ray diffraction). The approaches, discussed in our contribution are based on combining fundamental physical ideas with the two efficient mathematical tools: Bayes’ theorem and Fisher information, which are quite often overlooked by physicists.

Fisher information [1] quantifies the sensitivity of the measured data to the parameters of interest and, therefore, gives us a hint on choosing the most suitable way of data acquisition. Cramer-Rao bound [2] connects Fisher information to the reliability of the obtained results and the possible correlations between the model features. We demonstrate that fully automatic analysis of Fisher information is suitable for choosing the most informative reflections and measurement geometries when panning high-resolution X-ray diffraction (HRXRD) measurements. The decision is made adaptively, by rating all possible sets of scans and reciprocal-space maps, as well as diffractometer configurations, on the base of the amount of their information on the investigated sample. Also, analysis of the Fisher information structure (namely, detection of a banded diagonal shape of the inverse Fisher matrix) helps to reconstruct the sample parameters in a more efficient way: a problem with locally correlated parameters can be solved by iterative consideration of only a subset of parameters to be reconstructed at each step [3,4]. We apply this technique to the problem of automatic decomposition of an X-ray spectrum, consisting of a large number of strongly overlapping peaks, into contributions of individual peaks.

Bayes’ theorem describes the update of our knowledge about the investigated sample by the obtained measurement results. It represents an efficient tool for quantitative ranking of models in the pattern recognition problems [3,5]. We apply a Bayesian approach to quantitative analysis of X-ray powder diffraction data (identification of phases from a measured X-ray spectrum), to peak indexing in HRXRD spectra (finding the correspondence between each measured peak with an expected Bragg peak, a layer thickness oscillation fringe or a superlattice fringe), and to the problem of decomposing strongly overlapping peaks (for power XRD data). The initial information about the investigated sample or dataset is encoded in prior probabilities for the models. The expected experimental inaccuracies caused by statistical and systematic noise are characterized by the likelihood function. Finally, models of the spectrum decomposition (peak identification, etc.) are ranked according to the estimated posterior probability. The approach is quite universal and can be easily adjusted to a particular physical problem: for example, additional systematic errors can be efficiently detected and corrected by introducing them into the analyzed model during powder phase identification. For all the mentioned tasks, the designed algorithms succeeded in automated solving of the problems.

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4. Mikhalychev, A., et al, Communications Physics, 2019, 2, 134.
5. Mikhalychev, A. and Ulyanenkov, A. J. Appl. Cryst. 2017, 50, 776-786.

Computer tomography has found broad application in material science and medical imaging, providing a versatile approach to visualize the internal structure of a 3D volume. For decades, there is extensive research on the improvement of reconstruction quality and fidelity to deal with the many challenges imposed by experimental data collection, such as noise and missing wedge. In this work, we introduce a neural network based method to tackle the missing wedge problem. Distinguished from existing machine learning architecture, we propose a new two-step model implemented through generative adversarial networks (GAN) and autoencoder to inpaint the miss-wedge sinogram. The results have demonstrated the state-of-the-art performance. More importantly, the proposed architecture is robust to insufficient training data, which provides uniqueness in distilling and expanding the knowledge learned from limited training data to un-seen categories as semi-unsupervised learning. We will also discuss the difference between our method and others’ work, especially in the sense of how we can consistently improve the model performance in practical scientific applications when ground truth is not available. The ability to reconstruct images in X-ray tomography with high accuracy and fidelity would gain us more reliable insights into objects' intrinsic structure and deepen the understanding of specific scientific problems. This work is supported by the LDRD program at the FXI facility at NSLS-II, Brookhaven National Laboratory (BNL).

The potentials of facilitating nanocrystals in novel materials design and of enhancing existing materials in the form of advanced nanocomposites are attracting increasing attention to nanomaterials research. Due to the strong correlation between physical and chemical properties of nanocrystals and their sizes as well as atomic configurations, their production requires utmost control and precision. Hence developing accurate, reliable and robust characterization methods targeting nanocrystals is becoming an even more critical component of today’s materials design and manufacturing activities. X-ray powder diffraction, being the gold standard of high-resolution materials characterization is the number one method employed in the analysis of nanocrystalline powders as well, although the fundamental principle behind the analysis of powder x-ray diffraction data is the assumption of infinitely-periodic stacking of atoms within individual grains, not strictly satisfied by nanocrystals due to their tiny sizes. That raises the question of whether we can use standard crystallographic analysis methods to solve for the average internal structure of nanocrystalline powders from their diffraction data.
In this talk I will address this question using computational modelling of powder diffraction from monodispersed nanocrystalline powders with grain sizes of 40 nm and below. To do that, I will first introduce our computational framework and present ideal diffraction data generated based on first-principle diffraction equations. This computed data will be treated as ‘ideal experimental data’ and then will be used to establish direct link between the diffracting nanocrystalline powder and its diffraction signature. Standard crystallographic analysis methodologies will be used to extract avarage structural characteristics of the nanocrystallne powder and they will be validated against the true structural parameters of the nanopowder by direct analysis of the atomic coordinates. Our conclusions are important in understanding the limits of applicability and validity of standard crystallographic analysis tools in x-ray diffraction data of nanocrystalline powders under ideal conditions, where the diffraction data is free from uncertainties and the diffracting sample is known down to the individual atomic positions. Moreover, our results will draw attention to the necessity of computational studies to investigate the diffraction phenomenon of x-rays from nanocrystalline powders and will motivate discussions on developing better data analysis algorithms compatible with the internal structure of nanocrystalline powders.

Synchrotron-based study of material behavior often involves the use of multiple modes of characterization, whether in a synchronous correlative microscopy approach or via sequential measurement. While synchronous multimodal characterization is a growing area, these studies most commonly consist of various measurements on different instruments at different times, each with their own quirks resulting from practical constraints like sample orientation and tool resolution. The difficulty in strictly correlating data generated across measurements can be quite high, especially so for samples with asymmetric and non-extended morphology such as individual micro- or nanoparticles and rough or porous films as can be found in solar cells and battery electrodes. To address this challenge, we present a morphology-informed ray-tracing approach to simulate probe-sample interactions in raster scanning instruments, allowing for proper spatial correlation of the data acquired across synchrotron-based and benchtop setups.

First, we generate a three-dimensional model of our sample from a map of local thickness. We then perform ray-tracing of the X-ray beam with our sample, accounting for the X-ray-sample interaction and the orientation of the beam, sample, and involved detectors. As a demonstrative example, we analyze sequential nanpoprobe X-ray diffraction and X-ray fluorescence maps of a state-of-the-art halide perovskite optoelectronic material. The ray-tracing yields a spatially-variant point-spread function weighting the contribution of all beam-intersected regions of the sample to the values recorded at the detectors at each point on the map, enabling deconvolution of the sample morphology from measured data and fair spatial correlation of data across measurements. Precise assessment of the sampled volume in correlative measurements will be increasingly necessary as experimental complexity increases at diffraction-limited storage rings.

Smectite hydration impacts dynamical properties of interlayer cations and thus the transfer and fate of H₂O, contaminants, and nutriments in surficial environments where these ubiquitous clay minerals are often one of the main mineral components. The influence of key crystal-chemical parameters on hydration, organization of interlayer species, and related properties has been described for tetrahedrally substituted trioctahedral smectites (saponites). Despite the ubiquitous character of octahedrally substituted smectites, that make most of the world bentonite deposits, the influence of charge location on smectite hydration properties has not largely investigated. In this work a set of octahedrally substituted trioctahedral smectites (hectorites) with a common structural formula Na_xMg_6-xLi_xSi_8.0O₂₀(OH)₄ and a layer charge (x) varying from 0.8 to 1.6 was synthesized hydrothermally from stoichiometric gels. The distribution of charge-compensating Na⁺ cations and of associated H^₂O molecules was determined experimentally from the modeling of X-ray diffraction data obtained along water vapor desorption isotherms. Distributions of charge-compensating cations and of associated H₂O molecules were also computed from GCMC simulations as a function of layer charge. Interlayer H₂O contents are similar in all Na-saturated smectite samples, independent of the location and amount of their layer charge. In contrast to synthetic saponite, for which stability of most hydrated layers was increased
by in-creasing layer charge, the stability of synthetic hectorite hydrates is only slightly affected by layer charge. Consistently, the layer-to-layer distance of Na-saturated hectorite 2W (and 1W) layers is independent of layer charge. The contrasting hydration behavior of synthetic Na-saturated saponite and hectorite is likely due to different electrostatic attraction between the 2:1 layer and interlayer cation. Combined with previous results on saponites, the present data and sample set provides key constraints to assess the validity of force fields simulating clay-water interactions for an unmatched variety of smectite with contrasting locations and amounts of layer charge deficits.

Innovations in laboratory x-ray source and x-ray imaging methodology are critical to realize intrinsic advantages of x-ray microscopy for a wide range of applications. X-ray imaging using absorption, phase, and scattering/darkfield contrasts (tri-contrast) have been shown to provide unique and complementary structural information critical to many imaging applications, often missing in absorption contrast imaging alone. For example, scatter contrast has been shown to be superior to absorption contrast for imaging fine cracks. Phase contrast is far superior for imaging low Z (soft) materials than absorption contrast.

Significant improvement in tri-contrast x-ray imaging with laboratory x-ray sources is desirable, including options for operating over a wide energy range to image objects of various sizes and compositions, and to achieve high spatial resolution to visualize fine features.

Significant progress has been made in recent years in developing laboratory x-ray sources and methodologies to advance tri-contrast x-ray imaging. Sigray has developed a novel x-ray source using matrix array anode source technology (MAAST™) with an anode comprised of arrays of metal (e.g. Cu, W) microstructures as x-ray emitters embedded in a diamond substrate with excellent thermal conductivity. Under electron bombardment, the localized metal microstructures are effectively cooled due to the large thermal gradients relative to the diamond substrate.

The common approach to tri-contrast x-ray imaging involves the Talbot-Lau interferometer, which consists of three gratings. The first of these, the source grating, is used to provide the required coherence, but it has a number of drawbacks, including inefficient use of source x-rays as it absorbs more than 50%, narrow angular collimation with high aspect ratio grating structures for high energy x-rays and the consequent limit in imaging field of view. Additionally, for high energy x-rays, the fabrication of the source grating is extremely challenging. The MAAST x-ray source removes the need for the source grating entirely. It overcomes the drawbacks and offers many advantages.

Using these and other innovations, Sigray has developed x-ray microscopes with excellent capabilities. The design of the microscopes and their imaging performance will be reported and discussed.

In the aerospace industry, single crystal nickel-based high-pressure turbine blades are the most critical part of the engine. The thermo-mechanical resistance of the blade is mostly due to the monocrystalline arrangement to increase the creep strength and to the design of internal cooling circuits with complex geometry to reduce the blade temperature.
To ensure the single crystal arrangement is maintained throughout the part after the foundry process, a non-destructive test (NDT) has been developed. Indeed, the presence of another grain into the part can critically impede the performance of the blade, which may cause irreversible damage to the engine motor.

The proposed solution is to develop a new industrial NDT system using high energy Laue transmission diffraction, which represents a technological breakthrough in the current industrial environment. A compact laboratory high energy Laue diffraction system has been designed, which uses a high-energy X-ray source, a motorized support sample setup and a high efficiency X-ray detector. A compact X-ray slit system is used to control the footprint of the beam on the sample and the motorized stage is used to scan the sample in front of the beam. Typical high energy X-ray sources are powerful enough to go through several millimeters of nickel-based alloy allowing to scan entire parts sur as small turbine blades. Our experiments showed that to detect diffraction spots from the illuminated volume, the use of hybrid photon counting detector is desirable to increase the system performances (both faster data collection and detection of weak intensity reflection beams).

A forward simulation model of the Laue diffraction physics under the kinematic approximation has also been developed and allows simulating any diffraction pattern according to the crystal structure. The forward model also takes into account the sample geometry, which can be as complex as a turbine blade with double walls and internal cavities. An in-house indexing algorithm based on the forward model, which takes into account the specificity of a laboratory system, allows to retrieve the crystal orientation from the experimental diffraction images and to detect new orientations in the pattern.

Experimental results show that Laue transmission diffraction method makes it possible to carry out an orientation mapping for an extended monocrystalline volume. Laue diffraction pattern analyses is able to reveal the potential presence of an undesirable grain in the volume.

X-ray microscopy and tomography using propagation-based phase contrast (PB-PC) are powerful techniques to study low absorption samples on the micrometer scale. The main benefit of the technique is an increased contrast given by edge enhancement, that is, by near-field interference fringes around sharp edges. In setups with a divergent source, a trade-off between the distance dependent flux and the source coherence must be made. We present a systematical experimental and theoretical investigation of this trade-off, based on experiments with two different laboratory setups with high-resolution detectors: a custom-built system with a Cu microfocus source and a commercial system (Zeiss Xradia) with a W source.
The fringe contrast, contrast-to-noise ratio and fringe separation for a low-absorption test sample were measured for 130 different combinations of magnification and overall distances. We find that these figures-of-merit are sensitive to the magnification and that a theoretical optimum can be found that is independent of the overall source-detector distance. In general, we show that the theoretical models show excellent agreement with the measurements, if the X-ray source spectrum and the energy dependence of the detector sensitivity are considered. These results can be used when designing and optimizing the geometry of an imaging system, especially concerning the used magnification.

Driven by needs from scientific research, healthcare and industrial manufacturing, X-ray microscopy has been successfully transferred from synchrotrons to the laboratory and the spatial resolution has been pushed to sub-micrometer. One way to further improve the resolution is to use an X-ray source with a very small focal spot. At Excillum, based on advanced electron beam and target technologies, a state-of-art nanofocus x-ray tube has been developed which enables an isotropic, resolution of 150 nm line-spacing.

Typical nanofocus X-ray tubes are normally limited in X-ray flux, which leads to long acquisition times when performing nano-CT outside of the synchrotrons. The newly developed nanofocus X-ray tube at Excillum, NanoTube N2, has a greatly improved brightness compared to its predecessor, achieving a minimum of 3x higher power loading while still maintaining the same sharp focus. The high brightness of Nanotube N2 brings the possibility of reduced scan times, helping to mitigate any motion blur from samples or imaging system to further improve the spatial resolution.

The advanced electron optics of the nanofocus X-ray tube has internal calibration and validation of the electron focus size, translating to the X-ray spot size. This gives the user a confirmation in what the maximum achievable resolution is for each scan, as well as a continuous feedback on the performance of the tube.

Until now the NanoTube has been integrated into different Nano-CT systems for applications of materials science [1], biomedical [2] and has recently been integrated in to commercially available NanoCT-systems [3]. This presentation will cover the technology enabling the new tube, as well as a few user examples of how the high resolution, high power density tube has helped researchers discover previously unseen features in their samples.

[1] C. Fella et al., Microscopy and Microanalysis, 24(S2), 234-235 (2018)
[2] S. Ferstl et al., IEEE Transactions on Medical Imaging, 1-1 (2019)
[3] https://www.procon-x-ray.com/ct-alpha-nanotube/

There is a large performance gap between conventional, electron-impact X-ray sources and synchrotron radiation sources. An Inverse Compton Scattering (ICS) X-ray source [1,2] can bridge this gap by providing a narrow-band, high-flux and tunable X-ray source that fits into a laboratory at a cost of a few percent of a large synchrotron facility. It works by colliding a high-power laser beam with a relativistic electron beam, in which case the energy of the backscattered photons is in the X-ray regime. So far, the only ICS source in regular user operation is the Munich Compact Light Source (MuCLS) [3], a combination of Lyncean Technologies’ commercially available Compact Light Source (CLS) [4] and a beamline with two endstations built by researchers at the Technical University of Munich [5]. The application focus of the MuCLS is biomedical imaging of centimeter-sized samples in the 15-35 keV energy range, well-matched to the beam properties of the Lyncean CLS with ~4 mrad divergence and spectral bandwidth of 3-5%.

Here we present a concept for an ICS X-ray source that is about two orders of magnitude brighter than the existing CLS design. Depending on configuration, it covers an X-ray energy range of about 30-90 keV, or 60-180 keV, well-suited to many applications in materials science. It will provide X-ray flux of up to 4 x 10¹² photons/s within a beam divergence of 4 mrad and a bandwidth of around 10%. This is well-suited for high resolution, micro-CT imaging of millimeter-sized samples at micron resolution, with a flux density similar to some high-energy synchrotron beamlines. The beam properties of the new design are also compatible with focused beam applications such as high-energy diffraction, since using a lower divergence part of the beam with lower bandwidth allows the use of several types of X-ray optics commonly used at synchrotron beamlines.

In this presentation, we will discuss the novel concepts applied to the design of this X-ray source as well as the resulting beam properties. We will discuss several application examples in the areas of imaging and diffraction where this system can approach or meet the performance of synchrotron beamlines. This will allow transferring many research and industrial applications from the synchrotron, where capacity is limited, and enable longitudinal studies that aren’t compatible with the synchrotron access model, to a local lab.

[1] R. Hajima, “Status and Perspectives of Compton Sources,” Physcs Proc 84, 35-39 (2016).
[2] M. Jacquet, “Potential of compact Compton sources in the medical field,” Phys Medica 32, 1790-1794 (2016).
[3] E. Eggl, M. Dierolf, K. Achterhold et al., “The Munich Compact Light Source: initial performance measures,” J Synchrotron Radiat 23, 1137–42 (2016)
[4] B. Hornberger, J. Kasahara, M. Gifford et al., “A compact light source providing high-flux, quasi-monochromatic, tunable X-rays in the laboratory,” Advances in Laboratory-based X-Ray Sources, Optics, and Applications VII, A. Murokh and D. Spiga, Eds., 2, SPIE, San Diego, United States (2019).
[5] B. Günther, R. Gradl, C. Jud et al., "The versatile X-ray beamline of the Munich Compact Light Source: design, instrumentation and applications,” J Synchrotron Radiat 27, 1395-1414 (2020).

A conventional X-ray tube generates X-rays when highly energetic electrons are stopped in a solid metal anode. The fundamental limit for the X-ray power generated from a given spot size is when the electron beam power is so high that it locally melts the anode. The liquid-metal-jet anode (MetalJet) technology solves this thermal limit by replacing the traditional anode by a thin high-speed jet of liquid metal. Melting the anode is therefore no longer a problem as it is already molten, and significantly (about 10x) higher e-beam power densities can therefore by used making the MetalJet the brightest microfocus x-ray tube. The liquid-metal-jet technology results in stable and operational X-ray tubes running in over 100 labs around the world.

The applications include X-ray diffraction and scattering, several publications have also shown very impressive imaging results using liquid-metal-jet anode technology, especially in 2-D or 3-D phase-contrast imaging and X-ray microscopy. MetalJet sources also show their applicability in industrial imaging applications.

Phase-contrast imaging achieves a significant improvement on the contrast and resolution of soft-tissue with hard X-rays, however, the imaging quality, has been compromised by the low flux and brilliance using traditional microfocus tubes or adding optical elements. Therefore, the high brilliance liquid-metal-jet technology enables the development of laboratory-scale phase-contrast imaging systems. The high stability of the source meets the requirements of an ideal phase-contrast imaging technique. Several application examples will be given during the conference, illustrating the capability of MetalJet in commercial or in-house built X-ray microscopy system. The Kα line of gallium, the main component of the liquid alloy is above absorption edge of copper making MetalJet beneficial for imaging copper structures with high contrast.

Excillum has recently introduced next generation MetalJet E1 increasing the brightness further by powering a 30 µm spot with 700W. The resulting flux is 70 times more than a conventional sealed tube microfocus tube in the energy range of 24-29 keV and 10 times more in the full spectrum. The applications where E1 dominates the performance are phase contrast imaging, high-pressure single crystal diffraction, small angle x-ray scattering, high speed x-ray imaging to name a few. The dual port capability provides flexibility to users in setting up experiments.