High-sensitivity nanoscale chemical imaging with hard x-ray nano-XANES

Image registration for in situ X-ray nano-imaging of a composite battery cathode with deformation

The structural and chemical evolution of battery electrodes at the nanoscale plays an important role in affecting the cell performance. Nano-resolution X-ray microscopy has been demonstrated as a powerful technique for characterizing the evolution of battery electrodes under operating conditions with sensitivity to their morphology, compositional distribution and redox heterogeneity. In real-world batteries, the electrode could deform upon battery operation, causing challenges for the image registration which is necessary for several experimental modalities, e.g. XANES imaging. To address this challenge, this work develops a deep-learning-based method for automatic particle identification and tracking. This approach was not only able to facilitate image registration with good robustness but also allowed quantification of the degree of sample deformation. The effectiveness of the method was first demonstrated using synthetic datasets with known ground truth. The method was then applied to an experimental dataset collected on an operating lithium battery cell, revealing a high degree of intra- and interparticle chemical complexity in operating batteries.

Nanoscale chemical imaging with structured X-ray illumination

High-resolution imaging with compositional and chemical sensitivity is crucial for a wide range of scientific and engineering disciplines. Although synchrotron X-ray imaging through spectromicroscopy has been tremendously successful and broadly applied, it encounters challenges in achieving enhanced detection sensitivity, satisfactory spatial resolution, and high experimental throughput simultaneously. In this work, based on structured illumination, we develop a single-pixel X-ray imaging approach coupled with a generative image reconstruction model for mapping the compositional heterogeneity with nanoscale resolvability. This method integrates a full-field transmission X-ray microscope with an X-ray fluorescence detector and eliminates the need for nanoscale X-ray focusing and raster scanning. We experimentally demonstrate the effectiveness of our approach by imaging a battery sample composed of mixed cathode materials and successfully retrieving the compositional variations of the imaged cathode particles. Bridging the gap between structural and chemical characterizations using X-rays, this technique opens up vast opportunities in the fields of biology, environmental, and materials science, especially for radiation-sensitive samples.

Fundamentals, status and challenges of direct recycling technologies for lithium ion batteries

Advancement in energy storage technologies is closely related to social development. However, a significant conflict has arisen between the explosive growth in battery demand and resource availability. Facing the upcoming large-scale disposal problem of spent lithium-ion batteries (LIBs), their recycling technology development has become key. Emerging direct recycling has attracted widespread attention in recent years because it aims to 'repair' the battery materials, rather than break them down and extract valuable products from their components. To achieve this goal, a profound understanding of the failure mechanisms of spent LIB electrode materials is essential. This review summarizes the failure mechanisms of LIB cathode and anode materials and the direct recycling strategies developed. We systematically explore the correlation between the failure mechanism and the required repair process to achieve efficient and even upcycling of spent LIB electrode materials. Furthermore, we systematically introduce advanced in situ characterization techniques that can be utilized for investigating direct recycling processes. We then compare different direct recycling strategies, focussing on their respective advantages and disadvantages and their applicability to different materials. It is our belief that this review will offer valuable guidelines for the design and selection of LIB direct recycling methods in future endeavors. Finally, the opportunities and challenges for the future of battery direct recycling technology are discussed, paving the way for its further development.

X-ray ptychographic and fluorescence microscopy using virtual single-pixel imaging based deconvolution with accurate probe images

Simultaneous measurement of X-ray ptychography and fluorescence microscopy allows high-resolution and high-sensitivity observations of the microstructure and trace-element distribution of a sample. In this paper, we propose a method for improving scanning fluorescence X-ray microscopy (SFXM) images, in which the SFXM image is deconvolved via virtual single-pixel imaging using different probe images for each scanning point obtained by X-ray ptychographic reconstruction. Numerical simulations confirmed that this method can increase the spatial resolution while suppressing artifacts caused by probe imprecision, e.g., probe position errors and wavefront changes. The method also worked well in synchrotron radiation experiments to increase the spatial resolution and was applied to the observation of S element maps of ZnS particles.

Nanoscale heterogeneity of arsenic and selenium species in coal fly ash particles: analysis using enhanced spectroscopic imaging and speciation techniques

Coal combustion byproducts are known to be enriched in arsenic (As) and selenium (Se). This enrichment is a concern during the handling, disposal, and reuse of the ash as both elements can be harmful to wildlife and humans if mobilized into water and soils. The leaching potential and bioaccessibility of As and Se in coal fly ash depends on the chemical forms of these elements and their association with the large variety of particles that comprise coal fly ash. The overall goal of this research was to determine nanoscale and microscale solid phase mineral associations and oxidation states of As and Se in fly ash. We utilized nanoscale 2D imaging (30-50 nm spot size) with the Hard X-ray Nanoprobe (HXN) in combination with microprobe X-ray capabilities (∼5 μm resolution) to determine the As and Se elemental associations. Speciation of As and Se was also measured at the nano- to microscale with X-ray absorption spectroscopy. The enhanced resolution of HXN showed As and Se as either diffusely located around or comingled with Ca- and Fe-rich particles. The results also showed nanoparticles of Se attached to the surface of fly ash grains. Overall, a comparison of As and Se species across scales highlights the heterogeneity and complexity of chemical associations for these trace elements of concern in coal fly ash.

Self-absorption correction on 2D X-ray fluorescence maps

X-ray fluorescence mapping (XRF) is a highly efficient and non-invasive technique for quantifying material composition with micro and nanoscale spatial resolutions. Quantitative XRF analysis, however, confronts challenges from the long-lasting problem called self-absorption. Moreover, correcting two-dimensional XRF mapping datasets is particularly difficult because it is an ill-posed inverse problem. Here we report a semi-empirical method that can effectively correct 2D XRF mapping data. The correction error is generally less than 10% from a comprehensive evaluation of the accuracy in various configurations. The proposed method was applied to quantify the composition distribution around the grain boundaries in an electrochemically corroded stainless steel sample. Highly localized Cr enrichment was found around the crack sites, which was invisible before the absorption correction.

A Critical Review on the Recycling Strategy of Lithium Iron Phosphate from Electric Vehicles

Electric vehicles (EVs) are one of the most promising decarbonization solutions to develop a carbon-negative economy. The increasing global storage of EVs brings out a large number of power batteries requiring recycling. Lithium iron phosphate (LFP) is one of the first commercialized cathodes used in early EVs, and now gravimetric energy density improvement makes LFP with low cost and robustness popular again in the market. Developments in LFP recycling techniques are in demand to manage a large portion of the EV batteries retired both today and around ten years later. In this review, first the operation and degradation mechanisms of LFP are revisited aiming to identify entry points for LFP recycling. Then, the current LFP recycling methods, from the pretreatment of the retired batteries to the regeneration and recovery of the LFP cathode are summarized. The emerging direct recovery technology is highlighted, through which both raw material and the production cost of LFP can be recovered. In addition, the current issues limiting the development of the LIBs recycling industry are presented and some ideas for future research are proposed. This review provides the theoretical basis and insightful perspectives on developing new recycling strategies by outlining the whole-life process of LFP.

Nanoscale 3D Tomography by In-Flight Fluorescence Spectroscopy of Atoms Sputtered by a Focused Ion Beam

Nanoscale fabrication and characterization techniques critically underpin a vast range of fields, including nanoelectronics and nanobiotechnology. Focused ion beam (FIB) techniques are appealing due to their high spatial resolution and widespread use for processing of nanostructured materials. Here, we introduce FIB-induced fluorescence spectroscopy (FIB-FS) as a nanoscale technique for spectroscopic detection of atoms sputtered by an ion beam. We use semiconductor heterostructures to demonstrate nanoscale lateral and depth resolution and show that it is limited by ion-induced intermixing of nanostructured materials. Sensitivity is demonstrated qualitatively by depth profiling of 3.5, 5, and 8 nm quantum wells and quantitatively by detection of trace-level impurities present at parts-per-million levels. The utility of the FIB-FS technique is demonstrated by characterization of quantum wells and Li-ion batteries. Our work introduces FIB-FS as a high-resolution, high-sensitivity, 3D analysis and tomography technique that combines the versatility of FIB nanofabrication techniques with the power of diffraction-unlimited fluorescence spectroscopy.

Multimodal X-ray nano-spectromicroscopy analysis of chemically heterogeneous systems

Understanding the nanoscale chemical speciation of heterogeneous systems in their native environment is critical for several disciplines such as life and environmental sciences, biogeochemistry, and materials science. Synchrotron-based X-ray spectromicroscopy tools are widely used to understand the chemistry and morphology of complex material systems owing to their high penetration depth and sensitivity. The multidimensional (4D+) structure of spectromicroscopy data poses visualization and data-reduction challenges. This paper reports the strategies for the visualization and analysis of spectromicroscopy data. We created a new graphical user interface and data analysis platform named XMIDAS (X-ray multimodal image data analysis software) to visualize spectromicroscopy data from both image and spectrum representations. The interactive data analysis toolkit combined conventional analysis methods with well-established machine learning classification algorithms (e.g. nonnegative matrix factorization) for data reduction. The data visualization and analysis methodologies were then defined and optimized using a model particle aggregate with known chemical composition. Nanoprobe-based X-ray fluorescence (nano-XRF) and X-ray absorption near edge structure (nano-XANES) spectromicroscopy techniques were used to probe elemental and chemical state information of the aggregate sample. We illustrated the complete chemical speciation methodology of the model particle by using XMIDAS. Next, we demonstrated the application of this approach in detecting and characterizing nanoparticles associated with alveolar macrophages. Our multimodal approach combining nano-XRF, nano-XANES, and differential phase-contrast imaging efficiently visualizes the chemistry of localized nanostructure with the morphology. We believe that the optimized data-reduction strategies and tool development will facilitate the analysis of complex biological and environmental samples using X-ray spectromicroscopy techniques.

Absolute EUV reflectivity measurements using a broadband high-harmonic source and an in situ single exposure reference scheme

We present a tabletop setup for extreme ultraviolet (EUV) reflection spectroscopy in the spectral range from 40 to 100 eV by using high-harmonic radiation. The simultaneous measurements of reference and sample spectra with high energy resolution provide precise and robust absolute reflectivity measurements, even when operating with spectrally fluctuating EUV sources. The stability and sensitivity of EUV reflectivity measurements are crucial factors for many applications in attosecond science, EUV spectroscopy, and nano-scale tomography. We show that the accuracy and stability of our in situ referencing scheme are almost one order of magnitude better in comparison to subsequent reference measurements. We demonstrate the performance of the setup by reflective near-edge x-ray absorption fine structure measurements of the aluminum L_2/3 absorption edge in α-Al₂O₃ and compare the results to synchrotron measurements.

Multimodal X-ray probe station at 9C beamline of Pohang Light Source-II

In this study, the conceptual design and performance of a multimodal X-ray probe station recently installed at the 9C coherent X-ray scattering beamline of the Pohang Light Source-II are presented. The purpose of this apparatus is to measure coherent X-ray diffraction, X-ray fluorescence and electrical properties simultaneously. A miniature vacuum probe station equipped with a four-point probe was mounted on a six-axis motion hexapod. This can be used to study the structural and chemical evolution of thin films or nanostructures, as well as device performance including electronic transport properties. This probe station also provides the capability of varying sample environments such as gas atmosphere using a mass-flow-control system and sample temperatures up to 600°C using a pyrolytic boron nitride heater. The in situ annealing of ZnO thin films and the performance of ZnO nanostructure-based X-ray photodetectors are discussed. These results demonstrate that a multimodal X-ray probe station can be used for performing in situ and operando experiments to investigate structural phase transitions involving electrical resistivity switching.

Dose-efficient multimodal microscopy of human tissue at a hard X-ray nanoprobe beamline

X-ray fluorescence microscopy performed at nanofocusing synchrotron beamlines produces quantitative elemental distribution maps at unprecedented resolution (down to a few tens of nanometres), at the expense of relatively long measuring times and high absorbed doses. In this work, a method was implemented in which fast low-dose in-line holography was used to produce quantitative electron density maps at the mesoscale prior to nanoscale X-ray fluorescence acquisition. These maps ensure more efficient fluorescence scans and the reduction of the total absorbed dose, often relevant for radiation-sensitive (e.g. biological) samples. This multimodal microscopy approach was demonstrated on human sural nerve tissue. The two imaging modes provide complementary information at a comparable resolution, ultimately limited by the focal spot size. The experimental setup presented allows the user to swap between them in a flexible and reproducible fashion, as well as to easily adapt the scanning parameters during an experiment to fine-tune resolution and field of view.

Exploring spectroscopic X-ray nano-imaging with Zernike phase contrast enhancement

Spectroscopic full-field transmission X-ray microscopy (TXM-XANES), which offers electrochemical imaging with a spatial resolution of tens of nanometers, is an extensively used unique technique in battery research. However, absorption-based bright-field imaging has poor detection sensitivity for nanoscale applications. Here, to improve the sensitivity, we explored spectroscopic X-ray nano imaging with Zernike phase contrast (ZPC-XANES). A pinhole-type Zernike phase plate, which was optimized for high-contrast images with minimal artifacts, was used in this study. When the absorption is weak, the Zernike phase contrast improves the signal-to-noise ratio and the contrast of images at all energies, which induces the enhancement of the absorption edge step. We estimated that the absorption of the samples should be higher than 2.2% for reliable spectroscopic nano-imaging based on XANES spectroscopy analysis of a custom-made copper wedge sample. We also determined that there is a slight absorption peak shift and sharpening in a small absorption sample due to the inflection point of the refractive index at the absorption edge. Nevertheless, in the case of sub-micron sized cathode materials, we believe that better contrast and higher resolution spectroscopic images can be obtained using ZPC-XANES.

Quantitative hyperspectral coherent diffractive imaging spectroscopy of a solid-state phase transition in vanadium dioxide

Solid-state systems can host a variety of thermodynamic phases that can be controlled with magnetic fields, strain, or laser excitation. Many phases that are believed to exhibit exotic properties only exist on the nanoscale, coexisting with other phases that make them challenging to study, as measurements require both nanometer spatial resolution and spectroscopic information, which are not easily accessible with traditional x-ray spectromicroscopy techniques. Here, we use coherent diffractive imaging spectroscopy (CDIS) to acquire quantitative hyperspectral images of the prototypical quantum material vanadium oxide across the vanadium L 2,3 and oxygen K x-ray absorption edges with nanometer-scale resolution. We extract the full complex refractive indices of the monoclinic insulating and rutile conducting phases of VO2 from a single sample and find no evidence for correlation-driven phase transitions. CDIS will enable quantitative full-field x-ray spectromicroscopy for studying phase separation in time-resolved experiments and other extreme sample environments where other methods cannot operate.

Micromachined Silicon Platform for Precise Assembly of 2D Multilayer Laue Lenses for High-Resolution X-ray Microscopy

We report on a developed micromachined silicon platform for the precise assembly of 2D multilayer Laue lenses (MLLs) for high-resolution X-ray microscopy. The platform is 10 × 10 mm2 and is fabricated on ~500 µm thick silicon wafers through multiple steps of photolithography and deep reactive-ion etching. The platform accommodates two linear MLLs in a pre-defined configuration with precise angular and lateral position control. In this work, we discuss the design and microfabrication of the platform, and characterization regarding MLLs assembly, position control, repeatability, and stability. The results demonstrate that a micromachined platform can be used for the assembly of a variety of MLLs with different dimensions and optical parameters. The angular misalignment of 2D MLLs is well controlled in the range of the designed accuracy, down to a few millidegrees. The separation distance between MLLs is adjustable from hundreds to more than one thousand micrometers. The use of the developed platform greatly simplifies the alignment procedure of the MLL optics and reduces the complexity of the X-ray microscope. It is a significant step forward for the development of monolithic 2D MLL nanofocusing optics for high-resolution X-ray microscopy.