Nanoscale determination of interatomic distance by ptychography-EXAFS method using advanced Kirkpatrick-Baez mirror focusing optics

Nanoscale domain imaging of Li-rich disordered rocksalt-type cathode materials with X-ray spectroscopic ptychography

Lithium-rich disordered rocksalt-type cathode materials are promising for high-capacity and high-power lithium-ion batteries. Many of them are synthesized by mechanical milling and may have heterogeneous structures and chemical states at the nanoscale. In this study, we performed X-ray spectroscopic ptychography measurements of Li-rich disordered rocksalt-type oxide particles synthesized by mechanical milling before and after delithiation reaction at the vanadium K absorption edge, and visualized their structures and chemical state with a spatial resolution of ∼100 nm. We classified multiple domains with different chemical states via clustering analysis. A comparison of the domain distribution trends of the particles before and after the delithiation reaction revealed the presence of domains, suggesting that the delithiation reaction was suppressed.

Method for restoration of X-ray absorption fine structure in sparse spectroscopic ptychography

The spectroscopic ptychography method, a technique combining X-ray ptychography imaging and X-ray absorption spectroscopy, is one of the most promising and powerful tools for studying the chemical states and morphological structures of bulk materials at high resolutions. However, this technique still requires long measurement periods because of insufficient coherent X-ray intensity. Although the improvements in hardware represent a critical solution, breakthroughs in software for experiments and analyses are also required. This paper proposes a novel method for restoring the spectrum structures from spectroscopic ptychography measurements with reduced energy points, by utilizing the Kramers–Kronig relationship. First, a numerical simulation is performed of the spectrum restoration for the extended X-ray absorption fine structure (EXAFS) oscillation from the thinned theoretical absorption and phase spectra. Then, this algorithm is extended by binning the noise removal to handle actual experimental spectral data. Spectrum restoration for the experimental EXAFS data obtained from spectroscopic ptychography measurements is also successfully demonstrated. The proposed restoration will help shorten the time required for spectroscopic ptychography single measurements and increase the throughput of the entire experiment under limited time resources.

Phase retrieval based on a total-variation-regularized Poisson model for X-ray ptychographic imaging of low-contrast objects

Hard X-ray ptychography has become an indispensable tool for observing the microscopic structure of a thick specimen. It measures diffraction patterns by scanning an X-ray beam and visualizes the complex-valued refractive index of the specimen by a computational reconstruction called phase retrieval. The quality of imaging is dependent on the used phase-retrieval algorithm, especially when the intensity of the diffraction patterns in the high-spatial-frequency range is low and/or when the spatial overlap of the illumination area is small. In this paper, a phase-retrieval algorithm, AMPAM, based on the Poisson model and total variation (TV) is proposed. It applies alternating minimization using primal-dual splitting and gradient-descent algorithms to compute the result without matrix inversion. The imaging capability of the proposed algorithm from low-dose and/or sparsely scanned data was investigated by numerical simulations. The proposed algorithm was compared with ADPr, which is the state-of-the-art algorithm based on the TV-regularized Poisson model. The results indicated that AMPAM can provide good-quality images with a computational cost 7–11 times less than ADPr. In addition, ink toner and macroporous silica particles were imaged at SPring-8 BL24XU to confirm the applicability of the algorithm to actual measurements.

X-ray Spectroptychography

X-ray spectroptychography is an emerging method for the chemical microanalysis of advanced nanomaterials such as catalysts and batteries. This method builds upon established synchrotron X-ray microscopy and spectromicroscopy techniques with added spatial resolution from ptychography, an algorithmic imaging technique. This minireview will introduce the technique of X-ray spectroptychography, where ptychography is performed with variable photon energy, and discuss recent results and prospects for this method.

Visualization of Structural Heterogeneities in Particles of Lithium Nickel Manganese Oxide Cathode Materials by Ptychographic X-ray Absorption Fine Structure

A heterogeneous phase/structure distribution in the bulk of spinel lithium nickel manganese oxides (LNMOs) is the key to maximizing the performance and stability of the cathode materials of lithium-ion batteries. Herein, we report the use of two-dimensional ptychographic X-ray absorption fine structure (XAFS) to visualize the density and valence maps of manganese and nickel in as-prepared LNMO particles and unsupervised learning to classify the three-phase group in terms of different elemental compositions and chemical states. The described approach may increase the supply of information for nanoscale characterization and promote the design of suitable structural domains to maximize the performance and stability of batteries.