Construction of the Scanning Transmission X-ray Microscope Beamline at UVSOR

Chemical-state distributions in charged LiCoO2 cathode particles visualized by soft X-ray spectromicroscopy

Lithium-ion deintercalation/intercalation during charge/discharge processes is one of the essential reactions that occur in the layered cathodes of lithium-ion batteries, and the performance of the cathode can be expressed as the sum of the reactions that occur in the local area of the individual cathode particles. In this study, the spatial distributions of the chemical states present in prototypical layered LiCoO₂ cathode particles were determined at different charging conditions using scanning transmission X-ray microscopy (STXM) with a spatial resolution of approximately 100 nm. The Co L₃- and O K-edge X-ray absorption spectroscopy (XAS) spectra, extracted from the same area of the corresponding STXM images, at the initial state as well as after charging to 4.5 V demonstrate the spatial distribution of the chemical state changes depending on individual particles. In addition to the Co L₃-edge XAS spectra, the O K-edge XAS spectra of the initial and charged LiCoO₂ particles are different, indicating that both the Co and O sites participate in charge compensation during the charging process possibly through the hybridization between the Co 3d and O 2p orbitals. Furthermore, the element maps of both the Co and O sites, derived from the STXM stack images, reveal the spatial distribution of the chemical states inside individual particles after charging to 4.5 V. The element mapping analysis suggests that inhomogeneous reactions occur on the active particles and confirm the existence of non-active particles. The results of this study demonstrate that an STXM-based spatially resolved electronic structural analysis method is useful for understanding the charging and discharging of battery materials.

Soft X-ray Fluorescence and Near-Edge Absorption Microscopy for Investigating Metabolic Features in Biological Systems: A Review

Scanning transmission X-ray microscopy (STXM) provides the imaging of biological specimens allowing the parallel collection of localized spectroscopic information by X-ray fluorescence (XRF) and/or X-ray Absorption Near Edge Spectroscopy (XANES). The complex metabolic mechanisms which can take place in biological systems can be explored by these techniques by tracing even small quantities of the chemical elements involved in the metabolic pathways. Here, we present a review of the most recent publications in the synchrotrons' scenario where soft X-ray spectro-microscopy has been employed in life science as well as in environmental research.

Redox Reaction in Ti-Mn Redox Flow Battery Studied by X-ray Absorption Spectroscopy

We performed X-ray absorption studies for the electrolytes of a Ti-Mn redox flow battery (RFB) to understand the redox reaction of the Ti/Mn ions and formation of precipitates in charged catholyte, because suppression of the disproportionation reaction is a key to improve the cyclability of Ti-Mn RFB and enhance the energy density. Hard X-ray absorption spectroscopy with a high transmittance and soft X-ray absorption spectroscopy to directly observe the 3d orbitals were complementarily employed. Moreover, the Ti/Mn 3d electronic structure for each precipitate and solution in the charged catholyte was investigated by using scanning transmission X-ray microscopy: the valence of Mn in the precipitate is mostly attributed to 4+, and the solution includes only Mn²⁺ . This charge disproportionation reaction should occur after the Mn ions in the catholyte should be oxidized from Mn²⁺ to Mn³⁺ by charge.

One-Year In Situ Incubation of Pyrite at the Deep Seafloor and Its Microbiological and Biogeochemical Characterizations

In this study, we performed a year-long in situ incubation experiment on a common ferrous sulfide (Fe-S) mineral, pyrite, at the oxidative deep seafloor in the hydrothermal vent field in the Izu-Bonin arc, Japan, and characterized its microbiological and biogeochemical properties to understand the microbial alteration processes of the pyrite, focusing on Fe(II) oxidation. The microbial community analysis of the incubated pyrite showed that the domain Bacteria heavily dominated over Archaea compared with that of the ambient seawater, and Alphaproteobacteria and Gammaproteobacteria distinctively codominated at the class level. The mineralogical characterization by surface-sensitive Fe X-ray absorption near-edge structure (XANES) analysis revealed that specific Fe(III) hydroxides (schwertmannite and ferrihydrite) were locally formed at the pyrite surface as the pyrite alteration products. Based on the Fe(III) hydroxide species and proportion, we thermodynamically calculated the pH value at the pyrite surface to be pH 4.9 to 5.7, indicating that the acidic condition derived from pyrite alteration was locally formed at the surface against neutral ambient seawater. This acidic microenvironment at the pyrite surface might explain the distinct microbial communities found in our pyrite samples. Also, the acidity at the pyrite surface indicates that the abiotic Fe(II) oxidation rate was much limited at the pyrite surface kinetically, 3.9 × 103- to 1.6 × 105-fold lower than that in the ambient seawater. Moreover, nanoscale characterization of microbial biomolecules using carbon near-edge X-ray absorption fine-structure (NEXAFS) analysis showed that the sessile cells attached to pyrite excreted the acidic polysaccharide-rich extracellular polymeric substances at the pyrite surface, which can lead to the promotion of biogenic Fe(II) oxidation and pyrite alteration. IMPORTANCE Pyrite is one of the most common Fe-S minerals found in submarine hydrothermal environments. Previous studies demonstrated that the Fe-S mineral can be a suitable host for Fe(II)-oxidizing microbes in hydrothermal environments; however, the details of microbial Fe(II) oxidation processes with Fe-S mineral alteration are not well known. The spectroscopic and thermodynamic examination in the present study suggests that a moderately acidic pH condition was locally formed at the pyrite surface during pyrite alteration at the seafloor due to proton releases with Fe(II) and sulfidic S oxidations. Following previous studies, the abiotic Fe(II) oxidation rate significantly decreases with a decrease in pH, but the biotic (microbial) Fe(II) oxidation rate is not sensitive to the pH decrease. Thus, our findings clearly suggest that the pyrite surface is a unique microenvironment where abiotic Fe(II) oxidation is limited and biotic Fe(II) oxidation is more prominent than that in neutral ambient seawater.

Improved Skin Permeability after Topical Treatment with Serine Protease: Probing the Penetration of Rapamycin by Scanning Transmission X-ray Microscopy

Drug penetration in human skin ex vivo following a modification of skin barrier permeability is systematically investigated by scanning transmission X-ray microscopy. Element-selective excitation is used in the O 1s regime for probing quantitatively the penetration of topically applied rapamycin in different formulations with a spatial resolution reaching <75 nm. The data were analyzed by a comparison of two methods: (i) two-photon energies employing the Beer-Lambert law and (ii) a singular value decomposition approach making use of the full spectral information in each pixel of the X-ray micrographs. The latter approach yields local drug concentrations more reliably and sensitively probed than the former. The present results from both approaches indicate that rapamycin is not observed within the stratum corneum of nontreated skin ex vivo, providing evidence for the observation that this high-molecular-weight drug inefficiently penetrates intact skin. However, rapamycin is observed to penetrate more efficiently the stratum corneum when modifications of the skin barrier are induced by the topical pretreatment with the serine protease trypsin for variable time periods ranging from 2 to 16 h. After the longest exposure time to serine protease, the drug is even found in the viable epidermis. High-resolution micrographs indicate that the lipophilic drug preferably associates with corneocytes, while signals found in the intercellular lipid compartment were less pronounced. This result is discussed in comparison to previous work obtained from low-molecular-weight lipophilic drugs as well as polymer nanocarriers, which were found to penetrate the intact stratum corneum exclusively via the lipid layers between the corneocytes. Also, the role of the tight junction barrier in the stratum granulosum is briefly discussed with respect to modifications of the skin barrier induced by enhanced serine protease activity, a phenomenon of clinical relevance in a range of inflammatory skin disorders.

A low-pass filtering Fresnel zone plate for soft x-ray microscopic analysis down to the lithium K-edge region

We have designed a new low-pass Fresnel zone plate (LPFZP) to extend soft x-ray absorption spectroscopy (XAS) to the lithium K absorption edge in a scanning transmission x-ray microscope (STXM). The performance of the LPFZP was evaluated in the STXM beamline at the UVSOR-III Synchrotron (Okazaki, Japan); the contribution of the higher-order harmonics is successfully suppressed to 0.1% of the fundamental energy, and a spatial resolution of 72 nm and an energy resolution (E/∆E) above 1000 are achieved as expected. XAS spectra of lithium are measured successfully in an electrode of a lithium-ion battery.

Lignans in Knotwood of Norway Spruce: Localisation with Soft X-ray Microscopy and Scanning Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy

Lignans are bioactive compounds that are especially abundant in the Norway spruce (Picea abies L. Karst.) knotwood. By combining a variety of chromatographic, spectroscopic and imaging techniques, we were able to quantify, qualify and localise the easily extractable lignans in the xylem tissue. The knotwood samples contained 15 different lignans according to the gas chromatography-mass spectrometry analysis. They comprised 16% of the knotwood dry weight and 82% of the acetone extract. The main lignans were found to be hydroxymatairesinols HMR1 and HMR2. Cryosectioned and resin-embedded ultrathin sections of the knotwood were analysed with scanning transmission X-ray microscopy (STXM). Cryosectioning was found to retain only lignan residues inside the cell lumina. In the resin-embedded samples, lignan was interpreted to be unevenly distributed inside the cell lumina, and partially confined in deposits which were either readily present in the lumina or formed when OsO₄ used in staining reacted with the lignans. Furthermore, the multi-technique characterisation enabled us to obtain information on the chemical composition of the structural components of knotwood. A simple spectral analysis of the STXM data gave consistent results with the gas chromatographic methods about the relative amounts of cell wall components (lignin and polysaccharides). The STXM analysis also indicated that a torus of a bordered pit contained aromatic compounds, possibly lignin.

Spatially Resolved Distribution of Fe Species around Microbes at the Submicron Scale in Natural Bacteriogenic Iron Oxides

Natural bacteriogenic iron oxides (BIOS) were investigated using local-analyzable synchrotron-based scanning transmission X-ray microscopy (STXM) with a submicron-scale resolution. Cell, cell sheath interface (EPS), and sheath in the BIOS were clearly depicted using C-, N-, and O- near edge X-ray absorption fine structure (NEXAFS) obtained through STXM measurements. Fe-NEXAFS obtained from different regions of BIOS indicated that the most dominant iron mineral species was ferrihydrite. Fe(II)- and/or Fe(III)-acidic polysaccharides accompanied ferrihydrite near the cell and EPS regions. Our STXM/NEXAFS analysis showed that Fe species change continuously between the cell, EPS, and sheath under several 10-nm scales.

Direct Detection of Fe(II) in Extracellular Polymeric Substances (EPS) at the Mineral-Microbe Interface in Bacterial Pyrite Leaching

We herein investigated the mechanisms underlying the contact leaching process in pyrite bioleaching by Acidithiobacillus ferrooxidans using scanning transmission X-ray microscopy (STXM)-based C and Fe near edge X-ray absorption fine structure (NEXAFS) analyses. The C NEXAFS analysis directly showed that attached A. ferrooxidans produces polysaccharide-abundant extracellular polymeric substances (EPS) at the cell-pyrite interface. Furthermore, by combining the C and Fe NEXAFS results, we detected significant amounts of Fe(II), in addition to Fe(III), in the interfacial EPS at the cell-pyrite interface. A probable explanation for the Fe(II) in detected EPS is the leaching of Fe(II) from the pyrite. The detection of Fe(II) also indicates that Fe(III) resulting from pyrite oxidation may effectively function as an oxidizing agent for pyrite at the cell-pyrite interface. Thus, our results imply that a key role of Fe(III) in EPS, in addition to its previously described role in the electrostatic attachment of the cell to pyrite, is enhancing pyrite dissolution.

Design and performance of a compact scanning transmission X-ray microscope at the Photon Factory

We present a new compact instrument designed for scanning transmission X-ray microscopy. It has piezo-driven linear stages, making it small and light. Optical components from the virtual source point to the detector are located on a single optical table, resulting in a portable instrument that can be operated at a general-purpose spectroscopy beamline without requiring any major reconstruction. Careful consideration has been given to solving the vibration problem common to high-resolution microscopy, so as not to affect the spatial resolution determined by the Fresnel zone plate. Results on bacteriogenic iron oxides, single particle aerosols, and rare-earth permanent magnets are presented as examples of its performance under diverse applications.