Transmission X-ray Microscopy Research Articles

Characterizing porous microaggregates and soil organic matter sequestered in allophanic paleosols on Holocene tephras using synchrotron-based X-ray microscopy and spectroscopy

Allophanic tephra-derived soils can sequester sizable quantities of soil organic matter (SOM). However, no studies have visualized the fine internal porous structure of allophanic soil microaggregates, nor studied the carbon structure preserved in such soils or paleosols. We used synchrotron radiation-based transmission X-ray microscopy (TXM) to perform 3D-tomography of the internal porous structure of dominantly allophanic soil microaggregates, and carbon near-edge X-ray absorption fine-structure (C NEXAFS) spectroscopy to characterize SOM in ≤ 12,000-year-old tephra-derived allophane-rich (with minor ferrihydrite) paleosols. The TXM tomography showed a vast network of internal, tortuous nano-pores within an allophanic microaggregate comprising nanoaggregates. SOM in the allophanic paleosols at four sites was dominated by carboxylic/carbonyl functional groups with subordinate quinonic, aromatic, and aliphatic groups. All samples exhibited similar compositions despite differences between the sites. That the SOM does not comprise specific types of functional groups through time implies that the functional groups are relict. The SOM originated at the land/soil surface: ongoing tephra deposition (intermittently or abruptly) then caused the land-surface to rise so that the once-surface horizons were buried more deeply and hence became increasingly isolated from inputs by the surficial/modern organic cycle. The presence of quinonic carbon, from biological processes but vulnerable to oxygen and light, indicates the exceptional protection of SOM and bio-signals in allophanic paleosols, attributable both to the porous allophane (with ferrihydrite) aggregates that occlude the relict SOM from degradation, and to rapid burial by successive tephra-fallout, as well as strong Al-organic chemical bonding. TXM and C NEXAFS spectroscopy help to unravel the fine structure of soils and SOM and are of great potential for soil science studies.

Nrf2 attenuates ferroptosis-mediated IIR-ALI by modulating TERT and SLC7A11

Acute lung injury (ALI) carries a mortality rate of ~50% and is a hot topic in the world of critical illness research. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a critical modulator of intracellular oxidative homeostasis and serves as an antioxidant. The Nrf2-related anti-oxidative stress is strongly associated with ferroptosis suppression. Meanwhile, telomerase reverse transcriptase (TERT), the catalytic portion of the telomerase protein, is reported to travel to the mitochondria to alleviate ROS. In our study, we found that TERT was significantly reduced in lung tissue of Nrf2−/− mice in the model of intestinal ischemia/reperfusion-induced acute lung injury (IIR-ALI). In addition, MDA levels showed marked increase, whereas GSH and GPX4 levels fell drastically in ALI models. Moreover, typical-related structural changes were observed in the type II alveolar epithelial cells in the IIR model. We further employed the scanning transmission X-ray microscopy (STXM) to examine Fe levels and distribution within cells. Based on our observations, massive aggregates of Fe were found in the MLE-12 cells upon OGD/R (oxygen and glucose deprivation/reperfusion) induction. Additionally, Nrf2 silencing dramatically reduced TERT and SLC7A11 levels, and further exacerbated cellular injuries. In contrast, TERT-overexpressing cells exhibited marked elevation in SLC7A11 levels and thereby inhibited ferroptosis. Collectively, these data suggest that Nrf2 can negatively regulate ferroptosis via modulation of TERT and SLC7A11 levels. The conclusion from this study brings insight into new candidates that can be targeted in future IIR-ALI therapy.

2D-to-3D image translation of complex nanoporous volumes using generative networks

Image-based characterization offers a powerful approach to studying geological porous media at the nanoscale and images are critical to understanding reactive transport mechanisms in reservoirs relevant to energy and sustainability technologies such as carbon sequestration, subsurface hydrogen storage, and natural gas recovery. Nanoimaging presents a trade off, however, between higher-contrast sample-destructive and lower-contrast sample-preserving imaging modalities. Furthermore, high-contrast imaging modalities often acquire only 2D images, while 3D volumes are needed to characterize fully a source rock sample. In this work, we present deep learning image translation models to predict high-contrast focused ion beam-scanning electron microscopy (FIB-SEM) image volumes from transmission X-ray microscopy (TXM) images when only 2D paired training data is available. We introduce a regularization method for improving 3D volume generation from 2D-to-2D deep learning image models and apply this approach to translate 3D TXM volumes to FIB-SEM fidelity. We then segment a predicted FIB-SEM volume into a flow simulation domain and calculate the sample apparent permeability using a lattice Boltzmann method (LBM) technique. Results show that our image translation approach produces simulation domains suitable for flow visualization and allows for accurate characterization of petrophysical properties from non-destructive imaging data.

Understanding Degradation Onset in High Temperature Electrolysis Cells with Transmission X-Ray Microscopy

High temperature electrolysis (HTE) cells struggle to reach lifetimes in the thousands of hours for hydrogen production from steam. While oxygen-conducting solid oxide electrolysis cells (o-SOECs) are a more mature technology than proton-conducting (p-SOECs) counterparts, both types of cell suffer from multiple decomposition modes including: delamination of layers, atomic migration, secondary phase formation, and reaction at the triple-phase boundaries at the electrodes. While the macroscopic results of these decomposition modes have been reported, the mechanisms driving onset and evolution of these decomposition modes is not well understood. In this work, we report on the results of a collaborative effort between four national laboratories to investigate the onset of decomposition in aged HTE cells using transmission X-ray microscopy (TXM) at SSRL at SLAC of o-SOEC and p-SOEC cells. Using TXM we volumetrically image, in 3D, the density of aged cells with 30 nm x 30 nm x 30 nm voxel (3D pixel) resolution. Using this technique, we investigate the nucleation of interfacial voids and the near-environment around those voids; revealing insight into the mechanism driving void formation. SSRL’s TXM also enables the use of X-ray absorption near edge structure (XANES) measurements at each voxel, which yields stoichiometric and oxidation state maps of key elements. This XANES data, combined with TXM, allows identification of how elemental migration, and oxidation state changes, drive the formation of voids. Similarly, the evolution of the triple-phase boundaries at the electrodes is investigated using a combination of TXM and XANES. Together, this work demonstrates a powerful technique for investigating the onset and evolution of decomposition in a range of HTE cells.

High-Performance LiNi0.8Mn0.1Co0.1O2 Cathodes By Atomic-Layer-Deposited Sulfide Coatings

Due to its higher capacity compared to the commercialized LiNixMnyCo1-x-yO2 (NMCs, 0< x, y <1) with lower Ni content (x≤0.6), LiNi0.8Mn0.1Co0.1O2 (NMC811) is now considered as the next promising cathode for lithium-ion batteries (LIBs). However, it still suffers from more serious performance degradation and safety hazard than the commercial ones. These existing issues are reflected as cation mixing, oxygen evolution, irreversible phase-transition, transition metal ion dissolution, and microcracking. Aimed at addressing these problems, surface coating has proven to be an important and effective approach. In recent years, atomic layer deposition (ALD) has emerged as an accurate tool to apply uniform and conformal coatings over NMCs at the atomic level, which have shown remarkable effects on the improved performance of batteries.1-4 Herein, for the first time we deposited ultrathin ALD Li2S coatings5 conformally over NMC811 composite electrodes. It was found that the ALD Li2S coatings enable to enhance performance of NMC811 cathodes with much better cyclability and rate capability. To clarify the effects of the ALD Li2S coatings, we utilized a suite of characterization tools including X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, and transmission X-ray microscopy. The results revealed that the ALD Li2S coatings can perfectly maintain the NMC structure during cycling, thus significantly suppress the crack formation. Furthermore, the Li2S layer can react with and eliminate H2O in electrolyte and O2 released from the NMC structure. In addition, the measurements of electrochemical impedance spectroscopy were applied, which confirms that the Li2S coatings serve as physical protection layers to prevent the interfacial reactions between the NMC cathode and liquid electrolyte. It can be foreseen that sulfides would be a new class of coating materials for addressing issues of NMC cathodes.1. Meng, X.; Yang, X. Q.; Sun, X. L., Advanced Materials 2012, 24 (27), 3589-3615.2. Liu, Y.; Wang, X.; Cai, J.; Han, X.; Geng, D.; Li, J.; Meng, X., Journal of Materials Science & Technology 2020, 54, 77-86.3. Wang, X.; Cai, J.; Liu, Y.; Han, X.; Ren, Y.; Li, J.; Liu, Y.; Meng, X., Nanotechnology 2020, 32 (11), 115401.4. Gao, H.; Cai, J.; Xu, G.-L.; Li, L.; Ren, Y.; Meng, X.; Amine, K.; Chen, Z., Chem. Mater. 2019, 31 (8), 2723-2730.5. Meng, X.; Comstock, D. J.; Fister, T. T.; Elam, J. W., ACS Nano 2014, 8 (10), 10963-10972.

Characterization of Polycrystalline Cathode Materials in Five Dimensions (5D)

Thermal stability is one of the most desired features for large-scale energy applications, such as batteries used in electronics and electric vehicles. Thermal runaway, heat generation, and gas release are likely to happen for batteries under thermal abuse conditions, leading to severe performance degradation and safety risks. Although the decomposition of electrolytes at high temperatures has been widely studied in the community, a systematic and in situ study of the intrinsic instability of the cathodes in Li ion batteries is lacking. Polycrystalline nickel-rich Li layered oxides (LiNi x Mn y Co1-x-y O2, NMC) were chosen as the platform materials considering the recent improvements in specific capacity but also the rising safety concerns in Ni-rich cathodes.Here we used one of state-of-the-art techniques in microscopy: the full-field transmission X-ray microscope (TXM) to capture the 3D tomography of charged NMC particles, together with the X-ray absorption near edge structure (XANES) spectroscopic capability for Ni oxidation state. Moreover, we performed the XANES-3DTXM measurements during the whole process of heating the NMC cathodes from room temperature up to 250°C, which enables us to monitor the full evolution of NMC secondary particles in real time in 5 dimensions (3D spatial + tunable X-ray energy + temperature).This in situ XANES-3DTXM approach allows us to observe the real-time morphological and chemical evolution at elevated temperatures. The large field of view and reasonably high spatial resolution offer the capability to analyze NMC cathodes at different length scales, ranging from voids of tens of nanometers, to cracks of hundreds of nanometers, to secondary particles of tens of micrometers.With quantification of morphological (e.g., relative volume change, porosity, crack propagation) and chemical (e.g., the oxidation state of Ni, local charge distribution) characteristics as a function of temperature and time, the fundamental degradation mechanisms in polycrystalline nickel-rich Li layered oxides under thermally abuse conditions are thereupon unveiled. Based on these analyses and discoveries, we proposed to alter the primary particle arrangement as an effective solution to alleviate the thermal issues in nickel-rich Li layered oxides.Figure: Schematic of the in situ heating setup, 3D rendering of a NMC secondary particle, and selected morphology section and Ni oxidation state mapping at different temperatures. Figure 1

X-Ray Spectromicroscopy Investigation of Heterogeneous Sodiation in Hard Carbon Nanosheets with Vertically Oriented (002) Planes.

Hard carbon (HC) is a promising anode material for sodium-ion batteries, but the performance remains unsatisfactory and the sodiation mechanism in HC is one of the most debated topics. Here, from self-assembled cellulose nanocrystal sheets with crystallographic texture, unique HC nanosheets with vertically oriented (002) planes are fabricated and used as a model HC to investigate the sodiation mechanisms using synchrotron scanning transmission X-ray microscopy (STXM) coupled with analytical transmission electron microscopy (TEM). The model HC simplifies the 3D sodiation in a typical HC particle into a 2D sodiation, which facilitates the visualization of phase transformation at different states of charge. The results for the first time unveil that the sodiation in HC initiates heterogeneously, with multiple propagation fronts proceeding simultaneously, eventually merging into larger aggregates. The spatial correlation between the preferential adsorption and nucleation sites suggests that the heterogeneous nucleation is driven by the local Na-ion concentration, which is determined by defects or heteroatoms that have strong binding to Na ions. By identifying intercalation as the dominant sodium storage mechanism in the model HC, the findings highlight the importance of engineering the graphene layer orientation and the structural heterogeneity of edge sites to enhance the performances.

Insight into the structure and metabolic function of iron-rich nanoparticles in anammox bacteria

Anaerobic ammonium-oxidizing (anammox) bacteria are iron abundant and depend heavily on iron-binding proteins. The iron demand of anammox bacteria is relatively large. However, it still remains some doubts where these large quantities of available iron come from and how they are regulated in anammox bacteria. Herein, iron-rich nanoparticles in anammoxosomes were detected by synchrotron soft X-ray tomography coupled with scanning transmission X-ray microscopy (STXM). The iron-rich nanoparticles were identified as ferric oxide (α-Fe2O3) mineral cores, and the local atomic structure of iron-rich nanoparticles was obtained by X-ray absorption fine-structure (XAFS) spectra. The bacterioferritin of Q1Q315 and Q1Q5F8 were detected by proteomics analysis. On this basis, the metabolic pathway centered on iron-rich nanoparticles was proposed.

Beneficial effect of gelatin on iron gall ink corrosion

Iron gall Inks corrosion causes paper degradation (browning, embrittlement) and treatments were developed to tackle this issue. They often include resizing with gelatin to reinforce the paper and its cellulosic fibers (of diameter approx. 10 µm). This work aimed at measuring the distribution of ink components at the scale of individual paper fibers so as to give a better understanding of the impact of gelatin (re-)sizing on iron gall ink corrosion. For this purpose, scanning transmission X-ray microscopy (STXM) was used at the Canadian light source synchrotron (CLS, Saskatoon). This technique combines nano-scale mapping (resolution of 30 nm) and near edge X-ray absorption fine structure (NEXAFS) analysis. Fe L-edge measurements enabled to map iron distribution and to locate iron(II) and iron(III) rich areas. N K-edge measurement made it possible to map gelatin distribution. C K-edge measurements allowed mapping and discrimination of cellulose, gallic acid, iron gall ink precipitate and gelatin. Three fibers were studied: an inked fiber with no size, a sized fiber that was afterwards inked and an inked fiber sprayed with gelatin. Analysis of gelatin and ink ingredients distribution indicated a lower amount of iron inside the treated cellulosic fiber, which may explain the beneficial effect of gelatin on iron gall ink corrosion.

Analysis of Cr(VI) Bioremediation by Citrobacter freundii Using Synchrotron Soft X-ray Scanning Transmission X-ray Microscopy

Scanning transmission X-ray microscopy (STXM) was utilized for analysing the bioremediation of Cr(VI) by Citrobacter freundii, a species of gram-negative bacteria. The biosorption and bioreduction processes were analysed by the chemical mapping of cells biosorbed at different concentrations of Cr(VI). STXM spectromicroscopy images were recorded at O K-edge and Cr L-edge. A thorough analysis of the X-ray absorption features corresponding to different oxidation states of Cr in the biosorbed cell indicated the coexistence of Cr(III) and Cr(VI) at higher concentrations. This signifies the presence of partially reduced Cr(VI) in addition to biosorbed Cr(VI). In addition, the Cr(III) signal is intense compared with Cr(VI) at different regions of the cell indicating excess of reduced Cr. Speciation of adsorbed Cr was analysed for the spectral features of biosorbed cell and comparison with Cr standards. Analysis of absorption onset, L3/L2 ratio and absorption fine structure concludes that adsorbed Cr is predominantly present as Cr(III) hydroxide or oxyhydroxide. The evolution of absorption features in the duration of biosorption process was also studied. These time lapse studies depict the gradual decrement in Cr(VI) signal as biosorption proceeds. A strong evidence of interaction of Cr with the cell material was also observed. The obtained results provide insights into the biosorption process and chemical speciation of Cr on the cells.

Deep-learning-based image registration for nano-resolution tomographic reconstruction.

Nano-resolution full-field transmission X-ray microscopy has been successfully applied to a wide range of research fields thanks to its capability of non-destructively reconstructing the 3D structure with high resolution. Due to constraints in the practical implementations, the nano-tomography data is often associated with a random image jitter, resulting from imperfections in the hardware setup. Without a proper image registration process prior to the reconstruction, the quality of the result will be compromised. Here a deep-learning-based image jitter correction method is presented, which registers the projective images with high efficiency and accuracy, facilitating a high-quality tomographic reconstruction. This development is demonstrated and validated using synthetic and experimental datasets. The method is effective and readily applicable to a broad range of applications. Together with this paper, the source code is published and adoptions and improvements from our colleagues in this field are welcomed.

A passive characterization method of the single-bounce ellipsoidal capillary for the full field transmission X-ray microscopy

A passive characterization method to evaluate the quality of the single-bounce ellipsoidal capillary (SBEC) for the full field transmission X-ray microscopy was designed. The simulation model was established by measuring the outer diameter of the SBEC. The simulated shape of the focusing ring consisted with that from the experiment. This passive characterization method could be used evaluate efficiently the quality of SBEC and provide a guidance for SBEC manufacturing.

Operando synchrotron transmission X-ray microscopy study on (Mg, Co, Ni, Cu, Zn)O high-entropy oxide anodes for lithium-ion batteries

(Mg,Co,Ni,Cu,Zn)O, a high-entropy oxide, has recently been proposed as an anode material for lithium-ion batteries (LIBs). It exhibits excellent cyclic stability, which is attributed to the high-entropy stabilization effect, as reported in previous studies. The presence of Mg may also help stabilize the electrode by helping conserve its original lattice structure during charging and discharging. In this work, (Mg,Co,Ni,Cu,Zn)O oxides with various amounts of Mg were synthesized, namely, (Mg,Co,Ni,Cu,Zn)O, (Mg0.8,Co,Ni,Cu,Zn)O, and (Co,Ni,Cu,Zn)O. To explore the impact of Mg in LIBs, cyclic voltammetry and galvanostatic charge–discharge measurements were conducted. In addition, changes in morphology were observed using operando synchrotron transmission X-ray microscopy. Through the aforementioned analyses, the role of magnesium was investigated, which is expected to assist in the development of high-entropy oxide electrodes for LIBs.

Carbon-Coated SiO2 Composites as Promising Anode Material for Li-Ion Batteries.

Porous silica-based materials are a promising alternative to graphite anodes for Li-ion batteries due to their high theoretical capacity, low discharge potential similar to pure silicon, superior cycling stability compared to silicon, abundance, and environmental friendliness. However, several challenges prevent the practical application of silica anodes, such as low coulombic efficiency and irreversible capacity losses during cycling. The main strategy to tackle the challenges of silica as an anode material has been developed to prepare carbon-coated SiO2 composites by carbonization in argon atmosphere. A facile and eco-friendly method of preparing carbon-coated SiO2 composites using sucrose is reported herein. The carbon-coated SiO2 composites were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry, transmission and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, cyclic voltammetry, and charge–discharge cycling. A C/SiO2-0.085 M calendered electrode displays the best cycling stability, capacity of 714.3 mAh·g−1, and coulombic efficiency as well as the lowest charge transfer resistance over 200 cycles without electrode degradation. The electrochemical performance improvement could be attributed to the positive effect of the carbon thin layer that can effectively diminish interfacial impedance.

Structural and chemical heterogeneity of Proterozoic organic microfossils of the ca. 1 Ga old Angmaat Formation, Baffin Island, Canada.

Organic microfossils in Meso- and Neoproterozoic rocks are of key importance to track the emergence and evolution of eukaryotic life. An increasing number of studies combine Raman spectroscopy with synchrotron-based methods to characterize these microfossils. A recurring observation is that Raman spectra of organic microfossils show negligible variation on a sample scale and that variation between different samples can be explained by differences in thermal maturation or in the biologic origin of organic precursor material. There is a paucity of work, however, that explores the extent to which the petrographic framework and diagenetic processes might influence the chemical structure of organic materials. We present a detailed Raman spectroscopy-based study of a complex organic microfossil assemblage in the ca. 1Ga old Angmaat Formation, Baffin Island, Canada. This formation contains abundant early diagenetic chert that preserves silicified microbial mats with numerous, readily identifiable organic microfossils. Individual chert beds show petrographic differences with discrete episodes of cementation and recrystallization. Raman spectroscopy reveals measurable variation of organic maturity between samples and between neighboring organic microfossils of the same taxonomy and taphonomic state. Scanning transmission X-ray microscopy performed on taphonomically similar coccoidal microfossils from the same thin section shows distinct chemical compositions, with varying ratios of aromatic compounds to ketones and phenols. Such observations imply that geochemical variation of organic matter is not necessarily coupled to thermal alteration or organic precursor material. Variation of the Raman signal across single samples is most likely linked to the diagenetic state of analyzed materials and implies an association between organic preservation and access to diagenetic fluids. Variation in the maturity of individual microfossils may be a natural outcome of local diagenetic processes and potentially exceeds differences derived from precursor organic material. These observations stress the importance of detailed in situ characterization by Raman spectroscopy to identify target specimens for further chemical analysis.

Multiscale operando X-ray investigations provide insights into electro-chemo-mechanical behavior of lithium intercalation cathodes

The electrochemical performance and cycle life of lithium-ion batteries (LIBs) depend on the electrochemical, chemical, and mechanical behavior of electrodes and electrolytes. Despite extensive studies conducted previously, challenges exist to decouple these behaviors, capture the evolution of electro-chemo-mechanical behavior in realistic conditions, and correlate atomic-scale stress evolution to micro-scale bulk mechanical degradation. Here, we report multiscale operando techniques to investigate polydisperse battery electrodes by integrating volume-averaged quantitative synchrotron X-ray scattering with high-resolution transmission X-ray microscopy (TXM). The former provides us information spanning a wide spatial range, from Angstrom-level atomic structures to micrometer-level particle scales, while the latter provides time-resolved 2D images of the particles during cycling. The complementarity of the two operando techniques is demonstrated by an over-lithiation test of LiCoO2 electrodes, where particles crack and eventually pulverize. Additionally, the techniques are applied to study LiCoO2 cycling stability from 3.0 V to 4.5 V. Operando X-ray scattering result shows nanometer-scale features keep forming in LiCoO2 electrodes during cycling, resulting in an increased projected area observed by the TXM experiment. The formation of such features is inhibited by a polymer coating on the electrode, leading to vastly improved cycling stability. The polymer coating alleviates LiCoO2 surface deterioration, reduces side product generation, and inhibits LiCoO2 particles volume expansion during the cycling test. These operando multimodal X-ray techniques presented herein thus offer a novel, multiscale diagnostic modality for studying existing and emerging battery materials, aiding the development of next-generation LIBs.

Time-lapse nanometre-scale 3D synchrotron imaging and image-based modelling of the response of shales to heating

The development of pore and fracture networks at the nano-scale as a response to heating can reveal coupled physical relationships relevant to several energy applications. A combination of time-lapse 3D imaging and finite-element modelling (FEM) was performed on two typical thermally immature shale samples, Kimmeridge Clay and Akrabou shale, to investigate thermal response at the nm-scale for the first time. Samples were imaged using Transmission X-ray Microscopy (TXM) with a voxel resolution of 34 nm at the I13–2 beamline at Diamond Light source, UK. Images were taken after heating to temperatures of 20 °C, 300 °C, 350 °C and 400 °C. The initiation of nano-pores within individual minerals and organic matter particles were observed and quantified alongside the evolution from nano-pores to micro-fractures. The major expansion of pore-volume occurred between 300 and 350 °C in both samples, with the pores elongating rapidly along the organic-rich bedding. The internal pressures induced by organic matter transformation influenced the development of microfractures. Mechanical properties and strain distributions within these two samples were modelled under a range of axial stresses using FEM. The results show that the overall stiffness of the shale reduced during heating, despite organic matter becoming stiffer. The varied roles of ductile (e.g., clay minerals, organic matter) and brittle materials (e.g., calcite, pyrite) within the rock matrix are also modelled and discussed. The configurations of organic matter, mineral components, porosity and connectivity impact elastic deformation during shale pyrolysis. This work extends our understanding of dynamic coupled processes of microstructure and elastic deformation in shales to the nm-scale, which also has applications to other subsurface energy systems such as carbon sequestration, geothermal and nuclear waste disposal.

Role of Oxygen Vacancy Sites on the Temperature-Dependent Photoluminescence of SnO2 Nanowires

The role of oxygen vacancies in temperature-dependent photoluminescence of SnO2 nanowires was investigated by X-ray absorption spectroscopy. Two types of oxygen vacancies are present in the nanowires: at out-of-plane sites and at in-plane sites; both play crucial roles in the temperature dependence of the photoluminescence. Oxygen vacancies at in-plane sites participate in photon emission at low temperature, whereas those at out-of-plane sites result in photoluminescence at room temperature. Accordingly, the luminescence color changes from orange (630 nm, 1.93 eV) to green (515 nm, 2.4 eV) at 100 K. The color change is accompanied with a notable change in the oxygen K-edge X-ray absorption spectra. The scanning transmission X-ray microscopy results indicate that more oxygen vacancies at in-plane sites are present in the surface region than in the bulk region, whereas more oxygen vacancies at out-of-plane sites are present in the bulk region than in the surface region. Overall, the results demonstrate that oxygen-vacancy-mediated fluorescence properties of SnO2 nanowires are temperature-dependent; i.e., the photoluminescence mechanisms of the nanowires are mediated by oxygen vacancies at different sites, and the bicolor fluorescence originates from charge transfer between the states.

STXM-XANES and computational investigations of adsorption of per- and polyfluoroalkyl substances on modified clay

The study investigated molecular mechanisms of per- and polyfluoroalkyl substances (PFAS) on a surfactant modified clay (SMC), which rivals or exceeds the performance of granular activated carbon in removing long-chain PFAS from contaminated water. The adsorption isotherms of four anionic and one neutral PFAS from 1 × 10–9 to 1 × 10–5 mol/L were measured to be piecewise, accompanied by the expansion of the SMC interlayer. Based on the spatial distribution of perfluorocarboxylic acid (PFOA) on SMC at the submicron scale, achieved by synchrotron-based scanning transmission X-ray microscopy (STXM) coupled with X-ray absorption near-edge structure spectroscopy (XANES), PFOA molecules were confirmed to enter the interlayer space of SMC and could form charge-charge interaction with the intercalants (quaternary ammonia cations). Revealed by the all-atom molecular dynamics (MD) simulation and density functional theory-based quantum calculations, the interactions between the positively charged surfactant and representative PFAS include charge-charge, charge-dipole, and dipole-dipole interactions. The adsorption mechanisms vary from one PFAS structure to another in terms of adsorption energy and spatial arrangement. Those interactions overcome the interaction between PFAS and water, allowing PFAS to be retained in the SMC's interlayer space. The study provides fundamental insights into how PFAS interact with clay-based materials, supporting the use of the materials for PFAS treatment and remediation.

Phase resolved observation of spin wave modes in antidot lattices

Antidot lattices have proven to be a powerful tool for spin wave band structure manipulation. Utilizing time-resolved scanning transmission x-ray microscopy, we are able to experimentally image edge-localized spin wave modes in an antidot lattice with a lateral confinement down to &amp;lt;80 nm×130 nm. At higher frequencies, spin wave dragonfly patterns formed by the demagnetizing structures of the antidot lattice are excited. Evaluating their relative phase with respect to the propagating mode within the antidot channel reveals that the dragonfly modes are not directly excited by the antenna but need the propagating mode as an energy mediator. Furthermore, micromagnetic simulations reveal that additional dispersion branches exist for a tilted external field geometry. These branches correspond to asymmetric spin wave modes that cannot be excited in a non-tilted field geometry due to the symmetry restriction. In addition to the band having a negative slope, these asymmetric modes also cause an unexpected transformation of the band structure, slightly reaching into the otherwise empty bandgap between the low frequency edge modes and the fundamental mode. The presented phase resolved investigation of spin waves is a crucial step for spin wave manipulation in magnonic crystals.