Scanning Transmission X-ray Microscopy Research Articles

Chemically coupling SnO2 quantum dots and MXene for efficient CO2 electroreduction to formate and Zn–CO2 battery

Electrochemical conversion of CO2 into formate is a promising strategy for mitigating the energy and environmental crisis, but simultaneously achieving high selectivity and activity of electrocatalysts remains challenging. Here, we report low-dimensional SnO2 quantum dots chemically coupled with ultrathin Ti3C2Tx MXene nanosheets (SnO2/MXene) that boost the CO2 conversion. The coupling structure is well visualized and verified by high-resolution electron tomography together with nanoscale scanning transmission X-ray microscopy and ptychography imaging. The catalyst achieves a large partial current density of -57.8 mA cm-2 and high Faradaic efficiency of 94% for formate formation. Additionally, the SnO2/MXene cathode shows excellent Zn-CO2 battery performance, with a maximum power density of 4.28 mW cm-2, an open-circuit voltage of 0.83 V, and superior rechargeability of 60 h. In situ X-ray absorption spectroscopy analysis and first-principles calculations reveal that this remarkable performance is attributed to the unique and stable structure of the SnO2/MXene, which can significantly reduce the reaction energy of CO2 hydrogenation to formate by increasing the surface coverage of adsorbed hydrogen.

Silicon as a potential limiting factor for phosphorus availability in paddy soils

Rice cultivation requires high amounts of phosphorus (P). However, significant amounts of P fertilizer additions may be retained by iron (Fe) oxides and are thus unavailable for plants. At the same time, rice cultivation has a high demand for silicic acid (Si), reducing Si availability after short duration of rice cultivation. By studying a paddy chronosequence with rice cultivation up to 2000 years, we show that Si limitation, observed as early as a few decades of rice cultivation, is limiting P availability along the paddy soils chronosequence. Using near edge X-ray absorption fine structure spectroscopy (NEXAFS) in a scanning transmission (soft) X-ray microscope (STXM) we show release of available P was linked to a Si-induced change in speciation of Fe-phases in soil particles and competition of Si with P for binding sites. Hence, low Si availability is limiting P availability in paddy soils. We propose that proper management of Si availability is a promising tool to improve the P supply of paddy plants.

Elemental changes in heart and coronaries after breast cancer radiotherapy assessed by synchrotron radiation soft X-ray spectromicroscopy

Radiotherapy (RT) plays a pivotal role in the treatment of breast cancer (BC) and various thoracic malignancies. Radiation induced heart disease (RIHD) is one such long term toxicity which can offset the improvement in cancer specific mortality. Long term normal tissue toxicity is becoming a bigger concern, as early diagnosis and the improvement in the treatment of these cancers has led to patients surviving longer. Our research group on Physics applied to biomedical sciences has been investigating the side effects of BC treatment (RT and chemotherapy) for more than ten years. The cardiac regeneration has been studied to better understand the damage that occurs following radiation procedures in the heart tissue after many thoracic cancer treatments. One possible complication is coronary artery disease induced by irradiation after radiotherapy in thoracic area. Studies on the structures of cardiac tissue and the distribution of low atomic weight element can help to understand mechanisms associated with damage to healthy tissue, as these are of fundamental importance to metabolism in biological systems. The present study aimed to elucidate how radiotherapy in the thoracic area causes damage in the coronary artery, and to verify the potential use of losartan in reducing, or even preventing, the side effects of irradiation in this artery. To assess elemental and morphological differences in aortic and coronary samples, the Low Energy X-Ray Fluorescence (LEXRF) technique using Synchrotron Radiation was employed. SR- LEXRF and scanning transmission X-ray microscopy measurements were carried out at the beamline TwinMic at Elettra Sincrotrone Triste, Italy.

Densification of a polymer glass under high-pressure shear flow

The properties of glasses can change significantly as they evolve toward equilibrium. Mechanical deformation appears to influence this physical aging process in conflicting ways, with experiments and simulations showing both effects associated with rejuvenation away from and overaging toward the equilibrium state. Here we report a significant densification effect in a polymer undergoing shear flow under high pressure. We used the high-aspect ratio geometry of the layer compression test to measure the uniform and homogeneous accumulation of plastic strain during isothermal confined compression of a deeply quenched film of polystyrene glass. Combined scanning transmission x-ray microscopy (STXM) and atomic force microscopy confirmed defect-free deformation leaving up to 1.2% residual densification under conditions of confined uniaxial strain. At higher peak strain, plastic shear flow extruded glass from below the compressing punch under conditions of a high background pressure. A further density increase of 2% was observed by STXM for a highly thinned residual thickness of polymer that nevertheless showed no signs of crystallization or internal strain localization. While the confined uniaxial densification can be accounted for by a simple elastic--plastic constitutive model, the high-pressure extrusion densification cannot.

Determine the coordination of Al and Si of Fe-rich fly ash: The challenge in NMR and how we probe its heterogeneity using X-ray spectromicroscopy

Scanning transmission X-ray microscopy (STXM) coupled with ptychographic imaging at Al and Si K-edge is a new probe to the microscale chemistry of heterogenous materials. Here, the combined techniques are applied to study local coordination environment of Fe-rich fly ash (FA). Ptychographic imaging at Al K- and Si K-edge highlights the fine Al- and Si-rich morphological features, respectively, at 6 nm pixel resolution. STXM visualizes the inter- and intra-particle variations in the silicate polymerization degree and two types of Al coordination environment in FA. The Si K-edge of SiO4 connected with four-fold coordinated Al is higher than SiO4 sharing oxygen with six-fold coordinated Al. The result is consistent with bulk nuclear magnetic resonance spectroscopy measurement of the Fe-rich sample which, however, is sensitive to paramagnetic Fe and time-consuming. We demonstrate that the combined method has great potential in the studies of chemically heterogenous aluminosilicates.

Revealing the Role of Liquid Electrolytes in Cycling of Garnet-Based Solid-State Lithium-Metal Batteries

Solid-state lithium-metal batteries (SS-LMBs) suffer from the very high resistance at the garnet electrolyte/cathode interface that hampers their commercialization. Herein, a carbonate-based liquid electrolyte (LE) is introduced at the interface of a Li6.5La2.9Ba0.1Zr1.4Ta0.6O12 (LLBZTO) garnet/LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode to lower the interfacial resistance and improve the battery performance. In this work, we conducted a thorough study on the role of liquid electrolytes at the interface using scanning transmission X-ray microscopy (STXM) associated with X-ray absorption spectroscopy (XAS). As a result, we have shown new data related to the formation and the chemical composition of the two formed interphases: a solid–liquid electrolyte interphase (SLEI) and the cathode–electrolyte interphase (CEI). Furthermore, we have presented evidence that LE decomposes during cycling into fluoride species including LiF and LaF3, oxides like Li2O, and carbonates (i.e., Li2CO3) as the main components of in situ-formed SLEI. Based on the synergy between SLEI and CEI, we demonstrate Li|garnet|LE|NMC 622 cells cycled with an initial discharge capacity of 168 mAh g–1 and a capacity retention of ∼82% after 28 cycles. We expect that our study of SLEI will accelerate the implementation of a new hybrid electrolyte (solid garnet and liquid electrolyte) approach in SS-LMBs.

The interaction between monosulfoaluminate and calcium chloride aqueous solution

Scanning transmission X-ray microscopy (STXM) and calcium L2,3-edge near-edge X-ray absorption fine structure (Nexafs) spectra were used to investigate the morphology and chemical information of cement-based materials. The interaction between calcium chloride (CaCl2) and monosulfoaluminate (Ms) was investigated and the intermediate phases were identified. With an increase in the concentration of the calcium chloride solution, calcium Ms was converted into ettringite, Kuzel's salt (Ks) and Friedel's salt (Fs) to varying degrees, while SO42− ions in the ettringite and Ks were continuously replaced by Cl− ions in the solution, eventually forming Fs and gypsum. Based on the calcium L2,3-edge Nexafs absorption spectra, ettringite, Ms, Ks and Ms were greatly distinguished by the number and shape of the leading peaks in the spectra due to the difference in SO42− content among the interlayer structures of Ms, Ks and Fs. The present work is based on the references for the STXM study of the calcium (sulfo)aluminates, for demonstrating a more complete understanding of the phase evolution under chloride environments.

Quantitative, in situ visualization of intracellular insulin vesicles in pancreatic beta cells

Characterizing relationships between Zn2+, insulin, and insulin vesicles is of vital importance to the study of pancreatic beta cells. However, the precise content of Zn2+ and the specific location of insulin inside insulin vesicles are not clear, which hinders a thorough understanding of the insulin secretion process and diseases caused by blood sugar dysregulation. Here, we demonstrated the colocalization of Zn2+ and insulin in both single extracellular insulin vesicles and pancreatic beta cells by using an X-ray scanning coherent diffraction imaging (ptychography) technique. We also analyzed the elemental Zn2+ and Ca2+ contents of insulin vesicles using electron microscopy and energy dispersive spectroscopy (EDS) mapping. We found that the presence of Zn2+ is an important characteristic that can be used to distinguish insulin vesicles from other types of vesicles in pancreatic beta cells and that the content of Zn2+ is proportional to the size of insulin vesicles. By using dual-energy contrast X-ray microscopy and scanning transmission X-ray microscopy (STXM) image stacks, we observed that insulin accumulates in the off-center position of extracellular insulin vesicles. Furthermore, the spatial distribution of insulin vesicles and their colocalization with other organelles inside pancreatic beta cells were demonstrated using three-dimensional (3D) imaging by combining X-ray ptychography and an equally sloped tomography (EST) algorithm. This study describes a powerful method to univocally describe the location and quantitative analysis of intracellular insulin, which will be of great significance to the study of diabetes and other blood sugar diseases.

Imaging magnonic frequency multiplication in nanostructured antidot lattices

Frequency multiplication is an essential part of electronics and optics which led to numerous indispensable applications. In this paper, we utilize a combination of scanning transmission x-ray microscopy and micromagnetic simulations to directly image magnonic frequency multiplication by means of dynamic real-space magnetization measurements. We experimentally demonstrate frequency multiplication up to the seventh order, which enables the generation of nanoscale spin waves at $6\phantom{\rule{0.16em}{0ex}}\mathrm{G}\mathrm{Hz}$ with excitation frequencies of less than $1\phantom{\rule{0.16em}{0ex}}\mathrm{G}\mathrm{Hz}$. Good agreement between the experiment and micromagnetic simulations allows us to build a micromagnetic model capable of predicting conversion efficiencies and multiplexing capabilities of the system. Furthermore, simulations reveal that more than two rows of antidots do not increase the conversion efficiency substantially. By enabling magnonic multiplexing with low input frequencies while not exceeding the size of a few microns, the device will lead to numerous applications, further advancing the capabilities of magnonic data transmission.

Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility

Abstract. Atmospheric deposition is one of the main sources of dissolved iron (Fe) in the ocean surfaces. Atmospheric processes are recognized as controlling fractional Fe solubility (Fesol%) in marine aerosol particles. However, the impact of these processes on Fesol% remains unclear. One of the reasons for this is the lack of field observations focusing on the relationship between Fesol% and Fe species in marine aerosol particles. In particular, the effects of organic ligands on Fesol% have not been thoroughly investigated in observational studies. In this study, Fe species in size-fractionated aerosol particles in the Pacific Ocean were determined using X-ray absorption fine structure (XAFS) spectroscopy. The internal mixing states of Fe and organic carbon were investigated using scanning transmission X-ray microscopy (STXM). The effects of atmospheric processes on Fesol% in marine aerosol particles were investigated based on the speciation results. Iron in size-fractionated aerosol particles was mainly derived from mineral dust, regardless of aerosol diameter, because the enrichment factor of Fe was almost 1 in both coarse (PM>1.3) and fine aerosol particles (PM1.3). Approximately 80 % of the total Fe (insoluble + labile Fe) was present in PM>1.3, whereas labile Fe was mainly present in PM1.3. The Fesol% in PM>1.3 was not significantly increased (2.56±2.53 %, 0.00 %–8.50 %, n=20) by the atmospheric processes because mineral dust was not acidified beyond the buffer capacity of calcite. In contrast, mineral dust in PM1.3 was acidified beyond the buffer capacity of calcite. As a result, Fesol% in PM1.3 (0.202 %–64.7 %, n=10) was an order of magnitude higher than that in PM>1.3. The PM1.3 contained ferric organic complexes with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes), and the abundance correlated with Fesol%. Iron(III)-HULIS was formed during transport in the Pacific Ocean because Fe(III)-HULIS was not found in aerosol particles in Beijing and Japan. The pH estimations of mineral dust in PM1.3 established that Fe was solubilized by proton-promoted dissolution under highly acidic conditions (pH < 3.0), whereas Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be reproduced by proton-promoted dissolution under moderately acidic conditions, the pH of mineral dust increased after proton-promoted dissolution. The cloud process in the marine atmosphere increases the mineral dust pH because the dust particles are covered with organic carbon and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS owing to its high water solubility. Thus, the organic complexation of Fe with HULIS plays a significant role in the stabilization of Fe that was initially solubilized by proton-promoted dissolution.

Nano-silica particles synergistically IgE-mediated mast cell activation exacerbating allergic inflammation in mice.

BackgroundAllergic respiratory diseases have increased dramatically due to air pollution over the past few decades. However, studies are limited on the effects of inorganic components and particulate matter with different particle sizes in smog on allergic diseases, and the possible molecular mechanism of inducing allergies has not been thoroughly studied.MethodsFour common mineral elements with different particle sizes in smog particles were selected, including Al2O3, TiO2, Fe2O3, and SiO2. We studied the relationship and molecular mechanism of smog particle composition, particle size, and allergic reactions using mast cells, immunoglobulin E (IgE)-mediated passive cutaneous anaphylaxis (PCA) model, and an ovalbumin (OVA)-induced asthmatic mouse model in vitro and in vivo, combined with transmission electron microscopy, scanning transmission X-ray microscopy analysis, and transcriptome sequencing.ResultsOnly 20 nm SiO2 particles significantly increased β-hexosaminidase release, based on dinitrophenol (DNP)-human serum albumin (HSA) stimulation, from IgE-sensitized mast cells, while other particles did not. Meanwhile, the PCA model showed that Evan’s blue extravasation in mice was increased after treatment with nano-SiO2 particles. Nano-SiO2 particles exposure in the asthmatic mouse model caused an enhancement of allergic airway inflammation as manifested by OVA-specific serum IgE, airway hyperresponsiveness, lung inflammation injury, mucous cell metaplasia, cytokine expression, mast cell activation, and histamine secretion, which were significantly increased. Nano-SiO2 particles exposure did not affect the expression of FcϵRI or the ability of mast cells to bind IgE but synergistically activated mast cells by enhancing the mitogen-activated protein kinase (MAPK) signaling pathway, especially the phosphorylation levels of the extracellular signal-regulated kinase (ERK)1/2. The ERK inhibitors showed a significant inhibitory effect in reducing β-hexosaminidase release.ConclusionOur results indicated that nano-SiO2 particles stimulation might synergistically activate IgE-sensitized mast cells by enhancing the MAPK signaling pathway and that nano-SiO2 particles exposure could exacerbate allergic inflammation. Our experimental results provide useful information for preventing and treating allergic diseases.

Particle phase-state variability in the North Atlantic free troposphere during summertime is determined by atmospheric transport patterns and sources

Abstract. Free tropospheric aerosol particles have important but poorly constrained climate effects due to transformations of their physicochemical properties during long-range transport. In this study, we investigate the chemical composition and provide an overview of the phase states of individual particles that have undergone long-range transport over the North Atlantic Ocean in June and July 2014, 2015, and 2017 to the Observatory of Mount Pico (OMP) in the Azores. The OMP is an ideal site for studying long-range-transported free tropospheric particles because local emissions have a negligible influence and contributions from the boundary layer are rare. We used the FLEXible PARTicle Lagrangian particle dispersion model (FLEXPART) to determine the origins and transport trajectories of sampled air masses and found that most of them originated from North America and recirculated over the North Atlantic Ocean. The FLEXPART analysis showed that the sampled air masses were highly aged (average plume age >10 d). Size-resolved chemical compositions of individual particles were probed using computer-controlled scanning electron microscopy with an energy-dispersive X-ray spectrometer (CCSEM-EDX) and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). CCSEM-EDX results showed that the most abundant particle types were carbonaceous (∼ 29.9 % to 82.0 %), sea salt (∼ 0.3 % to 31.6 %), and sea salt with sulfate (∼ 2.4 % to 31.5 %). We used a tilted stage interfaced within an environmental scanning electron microscope (ESEM) to determine the phase states of individual submicron particles. We found that most particles (∼ 47 % to 99 %) were in the liquid state at the time of collection due to inorganic inclusions. Moreover, we also observed substantial fractions of solid and semisolid particles (∼ 0 % to 30 % and ∼ 1 % to 42 %, respectively) during different transport patterns and events, reflecting the particles' phase-state variability for different atmospheric transport events and sources. Combining phase state measurements with FLEXPART CO tracer analysis, we found that wildfire-influenced plumes can result in particles with a wide range of viscosities after long-range transport in the free troposphere. We also used temperature and RH values extracted from the Global Forecast System (GFS) along the FLEXPART-simulated path to predict the phase state of the particles during transport and found that neglecting internal mixing with inorganics would lead to an overestimation of the viscosity of free tropospheric particles. Our findings warrant future investigation aiming at the quantitative assessment of the influence of internal mixing on the phase states of the individual particles. This study also provides insights into the chemical composition and phase state of free tropospheric particles, which can help models to reduce uncertainties about the effects of ambient aerosol particles on climate.

Chemical Structure and Distribution in Nickel-Nitrogen-Carbon Catalysts for CO2 Electroreduction Identified by Scanning Transmission X-ray Microscopy.

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are a class of electrocatalysts for fuel cell and electrochemical CO2 reduction (CO2R) applications. However, it is challenging to characterize the identity and concentration of catalytically active species owing to the structural heterogeneity of M-N-C materials. We utilize scanning transmission X-ray microscopy (STXM) as a correlative spectromicroscopy approach for spatially resolved imaging, identification, and quantification of structures and chemical species in mesoscale regions of nickel-nitrogen-carbon (Ni-N-C) catalysts, thereby elucidating the relationship between Ni content/speciation and CO2R activity/selectivity. STXM results are correlated with conventional characterization approaches relying on either bulk average (X-ray absorption spectroscopy) or spatially localized (scanning transmission electron microscopy with electron energy loss spectroscopy) measurements. This comparison illustrates the advantages of soft X-ray STXM to provide spatially resolved identification and quantification of active structures in Ni-N-C catalysts. The active site structures in these catalysts are identified to be atomically dispersed NiN x /C sites distributed throughout entire catalyst particles. The NiN x /C sites were notably demonstrated by spectroscopy to possess a variety of chemical structures with a spectroscopic signature that most closely resembles nickel(II) tetraphenylporphyrin molecules. The quantification and spatial distribution mapping of atomically dispersed Ni active sites achieved by STXM address a target that was elusive to the scientific community despite its importance in guiding advanced material designs.

Understanding the Role of Liquid Electrolytes in Performance Improvement of Solid-State Lithium Metal Batteries

Garnet-type Li7La3Zr2O12 (LLZO) Solid-State Electrolytes (SSEs) enable Solid-State Lithium Metal Batteries (SSLMBs) with high power density due to their superior ionic conductivity over 1 mS cm-1 at room temperature and good chemical stability against Lithium (Li) metal. A major cause of failure in SSLMBs is the large interfacial resistance between LLZO and electrodes. The high resistance at the interfaces is normally associated with insufficient solid-solid surface contact. It is a common practice to introduce a Liquid Electrolyte (LE) in SSLMBs either in combination with SSEs to form quasi-solid electrolytes or as the interface to enhance battery cycling performance. Several studies are conducted on resolving the contact issue between LLZO and the Li-metal anode but very few focused on the LLZO/cathode interface.In this research, a carbonate-based LE was introduced at the interface of Li6.5La2.9Ba0.1Zr1.4Ta0.6O12 (LLBZTO) | LiNi0.6Mn0.6Co0.2O2 (NMC 622) cathode with the aim of understanding the mechanism which the LE enhances the SSLMBs performance, using the Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Scanning (XAS). The assembled Li | LLBZTO SSEs | LE | NMC 622 cell exhibited an initial discharge capacity of 168 mAh g-1 with a capacity retention ratio of ~82 % after 30 cycles. The results from the STXM revealed the reactions of the LE with LLZO and NMC 622. The XAS analysis showed the formation of two new interfaces: Cathode-Electrolyte Interface (CEI) and Solid-Liquid Electrolyte Interface (SLEI). Also, the result indicated that the LE decomposed completely in the cell after 30 cycles and transformed to a dense and robust SLEI. This in turn led to the enhanced interfacial contact with the cathode and an improved Li+ ion transport at the interface. In addition, fluorides (i.e., LiF and LaF3) and carbonates (i.e., Li2CO3) were confirmed as the main components of the SLEI. In this study, two interfaces in SSLMBs (CEI and SLEI) were characterized. Fully understanding the roles of LE as the interface would enhance the practical application of quasi-solid electrolytes in SSLMBs. Keywords Solid-state lithium metal batteries; Garnet; Interface; Ceramic electrolyte; STXM

(Invited) Probing the Atomic and Electronic Structure of Working Energy Materials with x-Ray Spectroscopy

Improving energy conversion/generation/storage efficiency of energy materials has always been a great challenge. Monitoring the atomic/electronic structures close to interface in many important energy materials, such as nanostructured catalysts, artificially photosynthesizing materials, smart materials, and energy storage devices, is of great importance. Designing such a material with improved performance without understanding its atomic/electronic structures, and their changes under operating conditions, is difficult. Understanding and controlling the interfacial electronic structures of energy materials require in-situ characterizations, of which synchrotron x-ray spectroscopy is the one with many unique features. The last decade has witnessed a golden age of in situ synchrotron x-ray spectroscopy for energy materials. X-ray absorption spectroscopy can be used to determine unoccupied electronic structures while X-ray emission spectroscopy can be utilized to examine occupied electronic structure. The additional use of resonant inelastic X-ray scattering further reveals inter-band d-d excitation or intra-band charge transfer excitation that can reflect the fundamental chemical and physical properties. An emerging technique, scanning transmission x-ray microscopy is a spectro-microscopic approach, providing regional x-ray absorption spectroscopy, is also gearing up for energy science. This presentation will report recent studies and perspectives of the application of in situ/operando synchrotron x-ray spectroscopy to energy materials. Tamkang University (TKU) end-stations constructed at the Taiwan Photon Source (TPS) 45A & 27A beamlines for the x-ray spectroscopic investigation of energy materials will also be introduced.

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. Figure 1

In situ Analysis of the Fate and Behavior of Inorganic Nanomaterials in Biological Systems by Synchrotron Radiation X-ray Probe Techniques

Background: The comprehensive understanding of nanomaterial behavior in biological systems is essential in accurately modeling and predicting nanomaterial fate and toxicity. Synchrotron radiation (SR) X-ray techniques, based on their ability to study electronic configuration, coordination geometry, or oxidative state of nanomaterials with high sensitivity and spatial resolution, have been introduced to analyze the transformation behavior of nanomaterials in biological systems. Methods: Previous research in this field are classified and summarized. Results: To start with, a brief introduction of a few widely used SR-based analytical techniques including X-ray absorption spectroscopy, X-ray fluorescence microprobe, scanning transmission X-ray microscopy and circular dichroism spectroscopy is provided. Then, the recent advances of their applications in the analysis of nanomaterial behaviors are elaborated based on different nanomaterial transformation forms such as biodistribution, biomolecule interaction, decomposition, redox reaction, and recrystallization/agglomeration. Finally, a few challenges faced in this field are proposed. Conclusion: This review summarizes the application of SR X-ray techniques in analyzing the fate of inorganic nanomaterials in biological systems. We hope it can help the readers to have a general understanding of the applications of SR-based techniques in studying nanomaterial biotransformation and to stimulate more insightful researches in relevant fields.

Full-field differential interference contrast imaging with radial-shearing Greek-ladder sieves

The traditional differential interference contrast (DIC) technique is an effective method of quantitative phase imaging, but it has the specific property of orientation and direction selectivity, which decreases the contrast of images in some degree. Here an approach of Radial-shearing DIC (RsDIC) is proposed to realize phase imaging of omnidirectional selectivity as well as high sensitivity, in which the key is an amplitude-only ancient Greek-ladder sieve. Two setups are proposed. One contains only one sieve, in which the interference occurs in the overlap region near to the two adjacent image planes. The other contains two confocal sieves, in which the interference occurs in the coincident image plane. The effectiveness of our proposed method is demonstrated by preliminary results obtained from the software GLAD simulation and experiment performed in visible light. RsDIC allows for full-field DIC imaging as well as for DIC scanning transmission x-ray microscopy, which can also provide a nanometer resolution nondestructive imaging tool in x-ray region for ultra-large-scale integrated circuits, living cells, etc.

Nanoscale chemical mapping of exometabolites at fungal-mineral interfaces.

Mineral‐associated organic matter is an integral part of soil carbon pool. Biological processes contribute to the formation of such organo‐mineral complexes when soil microbes, and in particular soil fungi, deposit a suite of extracellular metabolic compounds and their necromass on the mineral surfaces. While studied in bulk, micro‐ to nanoscale fungal–mineral interactions remain elusive. Of particular interest are the mutual effects at the interface between the fungal exometabolites and proximal mineral particles. In this work, we have grown saprotrophic and symbiotic fungi in contact with two soil minerals with contrasting properties: quartz and goethite, on top of X‐ray transparent silicon nitride membrane windows and analyzed fungal hyphae by synchrotron‐based scanning transmission X‐ray microscopy in combination with near edge X‐ray fine structure spectroscopy at C(K) and Fe(L) absorption edges. In the resultant chemical maps, we were able to visualize and differentiate organic compounds constituting the fungal cells, their extracellular metabolites, and the exometabolites adsorbing on the minerals. We found that the composition of the exometabolites differed between the fungal functional guilds, particularly, in their sugar to protein ratio and potassium concentration. In samples with quartz and goethite, we observed adsorption of the exometabolic compounds on the mineral surfaces with variations in their chemical composition around the particles. Although we did not observe clear alteration in the exometabolite chemistry upon mineral encounters, we show that fungal–mineral interaction result in reduction of Fe(III) in goethite. This process has been demonstrated for bulk systems, but, to our knowledge, this is the first observation on a single hypha scale offering insight into its underlying biological mechanisms. This demonstrates the link between processes initiated at the single‐cell level to macroscale phenomena. Thus, spatially resolved chemical characterization of the microbial–mineral interfaces is crucial for an increased understanding of overall carbon cycling in soil.

Hygroscopicity and Ice Nucleation Properties of Dust/Salt Mixtures Originating from the Source of East Asian Dust Storms

Dust storms are common meteorological events that occur frequently in the late spring and early summer in arid and semi-arid areas. The resulting lofted dust and salt mixtures can impact atmospheric chemistry and climate systems through the many pathways represented by aerosol-cloud-climate interactions. In this study, dust/salt samples were collected from important sources of the East Asian dust storm, including the Badain Jaran Desert, the Tengger Desert and the Ulan Buh Desert in northwestern China. Ion chromatography (IC) measurements were performed to determine the concentrations of cations and anions. The ionic concentrations, pH and dissolvable fractions of sand samples show a positive correlation, indicating that the dissolved content is rich in alkaline ions. A positive matrix factorization (PMF) receptor model was employed to analyze the IC results, and from the PMF solutions non-obvious connections to local geography emerge. The results of hygroscopic experiments of sand samples which were measured by a vapor sorption analyzer indicate that the hygroscopicity may be related to the soluble content of samples, and the observed hygroscopic behavior can be well described by a thermodynamic model. The morphology of individual particles was chemically mapped by the synchrotron-based scanning transmission X-ray microscopy, and needle-shaped CaCO3 particles were observed to adhere to more irregular high K-containing particles. Moreover, a continuous flow diffusion chamber was used to investigate the ice nucleation abilities of typical salts, with both homogeneous freezing and deposition nucleation being observed. The results indicate that the salts primarily act as cloud condensation nuclei but can also act as ice nucleating particles at low temperatures.