Soft X-ray Imaging Research Articles

Analysis of so2 Contamination Effects on PEFC Performance and Water Distribution By in-Situ Soft X-Ray Microscopy

Durability is a major hindrance to the mass commercialization of polymer electrolyte fuel cell (PEFC) combined heat and power (CHP) systems and is adversely affected by contaminants. Fuel and air contaminants are major sources of contamination, and these contaminants cause performance degradation and irreversible damage to PEFCs. The performance degradation is manifested as kinetic, ohmic, and mass transfer losses. The most devastating consequence of fuel and air impurities in PEFCs is manifested as kinetic loss, and catalyst poisoning is the main cause of this phenomenon. The catalyst poisoning occurs when impurities adsorb on the surface of Platinum catalyst and blocks the active site of the catalyst. Ambient air is the most practical source of oxygen for PEFCs, but impurities in air can severely degrade PEFC performance, and the Sulfur contaminants, such as SOx, are the most detrimental to PEFCs [1]. From this background, extensive number of research for understanding and mitigating the catalyst poisoning has been carried out. The bipolar plate has the rib and the channel geometry in order to make electron transport pass to current collectors, to supply enough oxygen to the reaction site, and to remove water from the cathode catalyst layer (CL) to gas channels, and the transport of contaminants to the catalyst site is not uniform. Therefore, current density distribution in the rib/channel direction might be affected by the contamination, and the increase of local current density leads to water flooding in the CL. However, there are limited studies on the impacts of contamination distribution on current density distribution and mass transport loss. In this study, we focused on the influence of Sulfur dioxide (SO2) contamination on the cell performance. To clarify the effect of SO2contamination on the performance distribution, change of the liquid water distribution within the membrane electrode assembly (MEA) was quantitatively visualized by in-situ soft X-ray imaging technique, and the change of electrochemical surface area (ECSA) was evaluated. Figure 1 shows the change of cell voltage at the current density of 1.0 A/cm2 during continuous injection of SO2. The cell temperature was 80 deg.C, and the relative humidity was 80%. High purity H2 was used for the anode feed, and 1 ppm SO2/Air was used for the cathode feed. Severe voltage decay caused by SO2 was observed. Figure 2 shows the change of cyclic voltammograms (CV), and significant decrease of the H-adsorption/desorption currents were clearly observed. Figure 3 shows the results of the soft X-ray imaging. Fig. 3(a) shows the original image, and the cell structure was clearly visualized. Fig. 3(b) and Fig. 3(c) show the water extracted images before and during SO2 injection, respectively. Before SO2injection, liquid water accumulates under the rib area, and the decrease of liquid water under the rib near the channel was observed. In addition, slight increase of liquid water at the center part of the rib was also observed. These results suggest that the catalyst under the channel area is deactivated, and the catalyst under the rib is mainly used for power generation. It might affect the mass transport loss and becomes more important under high current density operation. Reference: [1] Yoshiki Nagahara, Seiho Sugawara, Kazuhiko Shinohara, The impact of air contaminants on PEMFC performance and durability, J. Power Sources, 182, 422-428 (2008) Figure 1

High Resolution 3-Dimensional Chemical and Morphological Imaging of Single Li x FePO4 Particles

Understanding chemical and morphological transitions within single nanoparticles of electrochemically active materials is crucial to overcome the performance limitations and degradation of batteries. Techniques that afford high chemical resolution at the nanoscale are ideally suited for this goal. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy (XAS) is a powerful suite which affords chemical and structural information on large volumes of material at spatial resolutions better than 5 nm.1 However, to date, this technique has been intrinsically limited to 2 dimensional observations in transmission mode, which causes complications during interpretation, especially in the case of overlapped particles, because the projection images represent an average over the X-ray penetration path within the crystals. In this study, soft X-ray tomography combined with ptychography, developed at beamline 5.3.2.1 at the Advanced Light Source (Berkeley, CA) is applied to assess the chemical and morphological consequences of electrochemical delithiation of aggregated nano-sized lithium iron phosphate (LiFePO4) plates (Figure 1). Our work provides quantitative analysis of oxidation states in 3 dimensions at the 10 nm scale. After segmentation, statistical analysis of the chemical phase for any given individual particle was achieved, and information was extracted of the particle interior. The ability to visualize the nanoscale chemical state distribution over functional volumes will revolutionize the study of energy storage materials and enable the design of optimized morphologies for the next generation of devices. Figure 1. 3 dimensional chemical volume rendering of Li x FePO4 crystals. Chemical phase information were extracted from 3 dimensional volumes collected at 708.25 eV and 710.25 eV. The red and blue areas indicate the highest content of LiFePO4 and FePO4, respectively. 1. D. A. Shapiro, Y.-S. Yu, T. Tyliszczak, J. Cabana, R. Celestre, W. Chao, K. Kaznatcheev, A. L. D. Kilcoyne, F. Maia, S. Marchesini, Y. S. Meng, T. Warwick, L. L. Yang, H. A. Padmore, Nat Photon 8, 765 (2014). Figure 1

In-Situ Analysis of Water Distribution within PEFC Catalyst Layer By Soft X-Ray Imaging

The polymer electrolyte fuel cells (PEFCs) are regarded as a promising alternative power source for automobiles (fuel cell electric vehicle; FCEV). Cost reduction and increasing power density of PEFCs are the key challenges for commercialization of FCEVs. In PEFC, the chemical energy of fuel is directly converted into electricity through the electrochemical reactions on Platinum catalyst. Since Platinum is a noble metal, reduction of Platinum amount in the catalyst layer (CL) is essential to achieve cost reduction of FCEVs. In order to accomplish the reduction of Platinum loading without sacrificing PEFC performance under high current density operation, it is important to make more effective use of Pt used in the CL of the membrane electrode assembly (MEA), and the mass transport of reactants within the CL should be enhanced significantly. From this background, extensive number of diagnostic research for the fundamental understanding of the transport phenomena in operating PEFCs has been carried out. It is known that imaging technique is highly important to reveal dynamics and distribution of water within PEFCs, which include magnetic resonance imaging, neutron imaging, and synchrotron X-ray imaging [1]. However, because of the fine structure and the complexity of mas transport phenomena within the CL, water distribution and mass transport phenomena within the CL is not fully understand yet. In our group, water visualization technique by soft X-ray radiography that can be used in ordinary laboratory for PEFC research has been developed (Figure 1), and we have been succeeded to visualize water distribution within the CL, micro porous layers, and the gas diffusion layers [2-4]. In this study, the effect of Platinum loading on the liquid water accumulation and the mass transport phenomena within the cathode CL was investigated. Liquid water distribution within the CL was quantitatively visualized by soft X-ray imaging technique, and the CL with low Platinum loading showed higher water saturation. The electrochemical impedance spectroscopy (EIS) measurement obtained under the high current density condition indicated that the charge transfer resistance of the CL with low Platinum loading is higher than that of the CL with high Platinum loading. It might be due to the increased reaction rate per platinum particle within the CL with low Platinum loading [5]. It would exacerbate the mass transport limitation within the cathode CL. To accomplish the reduction of Platinum loading without sacrificing PEFC performance under high current density operation, further understanding on water distribution and mass transport phenomena within the CL is required. Soft X-ray imaging technique can visualize water distribution within the CL in-situ, and more detailed research will make it possible to optimize the structure of the CL. Acknowledgement: The authors acknowledged Dr. Kazuhiko Shinohara in Nissan Motor Co., Ltd. for his pioneering effort on soft X-ray application for PEFCs. This work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

PROMINENCE VISIBILITY INHINODE/XRT IMAGES

In this paper we study the soft X-ray (SXR) signatures of one particular prominence. The X-ray observations used here were made by the Hinode/XRT instrument using two different filters. Both of them have a pronounced peak of the response function around 10 A. One of them has a secondary smaller peak around 170 A, which leads to a contamination of SXR images. The observed darkening in both of these filters has a very large vertical extension. The position and shape of the darkening corresponds nicely with the prominence structure seen in SDO/AIA images. First we have investigated the possibility that the darkening is caused by X-ray absorption. But detailed calculations of the optical thickness in this spectral range show clearly that this effect is completely negligible. Therefore the alternative is the presence of an extended region with a large emissivity deficit which can be caused by the presence of cool prominence plasmas within otherwise hot corona. To reproduce the observed darkening one needs a very large extension along the line-of-sight of the region amounting to around 10$^5$ km. We interpret this region as the prominence spine, which is also consistent with SDO/AIA observations in EUV.

Invited Article: First flight in space of a wide-field-of-view soft x-ray imager using lobster-eye optics: Instrument description and initial flight results.

We describe the development, launch into space, and initial results from a prototype wide field-of-view soft X-ray imager that employs lobster-eye optics and targets heliophysics, planetary, and astrophysics science. The sheath transport observer for the redistribution of mass is the first instrument using this type of optics launched into space and provides proof-of-concept for future flight instruments capable of imaging structures such as the terrestrial cusp, the entire dayside magnetosheath from outside the magnetosphere, comets, the Moon, and the solar wind interaction with planetary bodies like Venus and Mars [Kuntz et al., Astrophys. J. (in press)].

Three-dimensional imaging of human stem cells using soft X-ray tomography.

Three-dimensional imaging of human stem cells using transmission soft X-ray tomography (SXT) is presented for the first time. Major organelle types--nuclei, nucleoli, mitochondria, lysosomes and vesicles--were discriminated at approximately 50 nm spatial resolution without the use of contrast agents, on the basis of measured linear X-ray absorption coefficients and comparison of the size and shape of structures to transmission electron microscopy (TEM) images. In addition, SXT was used to visualize the distribution of a cell surface protein using gold-labelled antibody staining. We present the strengths of SXT, which include excellent spatial resolution (intermediate between that of TEM and light microscopy), the lack of the requirement for fixative or contrast agent that might perturb cellular morphology or produce imaging artefacts, and the ability to produce three-dimensional images of cells without microtome sectioning. Possible applications to studying the differentiation of human stem cells are discussed.

MISTRAL: a transmission soft X-ray microscopy beamline for cryo nano-tomography of biological samples and magnetic domains imaging.

The performance of MISTRAL is reported, the soft X-ray transmission microscopy beamline at the ALBA light source (Barcelona, Spain) which is primarily dedicated to cryo soft X-ray tomography (cryo-SXT) for three-dimensional visualization of whole unstained cells at spatial resolutions down to 30 nm (half pitch). Short acquisition times allowing for high-throughput and correlative microscopy studies have promoted cryo-SXT as an emerging cellular imaging tool for structural cell biologists bridging the gap between optical and electron microscopy. In addition, the beamline offers the possibility of imaging magnetic domains in thin magnetic films that are illustrated here with an example.

Extreme ultraviolet and soft X-ray imaging with compact, table top laser plasma EUV and SXR sources

We present a few examples of imaging experiments, which were possible using a compact laser-plasma extreme ultraviolet (EUV) and soft X-ray (SXR) source, based on a double stream gas puff target. This debris-free source was used in full-field EUV imaging to obtain magnified images of test samples, ZnO nanofibers and images of the membranes coated with salt crystals. The source was also employed for SXR microscopy in the “water-window” spectral range using grazing incidence Wolter type-I objective to image test samples and to perform the initial studies of biological objects. Gas puff target EUV source, spectrally tuned for 13.5nm wavelength with multilayer mirror and thin film filters, was also used in variety of shadowgraphy experiments to study the density of newly developed modulated density gas puff targets. Finally, the source was also employed in EUV tomography experiments of low density objects with the goal to measure and optimize the density of the targets dedicated to high harmonic generation.

(Invited) Imaging and Quantitative Chemical Mapping of PEM-FC Catalyst Layers By Scanning Transmission X-Ray Microscopy

Low temperature, hydrogen-fueled, proton exchange membrane fuel cell (PEM-FC) based engines are being developed rapidly for near-term implementation in mass production, personal automobiles. Materials and process research aiming to further optimize these systems is focused on understanding and controlling various degradation processes (carbon corrosion, Pt migration, cold start), and reducing cost by reducing or eliminating Pt in the electro-catalyst, especially for the oxygen reduction reaction (ORR), and optimizing the nanoscale distribution of the cathode components. Soft X-ray scanning transmission X-ray microscopy (STXM) [1] is a powerful tool to study PEM-FC catalyst layers (membrane electrode assemblies, MEA). STXM provides spectroscopic identification and quantitative mapping of chemical components with 30 nm spatial resolution in both 2D projection and 3D spectro-tomography. For a given radiation dose, it provides much more chemical information than analytical transmission electron microscopy (TEM) and thus it has significant advantages for mapping ionomer in MEA cathodes [2, 3], which has proven to be a very challenging component to detect by TEM due to the high sensitivity of ionomer to radiation damage. This tutorial will describe the instrumentation, methodology and data analysis involved in applying STXM to PEM-FC catalyst layers, and illustrate its capabilities with results from recent studies [4, 5]. STXM performed on BL 10ID1 at the Canadian Light Source and on BL 5.3.2.2 at the Advanced Light Source. Research supported by AFCC, NSERC, Canada Research Chairs, and the Catalyst Research for Polymer Electrolyte Fuel Cells (CaRPE-FC) network. [1] A.P. Hitchcock, Soft X-ray Imaging and Spectromicroscopy in Handbook on Nanoscopy, eds.G. Van Tendeloo, D. Van Dyck and S. J. Pennycook 2012. (Wiley) [2] D. Susac, V. Berejnov, A.P. Hitchcock, and J. Stumper, ECS Transactions 41 (2011) 629. [3] D. Susac, V. Berejnov, A.P. Hitchcock and J. Stumper, ECS Transactions 50 (2012) 405 [4] A.P. Hitchcock, et al., J. Power Sources 266 (2014) 66 [5] V. Lee, et al. J. Power Sources 263 (2014) 163 Figure 1

Spatially Resolved Spectro-Electrochemistry Using Soft X-Ray Scanning Transmission X-Ray Microscopy

We are using soft X-ray scanning transmission X-ray microscopy (STXM) [1] at CLS beamline 10ID1 (SM) and at ALS beamline 5.3.2.2 to investigate Cu deposition onto, and stripping from a Au surface. Electrochemical reduction of Cu(II) under acid conditions is a commonly used process to deposit copper for integrated circuit interconnects. The reduction of Cu(II) to Cu(0) proceeds via a Cu(I) intermediate, which can be detected under neutral or basic conditions. Cu 2p and O 1s spectromicroscopy is used to analyze initial and final states, follow the process in situ, and search for intermediate species. The apparatus and techniques for spectro-electrochemical-microscopy will be described. Ex situ and in situ deposition & stripping of copper from CuCl2(aq) and CuSO4(aq) electrolytic solutions will be described. Progress towards an in situ flow electrochemical cell and a faster response time for kinetics measurements will be presented. STXM performed on BL 10ID1 at CLS and on BL 5.3.2.2 at ALS. Research supported by NSERC and the Catalyst Research for Polymer Electrolyte Fuel Cells (CaRPE-FC) network. [1] A.P. Hitchcock, Soft X-ray Imaging and Spectromicroscopy in Handbook on Nanoscopy, eds. G. Van Tendeloo, D. Van Dyck and S. J. Pennycook 2012. (Wiley) Figure 1

Measurement of the modulation transfer function of an X-ray microscope based on multiple Fourier orders analysis of a Siemens star.

Soft X-ray tomography (SXT) is becoming a powerful imaging technique to analyze eukaryotic whole cells close to their native state. Central to the analysis of the quality of SXT 3D reconstruction is the estimation of the spatial resolution and Depth of Field of the X-ray microscope. In turn, the characterization of the Modulation Transfer Function (MTF) of the optical system is key to calculate both parameters. Consequently, in this work we introduce a fully automated technique to accurately estimate the transfer function of such an optical system. Our proposal is based on the preprocessing of the experimental images to obtain an estimate of the input pattern, followed by the analysis in Fourier space of multiple orders of a Siemens Star test sample, extending in this way its measured frequency range.

Accessing the population of high-redshift Gamma Ray Bursts

Gamma Ray Bursts (GRBs) are a powerful probe of the high redshift Universe. We present a tool to estimate the detection rate of high-z GRBs by a generic detector with defined energy band and sensitivity. We base this on a population model that reproduces the observed properties of GRBs detected by Swift, Fermi and CGRO in the hard X-ray and gamma-ray bands. We provide the expected cumulative distributions of the flux and fluence of simulated GRBs in different energy bands. We show that scintillator detectors, operating at relatively high energies (e.g. tens of keV to the MeV), can detect only the most luminous GRBs at high redshifts due to the link between the peak spectral energy and the luminosity (Ep-Liso) of GRBs. We show that the best strategy for catching the largest number of high-z bursts is to go softer (e.g. in the soft X-ray band) but with a very high sensitivity. For instance, an imaging soft X-ray detector operating in the 0.2-5 keV energy band reaching a sensitivity, corresponding to a fluence of ~10^-8 erg cm^-2, is expected to detect ~40 GRBs yr^-1 sr^-1 at z>5 (~3 GRBs yr^-1 sr^-1 at z>10). Once high-z GRBs are detected the principal issue is to secure their redshift. To this aim we estimate their NIR afterglow flux at relatively early times and evaluate the effectiveness of following them up and construct usable samples of events with any forthcoming GRB mission dedicated to explore the high-z Universe.

Target strengths of two abundant mesopelagic fish species.

Mesopelagic fish of the Myctophidae and Sternoptychidae families dominate the biomass of the oceanic deep scattering layers and, therefore, have important ecological roles within these ecosystems. Interest in the commercial exploitation of these fish is growing, so the development of techniques for estimating their abundance, distribution and, ultimately, sustainable exploitation are essential. The acoustic backscattering characteristics for two size classes of Maurolicus muelleri and Benthosema glaciale are reported here based on swimbladder morphology derived from digitized soft x-ray images, and empirical (in situ) measurements of target strength (TS) derived from an acoustic survey in a Norwegian Sea. A backscattering model based on a gas-filled prolate spheroid was used to predict the theoretical TS for both species across a frequency range between 0 and 250 kHz. Sensitivity analyses of the TS model to the modeling parameters indicate that TS is rather sensitive to the viscosity, swimbladder volume ratio, and tilt, which can result in substantial changes to the TS. Theoretical TS predictions close to the resonance frequency were in good agreement (±2 dB) with mean in situ TS derived from the areas acoustically surveyed that were spatially and temporally consistent with the trawl information for both species.

Effect of aging on the osteoinductive activity of recombinant human bone morphogenetic protein-2 in rats

BackgroundBone morphogenetic proteins may hold broad potential for use in the reconstruction of bone defects resulting from tumor resection or trauma and in assisting bone healing thanks to methods enabling the synthesis of recombinant human bone morphogenetic protein-2 (rhBMP-2). MethodsrhBMP-2 was implanted with atelopeptide type I collagen as a carrier into the calf muscles of 3-, 8-, and 48-wk-old Wistar/ST male rats. After 21 d, the formation of ectopic neoplastic bone was examined in soft x-ray imaging, and the bone mineral content, bone area, and bone mineral density (BMD) were measured by dual-energy x-ray absorptiometry. In addition, hematoxylin-eosin and von Kossa staining and proliferation cell nuclear antigen immunostaining were performed. ResultsBMD values determined by dual-energy x-ray absorptiometry were 29.40 (standard deviation ±5.47), 24.15 (±2.33), and 19.01 (±2.02) mg/cm2 in the 3-, 8-, and 48-wk-old rats, respectively, demonstrating that BMD significantly decreased with aging (P < 0.05). The von Kossa stain-positive area decreased significantly with aging (P < 0.01). The number of proliferation cell nuclear antigen-positive cells also decreased significantly with aging (P < 0.01). ConclusionsThe capacity of rhBMP-2 to induce ectopic bone formation decreases with aging. These findings will be of considerable benefit in the development of clinical treatments for the regeneration of cranio-maxillofacial bone in elderly patients.

Cryo-STEM Tomography of Intact Vitrified Fibroblasts

Cryo-tomography of intact, vitrified cells provides a three dimensional view of their structure and organization in a snapshot of the living state. Lacking heavy metal stains, tilt series images are typically produced by defocus phase contrast. Recently, a number of other methods have been introduced for 3D cryo-imaging. These include phase plate imaging, soft X-ray tomography, serial surface imaging using the focused ion beam-scanning electron microscope, and cryo-STEM tomography (CSTET). Here we explain the basis of the STEM setup and demonstrate the capabilities of CSTET to study unfixed, fully hydrated mammalian cells. Numerous cellular features are recognized in CSTET reconstructions, including membranes, vesicles, cytoskeleton, extracellular matrix, coated pits, and ribosomes. STEM signal acquisition configuration is more flexible than defocus phase contrast, and it imposes a much less severe spatial filter on the original images. Because low spatial frequency information is retained, the STEM tomographic reconstruction more faithfully represents the mass density distribution in the specimen.

Analysis of ER-mitochondria contacts using correlative fluorescence microscopy and soft X-ray tomography of mammalian cells.

Mitochondrial fission is important for organelle transport, quality control and apoptosis. Changes to the fission process can result in a wide variety of neurological diseases. In mammals, mitochondrial fission is executed by the GTPase dynamin-related protein 1 (Drp1; encoded by DNM1L), which oligomerizes around mitochondria and constricts the organelle. The mitochondrial outer membrane proteins Mff, MiD49 (encoded by MIEF2) and MiD51 (encoded by MIEF1) are involved in mitochondrial fission by recruiting Drp1 from the cytosol to the organelle surface. In addition, endoplasmic reticulum (ER) tubules have been shown to wrap around and constrict mitochondria before a fission event. Up to now, the presence of MiD49 and MiD51 at ER-mitochondrial division foci has not been established. Here, we combine confocal live-cell imaging with correlative cryogenic fluorescence microscopy and soft x-ray tomography to link MiD49 and MiD51 to the involvement of the ER in mitochondrial fission. We gain further insight into this complex process and characterize the 3D structure of ER-mitochondria contact sites.

Coronal mass ejections: a driver of severe space weather

Coronal mass ejections: a driver of severe space weather

時系列解析のための年縞堆積物の特徴を検出する手法の適用 : 蒜山原層の年縞堆積物の軟X線画像を用いた例

時系列解析のための年縞堆積物の特徴を検出する手法の適用 : 蒜山原層の年縞堆積物の軟X線画像を用いた例

表面化学反応の実時間・実空間分解分光への挑戦： 不可逆かつ不均一な反応の追跡を目指して

A novel experimental technique, time-resolved wavelength-dispersive soft X-ray imaging spectroscopy, is proposed in order to achieve real-time and real-space resolved spectroscopy for the observation of irreversible and inhomogeneous surface chemical reactions. By combining the wavelength-dispersed soft X rays, in which the X-ray wavelength (photon energy) changes as a function of position on the sample, with the photoelectron emission microscope, the soft X-ray absorption spectra are separately obtained at different positions on the sample without scanning the X-ray monochromator. Therefore, the real-time resolved measurement of site-selective soft X-ray absorption spectroscopy is realized in one event without repeating the chemical reaction. It is expected that the spatial distribution of different chemical species is traced during the surface chemical reaction, which is essential to understand the reaction mechanism.

Plasma response measurements of non-axisymmetric magnetic perturbations on DIII-D via soft x-ray imaging

Recent observations on DIII-D have advanced the understanding of plasma response to applied resonant magnetic perturbations (RMPs) in both H-mode and L-mode plasmas. Three distinct 3D features localized in minor radius are imaged via filtered soft x-ray emission: (i) the formation of lobes extending from the unperturbed separatrix in the X-point region at the plasma boundary, (ii) helical kink-like perturbations in the steep-gradient region inside the separatrix, and (iii) amplified islands in the core of a low-rotation L-mode plasma. These measurements are used to test and to validate plasma response models, which are crucial for providing predictive capability of edge-localized mode control. In particular, vacuum and two-fluid resistive magnetohydrodynamic (MHD) responses are tested in the regions of these measurements. At the plasma boundary in H-mode discharges with n = 3 RMPs applied, measurements compare well to vacuum-field calculations that predict lobe structures. Yet in the steep-gradient region, measurements agree better with calculations from the linear resistive two-fluid MHD code, M3D-C1. Relative to the vacuum fields, the resistive two-fluid MHD calculations show a reduction in the pitch-resonant components of the normal magnetic field (screening), and amplification of non-resonant components associated with ideal kink modes. However, the calculations still over-predict the amplitude of the measured perturbation by a factor of 4. In a slowly rotating L-mode plasma with n = 1 RMPs, core islands are observed amplified from vacuum predictions. These results indicate that while the vacuum approach describes measurements in the edge region well, it is important to include effects of extended MHD in the pedestal and deeper in the plasma core.