Scanning Ion Microscopy Research Articles

Rubidium and Cesium Ion-Induced Electron and Ion Signals for Scanning Ion Microscopy Applications.

Scanning ion microscopy applications of novel focused ion beam (FIB) systems based on ultracold rubidium (Rb) and cesium (Cs) atoms were investigated via ion-induced electron and ion yields. Results measured on the Rb+ and Cs+ FIB systems were compared with results from commercially available gallium (Ga+) FIB systems to verify the merits of applying Rb+ and Cs+ for imaging. The comparison shows that Rb+ and Cs+ have higher secondary electron (SE) yields on a variety of pure element targets than Ga+, which implies a higher signal-to-noise ratio can be achieved for the same dose in SE imaging using Rb+/Cs+ than Ga+. In addition, analysis of the ion-induced ion signals reveals that secondary ions dominate Cs+ induced ion signals while the Rb+/Ga+ induced signals contain more backscattered ions.

Abstract P213: Mechanisms of Renin-Angiotensin System-Mediated Nitric Oxide Signaling in Podocytes

Introduction: The renin-angiotensin system (RAS) is a crucial cardiovascular and renal function regulator. Podocytes, glomerular epithelial cells that play a pivotal role in maintaining the renal filtration barrier, are key targets for RAS peptides. Our findings showed that RAS can promote calcium (Ca 2+ ) and nitric oxide (NO) signaling in podocytes. Moreover, a decrease in NO bioavailability directly correlates with glomerular filtration barrier damage, Ca 2+ overload, and the development of salt-sensitive hypertension. We hypothesized that RAS-mediated NO production is crucial for Ca 2+ control and cytoskeletal rearrangements in podocytes, contributing to glomerular filtration regulation. Methods: We performed live confocal imaging on human podocytes and freshly isolated rat glomeruli to detect the production of NO (DAF-FM) and Ca 2+ (Fluo-8). RAS peptides (Ang II, III, IV, 1-7, 1-9, and TRV120027) were used to stimulate cells, and NO and Ca 2+ production were measured. Blockers for Ang II Type 1 (AT1R), Ang II Type 2 (AT2R), and MAS receptors were used to identify the pathways involved in NO production. The dynamic changes in podocyte cytoskeleton mediated by RAS-NO intracellular signaling were detected using rhodamine-phalloidin staining and scanning ion microscopy. The NOS isoform-specific blockers were used to determine the source of NO in podocytes. ANOVA with post-hoc was used for comparisons. Results: Angiotensins II and III generate the most profound increases in NO levels in podocytes. Ang II, Ang III, and Ang 1-7 promote NO production by activating AT2R (n ≥ 20, p < 0.01). Interestingly, the increase in NO modulates AT1R- and β-arrestin-mediated Ca 2+ signaling (n ≥ 20, p < 0.05), suggesting the role of the NO/AT2R axis in Ca 2+ control in podocytes. NO production correlates with podocyte volume increase, and scanning ion microscopy experiments further confirmed that AT2R activation and corresponding NO elevation are responsible for the protrusion of podocyte's lamellipodia. Finally, we found that in podocytes, NOS1 is responsible for NO bioavailability, accounting for 69±5% of the total NO response, while the remaining NO levels are generated by NOS2 (39±5%). Conclusion: Our data show that RAS activation promotes NO production in podocytes, mainly via the AT2R pathway. NO is crucial for Ca 2+ control in podocytes and lamellipodia formation, suggesting the essential role of NO in glomerular filtration barrier function.

Stimulation of microvesicle secretion in Trichomonas vaginalis

Trichomonas vaginalis is an extracellular flagellate protozoan and the etiological agent of human trichomoniasis, a sexually transmitted infection (STI) with a high incidence. Several reports have shown that this protozoan releases microvesicles into the culture medium, which show high potential in modulating cell-to-cell communication and the host response to infections. However, the biogenesis of these vesicles has not been analyzed in detail. In the present study, high-resolution ion scanning microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the surface of control cells and cells incubated in the presence of Ca2+ alone or with A 23187 calcium ionophore. Two different strains of T. vaginalis were analyzed. Most control cells displayed relatively smooth surfaces, whereas cells incubated with Ca2+ had many surface projections of variable shape and size (from 40 nm to around 1 μm). Quantitative analyses were performed directly in the scanning electron microscope and showed a significant increase in the number of cells with surface projections after incubation in the presence of calcium. TEM showed that treated cells presented several cytoplasmic multivesicular structures, suggesting membrane fusion and exosomes in the extracellular medium. The amount and size of the released vesicles were quantitatively analyzed using light scattering and TEM on negatively stained samples.The observations show that incubation of both parasite strains in the presence of Ca2+ significantly increased the release of microvesicles into the extracellular medium in a time-dependent process. Sequential incubation in the presence of Ca2+ and the calcium ionophore A23187 increases the presence of vesicles on the parasite surface only at a short incubation time (5 min). Transmission electron microscopy showed that at least part of the vesicles are originated from cytoplasmic multivesicular structures. This information contributes to a better understanding of the biogenesis of extracellular vesicles secreted by T. vaginalis.

Scanning Ion Microscopy and Its Application in Microbiology

Helium ion microscopy, a scanning microscope operating with ions rather than electrons, is one of the best equipment to analyze the surface of cells and the surface of intracellular compartments exposed by different methods. This short review aims to show the advantages of resolution and depth of focus in some microorganisms such as viruses, bacteria, fungi and parasitic protists.

Inspection of Surface Damage in Composite Materials with Different Techniques

Due to their excellent physical properties and high strength and stiffness relative to density, aerospace industry research is producing high-performance structural materials, such as composites, which are used in many critical structural parts like airframes, wings, rotor blades, propellers, and other components. However, during flight, these materials may be damaged by impact, thermal stress, moisture, and ultraviolet radiation. One of the most prevalent issues with composite materials is their challenging nature in terms of flaw detection during both manufacturing and use. When they are employed in the crucial areas that were previously indicated, this becomes a very serious issue. When evaluating the structural integrity of composites and looking for any damage, microscopes are a very useful instrument. Effective methods for identifying and analyzing damage include microscopic procedures like optical microscopy, stereomicroscopy, scanning electron microscopy (SEM), scanning ion microscopy (SIM), and atomic force microscopy (AFM). A variety of methods may be employed with microscopes to examine and identify deterioration in composite materials. It is often possible to examine overt deterioration on the surface of composite materials under the microscope utilizing a number of different approaches and procedures. Determining the kind, extent, distribution, and impact of the damage requires these inspections. Often employed techniques consist of: SEM is a method for high-resolution imaging of surface damage. It entails shining an electron beam onto the sample's surface and capturing pictures. SEM is a useful tool for identifying erosion, delamination, and microcracks. It is also possible to measure things like the damage's breadth and depth. Optical microscopes have a large field of view and look at damaged regions. This makes it possible to find tiny fractures or cracks that are invisible to the unaided eye. Furthermore, details on the degree of harm, the roughness of the surface, and the breadth and depth of the fractures may be acquired. To see damaged objects, optical microscopy is utilized. Cracks and damage locations are visible with optical microscopy. Optical microscopes can identify different kinds of damage by looking at the surface of the material. Damage like delamination, fiber breakage, cracks, and deformations are a few examples of these. This study examines the efficacy of microscopic methods and non-destructive testing in assessing the different kinds of damage that can occur at the interfaces between holes in composite materials. Composite test materials were chosen from glass fiber reinforced phenolic matrix composites that were produced in compliance with aerospace standards. The measurements led to the conclusion that using microscopic techniques has benefits like speed and field suitability. However, the continuous development and improvement of new methods in this field will contribute to a better understanding of layered composite materials and the development of safer and more durable structures.

Strain Rate and Temperature Effects in Nanoindentation Testing on Hardness in Selective Laser Melting IN718

AbstractThe microstructure and mechanical hardness of Inconel 718 (INC718) hexagonal honeycomb cellular structure manufactured by selective laser melting (SLM) was studied in this work. Non-heat-treated SLM-produced samples with cell wall thicknesses of 0.4, 0.6, and 0.8 mm were studied. The hardness was measured using MTS Nanoindenter at different temperatures and strain rates. At room temperature, continuous hardness measurements through a penetration depth of 2 µm using three different strain rates (0.02, 0.05, and 0.08 s−1) were performed. At the temperatures 100 and 200 °C, single hardness measurements at eight different maximum loads were performed. Using scanning ion microscopy (SIM), the grain size was found to change significantly as the cell wall thickness reduced from 0.6 mm to 0.4 mm compared to the change from 0.8 mm to 0.6 mm. A similar trend in mechanical hardness reduction was observed in the three samples. The microstructure, hardness, and strain rate sensitivity displayed anisotropy in properties between the planes parallel and perpendicular to the build direction. A model describing the temperature, strain rate, and indentation size effects on hardness developed by the second author was modified and used to evaluate the intrinsic material length scale used in gradient plasticity theory.

Changes in Microstructure of NiCo-Dispersed SDC Hydrogen Electrodes for the Improvement of Durability via Reversible Cycling Operation Between SOEC and SOFC-Modes

A reversible solid oxide cell (R-SOC, operating as solid oxide electrolysis cell, SOEC and solid oxide fuel cell, SOFC) is a promising direct energy converter between hydrogen and electricity (1). We have engaged in the research and development of high-performance, durable electrodes with novel architecture for the R-SOC (2-12). Very recently, we found that the durability of a double-layer H2 (DL) electrode, consisting of a SDC scaffold [samaria-doped ceria (CeO2)0.8(SmO1.5)0.2] with highly dispersed Ni0.9Co0.1 nanoparticles as the catalyst layer (CL) and a thin current collecting layer (CCL) of Ni–YSZ cermet, was improved greatly by reversible cycling operation between the SOEC and SOFC modes (12). This presentation focuses on a stabilization of the microstructure of the CL in our hydrogen electrode via a reversible cycling operation. We prepared a coin-size cell with an air reference electrode (ARE) (6, 9-12):DL-H2 electrode│YSZ (0.5 mm)│SDC interlayer│LSCF–SDC O2 electrodeFor the DL-H2 electrode, 7.2 vol.% Ni0.9Co0.1 nanocatalyst was dispersed on SDC scaffold in the CL with addition of 10 vol.% three-dimensionally-connected Ni0.8Co0.2 (12, 13), and 60 vol.% Ni‒YSZ CCL was prepared on the CL. Test cells were operated in two operation protocols: a constant current density operation at −0.50 A cm−2 (SOEC-mode only) and a reversible cycling operation between −0.50 A cm−2 (SOEC-mode for 11 h) and 0.50 A cm−2 (SOFC-mode for 11 h) at 800ºC. Changes in the microstructure of the CL were analyzed by scanning ion microscopy (SIM) in a focused-ion beam system (FIB) in the depth direction from the CL/YSZ interface. In order to compare the actual degradation rates in the SOEC-mode for the two operation protocols, the values of IR-free potential E (vs. ARE) of each electrode and the ohmic resistance of the O2 and H2 electrode sides (R O2-side and R H2-side) during the operation at −0.50 A cm−2 are plotted in Fig. 1, while the inset shows changes in E as a function of the overall operation time. The degradation rate for R H2-side in the initial 200 h decreased as low as ca. 1/10 as a result of the cycling operation. In contrast to the negative shift in E for the SOEC-mode only, the positive shift in E at the H2 electrode in the cycling operation is clearly seen, i.e., the performance was improved. In the SIM image of pristine sample, fine Ni‒Co particles (ca. ⩽ 50 nm) are highly dispersed on the SDC scaffold. After the operation with SOEC-mode only, SDC particles are found to have agglomerated considerably, enclosing Ni‒Co particles, while fine Ni‒Co particles (ca. 50 nm) are dispersed on the surface. After the cycling operation, fine Ni‒Co particles still remain and agglomerated ones are also observed. Interestingly, the lower parts of many Ni‒Co particles are anchored tightly on the SDC support, and some portions are coated with SDC. Quantitative analyses of Ni‒Co are in progress, as a function of the distance from the interface. This work was supported by funds for the “Collaborative Industry-Academia-Government R&D Project for Solving Common Challenges toward Dramatically Expanded Use of Fuel Cells” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References S. D. Ebbesen, S. H. Jensen, A. Hauch, and M. B. Mogensen, Chem. Rev., 114, 10697 (2014). H. Uchida, N. Osada, and M. Watanabe, Electrochem. Solid-State Lett., 7, A500 (2004). N. Osada, H. Uchida, and M. Watanabe, J. Electrochem. Soc., 153, A816 (2006). Y. Tao, H. Nishino, S. Ashidate, H. Kokubo, M. Watanabe, and H. Uchida, Electrochim. Acta, 54, 3309 (2009). R. Nishida, P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, M. Watanabe, and H. Uchida, RSC Adv., 4, 16260 (2014). H. Uchida, P. Puengjinda, K. Miyano, K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and M. Watanabe, ECS Trans., 68 (1), 3307 (2015). K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, Electrochim. Acta, 225, 114 (2017). K. Shimura, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, J. Ceram. Soc. Jpn., 125, 218 (2017). P. Puengjinda, H. Nishino, K. Kakinuma, M. E. Brito, and H. Uchida, J. Electrochem. Soc., 164, F889 (2017). H. Uchida, P. Puengjinda, K. Shimura, H. Nishino, K. Kakinuma, and M. E. Brito, ECS Trans., 78 (1), 3189 (2017). H. Uchida, H. Nishino, K. Kakinuma, and M. E. Brito, ECS Trans., 91 (1), 2379 (2019). H. Uchida, H. Nishino, P. Puengjinda, and K. Kakinuma, J. Electrochem. Soc., 167, 134516 (2020). Figure 1

Application of ZnO Nanoparticles in Sn99Ag0.3Cu0.7-Based Composite Solder Alloys

The properties of Sn99Ag0.3Cu0.7 (SACX0307) solder alloy reinforced with ZnO nanoparticles were investigated. The primary ZnO particle sizes were 50, 100, and 200 nm. They were added to a solder paste at a ratio of 1.0 wt %. The wettability, the void formation, the mechanical strength, and the thermoelectric parameters of the composite solder alloys/joints were investigated. Furthermore, microstructural evaluations were performed using scanning electron and ion microscopy. ZnO nanoparticles decreased the composite solder alloys’ wettability, which yielded increased void formation. Nonetheless, the shear strength and the thermoelectric parameters of the composite solder alloy were the same as those of the SACX0307 reference. This could be explained by the refinement effects of ZnO ceramics both on the Sn grains and on the Ag3Sn and Cu6Sn5 intermetallic grains. This could compensate for the adverse impact of lower wettability. After improving the wettability, using more active fluxes, ZnO composite solder alloys are promising for high-power applications.

Functionalization of polyamide microfiltration membranes by supercritical solvent impregnation

The study reports the application of supercritical solvent impregnation to deliver antibacterial substance thymol to the defined polymeric structure of commercial polyamide microfiltration membranes. The process performed at a temperature of 40 °C and pressures of 10, 15, and 20 MPa was characterized by the fast impregnation in the first 30 min with thymol loadings up to 29 wt%. The maximal achieved thymol loading in the process was around 42 wt%, regardless the pressure. The scanning electron and ion microscopy analyses revealed that the membranes’ microstructure was preserved with a thymol content of 20 wt%, while a more prominent swelling effect was observed in samples with 35 wt% of thymol. The cross-flow filtration tests showed that the impregnation process did not harm the membranes’ functionality in samples with 20 wt% of thymol. These membranes exhibited strong anti-biofilm activity, and were less prone to the blockage with bacteria in comparison to neat membranes.

Surface structures consisting of chromatin fibers in isolated barley (Hordeum vulgare) chromosomes revealed by helium ion microscopy.

The chromosome compaction of chromatin fibers results in the formation of the nucleosome, which consists of a DNA unit coiled around a core of histone molecules associated with linker histone. The compaction of chromatin fibers has been a topic of controversy since the discovery of chromosomes in the 19th century. Although chromatin fibers were first identified using electron microscopy, the chromatin fibers on the surface of chromosome structures in plants remain unclear due to shrinking and breaking caused by prior chromosome isolation or preparation with alcohol and acid fixation, and critical point drying occurred into dehydration and denatured chromosomal proteins. This study aimed to develop a high-quality procedure for the isolation and preparation of plant chromosomes, maintaining the native chromosome structure, to elucidate the organization of chromatin fibers on the surface of plant chromosomes by electron microscopy. A simple technique to isolate intact barley (Hordeum vulgare) chromosomes with a high yield was developed, allowing chromosomes to be observed with a high-resolution scanning ion microscopy and helium ion microscopy (HIM) imaging technology, based on a scanning helium ion beam. HIM images from the surface chromatin fibers were analyzed to determine the size and alignment of the chromatin fibers. The unit size of the chromatin fibers was 11.6 ± 3.5 nm and was closely aligned to the chromatin network model. Our findings indicate that compacting the surface structure of barley via a chromatin network and observation via HIM are powerful tools for investigating the structure of chromatin.

Estimation of needle height using relative parallax between two SIM images in single-column focused ion beam instrument

Gallium liquid metal ion source focused ion beam (FIB) instruments are widely used for cross-sectional sample preparation of specific areas of interest for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Most FIB instruments are equipped with a metal needle for manipulation of the sample in the sample chamber most commonly as a micro-sampling probe for preparing TEM samples. Automatic needle manipulation has not yet been achieved for a conventional single-column FIB instrument without an SEM column because a reliable method for measuring needle height has not been established yet. This study investigated the use of scanning ion microscope (SIM) image processing to measure needle height from the sample surface in a conventional single-column FIB instrument without an SEM column. The needle height is measured using the relative parallax between two SIM images in which the needle is observed from two directions using a conventional aligner without the use of any special devices. It was demonstrated that the relative parallax was proportional to the needle height. The estimation precision was about several 10 μm, which is sufficient for automatic manipulation and safe touchdown of a needle in practical micro-sampling.

Low Temperature Growth of the Nanotextured Island and Solid 3C-SiC Layers on Si from Hydric Si, Ge and C Compounds

Different growth stages and surface morphology of the epitaxial 3C-SiC/Si(100) structures were studied. Heterocompositions were grown in vacuum from hydric compounds at a lower temperature. The composition, surface morphology and crystal structure of the 3C-SiC films were tested using X-ray diffraction, second ion mass spectrometry, scanning ion and electron microscopy, photo- and cathode luminescence. It was demonstrated that the fine crystal structure of the 3C-SiC islands was formed by the close-packed nanometer-size grains and precipitated on the underlying solid carbonized Si layer. Luminescence spectral lines of the solid carbonized Si layer, separated island and solid textured 3C-SiC layer were shifted toward the high ultraviolet range. The spectra measured by different methods were compared and the nature of the revealed lines was considered. This article discusses a quantum confinement effect observation in the 3C-SiC nanostructures and a perspective for the use of nanotextured island 3C-SiC layers as a two-dimensional surface quantum superlattice for high-frequency applications. The conductivity anisotropy and current-voltage characteristics of the two-dimensional superlattices with a non-additive electron dispersion law in the presence of a strong electric field were studied theoretically. Main efforts were focused on a search of the mechanisms allowing realization of the high-frequency negative dynamical conductivity for the structures having a positive static differential conductivity.

Controlled Focused Ion Beam Milling of Composite Solid State Nanopore Arrays for Molecule Sensing.

Various nanoscale fabrication techniques are elaborated to form artificial nanoporous/nanochannel membranes to be applied for biosensing: one of the most prevalent is the micro-electromechanical systems (MEMS) compatible focused ion beam (FIB) milling. This technique can be easily adopted in micro- and nanomachining process sequences to develop composite multi-pore structures, although its precision and reproducibility are key points in the case of these thick multi-layered membranes. This work is to demonstrate a comprehensive characterisation of FIB milling to improve the reliability of the fabrication of solid state nanopore arrays with precisely predetermined pore geometries for a targeted molecule type to be recognised. The statistical geometric features of the fabricated nanopores were recorded as the function of the process parameters, and the resulting geometries were analysed in detail by high resolution scanning electron microscope (SEM), transmission electron microscope (TEM) and ion scanning microscopy. Continuous function of the pore diameter evolution rate was derived from the experimental results in the case of different material structures, and compared to former dissentient estimations. The additional metal layer was deposited onto the backside of the membrane and grounded during the ion milling to prevent the electrical charging of dielectric layers. The study proved that the conformity of the pore geometry and the reliability of their fabrication could be improved significantly. The applicability of the developed nanopore arrays for molecule detection was also considered by characterising the pore diameter dependent sensitivity of the membrane impedance modulation based measurement method.

Progression of diabetic kidney disease in T2DN rats.

Diabetic kidney disease (DKD) is one of the leading pathological causes of decreased renal function and progression to end-stage kidney failure. To explore and characterize age-related changes in DKD and associated glomerular damage, we used a rat model of type 2 diabetic nephropathy (T2DN) at 12 wk and older than 48 wk. We compared their disease progression with control nondiabetic Wistar and diabetic Goto-Kakizaki (GK) rats. During the early stages of DKD, T2DN and GK animals revealed significant increases in blood glucose and kidney-to-body weight ratio. Both diabetic groups had significantly altered renin-angiotensin-aldosterone system function. Thereafter, during the later stages of disease progression, T2DN rats demonstrated a remarkable increase in renal damage compared with GK and Wistar rats, as indicated by renal hypertrophy, polyuria accompanied by a decrease in urine osmolarity, high cholesterol, a significant prevalence of medullary protein casts, and severe forms of glomerular injury. Urinary nephrin shedding indicated loss of the glomerular slit diaphragm, which also correlates with the dramatic elevation in albuminuria and loss of podocin staining in aged T2DN rats. Furthermore, we used scanning ion microscopy topographical analyses to detect and quantify the pathological remodeling in podocyte foot projections of isolated glomeruli from T2DN animals. In summary, T2DN rats developed renal and physiological abnormalities similar to clinical observations in human patients with DKD, including progressive glomerular damage and a significant decrease in renin-angiotensin-aldosterone system plasma levels, indicating these rats are an excellent model for studying the progression of renal damage in type 2 DKD.

Channeling Contrast Simulation of Secondary Electron Images in Scanning Ion Microscopes

Channeling Contrast Simulation of Secondary Electron Images in Scanning Ion Microscopes

The influence of the crystallographic structure of the intermetallic grains on tin whisker growth

In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (∼400 nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallographic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones.

Unsupported Pt3ni Aerogels As High Stability Catalysts for PEFC Anodes Under Fuel Starvation Conditions

In polymer electrolyte fuel cells (PEFCs), both anodic and cathodic Pt/C catalysts suffer from significant corrosion of the carbon support during the high potential excursions (> 1 V vs. the reversible hydrogen electrode) concomitant to PEFC operation, which limit the device’s service life. Therefore, further cost reductions could be achieved using catalysts with higher durability, also allowing lower Pt loadings. In this respect, anode catalysts with high stability in cases of gross hydrogen starvation events constitute a pressing need. The latter fuel starvation events are caused by the blockage of the hydrogen gas flow in an anode flow field by water droplets, leading to anode potential increases from ≈ 0 V to ≥ 1.5 V.1 At these potentials, significant corrosion of the carbon support in commercial Pt on carbon black (Pt/CB) catalysts and concomitant performance decreases have been reported.2 Motivated by our previous study, in which an unsupported Pt3Ni aerogel demonstrated remarkable corrosion stability as a PEFC cathode catalyst,3 in this work, the applicability of the former material on the anode side was investigated. Pt3Ni aerogel catalyst was synthesized according to the steps described in reference 4, and commercial Pt/CB (47 wt% Pt, TKK, TEC10E50E) and Pt on graphitized carbon black (Pt/GCB, 30 wt% Pt, TKK, TEC10EA30E) catalysts were used as benchmarks. The hydrogen starvation events were simulated by an accelerated stress test (AST) performed at 80°C, 100% RH, ambient pressure, and H2 / N2 flows of 100 ml/min at cathode and anode, respectively. Under these conditions, 250 potential cycles in a square wave voltammetry pattern between 0 and 1.5 V with a holding time of 10 s at each potential were applied to the anode side (Figure 1). Figure 2 shows polarization curves of membrane electrode assemblies (MEAs) utilizing Pt3Ni aerogel, Pt/CB or Pt/GCB as anode catalysts (with loadings of ≈ 0.05 mgPt/cm2 anode) at beginning and end-of-life (BOL, EOL). The agreement of the BOL data indicates that the performance attained with the aerogel CLs is identical to that obtained with the commercial benchmark catalyst. Interestingly, the AST caused a large performance deterioration for the MEA using Pt/CB or Pt/GCB at the anode, whereas the cell using Pt3Ni was not affected at all. The reasons for the former degradation were investigated using electrochemical impedance spectroscopy and hydrogen pump tests to decouple the overpotential contributions to the materials’ BOL and EOL performance. Figure 2 displays the hydrogen oxidation/evolution polarization curves recorded in these H2-pump experiments, whereby the measured potential was corrected for the cell resistance (R). H2-pump polarization curves in Figure 3A recorded on the Pt3Ni aerogel at BOL and EOL almost completely overlay, indicating minimal kinetic and/or mass transport losses. On the other hand, the overall potential increased for Pt/CB and Pt/GCB (Figures 3B and 3C). The EOL polarization curves for Pt/CB and Pt/GCB deviate from the purely kinetic response derived from the fitting to the Butler-Volmer equation at current densities above 0.5 A/cm2 (see insets in Figures 3B and 3C), pointing at significant mass transport limitations by the end of the AST. To understand the reason for the profound increases in ηtx,anode of Pt3Ni, Pt/CB and Pt/GCB anodes, their catalyst layer structure was investigated by scanning ion microscopy and compared to that of the initial state (Figure 4). For the images of Pt3Ni catalyst surfaces, no change was observed. On the other hand, the Pt/CB and Pt/GCB catalysts at EOL were collapsed and became dense compared to their initial structure, thereby explaining the poor gas transport in the catalyst layers. Ultimately, this approach leads to the conclusion that the majority of the performance losses are related to changes in the anodic CL mass transport properties. It also illustrates the superiority of the Pt3Ni aerogel vs. Pt/CB and Pt/GCB as a PEFC anode catalyst. Acknowledgement This work was carried out in the Electrochemistry Laboratory of Paul Scherrer Institute and funded by the Swiss National Science Foundation (20001E_151122/1), the German Research Foundation (EY 16/18-1) and the European Research Council (ERC AdG 2013 AEROCAT). References 1) P. Rodriguez, T.J. Schmidt, Encyclopedia of Applied Electrochemistry, Springer New York, New York, NY, 1606(2014). 2) J. Speder, A. Zana, I. Spanos, J.J.K. Kirkensgaard, K. Mortensen, M. Hanzlik, M. Arenz, J. Power Sources 261, 14(2014). 3) S. Henning, J. Herranz, H. Ishikawa, B.J. Kim, D. Abbott, L. Kühn, A. Eychmüller, T.J. Schmidt, J. Electrochem. Soc. 164, F1136(2017). 4) S. Henning, L. Kühn, J. Herranz, J. Durst, T. Binninger, M. Nachtegaal, M. Werheid, W. Liu, M. Adam, S. Kaskel, A. Eychmüller, T.J. Schmidt, J. Electrochem. Soc. 163, F998(2016). Figure 1

Simulation of channeling contrast in scanning ion microscope images

The scanning ion microscope (SIM) provides a distinct channeling contrast in backscattered ion (BSI) and secondary electron (SE) images owing to its wide critical angle for ion channeling. In this report, we present a molecular dynamics (MD) simulation of a crystalline sample’s channeling contrast that has been scanned by ion beams of 30 keV He, Ne, and Ga in the SIM. A middle portion of the sample surface inclined at different angles against neighboring sides oriented toward the ions’ channeling direction. Line profiles of the BSI and SE yields along the surface reproduced crystalline-oriented changes that are expected for a transparency model. Nevertheless, a trajectory simulation of the ions in the sample according to the MD technique suggests some contrast differences from that of the model for the BSI and SE images and for different ion species.

Selective production of hydrogen ion species at atomically designed nanotips

Hydrogen scanning ion microscopy systems rely on nanotip gas field ion sources to generate the hydrogen ion beam. The exact structure of the nanotip and the applied electric field are shown to be important. It is demonstrated that hydrogen ion beams are found to occur as mixtures of H+, H2+ and H3+ depending on the electric field strength and the nanotip structure. Various nanotips were prepared, including single atom tips (SATs), trimers and other nano-structured tips to compare the contents of hydrogen ion beams. It was found that single atom tips produce primarily H2+ at low operating voltages, but as the voltage is increased, H3+ dominates. For the trimer case, H2+ becomes a significant species and equals the H3+ current but H3+ can be isolated at higher voltages. For the hexamer tip structure, H2+ almost completely dominates with little H3+ being produced. H+ is only observed in small quantities for all tip structures until a high voltage regime, where apex atom resolution is not observed. Comparisons W SATs and Ir SATs showed similar H3+/H2+ product ratios indicating the nanotip structure plays a key role in the catalytic formation of H3+. Temperature affects are also discussed and operating parameters for single species ion beams are discussed.

Ultrastructural Characterization of the Glomerulopathy in Alport Mice by Helium Ion Scanning Microscopy (HIM)

The glomerulus exercises its filtration barrier function by establishing a complex filtration apparatus consisting of podocyte foot processes, glomerular basement membrane and endothelial cells. Disruption of any component of the glomerular filtration barrier leads to glomerular dysfunction, frequently manifested as proteinuria. Ultrastructural studies of the glomerulus by transmission electron microscopy (TEM) and conventional scanning electron microscopy (SEM) have been routinely used to identify and classify various glomerular diseases. Here we report the application of newly developed helium ion scanning microscopy (HIM) to examine the glomerulopathy in a Col4a3 mutant/Alport syndrome mouse model. Our study revealed unprecedented details of glomerular abnormalities in Col4a3 mutants including distorted podocyte cell bodies and disorganized primary processes. Strikingly, we observed abundant filamentous microprojections arising from podocyte cell bodies and processes, and presence of unique bridging processes that connect the primary processes and foot processes in Alport mice. Furthermore, we detected an altered glomerular endothelium with disrupted sub-endothelial integrity. More importantly, we were able to clearly visualize the complex, three-dimensional podocyte and endothelial interface by HIM. Our study demonstrates that HIM provides nanometer resolution to uncover and rediscover critical ultrastructural characteristics of the glomerulopathy in Col4a3 mutant mice.