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Understanding how water interacts with nanopores of carbonaceous electrodes is crucial for energy storage and conversion applications. A high surface area of carbonaceous materials does not necessarily need to translate to a high electrolyte‐solid interface area. Herein, we study the interaction of water with nanoporous C1N1 materials to explain their very low specific capacitance in aqueous electrolytes despite their high surface area. Water was used to probe chemical environments, provided by pores of different sizes, in 1H MAS NMR experiments. We observe that regardless of their high hydrophilicity, only a negligible portion of water can enter the nanopores of C1N1, in contrast to a reference pure carbon material with a similar pore structure. The common paradigm that water easily enters hydrophilic pores does not apply to C1N1 nanopores below a few nanometers. Calorimetric and sorption experiments demonstrated strong water adsorption on the C1N1 surface, which restricts water mobility across the interface and impedes its penetration into the nanopores. [ABSTRACT FROM AUTHOR]

Nanofiber mats with a high surface-to-volume ratio can be prepared by electrospinning. The Porosity is sometimes reported to be tunable by blending different materials, e.g., water-soluble poly(ethylene oxide) (PEO) with not water-soluble poly(acrylonitrile) (PAN). Here, nanofiber mats were electrospun from different PAN:PEO ratios, using a wire-based electrospinning machine "Nanospider Lab". Investigations of the as-spun nanofiber mats as well as of membranes after washing off the water-soluble PEO by scanning electron microscopy (SEM) revealed severe differences in the nanofiber mat morphologies, such as varying fiber diameters and especially non-fibrous areas in the carbonized nanofiber mats, depending on the amount of PEO in the nanofiber mat as well as the molecular weight of the PEO. Similarly, the ratio and molecular weight of PEO influenced the results of stabilization and carbonization. This paper discusses the possibility of tailoring nanofiber porosity for the potential use of PAN nanofiber mats in tissue engineering, filtration, and other applications. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) is a unidirectional magnetic anisotropy that is found in structures containing exchange-coupled ferromagnetic/antiferromagnetic interfaces. The EB usually manifests as a horizontal shift of the hysteresis after cooling the system through the Néel temperature of the antiferromagnet in the presence of an external magnetic field. A vertical shift and an asymmetry of the magnetization loop are also possible. At present, the EB is often investigated for its effect on an application in magnetic devices in a variety of material systems and applications. The EB bilayer systems Fe/FeF2 and Fe/MnF2 represent an interesting case of structural similarities. In this paper, we show that differences between magnetic material orders and disorder contributions, found at the microscale, make them model systems for the occurrence of specific magneto-crystalline anisotropies and specific angular dependencies of the EB with significant implications for magneto-electronic applications. [ABSTRACT FROM AUTHOR]

Electric field control of magnetic properties offers a broad and promising toolbox for enabling ultra-low power electronics. A key challenge with high technological relevance is to master the interplay between the magnetic anisotropy of a ferromagnet and the exchange coupling to an adjacent antiferromagnet. Here, we demonstrate that magneto-ionic gating can be used to achieve a very stable out-of-plane (OOP) oriented magnetization with strong exchange bias in samples with as-deposited preferred in-plane (IP) magnetization. We show that the perpendicular interfacial anisotropy can be increased by more than a factor 2 in the stack Ta/Pt/PtMn/Co/HfO2 by applying −2.5 V gate voltage over 3 nm HfO2, causing a reorientation of the magnetization from IP to OOP with a strong OOP exchange bias of more than 50 mT. Comparing two thicknesses of PtMn, we identify a notable trade-off: while thicker PtMn yields a significantly larger exchange bias, it also results in a slower response to ionic liquid gating within the accessible gate voltage window. These results pave the way for post-deposition electrical tailoring of magnetic anisotropy and exchange bias in samples requiring significant exchange bias. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) is a unidirectional anisotropy that occurs, e.g., upon field‐cooling ferromagnet/antiferromagnet systems. In many material systems, the EB field is reduced from one hysteresis loop to the next measurement. This so‐called training effect (TE) has been investigated in experiments and by means of theoretical efforts by many research groups. The reduction of the EB field as a result of subsequent magnetization reversal processes is often fitted by a power law, usually with the exception of n = 1, or with an equation based on the discretized Landau–Khalatnikov equation, as first suggested by Binek. Few other models, usually with more fitting parameters, have been proposed yet. Herein, it is shown that for large numbers of subsequent magnetization reversal processes in Co/CoO thin film samples, a modified power law or a logarithmic fit can model the TE in most cases as well as the abovementioned, commonly used models. [ABSTRACT FROM AUTHOR]

Many metals form nanometer‐thin self‐passivating oxide layers upon exposure to the atmosphere, which affects a wide range of interfacial properties and shapes the way how metals interact with their environment. Such native oxide layers are commonly analyzed by X‐ray photoelectron spectroscopy (XPS), which provides a depth‐resolved chemical state and compositional analysis either by ion etching or modeling of the electron escape depths. The latter is commonly used to calculate the average thickness of a native oxide layer. However, the measurement of concentration profiles at the oxide‐metal interface remains challenging. Here, a simple and accessible approach for the depth profiling of ultrathin oxide layers within single fixed‐angle XPS spectra is proposed. Instead of using only one peak in the spectrum, as is usually the case, all peaks within the energy range of a standard lab device are utilized, thus resembling energy‐resolved XPS without the need for a synchrotron. New models that allow the calculation of depth‐resolved concentration profiles at the oxide‐metal interface are derived and tested, which are also valid for angular‐ and energy‐resolved XPS. The proposed method not only improves the accuracy of earlier approaches but also paves the way for a more holistic understanding of the XPS spectrum. [ABSTRACT FROM AUTHOR]

Exchange bias (EB) is a unidirectional anisotropy caused by interface coupling between a ferromagnet and an antiferromagnet. It causes a preferential direction of magnetization in the ferromagnet, which manifests as a shift of the hysteresis loop along the magnetic field axis. Here, we demonstrate a large EB of over 1000 Oe at 20 K in a twinned Co(111)/Co3O4(111) thin film epitaxially grown on sapphire(0001) with sixfold rotational lattice symmetry, which is among the highest values reported for Co/Co1−yO systems. In such systems, the effect intensity is largest along the magnetic easy axes, which usually results in an anisotropy of the EB in epitaxial interfaces. However, we observed identical EB values for 0°, 15°, and 30° angles between the magnetic field and the nearest Co[002] magnetic easy axes. The measurements imply a relaxation of the magnetization to the nearest easy axis, suggesting increasingly isotropic EB fields with higher orders of rotational lattice symmetry. [ABSTRACT FROM AUTHOR]

Exchange bias (EB) is a unidirectional anisotropy occurring in exchange-coupled ferromagnetic/antiferromagnetic systems, such as thin films, core–shell particles, or nanostructures. In addition to a horizontal shift of the hysteresis loop, defining the exchange bias, asymmetric loops and even vertical shifts can often be found. While the effect is used in hard disk read heads and several spintronics applications, its origin is still not fully understood. Especially in nanostructures with their additional shape anisotropies, interesting and often unexpected effects can occur. Here, we provide an overview of the most recent experimental findings and theoretical models of exchange bias in nanostructures from different materials. [ABSTRACT FROM AUTHOR]

The hysteresis loops of magnetic samples can be measured by the magneto‐optical Kerr effect (MOKE), while magnetic force microscopy (MFM) is used to depict domain walls or spatially resolved magnetization orientation in magnetic nanostructures or thin films. Both methods are commonly applied on thin films with a perfectly flat surface or on nanostructures. Here, we report MOKE and MFM measurements on a new class of magnetic materials, namely electrospun mats of randomly oriented nanofibers which influence the 30 nm Co coating layer, proving especially the MOKE method utilizable for rough surfaces. Possible interpretations of these first MOKE measurements on highly randomly structured magnetic layers are given. [ABSTRACT FROM AUTHOR]

Vacuum casting (VC) of reactive polymer resins in silicone molds is one of the oldest rapid tooling methods. It is widely used in the industry for prototype and small‐series production of thermoset plastic parts. Despite its widespread use, its scientific exploration is still scarce compared to other prototyping methods, such as three‐dimensional (3D) printing. Compared to conventional 3D printing methods, a wide range of excellent material properties can be achieved, making it well suited for the production of functional prototypes and even final products. The properties of the thermosets are comparable to those of injection molding in terms of viable shapes, mold fidelity, and material properties. However, due to the high cycle time and limited service life of the molds, VC is rarely utilized for mid‐ or large‐series production. Here, we provide a comprehensive overview of the state of the art and recent advances in the field. The review also provides a detailed technical introduction to the mold production, the process flow, and the materials used. A particular focus is on the key challenges facing industrial‐scale VC today—how to reduce cycle time, and how to increase mold service life? [ABSTRACT FROM AUTHOR]

Vacuum casting of polyurethane (PUR) in silicone molds is used industrially for the production of prototypes and small series as well as in various noncommercial research areas. This includes the reproduction of archeological findings, biological samples or electronic devices. In this study, the authors investigate the molding accuracy of different commercial silicones and PUR casting resins both on microscopic and macroscopic scales. For this, they used a variety of master models to generate silicone rubber casting molds. The resulting PUR castings are investigated by helium ion microscopy, confocal laser scanning microscopy, and optical 3D‐scanning. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile can be used as a base material for thermochemical conversion into carbon. Especially nanofiber mats, produced by electrospinning, are of interest to create carbon nanofibers. Optimal stabilization and carbonization parameters, however, strongly depend on the spatial features of the original material. While differences between nano- and microfibers are well known, this paper shows that depending on the electrospinning method and the solvent used, considerable differences between various nanofiber mats have to be taken into account for the optimization of the stabilization conditions. Here, we examine for the first time polyacrylonitrile nanofiber mats, electrospun with wire electrospinning from the low-toxic dimethyl sulfoxide as a solvent, instead of the typically used needle electrospinning from the toxic dimethylformamide. Additionally, we used inexpensive polyacrylonitrile from knitting yarn instead of highly specialized material, tailored for carbonization. Our results show that by carefully controlling the maximum stabilization temperature and especially the heating rate, fully stabilized polyacrylonitrile fibers without undesired interconnections can be created as precursors for carbonization. [ABSTRACT FROM AUTHOR]

Vacuum casting of polyurethane in silicone molds is a widely used method for prototype replication and holds great potential for application in small batch production. Products produced in this way offer extremely good shape accuracy even in the nanometer range and high surface quality, as well as flexible material properties that are convenient for serial production. In this work, we present a new method for increasing the feasible output of silicone casting molds in vacuum casting processes. By supplementation of polyamide 12 powder, which is a waste product of the selective laser sintering process, to the silicone rubber the maximum output of the casting molds could be increased by up to 38.5% while the amount of new silicone used has been substituted by up to 20%. Both generic silicone samples and representative silicone molds have shown that with increasing polyamide content, aging characteristics decrease as the output increases. The improvement was quantified by comparative weight, hardness and thermogravimetric measurements. As surface energy and roughness measurements as well as extensive casting experiments have shown, the silicone surface and thus the product surface remains unimpaired. [ABSTRACT FROM AUTHOR]

Textile fabrics are often subject to abrasion, starting from exposed parts of garments to a variety of technical textiles. Abrasion protection by usual coatings, however, can significantly decrease the water vapor transport through a fabric which is often not desired, especially in the case of garments. In our paper, we report on an approach to combine increased abrasion resistance with sufficient water vapor transport properties. For this, different polymers (poly(methyl methacrylate), acrylonitrile butadiene styrene, or amorphous polyamides) were coated on cotton and polyester woven fabrics. The results of abrasion tests against sandpaper show significantly increased abrasion resistance. The absolute evaporation resistance, measured by a Permetest testing device, was only slightly increased up to values still acceptable for typical garments. Images of all coatings by helium ion microscopy deliver an explanation for the measuring results. Polymer coatings on the polyester fabric resulted in a slight reduction of the hydrophobicity, while coating the cotton fabric severely increased the contact angles of the originally superhydrophilic material. [ABSTRACT FROM AUTHOR]

We present an in-depth investigation of the aging effects in silicone molds for vacuum casting processes. Their lifetime is limited to a few production cycles due to contamination with the diisocyanate component of polyurethane casting materials. Using thermogravimetric analysis measurements, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and helium-ion-microscopy the chemical and physical mechanisms of the aging process have been identified. It has been shown that a diffusion process of diisocyanate into the cavity surface leads to the formation of interpenetrating polymer networks of polyurea derivatives in silicone rubber. This has been proven by extracting and analyzing polyurea of low molecular weights from the silicone. [ABSTRACT FROM AUTHOR]

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Carbon nanofibers are used for a broad range of applications, from nano-composites to energy storage devices. They are typically produced from electrospun poly(acrylonitrile) nanofibers by thermal stabilization and carbonization. The nanofiber mats are usually placed freely movable in an oven, which leads to relaxation of internal stress within the nanofibers, making them thicker and shorter. To preserve their pristine morphology they can be mechanically fixated, which may cause the nanofibers to break. In a previous study, we demonstrated that sandwiching the nanofiber mats between metal sheets retained their morphology during stabilization and incipient carbonization at 500 °C. Here, we present a comparative study of stainless steel, titanium, copper and silicon substrate sandwiches at carbonization temperatures of 500 °C, 800 °C and 1200 °C. Helium ion microscopy revealed that all metals mostly eliminated nanofiber deformation, whereas silicone achieved the best results in this regard. The highest temperatures for which the metals were shown to be applicable were 500 °C for silicon, 800 °C for stainless steel and copper, and 1200 °C for titanium. Fourier transform infrared and Raman spectroscopy revealed a higher degree of carbonization and increased crystallinity for higher temperatures, which was shown to depend on the substrate material. [ABSTRACT FROM AUTHOR]

Electrospun poly(acrylonitrile) (PAN) nanofibers are typical precursors of carbon nanofibers. During stabilization and carbonization, however, the morphology of pristine PAN nanofibers is not retained if the as-spun nanofiber mats are treated without an external mechanical force, since internal stress tends to relax, causing the whole mats to shrink significantly, while the individual fibers thicken and curl. Stretching the nanofiber mats during thermal treatment, in contrast, can result in fractures due to inhomogeneous stress. Previous studies have shown that stabilization and carbonization of PAN nanofibers electrospun on an aluminum substrate are efficient methods to retain the fiber mat dimensions without macroscopic cracks during heat treatment. In this work, we studied different procedures of mechanical fixation via metallic substrates during thermal treatment. The influence of the metallic substrate material as well as different methods of double-sided covering of the fibers, i.e., sandwiching, were investigated. The results revealed that sandwich configurations with double-sided metallic supports not only facilitate optimal preservation of the original fiber morphology but also significantly accelerate the carbonization process. It was found that unlike regularly carbonized nanofibers, the metal supports allow complete deoxygenation at low treatment temperature and that the obtained carbon nanofibers exhibit increased crystallinity. [ABSTRACT FROM AUTHOR]

The use of a political marketing framework to describe modern party election campaigns can be useful for comparison overtime, between and within countries. This paper concentrates on inter-country comparisons, examining the election campaigns of the West German Christian Democrats in 1983. the British Conservatives in 1983 and the Irish Fine Gael party in 1981. Political marketing is defined as the application of promotional activities to direct an exchange with voters through the use of such instruments as product policy, communications policies and distribution. Among the paper's main findings are, first, that the (DU were the only party to have communications policies which closely matched their product policy and, second, that distribution activities appear to be where future campaign developments arc likely to concentrate. The paper concludes with a discussion on some specific aspects of political marketing including effects, financial corruption and the part political marketing plays in the general evolution of the electoral process. [ABSTRACT FROM AUTHOR]

Electrospinning can be used to prepare nanofibers from various polymers and polymer blends. The adhesion of nanofibers to the substrates on which they are electrospun varies greatly with the substrate material and structure. In some cases, good adhesion is desired to produce sandwich structures by electrospinning one material directly onto another. This is the case, e.g., with dye-sensitized solar cells (DSSCs). While both pure foil DSSCs and pure electrospun DSSCs have been examined, a combination of both technologies can be used to combine their advantages, e.g., the lateral strength of foils with the large surface-to-volume ratio of electrospun nanofibers. Here, we investigate the morphology and adhesion of electrospun nanofibers on different foil substrates containing materials commonly used in DSSCs, such as graphite, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) or TiO2. The results show that the foil material strongly influences the adhesion, while a plasma pretreatment of the foils showed no significant effect. Moreover, it is well known that conductive substrates can alter the morphology of nanofiber mats, both at microscopic and macroscopic levels. However, these effects could not be observed in the current study. [ABSTRACT FROM AUTHOR]

Polyacrylonitrile (PAN) nanofibers, prepared by electrospinning, are often used as a precursor for carbon nanofibers. The thermal carbonization process necessitates a preceding oxidative stabilization, which is usually performed thermally, i.e., by carefully heating the electrospun nanofibers in an oven. One of the typical problems occurring during this process is a strong deformation of the fiber morphologies—the fibers become thicker and shorter, and show partly undesired conglutinations. This problem can be solved by stretching the nanofiber mat during thermal treatment, which, on the other hand, can lead to breakage of the nanofiber mat. In a previous study, we have shown that the electrospinning of PAN on aluminum foils and the subsequent stabilization of this substrate is a simple method for retaining the fiber morphology without breaking the nanofiber mat. Here, we report on the impact of different aluminum foils on the physical and chemical properties of stabilized PAN nanofibers mats, and on the following incipient carbonization process at a temperature of max. 600 °C, i.e., below the melting temperature of aluminum. [ABSTRACT FROM AUTHOR]

Electrospinning is a frequently used method to prepare air and water filters. Electrospun nanofiber mats can have very small pores, allowing for filtering of even the smallest particles or molecules. In addition, their high surface-to-volume ratio allows for the integration of materials which may additionally treat the filtered material through photo-degradation, possess antimicrobial properties, etc., thus enhancing their applicability. However, the fine nanofiber mats are prone to mechanical damage. Possible solutions include reinforcement by embedding them in composites or gluing them onto layers that are more mechanically stable. In a previous study, we showed that it is generally possible to stabilize electrospun nanofiber mats by 3D printing rigid polymer layers onto them. Since this procedure is not technically easy and needs some experience to avoid delamination as well as damaging the nanofiber mat by the hot nozzle, here we report on the reversed technique (i.e., first 3D printing a rigid scaffold and subsequently electrospinning the nanofiber mat on top of it). We show that, although the adhesion between both materials is insufficient in the case of a common rigid printing polymer, nanofiber mats show strong adhesion to 3D printed scaffolds from thermoplastic polyurethane (TPU). This paves the way to a second approach of combining 3D printing and electrospinning in order to prepare mechanically stable filters with a nanofibrous surface. [ABSTRACT FROM AUTHOR]

Electrospinning is a new technology whose scope is gradually being developed. For this reason, the number of known polymer–solvent combinations for electrospinning is still very low despite the enormous variety of substances that are potentially available. In particular, electrospinning from low-toxic solvents, such as the use of dimethyl sulfoxide (DMSO) in medical technology, is rare in the relevant scientific literature. Therefore, we present in this work a series of new polymers that are applicable for electrospinning from DMSO. From a wide range of synthetic polymers tested, poly(vinyl alcohol) (PVOH), poly(2ethyl2oxazolene) (PEOZ), and poly(vinylpyrrolidone) (PVP) as water-soluble polymers and poly(styrene-co-acrylonitrile) (SAN), poly(vinyl alcohol-co-ethylene) (EVOH), and acrylonitrile butadiene styrene (ABS) as water-insoluble polymers were found to be suitable for the production of nanofibers. Furthermore, the influence of acetone as a volatile solvent additive in DMSO on the fiber morphology of these polymers was investigated. Analyses of the fiber morphology by helium ion microscopy (HIM) showed significantly different fiber diameters for different polymers and a reduction in beads and branches with increasing acetone content. [ABSTRACT FROM AUTHOR]

Recently, a mass spectrometer for liquid metal ion sources (LMIS) has been built and set into operation. This device uses an E × B-filter as mass dispersive element and provides sufficient resolution to analyse the emission of clusters from LMIS to much higher mass ranges (>2000 amu) than commercially available mass filters for focused ion beam systems. It has also been shown that for small masses the composition of clusters from different isotopes can be resolved. Furthermore, a rather high fluence of monodisperse clusters in the range of 106-107 clusters/s can be achieved with this setup. This makes it a promising tool for the preparation of mass selected clusters. In this contribution, theoretical considerations as well as technical details and the results of first measurements are presented. [ABSTRACT FROM AUTHOR]

Understanding how water interacts with nanopores of carbonaceous electrodes is crucial for energy storage and conversion applications. A high surface area of carbonaceous materials does not necessarily need to translate to a high electrolyte-solid interface area. Herein, we study the interaction of water with nanoporous C 1 N 1 materials to explain their very low specific capacitance in aqueous electrolytes despite their high surface area. Water was used to probe chemical environments, provided by pores of different sizes, in 1 H MAS NMR experiments. We observe that regardless of their high hydrophilicity, only a negligible portion of water can enter the nanopores of C 1 N 1 , in contrast to a reference pure carbon material with a similar pore structure. The common paradigm that water easily enters hydrophilic pores does not apply to C 1 N 1 nanopores below a few nanometers. Calorimetric and sorption experiments demonstrated strong water adsorption on the C 1 N 1 surface, which restricts water mobility across the interface and impedes its penetration into the nanopores., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Helium ion microscopy (HIM) offers the opportunity to obtain direct views of biological samples such as cellular structures, virus particles, and microbial interactions. Imaging with the HIM combines sub-nanometer resolution, large depth of field, and high surface sensitivity. Due to its charge compensation capability, the HIM can image insulating biological samples without additional conductive coatings. Here, we present an exploratory HIM study of SARS-CoV-2 infected Vero E6 cells, in which several areas of interaction between cells and virus particles, as well as among virus particles, were imaged. The HIM pictures show the three-dimensional appearance of SARS-CoV-2 and the surface of Vero E6 cells at a multiplicity of infection of approximately 1 with great morphological detail. The absence of a conductive coating allows for a distinction between virus particles bound to the cell membrane and virus particles lying on top of the membrane. After prolonged imaging, it was found that ion-induced deposition of hydrocarbons from the vacuum renders the sample sufficiently conductive to allow for imaging even without charge compensation. The presented images demonstrate the potential of the HIM in bioimaging, especially for the imaging of interactions between viruses and their host organisms., (Copyright © 2021, Frese et al.)

A freestanding ultrathin hybrid membrane was synthesized comprising two functional layers, that is, first, a carbon nanomembrane (CNM) produced by electron irradiation-induced cross-linking of a self-assembled monolayer (SAM) of 4'-nitro-1,1'-biphenyl-4-thiol (NBPT) and second, purple membrane (PM) containing genetically modified bacteriorhodopsin (BR) carrying a C-terminal His-tag. The NBPT-CNM was further modified to carry nitrilotriacetic acid (NTA) terminal groups for the interaction with the His-tagged PMs forming a quasi-monolayer of His-tagged PM on top of the CNM-NTA. The formation of the Ni-NTA/His-tag complex leads to the unidirectional orientation of PM on the CNM substrate. Electrophoretic sedimentation was employed to optimize the surface coverage and to close gaps between the PM patches. This procedure for the immobilization of oriented dense PM facilitates the spontaneous fusion of individual PM patches, forming larger membrane areas. This is, to our knowledge, the very first procedure described to induce the oriented fusion of PM on a solid support. The resulting hybrid membrane has a potential application as a light-driven two-dimensional proton-pumping membrane, for instance, for light-driven seawater desalination as envisioned soon after the discovery of PM., (Copyright © 2021, Riedel et al.)