Swiss Federal Laboratories for Materials Science and Technology
Recent publications
Small adjustments in atomic configurations can significantly impact the magnetic properties of matter. Strain, for instance, can alter magnetic anisotropy and enable fine-tuning of magnetism. However, the effects of these changes on nanoscale magnetism remain largely unexplored. In particular, when strain fluctuates at the nanoscale, directly linking structural changes with magnetic behavior poses a substantial challenge. Here, we develop an approach, LA-Ltz-4D-STEM, to map structural information and magnetic fields simultaneously at the nanoscale. This approach opens avenues for an in-depth study of structure-property correlations of magnetic materials at the nanoscale. We applied LA-Ltz-4D-STEM to image strain, atomic packing, and magnetic fields simultaneously in a deformed amorphous ferromagnet with complex strain variations at the nanoscale. An anomalous magnetic configuration near shear bands, which reside in a magnetostatically high-energy state, was observed. By performing pixel-to-pixel correlation of the different physical quantities across a large field of view, a critical aspect for investigating industrial ferromagnetic materials, the magnetic moments were classified into two distinct groups: one influenced by magnetoelastic coupling and the other oriented by competition with magnetostatic energy.
Identification of crystallographic slip in metals and alloys is crucial to understand and improve their mechanical behaviour. Recently, a novel slip system identification framework, termed SSLIP (for slip system–based local identification of plasticity), was introduced to leap from conventional trace‐based identification to automated, point‐by‐point identification, exploiting the full deformation kinematics. Using sub‐micron‐scale digital image correlation (DIC) deformation fields aligned to electron backscatter diffraction (EBSD) data, SSLIP matches the measured in‐plane displacement gradient tensor to the kinematics of the optimal combination of multiple slip system activities, at each DIC datapoint. SSLIP was demonstrated to be successful on virtual and experimental case studies of FCC and BCC metals. However, for more challenging HCP crystal structures, the complete identification of all slip systems was found to be more challenging, posing limitations on automation and flexibility. To extend the capabilities of SSLIP, we propose an extended framework, hereinafter referred to as the +SSLIP method, which includes (i) a preselection of slip systems using a Radon transform, (ii) robustness to measured rigid body rotation by simultaneous identification of the local rotation field, (iii) identification of the two best matching slip systems for each data point and (iv) a procedure to determine groups of slip systems with in‐plane displacement gradient tensors that cannot be discriminated. This procedure yields the full (HCP) slip system activity maps for every slip system in each grain. The resulting objective identification method does not rely on the Schmid factor to select which slip system is active at each point. We show how slip systems from multiple slip families are successfully identified on virtual and real experiments on a Zn polycrystalline coating.
In this work, we introduce a combined DFT and machine learning approach to obtain insights into the chemical design of metal-organic framework (MOF) photocatalysts for hydrogen (HER) and oxygen (OER) evolution reactions. To train our machine learning models, we evaluated a dataset of 314 MOFs using a dedicated DFT workflow that computes a set of five descriptors for both closed and open shell MOFs. Our dataset is composed of a diverse selection of the QMOF database and experimentally reported MOF photocatalysts. In addition, to ensure a balanced dataset, we designed a set of MOFs (CDP–MOF) inspired by insights obtained regarding different types of photocatalytic materials. Our machine-learning approach allowed us to screen the entire QMOF and CDP–MOF databases for promising candidates. Our analysis of the chemical design space shows that we have many materials with a suitable spatial overlap of electron and hole, band gap, band-edge alignment to HER, and charge-carrier effective masses. However, we have identified in the QMOF database only a very small percentage of materials that also have the right band edge alignment to OER. With the CDP–MOF database, we successfully targeted building blocks that potentially have the correct OER band alignment, and indeed obtained a larger percentage of materials that obey this criteria. Among those, a few motifs stood out, such as Au-pyrazolate, Ti clusters and rod-shaped metal nodes, and a particular MOF designed with the Mn4Ca cluster, which mimics the OER center in the photosystem II of photosynthesis.
Solitary wild bees play a key role as pollinators of wild plants and crops, but they are increasingly at risk from anthropogenic global change, such as climate warming. However, how warmer temperature during overwintering affects reproductive success of those bees remains largely unknown. In a semi-field experiment we assessed individual life-long reproductive success of 144 females of the solitary bee species Osmia bicornis that had been wintered at three different temperatures. Overwintering mortality of bees was on average 32% higher at winter temperatures of 8 °C compared to 4.5 °C–0 °C, at which almost all bees successfully emerged. After wintering at 4.5 °C and 8 °C females produced less offspring than after overwintering at 0 °C (26% or 36% less offspring, respectively). Although longevity and daily offspring production rate were not significantly affected, nesting duration of females wintered at 0 °C tended to be longer (+ 2.5 days) than that of bees wintered at 4.5 °C, which likely contributed to the higher offspring production at colder overwintering temperatures. Mortality and sex ratio of offspring was not significantly affected. While future studies should also consider climatic variation during winter, these findings indicate that increasing mean overwintering temperatures could threaten O. bicornis and potentially other solitary bee populations.
We extend (EUCLID Efficient Unsupervised Constitutive Law Identification and Discovery)—a data-driven framework for automated material model discovery—to pressure-sensitive plasticity models, encompassing arbitrarily shaped yield surfaces with convexity constraints and non-associated flow rules. The method only requires full-field displacement and boundary force data from one single experiment and delivers constitutive laws as interpretable mathematical expressions. We construct a material model library for pressure-sensitive plasticity models with non-associated flow rules in four steps: (1) a Fourier series describes an arbitrary yield surface shape in the deviatoric stress plane; (2) a pressure-sensitive term in the yield function defines the shape of the shear failure surface and determines plastic deformation under tension; (3) a compression cap term determines plastic deformation under compression; (4) a non-associated flow rule may be adopted to avoid the excessive dilatancy induced by plastic deformations. In contrast to traditional parameter identification methods, EUCLID is equipped with a sparsity promoting regularization to restrain the number of model parameters (and thus modeling features) to the minimum needed to accurately interpret the data, thus achieving a compromise between model simplicity and accuracy. The convexity of the learned yield surface is guaranteed by a set of constraints in the inverse optimization problem. We demonstrate the proposed approach in multiple numerical experiments with noisy data, and show the ability of EUCLID to accurately select a suitable material model from the starting library.
Graphene is the first 2D atomic crystal, and its isolation heralded a new era in materials science with the emergence of several other atomically thin materials displaying multifunctional properties. The safety assessment of new materials is often something of an afterthought, but in the case of graphene, the initial isolation and characterization of the material was soon followed by the assessment of its potential impact on living systems. The Graphene Flagship project addressed the health and environmental aspects of graphene and other 2D materials, providing an instructive lesson in interdisciplinarity – from materials science to biology. Here, the outcomes of the toxicological and ecotoxicological studies performed on graphene and its derivatives, and the key lessons learned from this decade‐long journey, are highlighted.
The transport and magnetic properties of the Magnéli phase tungsten oxide WO2.90, prepared via spark plasma sintering, were investigated across a broad temperature range of 4–550 K, including the previously unexplored low-temperature region below 300 K. Microstructure analysis shows that obtained pellets are fully dense, enabling reliable measurement of transport properties. Resistivity measurements reveal typical metallic behavior of WO2.90 at low temperatures. Above room temperature, resistivity tends to saturate by reaching a maximum value near 430 K. The resistivity saturation indicates that Mott-Ioffe-Regel limit is approached, where the charge carrier mean free path becomes comparable to the interatomic spacing. The temperature dependence of the resistivity can be well described by the phenomenological parallel resistor model. Significant positive magnetoresistance was observed at low temperatures, with an unusual linear dependence on the magnetic field. Despite its metallic conductivity, WO2.90 displays weak diamagnetism, likely due to the substantial core diamagnetism of tungsten and the bipolaronic pairing of charge carriers.
Surface‐mediated transmission of pathogens plays a key role in healthcare‐associated infections. However, proper techniques for its quantitative analysis are lacking, making it challenging to develop novel antimicrobial and anti‐fouling surfaces to reduce pathogen spread via environmental surfaces. This study demonstrates a gelatin hydrogel‐based touch transfer test, the HydroTouch test, to evaluate pathogen transmission on high‐touch surfaces under semi‐dry conditions. The HydroTouch test employs gelatin as a finger mimetic, facilitating testing with pathogenic bacteria under controlled conditions. The thermoresponsive sol–gel transition of gelatin allows easy recovery and quantification of bacteria before and after testing. The HydroTouch test demonstrates that methicillin‐resistant Staphylococcus aureus has a high transmission efficiency of ≈16% onto stainless steel, compared to <3% for Escherichia coli or Pseudomonas aeruginosa. Polyurethane surfaces exhibit strong resistance to bacterial contamination with a transmission efficiency of ≈0.6%, while polytetrafluoroethylene shows a transmission efficiency approximately four times higher than polyurethane. Additionally, quaternary ammonium‐based antimicrobial coatings reduce the transmission efficiency of live bacteria on stainless steel to ≈4% of the original level. The HydroTouch test provides a reliable method for assessing pathogen transmission on various surfaces under semi‐dry settings, supporting the development of effective antimicrobial, anti‐transmission coatings to reduce healthcare‐associated infections.
Surface functionalization technologies of fibrous or porous materials are often considered relatively unstable with a shelf life of several weeks or months at most, evoked by heterogeneous treatment of their internal surface areas. Here, it is demonstrating that the fine balance of plasma etching, deposition, and oxidation involving different reactive species, strongly enhances penetration depth within complex structures. On this basis, capillary wicking is maintained over >10 years after plasma functionalization of a scaffold material used for biomedical engineering. Electrospun membranes of poly(ε‐caprolactone) are coated with an oxygen‐functional hydrocarbon layer, deposited in a competitive ablation and plasma polymerization process with CO2 and C2H4 as reactive gases. Chemical analysis immediately after coating, 9 months later, and after storing at ambient conditions for over 10 years, indicate a stable surface coating. Using defined geometries such as a cavity and an undercut, the underlying plasma interaction mechanisms are revealed, showing different synergies of energetic particles, depositing species with different surface reactivities, and oxidizing species. A concerted action of such species during plasma functionalization is key to enabling long‐term wetting properties. This has a major implication for the surface functionalization of scaffolds, textiles, membranes, or foams used in diverse fields.
The complexity of the intrinsic oxygen evolution reaction (OER) mechanism, particularly the precise relationships between the local coordination geometry of active metal centers and the resulting OER kinetics, remains to be fully understood. Herein, we construct a series of 3 d transition metal-incorporated cobalt hydroxide-based nanobox architectures for the OER which contain tetrahedrally coordinated Co(II) centers. Combination of bulk- and surface-sensitive operando spectroelectrochemical approaches reveals that tetrahedral Co(II) centers undergo a dynamic transformation into highly active Co(IV) intermediates acting as the true OER active species which activate lattice oxygen during the OER. Such a dynamic change in the local coordination geometry of Co centers can be further facilitated by partial Fe incorporation. In comparison, the formation of such active Co(IV) species is found to be hindered in CoOOH and Co-FeOOH, which are predominantly containing [CoIIIO6] and [CoII/FeIIIO6] octahedra, respectively, but no mono-μ-oxo-bridged [CoIIO4] moieties. This study offers a comprehensive view of the dynamic role of local coordination geometry of active metal centers in the OER kinetics.
Photostable and efficient 1.8 eV wide‐bandgap (WBG) perovskites are needed for all‐perovskite tandem photovoltaic (PV) applications, but the high bromine (Br) content can cause halide segregation. To achieve the same bandgap with a lower Br content, MAPbCl 3 can be added to form triple‐halide perovskites. However, most triple‐halide WBG perovskites are still fabricated by antisolvent spin coating with perovskite inks that cannot be transferred to scalable deposition methods. Furthermore, the role of the Cl additives on the bandgap and the photostability remains elusive. Here, Cl‐additives, such as ACl, PbCl 2 , and APbCl 3 (where A denotes MA, FA, Cs, Rb), are systematically investigated to form 1.8 eV triple‐halide perovskites with 30 mol% Br by N 2 ‐assisted blade coating. It is found that PbCl 2 and APbCl 3 can increase the bandgap by several tens of meV, while ACl can only increase the bandgap by few meV. CsPbCl 3 emerges as a promising alternative to MAPbCl 3 , enabling 17.2% efficient MA‐free 1.8 eV triple‐halide perovskite solar cells (0.062 cm ² ) with enhanced phase‐ and photostability. Its scalability is demonstrated by slot‐die coating a ≈10% efficient WBG perovskite solar module with an aperture area of 52.8 cm ² .
Recycling thermosetting materials presents itself as a major challenge in achieving sustainable material use. Dynamic covalent cross‐linking of polymers has emerged as a viable solution that can combine the structural integrity of thermosetting materials with the (re−)processability of thermoplastics. Thioether linkages between polymer chains are quite common, and their use dates back to the vulcanization of rubbers. While it is known that thioether bonds can be triggered to exchange through transalkylation reactions, this process is usually slow, as thioether moieties not only have to be activated by an alkylating agent, but the activated thioether also has to associate with a second thioether moiety in a classical SN2‐type process. Here, we present the rational design of dynamic polymer networks based on simple dithiol‐based monomers and a fatty acid derived triene. Two neighboring thioethers can undergo a much faster bond exchange reaction, and we found that the exchange dynamics can be further tuned over almost three orders of magnitude by tailoring the distance between two thioether functionalities. This resulted in thioether‐cross‐linked materials that could be processed by extrusion, a continuous reprocessing technique that was previously not accessible for this class of cross‐linked materials, while still exhibiting appealing creep‐resistance below 70 °C.
As demand for low‐cost, high‐energy‐density all‐solid‐state batteries continues to rise, exploring novel cathodes composed of earth‐abundant elements is imperative. Iron hydroxy fluorides with the pyrochlore structure (Pyr‐IHF) emerge as compelling cathode materials due to abundant natural reserves of their constituent elements, high energy density, and rate capability. In this work, we explore the viability of Pyr‐IHF as a cathode material in all‐solid‐state batteries when paired with argyrodite‐type Li6PS5Cl (LPSCl) solid‐state electrolyte. Our findings show that the Pyr‐IHF/LPSCl cathode delivers a high initial charge capacity of 172 mAh g⁻¹ at a 0.1 C rate, with ca. 65 % capacity retention after 50 cycles. Advanced characterization techniques, including focused ion beam‐scanning electron microscopy, scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy, and X‐ray absorption spectroscopy, indicate a pronounced redox reaction between Pyr‐IHF and LPSCl upon cell preparation, resulting in significant capacity contributions from the sulfur redox of LPSCl decomposition products during electrochemical cycling.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
879 members
Binod Prasad Koirala
  • Urban energy systems
Laura Merotto
  • Department Mobility, Energy and Environment
Anant Parghi P.Eng. C.Eng.
  • Department of Structural Engineering
Arie Bruinink
  • Department Advanced Materials and Surfaces
Information
Address
Dübendorf, Switzerland
Head of institution
Prof. Dr. Gian-Luca Bona