Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

Below, you can either scroll through the complete list of our annually published material, or search for a specific author or term via the free text search to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

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  • 2024 • 89 Methanol Dehydration to Dimethyl Ether on Ball Milling-Derived High-Surface-Area Alpha-Alumina Catalysts
    Agbaba, Özgül and Amrute, Amol P. and Ochoa-Hernandez, Cristina and Triller, Sarah and Schüth, Ferdi
    ChemCatChem 16 (2024)
    Alpha alumina (α-Al2O3) catalysts synthesized by ball milling are investigated in the dehydration of methanol to dimethyl ether (DME). The activity and stability of the catalysts were studied in a fixed-bed continuous-flow reactor setup. The effect of water vapor in the feed was studied as well. Among different alumina polymorphs studied, γ- alumina has been known to be the most effective for this reaction; however, the high surface area α-Al2O3, which had been synthesized by ball milling, resulted in a comparable rate of methanol conversion, while it revealed a more stable performance under the influence of water vapor. The surface area, the number, and the nature of the acidic sites were found to be relevant parameters for the conversion of methanol to DME. The selectivity was as high as 99 % towards DME. © 2023 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202301159
  • 2024 • 88 Optimizing the use of a gas diffusion electrode setup for {CO2} electrolysis imitating a zero-gap {MEA} design
    Alinejad, S. and Quinson, J. and Li, Y. and Kong, Y. and Reichenberger, S. and Barcikowski, S. and Broekmann, P. and Arenz, M.
    Journal of Catalysis 429 (2024)
    doi: 10.1016/j.jcat.2023.115209
  • 2024 • 87 Deep Reconstruction of Mo-based OER Pre-Catalysts in Water Electrolysis at High Current Densities
    Antony, Rajini P. and Cechanaviciute, Ieva A. and Quast, Thomas and Zerdoumi, Ridha and Saddeler, Sascha and Junqueira, João R. C. and Schuhmann, Wolfgang
    ChemCatChem 16 (2024)
    Evaluating the dynamic structural reconstruction processes of transition metal-based oxygen evolution reaction (OER) catalysts at industrial current densities in a membrane electrode assembly (MEA) configuration of an anion exchange membrane (AEM) electrolyzer is required for the practical application of OER electrodes in AEM-type next-generation electrolyzers. This study unveils the deep reconstruction phenomenon of a Mo-containing OER catalyst anode during electrolysis at high current densities. A complete reconstruction of the catalyst due to selective Mo-leaching is inevitable during high current operation and thereby new catalytic surfaces of the Mo-containing Ni-based electrodes for sustainable water electrolysis are exposed. The reconstruction was confirmed by ex situ and in situ surface characterization techniques. A scalable route for electrode fabrication demonstrated and it is shown that the reconstruction mechanism of the catalyst leads to a more sustainable operation of the electrolyzer at high current densities. © 2023 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202301023
  • 2024 • 86 PECVD and PEALD on polymer substrates (part I): Fundamentals and analysis of plasma activation and thin film growth
    de los Arcos, Teresa and Awakowicz, Peter and Benedikt, Jan and Biskup, Beatrix and Böke, Marc and Boysen, Nils and Buschhaus, Rahel and Dahlmann, Rainer and Devi, Anjana and Gergs, Tobias and Jenderny, Jonathan and von Keudell, ...
    Plasma Processes and Polymers 21 (2024)
    This feature article presents recent results on the analysis of plasma/polymer interactions and the nucleation of ultra-thin plasma films on polymeric substrates. Because of their high importance for the understanding of such processes, in situ analytical approaches of the plasma volume as well as the plasma/substrate interfaces are introduced before the findings on plasma surface chemistry. The plasma activation of polymeric substrates is divided into the understanding of fundamental processes on model substrates and the relevance of polymer surface complexity. Concerning thin film nucleation and growth, both plasma-enhanced chemical vapor deposition and plasma-enhanced atomic layer deposition processes as well as the combination of both processes are considered both for model substrates and technical polymers. Based on the comprehensive presentation of recent results, selective perspectives of this research field are discussed. © 2023 Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ppap.202300150
  • 2024 • 85 Martensite content effect on fatigue crack growth and fracture energy in dual-phase steels
    Avendaño-Rodríguez, D. and Rodriguez-Baracaldo, R. and Weber, S. and Mujica-Roncery, L.
    Fatigue and Fracture of Engineering Materials and Structures 47 884 – 902 (2024)
    The effect of different microstructural factors on crack growth and fatigue fracture mechanisms in dual-phase (DP) steels has yet to be fully understood. The present research examines the relationship between crack growth, microstructure, and fracture mechanisms. The samples were intercritically annealed at different temperatures to produce three different martensite volume fractions (MVFs). The results show that the mechanical incompatibility of ferrite and martensite promotes continuous crack tip deflection. MVF increases are associated with elevated fracture tortuosity, more significant fracture energy surface formation, and higher Paris law exponent m values. The interaction of the microstructure with the crack tip, the strain energy density, and the softening caused by secondary microcrack propagation are all illustrated by Electron backscatter diffraction (EBSD) maps. Increasing MVF promotes slow crack growth and a fracture energy increase of 22.9% between the as-received and heat-treated steels. © 2023 John Wiley & Sons, Ltd.
    view abstractdoi: 10.1111/ffe.14209
  • 2024 • 84 A computational framework for pharmaco-mechanical interactions in arterial walls using parallel monolithic domain decomposition methods
    Balzani, Daniel and Heinlein, Alexander and Klawonn, Axel and Knepper, Jascha and Nurani Ramesh, Sharan and Rheinbach, Oliver and Saßmannshausen, Lea and Uhlmann, Klemens
    GAMM Mitteilungen (2024)
    A computational framework is presented to numerically simulate the effects of antihypertensive drugs, in particular calcium channel blockers, on the mechanical response of arterial walls. A stretch-dependent smooth muscle model by Uhlmann and Balzani is modified to describe the interaction of pharmacological drugs and the inhibition of smooth muscle activation. The coupled deformation-diffusion problem is then solved using the finite element software FEDDLib and overlapping Schwarz preconditioners from the Trilinos package FROSch. These preconditioners include highly scalable parallel GDSW (generalized Dryja–Smith–Widlund) and RGDSW (reduced GDSW) preconditioners. Simulation results show the expected increase in the lumen diameter of an idealized artery due to the drug-induced reduction of smooth muscle contraction, as well as a decrease in the rate of arterial contraction in the presence of calcium channel blockers. Strong and weak parallel scalability of the resulting computational implementation are also analyzed. © 2024 The Authors. GAMM - Mitteilungen published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/gamm.202370002
  • 2024 • 83 Multidimensional rank-one convexification of incremental damage models at finite strains
    Balzani, D. and Köhler, M. and Neumeier, T. and Peter, M.A. and Peterseim, D.
    Computational Mechanics 73 27 – 47 (2024)
    This paper presents computationally feasible rank-one relaxation algorithms for the efficient simulation of a time-incremental damage model with nonconvex incremental stress potentials in multiple spatial dimensions. While the standard model suffers from numerical issues due to the lack of convexity, our experiments showed that the relaxation by rank-one convexification delivering an approximation to the quasiconvex envelope prevents mesh dependence of the solutions of finite element discretizations. By the combination, modification and parallelization of the underlying convexification algorithms, the novel approach becomes computationally feasible. A descent method and a Newton scheme enhanced by step-size control prevent stability issues related to local minima in the energy landscape and the computation of derivatives. Numerical techniques for the construction of continuous derivatives of the approximated rank-one convex envelope are discussed. A series of numerical experiments demonstrates the ability of the computationally relaxed model to capture softening effects and the mesh independence of the computed approximations. An interpretation in terms of microstructural damage evolution is given, based on the rank-one lamination process. © 2023, The Author(s).
    view abstractdoi: 10.1007/s00466-023-02354-3
  • 2024 • 82 Testing equivalence of multinomial distributions — A constrained bootstrap approach
    Bastian, P. and Dette, H. and Koletzko, L.
    Statistics and Probability Letters 206 (2024)
    In this paper we develop a novel bootstrap test for the comparison of two multinomial distributions. The two distributions are called equivalent or similar if a norm of the difference between the class probabilities is smaller than a given threshold. In contrast to most of the literature our approach does not require differentiability of the norm and is in particular applicable for the maximum- and L1-norm. © 2023 Elsevier B.V.
    view abstractdoi: 10.1016/j.spl.2023.109999
  • 2024 • 81 Comparing regression curves: an L 1-point of view
    Bastian, Patrick and Dette, Holger and Koletzko, Lukas and Möllenhoff, Kathrin
    Annals of the Institute of Statistical Mathematics 76 159 – 183 (2024)
    In this paper, we compare two regression curves by measuring their difference by the area between the two curves, represented by their L1 -distance. We develop asymptotic confidence intervals for this measure and statistical tests to investigate the similarity/equivalence of the two curves. Bootstrap methodology specifically designed for equivalence testing is developed to obtain procedures with good finite sample properties and its consistency is rigorously proved. The finite sample properties are investigated by means of a small simulation study. © 2023, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-023-00880-8
  • 2024 • 80 Millimeter Wave Indoor SAR Sensing Assisted With Chipless Tags-Based Self-Localization System: Experimental Evaluation
    Batra, Aman and Abbas, Ali Alhaj and Sanchez-Pastor, Jesus and El-Absi, Mohammed and Jimenez-Saez, Alejandro and Khaliel, Maher and Barowski, Jan and Wiemeler, Michael and Gohringer, Diana and Rolfes, Ilona and Jakoby, Rolf and Ka...
    IEEE Sensors Journal 24 844 – 857 (2024)
    This article addresses indoor environment mapping by employing the synthetic aperture radar (SAR) technique at millimeter wave (mmWave) frequencies. The mmWave-based SAR can provide a high-resolution map, for example, of an emergency scenario like a burning room. The high-resolution map drives a new era of SAR applications such as object detection, classification, characterization, and precise localization. A major requirement at high frequencies is the precise knowledge of SAR trajectory, where radar sensors are mounted on a mobile platform such as a drone or unmanned aerial vehicle (UAV). State-of-the-art localization methods such as global positioning system (GPS)-aided inertial measurement units (IMUs) are not valid due to limited coverage and accuracy. One of the primary solutions could be the SAR assisted with an indoor localization system, which is exploited in the work. The presented indoor localization system comprises two types of passive chipless frequency-coded tags, based on dielectric resonators (DRs) and frequency-selective surfaces. In this work, first, the proposed method of integrating SAR and localization systems is evaluated in a single-tag environment. Further, a version of a room equipped with a multitag system is considered for real-time applications, and a successful demonstration of indoor environment mapping for the frequency spectrum of 75-110 GHz is presented. © 2001-2012 IEEE.
    view abstractdoi: 10.1109/JSEN.2023.3332431
  • 2024 • 79 Experimental determination of the high-temperature thermal conductivity of steel powders
    Berger, A. and Ziesing, U. and Benito, S. and Weber, S.
    Powder Technology 431 (2024)
    The PBF-LB/M process is highly suitable for the additive manufacturing of complex parts with precise geometrical accuracy using metallic powders. However, certain unknown variables exist within the process. Particularly, the thermal conductivity introduces a significant level of uncertainty due to the substantial impact of heat transfer from the part solid to the bulk material. Insufficient experimental data on the thermophysical properties of powder and a limited understanding of the influencing factors further exacerbate this issue. This study presents the thermophysical properties of steel powders commonly employed in the PBF-LB/M process, utilizing a newly-developed powder container for laser flash analysis. Through a quantitative comparative analysis with the corresponding solid materials, it has been demonstrated that the chemical composition and microstructure play a secondary role in determining the heat conductivity of the powder bed. Instead, it is the powder size distribution that serves as the primary parameter governing the observed behavior. © 2023 Elsevier B.V.
    view abstractdoi: 10.1016/j.powtec.2023.119022
  • 2024 • 78 Segregation-induced strength anomalies in complex single-crystalline superalloys
    Bezold, Andreas and Vollhüter, Jan and Karpstein, Nicolas and Lenz, Malte and Subramanyam, Aparna P. A. and Zenk, Christopher H. and Hammerschmidt, Thomas and Spiecker, Erdmann and Göken, Mathias and Neumeier, Steffen
    Communications Materials 5 (2024)
    Pushing the maximum service temperature of aircraft engines and industrial gas turbines is the major pathway to improve their energy efficiency and reduce CO2 emissions. This maximum is mostly limited by the temperature capability of key-component materials, including superalloys. In this alloy class, segregation of elements facilitates plastic deformation and is generally considered to cause softening during high-temperature deformation. Here, we show that segregation-assisted processes can also lead to strengthening and induce an anomalous increase of the yield strength. Atomic-resolution transmission electron microscopy and density functional theory calculations reveal a segregation-assisted dissociation process of dislocations at precipitate-matrix interfaces in combination with atomic-scale reordering processes. These processes lead to an inhibition of athermal deformation mechanisms and a transition to stacking fault shearing, which causes the strengthening effect. Unraveling these elementary mechanisms might guide a mechanism-based alloy design of future superalloys with enhanced high-temperature capabilities. © 2024, The Author(s).
    view abstractdoi: 10.1038/s43246-024-00447-x
  • 2024 • 77 Coupling of alloy chemistry, diffusion and structure by grain boundary engineering in Ni–Cr–Fe
    Bian, Baixue and Taheriniya, Shabnam and Muralikrishna, G. Mohan and Sen, Sandipan and Gammer, Christoph and Steinbach, Ingo and Divinski, Sergiy V. and Wilde, Gerhard
    Acta Materialia 264 (2024)
    The diffusion–microstructure correlations for grain boundaries (GBs) in the technologically-relevant Ni-based 602CA alloy are investigated. Prolonged annealing treatments up to 744 h create distinct GB complexions with specific segregation–precipitation–structure states. Globular M23C6-type carbides at straight GBs and plate-like carbides together with NiAl-enriched (γ′-type) particles at hackly GBs are found to co-exist. Moreover, an atomic-scale GB spinodal-like decomposition, especially at straight GBs, is observed. The co-existence of the two distinct states of general high-angle GBs, indicated by tracer diffusion experiments and verified by a detailed structure examination, is explained via state-of-the-art measurements of local elastic strains. In a course of annealing at 873 K, the relatively “fast” diffusivities are found to increase by a factor of 10 or more as a result of a coupled evolution of the GB plate-like precipitates and the irregular GB structures, whereas the relatively ”slow” diffusivites remained practically unchanged representing the contributions of straight interfaces with spherical precipitates. Thus, the diffusion properties of high-angle GBs evolve together with characteristic changes of GB complexions distinguished by a growth of carbide- and γ′-type precipitates and a concomitant generation of GB dislocation networks. The obtained results provide novel insights into grain boundary tailoring by utilizing structure – kinetics correlations involving segregation, precipitation and the evolution of interface defects. © 2023 The Authors
    view abstractdoi: 10.1016/j.actamat.2023.119602
  • 2024 • 76 Investigating the inflow into a granular bed using a locally resolved method
    Brömmer, M. and Scharnowski, M. and Illana Mahiques, E. and Wirtz, S. and Scherer, V.
    Particuology 85 89-101 (2024)
    doi: 10.1016/j.partic.2023.03.022
  • 2024 • 75 Activation of heteroallenes by metal-substituted electron-rich tetrylenes
    Bücker, A. and Wölper, C. and Schulz, S.
    Polyhedron 247 (2024)
    doi: 10.1016/j.poly.2023.116702
  • 2024 • 74 Integrated BIM-based modeling and simulation of segmental tunnel lining by means of isogeometric analysis
    Bui, Hoang-Giang and Ninić, Jelena and Koch, Christian and Hackl, Klaus and Meschke, Günther
    Finite Elements in Analysis and Design 229 (2024)
    With the increasing demand for underground transport infrastructures in urban areas, and associated hazards during the construction of these complex structures characterized with a number of uncertainties, there is an acute need for the development of methods and tools that enable efficient and accurate exploration of the design options to minimize risks induced to the environment. Mechanized tunneling, although it requires high initial investments compared to other tunneling methods, offers a safe and productive way to construct urban tunnels. In the mechanized tunneling process, the lining plays a critical role to provide the support for internal structures, i.e roads, facilities. At the same time, it helps stabilize the ground condition. Together with the jacking system, the lining provides the mean to thrust the tunnel shield (TBM) during excavation. In this work, we address the problem of effective modeling and simulation of the tunnel lining segment. The objective is to demonstrate a systematic and versatile approach to analyze the tunnel lining in different practical scenarios. In terms of modeling, a BIM-based approach is used, which connects the user-friendly software interface used in daily engineering practice with effective simulation tools. The proposed approach utilizes high-order definition of geometry in the design model as well as parametric model definitions to reconstruct the corresponding high-order numerical models. This results in a high-accuracy and computationally low-cost model to analyze a complex structure including an interaction with the soil based on a nonlinear surface springs model. In addition, it allows to analyze the stress and bending moment in the lining segment with high accuracy. The numerical results show that negligible modeling efforts and a reduced computational time up to ten times for given accuracy are achieved. © 2023 Elsevier B.V.
    view abstractdoi: 10.1016/j.finel.2023.104070
  • 2024 • 73 Xylan fast pyrolysis: An experimental and modelling study of particle changes and volatiles release
    Cerciello, F. and Freisewinkel, E. and Coppola, A. and Ontyd, C. and Tarlinski, D. and Schiemann, M. and Senneca, O. and Salatino, P. and Allouis, C. and Scherer, V. and Fletcher, Thomas H.
    Fuel 357 (2024)
    Biomass char particles produced by pyrolysis may have different morphologies, which has important implications on burning mode, conversion rate and boiler efficiency. These features are difficult to address due to the complexity of biomass structure and pyrolysis reaction models. The present work reports preliminary results on the morphological changes and volatile release that solid particles of Xylan experience upon fast heating in a Drop Tube Reactor (DTR) and in a Heated Strip Reactor (HSR) in a range of temperature between 1100 and 1573 K under inert atmosphere with heating rate in the order of 103 K/s. Two different Xylan samples were chosen as representative of Hemicellulose in angiosperm biomass: xylooligosaccharide extracted from Beechwood (hardwood biomass) and from Corn Cob (herbaceous biomass). During the heatup phase, Xylan particles do not retain the original shape and morphology, neither in DTR nor in HSR experiments. In the early pyrolysis stage, Xylan particles melt and form viscous droplets. As devolatilization proceeds these droplets in the DTR evolve into highly viscous sponge-like particles with spherical shape, which swell and eventually shrink, ultimately producing highly porous spherical char particles. The experimental results are compared with the predictions obtained by the Bio-CPD Xylan pyrolysis model. The model is fairly able to calculate the pyrolysis yields in the DTR, but predicts unexpectedly low extent of metaplast formation. To explain the remarkable melting phenomena and morphological changes observed in the experiments, tuning of some CPD parameters and inclusion of mass transfer and pressure build-up within the particles might be necessary in future work. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.fuel.2023.129983
  • 2024 • 72 Sampling the Materials Space for Conventional Superconducting Compounds
    Cerqueira, Tiago F. T. and Sanna, Antonio and Marques, Miguel A. L.
    Advanced Materials 36 (2024)
    A large scale study of conventional superconducting materials using a machine-learning accelerated high-throughput workflow is performed, starting by creating a comprehensive dataset of around 7000 electron–phonon calculations performed with reasonable convergence parameters. This dataset is then used to train a robust machine learning model capable of predicting the electron–phonon and superconducting properties based on structural, compositional, and electronic ground-state properties. Using this machine, the transition temperatures (Tc) of approximately 200 000 metallic compounds are evaluated, all of which are on the convex hull of thermodynamic stability (or close to it) to maximize the probability of synthesizability. Compounds predicted to have Tc values exceeding 5 K are further validated using density-functional perturbation theory. As a result, 541 compounds with Tc values surpassing 10 K, encompassing a variety of crystal structures and chemical compositions, are identified. This work is complemented with a detailed examination of several interesting materials, including nitrides, hydrides, and intermetallic compounds. Particularly noteworthy is LiMoN2, which is predicted to be superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38 K. LiMoN2 has previously been synthesized in this phase, further heightening its potential for practical applications. © 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/adma.202307085
  • 2024 • 71 Electrocatalytic Epoxidation of Cyclooctene on Surface Modified Ni Foam Using Water as Oxygen Source
    Chandra, Shubhadeep and Koul, Adarsh and Zhang, Jian and Seisel, Sabine and Schuhmann, Wolfgang
    Chemistry - A European Journal (2024)
    Electrochemical epoxidation of olefins using water as an oxygen atom source is emerging as an alternative approach for an atom economic and sustainable method towards a highly selective synthesis of epoxides. We report an electrochemical procedure for epoxidation of cyclooctene using water as the sole oxygen atom source over a sodium dodecyl sulfonate (SDS) modified nickel hydroxide Ni(OH)2 catalyst directly grown on Ni foam. The SDS modification facilitates the mass transfer of cyclooctene towards the anode, thus achieving a 2.5-fold higher conversion with more than 90 % selectivity towards the corresponding epoxide compared with pure Ni(OH)2 catalyst. © 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/chem.202303830
  • 2024 • 70 Hydrogen-based direct reduction of combusted iron powder: Deep pre-oxidation, reduction kinetics and microstructural analysis
    Choisez, Laurine and Hemke, Kira and Özgün, Özge and Pistidda, Claudio and Jeppesen, Henrik and Raabe, Dierk and Ma, Yan
    Acta Materialia 268 (2024)
    Iron powder can be a sustainable alternative to fossil fuels in power supply due to its high energy density and abundance. Iron powder releases energy through exothermic oxidation (combustion), and stores back energy through its subsequent hydrogen-based reduction, establishing a circular loop for renewable energy supply. Hydrogen-based direct reduction is also gaining global momentum as possible future backbone technology for sustainable iron and steel production, with the aim to replace blast furnaces. Here, we investigate the microstructural formation mechanisms and reduction kinetics behind hydrogen-based direct reduction of combusted iron powder at moderate temperatures (400–500 °C) using thermogravimetry, ex-situ X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscatter diffraction, as well as in-situ high-energy X-ray diffraction. The influence of pre-oxidation treatment was studied by reducing both as-combusted iron powder (50 % magnetite and 50 % hematite) and the same powder after pre-oxidation (100 % hematite). A gas diffusion-limited reaction was obtained during the in-situ high-energy X-ray diffraction experiment, with successive hematite and magnetite reduction, and a strong increase in reduction kinetics with initial hematite content. Faster reduction kinetics were obtained during the thermogravimetry experiment, with simultaneous hematite and magnetite reduction. In this case, the reduction reaction was limited by a mix of phase boundary and nucleation and growth models, as analyzed by multi-step model fitting methods as well as by microstructural investigation. When not limited by gas diffusion, the pre-oxidation treatment showed almost no influence on the reduction time but a strong effect on the final microstructure of the reduced powder. © 2024
    view abstractdoi: 10.1016/j.actamat.2024.119752
  • 2024 • 69 Machine learning enhanced evaluation of semiconductor quantum dots
    Corcione, Emilio and Jakob, Fabian and Wagner, Lukas and Joos, Raphael and Bisquerra, Andre and Schmidt, Marcel and Wieck, Andreas D. and Ludwig, Arne and Jetter, Michael and Portalupi, Simone L. and Michler, Peter and Tarín, Cristina
    Scientific Reports 14 (2024)
    A key challenge in quantum photonics today is the efficient and on-demand generation of high-quality single photons and entangled photon pairs. In this regard, one of the most promising types of emitters are semiconductor quantum dots, fluorescent nanostructures also described as artificial atoms. The main technological challenge in upscaling to an industrial level is the typically random spatial and spectral distribution in their growth. Furthermore, depending on the intended application, different requirements are imposed on a quantum dot, which are reflected in its spectral properties. Given that an in-depth suitability analysis is lengthy and costly, it is common practice to pre-select promising candidate quantum dots using their emission spectrum. Currently, this is done by hand. Therefore, to automate and expedite this process, in this paper, we propose a data-driven machine-learning-based method of evaluating the applicability of a semiconductor quantum dot as single photon source. For this, first, a minimally redundant, but maximally relevant feature representation for quantum dot emission spectra is derived by combining conventional spectral analysis with an autoencoding convolutional neural network. The obtained feature vector is subsequently used as input to a neural network regression model, which is specifically designed to not only return a rating score, gauging the technical suitability of a quantum dot, but also a measure of confidence for its evaluation. For training and testing, a large dataset of self-assembled InAs/GaAs semiconductor quantum dot emission spectra is used, partially labelled by a team of experts in the field. Overall, highly convincing results are achieved, as quantum dots are reliably evaluated correctly. Note, that the presented methodology can account for different spectral requirements and is applicable regardless of the underlying photonic structure, fabrication method and material composition. We therefore consider it the first step towards a fully integrated evaluation framework for quantum dots, proving the use of machine learning beneficial in the advancement of future quantum technologies. © The Author(s) 2024.
    view abstractdoi: 10.1038/s41598-024-54615-7
  • 2024 • 68 Ni-Alloyed Copper Iodide Thin Films: Microstructural Features and Functional Performance
    Dethloff, Christiane and Thieme, Katrin and Selle, Susanne and Seifert, Michael and Vogt, Sofie and Splith, Daniel and Botti, Silvana and Grundmann, Marius and Lorenz, Michael
    Physica Status Solidi (B) Basic Research (2024)
    To tailor electrical properties of often degenerate pristine CuI, Ni is introduced as alloy constituent. Cosputtering in a reactive, but also in an inert atmosphere as well as pulsed laser deposition (PLD), is used to grow (Formula presented.) thin films. The Ni content within the alloy thin films is systematically varied for different growth techniques and growth conditions. A solubility limit is evidenced by an additional (Formula presented.) phase for Ni contents (Formula presented.), observed in X-Ray diffraction and atomic force microscopy by a change in surface morphology. Furthermore, metallic, nanoscaled nickel clusters, revealed by X-Ray photoelectron spectroscopy and high-resolution transmission electron microscopy (HRTEM), underpin a solubility limit of Ni in CuI. Although no reduction of charge carrier density is observed with increasing Ni content, a dilute magnetic behavior of the thin films is observed in vibrating sample magnetometry. Further, independent of the deposition technique, unique multilayer features are observed in HRTEM measurements for thin films of a cation composition of (Formula presented.). Opposite to previous claims, no transition to n-type behavior was observed, which was also confirmed by density functional theory calculations of the alloy system. © 2024 The Authors. physica status solidi (b) basic solid state physics published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/pssb.202300492
  • 2024 • 67 Statistical inference for function-on-function linear regression
    Dette, Holger and Tang, Jiajun
    Bernoulli 30 304 – 331 (2024)
    We propose a reproducing kernel Hilbert space approach for statistical inference regarding the slope in a function-on-function linear regression via penalised least squares, regularized by the thin-plate spline smoothness penalty. We derive a Bahadur expansion for the slope surface estimator and prove its weak convergence as a process in the space of all continuous functions. As a consequence of these results, we construct minimax optimal estimates, simultaneous confidence regions for the slope surface and simultaneous prediction bands. Moreover, we derive new tests for the hypothesis that the maximum deviation between the “true” slope surface and a given surface is less than or equal to a given threshold. In other words, we are not trying to test for exact equality (because in many applications this hypothesis is hard to justify), but rather for pre-specified deviations under the null hypothesis. To ensure practicability, non-standard bootstrap procedures are developed addressing particular features that arise in these testing problems. We also demonstrate that the new methods have good finite sample properties by means of a simulation study and illustrate their practicability by analyzing a data example. © 2024 ISI/BS.
    view abstractdoi: 10.3150/23-BEJ1598
  • 2024 • 66 Phase formation and electrical properties of reactively sputtered Fe1−x O thin films
    Evertz, S. and Nicolin, N. and Cheng, N. and Primetzhofer, D. and Best, J.P. and Dehm, G.
    Journal of Physics D: Applied Physics 57 (2024)
    Wüstite, Fe1−x O, is a crucial phase for the transition to CO2-free steel manufacturing as well as promising for electrochemical applications such as water splitting and ammonia synthesis. To study the effect of interfaces in these applications, thin-film model systems with defined interfaces are ideal. Previous studies lack a description of the growth mechanism to obtain Fe1−x O thin films. Here, we investigate the phase formation of metastable Fe1−x O during reactive magnetron sputtering while systematically varying the O2/Ar flow ratio from 1.8% to 7.2% and the pressure-distance product between 3.5 and 7.2 Pa cm. If bulk diffusion is minimized, thin films containing 96 vol.% wüstite and 4 vol.% Fe as impurity phase were achieved. Therefore, the wüstite phase formation appears to be surface diffusion dominated. To reveal the influence of impurity phases in wüstite on the electrical resistivity, systematic electrical resistivity measurements while cooling in situ were performed for the first time. The electrical resistivity was lower than that of single crystals of the respective iron oxides. This is attributed to the formation of Fe-rich layers at the substrate-film interface, which serve as additional conduction paths. © 2023 The Author(s). Published by IOP Publishing Ltd
    view abstractdoi: 10.1088/1361-6463/ad0a3e
  • 2024 • 65 Prediction of high- Tc superconductivity in ternary actinium beryllium hydrides at low pressure
    Gao, Kun and Cui, Wenwen and Shi, Jingming and Durajski, Artur P. and Hao, Jian and Botti, Silvana and Marques, Miguel A. L. and Li, Yinwei
    Physical Review B 109 (2024)
    Hydrogen-rich superconductors are promising candidates to achieve room-temperature superconductivity. However, the extreme pressures needed to stabilize these structures significantly limit their practical applications. An effective strategy to reduce the external pressure is to add a light element M that binds with H to form MHx units, acting as a chemical precompressor. We exemplify this idea by performing ab initio calculations of the Ac-Be-H phase diagram, proving that the metallization pressure of Ac-H binaries, for which critical temperatures as high as 200 K were predicted at 200 GPa, can be significantly reduced via beryllium incorporation. We identify three thermodynamically stable (AcBe2H10, AcBeH8, and AcBe2H14) and four metastable compounds (fcc AcBeH8, AcBeH10, AcBeH12 and AcBe2H16). All of them are superconductors. In particular, fcc AcBeH8 remains dynamically stable down to 10 GPa, where it exhibits a superconducting-transition temperature Tc of 181 K. The Be-H bonds are responsible for the exceptional properties of these ternary compounds and allow them to remain dynamically stable close to ambient pressure. Our results suggest that high-Tc superconductivity in hydrides is achievable at low pressure and may stimulate experimental synthesis of ternary hydrides. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.109.014501
  • 2024 • 64 Comparing two IBM implementations for the simulation of uniform packed beds
    Gorges, C. and Brömmer, M. and Velten, C. and Wirtz, S. and Mahiques, E.I. and Scherer, V. and Zähringer, K. and van Wachem, B.
    Particuology 86 1-12 (2024)
    doi: 10.1016/j.partic.2023.04.006
  • 2024 • 63 pH-Dependent photocatalytic performance of faceted BiOBr semiconductor particles in degradation of dyes
    Guo, Yuxi and Siretanu, Igor and Mugele, Frieder and Mul, Guido and Mei, Bastian
    Molecular Catalysis 553 (2024)
    Bismuth oxyhalides, such as bismuth-oxy-bromide (BiOBr), show high performance in photocatalytic oxidation of water pollutants. Process conditions, and in particular the pH of the solution, largely affect the photocatalytic efficacy, which is fundamentally poorly understood. We prepared {001} faceted bismuth-oxy-bromide (BiOBr), and determined by advanced AFM analysis that the surface charge of the {001} facet of BiOBr is slightly positive at acidic pH (pH 3) and significantly negative and increasing in negative surface charge in the order pH 6 < pH 9. Decomposition of MB or RhB by illumination of BiOBr is strongly favored by basic conditions (pH 9-10), as evident from discoloration experiments, and determination of the TOC as a function of time of illumination. Reference experiments show the pH dependent degradation profiles cannot be explained by differences in quantities of adsorption of the dye, but rather by the lifetime and/or quantity of BiOBr related photoexcited (surface) charge carriers (holes and electrons) – correlating with surface charge. Using MeOH and other scavengers, we show oxidation of MB or RhB is mainly induced by superoxide anions (•O2− radicals) at low pH and by holes or hydroxyl radicals at high pH – in agreement with surface charge induced band bending. This study provides novel understanding of the pH dependence of the rates of photocatalytic degradation of dyes using BiOBr photocatalysts. © 2023
    view abstractdoi: 10.1016/j.mcat.2023.113753
  • 2024 • 62 Influence of pre-existing configurations of dislocations on the initial pop-in load during nanoindentation in a CrCoNi medium-entropy alloy
    Habiyaremye, Frederic and Guitton, Antoine and Chen, Xiaolei and Richeton, Thiebaud and Berbenni, Stéphane and Schäfer, Florian and Laplanche, Guillaume and Maloufi, Nabila
    Philosophical Magazine 104 137 – 160 (2024)
    The origin and mechanisms responsible for incipient plasticity in metals are still poorly understood. Moreover, the reasons for the recently reported large scattering of the initial pop-in load remain unclear. Hence, this study addresses these issues through a combination of nanoindentation tests and electron channelling contrast imaging characterisation considering a CrCoNi medium-entropy alloy. Experimental findings were also supported by elastic calculations that consider both the indentation and dislocation stress fields. A wide scatter in the maximum shear stress underneath the indenter, as expected, was observed for the analysis based on dislocation density. As a consequence, the spatial arrangement of dislocations within the indented region or local dislocation configuration is introduced as a new parameter to overcome overly simple analysis based on the dislocation density. The maximum shear stress underneath the indenter increased from 6 GPa for dislocation closer to the indentation axis to 11 GPa at 600 nm for dislocation far away from it. Additionally, elastic calculations revealed that the response to the incoming nanoindenter was different for dislocations with different configurations. Thus, the complex interactions of stress fields due to configurations of dislocations and indentation account for the large scatter of the maximum shear stress beneath the indenter. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/14786435.2023.2290541
  • 2024 • 61 Mechanical Characterisation of Bond Formation during Overprinting of PEEK Laminates
    Hümbert, Simon and Atzler, Fynn and Voggenreiter, Heinz
    Materials 17 (2024)
    The latest generation of high-temperature 3D printers enables the production of complex structural components from aerospace-grade thermoplastics such as PEEK (polyether ether ketone). However, adding long or continuous fibres is currently limited, and thermal stresses introduced during the process restrict the maximum part dimensions. Combining 3D-printed components with continuous fibre-reinforced components into one hybrid structure has the potential to overcome such limitations. This work aims to determine whether in situ bonding between PEEK laminates and PEEK 3D printing during overprinting is feasible and which process parameters are significantly responsible for the bonding quality. To this end, the bonding is analysed experimentally in two steps. Firstly, the influence of the process parameters on the thermal history and the strength of the bond is investigated. In the second step, a detailed investigation of the most critical parameters is carried out. The investigation showed the feasibility of overprinting with bonding strengths of up to 15 MPa. It was shown that the bonding strength depends primarily on the temperature in the interface. Additionally, the critical parameters to control the process were identified. The process influences that were displayed form the basis for future hybrid component and process designs. © 2023 by the authors.
    view abstractdoi: 10.3390/ma17010161
  • 2024 • 60 Chemo-mechanical failure mechanisms of the silicon anode in solid-state batteries
    Huo, Hanyu and Jiang, Ming and Bai, Yang and Ahmed, Shamail and Volz, Kerstin and Hartmann, Hannah and Henss, Anja and Singh, Chandra Veer and Raabe, Dierk and Janek, Jürgen
    Nature Materials (2024)
    Silicon is a promising anode material due to its high theoretical specific capacity, low lithiation potential and low lithium dendrite risk. Yet, the electrochemical performance of silicon anodes in solid-state batteries is still poor (for example, low actual specific capacity and fast capacity decay), hindering practical applications. Here the chemo-mechanical failure mechanisms of composite Si/Li6PS5Cl and solid-electrolyte-free silicon anodes are revealed by combining structural and chemical characterizations with theoretical simulations. The growth of the solid electrolyte interphase at the Si|Li6PS5Cl interface causes severe resistance increase in composite anodes, explaining their fast capacity decay. Solid-electrolyte-free silicon anodes show sufficient ionic and electronic conductivities, enabling a high specific capacity. However, microscale void formation during delithiation causes larger mechanical stress at the two-dimensional interfaces of these anodes than in composite anodes. Understanding these chemo-mechanical failure mechanisms of different anode architectures and the role of interphase formation helps to provide guidelines for the design of improved electrode materials. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41563-023-01792-x
  • 2024 • 59 Systematic Approach to Optimize Technological and Economical Aspects of Atmospheric Plasma Sprayed Thermal Barrier Coatings
    Igel, Jens and Mauer, Georg and Guillon, Olivier and Vaßen, Robert
    Advanced Engineering Materials 26 (2024)
    Plasma-sprayed yttria-stabilized zirconia coatings have been used in gas turbines for decades. They are applied for thermal insulation to increase operating temperature and hence efficiency and component's lifetime. To keep manufacturing costs low, especially deposition efficiency is important. However, increasing it is also related to a reduction in porosity, affecting the insulating properties of the layer. To find an optimal combination of efficiency and technological performance, a systematic study of the most affecting parameters of the atmospheric plasma spraying process is conducted, using response surface methodology. In detail, the influence of current, spraying distance, and hydrogen gas flow is investigated with respect to the deposition efficiency, porosity, microstructure, and mechanical properties of the coatings. Characterization is carried out by scanning electron microscopy, microindentation tests, and three-point bending tests. The models generated based on these measured properties allow predictions of the system responses for any parameter variation in the investigated design space. In addition, a numerical model is developed for targeted optimization of the coating properties. This can be used to produce optimized coatings for load-flexible gas turbines with high deposition efficiency, high porosity, and at the same time advantageous mechanical properties. © 2023 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/adem.202300623
  • 2024 • 58 Simulation of reacting flows in packed beds using flamelet generated manifolds
    Illana, E. and Merten, H. and Bergold, T. and Khodsiani, M. and Hosseini, S. and Mira, D. and Beyrau, F. and Thévenin, D. and Scherer, V.
    Thermal Science and Engineering Progress 47 (2024)
    The propagation speed is a key characteristic of a premixed flame since it determines its location and shape. Its correct prediction is particularly important when the flame propagates in a packed bed due to the acceleration of the inflow mixture as it passes through the interstices and the potential interaction with the walls surrounding the interstices. Since the kinetic mechanism has an effect on the propagation speed, the use of detailed chemical kinetics is desired. To limit the cost of chemistry resolution, the feasibility of using the flamelet generated manifolds method (FGM) is investigated. A 2D laminar premixed methane/air flame with a co-flow of air, which propagates into a packed bed, is set up as a test case. The packed bed is either represented by a porous medium or by a resolved approach where particle shapes are fully resolved. The solutions using chemistry tables and finite rate chemistry with a detailed mechanism (GRI3.0) under adiabatic conditions and with heat exchange between the two phases are in good agreement. In addition, the computational effort using FGM is about 13 times lower. In a next step, the employed FGM approach is validated against experiments. For this purpose, an experimentally investigated 2D premixed flame confined by three isothermal cylinders is simulated using flamelet generated manifolds for three operating conditions. Comparison of simulated and measured flame shape and location shows reasonable agreement. This proves that the flamelet generated manifolds method is suitable and cost-effective to simulate reacting flows within packed beds. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.tsep.2023.102264
  • 2024 • 57 Shape-changing particles for locally resolved particle geometry in DEM simulations
    Illana, Enric and Qyteti, Klidi and Scharnowski, Maik and Brömmer, Maximilian and Wirtz, Siegmar and Scherer, Viktor
    Particuology 89 185 – 190 (2024)
    Taking into account the complex shape of particles in discrete element method (DEM) simulations of large-scale granular systems is computationally demanding due to the time-consuming contact detection algorithms for polyhedral particles. In this short communication, a novel approach that locally resolves the particle shapes where needed and uses a simplified representation elsewhere, to accelerate simulations without compromising accuracy, is presented. For this purpose, a method employing a smooth transition of the particle shape representation from analytical spheres to shape-resolving polyhedra is introduced in DEM. The feasibility and correct implementation of this approach are demonstrated through simulations of hopper discharge involving spherical and dodecahedral particles from a flat bottom silo or shaft kiln. The model capabilities, in terms of accuracy as well as reduction in computational effort, are quantified for a moving bed with continuous outflow. © 2023 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences
    view abstractdoi: 10.1016/j.partic.2023.11.003
  • 2024 • 56 Multi-phase-field approach to fracture demonstrating the role of solid-solid interface energy on crack propagation
    Jafarzadeh, Hossein and Shchyglo, Oleg and Steinbach, Ingo
    International Journal of Fracture (2024)
    A multi-phase-field approach for crack propagation considering the contribution of the interface energy is presented. The interface energy is either the grain boundary energy or the energy between a pair of solid phases and is directly incorporated into to the Ginzburg–Landau equation for fracture. The finite difference method is utilized to solve the crack phase-field evolution equation and fast Fourier method is used to solve the mechanical equilibrium equation in three dimensions for a polycrystalline material. The importance of the interface (grain boundary) energy is analyzed numerically for various model problems. The results show how the interface energy variations change the crack trajectory between the intergranular and transgranular fracture. © The Author(s) 2024.
    view abstractdoi: 10.1007/s10704-024-00762-x
  • 2024 • 55 A variational approach to effective models for inelastic systems
    Jezdan, Ghina and Govindjee, Sanjay and Hackl, Klaus
    International Journal of Solids and Structures 286-287 (2024)
    Given a set of inelastic material models, a microstructure, a macroscopic structural geometry, and a set of boundary conditions, one can in principle always solve the governing equations to determine the system's mechanical response. However, for large systems this procedure can quickly become computationally overwhelming, especially in three-dimensions when the microstructure is locally complex. In such settings multi-scale modeling offers a route to a more efficient model by holding out the promise of a framework with fewer degrees of freedom, which at the same time faithfully represents, up to a certain scale, the behavior of the system. In this paper, we present a methodology that produces such models for inelastic systems upon the basis of a variational scheme. The essence of the scheme is the construction of a variational statement for the free energy as well as the dissipation potential for a coarse scale model in terms of the free energy and dissipation functions of the fine scale model. From the coarse scale energy and dissipation we can then generate coarse scale material models that are computationally far more efficient than either directly solving the fine scale model or by resorting to FE2 type modeling. Moreover, the coarse scale model preserves the essential mathematical structure of the fine scale model. An essential feature for such schemes is the proper definition of the coarse scale inelastic variables. By way of concrete examples, we illustrate the needed steps to generate successful models via application to problems in classical plasticity, included are comparisons to direct numerical simulations of the microstructure to illustrate the accuracy of the proposed methodology. © 2023 The Author(s)
    view abstractdoi: 10.1016/j.ijsolstr.2023.112567
  • 2024 • 54 Corrigendum to “On the role of the thermal treatment of sulfided Rh/CNT catalysts applied in the oxygen reduction reaction” [Electrochimica Acta 54 (2009) 7186 - 7193](S0013468609008755)(10.1016/j.electacta.2009.06.095)
    Jin, Chen and Xia, Wei and Nagaiah, Tharamani Chikka and Guo, Junsong and Chen, Xingxing and Bron, Michael and Schuhmann, Wolfgang and Muhler, Martin
    Electrochimica Acta 478 (2024)
    In Fig. 5a, the S 2p trace labelled 400°C had been initially plotted using data of the sample treated at 650°C by mistake. Fig. 5a was replotted using the original XPS data as shown below. The content of the manuscript including discussion and conclusions is not affected by the exchange of the S 2p spectrum. The authors would like to apologize for any inconvenience caused. © 2024
    view abstractdoi: 10.1016/j.electacta.2024.143843
  • 2024 • 53 Green steel from red mud through climate-neutral hydrogen plasma reduction
    Jovičević-Klug, Matic and Souza Filho, Isnaldi R. and Springer, Hauke and Adam, Christian and Raabe, Dierk
    Nature 625 703 – 709 (2024)
    Red mud is the waste of bauxite refinement into alumina, the feedstock for aluminium production 1. With about 180 million tonnes produced per year 1, red mud has amassed to one of the largest environmentally hazardous waste products, with the staggering amount of 4 billion tonnes accumulated on a global scale 1. Here we present how this red mud can be turned into valuable and sustainable feedstock for ironmaking using fossil-free hydrogen-plasma-based reduction, thus mitigating a part of the steel-related carbon dioxide emissions by making it available for the production of several hundred million tonnes of green steel. The process proceeds through rapid liquid-state reduction, chemical partitioning, as well as density-driven and viscosity-driven separation between metal and oxides. We show the underlying chemical reactions, pH-neutralization processes and phase transformations during this surprisingly simple and fast reduction method. The approach establishes a sustainable toxic-waste treatment from aluminium production through using red mud as feedstock to mitigate greenhouse gas emissions from steelmaking. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41586-023-06901-z
  • 2024 • 52 Plasma sheath tailoring by a magnetic field for three-dimensional plasma etching
    Jüngling, Elia and Wilczek, Sebastian and Mussenbrock, Thomas and Böke, Marc and von Keudell, Achim
    Applied Physics Letters 124 (2024)
    Three-dimensional (3D) etching of materials by plasmas is an ultimate challenge in microstructuring applications. A method is proposed to reach a controllable 3D structure by using masks in front of the surface in a plasma etch reactor in combination with local magnetic fields to steer the incident ions in the plasma sheath region toward the surface to reach 3D directionality during etching and deposition. This effect has the potential to be controlled by modifying the magnetic field and/or plasma properties to adjust the relationship between sheath thickness and mask feature size. However, because the guiding length scale is the plasma sheath thickness, which for typical plasma densities is at least tens of micrometers or larger, controlled directional etching and deposition target the field of microstructuring, e.g., of solids for sensors, optics, or microfluidics. In this proof-of-concept study, it is shown that E → × B → drifts tailor the local sheath expansion, thereby controlling the plasma density distribution and the transport when the plasma penetrates the mask during an RF cycle. This modified local plasma creates a 3D etch profile. This is shown experimentally as well as using 2d3v particle-in-cell/Monte Carlo collisions simulation. © 2024 Author(s).
    view abstractdoi: 10.1063/5.0187685
  • 2024 • 51 Particle-based simulations of electrophoretic deposition with adaptive physics models
    Karnes, J.J. and Pascall, A.J. and Rehbock, C. and Ramesh, V. and Worsley, M.A. and Barcikowski, S. and Lee, E. and Giera, B.
    Computer Physics Communications 297 (2024)
    doi: 10.1016/j.cpc.2023.109062
  • 2024 • 50 Spacer Effects in Sulfo- and Sulfabetaine Polymers on Their Resistance against Proteins and Pathogenic Bacteria
    Karthäuser, Jana F. and Kopecz, Regina and Schönemann, Eric and Martínez Guajardo, Alejandro and Laschewsky, André and Rosenhahn, Axel
    Advanced Materials Interfaces 11 (2024)
    The resistance of zwitterionic polymer coatings against the adsorption of proteins and the attachment of pathogenic bacteria is influenced by the precise molecular architecture of the polymers. Two until now rarely studied molecular variables in this context are side chain spacer groups separating the zwitterionic moieties from the polymer backbone and spacer groups separating the cationic and anionic groups within the zwitterionic moiety. Therefore, a set of six poly(sulfobetaine)s and poly(sulfabetaine)s is prepared, in which these spacer groups are systematically varied, incorporating ethylene, propylene, and undecylene side chain spacers, as well as ethylene, propylene, and butylene inter-charge spacers, and their effects on the antifouling behavior are explored. Hence, the corresponding zwitterionic methacrylates are copolymerized with a photo-reactive methacrylate bearing a benzophenone moiety. All zwitterionic coatings reveal hydrophilic properties when immersed in water and those with relatively short spacers show effective suppression of non-specific protein adsorption. Polysulfobetaines outperform the polysulfabetaine ones in terms of resistance against adhesion of bacteria. The overall best fouling protection is observed for the polysulfobetaine bearing a propylene side chain spacer, which coincides with their relatively highest water solubility. The results corroborate previous findings that even apparently minor molecular changes of polyzwitterions can strongly affect their antifouling performance. © 2023 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/admi.202300873
  • 2024 • 49 Direct Recycling of Hot-Deformed Nd–Fe–B Magnet Scrap by Field-Assisted Sintering Technology
    Keszler, Monica and Grosswendt, Felix and Assmann, Anna-Caroline and Krengel, Martin and Maccari, Fernando and Gutfleisch, Oliver and Sebold, Doris and Guillon, Olivier and Weber, Sebastian and Bram, Martin
    Advanced Energy and Sustainability Research 5 (2024)
    Recycling of Nd–Fe–B magnets is an ongoing challenge regarding circular economy. State-of-the-art magnet production methods, such as hot deformation, have limitations with respect to direct recycling of magnet scrap particles that differ from pristine melt-spun Nd–Fe–B powder. Recent work has shown that a combination of presintering by field-assisted sintering technology/spark plasma sintering (FAST/SPS) and hot deformation by flash spark plasma sintering (flash SPS) has the potential to directly produce Nd–Fe–B magnets from 100% scrap material. Both processes have the capability to adjust and monitor process parameters closely, resulting in recycled magnets with properties similar to commercial magnets but made directly from crushed and recycled Nd–Fe–B powder that partially or completely replaces pristine melt-spun Nd–Fe–B powder. Herein, a systematic study is done inserting recycled magnet particles into a flash SPS deformed magnet, considering the effects of different weight percentages of scrap material of varied particle size fractions. In some cases, coercivity HcJ of >1400 kAm−1 and remanence Br of 1.1 T can be achieved with 20 wt% scrap material. The relationship between particle size fraction, oxygen uptake, and percentage of recyclate in a final magnet are all explored and discussed with respect to magnets made from pristine material. © 2023 The Authors. Advanced Energy and Sustainability Research published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/aesr.202300184
  • 2024 • 48 Microscopic insights on field induced switching and domain wall motion in orthorhombic ferroelectrics
    Khachaturyan, Ruben and Yang, Yijing and Teng, Sheng-Han and Udofia, Benjamin and Stricker, Markus and Grünebohm, Anna
    Physical Review Materials 8 (2024)
    Surprisingly little is known about the microscopic processes that govern ferroelectric switching in orthorhombic ferroelectrics. To study these processes, we combine ab initio-based molecular dynamics simulations and data science on the prototypical material BaTiO3. We reveal two different field regimes: For moderate field strengths, the switching is dominated by domain wall motion, while a fast bulklike switching can be induced for large fields. Switching in both field regimes follows a multistep process via polarization directions perpendicular to the applied field. In the former case, the moving wall is of Bloch character and hosts dipole vortices due to nucleation, growth, and crossing of two-dimensional 90° domains. In the second case, the local polarization shows a continuous correlated rotation via an intermediate tetragonal multidomain state. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.8.024403
  • 2024 • 47 Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed
    Khodsiani, M. and Namdar, R. and Varnik, F. and Beyrau, F. and Fond, B.
    Particuology 85 167-185 (2024)
    doi: 10.1016/j.partic.2023.03.011
  • 2024 • 46 On the inherent strength of Cr23C6 with the complex face-centered cubic D84 structure
    Kishida, Kyosuke and Ito, Mitsuhiro and Inui, Haruyuki and Heilmaier, Martin and Eggeler, Gunther
    Acta Materialia 263 (2024)
    The deformation behavior of single crystals of Cr23C6 with the complex D84 crystal structure based on the face-centered cubic lattice has been investigated by micropillar compression as a function of crystal orientation and specimen size at room temperature. For the first time, the {111}<1‾01> slip system is identified to be the only operative slip system. The 1/2<1‾01> dislocation dissociates into two partial dislocations with identical collinear Burgers vectors (b) as confirmed by transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM). The energy of the stacking fault bounded by two coupled partial dislocations with the b = 1/4<1‾01> is evaluated from their separation distances to be 840 mJ/m2. The critical resolved shear stress (CRSS) for {111}<1‾01> slip increases with the decrease in the specimen size, following the inverse power-law relationship with a relatively low exponent of ∼ -0.19. The room-temperature bulk CRSS value evaluated by extrapolating this inverse relationship to the specimen size of 20∼30 μm is 0.79 ± 0.15 GPa. The exact position of the slip plane among many different parallel {111} atomic planes and possible dislocation dissociations on the relevant slip planes are discussed based on the calculated generalized stacking fault energy (GSFE) curves. The inter-block layer slip is deduced to occur for {111}<1‾01> slip based on the TEM/STEM observations and the result of GSFE calculations. Finally, plausible atomic structures for stacking faults on (111) and coherent twin boundaries are discussed. © 2023 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2023.119518
  • 2024 • 45 Coupling radiative properties with detailed char conversion kinetics
    Koch, Matthias and Pielsticker, Stefan and Tarlinski, David and Scherer, Viktor and Kneer, Reinhold
    Fuel 363 (2024)
    In pulverized solid fuel combustion, radiation is the primary heat transfer mechanism. Especially in the near-burner region with high particle loadings, particle radiation dominates gas radiation. Thus, adequate modeling of particle-radiation interactions in full-scale simulations of combustion chambers may primarily affect the overall accuracy. The radiation behavior depends strongly on the particles? optical properties, characterized by the complex index of refraction (IOR). The IOR depends on particle morphology and material composition which change during pyrolysis and char conversion. For char conversion, the focus of the present paper, the change depends on how the structural transformations take place inside the particle, characterizes by the reaction regimes, boundary layer diffusion limited, pore diffusion limited or kinetically controlled. The formation of an outer ash film layer with progressing burnout can complicate the situation even more. To quantify the effects of the structural changes during the char conversion process on the radiative properties, the output data of the char conversion kinetics (CCK) model (particle size, ash/carbon content, pore fraction) are used to build artificial particles at different conversion degrees and for the different regimes. Finally, the radiation interaction is calculated by applying an extension of the Mie theory for coated particles, and these results are compared to simplified approaches. Simplified approaches were tested to derive the IOR by applying mixing rules based on the available char and ash content with progressing char conversion. The results indicate that only a non-linear mixing rule for the IORs of ash and char lead to appropriate approximations of the radiation behavior of the particle. Furthermore, it is not necessary to model the spatial arrangement of carbon core and ash film for the radiative properties. Modeling a sphere and calculating an effective IOR depending on the carbon, ash, and pore volume fraction results in an average deviation of less than 3 % to the exact solution. © 2024 The Author(s)
    view abstractdoi: 10.1016/j.fuel.2024.130973
  • 2024 • 44 Experimental study on influence of blade angle and particle size on particle mechanics on a batch-operated single floor of a multiple hearth furnace
    Kriegeskorte, Max and Hilse, Nikoline and Spatz, Phil and Scherer, Viktor
    Particuology 85 224 – 240 (2024)
    In industry, multiple hearth furnaces are used for the thermal treatment of particulate material. The current contribution concentrates on the experimental analysis of particle mechanics for a batch-operated single floor of a multiple hearth furnace. The particles are agitated on the circular floor by a single, rotating rabble arm equipped with three flat rabble blades of 10 mm thickness. The blade angle, defined as the angle, which the blade is inclined against the tangential direction, is varied from 0° to 90°. A single layer of spherical polyoxymethylene (POM) particles with three different diameters (5, 10 and 20 mm) is placed on the floor. To analyze the results, two parameters have been extracted from image analysis when the bed of particles is agitated, first, the area not covered by particles and second, the frequency distribution of the mean distance among the particles. The particle free surface area increases with the inclination of the blades. The evolution of the particle free surface area differs for the different particle diameters. In general, the maximum particle free area for all blade angles is the largest for the 5 mm particles followed by the 20 mm particles. For the 10 mm particles, the particle free surface area starts for a blade angle of 0° at larger values than for the 20 mm particles but the values fall below the values for the 20 mm particles for larger blade angles. The reason for this behavior is discussed in detail. The mean distance among the particles is a parameter characterizing the length scales dominating the effects on the floor. The frequency distribution of the mean distance among particles provides information about the morphology of the particle bulk, for example, whether the free surface area is interspersed with particles. © 2023
    view abstractdoi: 10.1016/j.partic.2023.06.009
  • 2024 • 43 Au Micro- and Nanoelectrodes as Local Voltammetric pH Sensors During Oxygen Evolution at Electrocatalyst-Modified Electrodes
    Li, Lejing and Limani, Ndrina and P Antony, Rajini and Dieckhöfer, Stefan and Santana Santos, Carla and Schuhmann, Wolfgang
    Small Science (2024)
    The scarcity of state-of-the-art oxygen evolution reaction (OER) electrocatalysts has led to intensive research on alternative viable electrocatalytic materials. While activity and cost are the main factors to be sought after, the catalyst stability under harsh acidic conditions is equally crucial. Considering that OER is a proton-coupled electron-transfer reaction that involves local acidification of the reaction environment by liberation of H+, the catalyst stability can be largely compromised in such conditions. Consequently, probing the pH value near the catalyst surface under operation leads to a deeper understanding of this process. The applicability of bare Au microelectrodes and nanoelectrodes as sensitive local pH probes during OER is shown in this work by using scanning electrochemical microscopy (SECM). Two case studies are presented, including the state-of-the-art OER catalyst (IrO2) in acidic media and a ZnGa2O4 catalyst in alkaline buffered solution, demonstrating the suitability of the Au probe to accurately determine the local pH value in a wide pH range. © 2024 The Authors. Small Science published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/smsc.202300283
  • 2024 • 42 Accelerated Adiabatic Passage of a Single Electron Spin Qubit in Quantum Dots
    Liu, Xiao-Fei and Matsumoto, Yuta and Fujita, Takafumi and Ludwig, Arne and Wieck, Andreas D. and Oiwa, Akira
    Physical Review Letters 132 (2024)
    Adiabatic processes can keep the quantum system in its instantaneous eigenstate, which is robust to noises and dissipation. However, it is limited by sufficiently slow evolution. Here, we experimentally demonstrate the transitionless quantum driving (TLQD) of the shortcuts to adiabaticity in gate-defined semiconductor quantum dots (QDs) to greatly accelerate the conventional adiabatic passage for the first time. For a given efficiency of quantum state transfer, the acceleration can be more than twofold. The dynamic properties also prove that the TLQD can guarantee fast and high-fidelity quantum state transfer. In order to compensate for the diabatic errors caused by dephasing noises, the modified TLQD is proposed and demonstrated in experiment by enlarging the width of the counterdiabatic drivings. The benchmarking shows that the state transfer fidelity of 97.8% can be achieved. This work will greatly promote researches and applications about quantum simulations and adiabatic quantum computation based on the gate-defined QDs. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevLett.132.027002
  • 2024 • 41 Dynamic Transformation of Functionalized Bismuth to Catalytically Active Surfaces for CO2 Reduction to Formate at High Current Densities
    Mahbub, Muhammad Adib Abdillah and Junqueira, João R. C. and Wang, Xin and Zhang, Jian and Dieckhöfer, Stefan and Seisel, Sabine and Das, Debanjan and Schuhmann, Wolfgang
    Advanced Functional Materials 34 (2024)
    A facile strategy to boost the activity and preserve the selectivity of CO2 reduction to formate using organic-functionalized metal catalysts, specifically 2-methyl-imidazole coordinated to Bi, Bi[2-MeIm], is reported, and the active surfaces are investigated during structural transformation under the applied cathodic potential necessary for CO2 reduction. Operando Raman spectroscopy unveils the structure evolution during the reaction and post-electrolysis analysis shows the formation of three phases of bismuth-based active surfaces. As a result, Bi[2-MeIm] achieves an excellent CO2 reduction performance with an average formate selectivity of ≈90% Faradaic efficiency and high activity reaching a current density of up to −1 A cm−2 in a narrow window of cathodic potentials from −0.46 to −0.78 V versus RHE. © 2023 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/adfm.202307752
  • 2024 • 40 Fouling Inhibition by Replenishable Plastrons on Microstructured, Superhydrophobic Carbon-Silicone Composite Coatings
    Manderfeld, Emily and Vogler, Louisa and Rosenhahn, Axel
    Advanced Materials Interfaces (2024)
    Superhydrophobic surfaces are known to resist diatom and bacteria adhesion if stable air layers are formed underwater (known as a plastron). However, most preparation techniques to obtain superhydrophobic surfaces need sophisticated chemical treatments and/or complicated chemical procedures. Here a 3D printing technique is used to create different molds for polymer casting. A conductive graphite-carbon black-silicone composite mixture is developed to fabricate different polymer surface casts from these molds. The obtained surfaces exhibited contact angles >145°, which led to a plastron formation on the surfaces underwater, and areas with intact plastrons protected the samples from diatom attachment. Due to the conductivity of the coatings, it is possible to replenish the plastrons by heating the surfaces. © 2024 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/admi.202300964
  • 2024 • 39 Ultrashort pulse ablation of printed circuit board materials using a Bessel beam
    Marx, Jan and Arthkamp, Nikolas and Esen, Cemal and Ostendorf, Andreas
    Journal of Laser Applications 36 (2024)
    In times of digitalization, multilayer composite materials became central components in an increasing number of application fields. Thus, there is a need for optimization of the cost-intensive and time-consuming processing of multilayer composites. In this contribution, an ultrashort pulse laser-based method is presented for precise and flexible ablation of a printed circuit board base material. Therefore, an 800 nm Gaussian laser beam was transformed into a Bessel beam by an axicon to get a small spot size and an ablation result with a high aspect ratio. The influence of the average laser power, the number of exposure cycles, and the pulse duration on the geometry as well as the surface quality of ablated structures was investigated and compared to Gaussian beam ablation. Furthermore, it is shown that the results can be transferred to microdrilling processes. With the presented method, it was possible to ablate the copper top layer of the printed circuit boards as well as the FR4 layer below with a precisely adjustable depth. © 2024 Author(s).
    view abstractdoi: 10.2351/7.0001170
  • 2024 • 38 Combined experimental and theoretical approach to improve measurement accuracy of temperature-dependent reflectance of copper for near-infrared lasers
    Mattern, Manuel and Kukreja, Lalit Mohan and Ostendorf, Andreas
    Welding in the World (2024)
    The low process stability of laser welding of copper with near-infrared lasers requires precise input data for process control and meaningful simulations. But meanwhile, available datasets of temperature-dependent reflectance or absorptance for near-infrared lasers on copper do not show good agreement between the different sources and often do not include the fusion process, which is of crucial importance for realistic laser welding simulations. Additionally, most of the datasets are only calculated. Therefore, in a previous study, temperature-dependent reflectance measurements were performed on electro tough-pitch copper using a near-infrared laser. The measurements revealed a reflectance drift, which was induced by the setup behavior during heating, and the time-dependence of chemical reactions like the redox-reaction as possible error sources. In this study, experiments on laser melting as the fundamental process of laser welding were performed, together with corresponding simulations using the measured reflectance values for oxide-reduced and for untreated copper from the previous study. Then, the simulations were compared with the experiments to estimate the accuracy of the reflectance measurements. To provide context, the same simulations were also conducted using reflectance datasets from other authors. In a second step, the reflectance data were corrected with respect to the reflectance drift and the effects of redox reactions were adapted to the conditions of the laser melting experiments. Using the resulting reflectance curves, an improved agreement of simulation results and the experiments was achieved over a range of different test cases, without the necessity of correction factors in the simulation model. © 2023, The Author(s).
    view abstractdoi: 10.1007/s40194-023-01672-7
    Miska, Niklas and Freitag, Steffen and Balzani, Daniel
    International Journal for Uncertainty Quantification 14 89 – 106 (2024)
    In this work, a new method is presented to quantify the sharpest bounds on the probability of failure while including local variations of properties in terms of random fields. The method is based on the extended optimal uncertainty quantification (OUQ) for polymorphic uncertainties. Therein, a special focus is on the incorporation of aleatory as well as epistemic uncertainties without the requirement of making unjustified assumptions regarding stochastic distribution functions for the epistemic uncertainties. Two approaches are proposed to incorporate the information gained from random field simulations in uncertainty quantifications in this paper: the first approach is based on a nested OUQ scheme to account for the potentially limited data, whereas the second approach focuses on artificial neural networks to build a surrogate model directly from the random field result data. The proposed approaches are numerically analyzed in detail by considering a sheet metal forming process as an engineering application example. © 2024 by Begell House, Inc.
    view abstractdoi: 10.1615/Int.J.UncertaintyQuantification.2023047256
  • 2024 • 36 An a priori irreversible phase-field formulation for ductile fracture at finite strains based on the Allen–Cahn theory: a variational approach and FE-implementation
    Montazer Hojjat, H. and Kozinov, S. and Balzani, D.
    Archive of Applied Mechanics (2024)
    In this paper, a new crack surface energy for the simulation of ductile fracture is proposed, which is based on the Allen–Cahn theory of diffuse interfaces. In contrast to existing fracture approaches, here, the crack surface energy density is a double-well potential based on a new interpretation of the crack surface. That is, the energy associated with the whole diffuse region between the fully cracked and intact regions is interpreted as crack surface energy. This kind of formulation, on the one hand, results in the balance of micromechanical forces and on the other hand, is a priori thermodynamically consistent. Furthermore, the proposed formulation is based on a gamma-convergent interface energy and it is in agreement with the classical solution of Irwin (Appl Mech Trans ASME E24:351–369, 1957). It is shown that in contrast to existing models, crack irreversibility is automatically fulfilled and no further constraints related to neither local nor global irreversibility are needed. To also account for potential plastic shear band localization, the approach is extended by a micromorphic plasticity model. By analyzing two different classical numerical benchmark problems, the proposed formulation is shown to enable mesh-independent results which are in agreement with the results of competing approaches. © 2024, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
    view abstractdoi: 10.1007/s00419-023-02527-9
  • 2024 • 35 MnFeNi-based composite as a case study of a bifunctional oxygen electrocatalyst under dynamically changing electrode potentials
    Morales, Dulce M. and Kazakova, Mariya A. and Medina, Danea and Villalobos, Javier and Schuck, Götz and Risch, Marcel and Schuhmann, Wolfgang
    ChemCatChem (2024)
    High-performance bifunctional electrocatalysts for the oxygen reduction (ORR) and oxygen evolution reaction (OER) are essential components in energy conversion and storage technologies. Yet, their poor reversibility hinders their applicability. A highly active ORR/OER catalyst, consisting of multiwalled carbon nanotubes-supported MnFeNiOx nanoparticles, was subjected to sequences of chronoamperometric steps alternating between the ORR, the OER and highly cathodic potentials (Ec). Rotating ring disk electrode methods revealed that applying Ec leads to a small increase in the current and peroxide species yield during the ORR while enhancing substantially the OER. X-ray absorption spectroscopy showed irreversible changes in the chemical state of MnFeNiOx correlating with its catalytic properties. The complexity of changes that a composite catalyst may undergo under varying potentials, the importance of monitoring product formation, and the convenience of using dynamic electrochemical sequences for the assessment of catalyst reversibility, as well as for the activation and/or restoration of their catalytic properties, are highlighted. © 2024 The Authors. ChemCatChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cctc.202301174
  • 2024 • 34 Numerical study of convective heat transfer in static arrangements of particles with arbitrary shapes: A monolithic hybrid lattice Boltzmann-finite difference-phase field solver
    Namdar, R. and Khodsiani, M. and Safari, H. and Neeraj, T. and Hosseini, S.A. and Beyrau, F. and Fond, B. and Thévenin, D. and Varnik, F.
    Particuology 85 186-197 (2024)
    doi: 10.1016/j.partic.2023.03.020
  • 2024 • 33 Investigating the platinum electrode surface during Kolbe electrolysis of acetic acid
    Olde Nordkamp, Margot and Ashraf, Talal and Altomare, Marco and Borca, Andrea Casanova and Ghigna, Paolo and Priamushko, Tatiana and Cherevko, Serhiy and Saveleva, Viktoriia A. and Atzori, Cesare and Minguzzi, Alessandro and He, X...
    Surfaces and Interfaces 44 (2024)
    Platinum is commonly applied as the anode material for Kolbe electrolysis of carboxylic acids thanks to its superior performance. Literature claims that the formation of a barrier layer on the Pt anode in carboxylic acid electrolyte suppresses the competing oxygen evolution and promotes anodic decarboxylation. In this work, we show by using a combination of complementary in situ and ex situ surface sensitive techniques, that the presence of acetate ions also prevents the formation of a passive oxide layer on the platinum surface at high anodic potentials even in aqueous electrolyte. Furthermore, Pt dissolves actively under these conditions, challenging the technical implementation of Kolbe electrolysis. Future studies exploring the activity-structure-stability relation of Pt are required to increase the economic viability of Kolbe electrolysis. © 2023 The Author(s)
    view abstractdoi: 10.1016/j.surfin.2023.103684
  • 2024 • 32 A simulation study for a cost-effective PET-like detector system intended to track particles in granular assemblies
    Oppotsch, J. and Athanassiadis, A. and Fritsch, M. and Heinsius, F.-H. and Held, T. and Hilse, N. and Scherer, V. and Steinke, M. and Wiedner, U.
    Particuology 84 117-125 (2024)
    doi: 10.1016/j.partic.2023.03.005
  • 2024 • 31 On-demand single-electron source via single-cycle acoustic pulses
    Ota, Shunsuke and Wang, Junliang and Edlbauer, Hermann and Okazaki, Yuma and Nakamura, Shuji and Oe, Takehiko and Ludwig, Arne and Wieck, Andreas D. and Sellier, Hermann and Bäuerle, Christopher and Kaneko, Nobu-Hisa and Kodera, ...
    Physical Review Applied 21 (2024)
    Surface acoustic waves (SAWs) are a reliable solution to the transport of single electrons with precision in piezoelectric semiconductor devices. Recently, highly efficient single-electron transport with a strongly compressed single-cycle acoustic pulse has been demonstrated. This approach, however, requires surface gates constituting the quantum dots, their wiring, and multiple gate movements to load and unload the electrons, which is very time-consuming. Here, on the contrary, we employ such a single-cycle acoustic pulse in a much simpler way - without any quantum dot at the entrance or exit of a transport channel - to perform single-electron transport between distant electron reservoirs. We observe the transport of a solitary electron in a single-cycle acoustic pulse via the appearance of the quantized acoustoelectric current. The simplicity of our approach allows for on-demand electron emission with arbitrary delays on a nanosecond time scale. We anticipate that enhanced synthesis of the SAWs will facilitate electron quantum optics experiments with multiple-electron flying qubits. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevApplied.21.024034
  • 2024 • 30 Misfit and the mechanism of high temperature and low stress creep of Ni-base single crystal superalloys
    Parsa, A.B. and Bürger, D. and Pollock, T.M. and Eggeler, G.
    Acta Materialia 264 (2024)
    The present work proposes a new elementary deformation mechanism which governs high temperature and low stress creep of single crystal superalloys (SXs), where the misfit between the γ- and the γ′-phase plays a central role. In the coherent two phase SX microstructure, there is a tendency to minimize the overall elastic strain energy. This is accomplished by the formation of dislocation networks in the γ-phase close to the γ/γ’-interfaces. The stress fields of the network dislocations and misfit stresses accommodate each other to keep the overall strain energy of the system at a minimum. Previous work has shown that dynamic recovery is associated with knitting-out reactions, where dislocations from the network shear the γ’-phase and annihilate with dislocations of opposite sign on the other side of the γ’-phase region. Due to the presence of the misfit this results in an increase of elastic strain energy which is counteracted by coupled knitting-in reactions where newly arriving γ-channel dislocations re-establish the minimum energy configuration. Here we provide microstructural evidence for knitting-out and knitting-in reactions and show that while these reactions clearly occur, dislocation network spacings stay constant. The misfit between the γ- and the γ′-phase accounts for a constant network spacing. Dislocation networks are not static but represent dynamic steady state equilibrium structures in an evolving microstructure. Knitting regular networks requires climb processes which are suggested to be rate controlling. This new view of high temperature and low stress creep mechanism of SXs allows to rationalize previous results published in the literature. © 2023
    view abstractdoi: 10.1016/j.actamat.2023.119576
  • 2024 • 29 Tunnel lining segments with enhanced bearing capacity using hybrid concrete concepts
    Petraroia, Diego N. and Plückelmann, Sven and Mark, Peter and Breitenbücher, Rolf
    Tunnelling and Underground Space Technology 143 (2024)
    In general, the design of tunnel lining segments used in mechanized tunneling is dominated by the joints. In fact, the effects of partial area loading dominate segmental failure and, consequently, the concrete bearing capacity of the central region remains underutilized. This paper presents two types of new hybrid segments with enhanced utilization ratios throughout their bodies. The first type comes with strengthened longitudinal joints using high performance steel fiber reinforced concrete, in addition to conventional reinforcement. The second incorporates one-sided barrel-shaped recesses in the central region, which yield volume savings of up to 23.8%. The performance of the new designs is experimentally evaluated on a full-size testing rig made from two steel frames with a capacity of 5 MN each. It captures the on-site conditions in tunnels during service (final state). The first type of segments shows a 74.3% higher loading capacity than a conventional specimen for reference. The second performs even better and possesses 97% higher capacity. In both cases, the failure occurs in the central region. This increases structural safety and simplifies the design. Especially the design of the central region subjected to bending and axial forces gains more relevance against the controversially discussed design of the longitudinal joints. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.tust.2023.105484
  • 2024 • 28 The catalytic effect of iron oxide phases on the conversion of cellulose-derived chars in diluted {O2} and {CO2}
    Pflieger, C. and Eckhard, T. and Böttger, J. and Schulwitz, J. and Herrendorf, T. and Schmidt, S. and Salamon, S. and Landers, J. and Wende, H. and Kleist, W. and Muhler, M. and Cerciello, F.
    Applied Energy 353 (2024)
    doi: 10.1016/j.apenergy.2023.122068
  • 2024 • 27 The catalytic effect of iron oxide phases on the conversion of cellulose-derived chars in diluted O2 and CO2
    Pflieger, Christin and Eckhard, Till and Böttger, Jannik and Schulwitz, Jonas and Herrendorf, Tim and Schmidt, Stefan and Salamon, Soma and Landers, Joachim and Wende, Heiko and Kleist, Wolfgang and Muhler, Martin and Cerciello, Francesca
    Applied Energy 353 (2024)
    The conversion of biomass-derived char is substantially influenced by its metal content. One of the main catalytically active metallic elements in biomass is Fe, which occurs in various mineral forms. For the implementation of catalytic effects into char conversion models, investigations on the role of mineral type and loading are required. In this work, the catalytic effect of an Fe sulfate loading series on the oxidation and gasification of an inherently mineral-free cellulose-derived char was analysed. Characterisation focused on the Fe phases present in the char identifying the transformation from FeSO4 to γ-Fe2O3 during doping, and further to ε-Fe2O3 and α-Fe2O3 upon char oxidation as well as to FeO and γ-Fe upon char gasification. Very high loading-dependent activities of ε-Fe2O3 and FeO were quantified by kinetic modelling. These iron oxides strongly catalyse char conversion, lowering the activation energy by up to 14% and 18%, respectively, relative to the mineral-free char. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.apenergy.2023.122068
  • 2024 • 26 Sputter-Deposited La–Co–Mn–O Nanocolumns as Stable Electrocatalyst for the Oxygen Evolution Reaction
    Piotrowiak, Tobias H. and Krysiak, Olga A. and Suhr, Ellen and Zhang, Jian and Zehl, Rico and Kostka, Aleksander and Schuhmann, Wolfgang and Ludwig, Al
    Small Structures (2024)
    A thin-film materials library (ML) of the La–Co–Mn–O system is fabricated by hot reactive combinatorial cosputter deposition and screened for its electrocatalytic activity for the oxygen evolution reaction. Within this ML, an area with superior catalytic activity is identified. In-depth characterization of this region reveals a unique columnar-grown microstructure showing a large catalytic surface and excellent stability during electrocatalytic measurements. A zoom-in into these structures shows that the columns are compositionally and structurally not homogeneous but are composed of a mixture of the perovskite phase LaCoMnO3 and Co–Mn–O oxide. Nanoelectrochemistry using the particle on a nanoelectrode approach confirms the high activity as well as stability of the single columns. © 2024 The Authors. Small Structures published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/sstr.202300415
  • 2024 • 25 Curved GaAs cantilever waveguides for the vertical coupling to photonic integrated circuits
    Qvotrup, Celeste and Liu, Zhe and Papon, Camille and Wieck, Andreas D. and Ludwig, Arne and Midolo, Leonardo
    Optics Express 32 3723 – 3734 (2024)
    We report the nanofabrication and characterization of optical spot-size converter couplers based on curved GaAs cantilever waveguides. Using the stress mismatch between the GaAs substrate and deposited Cr-Ni-Au strips, single-mode waveguides can be bent out-of-plane in a controllable manner. A stable and vertical orientation of the out-coupler is achieved by locking the spot-size converter at a fixed 90° angle via short-range forces. The optical transmission is characterized as a function of temperature and polarization, resulting in a broad-band chip-to-fiber coupling extending over 150 nm wavelength bandwidth at cryogenic temperatures, with the lower bound for the coupling efficiency into the TE mode being 16± 2% in the interval 900-1050 nm. The methods reported here are fully compatible with quantum photonic integrated circuit technology with quantum dot emitters, and open opportunities to design novel photonic devices with enhanced functionality. © 2024 Optica Publishing Group.
    view abstractdoi: 10.1364/OE.510799
  • 2024 • 24 Convective drying of wood chips: Accelerating coupled DEM-CFD simulations with parametrized reduced single particle models
    Reineking, L. and Fischer, J. and Mjalled, A. and Illana, E. and Wirtz, S. and Scherer, V. and Mönnigmann, M.
    Particuology 84 158-167 (2024)
    doi: 10.1016/j.partic.2023.03.012
  • 2024 • 23 Reaction Mechanisms and Plasma-Catalyst Interaction in Plasma-Assisted Oxidation of n-Butane: A Data-Driven Approach
    Reiser, D. and von Keudell, A.
    Plasma Chemistry and Plasma Processing (2024)
    Experimental investigations of n-butane oxidation under atmospheric-pressure plasma conditions and in He-dilution have provided detailed information on the power-dependence of the conversion of C 4H 10 into CO and CO 2 at 450 K surface temperature. The rf-plasma discharge has been equipped with a MnO 2 -catalyst, and a significant impact on the reaction chain due to the presence of the catalyst surface could be observed. We report on ongoing data-based model development. Recently, a reaction kinetic model has been published, which agrees well with the experimental data (Stewig et al. in Plasma Sources Sci Technol 32:105006, 2023). However, that model could not clearly identify the main mechanisms in the interaction of plasma and catalyst. We show that various models can be found that explain the data similarly well. Detailed sensitivity analysis shows that only a maximum of three parameters can be identified in all the models considered for the currently limited data. Despite this limitation, we intend to continue the data analysis using more general models and introduce possible surface effects. Such unified models simultaneously describe the experimental data from both measurements with and without catalyst using a single set of physical parameters. To evaluate the hypotheses, we present numerical results for certain ranges of experimental parameters, which, in a subsequent experimental verification, allows to exclude or confirm one or another model. © 2024, The Author(s).
    view abstractdoi: 10.1007/s11090-023-10443-7
  • 2024 • 22 Stability of binary colloidal mixtures of {Au} noble metal and {ZnS} semiconductor nanoparticles
    Rezvani, A. and Li, Y. and Neumann, S. and Anwar, O. and Rafaja, D. and Reichenberger, S. and Segets, D.
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 682 (2024)
    doi: 10.1016/j.colsurfa.2023.132832
  • 2024 • 21 Non-collinear magnetic atomic cluster expansion for iron
    Rinaldi, Matteo and Mrovec, Matous and Bochkarev, Anton and Lysogorskiy, Yury and Drautz, Ralf
    npj Computational Materials 10 (2024)
    The Atomic Cluster Expansion (ACE) provides a formally complete basis for the local atomic environment. ACE is not limited to representing energies as a function of atomic positions and chemical species, but can be generalized to vectorial or tensorial properties and to incorporate further degrees of freedom (DOF). This is crucial for magnetic materials with potential energy surfaces that depend on atomic positions and atomic magnetic moments simultaneously. In this work, we employ the ACE formalism to develop a non-collinear magnetic ACE parametrization for the prototypical magnetic element Fe. The model is trained on a broad range of collinear and non-collinear magnetic structures calculated using spin density functional theory. We demonstrate that the non-collinear magnetic ACE is able to reproduce not only ground state properties of various magnetic phases of Fe but also the magnetic and lattice excitations that are essential for a correct description of finite temperature behavior and properties of crystal defects. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41524-024-01196-8
  • 2024 • 20 Tunable {Syngas} {Formation} at {Industrially} {Relevant} {Current} {Densities} via {CO2} {Electroreduction} and {Hydrogen} {Evolution} over {Ni} and {Fe}-derived {Catalysts} obtained via {One}-{Step} {Pyrolysis} of {Polybenzoxazine} {Based} {Composites}
    Sanjuán, I. and Kumbhar, V. and Chanda, V. and Machado, R.R.L. and Jaato, B.N. and Braun, M. and Mahbub, M.A.A. and Bendt, G. and Hagemann, U. and Heidelmann, M. and Schuhmann, W. and Andronescu, C.
    Small (2024)
    doi: 10.1002/smll.202305958
  • 2024 • 19 Tunable Syngas Formation at Industrially Relevant Current Densities via CO2 Electroreduction and Hydrogen Evolution over Ni and Fe-derived Catalysts obtained via One-Step Pyrolysis of Polybenzoxazine Based Composites
    Sanjuán, Ignacio and Kumbhar, Vaibhav and Chanda, Vimanshu and Machado, Raíssa R. L. and Jaato, Bright N. and Braun, Michael and Mahbub, Muhammad A. A. and Bendt, Georg and Hagemann, Ulrich and Heidelmann, Markus and Schuhmann, ...
    Small (2024)
    Simultaneous electroreduction of CO2 and H2O to syngas can provide a sustainable feed for established processes used to synthesize carbon-based chemicals. The synthesis of MOx/M-N-Cs (M = Ni, Fe) electrocatalysts reported via one-step pyrolysis that shows increased performance during syngas electrosynthesis at high current densities with adaptable H2/CO ratios, e.g., for the Fischer–Tropsch process. When embedded in gas diffusion electrodes (GDEs) with optimized hydrophobicity, the NiOx/Ni-N-C catalyst produces syngas (H2/CO = 0.67) at −200 mA cm−2 while for the FeOx/Fe-N-C syngas production occurs at ≈−150 mA cm−2. By tuning the electrocatalyst's microenvironment, stable operation for >3 h at −200 mA cm−2 is achieved with the NiOx/Ni-N-C GDE. Post-electrolysis characterization revealed that the restructuring of the catalyst via reduction of NiOx to metallic Ni NPs still enables stable operation of the electrode at −200 mA cm−2, when embedded in an optimized microenvironment. The ionomer and additives used in the catalyst layer are important for the observed stable operation. Operando Raman measurements confirm the presence of NiOx during CO formation and indicate weak adsorption of CO on the catalyst surface. © 2024 The Authors. Small published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/smll.202305958
  • 2024 • 18 Investigating the Influence of Treatments on Carbon Felts for Vanadium Redox Flow Batteries
    Schilling, Monja and Eifert, László and Köble, Kerstin and Jaugstetter, Maximilian and Bevilacqua, Nico and Fahy, Kieran F. and Tschulik, Kristina and Bazylak, Aimy and Zeis, Roswitha
    ChemSusChem 17 (2024)
    Vanadium redox flow battery (VRFB) electrodes face challenges related to their long-term operation. We investigated different electrode treatments mimicking the aging processes during operation, including thermal activation, aging, soaking, and storing. Several characterization techniques were used to deepen the understanding of the treatment of carbon felts. Synchrotron X-ray imaging, electrochemical impedance spectroscopy (EIS) with the distribution of relaxation times analysis, and dynamic vapor sorption (DVS) revealed differences between the wettability of felts. The bulk saturation after electrolyte injection into the carbon felts significantly differed from 8 % to 96 %. DVS revealed differences in the sorption/desorption behavior of carbon felt ranging from a slight change of 0.8 wt % to over 100 wt %. Additionally, the interactions between the water vapor and the sample change from type V to type H2. After treatment, morphology changes were observed by atomic force microscopy and scanning electron microscopy. Cyclic voltammetry and EIS were used to probe the electrochemical performance, revealing different catalytic activities and transport-related impedances for the treated samples. These investigations are crucial for understanding the effects of treatments on the performance and optimizing materials for long-term operation. © 2023 The Authors. ChemSusChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/cssc.202301063
  • 2024 • 17 Effect of stacking fault energy on the thickness and density of annealing twins in recrystallized FCC medium and high-entropy alloys
    Schneider, Mike and Couzinié, Jean-Philippe and Shalabi, Amin and Ibrahimkhel, Farhad and Ferrari, Alberto and Körmann, Fritz and Laplanche, Guillaume
    Scripta Materialia 240 (2024)
    This work aims to predict the microstructure of recrystallized medium and high-entropy alloys (MEAs and HEAs) with a face-centered cubic structure, in particular the density of annealing twins and their thickness. Eight MEAs and five HEAs from the Cr-Mn-Fe-Co-Ni system are considered, which have been cast, homogenized, cold-worked and recrystallized to obtain different grain sizes. This work thus provides a database that could be used for data mining to take twin boundary engineering for alloy development to the next level. Since the stacking fault energy is known to strongly affect recrystallized microstructures, the latter was determined at 293 K using the weak beam dark-field technique and compared with ab initio simulations, which additionally allowed to calculate its temperature dependence. Finally, we show that all these data can be rationalized based on theories and empirical relationships that were proposed for pure metals and binary Cu-based alloys. © 2023
    view abstractdoi: 10.1016/j.scriptamat.2023.115844
  • 2024 • 16 A Radar Echo Simulator for the Synthesis of Randomized Training Data Sets in the Context of AI-Based Applications
    Schorlemer, Jonas and Altholz, Jochen and Barowski, Jan and Baer, Christoph and Rolfes, Ilona and Schulz, Christian
    Sensors 24 (2024)
    Supervised machine learning algorithms usually require huge labeled data sets to produce sufficiently good results. For many applications, these data sets are still not available today, and the reasons for this can be manifold. As a solution, the missing training data can be generated by fast simulators. This procedure is well studied and allows filling possible gaps in the training data, which can further improve the results of a machine learning model. For this reason, this article deals with the development of a two-dimensional electromagnetic field simulator for modeling the response of a radar sensor in an imaging system based on the synthetic aperture radar principle. The creation of completely random scenes is essential to achieve data sets with large variance. Therefore, special emphasis is placed on the development of methods that allow creating random objects, which can then be assembled into an entire scene. In the context of this contribution, we focus on humanitarian demining with regard to improvised explosive devices using a ground-penetrating radar system. This is an area where the use of trained classifiers is of great importance, but in practice, there are little to no labeled datasets for the training process. The simulation results show good agreement with the measurement results obtained in a previous contribution, demonstrating the possibility of enhancing sparse training data sets with synthetic data. © 2024 by the authors.
    view abstractdoi: 10.3390/s24030836
  • 2024 • 15 Mode Transition Induced by Gas Heating Along the Discharge Channel in Capacitively Coupled Atmospheric Pressure Micro Plasma Jets
    Schulenberg, David A. and Vass, Máté and Klich, Maximilian and Donkó, Zoltán and Klotz, Jeldrik and Bibinov, Nikita and Mussenbrock, Thomas and Schulze, Julian
    Plasma Chemistry and Plasma Processing (2024)
    The effects of neutral gas heating along the direction of the gas flow inside the discharge channel of a parallel plate micro atmospheric pressure plasma jet, the COST-jet, on the spatio-temporal dynamics of energetic electrons are investigated by experiments and simulations. The plasma source is driven by a single frequency sinusoidal voltage waveform at 13.56 MHz in helium with an admixture (0.05–0.2%) of nitrogen. Optical emission spectroscopy measurements are applied to determine the spatio-temporally resolved electron impact excitation dynamics from the ground state into the He I (3s) 3 S 1 state and the rotational temperature of nitrogen molecules at different positions along the direction of the gas flow inside the 30 mm long discharge channel. The gas temperature, which is assumed to be equal to the N 2 rotational temperature, is found to increase along the discharge channel. This effect is attenuated as the nitrogen concentration is increased in the gas mixture, leading to an eventually constant temperature profile. The experimental data also reveal a plasma operating mode transition along the discharge channel from the Ω - to the Penning-mode and show good agreement with the results of 1d3v kinetic simulations, which spatially resolve the inter-electrode space and use the gas temperature as an input value. The simulations demonstrate that the increase of the gas temperature leads to the observed mode transition. The results suggest the possibility of using the nitrogen admixture and the feed gas temperature as additional control parameters, (i) to tailor the plasma operating mode along the direction of the gas flow so that the production of specific radicals is optimized; and (ii) to control the final gas temperature of the effluent. The latter could be particularly interesting for biological applications, where the upper gas temperature limit is dictated by the rather low thermal damage threshold of the treated material. © 2024, The Author(s).
    view abstractdoi: 10.1007/s11090-023-10444-6
  • 2024 • 14 Validation of in situ diagnostics for the detection of OH and H2O2 in liquids treated by a humid atmospheric pressure plasma jet
    Schüttler, Steffen and Jolmes, Ludwig and Jeß, Emanuel and Tschulik, Kristina and Golda, Judith
    Plasma Processes and Polymers 21 (2024)
    A humid atmospheric pressure plasma jet was used to treat an aqueous liquid. The transport of hydrogen peroxide and hydroxyl from the plasma to the liquid was analyzed. Two in situ liquid diagnostics for each species were compared and validated. In the case of H2O2, a spectrophotometric approach using ammonium metavanadate and electrochemical sensing based on Prussian blue carbon paste electrodes was applied. Both methods show very good agreement in trends and absolute values. The detection of OH was performed by terephthalic acid (TA) dosimetry and its distribution was visualized by the chemiluminescence of luminol. There, the measurement using TA resembles the luminol measurements and vice versa, and a very good agreement between both methods was found. © 2023 The Authors. Plasma Processes and Polymers published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/ppap.202300079
  • 2024 • 13 Extending the variational quantum eigensolver to finite temperatures
    Selisko, Johannes and Amsler, Maximilian and Hammerschmidt, Thomas and Drautz, Ralf and Eckl, Thomas
    Quantum Science and Technology 9 (2024)
    We present a variational quantum thermalizer (VQT), called quantum-VQT (qVQT), which extends the variational quantum eigensolver to finite temperatures. The qVQT makes use of an intermediate measurement between two variational circuits to encode a density matrix on a quantum device. A classical optimization provides the thermal state and, simultaneously, all associated excited states of a quantum mechanical system. We demonstrate the capabilities of the qVQT for two different spin systems. First, we analyze the performance of qVQT as a function of the circuit depth and the temperature for a one-dimensional Heisenberg chain. Second, we use the excited states to map the complete, temperature dependent phase diagram of a two-dimensional J1-J2 Heisenberg model. Numerical experiments on both quantum simulators and real quantum hardware demonstrate the efficiency of our approach, which can be readily applied to study various quantum many-body systems at finite temperatures on currently available noisy intermediate-scale quantum devices. © 2023 IOP Publishing Ltd
    view abstractdoi: 10.1088/2058-9565/ad1340
  • 2024 • 12 In Nanoconfined Environments, Larger Ions in the Electrolyte Influence the Local Proton Availability for the Oxygen Reduction Reaction
    Sims, Matthew and Wang, Minzhi and Wordsworth, Johanna and Alinezhad, Ali and Tilley, Richard D. and Schuhmann, Wolfgang and Ho, Junming and Benedetti, Tania M. and Gooding, J. Justin
    Journal of Physical Chemistry C 128 157 – 165 (2024)
    The impact of the electrolyte ion size on electrocatalytic reactions that occur within nanoconfined volumes is currently unknown. Herein, the effect of the size of solvated alkali metal ions on the oxygen reduction reaction (ORR) in acidic electrolytes was explored by using nanoparticles that contain isolated Pt nanochannels of 1-2 nm in diameter. The exterior surface of the nanoparticles was passivated to ensure that the ORR occurred only in the nanoconfined volume defined by the nanochannels. A number of alkali metal ions, with different hydrated sizes, were added into the acidic electrolyte, and different electrolyte ionic strengths were used to establish different levels of nanoconfinement. The results show that the ORR activity at comparatively positive applied potentials is not affected by the presence and nature of the alkali metal ions in the electrolyte. At less positive potentials, however, the activity is influenced by the presence of alkali metal ions in the electrolyte, and this is dependent on both the identity of the alkali metal ions and the electrolyte ionic strength. The differences in activities at less positive potentials are attributed to differences in the alkali metal ions’ accessibility to the nanoconfined space with Li+ being accessible and decreasing the electrocatalytic activity relative to inaccessible K+ ions that cannot enter the nanoconfined channels. This was corroborated by molecular dynamics modeling suggesting that the energy penalty for the alkali metal ions to enter the nanochannels is different for the different alkali metal ions and is affected by the surface charge of the nanochannel walls. © 2023 American Chemical Society
    view abstractdoi: 10.1021/acs.jpcc.3c07344
  • 2024 • 11 Impact of the Electrochemically Inert Furan Ring on the Oxidation of the Alcohol and Aldehyde Functional Group of 5-Hydroxymethylfurfural (HMF)
    Sobota, Lennart and Bondue, Christoph J. and Hosseini, Pouya and Kaiser, Christoph and Spallek, Marius and Tschulik, Kristina
    ChemElectroChem 11 (2024)
    The electrochemical oxidation of bio-based 5-hydroxymethylfurfural (HMF) results in 2,5-furandicarboxylic acid (FDCA), which is a renewable and environmentally friendly alternative to terephthalic acid. Using a gold electrode, we compare the electrochemical oxidation of the aldehyde and alcohol functionality in HMF to the isolated functionalities represented by ethanol and acetaldehyde. Thereby, we investigate the effect of the inert furan ring on the electrochemical reaction. The linear sweep voltammogram (LSV) of HMF in a weakly adsorbing electrolyte differs only marginally from the superposition of LSVs obtained in ethanol and acetaldehyde containing electrolytes. However, in the presence of strong adsorbates, only the kinetics of ethanol and acetaldehyde oxidation but not of HMF oxidation are hampered. We assign this to a stronger adsorption of HMF through the furan ring than through the alcohol and carbonyl functionality of ethanol and acetaldehyde. Hence, HMF is better equipped to compete for adsorption sites than aliphatic compounds. © 2023 The Authors. ChemElectroChem published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/celc.202300151
  • 2024 • 10 Sustainable Ironmaking Toward a Future Circular Steel Economy: Exploiting a Critical Oxygen Concentration for Metallurgical Cu Removal from Scrap-Based Melts
    Souza Filho, Isnaldi R. and da Silva, Alisson K. and Büyükuslu, Ömer K. and Raabe, Dierk and Springer, Hauke
    Steel Research International (2024)
    A circular steel economy based on recycling scrap is severely hampered by the increasing accumulation of Cu returning from more and more electrified products, which severely limits processing, application, and safety of steels. As of yet, no viable strategies for its removal have been developed, and the increasing Cu contamination can only be diluted with fresh primary iron. This is not only evoking CO2 emissions from conventional reduction processes, but also merely delays the problem until global demands allow for a circular steel economy. However, the ongoing transformation toward green steel making may offer pathways to overcome this complex metallurgical challenge. It is demonstrated that Cu can be effectively evaporated from Fe–Cu–O melts—representing Fe ore mixed with Cu-contaminated steel scrap—during hydrogen plasma-based smelting reduction. This evaporation is found to be strongly influenced by the Cu activity determined by the concentration of oxygen in the liquid, with a critical O concentration of about 22 wt%. Even without the presence of hydrogen, Cu concentrations can thereby be drastically reduced from 1 to less than 0.1 wt%. Potentials and challenges for leveraging these fundamental findings on a laboratory scale for future industrial production of green steel are outlined and discussed. © 2024 The Authors. Steel Research International published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/srin.202300785
  • 2024 • 9 Concept of introverted space: is multidimensional, extroverted space an illusion?
    Steinbach, Ingo
    Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences (2024)
    The quantum-phase-field concept of matter is revisited with special emphasis on the introverted view of space. Extroverted space surrounds physical objects, while introverted space lies in between physical objects. Space between objects leads to a network structure of matter: a network in which one-dimensional spaces connect individual particles. © 2023 the author(s), published by De Gruyter.
    view abstractdoi: 10.1515/zna-2023-0288
  • 2024 • 8 Parametrization protocol and refinement strategies for accurate and transferable analytic bond-order potentials: Application to Re
    Subramanyam, Aparna P. A. and Jenke, Jan and Ladines, Alvin N. and Drautz, Ralf and Hammerschmidt, Thomas
    Physical Review Materials 8 (2024)
    Interatomic potentials provide a means to simulate extended length and time scales that are outside the reach of ab initio calculations. The development of an interatomic potential for a particular material requires the optimization of the parameters of the functional form of the potential. We present a parametrization protocol for analytic bond-order potentials (BOPs) that provides a physically transparent and computationally efficient description of the interatomic interaction. The parametrization protocol of the BOP follows the derivation of the BOP along the coarse-graining of the electronic structure from density-functional theory (DFT) to the tight-binding (TB) bond model to analytic BOPs. In particular, it starts from TB parameters that are obtained by downfolding DFT eigenstates of two-atomic molecules to an sd-valent minimal basis. This sd-valent Hamiltonian is combined with a pairwise repulsion to obtain an initial binding energy relation. The s electrons are then removed from the Hamiltonian and instead represented by an isotropic embedding term. In the final step, the parameters of the remaining d-d interaction, the pair repulsion, and the embedding term are optimized simultaneously. We demonstrate that the application of this parametrization protocol leads to a basic BOP for Re with good transferability. We discuss different strategies to refine the basic BOP towards global transferability or towards local accuracy. We demonstrate that homogeneous samplings of the structural phase space in a map of local atomic environments can be used to systematically increase the global transferability. We also demonstrate the influence of training data weighting on local accuracy refinements with a Pareto-front analysis, and we suggest further requirements to select a final BOP. The local accuracy and global transferability of the final BOP is also shown and compared to DFT. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.8.013803
  • 2024 • 7 Effect of Deformation on the Magnetic Properties of C + N Austenitic Steel
    Torres-Mejía, Laura Gabriela and Paredes-Gil, Katherine and Parra Vargas, Carlos Arturo and Lentz, Jonathan and Weber, Sebastian and Mujica-Roncery, Lais
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 55 150 – 160 (2024)
    In this investigation, the effect of deformation on magnetic properties at low temperatures of FeCr18.2Mn18.9–0.96C + N high interstitial steel was studied. Tensile tests were carried out at room temperature and interrupted at 10, 20, and 30 pct deformation. Magnetic measurements were performed through the vibrating sample magnetometry (VSM) technique from 50 K to 370 K. Microstructural, morphological, and crystalline structural analyses by means of XRD and SEM showed that the material consisted of a homogenous and stable austenitic structure with no presence of α-martensite or ε-martensite. Twinning and dislocation cells are suggested as main deformation mechanisms. The material exhibits a paramagnetic–antiferromagnetic (T Néel) transition below 235 K. The Néel temperature of the material tends to increase due to the deformation. A decrease of the magnetization and magnetic susceptibility for the deformed material was measured. Ab initio calculations were performed and showed that the FCC phase is more stable when carbon and nitrogen are added as interstitial elements compared with the free C + N system, additionally, the critical transition temperature was calculated, with a value in agreement with the experimental data. An influence of the magnetic contribution on the SFE was established, being in the order of 5 mJ/m2. © 2023, The Author(s).
    view abstractdoi: 10.1007/s11661-023-07237-z
  • 2024 • 6 Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis
    Vorhauer-Huget, Nicole and Seidenbecher, Jakob and Bhaskaran, Supriya and Schenkel, Francesca and Briest, Lucas and Gopalkrishna, Suresh and Barowski, Jan and Dernbecher, Andrea and Hilfert, Liane and Rolfes, Ilona and Dieguez-Alonso, Alba
    Particuology 86 291 – 303 (2024)
    Pyrolysis of thermally thick beech wood blocks with a size of around 2.5 × 8 × 6 cm3 (width × length × height) was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz, operated, both, at 300 W and 600 W under inert conditions, using N2 at around 400 mbar absolute pressure. The microwave cavity had a size of 20 × 20 × 20 cm3. The specific energy supply referred to the untreated wood block was 4–8 W/g, with slight variations depending on the initial water content. The mass loss and the reflected microwave power were in-situ monitored during the experiments. The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple, respectively. Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials. It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process, with increasing heating properties as the conversion process evolved. This was easily achieved using 600 W without susceptors. However, 300 W was not enough to achieve a high conversion degree, independently of the irradiation time. This, together with the physico-chemical analyses of the solids, hinted to the importance of the transport kinetics in thermally thick materials, although further investigation is still required. © 2023 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences
    view abstractdoi: 10.1016/j.partic.2023.07.004
  • 2024 • 5 Influence of the catalyst precursor for cobalt on activated carbon applied in ammonia decomposition
    Winter, Franziska Luise and Diehl, Patrick and Telaar, Pascal and Watermann, Clara Maria and Kaluza, Stefan and Muhler, Martin and Apfel, Ulf-Peter and Zeidler-Fandrich, Barbara
    Catalysis Today (2024)
    Ammonia is a key compound for storing and transporting green hydrogen. However, the efficient release of stored hydrogen through thermocatalytic ammonia decomposition is achievable only at temperatures around 600 °C, particularly with non-noble metal-based catalysts, which prove to be both ecologically and economically more feasible. In this study, electrically conductive activated carbon was selected as the catalyst support, chosen specifically for its suitability in achieving more energy-efficient direct reactor heating through the ohmic resistance of the catalysts. Cobalt salts were wet impregnated on activated carbon investigating the influence of different precursors (cobalt nitrate and cobalt acetate) and pyrolysis temperatures (400 °C and 600 °C) under N2 flow on the cobalt particle size and the incorporation of cobalt into the carbon matrix. TEM imaging and CO-chemisorption revealed well dispersed cobalt particles with sizes below 10 nm for the catalysts synthesized from the cobalt nitrate precursor. On the other hand, cobalt acetate led to about nine times larger Co agglomerates, which were partially detached from the carbon matrix. Moreover, this substantial difference in the Co particle size results in a significantly higher ammonia conversion for cobalt nitrate-based catalysts, achieving 94 % of ammonia conversion at 600 °C. Furthermore, the long-term stability test of the cobalt nitrate-based catalyst resulted in a slight deactivation of only 2 % ammonia conversion at 500 °C. © 2024 The Authors
    view abstractdoi: 10.1016/j.cattod.2023.114502
  • 2024 • 4 Quantum key distribution using deterministic single-photon sources over a field-installed fibre link
    Zahidy, Mujtaba and Mikkelsen, Mikkel T. and Müller, Ronny and Da Lio, Beatrice and Krehbiel, Martin and Wang, Ying and Bart, Nikolai and Wieck, Andreas D. and Ludwig, Arne and Galili, Michael and Forchhammer, Søren and Lodahl, ...
    npj Quantum Information 10 (2024)
    Quantum-dot-based single-photon sources are key assets for quantum information technology, supplying on-demand scalable quantum resources for computing and communication. However, long-lasting issues such as limited long-term stability and source brightness have traditionally impeded their adoption in real-world applications. Here, we realize a quantum key distribution field trial using true single photons across an 18-km-long dark fibre, located in the Copenhagen metropolitan area, using an optimized, state-of-the-art, quantum-dot single-photon source frequency-converted to the telecom wavelength. A secret key generation rate of > 2 kbits/s realized over a 9.6 dB channel loss is achieved with a polarization-encoded BB84 scheme, showing remarkable stability for more than 24 hours of continuous operation. Our results highlight the maturity of deterministic single-photon source technology while paving the way for advanced single-photon-based communication protocols, including fully device-independent quantum key distribution, towards the goal of a quantum internet. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41534-023-00800-x
  • 2024 • 3 Combinatorial Screening of Electronic and Geometric Effects in Compositionally Complex Solid Solutions Toward a Rational Design of Electrocatalysts
    Zerdoumi, Ridha and Savan, Alan and Amalraj, Marshal and Tetteh, Emmanuel Batsa and Lourens, Florian and Krysiak, Olga A. and Junqueira, João R. C. and Ludwig, Al and Schuhmann, Wolfgang
    Advanced Energy Materials 14 (2024)
    Alloying dissimilar elements presents an effective strategy for enhancing the electrocatalytic properties of multi-metal materials. This enhancement can be attributed to the modification of electronic and geometric effects, which play a crucial role in determining the overall electrocatalytic performance. However, these effects are intricately intertwined and often interrelated due to their coexistence. As a result, the improved catalytic performance of multi-metal systems is frequently attributed to synergistic or “cocktail” effects, without clear explanations of the role of alloying and the individual contribution of each element. A high-throughput experimentation approach is employed to investigate 342 compositions within the quaternary thin film system Pd─Ag─Cu─Fe. The substitution of Cu with Fe (different number of valence electrons) or Ag (different atomic sizes) allows for selective manipulation of electronic or geometric effects, respectively. The substitution of Ag with Fe allows for the simultaneous variation of both effects. The number of valence electrons per unit cell volume is used as a descriptor for electrocatalytic activity, specifically with respect to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which can be optimized through independent or simultaneous alteration of electronic and geometric effects. © 2023 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/aenm.202302177
  • 2024 • 2 How solute atoms control aqueous corrosion of Al-alloys
    Zhao, Huan and Yin, Yue and Wu, Yuxiang and Zhang, Siyuan and Mingers, Andrea M. and Ponge, Dirk and Gault, Baptiste and Rohwerder, Michael and Raabe, Dierk
    Nature Communications 15 (2024)
    Aluminum alloys play an important role in circular metallurgy due to their good recyclability and 95% energy gain when made from scrap. Their low density and high strength translate linearly to lower greenhouse gas emissions in transportation, and their excellent corrosion resistance enhances product longevity. The durability of Al alloys stems from the dense barrier oxide film strongly bonded to the surface, preventing further degradation. However, despite decades of research, the individual elemental reactions and their influence on the nanoscale characteristics of the oxide film during corrosion in multicomponent Al alloys remain unresolved questions. Here, we build up a direct correlation between the near-atomistic picture of the corrosion oxide film and the solute reactivity in the aqueous corrosion of a high-strength Al-Zn-Mg-Cu alloy. We reveal the formation of nanocrystalline Al oxide and highlight the solute partitioning between the oxide and the matrix and segregation to the internal interface. The sharp decrease in partitioning content of Mg in the peak-aged alloy emphasizes the impact of heat treatment on the oxide stability and corrosion kinetics. Through H isotopic labelling with deuterium, we provide direct evidence that the oxide acts as a trap for this element, pointing at the essential role of the Al oxide might act as a kinetic barrier in preventing H embrittlement. Our findings advance the mechanistic understanding of further improving the stability of Al oxide, guiding the design of corrosion-resistant alloys for potential applications. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41467-024-44802-5
  • 2024 • 1 The interplay between electron tunneling and Auger emission in a single quantum emitter weakly coupled to an electron reservoir
    Zöllner, M. and Mannel, H. and Rimek, F. and Maib, B. and Schwarz, N. and Wieck, A.D. and Ludwig, A. and Lorke, A. and Geller, M.
    Applied Physics Letters 124 (2024)
    In quantum dots (QDs), the Auger recombination is a non-radiative scattering process in which the optical transition energy of a charged exciton (trion) is transferred to an additional electron leaving the dot. Electron tunneling from a reservoir is the competing process that replenishes the QD with an electron again. Here, we study the dependence of the tunneling and Auger recombination rate on the applied electric field using high-resolution time-resolved resonance fluorescence (RF) measurements. With the given p-i-n diode structure and a tunnel barrier between the electron reservoir and the QD of 45 nm, we measured a tunneling rate into the QD in the order of ms−1. This rate shows a strong decrease by almost an order of magnitude for decreasing electric field, while the Auger emission rate decreases by a factor of five in the same voltage range. Furthermore, we study in detail the influence of the Auger recombination and the tunneling rate from the charge reservoir into the QD on the intensity and linewidth of the trion transition. In addition to the well-known quenching of the trion transition, we observe in our time-resolved RF measurements a strong influence of the tunneling rate on the observed linewidth. The steady-state RF measurement yields a broadened trion transition of about 1.5 GHz for an Auger emission rate of the same order as the electron tunneling rate. In a non-equilibrium measurement, the Auger recombination can be suppressed, and a more than four times smaller linewidth of 340 MHz (1.4 μeV) is measured. © 2024 Author(s).
    view abstractdoi: 10.1063/5.0183821