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 • 23 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 abstract doi: 10.1002/cctc.202301159 2024 • 22 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 • 21 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 abstract doi: 10.1002/cctc.202301023 2024 • 20 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 abstract doi: 10.1002/ppap.202300150 2024 • 19 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 abstract doi: 10.1111/ffe.14209 2024 • 18 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 abstract doi: 10.1002/gamm.202370002 2024 • 17 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 abstract doi: 10.1007/s00466-023-02354-3 2024 • 16 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 abstract doi: 10.1016/j.spl.2023.109999 2024 • 15 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 abstract doi: 10.1007/s10463-023-00880-8 2024 • 14 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 abstract doi: 10.1109/JSEN.2023.3332431 2024 • 13 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 abstract doi: 10.1016/j.powtec.2023.119022 2024 • 12 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 abstract doi: 10.1038/s43246-024-00447-x 2024 • 11 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 Authorsview abstract doi: 10.1016/j.actamat.2023.119602 2024 • 10 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 • 9 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 • 8 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 abstract doi: 10.1016/j.finel.2023.104070 2024 • 7 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 Ltdview abstract doi: 10.1016/j.fuel.2023.129983 2024 • 6 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 abstract doi: 10.1002/adma.202307085 2024 • 5 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 abstract doi: 10.1002/chem.202303830 2024 • 4 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. © 2024view abstract doi: 10.1016/j.actamat.2024.119752 2024 • 3 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 abstract doi: 10.1038/s41598-024-54615-7 2024 • 2 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 abstract doi: 10.1002/pssb.202300492 2024 • 1 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 abstract doi: 10.3150/23-BEJ1598