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End date: 2023 × Start date: 2023 × DDC: 600 × Has files: Yes × WGL Institute: IFWD ×

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    In Situ Fabrication of Freestanding Single-Atom-Thick 2D Metal/Metallene and 2D Metal/ Metallene Oxide Membranes: Recent Developments
    (Weinheim : Wiley-VCH, 2021) Ta, Huy Q.; Mendes, Rafael G.; Liu, Yu; Yang, Xiaoqin; Luo, Jingping; Bachmatiuk, Alicja; Gemming, Thomas; Zeng, Mengqi; Fu, Lei; Liu, Lijun; Rümmeli, Mark H.
    In recent years, two-dimensional (2D) materials have attracted a lot of research interest as they exhibit several fascinating properties. However, outside of 2D materials derived from van der Waals layered bulk materials only a few other such materials are realized, and it remains difficult to confirm their 2D freestanding structure. Despite that, many metals are predicted to exist as 2D systems. In this review, the authors summarize the recent progress made in the synthesis and characterization of these 2D metals, so called metallenes, and their oxide forms, metallene oxides as free standing 2D structures formed in situ through the use of transmission electron microscopy (TEM) and scanning TEM (STEM) to synthesize these materials. Two primary approaches for forming freestanding monoatomic metallic membranes are identified. In the first, graphene pores as a means to suspend the metallene or metallene oxide and in the second, electron-beam sputtering for the selective etching of metal alloys or thick complex initial materials is employed to obtain freestanding single-atom-thick 2D metal. The data show a growing number of 2D metals/metallenes and 2D metal/ metallene oxides having been confirmed and point to a bright future for further discoveries of these 2D materials.
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    Charge‐Compensated N‐Doped π ‐Conjugated Polymers: Toward both Thermodynamic Stability of N‐Doped States in Water and High Electron Conductivity
    (Weinheim : Wiley-VCH, 2022) Borrmann, Fabian; Tsuda, Takuya; Guskova, Olga; Kiriy, Nataliya; Hoffmann, Cedric; Neusser, David; Ludwigs, Sabine; Lappan, Uwe; Simon, Frank; Geisler, Martin; Debnath, Bipasha; Krupskaya, Yulia; Al‐Hussein, Mahmoud; Kiriy, Anton
    The understanding and applications of electron-conducting π-conjugated polymers with naphtalene diimide (NDI) blocks show remarkable progress in recent years. Such polymers demonstrate a facilitated n-doping due to the strong electron deficiency of the main polymer chain and the presence of the positively charged side groups stabilizing a negative charge of the n-doped backbone. Here, the n-type conducting NDI polymer with enhanced stability of its n-doped states for prospective “in-water” applications is developed. A combined experimental–theoretical approach is used to identify critical features and parameters that control the doping and electron transport process. The facilitated polymer reduction ability and the thermodynamic stability in water are confirmed by electrochemical measurements and doping studies. This material also demonstrates a high conductivity of 10−2 S cm−1 under ambient conditions and 10−1 S cm−1 in vacuum. The modeling explains the stabilizing effects for various dopants. The simulations show a significant doping-induced “collapse” of the positively charged side chains on the core bearing a partial negative charge. This explains a decrease in the lamellar spacing observed in experiments. This study fundamentally enables a novel pathway for achieving both thermodynamic stability of the n-doped states in water and the high electron conductivity of polymers.
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    Intermixing-Driven Surface and Bulk Ferromagnetism in the Quantum Anomalous Hall Candidate MnBi6Te10
    (Weinheim : Wiley-VCH, 2023) Tcakaev, Abdul‐Vakhab; Rubrecht, Bastian; Facio, Jorge I.; Zabolotnyy, Volodymyr B.; Corredor, Laura T.; Folkers, Laura C.; Kochetkova, Ekaterina; Peixoto, Thiago R. F.; Kagerer, Philipp; Heinze, Simon; Bentmann, Hendrik; Green, Robert J.; Gargiani, Pierluigi; Valvidares, Manuel; Weschke, Eugen; Haverkort, Maurits W.; Reinert, Friedrich; van den Brink, Jeroen; Büchner, Bernd; Wolter, Anja U. B.; Isaeva, Anna; Hinkov, Vladimir
    The recent realizations of the quantum anomalous Hall effect (QAHE) in MnBi2Te4 and MnBi4Te7 benchmark the (MnBi2Te4)(Bi2Te3)n family as a promising hotbed for further QAHE improvements. The family owes its potential to its ferromagnetically (FM) ordered MnBi2Te4 septuple layers (SLs). However, the QAHE realization is complicated in MnBi2Te4 and MnBi4Te7 due to the substantial antiferromagnetic (AFM) coupling between the SLs. An FM state, advantageous for the QAHE, can be stabilized by interlacing the SLs with an increasing number n of Bi2Te3 quintuple layers (QLs). However, the mechanisms driving the FM state and the number of necessary QLs are not understood, and the surface magnetism remains obscure. Here, robust FM properties in MnBi6Te10 (n = 2) with Tc ≈ 12 K are demonstrated and their origin is established in the Mn/Bi intermixing phenomenon by a combined experimental and theoretical study. The measurements reveal a magnetically intact surface with a large magnetic moment, and with FM properties similar to the bulk. This investigation thus consolidates the MnBi6Te10 system as perspective for the QAHE at elevated temperatures.
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    The Role of Al2O3 ALD Coating on Sn-Based Intermetallic Anodes for Rate Capability and Long-Term Cycling in Lithium-Ion Batteries
    (Weinheim : Wiley-VCH, 2022) Soltani, Niloofar; Abbas, Syed Muhammad; Hantusch, Martin; Lehmann, Sebastian; Nielsch, Kornelius; Bahrami, Amin; Mikhailova, Daria
    The electrochemical performances of CoSn2 and Ni3Sn4 as potential anode materials in lithium-ion batteries (LIBs) are investigated using varying thicknesses of an alumina layer deposited by the atomic layer deposition (ALD) technique. Rate capability results showed that at high current densities, Al2O3-coated CoSn2 and Ni3Sn4 electrodes after 10-ALD cycles outperformed uncoated materials. The charge capacities of coated CoSn2 and Ni3Sn4 electrodes are 571 and 134 mAh g−1, respectively, at a high current density of 5 A g−1, while the capacities of uncoated electrodes are 363 and 11 mAh g−1. When the current density is reduced to 1 A g−1, however, the cycling performances of Al2O3-coated CoSn2 and Ni3Sn4 electrodes fade faster after almost 40 cycles than uncoated electrodes. The explanation is found in the composition of the solid-electrolyte interface (SEI), which strongly depends on the current rate. Thus, X-ray photoelectron spectroscopy analysis of SEI layers on coated samples cycles at a low current density of 0.1 Ag−1, revealed organic carbonates as major products, which probably have a low ionic conductivity. In contrast, the SEI of coated materials cycled at 5 Ag−1 consists mostly of mixed inorganic/organic fluorine-rich Al-F and C-F species facilitating a higher ionic transport, which improves electrochemical performance.
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    Transparent Power-Generating Windows Based on Solar-Thermal-Electric Conversion
    (Weinheim : Wiley-VCH, 2021) Zhang, Qihao; Huang, Aibin; Ai, Xin; Liao, Jincheng; Song, Qingfeng; Reith, Heiko; Cao, Xun; Fang, Yueping; Schierning, Gabi; Nielsch, Kornelius; Bai, Shengqiang; Chen, Lidong
    Integrating transparent solar-harvesting systems into windows can provide renewable on-site energy supply without altering building aesthetics or imposing further design constraints. Transparent photovoltaics have shown great potential, but the increased transparency comes at the expense of reduced power-conversion efficiency. Here, a new technology that overcomes this limitation by combining solar-thermal-electric conversion with a material's wavelength-selective absorption is presented. A wavelength-selective film consisting of Cs0.33WO3 and resin facilitates high visible-light transmittance (up to 88%) and outstanding ultraviolet and infrared absorbance, thereby converting absorbed light into heat without sacrificing transparency. A prototype that couples the film with thermoelectric power generation produces an extraordinary output voltage of ≈4 V within an area of 0.01 m2 exposed to sunshine. Further optimization design and experimental verification demonstrate high conversion efficiency comparable to state-of-the-art transparent photovoltaics, enriching the library of on-site energy-saving and transparent power generation.
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    Current State-of-the-Art in the Interface/Surface Modification of Thermoelectric Materials
    (Weinheim : Wiley-VCH, 2021) He, Shiyang; Lehmann, Sebastian; Bahrami, Amin; Nielsch, Kornelius
    Thermoelectric (TE) materials are prominent candidates for energy converting applications due to their excellent performance and reliability. Extensive efforts for improving their efficiency in single-/multi-phase composites comprising nano/micro-scale second phases are being made. The artificial decoration of second phases into the thermoelectric matrix in multi-phase composites, which is distinguished from the second-phase precipitation occurring during the thermally equilibrated synthesis of TE materials, can effectively enhance their performance. Theoretically, the interfacial manipulation of phase boundaries can be extended to a wide range of materials. High interface densities decrease thermal conductivity when nano/micro-scale grain boundaries are obtained and certain electronic structure modifications may increase the power factor of TE materials. Based on the distribution of second phases on the interface boundaries, the strategies can be divided into discontinuous and continuous interfacial modifications. The discontinuous interfacial modifications section in this review discusses five parts chosen according to their dispersion forms, including metals, oxides, semiconductors, carbonic compounds, and MXenes. Alternatively, gas- and solution-phase process techniques are adopted for realizing continuous surface changes, like the core–shell structure. This review offers a detailed analysis of the current state-of-the-art in the field, while identifying possibilities and obstacles for improving the performance of TE materials.
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    Machine learning for additive manufacturing: Predicting materials characteristics and their uncertainty
    (Amsterdam [u.a.] : Elsevier Science, 2023) Chernyavsky, Dmitry; Kononenko, Denys Y.; Han, Jun Hee; Kim, Hwi Jun; van den Brink, Jeroen; Kosiba, Konrad
    Additive manufacturing (AM) is known for versatile fabrication of complex parts, while also allowing the synthesis of materials with desired microstructures and resulting properties. These benefits come at a cost: process control to manufacture parts within given specifications is very challenging due to the relevance of a large number of processing parameters. Efficient predictive machine learning (ML) models trained on small datasets, can minimize this cost. They also allow to assess the quality of the dataset inclusive of uncertainty. This is important in order for additively manufactured parts to meet property specifications not only on average, but also within a given variance or uncertainty. Here, we demonstrate this strategy by developing a heteroscedastic Gaussian process (HGP) model, from a dataset based on laser powder bed fusion of a glass-forming alloy at varying processing parameters. Using amorphicity as the microstructural descriptor, we train the model on our Zr52.5Cu17.9Ni14.6Al10Ti5 (at.%) alloy dataset. The HGP model not only accurately predicts the mean value of amorphicity, but also provides the respective uncertainty. The quantification of the aleatoric and epistemic uncertainty contributions allows to assess intrinsic inaccuracies of the dataset, as well as identify underlying physical phenomena. This HGP model approach enables to systematically improve ML-driven AM processes.
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    Laser powder bed fusion of a superelastic Cu-Al-Mn shape memory alloy
    (Amsterdam [u.a.] : Elsevier Science, 2021) Babacan, N.; Pauly, S.; Gustmann, T.
    Dense and crack-free specimens of the shape memory alloy Cu71.6Al17Mn11.4 (at.%) were produced via laser powder bed fusion across a wide range of process parameters. The microstructure, viz. grain size, can be directly tailored within the process and with it the transformation temperatures (TTs) shifted to higher values by raising the energy input. The microstructure, and the superelastic behavior of additively manufactured samples were assessed by a detailed comparison with induction melted material. The precipitation of the α phase, which inhibit the martensitic transformation, were not observed in the additively manufactured samples owing to the high intrinsic cooling rates during the fabrication process. Fine columnar grains with a strong [001]-texture along the building direction lead to an enhanced yield strength compared to the coarse-grained cast samples. A maximum recoverable strain of 2.86% was observed after 5% compressive loading. The first results of our approach imply that laser powder bed fusion is a promising technique to directly produce individually designed Cu-Al-Mn shape memory parts with a pronounced superelasticity at room temperature.
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    Mo3Ni2N Nanoparticle Generation by Spark Discharge
    (Basel : MDPI, 2023) Elmroth Nordlander, Jonas; Bermeo, Marie; Ternero, Pau; Wahlqvist, David; Schmeida, Toni; Blomberg, Sara; Messing, Maria E.; Ek, Martin; Hübner, Julia-Maria
    Spark ablation is an advantageous method for the generation of metallic nanoparticles with defined particle sizes and compositions. The reaction of the metal particles with the carrier gas during the synthesis and, therefore, the incorporation of those light elements into structural voids or even compound formation was confirmed for hydrides and oxides but has only been suspected to occur for nitrides. In this study, dispersed nanoparticles of Mo3Ni2N and Mo with Janus morphology, and defined particle sizes were obtained by spark discharge generation as a result of carrier gas ionization and characterized using transmission electron microscopy and powder X-ray diffraction. Metal nitrides possess beneficial catalytic and thermoelectric properties, as well as high hardness and wear resistance. Therefore, this method offers the possibility of controlled synthesis of materials which are interesting for numerous applications.
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    Erratum: Exploring the 3D structure and defects of a self-assembled gold mesocrystal by coherent X-ray diffraction imaging (Nanoscale (2021) DOI: 10.1039/D1NR01806J)
    (Cambridge : RSC Publ., 2021) Carnis, Jerome; Kirner, Felizitas; Lapkin, Dmitry; Sturm, Sebastian; Kim, Young Yong; Baburin, Igor A.; Khubbutdinov, Ruslan; Ignatenko, Alexandr; Iashina, Ekaterina; Mistonov, Alexander; Steegemans, Tristan; Wieck, Thomas; Gemming, Thomas; Lubk, Axel; Lazarev, Sergey; Sprung, Michael; Vartanyants, Ivan A.; Sturm, Elena V.
    Correction for ‘Exploring the 3D structure and defects of a self-assembled gold mesocrystal by coherent X-ray diffraction imaging’ by Jerome Carnis et al., Nanoscale, 2021, DOI: 10.1039/D1NR01806J.