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End date: 2021 × Start date: 2019 × DDC: 600 × WGL Institute: IFWD ×

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Now showing 1 - 10 of 15
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    Highly Symmetric and Extremely Compact Multiple Winding Microtubes by a Dry Rolling Mechanism
    (Weinheim : Wiley-VCH, 2020) Moradi, Somayeh; Naz, Ehsan Saei Ghareh; Li, Guodong; Bandari, Nooshin; Bandari, Vineeth Kumar; Zhu, Feng; Wendrock, Horst; Schmidt, Oliver G.
    Rolled-up nanotechnology has received significant attention to self-assemble planar nanomembranes into 3D micro and nanotubular architectures. These tubular structures have been well recognized as novel building blocks in a variety of applications ranging from microelectronics and nanophotonics to microbatteries and microrobotics. However, fabrication of multiwinding microtubes with precise control over the winding interfaces, which is crucial for many complex applications, is not easy to achieve by existing materials and technologies. Here, a dry rolling approach is introduced to tackle this challenge and create tight windings in compact and highly symmetric cylindrical microstructures. This technique exploits hydrophobicity of fluorocarbon polymers and the thermal expansion mismatch of polymers and inorganic films upon thermal treatment. Quality parameters for rolled-up microtubes, against which different fabrication technologies can be benchmarked are defined. The technique offers to fabricate long freestanding multiwinding microtubes as well as hierarchical architectures incorporating rolled-up wrinkled nanomembranes. This work presents an important step forward toward the fabrication of more complex but well-controlled microtubes for advanced high-quality device architectures. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Advances and Trends in Chemically Doped Graphene
    (Weinheim : Wiley-VCH, 2020) Ullah, Sami; Shi, Qitao; Zhou, Junhua; Yang, Xiaoqin; Ta, Huy Q.; Hasan, Maria; Ahmad, Nasir Mahmood; Fu, Lei; Bachmatiuk, Alicja; Rümmeli, Mark H.
    Chemically doped graphene materials are fascinating because these have different desirable attributes with possible synergy. The inert and gapless nature of graphene can be changed by adding a small number of heteroatoms to substitute carbon in the lattice. The doped material may display superior catalytic activities; durable, fast, and selective sensing; improved magnetic moments; photoresponses; and activity in chemical reactions. In the current review, recent advances are covered in chemically doped graphene. First, the different types of heteroatoms, their bonding configurations, and briefly their properties are discussed. This is followed by the description of various synthesis and analytical methods essential for assessing the characteristics of heterographene with specific focus on the selected graphene materials of different dopants (particularly, single dopants, including N, B, S, P, first three halogens, Ge, and Ga, and codopants, such as N/O), and more importantly, up-to-date applications enabled by the intentional doping. Finally, outlook and perspectives section review the existing challenges, future opportunities, and possible ways to improve the graphitic materials. The goal is to update and inspire the readers to establish novel doped graphene with valuable properties and for current and futuristic applications. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB2 Wires
    (Basel : MDPI, 2021) Gajda, Daniel; Zaleski, Andrzej J.; Morawski, Andrzej J.; Małecka, Malgorzata; Nenkov, Konstantin; Rindfleisch, Matt; Hossain, Md Shahriar A.; Czujko, Tomasz
    Annealing undoped MgB2 wires under high isostatic pressure (HIP) increases transport critical current density (Jtc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases Jtc by 25% in range magnetic fields from 2 T to 4 T and does not increase Jtc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the Jtc by 40% at 4.2 K in magnetic fields above 6 T and reduces Jtc by one order at 20 K in MgB2 wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB2 material and the number of connections between grains compared to MgB2 wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB2 material and more connections between grains during the liquid-state Mg reaction.
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    Wear Behavior of a Heat-Treatable Al-3.5Cu-1.5Mg-1Si Alloy Manufactured by Selective Laser Melting
    (Basel : MDPI, 2021) Wang, Pei; Lei, Yang; Qi, Jun-Fang; Yu, Si-Jie; Setchi, Rossitza; Wu, Ming-Wei; Eckert, Jürgen; Li, Hai-Chao; Scudino, Sergio
    In this study, the wear behavior of a heat-treatable Al-7Si-0.5Mg-0.5Cu alloy fabricated by selective laser melting was investigated systematically. Compared with the commercial homogenized AA2024 alloy, the fine secondary phase of the SLM Al-Cu-Mg-Si alloy leads to a low specific wear rate (1.8 ± 0.11 × 10-4 mm3(Nm)-1) and a low average coefficient of friction (0.40 ± 0.01). After the T6 heat treatment, the SLM Al-Cu-Mg-Si alloy exhibits a lower specific wear rate (1.48 ± 0.02 × 10-4 mm3(Nm)-1), but a similar average coefficient of friction (0.34 ± 0.01) as the heat-treated AA2024 alloy. Altogether, the SLM Al-3.5Cu-1.5Mg-1Si alloy is suitable for the achievement of not only superior mechanical performance, but also improved tribological properties.
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    Advances in magneto-ionic materials and perspectives for their application
    (College Park, MD : American Institute of Physics, 2021) Nichterwitz, M.; Honnali Sudheendra, S.; Kutuzau, M.; Guo, S.; Zehner, J.; Nielsch, K.; Leistner, K.
    The possibility of tuning magnetic material properties by ionic means is exciting both for basic science and, especially in view of the excellentenergy efficiency and room temperature operation, for potential applications. In this perspective, we shortly introduce the functionality ofmagneto-ionic materials and focus on important recent advances in this field. We present a comparative overview of state-of-the-art magneto-ionic materials considering the achieved magnetoelectric voltage coefficients for magnetization and coercivity and the demonstrated timescales for magneto-ionic switching. Furthermore, the application perspectives of magneto-ionic materials in data storage and computing,magnetic actuation, and sensing are evaluated. Finally, we propose potential research directions to push this field forward and tackle thechallenges related to future applications
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    Efficient and affordable thermomagnetic materials for harvesting low grade waste heat
    (College Park, ML : American Institute of Physics, 2021) Dzekan, Daniel; Waske, Anja; Nielsch, Kornelius; Fähler, Sebastian
    Industrial processes release substantial quantities of waste heat, which can be harvested to generate electricity. At present, the conversion of low grade waste heat to electricity relies solely on thermoelectric materials, but such materials are expensive and have low thermodynamic efficiencies. Although thermomagnetic materials may offer a promising alternative, their performance remains to be evaluated, thereby hindering their real-world application. Here, the efficiency and cost effectiveness of thermomagnetic materials are evaluated for the usage in motors, oscillators, and generators for converting waste heat to electricity. The analysis reveals that up to temperature differences of several 10 K, the best thermomagnetic materials have the potential to compete with thermoelectric materials. Importantly, it is found that the price per watt of some thermomagnetic materials is much lower compared to that of present-day thermoelectrics, which can become competitive with conventional power plants. This materials library enables the selection of the best available thermomagnetic materials for harvesting waste heat and gives guidelines for their future development.
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    Magnetoelectric materials, phenomena, and devices
    (College Park, MD : American Institute of Physics, 2021) Herrera Diez, L.; Kruk, R.; Leistner, K.; Sort, J.
    [no abstract available]
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    Phonons and Thermal Transport in Si/SiO2 Multishell Nanotubes: Atomistic Study
    (Basel : MDPI, 2021) Isacova, Calina; Cocemasov, Alexandr; Nika, Denis L.; Fomin, Vladimir M.
    Thermal transport in the Si/SiO2 multishell nanotubes is investigated theoretically. The phonon energy spectra are obtained using the atomistic lattice dynamics approach. Thermal conductivity is calculated using the Boltzmann transport equation within the relaxation time approximation. Redistribution of the vibrational spectra in multishell nanotubes leads to a decrease of the phonon group velocity and the thermal conductivity as compared to homogeneous Si nanowires. Phonon scattering on the Si/SiO2 interfaces is another key factor of strong reduction of the thermal conductivity in these structures (down to 0.2 Wm−1K−1 at room temperature). We demonstrate that phonon thermal transport in Si/SiO2 nanotubes can be efficiently suppressed by a proper choice of nanotube geometrical parameters: lateral cross section, thickness and number of shells. We argue that such nanotubes have prospective applications in modern electronics, in cases when low heat conduction is required.
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    A Novel Large-Scale, Multilayer, and Facilely Aligned Micropatterning Technique Based on Flexible and Reusable SU-8 Shadow Masks
    (Weinheim : Wiley, 2019) Moradi, Somayeh; Bandari, Nooshin; Bandari, Vineeth Kumar; Zhu, Feng; Schmidt, Oliver G.
    A simple method to fabricate flexible, mechanically robust, and reusable SU-8 shadow masks is demonstrated. This shadow mask technology has high pattern flexibility as various shapes with different dimensions can be created. The fabricated shadow masks are characterized in terms of the resolution, reusability, and capability of multilayer surface micropatterning. Fabrication of a new plastic photomask for the exposure process simplifies the shadow mask fabrication process and results in higher resolution in the shadow mask structures compared to the commercial chromium photomasks. For the multilayer surface micropatterning technology, a simple and fast alignment technique based on SU-8 pillars and without usage of any microscopic tools is reported. This unique method leads to a less complicated alignment process with the alignment accuracy of ≈2 µm. The proposed shadow mask technology can be easily employed for wafer-scale micropatterning process. The capability of fabricated SU-8 shadow masks in micropatterning on polymer thin films is evaluated by fabricating metallic contacts on poly(3,4-ethylenedioxythiophene) samples and electrical characterization. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    In Situ Observations of Freestanding Single-Atom-Thick Gold Nanoribbons Suspended in Graphene
    (Weinheim : Wiley-VCH, 2020) Zhao, Liang; Ta, Huy Q.; Mendes, Rafael G.; Bachmatiuk, Alicja; Rummeli, Mark H.
    Bulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period ≈40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single-atom-thick two-dimensional (2D) metals exist. This work shows single-atom-thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single-atom-thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim