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- ItemAmorphous Silicon Thin-Film Solar Cells on Fabrics as Large-Scale Detectors for Textile Personal Protective Equipment in Active Laser Safety †(Basel : MDPI, 2023) Gawlik, Annett; Brückner, Uwe; Schmidl, Gabriele; Wagner, Volker; Paa, Wolfgang; Plentz, JonathanLaser safety is starting to play an increasingly important role, especially when the laser is used as a tool. Passive laser safety systems quickly reach their limits and, in some cases, provide inadequate protection. To counteract this, various active systems have been developed. Flexible and especially textile-protective materials pose a special challenge. The market still lacks personal protective equipment (PPE) for active laser safety. Covering these materials with solar cells as large-area optical detectors offers a promising possibility. In this work, an active laser protection fabric with amorphous silicon solar cells is presented as a large-scale sensor for continuous wave and pulsed lasers (down to ns). First, the fabric and the solar cells were examined separately for irradiation behavior and damage. Laser irradiation was performed at wavelengths of 245, 355, 532, and 808 nm. The solar cell sensors were then applied directly to the laser protection fabric. The damage and destruction behavior of the active laser protection system was investigated. The results show that the basic safety function of the solar cell is still preserved when the locally damaged or destroyed area is irradiated again. A simple automatic shutdown system was used to demonstrate active laser protection within 50 ms.
- ItemInfluence of Lattice Mismatch on Structural and Functional Properties of Epitaxial Ba0.7Sr0.3TiO3 Thin Films(Basel : MDPI, 2023) Wawra, Jonas; Nielsch, Kornelius; Hühne, RubenSubstrate-induced strains can significantly influence the structural properties of epitaxial thin films. In ferroelectrics, this might lead to significant changes in the functional properties due to the strong electromechanical coupling in those materials. To study this in more detail, epitaxial Ba0.7Sr0.3TiO3 films, which have a perovskite structure and a structural phase transition close to room temperature, were grown with different thicknesses on REScO3 (RE–rare earth element) substrates having a smaller lattice mismatch compared to SrTiO3. A fully strained SrRuO3 bottom electrode and Pt top contacts were used to achieve a capacitor-like architecture. Different X-ray diffraction techniques were applied to study the microstructure of the films. Epitaxial films with a higher crystalline quality were obtained on scandates in comparison to SrTiO3, whereas the strain state of the functional layer was strongly dependent on the chosen substrate and the thickness. Differences in permittivity and a non-linear polarization behavior were observed at higher temperatures, suggesting that ferroelectricity is supressed under tensile strain conditions in contrast to compressive strain for our measurement configuration, while a similar reentrant relaxor-like behavior was found in all studied layers below 0°C.
- ItemSelf-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers(Basel : MDPI, 2023) Hartmann, Frank; Bitsch, Martin; Niebuur, Bart-Jan; Koch, Marcus; Kraus, Tobias; Dietz, Christian; Stark, Robert W.; Everett, Christopher R.; Müller-Buschbaum, Peter; Janka, Oliver; Gallei, MarkusThe fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene-b-poly(methyl methacrylate) block copolymer (PS-b-PMMA) was synthesized through anionic polymerization. The influence of the addition of different ratios of PMMA-coated FePt nanoparticles (NPs) on the self-assembled morphology was investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The self-assembly of the NPs inside the PMMA phase at low particle concentrations was analyzed statistically, and the negative effect of higher particle ratios on the lamellar BCP morphology became visible. The placement of the NPs inside the PMMA phase was also compared to theoretical descriptions. The magnetic addressability of the FePt nanoparticles inside the nanocomposite films was finally analyzed using bimodal magnetic force microscopy and proved the magnetic nature of the nanoparticles inside the microphase-separated BCP films.
- ItemAluminum-Doped Zinc Oxide Improved by Silver Nanowires for Flexible, Semitransparent and Conductive Electrodes on Textile with High Temperature Stability(Basel : MDPI, 2023) Hupfer, Maximilian Lutz; Gawlik, Annett; Dellith, Jan; Plentz, JonathanIn order to facilitate the design freedom for the implementation of textile-integrated electronics, we seek flexible transparent conductive electrodes (TCEs) that can withstand not only the mechanical stresses encountered during use but also the thermal stresses of post-treatment. The transparent conductive oxides (TCO) typically used for this purpose are rigid in comparison to the fibers or textiles they are intended to coat. In this paper, a TCO, specifically aluminum-doped zinc oxide (Al:ZnO), is combined with an underlying layer of silver nanowires (Ag-NW). This combination brings together the advantages of a closed, conductive Al:ZnO layer and a flexible Ag-NW layer, forming a TCE. The result is a transparency of 20–25% (within the 400–800 nm range) and a sheet resistance of 10 Ω/sq that remains almost unchanged, even after post-treatment at 180 °C.
- ItemSpecial Issue on Computational Ultrasound Imaging and Applications(Basel : MDPI, 2024) Nauber, Richard; Büttner, Lars; Czarske, Jürgen[No abstract available]