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- ItemPlasma-based VAD process for multiply doped glass powders and high-performance fiber preforms with outstanding homogeneity(Hoboken, NJ : Wiley Interscience, 2020) Trautvetter, Tom; Schäfer, Jan; Benzine, Omar; Methling, Ralf; Baierl, Hardy; Reichel, Volker; Dellith, Jan; Köpp, Daniel; Hempel, Frank; Stankov, Marjan; Baeva, Margarita; Foest, Rüdiger; Wondraczek, Lothar; Wondraczek, Katrin; Bartelt, HartmutAn innovative approach using the vapor axial deposition (VAD), for the preparation of silica-based high-power fiber laser preforms, is described in this study. The VAD uses a plasma deposition system operating at atmospheric pressure, fed by a single, chemically adapted solution containing precursors of laser-active dopants (e.g., Yb2O3), glass-modifier species (e.g., Al2O3), and the silica matrix. The approach enables simultaneous doping with multiple optically active species and overcomes some of the current technological limitations encountered with well-established fiber preform technologies in terms of dopant distribution, doping levels, and achievable active core diameter. The deposition of co-doped silica with outstanding homogeneity is proven by Raman spectroscopy and electron probe microanalysis. Yb2O3 concentrations are realized up to 0.3 mol% in SiO2, with simultaneous doping of 3 mol% of Al2O3.
- ItemInternal Crack Initiation and Growth Starting from Artificially Generated Defects in Additively Manufactured Ti6Al4V Specimen in the VHCF Regime(Basel : MDPI, 2021) Wickmann, Carsten; Benz, Christopher; Heyer, Horst; Witte-Bodnar, Kerstin; Schäfer, Jan; Sander, ManuelaThe aim of the present work was to investigate the ‘fine granular area’ (FGA) formation based on artificially generated internal defects in additively manufactured Ti6Al4V specimens in the early stage of fatigue crack growth in the ‘very high cycle fatigue’ (VHCF) regime. Fatigue tests were performed with constant amplitude at pure tension-compression loading (R = −1) using an ultrasonic fatigue testing setup. Failed specimens were investigated using optical microscopy, high-resolution ‘scanning electron microscopy’ (SEM), and ‘focused ion beam’ (FIB) techniques. Further, the paper introduces alternative proposals to identify the FGA layer beneath the fracture surfaces in terms of the ‘cross section polishing’ (CSP) technique and metallic grindings with special attention paid to the crack origin, the surrounding microstructure, and the expansion of the nanograin layer beneath the fracture surface. Different existing fracture mechanical approaches were applied to evaluate if an FGA formation is possible. Moreover, the results were discussed in comparison to the experimental findings.
- ItemHelixJet: An innovative plasma source for next-generation additive manufacturing (3D printing)(Hoboken, NJ : Wiley Interscience, 2020) Schäfer, Jan; Quade, Antje; Abrams, Kerry J.; Sigeneger, Florian; Becker, Markus M.; Majewski, Candice; Rodenburg, CorneliaA novel plasma source (HelixJet) for use in additive manufacturing (AM)/3D printing is proposed. The HelixJet is a capacitively coupled radio frequency plasma with a double-helix electrode configuration that generates a surprisingly stable and homogeneous glow plasma at low flow rates of argon and its mixtures at atmospheric pressure. The HelixJet was tested on three polyamide powders usually used to produce parts by laser sintering, a powder-based AM process, to form local deposits. The chemical composition of such plasma-printed samples is compared with thermally produced and laser-sintered samples with respect to differences in morphology that result from the different thermal cycles on several length scales. Plasma prints exhibit unique features attributable to the nonequilibrium chemistry and to the high-speed heat exchange.
- ItemX-ray Ptychographic Imaging and Spectroscopic Studies of Plasma-Treated Plastic Films(Basel : MDPI, 2022) Ravandeh, Mehdi; Mehrjoo, Masoud; Kharitonov, Konstantin; Schäfer, Jan; Quade, Antje; Honnorat, Bruno; Ruiz-Lopez, Mabel; Keitel, Barbara; Kreis, Svea; Pan, Rui; Gang, Seung-gi; Wende, Kristian; Plönjes, ElkePolyethylene terephthalate (PET) is a thermoplastic polyester with numerous applications in industry. However, it requires surface modification on an industrial scale for printing and coating processes and plasma treatment is one of the most commonly used techniques to increase the hydrophilicity of the PET films. Systematic improvement of the surface modification by adaption of the plasma process can be aided by a comprehensive understanding of the surface morphology and chemistry. However, imaging large surface areas (tens of microns) with a resolution that allows understanding the surface quality and modification is challenging. As a proof-of-principle, plasma-treated PET films were used to demonstrate the capabilities of X-ray ptychography, currently under development at the soft X-ray free-electron laser FLASH at DESY, for imaging macroscopic samples. In combination with scanning electron microscopy (SEM), this new technique was used to study the effects of different plasma treatment processes on PET plastic films. The studies on the surface morphology were complemented by investigations of the surface chemistry using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). While both imaging techniques consistently showed an increase in roughness and change in morphology of the PET films after plasma treatment, X-ray ptychography can provide additional information on the three-dimensional morphology of the surface. At the same time, the chemical analysis shows an increase in the oxygen content and polarity of the surface without significant damage to the polymer, which is important for printing and coating processes.
- ItemHighly active heterogeneous hydrogenation catalysts prepared from cobalt complexes and rice husk waste(London : RSC Publ., 2022) Unglaube, Felix; Schlapp, Janina; Quade, Antje; Schäfer, Jan; Mejía, EstebanThe utilization and valorization of agricultural waste is a key strategy for the implementation of a sustainable economy to lessen the environmental footprint of human activities on Earth. This work describes the use of rice husk (RH) from agricultural waste to prepare a highly active catalyst for the reduction of nitro compounds. RH was impregnated with various cobalt complexes bearing N-donor ligands, then pyrolyzed and the resulting composite was etched with a base to remove the silica domains. The composition and morphology of the prepared materials were investigated by IR, AAS, ICP-OES, XRD, BET, XPS and SEM technics. The material showed excellent activity and selectivity in the hydrogenation of nitro groups in aromatic and aliphatic substrates. A remarkable selectivity towards nitro groups was found in the presence of various reactive functionalities, including halogens, carbonyls, borates, and nitriles. Apart from their excellent activity and selectivity, these catalysts showed remarkable stability, allowing their easy recovery and multiple reuse without requiring re-activation.
- ItemAdamant: a JSON schema-based metadata editor for research data management workflows [version 1; peer review: 2 approved](London : F1000 Research Ltd, 2022) Chaerony Siffa, Ihda; Schäfer, Jan; Becker, Markus M.The web tool Adamant has been developed to systematically collect research metadata as early as the conception of the experiment. Adamant enables a continuous, consistent, and transparent research data management (RDM) process, which is a key element of good scientific practice ensuring the path to Findable, Accessible, Interoperable, Reusable (FAIR) research data. It simplifies the creation of on-demand metadata schemas and the collection of metadata according to established or new standards. The approach is based on JavaScript Object Notation (JSON) schema, where any valid schema can be presented as an interactive web-form. Furthermore, Adamant eases the integration of numerous available RDM methods and software tools into the everyday research activities of especially small independent laboratories. A programming interface allows programmatic integration with other software tools such as electronic lab books or repositories. The user interface (UI) of Adamant is designed to be as user friendly as possible. Each UI element is self-explanatory and intuitive to use, which makes it accessible for users that have little to no experience with JSON format and programming in general. Several examples of research data management workflows that can be implemented using Adamant are introduced. Adamant (client-only version) is available from: https://plasma-mds.github.io/adamant.
- ItemPlasma-MDS, a metadata schema for plasma science with examples from plasma technology(London : Nature Publ. Group, 2020) Franke, Steffen; Paulet, Lucian; Schäfer, Jan; O'Connell, Deborah; Becker, Markus M.A metadata schema, named Plasma-MDS, is introduced to support research data management in plasma science. Plasma-MDS is suitable to facilitate the publication of research data following the FAIR principles in domain-specific repositories and with this the reuse of research data for data driven plasma science. In accordance with common features in plasma science and technology, the metadata schema bases on the concept to separately describe the source generating the plasma, the medium in which the plasma is operated in, the target the plasma is acting on, and the diagnostics used for investigation of the process under consideration. These four basic schema elements are supplemented by a schema element with various attributes for description of the resources, i.e. the digital data obtained by the applied diagnostic procedures. The metadata schema is first applied for the annotation of datasets published in INPTDAT—the interdisciplinary data platform for plasma technology. © 2020, The Author(s).
- ItemUnderstanding Surface Modifications Induced via Argon Plasma Treatment through Secondary Electron Hyperspectral Imaging(Weinheim : Wiley-VCH, 2021) Farr, Nicholas; Thanarak, Jeerawan; Schäfer, Jan; Quade, Antje; Claeyssens, Frederik; Green, Nicola; Rodenburg, CorneliaUnderstanding the effects that sterilization methods have on the surface of a biomaterial is a prerequisite for clinical deployment. Sterilization causes alterations in a material's surface chemistry and surface structures that can result in significant changes to its cellular response. Here we compare surfaces resulting from the application of the industry standard autoclave sterilisation to that of surfaces resulting from the use of low-pressure Argon glow discharge within a novel gas permeable packaging method in order to explore a potential new biomaterial sterilisation method. Material surfaces are assessed by applying secondary electron hyperspectral imaging (SEHI). SEHI is a novel low-voltage scanning electron microscopy based characterization technique that, in addition to capturing topographical images, also provides nanoscale resolution chemical maps by utilizing the energy distribution of emitted secondary electrons. Here, SEHI maps are exploited to assess the lateral distributions of diverse functional groups that are effected by the sterilization treatments. This information combined with a range of conventional surface analysis techniques and a cellular metabolic activity assay reveals persuasive reasons as to why low-pressure argon glow discharge should be considered for further optimization as a potential terminal sterilization method for PGS-M, a functionalized form of poly(glycerol sebacate) (PGS).
- ItemPlasma-Functionalized Water: from Bench to Prototype for Fresh-Cut Lettuce(New York : Springer, 2020) Schnabel, Uta; Handorf, Oliver; Stachowiak, Joerg; Boehm, Daniela; Weit, Christoph; Weihe, Thomas; Schäfer, Jan; Below, Harald; Bourke, Paula; Ehlbeck, JoergFresh-cut produce like lettuce may contain a very high microbial load, including human pathogens. Therefore, the need for antimicrobial agents at post-harvest stages to mitigate microbial cross-contamination and growth is evident. Sanitation based on non-thermal plasma (NTP) reveals innovative food processing possibilities by application at different points along the food chain, for production, modification, and preservation, as well as in packaging of plant- and animal-based food. The aim of the present study was to evaluate the applicability of plasma-treated water (PTW) as antimicrobial process water additives for washing in fresh-cut lettuce processing. Antibacterial activities of PTW the natural occurring microflora of lettuce were examined. Different process variants of PTW application inside the washing process were investigated. Fresh-cut lettuce were investigated regarding microbiological safety and food quality. Samples were analyzed for antimicrobial and metabolic activity as well as metabolic vitality to prove food safety. The investigations for food quality included color and texture analyses and nitrate concentration detection in fresh tissue as well as microscopic measurements by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for tissue surface structure and transmission electron microscopy (TEM) for cell organelle investigations. The application of PTW allowed up to 5 log10 cycle reduction, depending on the process variant and scale (lab and pilot scale). The increase of antimicrobial activity was accompanied by a reduction of metabolic activity, but not consequently by a decrease in metabolic vitality. Food quality was not affected by the use of PTW in the washing process of the fresh-cut lettuce. The promising results in color and texture were supported by the results of the microscopic assays. These promising results may lead to an industrial application of PTW as process water additive in fresh-cut produce processing to reduce the microbial load on the food surface and in addition in the process water or on food processing surfaces. © 2020, The Author(s).
- ItemPlasma-Treated Water Affects Listeria monocytogenes Vitality and Biofilm Structure(Lausanne : Frontiers Media, 2021) Handorf, Oliver; Pauker, Viktoria Isabella; Weihe, Thomas; Schäfer, Jan; Freund, Eric; Schnabel, Uta; Bekeschus, Sander; Riedel, Katharina; Ehlbeck, JörgBackground: Plasma-generated compounds (PGCs) such as plasma-processed air (PPA) or plasma-treated water (PTW) offer an increasingly important alternative for the control of microorganisms in hard-to-reach areas found in several industrial applications including the food industry. To this end, we studied the antimicrobial capacity of PTW on the vitality and biofilm formation of Listeria monocytogenes, a common foodborne pathogen. Results: Using a microwave plasma (MidiPLexc), 10 ml of deionized water was treated for 100, 300, and 900 s (pre-treatment time), after which the bacterial biofilm was exposed to the PTW for 1, 3, and 5 min (post-treatment time) for each pre-treatment time, separately. Colony-forming units (CFU) were significantly reduced by 4.7 log10 ± 0.29 log10, as well as the metabolic activity decreased by 47.9 ± 9.47% and the cell vitality by 69.5 ± 2.1%, compared to the control biofilms. LIVE/DEAD staining and fluorescence microscopy showed a positive correlation between treatment and incubation times, as well as reduction in vitality. Atomic force microscopy (AFM) indicated changes in the structure quality of the bacterial biofilm. Conclusion: These results indicate a promising antimicrobial impact of plasma-treated water on Listeria monocytogenes, which may lead to more targeted applications of plasma decontamination in the food industry in the future.