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- ItemDoes the energy transfer from Ar(1s) atoms to N2 lead to dissociation?(Hoboken, NJ : Wiley Interscience, 2020) Klages, Claus‐Peter; Martinovs, Andris; Bröcker, Lars; Loffhagen, DetlefDielectric-barrier discharges (DBDs) in Ar–N2 mixtures, with N2 fractions in 0.1–1% range, would be attractive alternatives to DBDs in pure N2 if energy-transfer reactions between Ar(1s) atoms and N2 molecules were an efficient source of N atoms. Attempts to functionalize polyolefins in flowing postdischarges fed by such DBDs, as well as the search for the First Positive System in the emission spectrum, however, failed. Evidently, the energy-transfer reactions do not produce N atoms. For Ar(1s3) and Ar(1s5) metastable states, this fact has already been reported in the literature. For Ar(1s2) and Ar(1s4) resonant states, a quantitative argument is derived in this paper: energy transfer from Ar(1s) atoms to N2 molecules is not an efficient source of N atoms.
- ItemPlasma medical oncology: Immunological interpretation of head and neck squamous cell carcinoma(Hoboken, NJ : Wiley Interscience, 2020) Witzke, Katharina; Seebauer, Christian; Jesse, Katja; Kwiatek, Elisa; Berner, Julia; Semmler, Marie‐Luise; Boeckmann, Lars; Emmert, Steffen; Weltmann, Klaus‐Dieter; Metelmann, Hans‐Robert; Bekeschus, SanderThe prognosis of patients suffering from advanced-stage head and neck squamous cell carcinoma (HNSCC) remains poor. Medical gas plasma therapy receives growing attention as a novel anticancer modality. Our recent prospective observational study on HNSCC patients suffering from contaminated tumor ulcerations without lasting remission after first-line anticancer therapy showed remarkable efficacy of gas plasma treatment, with the ulcerated tumor surface decreasing by up to 80%. However, tumor growth relapsed, and this biphasic response may be a consequence of immunological and molecular changes in the tumor microenvironment that could be caused by (a) immunosuppression, (b) tumor cell adaption, (c) loss of microbe-induced immunostimulation, and/or (d) stromal cell adaption. These considerations may be vital for the design of clinical plasma trials in the future.
- ItemEfficiency of plasma-processed air for biological decontamination of crop seeds on the premise of unimpaired seed germination(Hoboken, NJ : Wiley Interscience, 2021) Wannicke, Nicola; Wagner, Robert; Stachowiak, Joerg; Nishime, Thalita M.C.; Ehlbeck, Joerg; Weltmann, Klaus‐Dieter; Brust, HenrikeIn this study, the antimicrobial effect of plasma-processed air (PPA) generated by a microwave-induced nonthermal plasma was investigated for preharvest utilization using three crop species: Barley, rape, and lupine. Bacillus atrophaeus spores were chosen as a model, inoculated onto seeds, and subsequently treated with PPA at two different flow rates, different filling regimes, and gas exposure times. PPA treatment was efficient in reducing viable spores of B. atrophaeus, reaching sporicidal effects in all species at certain parameter combinations. Maximum germination of seeds was strongly reduced in barley and rape seeds at some parameter combination, whereas it had a modest effect on lupine seeds. Seed hydrophilicity was not altered. Overall, PPA investigated in this study proved suitable for preharvest applications.
- ItemDevelopment of a model for ultra-precise surface machining of N-BK7® using microwave-driven reactive plasma jet machining(Hoboken, NJ : Wiley Interscience, 2019) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasIn this paper, extensive studies are conducted as key to overcoming several challenging limitations in applying fluorine-based reactive plasma jet machining (PJM) to surface machining of N-BK7®, particularly regarding the manufacture of freeform optical elements. The chemical composition and lateral distributions of the residual layer are evaluated by X-ray photoelectron spectroscopy and scanning electron microscopy/energy-dispersive X-ray spectroscopy analysis aiming at clarifying the exact chemical kinetics between plasma generated active particles and the N-BK7 surface atoms. Subsequently, a model is developed by performing static etchings to consider the time-varying nonlinearity of the material removal rate and estimate the local etching rate function. Finally, the derived model is extended into the dynamic machining process, and the outcomes are compared with the experimental results.
- 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.
- ItemEffect of cold atmospheric pressure plasma treatment of eggshells on the total bacterial count inoculated Salmonella Enteritidis and selected quality parameters(Hoboken, NJ : Wiley Interscience, 2021) Moritz, Maike; Wiacek, Claudia; Weihe, Thomas; Ehlbeck, Jörg; Weltmann, Klaus‐Dieter; Braun, Peggy G.In the European Union, foodborne outbreaks caused by Salmonella Enteritidis, related to eggs and egg products, have even been reported in 2018. Atmospheric pressure plasma is becoming increasingly important as a decontamination method. A semidirect cold atmospheric pressure plasma, the flexible electrode plasma source, was developed for treating whole hen's eggs. An average reduction of 1.16 and 0.95 log colony-forming units (CFU)/egg was achieved for the total bacterial count of clean and dirty eggs, respectively. An inactivation of 4.1 log CFU/egg Salmonella Enteritidis was achieved with artificially inoculated eggshells. Selected quality parameters and sensory properties were analysed. Overall, the present study yielded promising results for a realistic implementation of an industrial prototype plasma source.
- ItemAn investigation on effectiveness of temperature treatment for fluorine-based reactive plasma jet machining of N-BK7®(Hoboken, NJ : Wiley Interscience, 2020) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasIn this study, a fluorine-based reactive plasma jet is investigated as a promising tool for ultraprecise surface machining of N-BK7®. Plasma-generated particles react with an N-BK7 surface to create volatile and nonvolatile compounds. The desorption of volatile compounds results in an etched surface, whereas nonvolatile compounds form a residual layer in the etched area, causing unpredictable effects on the etching rate. Surface temperature treatment is proposed to improve the machining procedure with respect to deterministic material removal, leading to predictable results. It is shown that, at an elevated surface temperature, the residual layer properties are modified in favor of improved etching performance. The etching behavior of N-BK7 is compared with fused silica to verify the optimality of the obtained results.
- ItemWhite paper on plasma for medicine and hygiene: Future in plasma health sciences(Hoboken, NJ : Wiley Interscience, 2019) Bekeschus, Sander; Favia, Pietro; Robert, Eric; von Woedtke, ThomasPlasma Science and Technology offer their valuable contribution to human health since more than 50 years, after decades of experiences in the field of biomaterials; and more than a decade in using plasmas for therapeutic uses in medicine. Current knowledge as well as key challenges and opportunities for the human health have been intensely discussed during the Future in Plasma Science II (FIPS II) workshop in February 2016 in Greifswald, Germany. This contribution summarizes the major outcomes of the meeting and the current literature and consensus with an emphasis on major challenges in the fields of Plasma Science and Technology for improving human health.
- ItemA novel Deal–Grove-inspired model for fluorine-based plasma jet etching of borosilicate crown optical glass(Hoboken, NJ : Wiley Interscience, 2021) Kazemi, Faezeh; Boehm, Georg; Arnold, ThomasThe Deal–Grove model is a state-of-the-art approach proposed for describing the thermal oxidation of silicon and the oxide thickness over time. In this study, the Deal–Grove concept provided the inspiration for a mathematical model for simulating plasma jet-based dry etching process of borosilicate crown glass (N-BK7®). The whole process is contained in two so-called Deal–Grove parameters, which are extracted from experimental data including local etching depth and surface temperature distribution. The proposed model is extended for the evolution of dynamic etch profiles, and the obtained results are validated experimentally. By establishing such a model, it is possible to predict the effect of the residual layer and surface temperature on the evolution of local etching depths over dwell time.
- ItemInactivation of airborne bacteria by plasma treatment and ionic wind for indoor air cleaning(Hoboken, NJ : Wiley Interscience, 2020) Prehn, Franziska; Timmermann, Eric; Kettlitz, Manfred; Schaufler, Katharina; Günther, Sebastian; Hahn, VeronikaAirborne bacteria are a general problem in medical or health care facilities with a high risk for nosocomial infections. Rooms with a continuous airflow, such as operation theaters, are of particular importance due to a possible dissemination and circulation of pathogens including multidrug-resistant microorganisms. In this regard, a cold atmospheric-pressure plasma (CAP) may be a possibility to support usual disinfection procedures due to its decontaminating properties. The aim of this study was to determine the antimicrobial efficacy of a plasma decontamination module that included a dielectric barrier discharge for plasma generation. Experimental parameters such as an airflow velocity of 4.5 m/s and microbial contaminations of approximately 6,000 colony-forming units (cfu)/m3 were used to simulate practical conditions of a ventilation system in an operating theater. The apathogenic microorganism Escherichia coli K12 DSM 11250/NCTC 10538 and the multidrug-resistant strains E. coli 21181 and 21182 (isolated from patients) were tested to determine the antimicrobial efficacy. In summary, the number of cfu was reduced by 31–89% for the tested E. coli strains, whereby E. coli K12 was the most susceptible strain toward inactivation by the designed plasma module. A possible correlation between the number or kind of resistances and susceptibility against plasma was discussed. The inactivation of microorganisms was affected by plasma intensity and size of the plasma treatment area. In addition, the differences of the antimicrobial efficacies caused through the nebulization of microorganisms in front (upstream) or behind (downstream) the plasma source were compared. The presence of ionic wind had no influence on the reduction of the number of cfu for E. coli K12, as the airflow velocity was too high for a successful precipitation, which would be a prerequisite for an increased antimicrobial efficacy. The inactivation of the tested microorganisms confirms the potential of CAP for the improvement of air quality. The scale-up of this model system may provide a novel tool for an effective air cleaning process.