@inproceedings{OschinowoForchelGruetzmacheretal.1991, author = {Oschinowo, John and Forchel, Alfred and Gr{\"u}tzmacher, Detlev and Stollenwerk, Manfred}, title = {RTA study of thermal stability and interdiffusion of InGaAs/InP quantum wells - the influence of InGaAs cap layers}, series = {Third International Conference Indium Phosphide and Related Materials Cardiff/Wales}, booktitle = {Third International Conference Indium Phosphide and Related Materials Cardiff/Wales}, pages = {606 -- 609}, year = {1991}, abstract = {A study of the thermal stability of InGaAs/InP quantum wells with different top barrier compositions that used rapid thermal annealing at temperatures between 600 degrees C and 950 degrees C (annealing time 1 min) is discussed. The thermal interdiffusion effects were evaluated by photoluminescence spectroscopy. From the temperature dependence of the luminescence energy shifts the interdiffusion coefficients and activation energies are determined.}, subject = {Photolumineszenzspektroskopie}, language = {en} } @article{ShiGruetzmacherStollenwerketal.1992, author = {Shi, Chang-Xin and Gr{\"u}tzmacher, Detlev and Stollenwerk, Manfred and Wang, Qing-Kang and Heime, Klaus}, title = {High-performance undoped InP/n-InP/GaAs MSM photodetectors grown by LP-MOVPE}, series = {IEEE Transactions on Electron Devices}, volume = {39}, journal = {IEEE Transactions on Electron Devices}, number = {5}, publisher = {IEEE}, pages = {1028 -- 1031}, year = {1992}, subject = {Indiumarsenid}, language = {en} } @article{StollenwerkDoehringFreudenmannetal.2021, author = {Stollenwerk, Manfred and D{\"o}hring, Thorsten and Freudenmann, Dominic and Sch{\"a}fer, Tobias and Stadtm{\"u}ller, Johannes and R{\"o}cke, Nicole}, title = {Sputtered highly effective iridium catalysts: a new approach for green satellite propulsion}, series = {Journal of Materials Science}, volume = {2021}, journal = {Journal of Materials Science}, number = {2021}, doi = {https://doi.org/10.1007/s10853-021-05897-z}, pages = {1 -- 11}, year = {2021}, abstract = {This work demonstrated the large potential of sputtered iridium metal for catalytic reactions shown by the example of decomposition of hydrogen peroxide (H2O2) for space propulsion systems. For this purpose, iridium was coated onto Al2O3 pellets by a sputter process under varied process parameters. Depending on previously selected parameters, the obtained metal-loaded pellets offer closed- and/or open-shell structures. Catalytic productivity of these first-generation iridium-sputtered catalysts was estimated in laboratory experiments and compared to platinum-loaded pellets. Under optimized sputter-process conditions, the reactivity is significantly improved compared to the platinum-impregnated pellets. The better catalytic productivity can be explained by the increased active surface area of the iridium layers on the pellets. The surface morphology and the microstructure of the iridium coating can be actively controlled by the sputter pressure. The results are in accordance with the sputtering process pressure tendency described by the Thornton Structure-Zone Model.}, subject = {Iridium}, language = {en} } @misc{DoehringStollenwerkStadtmuelleretal.2021, author = {D{\"o}hring, Thorsten and Stollenwerk, Manfred and Stadtm{\"u}ller, Johannes and Freudenmann, Dominic and R{\"o}cke, Nicole}, title = {Nanostructured iridium catalysts for effective hydrogen peroxide decomposition}, series = {EuroNanoForum}, volume = {2021}, journal = {EuroNanoForum}, organization = {TH Aschaffenburg}, pages = {1}, year = {2021}, abstract = {The EU intends to restrict the use of critical fuels in space propulsion systems. These propellants like hydrazine are chemically aggressive, toxic and carcinogenic. Space propulsion of the future should be environmentally friendly, inexpensive, and easy to handle. Aschaffenburg University and DLR are currently developing environmentally friendly technologies for future satellite engines. Thereby rocket-grade hydrogen peroxide, which is foreseen as a substitute, is converted to uncritical water vapour and oxygen by an exothermic catalytic reaction on nanostructured iridium layers. The resulting hot gases provide the required amount of thrust. The iridium catalyst layers are coated onto ceramic pellets, using RF magnetron sputtering technology. The catalytic functionality was tested afterwards at the chemical laboratories of DLR. First experimental results show a significantly higher catalytic activity for nanostructured iridium surfaces than for smoother crystalline layers.}, subject = {Iridium}, language = {en} } @inproceedings{StanikDoehringPregleretal.2024, author = {Stanik, Eva and D{\"o}hring, Thorsten and Pregler, Jan and Stollenwerk, Manfred and Hildenbrand, Georg}, title = {Spectral measurements and life science experiments using extreme radiation exposures at high altitude}, series = {Proceedings of SPIE}, volume = {2024}, booktitle = {Proceedings of SPIE}, number = {13024}, doi = {10.1117/12.3028519}, pages = {130240M -- 130240M}, year = {2024}, abstract = {The ASTRABAX project ("Aschaffenburg Stratospheric Balloon Experiment"), being funded for the years 2024 to 2026, is designed as a multimodal platform for the investigation of radiation exposures at high altitude. The UV-C spectral region is of special interest. Spectral measurements observe this region of interest using miniature UV-VIS spectrometers. The platform also contains a radiation dosimetry, a power source for on-board electronics, and common shielding setups for multiple spectral combinations. Human cells are exposed simultaneously to radiation of different compositions as particle, X-ray and UV radiation. After the flight, possible changes in the spatial chromatin organization are examined. Material samples intended for the development of satellite components are irradiated also. Investigations under such conditions are realistic and crucial for high altitude flights in the atmosphere, for space flights as well as for comparable exposures on other objects of the solar system, and even for exoplanet habitats to some extent.}, subject = {Spektroskopie}, language = {en} } @misc{DoehringStanikPregleretal.2024, author = {D{\"o}hring, Thorsten and Stanik, Eva and Pregler, Jan and Stollenwerk, Manfred and Hildenbrand, Georg}, title = {Forschung zu Strahlensch{\"a}den mit dem Stratosph{\"a}renballon-Experiment ASTRABAX}, organization = {Technische Hochschule Aschaffenburg}, pages = {1 -- 1}, year = {2024}, abstract = {Das f{\"u}r die Jahre 2024 bis 2026 gef{\"o}rderte Projekt ASTRABAX („Aschaffenburger Stratosph{\"a}renballon- Experiment") ist als multimodale Plattform der Material- und Biowissenschaften f{\"u}r Untersuchungen bei extremen Strahlenbelastungen in großer H{\"o}he konzipiert. Dabei ist der UV-C-Spektralbereich von besonderem Interesse und wird mit Miniatur-UV-Spektrometern untersucht. Die Plattform des Ballonexperimentes umfasst eine gemeinsame Strahlungsdosimetrie, eine Stromquelle f{\"u}r die Bordelektronik und Abschirmungen f{\"u}r mehrere Bestrahlungskombinationen. Biologische Zellen werden Kombinationen aus Partikel-, R{\"o}ntgen- und UV-Strahlung ausgesetzt. Nach dem Flug werden m{\"o}gliche Ver{\"a}nderungen in der r{\"a}umlichen Chromatinorganisation mittels hochaufl{\"o}sender Mikroskopie untersucht. Auswirkungen von Kombinationen aus hoch- und niederenergetischer Strahlung sind bisher nicht ausreichend erforscht und beschrieben. Zus{\"a}tzlich werden auch f{\"u}r Satelliten relevante Materialproben bestrahlt. Untersuchungen unter solchen Bedingungen sind realistisch und relevant f{\"u}r Fl{\"u}ge in der Stratosph{\"a}re, f{\"u}r Raumfl{\"u}ge sowie f{\"u}r vergleichbare Expositionen bei anderen Objekten des Sonnensystems oder Exoplaneten-Habitaten.}, subject = {Stratosph{\"a}ren-Ballon}, language = {de} } @incollection{MannWenzlerDoehringetal.2022, author = {Mann, Michael and Wenzler, Sebastian and D{\"o}hring, Thorsten and Stollenwerk, Manfred and Pribulla, Theodor and Sivanič, Peter and Komž{\´i}k, Richard}, title = {Stromversorgung als Umweltfaktor: Analyse der elektrischen Netzqualit{\"a}t in astronomischen Observatorien}, series = {Umwelteinfl{\"u}sse erfassen, simulieren, bewerten}, volume = {2022}, booktitle = {Umwelteinfl{\"u}sse erfassen, simulieren, bewerten}, editor = {Karl Friedrich, Zieghahn}, publisher = {Gesellschaft f{\"u}r Umweltsimulation e.V.}, isbn = {978-3-9818507-7-2}, pages = {193 -- 207}, year = {2022}, subject = {Sternwarte}, language = {de} } @misc{StanikDoehringPregleretal.2024, author = {Stanik, Eva and D{\"o}hring, Thorsten and Pregler, Jan and Stollenwerk, Manfred and Hildenbrand, Georg}, title = {Spectral measurements and life science experiments using extreme radiation exposures at high altitude}, organization = {Technische Hochschule Aschaffenburg}, pages = {1}, year = {2024}, abstract = {The ASTRABAX project ("Aschaffenburg Stratospheric Balloon Experiment"), being funded for the years 2024 to 2026, is designed as a multimodal platform for the investigation of radiation exposures at high altitude. Miniature UV-VIS spectrometers observe the UV-C spectral region. The platform also contains a radiation dosimetry, a power source for on-board electronics, and common shielding setups for multiple spectral combinations. The effects of combinations of high- and low-energy rays on human cells haven´t been sufficiently investigated and described so far. Investigations under such conditions are realistic and crucial for high altitude flights in the atmosphere, for space flights as well as for comparable exposures on other objects of the solar system, and even for exoplanet habitats to some extent.}, subject = {Stahlenbelastung}, language = {en} } @inproceedings{MannDoehringStollenwerketal.2024, author = {Mann, Michael and D{\"o}hring, Thorsten and Stollenwerk, Manfred and Priebsch, Alessandro and Pribulla, Theodor and Komž{\´i}k, Richard M. and Sivanic, Peter}, title = {Advanced power quality measurement techniques at the electric power grid of astronomical observatories}, series = {Observatory Operations: Strategies, Processes, and Systems X, Conference of SPIE 13098, 17 - 20 June 2024}, booktitle = {Observatory Operations: Strategies, Processes, and Systems X, Conference of SPIE 13098, 17 - 20 June 2024}, editor = {Storrie-Lombardi, Lisa J. and Benn, Chris R. and Chrysostomou, Antonio}, publisher = {SPIE}, doi = {10.1117/12.3016562}, year = {2024}, subject = {Sternwarte}, language = {en} } @inproceedings{MannDoehringStollenwerketal.2022, author = {Mann, Michael and D{\"o}hring, Thorsten and Stollenwerk, Manfred and Wenzler, Sebastian and Pribulla, Theodor and Komž{\´i}k, Richard M. and Sivanic, Peter}, title = {On the importance of the electrical grid power quality for astronomical observatories}, series = {Proceedings of SPIE: Observatory Operations: Strategies, Processes, and Systems IX}, booktitle = {Proceedings of SPIE: Observatory Operations: Strategies, Processes, and Systems IX}, editor = {Benn, Chris R. and Seaman, Robert L. and Adler, David S.}, publisher = {SPIE}, doi = {http://dx.doi.org/10.1117/12.2627227}, year = {2022}, subject = {Elektrizit{\"a}tsversorgung}, language = {en} } @inproceedings{DoehringStanikPregleretal.2024, author = {D{\"o}hring, Thorsten and Stanik, Eva and Pregler, Jan and Stollenwerk, Manfred and Hildenbrand, Georg}, title = {Forschung zu Strahlensch{\"a}den mit dem Stratosph{\"a}renballon-Experiment ASTRABAX}, series = {DGaO-Proceedings}, volume = {2024}, booktitle = {DGaO-Proceedings}, number = {125}, pages = {1 -- 2}, year = {2024}, abstract = {Das Stratosph{\"a}renballon-Experiment ASTRABAX ist als multimodale Plattform der Material- und Biowissenschaften f{\"u}r Untersuchungen bei extremen Strahlenbelastungen konzipiert, mit Fokus auf dem UV-C-Spektralbereich und der kosmischen H{\"o}henstrahlung. Auswirkungen von Kombinationen aus hoch- und niederenergetischer Strahlung sind relevant, jedoch nicht ausreichend erforscht.}, subject = {Stratosph{\"a}ren-Ballon}, language = {de} } @article{AmorimSperaNicoaraetal.2024, author = {Amorim, Isilda and Spera, Natalia C.M. and Nicoara, Nicoleta and Ramasamy, Devaraj and Alves, Diana F. and Stollenwerk, Manfred and Stadtm{\"u}ller, Johannes and D{\"o}hring, Thorsten and Sadewasser, Sascha and Kolen'ko, Yury V. and Sousa, Juliana P.S.}, title = {Overall alkaline water electrolysis over active, stable, low loading iridium catalysts sputtered on nickel foam}, series = {International Journal of Hydrogen Energy}, volume = {92}, journal = {International Journal of Hydrogen Energy}, publisher = {Elsevier BV}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2024.10.306}, pages = {852 -- 864}, year = {2024}, subject = {Iridium}, language = {en} } @incollection{WisselFreudenmannPerezetal.2025, author = {Wissel, Julian and Freudenmann, Dominic and Perez, Nicolas and D{\"o}hring, Thorsten and Stadtm{\"u}ller, Johannes and Stollenwerk, Manfred}, title = {Various highly effective sputtered layer structures as catalysts for H2O2 decomposition for use in satellite engines}, series = {MaterialsWeek 2025 - Book of Abstracts}, booktitle = {MaterialsWeek 2025 - Book of Abstracts}, publisher = {Deutsche Gesellschaft f{\"u}r Materialkunde e.V. (DGM)}, address = {Sankt Augustin}, isbn = {978-3-88355-446-4}, pages = {53 -- 53}, year = {2025}, abstract = {Catalysts are frequently employed in both research and industrial applications to facilitate or accelerate chemical reactions. One such application is in monopropellant thrusters for space propulsion systems, where hydrogen peroxide (H2O2) is used as a liquid propellant. The decomposition of liquid hydrogen peroxide into water and oxygen gas, which ultimately generates thrust, can be achieved using noble metal catalysts from the platinoid group, such as platinum and iridium. This promotes the use of more environmentally friendly and less toxic propellants, such as H2O2, instead of hydrazine and nitrogen tetroxide (NTO). The optimization of coating structures with these catalytic materials is essential for future space applications, as it aims to extend the lifespan of catalyst materials and results in a better utilization of H2O2 in satellite engines. Therefore, different layer structures were deposited onto Duranit D99 pellets using a controlled magnetron sputtering process. Previous studies have shown that the used sputtering pressure has a strong influence on the structure of the deposited coatings [2][3]. Certain parameter combinations produce catalytic layers with rough textures and a highly porous microstructure, see figure 1 [1]. To improve the thermal and mechanical stability of the sputtered layers, thin adhesive layers of Titanium and Zirconium were applied beneath the catalytic layer. The pellets were then heated in an oven at 640°C for one minute to simulate the thermal effects experienced in a satellite engine during ignition. Following this, the catalytic performance of the pellets was tested in laboratory experiments using 30\% H2O2. Pellets with sputtered platinum as the catalytic coating delivered the best results. These coatings will be further evaluated in an engine test conducted at the German Aerospace Centre (DLR). Hydrogen peroxide is also expected to play a crucial role in future lunar and Martian colonization efforts. In this context, catalytic coatings would be used to decompose H2O2 to supply astronauts with water and oxygen, rather than to generate thrust in satellite engines.}, subject = {Satellitentechnik}, language = {en} }