@phdthesis{Berndt, author = {Berndt, Dominik}, title = {Thermische Wasserstoffsensoren f{\"u}r den Automobilbereich}, address = {Regensburg}, abstract = {F{\"u}r den sicheren Betrieb eines Brennstoffzellenfahrzeugs sind Sensoren wichtig, welche die Wasserstoffkonzentration im Fahrzeuginterieur kontinuierlich {\"u}berwachen, um m{\"o}glichen Entz{\"u}ndungen bzw. Explosionen vorzubeugen. Daf{\"u}r wurden von verschiedenen nationalen und internationalen Instanzen bestimmte Kriterien definiert, die Wasserstoffsensoren f{\"u}r einen Einsatz in Brennstoffzellenfahrzeugen erf{\"u}llen m{\"u}ssen. Im Jahr 2020gab es noch keinen einzigen kommerziell erh{\"a}ltlichen Sensor, der alle diese Kriterien bedienen konnte. In der vorliegenden Arbeit wurde f{\"u}r zwei verschiedene Sensoren die Eignung des thermischen Wirkprinzips f{\"u}r die Detektion von Wasserstoff im Kontext dieser Sicherheitskriterien untersucht. Dabei wurden mit einem MEMS-Sensor und einem Mikrodrahtsensor zwei vergleichsweise einfache Geometrien herangezogen, welche den eindimensionalen und zylindersymmetrischen Fall abbilden sollen. F{\"u}r zwei dynamische Operationsmodi (gepulste Str{\"o}me und 3ω-Methode) wurden darauf aufbauend analytische Modelle basierend auf vereinfachten Sensorgeometrien entwickelt, um die Temperaturentwicklung des Sensorelements in Abh{\"a}ngigkeit der Zeit zu charakterisieren. Diese Studien wurden anschließend anhand von detaillierteren Modellen mithilfe von FEM-Simulationen erg{\"a}nzt und spezifiziert. Darin konnte gezeigt werden, dass f{\"u}r den gepulsten Betrieb sowohl die Pulsh{\"o}he als auch die Zeitkonstante des gemessenen Widerstands- bzw. Temperaturpulses als Messgr{\"o}ße herangezogen werden kann. Beim 3ω-Betrieb konnte zudem eine starke Frequenzabh{\"a}ngigkeit dieser Widerstands- bzw. Temperaturcharakteristik beobachtet werden. Die analytischen und numerischen Studien wurden anschließend durch experimentelle Ergebnisse best{\"a}tigt. Im Hinblick auf die zuvor definierten Kriterien stellte sich heraus, dass die Auswertung der Zeitkonstante beim gepulsten Betrieb im Hinblick auf Sensitivit{\"a}t und Aufl{\"o}sungsgrenze der Auswertung der Pulsh{\"o}he deutlich unterlegen ist. Beim 3ω-Betrieb k{\"o}nnen durch die hochintegrierte Messumgebung deutlich h{\"o}here Genauigkeiten und Aufl{\"o}sungsgrenzen erzielt werden. F{\"u}r den MEMS-Sensor wurde bei einer Anregungsfrequenz von 1 Hz mit 55 ppm die bislang geringste in der Literatur berichtete Aufl{\"o}sungsgrenze f{\"u}r einen thermischen Wasserstoffsensor erreicht. Der Leistungsverbrauch ist dabei im Vergleich zum Pulsbetrieb entsprechend des jeweiligen Tastgrads leicht bis m{\"a}ßig erh{\"o}ht, die Ansprechzeit wird bei beiden Operationsmodi maßgeblich durch die Sensorgeometrie beeinflusst. Die geometrischen Parameter der jeweiligen Sensoren haben ferner einen starken Einfluss auf die Sensitivit{\"a}t, womit die Divergenz in der Performance von MEMS-Chip und Drahtsensor erkl{\"a}rt werden kann. Es besteht ferner eine starke Temperatur- und Feuchtigkeitsabh{\"a}ngigkeit des Sensorsignals, welches bei beiden Operationsmodi indirekt proportional zur W{\"a}rmeleitf{\"a}higkeit des betrachteten Gasgemischs ist. Die Abh{\"a}ngigkeit vom definierten Umgebungsdruck ist lediglich f{\"u}r die Zeitkonstante relevant, bei der Pulsh{\"o}he besteht keine Druckabh{\"a}ngigkeit. Es konnte eine grunds{\"a}tzliche Eignung des thermischen Messprinzips f{\"u}r den Einsatz eines Wasserstoffsensors im Automobilbereich festgestellt werden. F{\"u}r eine Anwendung m{\"u}ssen allerdings Referenzsensoren f{\"u}r Temperatur, Feuchtigkeit und Druck implementiert werden und eine Kalibrierung in Abh{\"a}ngigkeit dieser Gr{\"o}ßen erfolgen. Der 3ωBetrieb ist aufgrund der h{\"o}heren Genauigkeit zu bevorzugen. W{\"a}hrend der MEMSSensor im Hinblick auf Sensitivit{\"a}t, Ansprechzeit und Leistungsaufnahme gut abschneidet, liegen die Vorteile des Mikrodrahtsensors in seiner Robustheit und der vergleichsweise einfachen Realisierbarkeit}, subject = {Kraftfahrzeugtechnik}, language = {de} } @article{MennickenPeterKaulenetal., author = {Mennicken, Max and Peter, Sophia Katharina and Kaulen, Corinna and Simon, Ulrich and Karth{\"a}user, Silvia}, title = {Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes}, series = {Beilstein journal of nanotechnology}, volume = {13}, journal = {Beilstein journal of nanotechnology}, publisher = {Beilstein-Institut zur F{\"o}rderung der Chemischen Wissenschaften}, doi = {10.3762/bjnano.13.16}, pages = {219 -- 229}, abstract = {The performance of nanoelectronic and molecular electronic devices relies strongly on the employed functional units and their addressability, which is often a matter of appropriate interfaces and device design. Here, we compare two promising designs to build solid-state electronic devices utilizing the same functional unit. Optically addressable Ru-terpyridine complexes were incorporated in supramolecular wires or employed as ligands of gold nanoparticles and contacted by nanoelectrodes. The resulting small-area nanodevices were thoroughly electrically characterized as a function of temperature and light exposure. Differences in the resulting device conductance could be attributed to the device design and the respective transport mechanism, that is, thermally activated hopping conduction in the case of Ru-terpyridine wire devices or sequential tunneling in nanoparticle-based devices. Furthermore, the conductance switching of nanoparticle-based devices upon 530 nm irradiation was attributed to plasmon-induced metal-to-ligand charge transfer in the Ru-terpyridine complexes used as switching ligands. Finally, our results reveal a superior device performance of nanoparticle-based devices compared to molecular wire devices based on Ru-terpyridine complexes as functional units.}, language = {en} } @article{HausladenBuchnerBartletal., author = {Hausladen, Matthias and Buchner, Philipp and Bartl, Mathias and Bachmann, Michael and Schreiner, Rupert}, title = {Integrated multichip field emission electron source fabricated by laser-micromachining and MEMS technology}, series = {Journal of Vacuum Science \& Technology B}, volume = {42}, journal = {Journal of Vacuum Science \& Technology B}, number = {1}, publisher = {AIP Publishing}, doi = {10.1116/6.0003233}, abstract = {In this work, high-current field emission electron source chips were fabricated using laser-micromachining and MEMS technology. The resulting chips were combined with commercially available printed circuit boards (PCBs) to obtain a multichip electron source. By controlling the separate electron sources using an external current control circuit, we were able to divide the desired total current evenly across the individual chips deployed in the PCB-carrier. In consequence, we were able to show a decreased degradation due to the reduced current load per chip. First, a single electron source chip was measured without current regulation. A steady-state emission current of 1 mA with a high stability of ±1.3\% at an extraction voltage of 250 V was observed. At this current level, a mean degradation slope of -0.7 μA/min with a nearly perfect transmission ratio of 99\% ± 0.4\% was determined. The measurements of a fully assembled multichip PCB-carrier electron source, using a current control circuit for regulation, showed that an even distribution of the desired total current led to a decreased degradation. This was determined by the increase in the required extraction voltage over time. For this purpose, two current levels were applied to the electron source chips of the PCB-carrier using an external current control circuit. First, 300 μA total current was evenly distributed among the individual electron source chips followed by the emission of 300 μA per electron source chip. This allows the observation of the influence of a distributed and nondistributed total current, carried by the electron source chips. Thereby, we obtained an increase in the mean degradation slope from +0.011 V/min (300 μA distributed) to +0.239 V/min (300 μA per chip), which is approximately 21 times higher. Moreover, our current control circuit improved the current stability to under 0.1\% for both current levels, 300 μA distributed and 300 μA per chip.}, language = {en} } @article{RemškarJelencCzepurnyietal., author = {Remškar, Maja and Jelenc, Janez and Czepurnyi, Nikolai and Malok, Matjaž and Pirker, Luka and Schreiner, Rupert and H{\"u}ttel, Andreas K.}, title = {Modulations of the work function and morphology of a single MoS2 nanotube by charge injection}, series = {Nanoscale Advances}, journal = {Nanoscale Advances}, publisher = {Royal Society of Chemistry (RSC)}, issn = {2516-0230}, doi = {10.1039/d4na00490f}, abstract = {Both the miniaturization of transistor components and the ongoing investigation of material systems with potential for quantum information processing have significantly increased current interest of researchers in semiconducting inorganic nanotubes. Here we report on an additional outstanding aspect of these nanostructures, namely the intrinsic coupling of electronic and mechanical properties. We observe electronic and morphology changes in a single MoS2 nanotube, exposed to charge injections by means of an atomic-force-microscopy tip. An elliptic deformation of the nanotube and helical twisting of the nanotube are visible, consistent with the reverse piezoelectric effect. Work-function changes are found to be dependent on the polarity of the injected carriers. An unexpected long-term persistence of the shape deformations is observed and explained with accumulation of structural defects and the resultant strain, which could cause a memory-like charge confinement and a long lasting modulation of the work function.}, language = {en} } @inproceedings{AliAhmmedAlEmranetal., author = {Ali, Md. Wajed and Ahmmed, Tanvir and Al Emran, Md and Roy, Dipon and Refat, Kawsar Ahmed and Khan, Robiul}, title = {Driver Fatigue Detection using CWT-Extracted Features and a Deep Learning Approach (CNNLSTM)}, series = {2024 IEEE International Conference on Biomedical Engineering, Computer and Information Technology for Health (BECITHCON), 28-29 Nov. 2024, Dhaka, Bangladesh}, booktitle = {2024 IEEE International Conference on Biomedical Engineering, Computer and Information Technology for Health (BECITHCON), 28-29 Nov. 2024, Dhaka, Bangladesh}, publisher = {IEEE}, address = {Piscataway, NJ}, isbn = {979-8-3315-3435-6}, doi = {10.1109/BECITHCON64160.2024.10962632}, pages = {77 -- 82}, abstract = {Driver fatigue is a leading reason behind traffic accidents globally, resulting in significant threats to public safety and substantial economic costs. Electroencephalography (EEG) has shown to be a critical tool for identifying driver fatigue as it can record brain activity associated with sleepiness, which gives it an advantage over other physiological modalities. Although raw EEG data can provide insightful information, accurate fatigue identification requires strong feature extraction techniques because of the inherent complexity of the data. This emphasizes how urgent it is to investigate revolutionary deep-learning architectures that can successfully extract discriminative features from raw EEG data. This study provides an innovative framework for driver fatigue identification from EEG that combines continuous wavelet transform (CWT) with convolutional neural networks (CNN) and long-short term memory (LSTM). In order to gain the advantage over the drawbacks of manual feature extraction, this study generates time-frequency spectrum representations of EEG data using the CWT. Following extracting information, each channel's time-frequency images are concatenated and fed into a CNN-LSTM architecture. This combination models the temporal and spatial characteristics of the EEG data and automatically learns discriminative features for identifying drivers' normal and fatigued states. A publicly available EEG dataset with recordings from twelve subjects is used to evaluate the proposed CWT-CNN-LSTM architecture. The result shows a prominent classification accuracy of 98.34\% for both the average of each subject and combined subjects. These findings show how well the CNN-LSTM framework captures EEG patterns associated with fatigue, which may result in more reliable driver fatigue detection systems and improved traffic safety.}, language = {en} } @article{HaynackTimothyKraenkeletal., author = {Haynack, Alexander and Timothy, Jithender J. and Kr{\"a}nkel, Thomas and Gehlen, Christoph and Thiel, Charlotte}, title = {Analyse des Frost-Tausalz-Widerstands zementgebundener Baustoffe mittels 3D-Laserscanning}, series = {ce/papers: Proceedings in Civil Engineering}, volume = {6}, journal = {ce/papers: Proceedings in Civil Engineering}, number = {6}, publisher = {Ernst \& Sohn}, issn = {2509-7075}, doi = {10.1002/cepa.2951}, pages = {1189 -- 1196}, abstract = {Eine Herausforderung performancebasierter Pr{\"u}fverfahren zur Bewertung der Dauerhaftigkeit ist die Beschleunigung nat{\"u}rlicher Mechanismen. Dies ist notwendig, um innerhalb kurzer Zeit die Langzeit-Leistungsf{\"a}higkeit ermitteln zu k{\"o}nnen. Die Bestimmung der Frost-Tausalzbest{\"a}ndigkeit von Beton kann durch den CDF-Test erfolgen, welcher f{\"u}r Betone mit ausreichendem Frost-Tausalz-Widerstand sehr gut funktioniert. Bei Proben mit einer unzureichenden bzw. unbekannten Performance k{\"o}nnen erh{\"o}hte Randabwitterungen auftreten, welche durch das Abl{\"o}sen des seitlichen Abdichtbands entstehen. Der zunehmende Randeinfluss f{\"u}hrt so zu einer Verf{\"a}lschung der Ergebnisse und zu einer Untersch{\"a}tzung der tats{\"a}chlichen Performance des Bauteils. In diesem Beitrag werden M{\"o}rtel- und Betonprobek{\"o}rper mit unterschiedlichen Abwitterungsraten in Anlehnung an das CDF-Verfahren untersucht. Zus{\"a}tzlich wird die Oberfl{\"a}chensch{\"a}digung der Proben anhand einer neuartigen Messmethode mittels hochaufl{\"o}sendem 3D-Laserscanning ausgewertet. Die Ergebnisse zeigen, dass die Randeffekte mit der Laserscan-Methode umgangen und vergleichbare Ergebnisse zu den CDF-Untersuchungen erzielt werden k{\"o}nnen. Somit k{\"o}nnen Betone ohne Randeinfl{\"u}sse charakterisiert und eine pr{\"a}zise Prognose der Langzeitbest{\"a}ndigkeit getroffen werden.}, language = {de} } @article{PeterDalmerLechneretal., author = {Peter, Daniel and Dalmer, Michael and Lechner, Alfred and Gigler, Alexander M. and Stark, Robert W. and Bensch, Wolfgang}, title = {The influence of liquid media on the fracture strength of polysilicon nanostructures}, series = {Solid State Phenomena}, volume = {187}, journal = {Solid State Phenomena}, publisher = {Trans Tech Publications}, doi = {10.4028/www.scientific.net/SSP.187.127}, pages = {127 -- 130}, abstract = {The mechanical stability of nanostructures depends on the surrounding medium. Their stability was probed by lateral force microscopy in liquid media. Previously reported data on water and isopropanol showed an increase in the fracture strength for the latter. Further tests with other alcohols (ethanol, 1-butanol) also showed an increasing strength. The interface between the liquid and the surface is the decisive factor for the influence of the media. When altering the interface with a cationic surfactant or a self-assembled monolayer, an increase of the fracture force by 100 \% compared to de-ionized water could be measured.}, language = {en} } @inproceedings{EscherRueckJobstetal., author = {Escher, Lukas and R{\"u}ck, Thomas and Jobst, Simon and K{\"o}nig, Martin and Bierl, Rudolf}, title = {Design and Characterization of a Low-Cost Photoacoustic Sensor for NO2 Using Lateral Illumination and Background Suppression}, series = {Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP): 11-15 July 2022, Vancouver, British Columbia, Canada}, booktitle = {Imaging and Applied Optics Congress 2022 (3D, AOA, COSI, ISA, pcAOP): 11-15 July 2022, Vancouver, British Columbia, Canada}, publisher = {Optica Publishing Group}, isbn = {978-1-957171-09-8}, doi = {10.1364/3D.2022.JTu2A.10}, abstract = {We introduce a low-cost photoacoustic NO2 sensor based on lateral LED illumination and optical background signal compensation. The 3σ limit of detection (LOD) was identified to be 24 ppbV.}, language = {en} } @unpublished{PangerlSukulRuecketal., author = {Pangerl, Jonas and Sukul, Pritam and R{\"u}ck, Thomas and Escher, Lukas and Miekisch, Wolfram and Bierl, Rudolf and Matysik, Frank-Michael}, title = {Photoacoustic Trace-Analysis of Breath Isoprene and Acetone Via Interband- and Quantum Cascade Lasers}, publisher = {Elsevier / SSRN}, doi = {10.2139/ssrn.4834735}, abstract = {This research presents two laser-based photoacoustic approaches for analyzing exhaled breath isoprene and acetone. The integration of a PTR-ToF-MS as a reference device ensured the reliability and accuracy of the PAS systems that is based on an ICL for isoprene and a QCL for acetone detection. The calibration yielded limits of detection of 26.9 ppbV and 1.7 ppbV, respectively, and corresponding normalized noise equivalent absorption coefficients (NNEAs) of 5.0E-9 Wcm-1Hz-0.5 and 4.9E-9 Wcm-1Hz-0.5. Laboratory as well as real breath sample measurements from alveolar breath revealed a robust system performance, with only one outlier within the static isoprene measurements. However, discrepancies emerged under dynamic breath sampling conditions, emphasizing the need for further optimization. Especially by knowing the dynamic nature and endogenous origin of exhaled isoprene our findings highlight the potential of breath analysis for non-invasive physio-metabolic and pathophysiological monitoring towards point-of-care devices.}, language = {en} } @article{PangerlSukulRuecketal., author = {Pangerl, Jonas and Sukul, Pritam and R{\"u}ck, Thomas and Escher, Lukas and Miekisch, Wolfram and Bierl, Rudolf and Matysik, Frank-Michael}, title = {Photoacoustic trace-analysis of breath isoprene and acetone via interband- and Quantum Cascade Lasers}, series = {Sensors and Actuators: B. Chemical}, volume = {424}, journal = {Sensors and Actuators: B. Chemical}, publisher = {Elsevier}, doi = {10.1016/j.snb.2024.136886}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-77024}, pages = {12}, abstract = {This research presents two laser-based photoacoustic approaches for analyzing exhaled breath isoprene and acetone. The integration of a PTR-ToF-MS as a reference device ensured the reliability and accuracy of the photoacoustic systems that is based on an ICL for isoprene and a QCL for acetone detection. The calibration yielded limits of detection of 26.9 ppbV and 1.7 ppbV, respectively, and corresponding normalized noise equivalent absorption coefficients (NNEAs) of 5.0E-9 Wcm 1Hz 0.5 and 4.9E-9 Wcm 1Hz 0.5. Laboratory as well as real breath sample measurements from alveolar breath revealed a robust system performance, with only one outlier within the static isoprene measurements. However, discrepancies emerged under dynamic breath sampling conditions, emphasizing the need for further optimization. Especially by knowing the dynamic nature and endogenous origin of exhaled isoprene our findings highlight the potential of breath analysis for non-invasive physio-metabolic and pathophysiological monitoring towards point-of-care devices}, language = {en} } @inproceedings{EscherMuellerRuecketal., author = {Escher, Lukas and M{\"u}ller, Max and R{\"u}ck, Thomas and Jobst, Simon and Bierl, Rudolf}, title = {Digitaler Zwilling photoakustischer Spurengassensoren zur Prozess{\"u}berwachung}, series = {16. Dresdner Sensor-Symposium 2022: Vortr{\"a}ge}, booktitle = {16. Dresdner Sensor-Symposium 2022: Vortr{\"a}ge}, publisher = {AMA (Association for Sensors + Measurement)}, isbn = {978-3-9819376-7-1}, doi = {10.5162/16dss2022/3.3}, abstract = {Stickstoffdioxid (NO2) wird haupts{\"a}chlich durch anthropogene Verbrennungsprozesse in Verkehr und Industrie in die Umgebungsluft eingebracht [1]. Die stark reaktive, oxidative Wirkung von NO2 kann bei Exposition mit h{\"o}heren Konzentrationen Reizungen und allergische Reaktionen in den Atemwegen hervorrufen. Weiter f{\"u}hrt NO2 zur Bildung von saurem Regen, Smog und Ozon (O3) die sich ebenso negativ auf die menschliche Gesundheit und Umwelt auswirken [2,3]. Aufgrund dieser Effekte wird die Spurengaskonzentration von NO2 in der Luft in Deutschland an ausgew{\"a}hlten, verkehrsreichen Orten gemessen.}, language = {de} } @article{RueckPangerlEscheretal., author = {R{\"u}ck, Thomas and Pangerl, Jonas and Escher, Lukas and Jobst, Simon and M{\"u}ller, Max and Bierl, Rudolf and Matysik, Frank-Michael}, title = {Kinetic cooling in mid-infrared methane photoacoustic spectroscopy: A quantitative analysis via digital twin verification}, series = {Photoacoustics}, volume = {40}, journal = {Photoacoustics}, publisher = {Elsevier}, doi = {10.1016/j.pacs.2024.100652}, abstract = {This study presents a detailed quantitative analysis of kinetic cooling in methane photoacoustic spectroscopy, leveraging the capabilities of a digital twin model. Using a quantum cascade laser tuned to 1210.01 cm⁻¹, we investigated the effects of varying nitrogen-oxygen matrix compositions on the photoacoustic signals of 15 ppmV methane. Notably, the photoacoustic signal amplitude decreased with increasing oxygen concentration, even falling below the background signal at oxygen levels higher than approximately 6 \%V. This phenomenon was attributed to kinetic cooling, where thermal energy is extracted from the surrounding gas molecules rather than added, as validated by complex vector analysis using a previously published digital twin model. The model accurately reproduced complex signal patterns through simulations, providing insights into the underlying molecular mechanisms by quantifying individual collision contributions. These findings underscore the importance of digital twins in understanding the fundamentals of photoacoustic signal generation at the molecular level.}, language = {en} } @article{LeonhardtGuertler, author = {Leonhardt, Carina and Guertler, Katherine}, title = {Unearthing Corporate Greenwashing: A Content Analysis of Sustainability Reporting in the Mining Sector}, series = {Tripodos}, volume = {2025}, journal = {Tripodos}, number = {57}, publisher = {Blanquerna School of Communication and International Relations}, address = {Barcelona}, issn = {1138-3305}, doi = {10.51698/tripodos.2025.57.06}, pages = {78 -- 97}, abstract = {Greenwashing is a common form of corporate disinformation that is often challenging for the general public to detect. Companies engage in greenwashing in their reporting to mislead shareholders and stakeholders about their environmental efforts, seeking to enhance legitimacy and gain competitive advantages. While systems for identifying greenwashing exist, they typically focus on advertising, leaving greenwashing in corporate reports underexamined. This study aims to address this gap by conducting a qualitative content analysis of a climate report from a mining and commodity trading company, considering the company's profile, the report's target audience, and current research. The findings reveal that the company employs numerous subtle greenwashing strategies to project a more sustainable image through strategic omissions, hedging and vague long-term goals. Moreover, this research broadens the scope of greenwashing analysis to include corporate reporting, which targets a more informed audience, such as shareholders and experts, rather than the general public. The results underscore the need for stricter regulation of sustainability reports and highlight the importance of fostering greater scrutiny among shareholders.}, language = {en} } @incollection{MuehlbergerSchoplocherSteffens, author = {M{\"u}hlberger, Thomas and Schoplocher, Paul Dragos and Steffens, Oliver}, title = {Thermische Geb{\"a}udesimulation: aktuelle Anwendungen und Erweiterungen mittels der Finite-Elemente-Methode}, series = {Bauphysik-Kalender 2025: Simulationen, BIM und KI}, booktitle = {Bauphysik-Kalender 2025: Simulationen, BIM und KI}, editor = {Fouad, Nabil A.}, publisher = {Ernst \& Sohn}, address = {Berlin}, isbn = {9783433034514}, doi = {10.1002/9783433612095.ch12}, pages = {435 -- 468}, abstract = {Nach einem kurzen historischen Abriss der Entwicklung der Geb{\"a}udesimulation wird die aktuell {\"u}bliche gleichungsbasierte Kompaktmodell-Simulation beschrieben und deren praktische Anwendung aufgezeigt. Dabei wird auf die Bedeutung der Validierung von Simulationstools und auf etablierte Validierungsstandards eingegangen. Geb{\"a}udesimulation dient der Optimierung des Bauens in allen Planungsphasen. Mit Praxisbeispielen vom sommerlichen W{\"a}rmeschutz bis hin zur Modellierung innovativer Konstruktionen werden unterschiedliche Einsatzbereiche demonstriert. Im zweiten Teil wird die Verwendung der Finite-Elemente-Methode (FEM) f{\"u}r die bauphysikalische Modellierung vorgestellt. Anhand von Beispielen zeigen wir, dass die (rechenzeitintensive) FEM aufgrund einer detaillierteren Modellierung von Geometrie, Strahlung und Konvektion pr{\"a}zisere Simulationsergebnisse liefert. Zum Abschluss werden Wege vorgeschlagen, wie dies zur Erweiterung der schnelleren Kompaktmodell-Simulation eingesetzt werden kann.}, language = {de} } @article{JobstRecumEcijaArenasetal.2023, author = {Jobst, Simon and Recum, Patrick and {\´E}cija-Arenas, {\´A}ngela and Moser, Elisabeth and Bierl, Rudolf and Hirsch, Thomas}, title = {Semi-Selective Array for the Classification of Purines with Surface Plasmon Resonance Imaging and Deep Learning Data Analysis}, series = {ACS sensors}, volume = {8}, journal = {ACS sensors}, number = {9}, publisher = {American Chemical Society}, doi = {10.1021/acssensors.3c01114}, pages = {3530 -- 3537}, year = {2023}, abstract = {In process analytics or environmental monitoring, the real-time recording of the composition of complex samples over a long period of time presents a great challenge. Promising solutions are label-free techniques such as surface plasmon resonance (SPR) spectroscopy. They are, however, often limited due to poor reversibility of analyte binding. In this work, we introduce how SPR imaging in combination with a semi-selective functional surface and smart data analysis can identify small and chemically similar molecules. Our sensor uses individual functional spots made from different ratios of graphene oxide and reduced graphene oxide, which generate a unique signal pattern depending on the analyte due to different binding affinities. These patterns allow four purine bases to be distinguished after classification using a convolutional neural network (CNN) at concentrations as low as 50 μM. The validation and test set classification accuracies were constant across multiple measurements on multiple sensors using a standard CNN, which promises to serve as a future method for developing online sensors in complex mixtures.}, language = {en} } @inproceedings{HauslerWunderlichFischeretal., author = {Hausler, Peter and Wunderlich, Lukas and Fischer, Johannes and Pfab, Christina and Heckscher, Simon and Hirsch, Thomas and Bierl, Rudolf}, title = {Surface plasmon resonance imaging for detection of drug metabolites in water}, series = {Proceedings of SPIE, Optical Sensors 2019, 1 - 4 April 2019, Prague, Czech Republic}, volume = {Vol. 11028}, booktitle = {Proceedings of SPIE, Optical Sensors 2019, 1 - 4 April 2019, Prague, Czech Republic}, issn = {0277-786X}, doi = {10.1117/12.2522324}, pages = {11}, abstract = {The analysis of surface water, groundwater, drinking water as well as sewage is important to get information about the contamination of the water cycle. Currently, these time-consuming investigations require special equipment, like for example hyphenated mass spectrometry. Surface plasmon resonance (SPR) is a faster alternative as it is highly sensitive to changes in the dielectric medium next to a thin metal layer and makes it a quasi-universal detector. Therefore, and due to the labelfree nature, SPR is a widely used sensing tool for real-time monitoring of molecular interactions of various analytes. SPR imaging (SPRi) has several advantages to standard surface plasmon resonance, as it allows to observe many analytes in parallel as well as the integration of referencing technologies. However, the homogenous illumination of a large area (several millimeters) with a small light source is challenging and demands new approaches. Allopurinol, a drug used to lower the blood concentration of urate and hence decrease the affection of gout, gets metabolized to oxipurinol in the body and dropped out almost entirely by urinary excretion. After wastewater treatment, concentrations of oxipurinol up to 21.7 μg•L-1 are detected. Further tracking of oxipurinol in the urban water cycle showed its presence in rivers and streams or even in groundwater. Therefore, the high biological stability of oxipurinol allows this molecule to be used as a marker for domestic wastewater in the environment. For the detection of oxipurinol by SPR graphene was used as receptive layer, as the analyte can bind via π-stacking to this surface. An SPRi technique was developed and compared to conventional SPR system for the detection of oxipurinol.}, language = {en} } @inproceedings{HauslerRothAumeretal., author = {Hausler, Peter and Roth, Carina and Aumer, F. and Vitzthumecker, Thomas and Genslein, Christa and Hirsch, Thomas and Bierl, Rudolf}, title = {Miniaturisiertes Sensorsystem zur Oberfl{\"a}chenplasmonenresonanzspektroskopie}, series = {118. Jahrestagung der deutschen Gesellschaft f{\"u}r angewandte Optik (DGaO), 6.-10. Juni 2017, Dresden}, booktitle = {118. Jahrestagung der deutschen Gesellschaft f{\"u}r angewandte Optik (DGaO), 6.-10. Juni 2017, Dresden}, abstract = {Die Oberfl{\"a}chenplasmonenresonanzspektroskopie (SPR) wird aufgrund ihrer Vorz{\"u}ge der zerst{\"o}rungs- und markierungsfreien Messung, sowie der hohen Sensitivit{\"a}t sehr erfolgreich im Labormaßstab eingesetzt. Aufgrund der hohen Kosten geschieht dies bislang haupts{\"a}chlich in der Bioanalytik und dem Wirkstoffscreening. Gezeigt wird ein Ansatz, mit dem diese Technologie auf ein ultrakompaktes, kosteng{\"u}nstiges Sensorsystem {\"u}bertragen wird, welches in der Lage ist, hoch-sensitiv {\"A}nderungen im Brechungsindex von 10-6 Einheiten (RIU) zu detektieren. F{\"u}r Wasser bewirkt eine Temperaturschwankung von 1 K bereits eine {\"A}nderung von 1 mRIU. Daher wird durch ein integriertes Referenzsystem, sowie die Miniaturisierung erreicht, dass das System gegen{\"u}ber Temperaturschwankungen, weitestgehend stabil ist. In dem MOEMS wird anstatt der konventionellen 1-Punkt bzw. 2-Punkt Messung ein bildgebendes Verfahren angewendet. Die Sensorfl{\"a}che von 15 x 15 mm wird dabei mit einem handels{\"u}blichen 4 Mio. Pixel CMOS Sensor ausgewertet. Um verl{\"a}ssliche Datenpunkte zu erhalten ben{\"o}tigt man eine Fl{\"a}che von 10 x 10 Pixel. Demzufolge k{\"o}nnen auf dem Sensor theoretisch bis zu 40.000 Sensorspots parallel ausgewertet werden.}, language = {de} } @inproceedings{HauslerGensleinRothetal., author = {Hausler, Peter and Genslein, Christa and Roth, Carina and Vitzthumecker, Thomas and Hirsch, Thomas and Bierl, Rudolf}, title = {Miniaturized Surface Plasmon Resonance based Sensor System}, series = {Proceedings of the 6th International Conference on Photonics, Optics and Laser Technology - PHOTOPTICS, Funchal, Madeira, Portugal}, booktitle = {Proceedings of the 6th International Conference on Photonics, Optics and Laser Technology - PHOTOPTICS, Funchal, Madeira, Portugal}, publisher = {SciTePress}, isbn = {978-989-758-286-8}, doi = {10.5220/0006555400630066}, pages = {63 -- 66}, abstract = {We describe the miniaturization of the Surface Plasmon Resonance (SPR) technology which mainly finds its applications in pharmaceutical screening and biotechnology so far. SPR spectroscopy is a label-free, non-destructive and highly sensitive measurement principle detecting changes in the refractive index in striking distance to a gold surface. A transfer of this technology to a miniaturized sensor will broaden the range of possible applications. A promising feature which is included in the miniaturized system is the angle-dependent recording of the SPR signals without moving parts. Commercial SPR assays are mainly working with a small number of sensing spots. In contrast, the SPR imaging system shown here will allow to use an array of many sensing spots. In combination with chemical receptors designed as an artificial nose, the simultaneous detection of many analytes is envisioned for future applications.}, language = {en} } @article{GensleinHauslerKirchneretal., author = {Genslein, Christa and Hausler, Peter and Kirchner, Eva-Maria and Bierl, Rudolf and Baeumner, Antje J. and Hirsch, Thomas}, title = {Graphene-enhanced plasmonic nanohole arrays for environmental sensing in aqueous samples}, series = {Beilstein Journal of Nanotechnology}, journal = {Beilstein Journal of Nanotechnology}, number = {7}, doi = {10.3762/bjnano.7.150}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:355-epub-398623}, pages = {1564 -- 1573}, abstract = {The label-free nature of surface plasmon resonance techniques (SPR) enables a fast, specific, and sensitive analysis of molecular interactions. However, detection of highly diluted concentrations and small molecules is still challenging. It is shown here that in contrast to continuous gold films, gold nanohole arrays can significantly improve the performance of SPR devices in angle-dependent measurement mode, as a signal amplification arises from localized surface plasmons at the nanostructures. This leads consequently to an increased sensing capability of molecules bound to the nanohole array surface. Furthermore, a reduced graphene oxide (rGO) sensor surface was layered over the nanohole array. Reduced graphene oxide is a 2D nanomaterial consisting of sp2-hybridized carbon atoms and is an attractive receptor surface for SPR as it omits any bulk phase and therefore allows fast response times. In fact, it was found that nanohole arrays demonstrated a higher shift in the resonance angle of 250-380\% compared to a continuous gold film. At the same time the nanohole array structure as characterized by its diameter-to-periodicity ratio had minimal influence on the binding capacity of the sensor surface. As a simple and environmentally highly relevant model, binding of the plasticizer diethyl phthalate (DEP) via π-stacking was monitored on the rGO gold nanohole array realizing a limit of detection of as low as 20 nM. The concentration-dependent signal change was studied with the best performing rGO-modified nanohole arrays. Compared to continuous gold films a diameter-to-periodicity ratio (D/P) of 0.43 lead to a 12-fold signal enhancement. Finally, the effect of environmental waters on the sensor was evaluated using samples from sea, lake and river waters spiked with analytically relevant amounts of DEP during which significant changes in the SPR signal are observed. It is expected that this concept can be successfully transferred to enhance the sensitivity in SPR sensors.}, language = {en} } @article{SokolowskiTintenBlomeBlumsetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Blums, Juris and Dietrich, Clemens and Tarsevitch, Alexander and Horn-von Hoegen, Michael and von der Linde, Dietrich and Cavalleri, Andrea and Kammler, Martin and Uschmann, Ingo and Foerster, Eckhart}, title = {Femtosecond X-ray Diffraction Study of Large Amplitude Coherent Optical Phonons in Laser-Excited Bismuth}, series = {Conference on Lasers and Electro-Optics, 1-6 June 2003, Baltimore, Maryland}, journal = {Conference on Lasers and Electro-Optics, 1-6 June 2003, Baltimore, Maryland}, publisher = {Optical Society of America}, abstract = {Femtosecond time-resolved X-ray diffraction was used to directly study optical phonons in laser-excited Bismuth. A periodic modulation of the diffraction efficiency reveals initially coherent lattice distortions with atomic displacements of nearly 10\% of the nearest- neighbor-distance.}, language = {en} } @inproceedings{HauslerGensleinRothetal., author = {Hausler, Peter and Genslein, Christa and Roth, Carina and Hirsch, Thomas and Bierl, Rudolf}, title = {Mikro-Opto-Elektro-Mechanisches Sensorsystem zur Oberfl{\"a}chenplasmonenresonanzspektroskopie}, series = {MikroSystemTechnik Kongress 2017 : MEMS, Mikroelektronik, Systeme 23.-25. Oktober 2017 in M{\"u}nchen}, booktitle = {MikroSystemTechnik Kongress 2017 : MEMS, Mikroelektronik, Systeme 23.-25. Oktober 2017 in M{\"u}nchen}, number = {CD-ROM}, publisher = {VDE-Verlag}, address = {Berlin}, isbn = {978-3-8007-4491-6}, pages = {645 -- 647}, abstract = {Gezeigt wird die Miniaturisierung eines Messsystems f{\"u}r Oberfl{\"a}chenplasmonenresonanzspektroskopie (SPR), einer markierungs-, sowie zerst{\"o}rungsfreien als auch hoch sensitiven Technologie. Aufgrund der hohen Kosten klassischer SPR-Ger{\"a}te wird sie bisher jedoch vornehmlich in der Bio- und Medizintechnik eingesetzt. Das Messprinzip erm{\"o}glicht die Erfassung von Brechungsindex{\"a}nderungen nahe einer Oberfl{\"a}che. Der Transfer dieser Technologie von Laborger{\"a}ten hin zu einem miniaturisierten Sensorsystem senkt die Kosten, macht das System robuster und erm{\"o}glicht so ein wesentlich breiteres Anwendungsspektrum. Ein sehr vielversprechendes Merkmal des hier vorgestellten Systems ist die M{\"o}glichkeit den SPR-Effekt winkelabh{\"a}ngig zur Lichtquelle ohne bewegliche Bauteile zu verfolgen. The miniaturization of Surface Plasmon Resonance (SPR) technology, which mainly finds its applications in pharmaceutical screening and biotechnology so far, is described. SPR spectroscopy is a label-free, non destructive and highly sensitive measurement principle which is capable of detecting changes in the refractive index in striking distance to a gold surface. A transfer of this technology to a miniaturized sensor will broaden the range of possible applications. A promising feature which is included in the miniaturized system is the angle-dependent recording of the SPR signals without moving parts.}, language = {de} } @article{LindnerPipaKarpenetal., author = {Lindner, Matthias and Pipa, Andrei V. and Karpen, Norbert and Hink, R{\"u}diger and Berndt, Dominik and Foest, R{\"u}diger and Bonaccurso, Elmar and Weichwald, Robert and Friedberger, Alois and Caspari, Ralf and Brandenburg, Ronny and Schreiner, Rupert}, title = {Icing Mitigation by MEMS-Fabricated Surface Dielectric Barrier Discharge}, series = {Applied Sciences}, volume = {11}, journal = {Applied Sciences}, number = {23}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/app112311106}, pages = {1 -- 17}, abstract = {Avoiding ice accumulation on aerodynamic components is of enormous importance to flight safety. Novel approaches utilizing surface dielectric barrier discharges (SDBDs) are expected to be more efficient and effective than conventional solutions for preventing ice accretion on aerodynamic components. In this work, the realization of SDBDs based on thin-film substrates by means of micro-electro-mechanical-systems (MEMS) technology is presented. The anti-icing performance of the MEMS SDBDs is presented and compared to SDBDs manufactured by printed circuit board (PCB) technology. It was observed that the 35 mu m thick electrodes of the PCB SDBDs favor surface icing with an initial accumulation of supercooled water droplets at the electrode impact edges. This effect was not observed for 0.3 mu m thick MEMS-fabricated electrodes indicating a clear advantage for MEMS-technology SDBDs for anti-icing applications. Titanium was identified as the most suitable material for MEMS electrodes. In addition, an optimization of the MEMS-SDBDs with respect to the dielectric materials as well as SDBD design is discussed.}, language = {en} } @inproceedings{GensleinHauserKirchneretal., author = {Genslein, Christa and Hauser, Peter and Kirchner, Eva-Maria and Bierl, Rudolf and Baeumner, Antje J. and Hirsch, Thomas}, title = {Detection of small molecules with surface plasmon resonance by synergistic plasmonic effects of nanostructured surfaces and graphene}, series = {SPIE Proceedings, Plasmonics in Biology and Medicine XIV, 2017, San Francisco, California}, volume = {10080}, booktitle = {SPIE Proceedings, Plasmonics in Biology and Medicine XIV, 2017, San Francisco, California}, number = {1008001F}, doi = {10.1117/12.2252256}, abstract = {Surface plasmon resonance depends on the dielectric medium at the vicinity and makes it a quasi-universal detector. Therefore, and due to the label-free nature, SPR is a widely used sensing tool for real-time monitoring molecular interactions of various analytes. However, detection of highly diluted analytes and small molecules (< 400 Da) is still challenging. Gold nanohole arrays provide plasmonic hotspots with improved surface sensitivity and 2D carbon nanomaterials enable binding near the surface. Both effects together are promising in the development of SPR sensors for the efficient determination of small molecules. Graphene is known for efficient binding of molecules with delocalized aromatic π-systems. Additionally, the electromagnetic field is locally enhanced and modulated by the interaction of graphene photonics with the plasmonics of metal nanostructures. The advantages of chemical vapor deposition (CVD) graphene over reduced graphene oxide (rGO) is illustrated by a proof of concept study. In comparison to substrates consisting of a continuous film the surface sensitivity is enhanced for a nanohole arrays and further improved for CVD graphene functionalization in contrast to rGO. The feasibility of the sensor was demonstrated for the detection of adenine down to a concentration of 0.9 μM.}, language = {en} } @inproceedings{HauslerHollerHirschetal., author = {Hausler, Peter and Holler, Sven and Hirsch, Thomas and Bierl, Rudolf}, title = {High integrated miniaturized sensor based on Surface Plasmon Resonance}, series = {International Biosensor Conference, 11th Workshop on Biosensors \& Bioanalytical Microtechniques in Environmental, Food \& Clinical Analysis, BBMEC 11, 26.-30. September 2015, Regensburg, Germany}, booktitle = {International Biosensor Conference, 11th Workshop on Biosensors \& Bioanalytical Microtechniques in Environmental, Food \& Clinical Analysis, BBMEC 11, 26.-30. September 2015, Regensburg, Germany}, language = {en} } @inproceedings{HauslerHollerHirschetal., author = {Hausler, Peter and Holler, Sven and Hirsch, Thomas and Bierl, Rudolf}, title = {Miniaturisierte Oberfl{\"a}chenplasmonenresonanz Sensorplattform}, series = {MEMS, Mikroelektronik, Systeme, MikroSystemTechnik Kongress 2015, 26.- 28. Oktober 2015, Karlsruhe, proceedings}, booktitle = {MEMS, Mikroelektronik, Systeme, MikroSystemTechnik Kongress 2015, 26.- 28. Oktober 2015, Karlsruhe, proceedings}, publisher = {VDE Verlag}, address = {Berlin}, isbn = {978-3-8007-4100-7}, language = {de} } @article{WallKrenzerWippermannetal., author = {Wall, Simone and Krenzer, Boris and Wippermann, Stefan and Sanna, Simone and Klasing, Friedrich and Hanisch-Blicharski, Anja and Kammler, Martin and Schmidt, Wolf Gero and Horn-von Hoegen, Michael}, title = {Atomistic picture of charge density wave formation at surfaces}, series = {Physical review letters}, volume = {109}, journal = {Physical review letters}, number = {18}, publisher = {APS}, doi = {10.1103/PhysRevLett.109.186101}, abstract = {We used ultrafast electron diffraction and density-functional theory calculations to gain insight into the charge density wave (CDW) formation on In/Si(111). Weak excitation by a femtosecond-laser pulse results in the melting of the CDW. The immediate freezing is hindered by a barrier for the motion of atoms during the phase transition: The melted CDW constitutes a long-lived, supercooled phase and is strong evidence for a first-order transition. The freezing into the CDW is triggered by preexisting adsorbates. Starting at these condensation nuclei, the CDW expands one dimensionally on the In/Si(111) surface, with a constant velocity of more than 80 m/s.}, language = {en} } @article{FriggeKalusKlasingetal., author = {Frigge, Tim and Kalus, Annika and Klasing, Friedrich and Kammler, Martin and Hanisch-Blicharski, Anja and Horn-von Hoegen, Michael}, title = {Nanoscale Heat Transport in Self-Organized Ge Clusters on Si(001)}, series = {MRS Online Proceedings Library}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/opl.2013.148}, pages = {45 -- 50}, abstract = {Ultrafast time resolved transmission electron diffraction (TED) in a reflection geometry was used to study the cooling behavior of self-organized, well defined nanoscale germanium hut and dome clusters on Si(001). The clusters were heated in a pump-probe scheme by fs-laser pulses. The resulting transient temperature rise was then determined from the drop in diffraction intensity caused by the Debye-Waller effect. From a cooling time of τ=177 ps we estimated a strongly reduced heat transfer compared with homogeneous films of equivalent thickness.}, language = {en} } @article{MoellenbeckHanischBlicharskiSchneideretal., author = {M{\"o}llenbeck, Simone and Hanisch-Blicharski, Anja and Schneider, Paul and Ligges, Manuel and Zhou, Ping and Kammler, Martin and Krenzer, Boris and Horn-von Hoegen, Michael}, title = {Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces}, series = {MRS Online Proceedings Library}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/PROC-1230-MM03-09}, abstract = {The dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4 {\~A}— 2) to a(2 {\~A}— 1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4 {\~A}— 2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4 {\~A}— 1) reconstruction which undergoes a Peierls like phase transition to a (8 {\~A}— "2") reconstruction below 100 K. Upon laser excitation with a fluence of 3.4 mJ/cm 2 at a temperature of 72 K the phase transition was strongly driven. The (8 {\~A}— "2")-diffraction spots instantaneously disappears, while the intensity of the (4 {\~A}— 1)-spots increases. This increase of the (4 {\~A}— 1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface. {\^A}© 2010 Materials Research Society.}, language = {en} } @article{LuNicoulShymanovichetal., author = {Lu, Wei and Nicoul, Matthieu and Shymanovich, Uladzimir and Tarsevitch, Alexander and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, Dietrich and Sokolowski-Tinten, Klaus}, title = {Extreme Phonon Softening in Laser-excited Bismuth - Towards an Inverse Peierls-transition}, series = {MRS Online Proceedings Library}, volume = {1230}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/PROC-1230-MM03-05}, abstract = {Large amplitude coherent optical phonons have been investigated in laser-excited Bismuth by means of femtosecond time-resolved X-ray diffraction. For absorbed laser fluences above 2 mJ/cm2, the experimental data reveal an extreme softening of the excited A1g-mode down to frequencies of about 1 THz, only 1/3 of the unperturbed A1g-frequency. At even stronger excitation the measured diffraction signals no longer exhibit an oscillatory behavior presenting strong indication that upon intense laser-excitation the Peierls-distortion, which defines the equilibrium structure of Bismuth, can be transiently reversed.}, language = {en} } @article{HanischBlicharskiKrenzerMoellenbecketal., author = {Hanisch-Blicharski, Anja and Krenzer, Boris and M{\"o}llenbeck, Simone and Ligges, Manuel and Zhou, Ping and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Transient Cooling of Ultrathin Epitaxial Bi(111)-Films on Si(111) Upon Femtosecond Laser Excitation Studied by Ultrafast Reflection High Energy Electron Diffraction}, series = {MRS Online Proceedings Library}, journal = {MRS Online Proceedings Library}, publisher = {Springer}, doi = {10.1557/PROC-1172-T04-08}, pages = {1 -- 6}, abstract = {With time resolved ultrafast electron diffraction the cooling process across the interface between a thin film and the underlying substrate was studied after excitation with short laser pulses. From the exponential decay of the surface temperature evolution a thermal boundary conductance of 1430 W/(cm2K) is determined for a 9.7 nm thin Bi(111) film on Si(111). A linear dependence between laser fluence and initial temperature rise was measured for film-thicknesses between 2.5 nm and 34.5 nm. The ratio of initial temperature rise and laser fluence for different film-thicknesses is compared to a model taking multilayer optics into account. The data agree well with this model.}, language = {en} } @article{AlFalouKammlerHornvonHoegen, author = {Al-Falou, A. A. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Strain state analysis of hetero-epitaxial systems}, series = {Europhysics Letters}, volume = {69}, journal = {Europhysics Letters}, number = {4}, publisher = {IOP}, doi = {10.1209/epl/i2004-10399-6}, pages = {570 -- 576}, abstract = {We present a new method to analyze the strain state of epitaxial hetero structures by high-resolution spot profile analysis low-energy electron diffraction. From the variation of the spot profiles with the vertical scattering vector we determine the hetero film roughness, the change of interlayer spacing due to tetragonal distortion, and the variation of the interlayer distance due to partial relaxation of the strained rough film. The practical implementation of this method is simple and can be used to determine the onset of strain-relieving defects during the growth process.}, language = {en} } @article{KammlerHornvonHoegen, author = {Kammler, Martin and Horn-von Hoegen, Michael}, title = {Low energy electron diffraction of epitaxial growth of bismuth on Si(111)}, series = {Surface Science}, volume = {576}, journal = {Surface Science}, number = {1-3}, publisher = {Elsevier}, doi = {10.1016/j.susc.2004.11.033}, pages = {56 -- 60}, abstract = {The epitaxial growth of Bi on Si(1 1 1) studied by spot profile analyzing low energy electron diffraction shows for low coverage rotationally disordered Bi cluster with preferred orientations following the threefold symmetry of the Si substrate. With further deposition the Bi cluster coalesces and the surface orientation changes from the pseudo cubic Bi(1 1 0) surface orientation of the Bi cluster into the hexagonal Bi(1 1 1) surface of the resulting Bi film.}, language = {en} } @inproceedings{SidersCavalleriTothetal., author = {Siders, C. W. and Cavalleri, Andrea and T{\´o}th, Csaba and Wilson, K. R. and Squier, Jeff A. and Barty, C. P. J. and Kammler, Martin and Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D.}, title = {Femtosecond X-ray diffraction of short-pulse irradiated semiconductors}, series = {Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 24-24 May 2002, Long Beach, CA, USA}, booktitle = {Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 24-24 May 2002, Long Beach, CA, USA}, publisher = {IEEE}, doi = {10.1109/CLEO.2002.1033997}, pages = {297 -- 298}, abstract = {Summary form only given, as follow. Ultrafast optical-pump, X-ray diffraction probe experiments are providing new ways to study transient processes including the direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place. Current table-top-terawatt femtosecond laser systems provide an attractive source of few-hundred femtosecond duration bursts of angstrom-scale X-ray radiation with fluxes comparable to standard rotating anode sources. Their compact size enables time resolved structural dynamics to be studied in the small laboratory with temporal resolution better than typical molecular vibrational periods. Ultrafast structural dynamics in crystalline samples are readily studied with such systems and experiments to be discussed in this talk include ultrafast non-thermal solid-to-liquid transition in thin single-crystal Ge-111 films grown on Si-111 substrates; ultrafast non-thermal solid-to-solid transitions in bulk vanadium dioxide from a low temperature insulating phase to a high temperature metallic phase; and harmonic and anharmonic coherent acoustic dynamics in layered Ge-111/Si-111 and bulk GaAs-111 samples. Future improvements in high-average power short-pulse lasers will enable the study of a wider class of materials such as amorphous solids or liquid-phase dynamics of simple molecules, while proposed 4th generation light sources based upon single-pass X-ray free-electron lasers will permit singleshot structural determination of complex biomolecules.}, language = {en} } @article{SokolowskiTintenBlomeBlumsetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Blums, Juris and Cavalleri, Andrea and Dietrich, Clemens and Tarasevitch, Alexander and Uschmann, Ingo and F{\"o}rster, Eckhard and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, Dietrich}, title = {Femtosecond X-ray measurement of coherent lattice vibrations near the Lindemann stability limit}, series = {Nature}, volume = {422}, journal = {Nature}, number = {6929}, publisher = {Springer}, doi = {10.1038/nature01490}, pages = {287 -- 289}, abstract = {The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10(-14) to 10(-12) s. Until recently, only optical techniques were capable of providing adequate time resolution, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-ray diffraction. However, the measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase, has to date remained obscure. Here we report time-resolved X-ray diffraction measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance-near the Lindemann limit-leads to a subsequent loss of long-range order, which is most probably due to melting of the material.}, language = {en} } @article{HildSeifertKammleretal., author = {Hild, R. and Seifert, C. and Kammler, Martin and Meyer zu Heringdorf, Frank-Joachim and Horn-von Hoegen, Michael and Zhachuk, R.A and Olshanetsky, B.Z}, title = {Kinetics of Au induced faceting of vicinal Si(111)}, series = {Surface Science}, volume = {512}, journal = {Surface Science}, number = {1-2}, publisher = {Elsevier}, doi = {10.1016/S0039-6028(02)01666-7}, pages = {117 -- 127}, abstract = {Au induced faceting of vicinal Si(1 1 1) has been studied during adsorption at elevated temperature by spot profile analyzing of low energy electron diffraction and after quenching to room temperature by scanning tunneling microscopy. On the surfaces inclined towards five different types of facets form with increasing Au coverage at adsorption temperatures Tads below 800 °C. They are (4 4 3), (7 7 5), (5 5 3), a stepped (2 2 1), and the (3 3 1) facets. Atomic models for the (5 5 3) and (7 7 5) facet planes are proposed on the basis of high resolution STM images. At C we found the formation of an ordered step train which covers the entire surface. With further increasing Au coverage the stepped surface decomposes again into (1 1 1) terraces and step bunches. Driving force is the formation of the Si(1 1 1)-(5×2)-Au reconstruction.}, language = {en} } @article{SokolowskiTintenHornvonHoegenvonderLindeetal., author = {Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Kammler, Martin}, title = {Transient lattice dynamics in fs-laser-excited semiconductors probed by ultrafast X-ray diffraction}, series = {Journal de Physique IV}, volume = {11}, journal = {Journal de Physique IV}, number = {Pr2}, publisher = {EDP}, doi = {10.1051/jp4:2001290}, pages = {473 -- 477}, abstract = {A study of lattice dynamics in fs-laser-excited crystalline bulk Ge and Ge/Si-heterostructures, using time-resolved x-ray diffraction, was presented. Fast energy transport deep into the bulk of the material, coherent acoustic phonon dynamics, lattice anharmonicity, and vibrational transport across a buried interfaces were observed. Graphs showing time-dependent shifts of the centroid of the measured rocking curves in the Ge-overlayer and in the Si-substrate for different fluences, were presented.}, language = {en} } @article{SokolowskiTintenCavalleriSidersetal., author = {Sokolowski-Tinten, Klaus and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Kammler, Martin and Horn-von Hoegen, Michael and von der Linde, D. and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R.}, title = {Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures}, series = {Chemical Physics}, volume = {66}, journal = {Chemical Physics}, publisher = {Springer}, doi = {10.1007/978-3-642-56546-5_81}, pages = {281 -- 283}, abstract = {Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed.}, language = {en} } @inproceedings{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Blums, Juris and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Structural dynamics in laser-excited solids investigated with femtosecond x-ray diffraction}, series = {2002 Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 19-24 May 2002, Long Beach, CA, USA}, booktitle = {2002 Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 19-24 May 2002, Long Beach, CA, USA}, publisher = {IEEE}, doi = {10.1109/QELS.2002.1031182}, pages = {115 -- 116}, abstract = {Summary form only given. Ultrashort x-ray pulses offer a unique combination of atomic-scale spatial and temporal resolution, which permits direct measurements of structural transients on an ultrafast time scale. Using time-resolved X-ray diffraction with femtosecond, multi-keV X-ray pulses we have studied transient lattice dynamics in optically excited semiconductors.}, language = {en} } @article{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Tarasevitch, A. and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Femtosecond x-ray measurement of ultrafast melting and large acoustic transients}, series = {Physical review letters}, volume = {87}, journal = {Physical review letters}, publisher = {APS}, doi = {10.1103/PhysRevLett.87.225701}, abstract = {Time-resolved x-ray diffraction with ultrashort ( approximately 300 fs), multi-keV x-ray pulses has been used to study the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germanium. Nonthermal melting is observed to take place within 300-500 fs. Following ultrafast melting we observe strong acoustic perturbations evolving on a picosecond time scale.}, language = {en} } @article{SokolowskiTintenBlomeDietrichetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Dietrich, Clemens and Tarasevitch, A. and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Squier, Jeff A. and Kammler, Martin}, title = {Femtosecond time-resolved X-ray diffraction study of ultrafast structural dynamics in laser-excited solids}, series = {International Conference on Ultrafast Phenomena, 12 May 2002, Vancouver Canada}, volume = {71}, journal = {International Conference on Ultrafast Phenomena, 12 May 2002, Vancouver Canada}, publisher = {Optica Publishing Grou}, doi = {10.1007/978-3-642-59319-2_10}, pages = {36 -- 38}, abstract = {Time-resolved x-ray diffraction with sub-300 fs, multi-keV x-ray pulses was used to study ultrafast lattice dynamics in laser-irradiated germanium and bismuth. In bismuth strong excitation of optical phonons is observed prior to disordering of the material.}, language = {en} } @unpublished{TringidesConradMenzeletal.2002, author = {Tringides, Michael C. and Conrad, E. H. and Menzel, Andreas and Voss, Neil R. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Dynamics of atomic steps on Si(001) studied by temporal LEED spectroscopy [Poster]}, year = {2002}, abstract = {While surface kinetics measurements for single atom diffusion have proliferated, little work exists attempting to measure surface dynamics under equilibrium conditions. We will present our recent work on developing Temporal LEED Spectroscopy (TLS) as a dynamic probe of surfaces capable of kinetics measurements at both high temperatures and surface coverages. By tuning the diffraction to specific structural entities such as steps, islands, etc., and monitoring the diffracted signal as a function of time, dynamics information about these structures can be obtained. As an example we will present TLS results for the dynamics of step fluctuations on Si(001) [1]. We have measured activation energies and identified step-edge diffusion as the rate limiting process for 950K < T < 1130K. Although this result is in apparent disagreement with earlier work, a careful analysis, considering crossover temperatures between different microscopic processes, can reconcile the differences. 1. M. Kammler, et al., Phys. Rev. B (in press).}, language = {en} } @article{HornvonHoegenMeyerzuHeringdorfKammleretal., author = {Horn-von Hoegen, Michael and Meyer zu Heringdorf, Frank-Joachim and Kammler, Martin and Schaeffer, C. and Reinking, D. and Hofmann, K. R.}, title = {Bi surfactant mediated epitaxy of Ge on Si(111)}, series = {Thin Solid Films}, volume = {343-344}, journal = {Thin Solid Films}, publisher = {Elsevier}, doi = {10.1016/S0040-6090(98)01659-9}, pages = {579 -- 582}, abstract = {We have tested Bi for the surfactant mediated epitaxy of Ge on Si(111). Islanding of Ge is prevented and a 2D layer growth of smooth and continuous Ge films is observed. The lattice mismatch is accommodated by a periodic array of dislocations confined to the Si/Ge interface. The large covalent radius of Bi reduces the binding energy, allowing Very efficient segregation and low doping levels even at low growth temperatures. Unfortunately, this results also in a high Bi desorption flux limiting the possible growth temperatures below 600 degrees C. Consequently the Ge films show a high defect density in the order of 10(8) cm(-2) for stacking faults and 10(9) cm(-2) for dislocations which limit electron Hall mobility to values below 700 cm(2)/V s at room temperature.}, language = {en} } @article{CavalleriSidersBrownetal., author = {Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and Leitner, D. M. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Kammler, Martin}, title = {Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction}, series = {Physical review letters}, volume = {85}, journal = {Physical review letters}, number = {3}, publisher = {APS}, doi = {10.1103/PhysRevLett.85.586}, pages = {586 -- 589}, abstract = {Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium.}, language = {en} } @article{SokolowskiTintenHornvonHoegenvonderLindeetal., author = {Sokolowski-Tinten, Klaus and Horn-von Hoegen, Michael and von der Linde, D. and Cavalleri, Andrea and Siders, C. W. and Brown, F. L. H. and T{\´o}th, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Kammler, Martin}, title = {Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures}, series = {International Conference on Ultrafast Phenomena , 9 July 2000, Charleston}, journal = {International Conference on Ultrafast Phenomena , 9 July 2000, Charleston}, publisher = {Optica}, abstract = {Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed.}, language = {en} } @article{SidersCavalleriSokolowskiTintenetal., author = {Siders, C. W. and Cavalleri, Andrea and Sokolowski-Tinten, Klaus and T{\´o}th, Csaba and Guo, T. and Kammler, Martin and Horn-von Hoegen, Michael and Wilson, K. R. and von der Linde, D. and Barty, C. P. J.}, title = {Detection of nonthermal melting by ultrafast X-ray diffraction}, series = {Science}, volume = {286}, journal = {Science}, number = {5443}, doi = {10.1126/science.286.5443.1340}, pages = {1340 -- 1342}, abstract = {Using ultrafast, time-resolved, 1.54 angstrom x-ray diffraction, thermal and ultrafast nonthermal melting of germanium, involving passage through nonequilibrium extreme states of matter, was observed. Such ultrafast, optical-pump, x-ray diffraction probe measurements provide a way to study many other transient processes in physics, chemistry, and biology, including direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place.}, language = {en} } @article{ReinkingKammlerHoffmannetal., author = {Reinking, D. and Kammler, Martin and Hoffmann, N. and Horn-von Hoegen, Michael and Hofmann, K. R.}, title = {Fabrication of high-mobility Ge p-channel MOSFETs on Si substrates}, series = {Electronics Letters}, volume = {35}, journal = {Electronics Letters}, number = {6}, publisher = {IET}, doi = {10.1049/el:19990349}, pages = {503 -- 504}, abstract = {The first fabrication of Ge p-channel MOSFETs (p-MOSFETs) on Si substrates is reported. A CMOS compatible process based on relaxed Ge layers grown on Si(111) substrates by surfactant mediated epitaxy (SME) was used. The non-optimised low temperature process yielded normally-off Ge p-MOSFETs with record channel drift mobilities of 430 cm2/Vs}, language = {en} } @incollection{KuhnFranziusMoelleretal., author = {Kuhn, Alexander and Franzius, Jan Niklas and M{\"o}ller, Dennis and Pralle, Norbert and Reich, Franziska and Hellmuth, Ren{\´e} and Tombeil, Anne-Sophie and Wenzel, G{\"u}nter and Linner, Thomas and Schmailzl, Marc and Hu, Rongbo and Bock, Thomas and Maufroy, Christophe and Kopp, Verena and B{\"o}lke, Nico and Daub, Urban}, title = {Kompetenzzentrum f{\"u}r Baurobotik im Hochbau (CONSAS) - F{\"o}rderkennzeichen 16SV8637}, series = {Roboter f{\"u}r Assistenzfunktionen: Konzeptstudien f{\"u}r die Interaktion in der Praxis}, booktitle = {Roboter f{\"u}r Assistenzfunktionen: Konzeptstudien f{\"u}r die Interaktion in der Praxis}, isbn = {9783731512448}, pages = {169 -- 207}, language = {de} } @article{SidersCavalleriSokolowskiTintenetal., author = {Siders, C. W. and Cavalleri, Andrea and Sokolowski-Tinten, Klaus and T{\´o}th, Csaba and Guo, T. and Kammler, Martin and Horn-von Hoegen, Michael and Wilson, K. R. and von der Linde, D. and Barty, C. P. J.}, title = {Direct Observation of Ultrafast Non-thermal Melting by Ultrafast X-ray Diffraction}, series = {Ultrafast Phenomena XII}, volume = {66}, journal = {Ultrafast Phenomena XII}, publisher = {Springer}, doi = {10.1007/978-3-642-56546-5_80}, pages = {276 -- 280}, abstract = {Ultrafast nonthermal melting of femtosecond laser-irradiated germanium was observed directly for the first time using sub-picosecond, 1.54-angstrom x-ray diffraction. Such measurements allow the study of transient atomic motion fundamental to many processes in physics, chemistry, and biology.}, language = {en} } @incollection{SokolowskiTintenvonderLindeSidersetal., author = {Sokolowski-Tinten, Klaus and von der Linde, D. and Siders, C. W. and Cavalleri, Andrea and T{\´o}th, Csaba and Guo, T. and Wilson, K. R. and Barty, C. P. J. and Kammler, Martin and Horn-von Hoegen, Michael}, title = {Lattice dynamics of femtosecond laser-excited semiconductors probed by ultrafast x-ray diffraction}, series = {Applications of High Field and Short Wavelength Sources VIII}, booktitle = {Applications of High Field and Short Wavelength Sources VIII}, publisher = {Optica}, doi = {10.1364/HFSW.1999.PD3}, abstract = {The present knowledge of the atomic structure of matter is to a large extent due to x-ray spectroscopies.}, language = {en} } @inproceedings{BuchnerWagnerHoeller, author = {Buchner, Stefan and Wagner, Marcus and H{\"o}ller, Christoph}, title = {Inverse Acoustic Characterization of Rigid Porous Media using Artificial Neural Networks}, series = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, booktitle = {Proceedings of DAS|DAGA 2025, 51st Annual Meeting on Acoustics, March 17-20, 2025, Copenhagen}, address = {Berlin}, organization = {Deutsche Gesellschaft f{\"u}r Akustik e.V. (DEGA), Berlin}, isbn = {978-3-939296-23-2}, doi = {10.71568/dasdaga2025.142}, pages = {847 -- 850}, abstract = {Porous sound absorbers can be described by the isotropic Biot model, and its fluid phase can be represented by the Champoux-Allard model. To apply these models to a given absorber material, the five acoustical and the four mechanical material parameters must be known. The direct measurement of these parameters is complex and requires cost-intensive measurement equipment. Current inverse methods to obtain these material parameters solve an optimization problem, trying to fit the absorption or impedance curve of the material model to the impedance tube measurement data. Solving this optimization problem, i.e. finding the global minimum, is not guaranteed in an acceptable amount of time, as the optimization problem possesses a multitude of local minima. This work proposes an alternative, data driven approach using artificial neural networks to obtain the material parameters necessary for the characterization of open porous materials. The approach only requires the results of standard impedance tube measurements. The characterization of rigid- and elastic frame materials has been investigated. The datasets were generated using the rigid and elastic frame models for porous absorbers. The approach shows good results for impedance curves generated by the analytical models, the validation with real-world impedance tube measurement data is currently under investigation.}, language = {en} }