FK 06 Fakultät für angewandte Naturwissenschaften und Mechatronik
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CIS (Cu(In,Ga)(S,Se)2) thin film solar cells show a high potential to achieve the efficiencies of Si wafer-based solar cells. The commonly applied patterning processes for the integrated interconnects are based on nanosecond laser ablation and mechanical scribing. Both methods introduce damages on the thin films by thermal effects and mechanical forces. By picosecond laser processing we realized all three patterning steps to the monolithic thin films CIS modules, namely the separation of the molybdenum back electrode, the absorber and the ZnO font electrode (P1, P2 and P3 respectively). We achieved an efficiency of 14.7% for 300 x 300 mm² modules.
A picosecond laser lift-off process of an about 0.5 μm thick Mo layer on a glass substrate can be induced by irradiating the layer from the glass side. A pump-probe setup for time- and space resolved microscopy is used to investigate the ablation process in a time domain from a few picoseconds up to 3.6 ns. The results display a bulging of Mo within 1 ns followed by a lift-off at times past 3.6 ns. Furthermore, the setup is used for in situ investigations of a multi pulse ablation through the whole layer stack (ZnO/CIS/Mo/Glass) of a CIS thin film solar cell.
Diese Vorlesung entstand aus dem Wunsch der Studenten heraus, einzelne Gebiete der Physik nach dem Absolvieren des Grundkurses Quantenphysik genauer zu durchleuchten. Dabei konnten die Studenten aus einem Gebietskanon auswählen. So ist zu erklären, dass nicht nur Themen der Quantenmechanik enthalten sind, sondern auch elementare Abschnitte über Schwingungen und Wellen sowie Dipole und die elektromagnetische Masse.
Thermodynamik
(2012)
Wir wollen uns mit thermodynamischen Gleichgewichten beschäftigen. Dazu arbeiten wir zunächst mit dem "naiven“ Begriff der Temperatur und untersuchen die thermischen Gesetzmäßigkeiten im Gas. Nach der Definition der Begriffe thermisches Gleichgewicht, thermodynamisches Gleichgewicht, abgeschlossenes, geschlossenes und offenes System erarbeiten wir uns die Grundlagen der kinetischen Gastheorie; dabei werden wir uns einen Einblick in qualitative statistische Methoden verschaffen, die zur Behandlung von Vielteilchensystemen erforderlich sind, bei denen sich zunächst deren Anzahl nicht ändern soll (kanonisches Ensemble). Es schließen sich der 1. und der 2. Hauptsatz der Thermodynamik an. Die Entropie wird über chemische Reaktionen und statistisch über die Mischungsentropie eingeführt, und damit die Richtung des Geschehens bei Prozessen definiert. Mit den Maxwellschen Relationen werden dann die Werkzeuge geschaffen, um bis dahin erwähnte unüberwindliche Schwierigkeiten elegant zu lösen. Mit der Zulassung der Änderung der Teilchenzahl (großkanonisches Ensemble) und der Definition des chemischen Potentials wenden wir uns dann physikalischen und chemischen Gleichgewichten zu. Abschließend widmen wir uns dem Problem, wie Ungleichgewichte durch Fluss von Materie und Wärme ausgeglichen werden.
Physik I : Mechanik
(2012)
Physik beschäftigt sich mit den Erscheinungen der unbelebten Natur. Ihre Beschreibung gelingt mit Hilfe eindeutig definierter Begriffe, die zu Gesetzen verdichtet werden. Dahinter steht die naturwissenschaftliche Denkmethodik, die Annahme der Gültigkeit universeller, reproduzierbarer Naturgesetze, die Beziehungen zwischen den Objekten oder Dingen in der Natur vermitteln. (...)
Dieses Skriptum ist das Ergebnis eigener iterativer Prozesse, grundlegende Denkstrukturen mitzuteilen, die sich in der Physik als erfolgreich erwiesen haben, um mechanische Sachverhalte zu verstehen. Bei den Übungsaufgaben wurde auf eigene Vorräte, aber auch auf Aufgabenstellungen verehrter Kollegen zurückgegriffen, die hier in extenso diskutiert werden.
A new iterative matrix algorithm has been applied to improve the precision of temperature and force decoupling in multi-parameter FBG sensing. For the first time, this evaluation technique allows the integration of nonlinearities in the sensor’s temperature characteristic and the temperature dependence of the sensor’s force sensitivity. Applied to a sensor cable consisting of two FBGs in fibers with 80 μm and 125 μm cladding diameter installed in a 7 m-long coiled PEEK capillary, this technique significantly reduced the uncertainties in friction-compensated temperature measurements. In the presence of high friction-induced forces of up to 1.6 N the uncertainties in temperature evaluation were reduced from several degrees Celsius if using a standard linear matrix approach to less than 0.5°C if using the iterative matrix approach in an extended temperature range between −35°C and 125°C.
For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm². At fluences above 2.0 J/cm² bump and jet formation can be observed that could be used for creating microstructures. For the investigation of the underlying mechanisms of the laser ablation process itself as well as of the bump or jet formation, pump probe microscopy is utilized to resolve the transient ablation behavior.
The effectiveness of antipredator defenses is greatly influenced by the environment in which an organism lives. In aquatic ecosystems, the chemical composition of the water itself may play an important role in the outcome of predator–prey interactions by altering the ability of prey to detect predators or to implement defensive responses once the predator’s presence is perceived. Here, we demonstrate that low calcium concentrations (<1.5 mg/L) that are found in many softwater lakes and ponds disable the ability of the water flea, Daphnia pulex to respond effectively to its predator, larvae of the phantom midge, Chaoborus americanus. This low-calcium environment prevents development of the prey’s normal array of induced defenses, which include an increase in body size, formation of neck spines, and strengthening of the carapace. We estimate that this inability to access these otherwise effective defenses results in a 50–186% increase in the vulnerability of the smaller juvenile instars of Daphnia, the stages most susceptible to Chaoborus predation. Such a change likely contributes to the observed lack of success of daphniids in most low-calcium freshwater environments, and will speed the loss of these important zooplankton in lakes where calcium levels are in decline.
Fundamental Investigations Regarding Barrier Properties of Grafted PVOH Layers : Research Article
(2012)
The current work focuses on fundamental investigations regarding the barrier properties of grafted PVOH layers produced by the Transfer Method. The layers (or papers) used for the different experiments were produced and grafted during the course of this work. Papers with different types of PVOH (different Mowiol types) were produced by coating. Experiments using different parameters (temperature, reaction duration, and concentration) were performed using the Transfer Method. Contact angle measurements and Cobb60 measurements were carried out on the grafted and untreated PVOH layers. Furthermore, the water vapour transmission rate of the PVOH layers was determined. The results of this work showed that the method of chromatogeny or chromatogenic chemistry improves the water vapour barrier properties of grafted PVOH layers enormously.
Reconstruction of the extensor mechanism is essential for good extremity function after endoprosthetic knee replacement following tumor resection. Only a few biological methods have been able to reliably restore a functional extensor mechanism, but they are often associated with significant complication rates. Reattachment of the patellar tendon to the prosthesis using an alloplastic patellar ligament (Trevira cord) can be an appropriate alternative. In vivo and in vitro studies have already shown that complete fibrous ingrowth in polyethylene chords can be seen after a period of six months. However, until now, no biomechanical study has shown the efficacy of an alloplastic cord and its fixation device in providing sufficient stability and endurance in daily life-activity until newly formed scar tissue can take over this function. In a special test bench developed for this study, different loading regimes were applied to simulate loads during everyday life. Failure loads and failure modes were evaluated. The properties of the cord were compared before and after physiological conditioning. It was shown that rubbing was the mode of failure under dynamic loading. Tensile forces up to 2558N did not result in material failure. Thus, using an artificial cord together with this fixation device, temporary sufficient stable fixation can be expected.
The production of CIS thin film solar cells is still employing some mechanical steps of structuring, where thin layers have to be selectively separated in three patterns (P1 to P3) for the monolithic serial interconnection. We report on the high speed structuring of these patterns by picosecond laser ablation at 1064 nm. We demonstrate on 100x100 mm2 samples, that the molybdenum back electrode can be structured with a process speed of up to 15 m/s. The ZnO front electrode film can be line separated with up to 15 m/s, the CIS absorber layer is structured with up to 4 m/s. Furthermore we extended our laser processes to 300 x 300 mm2 pilot line samples which were displaying efficiencies of 13.4%.
Although head injuries in football having approximately the same incidence as in American football and ice hockey, head protectors are barely used for prophylaxis. A detailed human head-neck model including force elements describing the material behaviour of human soft tissue structures such as ligaments, tendons, cartilage layers, intervertebral discs and muscles has been developed using multi-body system (MBS) modelling techniques to investigate the effectiveness of commercial headgear. For ball-head impacts at ball velocity of about v = 20 m/s the simulations calculate a Head Impact Power (HIP) index of 4.1 kW resulting in a five percent injury risk for concussion. When using headgear the resulting HIP-value comes to 3.91 kW meaning that the reduction of the injury risk is very small.
Ferroelectric field- effect-transistors, based on Zirconia or Hafnia, have the potential to play an important roll in future non-volatile electronic memory devices. Artificial stabilization of the ferroelectric phase is necessary, since the ferroelectric phase is not the natural occurring phase of those materials. The intension of this work is to investigate the influence of II- and IV-valent dopants on the phase stability of Zirconia, using Ab Initio calculations based on density functional theory. Experimental results show ferroelectricity for dopant concentrations in the percent margins. Therefore the necessity to use large 96 atomic supercells arises, in which individual atoms can be removed or replaced with a dopant atom. The calculations were performed on the ICE1-segment of the Leibniz Rechenzentrum in Munich, using the program Abinit. Parallelization occurred, using up to 120 cores. The used exchange correlation method was PW92 at a cut off energy of 30 Ha, the atomic positions were optimized using the Broyden-Fletcher-Goldfarb-Shanno-Minimization-Method. Several different external constraints to optimize lattice parameters were investigated. The results show, that for the chosen dopant concentration the monoclinic phase is always favored. That implies that other effects like thermal energy or surface tension might also play a roll in stabilizing the ferroelectric phase. None the less dopants have a big impact on the total energy of the different phases, especially the tetragonal phase. Since in contrast to experimental results the dopants did not stabilize the ferroelectric phase in Zirconia, calculations including III-valent dopants as well as thermal and surface energies for both Zirconia and Hafnia are necessary.