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Dissertation
Existence and Regularity Results of a Ferroelectric Phase-Field Model
(2019)
In this thesis, we investigate the existence and regularity results of a ferroelectric phase-field model, which is a state-of-the-art model arising in recent years from the engineering area for the ferroelectric study.
Dissertation
Gold Surface Nanostructuring with Ultrashort Laser Pulses - Study of Non-equilibrium Effects
(2019)
Laser material interaction and structure formation in metals under controlled ultrashort laser pulse conditions are discussed in this work. A novel approach is presented describing the exact amount of energy deposited by a laser pulse in a gold surface, applicable under a variety of structuring conditions. The presented model is validated by a new introduced broad-band pump-probe reflectivity measurement method. A technique also applicable to investigate other phenomenas where 20 fs resolution combined with an octave ...
Dissertation
High-Speed 1.55 µm Quantum Dot Lasers with Electronically Coupled Quantum Well - Dot Active Regions
(2019-07-31)
The expansion of long-distance data communication at a wavelength of 1.55 µm calls for larger data transfer rates. Consequently, an improvement of emission and modulation properties of lasers emitting in this wavelength region is of high interest. The utilization of so-called tunnel-injection (TI) structures in InP-based quantum dot (QD) lasers is promising to fulfill this task. The aim of this thesis was the realization and analysis of TI structures in the lattice matched InP material system and incorporation into ...
Dissertation
Berücksichtigung von Studierendenvorstellungen zum Thema Gehirn und Lernen in der Lehrkräfteausbildung Biologie
(2019-11)
Lehrer*innenbildung hat das Ziel, Studierende zu Fachleuten für das Lehren und Lernen auszubilden. Zahlreiche empirische Studien zeigen jedoch sowohl bei angehenden als auch praktizierenden Lehrkräften eine hohe Verbreitung von Fehlvorstellungen zum Thema Gehirn und Lernen – sogenannte Neuromythen. Für Biologielehrkräfte ist das Thema Gehirn und Lernen auch als Unterrichtsinhalt relevant. Sie unterrichten Themen wie Bau und Funktion des Gehirns oder Langzeitpotenzierung. Demnach ist es besonders wichtig, dass sie ...
Dissertation
1.55 μm Quantum Dot Lasers for Telecommunication
(2019)
The thesis at hand investigates the suitability of quantum dot (QD) material for use in long-distance coherent communication. The thesis was written in the frame of the SASER project MONOLOP that is aiming for a compact, monolithically integrated light source with a tunable wavelength covering the C+-band and narrow spectral linewidth below 500 kHz.
The thesis reviews the theoretical background of quantum dot material based on the InP material system and distributed feedback (DFB) lasers with lateral gratings as ...
Dissertation
Role of neurotransmitter GABA in the brain of the Madeira cockroach Rhyparobia maderae with focus on the circadian system
(2019-02)
All living things are subject to biological rhythms. Circadian rhythms are generated by internal clocks which influence many biochemical and physiological processes, as well as various behaviors of an organism. These oscillators are synchronized by external "Zeitgeber" signals such as light-dark changes, temperature changes, as well as social contacts. Different studies identified the accessory medulla (AME), small neuropil at the ventromedian edge of the medulla, as the circadian pacemaker center of the cockroach ...
Dissertation
Energy transfer in free-standing van der Waals heterostructures after optical excitation
(2019)
The wide range of layered van der Waals materials is interesting due to its plenty of deviating characteristics. The structure of all these materials is built from covalently joined layers, which are stacked by van der Waals forces. Aside from this structural similarity the specific characteristics spread out in a variety of electronic and optical properties. The electronic properties of layered materials vary from pure insulators to metallic conductors and can even depend on the number of layers. In the work presented ...
Dissertation
Ab-initio analysis of the structural response of solids after femtosecond-laser-pulse excitation
(2019)
After an intense femtosecond-laser excitation extreme non-equilibrium conditions are induced in materials. The high photon density in such an ultrashort-laser pulse interacts directly with the electronic system of the material. By absorbing the photon energy the electrons are excited in high energy states, where they form a non-equilibrium distribution shortly after the excitation. Due to fast electron-electron scattering and cascading processes equilibrates the electronic system within several femtoseconds to a ...