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Now showing items 31-40 of 121
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
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 ...
Dissertation
InP - based quantum dots for telecom wavelengths ranges
(2019-12)
Long-distance quantum communication applications require sources of single photons, emitting at telecom wavelengths (around 1550 nm) with minimum attenu-ation losses of silica fiber.
Semiconductor self-assembled InAs/InP-based quantum dots (QDs) are possible candidates to
reach this spectral region. One of the challenges on the way is a QD asymmetry, which limits the fidelity of entangled photons. Therefore, morphological and optical properties of QDs should be improved in order to achieve the necessary quality and ...
Dissertation
Abhängigkeit des Exchange-Bias Feldes und des Koerzitivfeldes von der mittels Röntgendiffraktometrie gemessenen Kornvolumenverteilung des Antiferromagneten in Exchange-Bias Schichtsystemen
(2019-10-02)
Der Exchange-Bias Effekt wird in vielen technischen Anwendungen, wie z.B. in magnetischen Speichermedien oder in Magnetsensorköpfen zum Pinnen der Magnetisierungsrichtung der Referenzelektrode, eingesetzt. Dieser Effekt tritt ausschließlich in dünnen Schichtsystemen, in denen sich ein dünner Ferromagnet mit einem dünnen Antiferromagneten in Kontakt befindet, auf und bewirkt eine Verschiebung der Hysteresekurve entlang der Magnetfeldachse. Solche Exchange-Bias Schichtsysteme können mittels Ionenbeschuss, d.h., leichte ...
Dissertation
Raumwinkeloptimierte Elektron-Photon Koinzidenzmessungen nach der Anregung mit Synchrotronstrahlung unter Verwendung zeitlich verschieden strukturierter Füllmuster des Speicherrings
(2021-05)
Für die Untersuchung von Relaxationspfaden von angeregten mikroskopischen Systemen nehmen Messmethoden eine zentrale Rolle ein, bei denen emittierte Teilchen so gemessen werden, dass eine physikalische Korrelation zwischen Ihnen nachgewiesen werden kann. Denn nur durch den Nachweis dieser Korrelationen ist es bei stark verzweigten und sich unter Umständen kreuzenden Relaxationspfaden, diese Pfade eindeutig nachzuverfolgen.
Diese sogenannten Koinzidenzmessungen werden seit ihren ersten Anwendungen in den 1920er Jahren ...
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
Organische Magnetooptoelektronik
(2014-09-25)
Im Rahmen der Organischen Optoelektronik wird der Weg vom Molekül zum Bauteil als Wertschöpfungskette verstanden, deren Kernziele wissenschaftlicher Erkenntnisfortschritt und Produktanwendungen sind. Eine besonders vielversprechende Möglichkeit diese Entwicklung auch in Zukunft erfolgreich und innovativ fortführen zu können, eröffnet sich durch das Einbeziehen magnetosensitiver Prozesse. Spinzustände werden als zusätzliche Regelgröße verstanden, die es erlauben, optoelektronische Abläufe zu optimieren und neuartige ...
Dissertation
Molecular-Frame Angular Distributions of Electrons Emitted by Photoionization and Interatomic Coulombic Decay
(2020)
The continuous refinement of the experimental and theoretical methods to study the electron angular emission distributions, and particularly in a molecule frame of reference, have contributed to a keen understanding of the structure of molecules and have provided deeper insight into fundamental physical phenomena.
Revealing many details of the ionization dynamics, the molecular-frame angular distributions (MFADs) of emitted electrons have been an appealing research topic for the last two decades. Owing to the ...
Dissertation
Energy landscapes and dynamics of magnetic nanostructures: disorder, structure, and magnetic field effects
(2020)
The static and dynamic magnetic properties of two-dimensional ensembles of dipole-coupled magnetic nanoparticles (NPs) are investigated from a theoretical perspective. Particular emphasis is put on the correlations between the geometrical arrangements of the NPs, their inherent structural disorder, and the cooperative magnetic dynamics of the nanostructures as a whole. To this aim a significant number of representative two-dimensional NP ensembles with different structural geometries and degrees of disorder are ...
Dissertation
Investigation of diamond nanostructures with incorporated color centers
(2018)
Diamond is a material with excellent properties due to its structure and composition. Its crystal lattice is a perfect host of different defect centers, so-called color centers, whose properties, especially the capability of emitting single photons, can serve in quantum information technologies (QIT). As a high refractive index material only a small part of the photons emitted by these color centers in diamond can be collected. To enhance the photon collection efficiency photonic structures are necessary. They can ...