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Dissertation
Surface modifications of nanocrystalline diamond films and their functionalization with phthalocyanines
(2016-06-30)
Boron-doped diamond is a promising electrode material for a number of applications providing efficient carrier transport, a high stability of the electrolytic performance with time, a possibility for dye-sensitizing with photosensitive molecules, etc. It can be functionalized with electron donor molecules, like phthalocyanines or porphyrins, for the development of light energy conversion systems. For effective attachment of such molecules, the diamond surface has to be modified by plasma- or photo-chemical processes ...
Dissertation
Fabrication of diamond nanostructures and investigation of the imbedded NV centers
(2015-02-24)
Diamant ist ein Material mit vielen außerordentlichen Eigenschaften, die ihn zu einem äußerst vielversprechenden Kandidaten für Anwendungen in Wissen-schaft und Technik machen. In den letzten Jahren wurde Diamant häufig als einzigartige Plattform für neue Anwendungen beispielsweise in der Quanteninformationstechnologie (QIT) oder in der Magnetometrie im Nanometermaßstab eingesetzt, wobei einer der wichtigsten lumineszierenden Gitterdefekte im Diamantgitter eingesetzt wird. Dabei handelt es sich um die sogenannten ...
Dissertation
1.55 µm High-Speed QDs Lasers for Optical Telecommunication Applications
(2014-12-19)
In this work investigation of the QDs formation and the fabrication of QD based semiconductor lasers for telecom applications are presented. InAs QDs grown on AlGaInAs lattice matched to InP substrates are used to fabricate lasers operating at 1.55 µm, which is the central wavelength for far distance data transmission. This wavelength is used due to its minimum attenuation in standard glass fibers.
The incorporation of QDs in this material system is more complicated in comparison to InAs QDs in the GaAs system. Due ...
Dissertation
Excitation of Phonons in Solids and Nanostructures by Intense Laser and XUV Pulses and by Low Energy Atomic Collision
(2016-02-17)
Intensive, ultrakurze Laserpulse regen Festkörper in einen Zustand an, in dem die Elektronen hohe Temperaturen erlangen, während das Gitter kalt bleibt. Die heißen Elektronen beeinflussen das sog. Laser-angeregte interatomare Potential bzw. die Potentialenergiefläche, auf der die Ionen sich bewegen. Dieses kann neben anderen ultrakurzen Prozessen zu Änderungen der Phononfrequenzen (phonon softening oder phonon hardening) führen. Viele ultrakurze strukturelle Phänomene in Festkörpern hängen bei hohen Laseranregungen ...
Dissertation
Molecular Beam Epitaxial Growth of III-V Semiconductor Nanostructures on Silicon Substrates
(2013-07-24)
The main focus and concerns of this PhD thesis is the growth of III-V semiconductor nanostructures (Quantum dots (QDs) and quantum dashes) on silicon substrates using molecular beam epitaxy (MBE) technique. The investigation of influence of the major growth parameters on their basic properties (density, geometry, composition, size etc.) and the systematic haracterization of their structural and optical properties are the core of the research work. The monolithic integration of III-V optoelectronic devices with silicon ...
Dissertation
Ab initio Molecular Dynamics Simulations of the Structural Response of Solids to Ultrashort Laser and XUV Pulses
(2015-04-10)
The theoretical model and underlying physics described in this thesis are about the interaction of femtosecond-laser and XUV pulses with solids. The key to understand the basics of such interaction is to study the structural response of the materials after laser interaction. Depending on the laser characteristics, laser-solid interaction can result in a wide range of structural responses such as solid-solid phase transitions, vacuum phonon squeezing, ultrafast melting, generation of coherent phonons, etc. During my ...
Dissertation
Interatomic Coulombic decay in noble gas clusters of varying sizes investigated by photon-induced (dispersed) fluorescence spectrometry
(2018-06-06)
The main topic of this thesis is to study experimentally an ultrafast and efficient non radiative mechanism – the well-known interatomic Coulombic decay (ICD) – in noble gas clusters by employing fluorescence spectrometry technique in combination with synchrotron radiation. Using Neon clusters as prototype systems, a special variety of ICD, termed resonant ICD (RICD), has been investigated by a selective excitation of one component of the cluster and for different mean cluster sizes. The first part of the thesis was ...
Dissertation
Magnetic interactions between transition metal impurities and clusters mediated by low-dimensional metallic hosts: A first principles theoretical investigation
(2015-03-31)
The magnetic properties and interactions between transition metal (TM) impurities and clusters in low-dimensional metallic hosts are studied using a first principles theoretical method. In the first part of this work, the effect of magnetic order in 3d-5d systems is addressed from the perspective of its influence on the enhancement of the magnetic anisotropy energy (MAE). In the second part, the possibility of using external electric fields (EFs) to control the magnetic properties and interactions between nanoparticles ...
Dissertation
Theoretical study of magnetism, structure and chemical order in transition-metal alloy clusters
(2012-02-27)
Research on transition-metal nanoalloy clusters composed of a few atoms is fascinating by their unusual properties due to the interplay among the structure, chemical order and magnetism. Such nanoalloy clusters, can be used to construct nanometer devices for technological applications by manipulating their remarkable magnetic, chemical and optical properties. Determining the nanoscopic features exhibited by the magnetic alloy clusters signifies the need for a systematic global and local exploration of their ...
Dissertation
Electron Dynamics Driven by Intense Coherent Femtosecond Laser Pulses: Dynamic Interference in Atoms and Photoelectron Circular Dichroism in Chiral Molecules
(2018-12)
Since humans have begun to explore nature, they came up with new ways and tools, which have been permanently improved. At some point, those tools allowed to look into the microworld and to study the quantum nature of matter. One of such tools to explore the quantum world is the light amplification by stimulated emission of radiation (laser). Since the first lasers were built almost 60 years ago, their capabilities improved permanently, allowing the study of hitherto-unknown physical phenomena. Two of such phenomena, ...