Universität Stuttgart
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Item Open Access Oleathydratase katalysierte stereoselektive Hydratisierungsreaktionen kurzkettiger Alkene(2025) Härterich, Natalie; Hauer, Bernhard (Prof. Dr.)Item Open Access Growth of oxide materials with Ruddlesden-Popper- and garnet-type structures via the optical float zone method: investigations of scintillation, optical, and magnetic properties, and post-growth modifications of single crystals via topochemical routes(2025) Yilmaz, Hasan; Clemens, Oliver (Prof. Dr.)With the continuous progress in materials science, the global market demand for high-performance functional materials, especially those with customized optical and magnetic properties, has increased significantly due to their critical role in next-generation technologies such as photonic devices, data storage systems, quantum computing, and biomedical applications. With this motivation, this dissertation is focused on the growth of high-quality oxide single crystals with Ruddlesden-Popper (RP) and garnet-type structures using the optical floating zone (OFZ) method and the detailed investigation of their scintillation, optical and magnetic properties. Furthermore, the use of chemical doping and post-growth topochemical modifications as strategies to modify material properties and stabilise metastable structures is also covered. With these approaches, we can classify this study into two parts: optical and magnetic properties. In the first part of this work, RP-type n = 1 LaSrGaO4 (LSGO) and Garnet-type Gd3In2Ga3O12 (GIGG) single crystals doped with different Rare Earths (RE) including Eu, Sm, Ho, Nd have been grown via OFZ method to investigate their luminescence, decay time kinetics and scintillation properties. To compare the scintillation behaviour, a well-known commercial scintillator, Gd2.98Ce0.02Al2Ga3O12 (0.02Ce:GAGG) single crystal, was synthesised and characterised using the same methods. This limits deviations in scintillation properties caused by different synthesis methods. Powder X-ray diffraction (XRD) and Single Crystal X-ray diffraction (SC-XRD) measurements together with Rietveld analysis confirmed phase purity and crystallinity, while Scanning Electron Microscopy (SEM-EDX) and backscatter electron imaging (BSE) confirmed the homogeneous distribution of the dopants. In addition to these analytical methods, Photoluminescence Spectroscopy (PL) and luminescence decay measurements have demonstrated that these RE-doped single crystals have strong emission, which is related to the low phonon energy of their host lattices. However, scintillation measurements under 137Cs gamma-ray point source excitation resulted in a limited gamma ray response. This response was significantly weaker than observed for the well-known commercial scintillator 0.02Ce:GAGG. Inefficient absorption of high-energy excitation or inadequate energy transfer to the activator ions in these materials are responsible for this relatively low scintillation performance. The second part of the thesis is focused on bilayer Ruddlesden-Popper nickelates. Single crystals of Sr3Ni2-xAlxO7-δ (SNAO) and its Y-substituted modification YᵧSr3-yNi2-xAlxO7-δ (YSNAO) have been grown by using strategically chemical substitutions and high oxygen pressure conditions to stabilize the RP phase. XRD and SC-XRD analysis confirmed the existence of the n = 2 RP-type structure by doping with Al, while thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) indicated successful oxygen incorporation and corresponding changes in the Ni oxidation state. Magnetic susceptibility measurements (SQUID magnetometry) have demonstrated the antiferromagnetic ordering transitions in these doped nickelate single crystals, and transport measurements have shown enhanced electrical conductivity compared to the undoped parent compound. In addition, a topochemical fluorination process has been investigated as a post-growth modification for n = 1 RP-type La2NiO4+δ single crystals. Fluorine has been introduced into the crystal lattice at moderate temperatures using polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and CuF2 as fluorination reagent. PTFE has been found to be the most effective fluorinating agent, resulting in partially fluorinated La2NiO4+δ with a diffusion-limited penetration pattern. EDX and EDX-mapping analyses have demonstrated an inhomogeneous F distribution, indicating that fluorine incorporation is limited by diffusion kinetics. This inhomogeneity should be carefully considered in future structural and functional analyses as it may affect the accurate characterisation of intrinsic properties in fluorinated crystals. In summary, the results of this thesis demonstrate the flexibility of the optical floating zone technique for the growth of high-quality functional oxides and show how structural stability, and functional properties can be modified using specific chemical doping approaches. To optimise scintillation performance in novel garnet-type hosts and to improve the magnetic and electronic behaviour of RP-type nickelates, the combined approach of crystal growth and post-growth modification could provide an additional parameter for material modification.Item Open Access Development and investigation of protonic ceramic cells for hydrogen production at intermediate temperatures(2024) Zheng, Haoyu; Thess, André (Prof. Dr.)Item Open Access Synthese von Tosyl-Samroiyotmycin und Samroiyotmycin-Derivaten : biologische Eigenschaften und neue Wege zum Aufbau der (2E,4E)-Dienon-Einheit(2024) Kolb, Benedikt; Laschat, Sabine (Prof. Dr.)Item Open Access Gold nanoparticle-mediated DNA origami nanoarchitectures(2024) Peil, Andreas; Na Liu, Laura (Prof. Dr.)Since its origin in the 1980s, DNA (deoxyribonucleic acid) nanotechnology has established itself as a captivating nanofabrication technique with ever increasing impact that combines aspects from physics, chemistry, and biology to construct artificial nanosystems by means of molecular self assembly. Within the field of DNA nanotechnology, the DNA origami technique represents one of the most versatile fabrication tools to craft functional two-dimensional (2D) and three-dimensional (3D) nanostructures from the bottom up. These structures offer precisely tailored geometries along with programmable functions, featuring positional addressability with sub-5 nm resolution and exceptional spatiotemporal accuracy. This thesis discusses strategies to employ the DNA origami technique to assemble intricate hybrid nanosystems with synergistically integrated gold nanoparticles (AuNPs). The AuNPs take over different roles; they grant (i) structural and (ii) functional features and enable the (iii) optical monitoring of the systems. This approach allows the fabrication of nanostructures piece by piece to explore their structural and functional properties at the nanoscale in detail. The first publication covers different strategies for the hierarchical assembly of topological DNA origami structures using a AuNP-templated self-assembly approach. The assembly of [2], [3], and [4]catenanes with interconnecting AuNPs is elucidated. The AuNPs can be controllably released to disconnect the individual rings, leaving only the mechanical bond of the catenane chain. In the second publication, a dynamic AuNP-DNA origami gear system is presented that is designed to emulate a planetary gearset with precise spatiotemporal control over its rotation dynamics. The AuNPs serve three crucial tasks. They (i) structurally link the origami ring modules, (ii) mediate the rotation and (iii) enable the real time optical tracking of the rotation via fluorescence spectroscopy. The system enables tightly orchestrated and programmable bidirectional rotations. In the third publication, reconfigurable chiral metastructures comprising multiple plasmonic particles that are accurately positioned in a helical manner around a DNA origami template are discussed. The implementation of a DNA ‘swingarm strategy’ enables the simultaneous and efficient relocation of multiple closely spaced AuNPs over large distances to precisely tune the chiroptical response of the system. The presented publications illustrate the beneficial synergies between DNA origami systems and rationally integrated AuNPs with the aim to advance and expand the application spectrum of these hybrid nanosystems within their scientific disciplines.