Universität Stuttgart
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Item Open Access Enzymatic asymmetric dihydroxylation of alkenes(2016) Gally, Christine; Hauer, Bernhard (Prof. Dr.)The introduction of chirality into C=C double bonds is of special interest in organic synthesis. In particular, the catalytic asymmetric dihydroxylation (AD) of alkenes has attracted considerable attention due to the facile transformation of the chiral diol products into valuable derivatives. By chemical means, the metal-catalyzed AD of olefins provides both stereo- and regiospecific cis-diol moieties. Next to their toxicity, however, these metal catalysts can also lead to byproduct formation as a result of oxidative fission. In nature, Rieske non-heme iron oxygenases (ROs) represent promising biocatalysts for this reaction since they are the only enzymes known to catalyze the stereoselective formation of vicinal cis-diols in one step. ROs are key enzymes in the degradation of aromatic hydrocarbons and can target a wide variety of different arenes. Despite their broad substrate scope, limited data is available for the conversion of unnatural substrates by this class of enzymes. To explore their potential for alkene oxidation, three ROs were tested for the oxyfunctionalization of a set of structurally diverse olefins including linear and cyclic arene-substituted alkenes, cycloalkenes as well as several terpenes. Naphthalene- (NDO), benzene- (BDO) and cumene dioxygenases (CDO) from different Pseudomonas strains where selected as they are amongst the RO enzymes that have already been reported to catalyze the oxidation of a small number of olefins. The majority of compounds from the selected substrate panel could be converted by NDO, BDO or CDO and products were either isolated and identified by NMR analysis or using the authentic standards. Dependent on the substrate, allylic monohydroxylation was found in addition to the corresponding diol products, a reaction which is chemically still most reliably achieved by the use of SeO2 in stoichiometric amounts. However, having been evolved for the dihydroxylation of aromatic compounds, wild type ROs displayed low conversions (< 50%) and modest stereoselectivities (≤ 80% ee/de) for several of the tested olefins. To overcome these limitations, changes in the active site topology of RO catalysts were introduced. A single targeted point mutation that was identified based on sequence and structural comparisons with other members of the RO family proved to be sufficient to generate BDO and CDO variants displaying remarkable changes in regio- and stereoselectivity for various substrates. In particular biotransformations with CDO M232A gave excellent stereoselectivities (≥ 95% ee/de) and good activities (> 90%) also for linear alkenes, which have been reported to be challenging substrates for RO-catalyzed oxyfunctionalizations. Site-saturation mutagenesis at position 232 in CDO revealed a correlation between the steric demand of the amino acid side chain and its influence on regio- and/ or stereoselectivities for styrene and indene. While the wild type enzyme almost exclusively catalyzed the dihydroxylation of the aromatic ring, the regioselectivity was shifted with decreasing side chain size to the terminal vinyl group of styrene, yielding up to 96% of the alkene-1,2-diol. For cis-1,2-indandiol formation, enantiocomplementary enzymes could be generated, a fact further highlighting the importance of position 232 for the engineering of ROs. Moreover, site-saturation mutagenesis of additional residues in the substrate binding pocket of CDO (F278, I288, I336 and F378) identified further positions having an influence on selectivity and product formation for alkene oxidation. To proof the applicability of ROs for organic synthesis, semi-preparative scale biotransformations (70 mg) of selected substrates were performed with CDO M232A. Without further optimization of the reaction set-up, products were successfully isolated in > 30% yield. In addition, up-scaling of (R)-limonene hydroxylation to 4 L in a bioreactor with growing cells gave final isolated product titers of 0.4 g L-1 even though substrate volatility and product toxicity diminished the yield. In conclusion, these examples demonstrated that a single point mutation was sufficient to transform CDO wild type into an efficient catalyst, furthermore constituting the first example of the rational engineering of CDO and BDO enzymes for the oxyfunctionalization of a broad range of alkenes.Item Open Access Spectroscopic investigations of the magnetic anisotropy of lanthanide- and cobalt-based molecular nanomagnets(2016) Rechkemmer, Yvonne; Slageren, Joris van (Prof. Dr.)Single-molecule magnets are metal complexes exhibiting an energy barrier for spin reversal, leading to magnetic bistability and slow relaxation of the magnetization. Their potential for practical applications such as high-density magnetic data storage was recognized early on and with the goal of achieving high energy barriers, different kinds of single-molecule magnets have been synthesized. The quadratic dependence of the barrier height on the spin motivated chemists to synthesize metal complexes with very high total spins; however, with limited success. It was shown that high spins come along with low anisotropies and increased interest thus focused on the synthesis and investigation of (mononuclear) complexes of highly anisotropic metal centers, e.g. lanthanide or cobalt complexes. Although rather high energy barriers can be achieved in such systems, practical application remains problematic and has not been realized yet. Reasons are for example the lack of rational design criteria and the complex interplay of different magnetic relaxation pathways. The aim of this work was therefore the comprehensive magnetic and spectroscopic investigation of selected molecular lanthanide and cobalt compounds in order to obtain a deeper insight into the correlation of molecular and electronic structures as well as the corresponding magnetic properties. The applied spectroscopic methods included electron paramagnetic resonance spectroscopy, far-infrared spectroscopy and optical methods. Special emphasis was placed on magnetic circular dichroism (MCD) spectroscopy, which served as a main tool for electronic structure determination. However, since the MCD-spectrometer was not part of the available experimental equipment at the University of Stuttgart, its design, setup and characterization were the first part of this work. In the further course of this work MCD-spectroscopy was employed for the electronic structure determination of selected lanthanide and cobalt compounds. The studied lanthanide compounds were literature-known molecular tetra-carbonates of erbium (1-Er) and dysprosium (1-Dy). Detailed magnetometric studies showed that both 1-Er and 1-Dy are field-induced single-molecule magnets; however, 1-Er and 1-Dy show significant differences in their magnetic relaxation behavior. The magnetic studies were complemented by detailed spectroscopic investigations.The combination of far-infrared-, luminescence- and MCD-spectroscopy allowed for the experimental determination of 48 energy levels for 1-Er and 55 levels for 1-Dy, which built the foundation for the subsequent crystal field analysis and electronic structure determination. In addition, the results of EPR-spectroscopic studies were used for fine-tuning and verifying the respectively determined crystal field parameters. Calculating the magnetic dipole strengths for transitions between the relevant states led to a quantitative understanding of the magnetic relaxation pathways. Besides the investigation of lanthanide compounds, this thesis deals with two classes of cobalt complexes. The first class comprises mononuclear complexes in which one Co(II) ion is ligated by the nitrogen donors of two doubly deprotonated 1,2-bis(methanesulfonamido)-benzene-ligands. Rather acute N-Co-N bite angles indicate strong deviations from ideal tetrahedral symmetry. The static magnetic properties hint at very high energy barriers for spin reversal and with the help of far-infrared spectroscopy, largely negative axial zero-field splitting parameters were determined. The corresponding energy barriers belong to the highest ever reported for 3d-transition metal complexes and investigating the dynamic magnetic properties confirmed single-molecule magnet behavior. The unique magnetic properties were fully explained by analyzing spectroscopic results. The MCD-spectra showed intense signals that were assigned to spin-allowed d-d-transitions. Subsequent crystal field analysis revealed that the strong axial crystal field generated by the ligands leads to a large splitting of the electronic terms and thus in turn to a relatively small energy gap between the electronic ground state and the first excited state. The resulting increase in second-order spin-orbit coupling explains the high energy barriers observed in the studied complexes. The second class of cobalt compounds studied in this work included dimers of distorted octahedrally coordinated Co(II) ions bridged by symmetrical or asymmetrical quinone based bridging ligands. The main focus of investigation lay on the impact of the bridging ligand on the magnetic coupling between the cobalt centers. Thus, the magnetic properties of the complexes were studied with the help of static susceptibility and magnetization measurements and analyzed by means of different models. Depending on the bridging ligand, different signs for the exchange coupling constants were found. The varying signs can be explained by different relative contributions of possible exchange paths, influenced by the different substituents at the bridging ligands or slight geometry differences. The observations indicate that electron withdrawing substituents favor ferromagnetic couplings, which are preferred in the context of molecular magnetism. All in all, it can be concluded that this work provides a contribution to the deeper understanding of the features relevant for single-molecule magnets. The electronic structure determination for selected lanthanide and cobalt complexes applying advanced magnetometric and spectroscopic techniques not only led to an understanding of the static and dynamic magnetic properties but also allowed for the development of design criteria and new approaches for improved single-molecule magnets in the future.Item Open Access Template controlled mineralization of functional ZnO thin films(2017) Blumenstein, Nina; Bill, Joachim (Prof. Dr.)In this thesis, the influence of different organic templates on the bioinspired deposition of ZnO thin films is investigated. Depending on the polarity of the templates, the growth and the properties of the films can be influenced. On a non-polar template, film growth is inhibited whereas homogeneous films grow on polar templates. Additionally, it was shown that on a template with high polarity a crystallographic texture is observed. This leads to a macroscopically measurable piezoelectric response of these samples. In the last part of this work, the incorporation of Al, Ga and In into the ZnO films was investigated. Measurements showed a blue shift of the UV photoluminescence emission and an improved electrical conductivity with increasing doping content.Item Open Access Prozessintensivierung einer anionischen Polymerisation von 1,3-Butadien in einem Kapillarreaktor(2017) Schulze, Simon Frank; Klemm, Elias (Prof. Dr.-Ing.)Zur Untersuchung der Prozessintensivierung einer anionischen Polymerisation von 1,3-Butadien wurden zwei experimentelle Aufbauten errichtet. Die Ergebnisse der Experimente, die in einem halbkontinuierlichen Rührkesselreaktor durchgeführt wurden, waren notwendig die Standardbedingungen zu definieren und um eine Rezeptur zur Produktion eines Polybutadiens mit einer Molmasse von 4500 g/mol, einem Vinylgehalt von etwa 75% und einer Polydispersität kleiner als 1.1 zu erstellen. Die Übertragung der anionischen Polymerisation in einen Kapillarreaktor führte zu Polybutadienen mit den geforderten Spezifikationen. Die Mikroreaktionstechnik erlaubt es, die Polymerisation in einem neuen Prozessfenster mit Reaktionstemperaturen über 70°C und Drücken über 15 bar durchzuführen. Die vorliegende Arbeit zeigt anhand Experimenten, numerischer Modellierung und dem Vergleich idealer Reaktormodelle, dass die fluiddynamischen Eigenschaften den minimal erzielbaren PDI auf 1.04 begrenzen. Zudem wurden die Rahmenbedingungen, wie isotherme Reaktionsführung oder eine vollständige Initiierungsphase durch Simulationen belegt. Zur Bestimmung des Potenzials der Prozessintensivierung wurden die Raum-Zeit-Ausbeuten der beiden Prozesse verglichen. Die Übertragung in einen kontinuierlich betriebenen Flussreaktor und der Einsatz der Mikroreaktionstechnik führen zu einer Intensivierung um etwa den Faktor 100. Im Rahmen des CoPIRIDE-Projekts (unterstützt durch die EU, FP7) flossen die Ergebnisse dieser Arbeit in den Aufbau einer Produktionsstätte im Standard-Container-Format mit ein.Item Open Access Lineare und β-verzweigte Thiophen-basierte Donor-π-Akzeptor-Chromophore für elektrooptische Modulatoren(2017) Rothe, Christian; Ludwigs, Sabine (Prof. Dr.)Mit den fortschreitenden technischen Anforderungen des laufenden Informationszeitalters und der damit verbundenen weltweiten Vernetzung wurden innerhalb der letzten Jahrzehnte in der Forschung immer weiter verbreitet Anstrengungen unternommen um Technologien und Materialien zu entwickeln, die diese Anforderungen erfüllen oder auch übertreffen können. Einen wichtigen Bereich stellt dabei die Entwicklung von Materialien dar, die das rasante Wachstum innerhalb der optischen Nachrichtentechnik unterstützen können. Elektrooptische Bauteile sind dafür unerlässlich und damit steigt die Nachfrage nach immer leistungsfähigeren nichtlinear-optisch aktiven Substanzen. Organische Chromophore spielen bei der Entwicklung dieser Materialien eine stetig wachsende Rolle. Sie übertreffen beispielsweise die elektrooptische Aktivität der etablierten anorganischen elektrooptischen Kristalle, machen kürzere Schaltzeiten möglich und sind in Hinsicht auf viele Eigenschaften hin über moderne Synthesemethoden optimierbar. Organische Moleküle, die eine molekulare sowie makroskopische nichtlinear-optische Aktivität zeigen, sind grundsätzlich asymmetrisch aufgebaut. Sie verfügen über einen Elektronen-Donor, der über ein konjugiertes π-System mit einem Elektronen-Akzeptor verknüpft ist. Dieser Aufbau ermöglicht Elektronenbewegungen innerhalb des Moleküls vom Donor zum Akzeptor und führt zu einer potentiell dipolaren Struktur. Aufgrund ihres Aufbaus werden solche Verbindungen auch Donor-π-Akzeptor- oder push-pull-Chromophore genannt. Über organische Synthesechemie steht ein nahezu unerschöpfliches Repertoire an Kombi-nationsmöglichkeiten der drei Bausteine dieser Substanzklasse zur Verfügung. Um mit Hilfe von solchen Chromophoren elektrooptisch aktive Materialien zu generieren, muss die molekulare Asymmetrie der Verbindungen auf die makroskopische Ebene übertragen werden. Dazu werden nichtlinear-optisch aktive Farbstoffe häufig in einer Polymermatrix molekular dispergiert und anschließend über der Glasübergangstemperatur dieser Matrix in einem elektrischen Feld ausgerichtet. Solche Systeme werden guest-host-Systeme genannt. Das Ziel dieser Arbeit war es, auf Basis von am Lehrstuhl Functional Polymers des Instituts für Polymerchemie der Universität Stuttgart bereits vorhandener Erfahrung im Bereich der Synthese und Charakterisierung von konjugierten Polymeren, eine Reihe von neuen Donor-π-Akzeptor-Chromophoren zu synthetisieren. Über Variationen im konjugierten π-System sowie am Akzeptor der Moleküle sollten Einflüsse dieser Variationen auf die Molekül- und Materialeigenschaften untersucht werden. In einer interdisziplinären Kooperation mit dem Institut für elektrische und optische Nachrichtentechnik der Universität Stuttgart (INT) sollten außerdem die elektrooptischen Eigenschaften der Moleküle in ihrer Anwendung in elektrooptischen Modulatoren untersucht werden. Im Rahmen dieser Fragestellungen wurde eine Reihe von zehn Chromophoren für eine Anwendung in guest-host-Systemen synthetisiert sowie ein weiteres, von dieser Reihe abgewandeltes Chromophor, welches als Monomer polymerisiert werden kann. Alle synthetisierten Chromophore tragen einen auf 2,2,4,7-Tetramethyl-1,2,3,4-tetrahydroquinolin basierenden Donor. Als Akzeptoren wurden Dicyanovinyl- (DCV) und Tricyanovinyleinheiten (TCV) verwendet. Die konjugierten π-Brücken der Chromophore wurden aus Thiophenen aufgebaut. Es wurden ein bis drei α-verknüpfte Thiophene zwischen Donor und Akzeptor eingebaut. Für jede lineare Variante wurde außerdem ebenfalls eine Variante mit einer β-verknüpften Verzweigung in Form eines Alkylthiophens synthetisiert (Beispiel s. Abbildung). Diese Variation sollte Rückschlüsse auf den Einfluss von β-Verzweigungen im Chromophor auf die nichtlinear-optischen Eigenschaften der Moleküle erlauben. Alle synthetisierten Chromophore wurden zusätzlich über DFT-Simulationen untersucht, um eine Korrelation mit den erhaltenen experimentellen Ergebnissen zu ermöglichen. Zusätzlich zu den synthetisierten Verbindungen wurden zwei weitere Chromophore mit einem stärkeren Tricyanovinyldihydrofuran-Akzeptor (TCF) simuliert. Absorptionsspektroskopie in unterschiedlichen Lösungsmitteln zeigte ein ausgeprägtes solvatochromes Verhalten aller Chromophore. FT-IR- und Ramanspektroskopie zeigten einen Einfluss der Akzeptorstärke auf die Lage der CN-Streckschwingungsbande. Die Temperatur-stabilität der Verbindungen wurde über thermogravimetrische Analyse bestimmt. Die ermittelten Zersetzungstemperaturen liegen im Bereich zwischen 270 °C und 420 °C. Mit Hilfe von Cyclovoltammetrie und Differential-Puls-Voltammetrie wurden die Energien von HOMO und LUMO der Moleküle bestimmt. Die erhaltenen HOMO-Energien lagen im Bereich zwischen -5.51 eV und -5.16 eV, die LUMO-Energien im Bereich zwischen -4.41 eV und -3.30 eV. Es ergaben sich elektrochemische Bandlücken von maximal 2.13 eV und minimal 1.14 eV. Die molekularen nichtlinear-optischen Eigenschaften der Chromophore wurden über feldinduzierte Frequenzverdopplung bestimmt. Dabei zeigten sich für die Moleküle mit TCV-Akzeptor im Vergleich zur jeweiligen DCV-Variante durchgängig deutlich höhere µβ-Werte. Der höchste Wert der Reihe wurde mit µβ = 10400 ∙ 10-48 esu vom linearen 3T-verbrückten Chromophor 3T-TCV erhalten. Die β-Verzweigungen führten im Vergleich zu den jeweils linearen Spezies zu einem Abfall der molekularen Hyperpolarisierbarkeiten. Die Simulation der TCF Moleküle sagte eine deutliche Überlegenheit gegenüber den anderen simulierten Chromophoren voraus. Alle anderen in den experimentellen Daten beobachteten Trends konnten mit Hilfe der simulierten Daten bestätigt werden. Die beiden am einfachsten aufgebauten Chromophore, mit jeweils einem Thiophen als π-Brücke sowie einmal mit DCV- und TCV-Akzeptor, wurden in bilayer-Solarzellen in Kombination mit dem Fulleren C60 getestet. Dabei konnte eine maximale Energieum-wandlungseffizienz von 1.04 % erreicht werden. Die am INT durchgeführten Experimente mit den Chromophoren auf Testsubstraten in einer Matrix aus PMMA bestätigten, dass die Verbindungen das Potential für hohe erreichbare elektrooptische Koeffizienten besitzen. Es konnten r33-Koeffizienten bis 350 pm/V gemessen werden. Als problematisch stellte sich die Langzeitstabilität der erreichten elektrooptischen Aktivität heraus. So fielen die erreichten r33-Koeffizienten innerhalb weniger Stunden um über die Hälfte ab. Die erreichte elektrooptische Aktivität der Testsubstrate war jedoch trotzdem äußerst vielversprechend. Daher wurde ebenfalls mit der Realisierung von Modulatoren experimentiert. Das Chromophor 3Tβ-TCV konnte erfolgreich in einem, auf einer neuartigen Wellenleiterstruktur basierenden, elektrooptischen Modulator eingesetzt werden. Dabei konnte auf dem verwendeten Chip ein elektrooptischer Koeffizient von r33 = 7.2 pm/V gemessen werden.Item Open Access Ion beam lithographic and multilayer fresnel zone plates for soft and hard X-rays: nanofabrication and characterization(2015) Keskinbora, Kahraman; Schütz, Gisela (Prof. Dr.)X-ray microscopy has become an important analytical characterization method for a plethora of applications in materials science, physics, chemistry and biology, thanks to the emergence of modern synchrotron radiation facilities. These facilities enable high brilliance, energy tunable, variable polarization X-rays which gives access to mass density, elemental, chemical, electronic and magnetic properties of materials. In the soft X-ray energies nearly all elements can be probed by spectromicroscopic methods. Another important property of synchrotron radiation is the time structure in the ns to ps range, which can be utilized for sophisticated time resolution studies. These opportunities can be combined with high spatial resolution which is determined by the focusing method and the optic. Focusing of X-rays has historically been a difficult task due to strong absorption and weak phase shift of X-rays within matter. The required phase shift of X-rays, which depends on the real part of the complex refractive index, differs from 1 (the vacuum refractive index) only on the order of 10^-2 to 10^-6 and conventional lenses do not work. One very successful X-ray optic is the Fresnel Zone Plate (FZP), a diffractive optic that act as a lens under certain conditions and can focus X-rays to nanometer sized spots. The resolution of the FZP depends on the width of the outermost zone and is highly correlated with the smallest feature that can be fabricated. Conventionally, the e-beam lithography (EBL) is used for production FZPs which could resolve up to 10 nm structures with serious limitations. One difficulty of EBL is its ever increasing complexity for many-step fabrication of smaller features or intricate geometries. Therefore, EBL is mostly constrained to planar, binary geometries with moderate efficiencies strongly decreasing with energy and not effective for hard X-rays. Special 3D geometries in the form of kinoform lenses can theoretically have 100 % focusing efficiencies. Attempts to approximate these geometries via EBL increased the number of process steps even further. The smallest FZP feature size even for low aspect ratios achievable via EBL is fundamentally limited due to the proximity effect which is the interaction and spread of electrons within the resist material. We addressed these issues by focusing our research on alternative FZP fabrication techniques as high-speed ion beam lithography (IBL), and gray scale ion lithography to realize efficient kinoforms. Another approach towards full-material multilayer FZPs with infinite aspect ratio was based on atomic layer deposition (ALD) with subsequent ion beam slicing. Each of these three methods targets specific challenges faced by the e-beam lithography based FZP fabrication techniques. All the fabricated FZPs were tested for their resolution and efficiency performances at a state of the art scanning transmission X-ray microscope at BESSY for soft X-rays and/or at optical test stations at ESRF and PETRA III for hard X-rays. Using IBL the rapid preparation of a 110 nm thick Au FZP with 50 µm diameter and 50 nm ∆r in less than 13 minutes is demonstrated. Employed for X-ray microscopy, the FZP clearly resolved 28.5 nm features with a cut-off of 24.3 nm at ~1120 eV. Additional process improvements were made towards smaller zones with higher zone quality. They allowed the preparation of a FZP with 30 nm outermost half-period remarkably, in about 8 min. This FZP was shown to clearly resolve 21 nm features on a multilayer test object with large room for improvement. This high through-put FZP production route is of special interest not only concerning the low cost and easy availability. A large array of these optical components is attractive, for experiments such as one-shot ultra-high brilliance FEL investigations due to the radiation damage or for instance for coded-aperture arrays for high-angle resolving X-ray astronomy. Towards fabrication of kinoforms for high efficiency X-ray focusing, we have performed various materials optimization studies in order to achieve a high surface quality optic. After various trials the materials were finally optimized and the fabricated lenses achieved more than 14 % absolute diffraction efficiency that is almost 90 % compared to the theoretical prediction. This confirms how closely we were able to replicate the ideal three dimensional surface relief structure for the first time. It was possible to carry out imaging with these lenses with half-pitch resolutions down to 60 nm. The kinoform lenses were tested at the soft X-ray range where a significant absorption is present in materials. These results also potentially pave the way for very high efficiency hard X-ray focusing which can in principle be utilized in laboratory based X-ray sources, X-ray astronomy and the new rising field of X-ray ptychography. To fabricate high resolution ML-FZPs, Al2O3/Ta2O5multilayers, deposited on a smooth glass optical fiber via atomic layer deposition using non-dedicated instruments were carefully cut-out, sliced and polished to a high quality surface finish using focused ion beams. Following the transfer of the slice to a TEM grid as holder the slices were polished to a high surface finish quality, also via a focused ion beam. Fabricated ML-FZPs were synchrotron tested using an in-house constructed 2-axis tilt stage specially designed for aligning ML-FZP with respect to the X-ray optical axis. The results showed that it was possible to resolve 21 nm features in direct imaging at 1200 eV and sub-30 nm focusing at 8 keV. This is the highest demonstrated resolving power for a multilayer type FZP, to date to the best of our knowledge. Results exhibit the potential for high-resolution hard X-ray focusing where this type of optics are especially efficient. For ultra-high resolution hard and soft X-ray imaging, with potentially achievable ∆r of a few nm is well below what can be achieved through any lithography method available today.Item Open Access Influencing the ionic space charge potential in grain boundaries of oxide ceramics(2017) Weissmayer, Michael Patrick; Maier, Joachim (Prof. Dr. rer. nat.)Item Open Access In situ characterization of phase evolution in LiFePO4(2015) Ohmer, Nils; Maier, Joachim (Prof. Dr.)Among the candidates for electrodes in future Li-based batteries, LiFePO4 (LFP) is one of the most important and most frequently studied materials, undergoing a phase transformation upon delithiation to FePO4 (FP). In spite of the great scientific and practical interest in this material, there is still an extensive debate on the mechanism of this phase transformation and the underlying factors of influence. Within the framework of this thesis, first studies are carried out ex situ on multi-particle, full electrode LFP materials, being electrochemically cycled and analyzed at various states of charge by a combination of highly spatially resolved methods (high-resolution transmission electron microscopy and electron energy loss spectroscopy (HRTEM, EELS)) and integral measurement techniques (analyzing the X-ray diffraction and X-ray absorption near edge structure (XRD, XANES)). This combination of characterization techniques allows one to distinguish between the cycling behaviour of differently sized crystallites within the same electrode. It is found that for electrodes with hydrothermally grown LFP as active material, a particle size dependent cycling behaviour exists, with nanosized particles apparently not participating in the charging process at all. A turbostratic stacking of layers in these nanosized particles is found and identified to be responsible for sluggish lithium insertion and extraction. These higher dimensional defects prevent the small particles from participating in the charging process, most likely by disturbing the lithium diffusion along the 1-dimensional channels, as well as impair the transport along the other directions in the LFP host structure and thus blocking the lithium transport, resulting in a comparibly lower practical capacity during electrochemical cycling. To study the lithium exchange mechanism upon charging a LFP thin film cathode, an all-solid-state thin film battery cell with a lateral design concept is developed and realized by pulsed laser deposition (PLD) and thermal evaporation techniques. Using PLD and shadow masks LFP cathode, Li2O-V2O5-SiO2 (LVSO) electrolyte and LiAl anode thin films are deposited sequentially in a way that the Li transport pathway in the resulting battery is along the X-ray transparent commercial Si3N4 membrane substrate. This enables the usability of synchrotron-based energy resolved scanning transmission X-ray microscopy (STXM) with its high chemical and spatial resolution to perform in situ absorption measurements at the Fe L3 edge. Upon delithiation, a shift in the main absorption feature from 708 to 710 eV is used to fingerprint the change in the local state of charge, identifying areas containing Fe2+ (lithiated) and Fe3+ (delithiated), respectively. The initial lithiation process of a LFP thin film cathode material has been followed by in situ STXM, with a lateral resolution of 30 nm, during electrochemical charging of the thin film battery. The observed initial lithiation process does not follow the classical particle by particle mechanism, typical for multi-particle LFP cathodes, but instead a rather simultaneous, although inhomogeneous, lithiation is observed. The reason for this change in mechanism, compared to multi-particle powder electrodes, is found in mechanical interactions within the thin film upon lithiation, i.e. in the corresponding volume expansion and formation of high energy surfaces, changing the shape of the single-particle chemical potential to a monotone form upon lithiation. This has far-reaching consequences: not only the many-particle mechanism is changed to a concurrent lithiation, but also the single-particle mechanism is changed from a two-phase to a single-phase mechanism upon lithiation. Furthermore, a vanishing hysteresis loop and the disappearing of the memory effect is predicted. These findings are rather general and applicable to all kind of thin films of phase separating intercalation materials, undergoing a volume change upon lithium exchange. To fill the gap in literature on in situ observations of the (L)FP phase evolution on a single-particle level with appreciable space and time resolution, a micrometer-sized all-solid-state thin film battery is built with a defect-chemically well characterized LFP single crystal as cathode material with dimensions of 16x1x0.2 micrometer. Using STXM, the phase evolution along the fast (010) orientation is followed during in situ electrochemical (de)lithiation on a micro-meter scale with a lateral resolution of 30 nm and with minutes of time resolution. Furthermore, the STXM measurements performed on this sample are one of the few experiments ever taken on LFP materials with a well defined defect chemistry, even though fundamentally necessary for an overall understanding of the materials behaviour. This combination discloses not only the mechanism of LFP transformation on a single-particle level, but also the significance of elastic effects on the (de)lithiation process. Using a defect chemical analysis, the position of phase formation is found to be determined by the defect chemical situation, while the growth pattern of both LFP and FP is found to be dominated by elastic effects.Item Open Access Einfluss von Platin-Abscheidungen auf die Membrandegradation in Polymerelektrolytbrennstoffzellen(2016) Helmly, Stefan; Friedrich, K. Andreas (Prof. Dr.)Item Open Access Validierung von Reaktionsmechanismen für biogene Kraftstoffkomponenten(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2016) Schuler, Dominik Friedemann; Zabel, Friedhelm (Prof. Dr.)In der vorliegenden Arbeit werden die Verbindungen Butanol, 2-Butanol, iso-Butanol und 2,5-Dimethylfuran bei Bedingungen, die für die technische Verbrennung relevant sind, untersucht (p=8.20 bar, T=1190-1520 K). Diese Verbindungen sind mögliche Komponenten zukünftiger Kraftstoffe. Die Experimente werden in Abwesenheit von Sauerstoff (Pyrolyse) in einem speziell für diese Untersuchungen konfigurierten Single-Pulse-Stoßrohr hinter reflektierten Stoßwellen durchgeführt. Die Experimente werden mit der Simulationsumgebung Chemkin II und kinetischen Reaktionsmodellen aus der Literatur simuliert, um die Produktverteilungen aus Experiment und Simulation gegenüber zu stellen. Zur besseren Charakterisierung der Unterschiede zwischen den Modellen werden Reaktionsfluss- und Störungsanalysen durchgeführt. Mit Hilfe dieser Daten kann Verbesserungspotential in den Mechanismen identifiziert werden und Ansätze für eine Optimierung können aufgezeigt werden. Bei der Pyrolyse der Butanolisomere wurden die Hauptprodukte Ethen, Ethin, Ethan, Methan und Propen quantifiziert. In geringeren Konzentrationen wurden die Produkte Ethanal, 1,3-Butadien, 1,3-Butadiin, 2-Buten, iso-Buten, Propen, Propin und Allen nachgewiesen. Bei den Simulationen zeigten sich einerseits teils erstaunlich gute Vorhersagen der experimentellen Daten, andererseits bei einigen Produktspezies auch eine große Diskrepanz der Vorhersagen der Mechanismen untereinander sowie zum Experiment. Bei der Pyrolyse von 2,5-Dimethylfuran wurden die Hauptprodukte Kohlenstoffmonoxid, Ethan, Ethen, Ethin und 1,3-Butenin nachgewiesen. Weitere quantifizierte Produkte sind Allen, Benzol, 1,3-Butadien, 1,3-Butadiin, 2-Buten, Butin, Cyclopentadien, 2-Methylfuran, Propen, Propin und Toluol. Die Mechanismen zeigen in den Hauptprodukten eine gute Übereinstimmung untereinander und mit den experimentell gewonnenen Daten. Bei den Nebenprodukten kommt es jedoch auf Grund der Unterschiede in den Mechanismen zu unterschiedlichen Vorhersagen. Neben den Untersuchungen im Single-Pulse-Stoßrohr wurde in einem weiteren Stoßrohr hinter reflektierten Stoßwellen zeitaufgelöst die Bildung von Kohlenstoffmonoxid bei der Pyrolyse von 2,5-Dimethylfuran gemessen. Kohlenstoffmonoxid wurde dabei mittels Absorptionsmessungen bei einer Wellenlänge von 151,0 nm detektiert. Das ebenfalls auf dieser Wellenlänge absorbierende Edukt 2,5-Dimethylfuran und das Produkt Ethin wurden bei der Vorhersage der Absorption berücksichtigt. Im Rahmen der Messgenauigkeit decken sich die gefundenen Absorptionen mit den von den Modellen vorhergesagten Werten, so dass die Messungen die Reaktionsmodelle unterstützen.