Universität Stuttgart
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Item Open Access Genetisch modifizierte Biotemplate zur Erzeugung von Zr-basierten Nanomaterialien(2019) Eisele, Rahel; Bill, Joachim (Prof. Dr.)In Biomineralisationsprozessen aus der belebten Natur scheiden sich anorganische Materialien auf organischen Templaten (Biomakromoleküle) ab. Funktionelle Gruppen der Makromoleküle steuern dabei die Abscheidung aus einer wässrigen Lösung sowie die Strukturierung des anorganischen Materials. Dabei sind spezifische Wechselwirkungen zwischen dem organischen Templat und dem anorganischen Material von Bedeutung. Die Materialbildung findet unter Umgebungsbedingungen in wässrigen Systemen statt. Für technisch interessante Materialien wie Zirkoniumdioxid (ZrO2) stellt die energieeffiziente Herstellung präziser Nanostrukturen eine technische Herausforderung dar. Daher wurden im Rahmen dieser Arbeit die Prinzipien der Biomineralisation auf die Herstellung von Zirkonium-basiertem Material (ZrbM) übertragen. Hierzu gehörte die Materialbildung durch Mineralisation aus einer ZrOCl2-Lösung sowie eine gezielte Mineralisation auf bioorganischen M13-Bakteriophagentemplaten. Um die „biologische Spezifität“ in Biomineralisationsprozessen auf die Bildung von ZrbM zu übertragen, wurden Peptide mittels Phagen-Display identifiziert, die spezifisch an ZrO2 binden. Mittels genetischer Modifikation wurden diese ZrO2 Bindepeptide auf der Phagenoberfläche präsentiert. Hierdurch wurde eine hohe Bindepeptiddichte und damit viele Interaktionspunkte zum anorganischen Material erzielt. Bevor der Einfluss dieser Bindepeptide auf die Mineralisation von ZrbM untersucht werden konnte, wurde zunächst der Partikelbildungs- und Partikelwachstumsprozess von ZrbM in einer ZrOCl2-Lösung und einem Ethanol-Wasser Lösungsmittelgemisch bei verschiedenen System- und Prozessparametern beschrieben. Auf Grundlage dieser Ergebnisse wurde eine Mineralisationslösung etabliert mit der der Einfluss der Bindepeptide - präsentiert auf der Phagenoberfläche - auf die Mineralisation von ZrbM untersucht werden konnte. Die Bindepeptide zeigten einen deutlichen Einfluss auf die Mineralisation von ZrbM. Im Vergleich zu Bakteriophagen ohne Bindepeptid wurde mit den genetisch modifizierten Bakteriophagen eine deutlich höhere Abscheiderate erzielt. Dieser Einfluss der Bindepeptide wurde auf Hydroxygruppen in Serineinheiten zurückgeführt. Diese führen zum einen zu einer starken Anziehung von molekularen Zr-Spezies an das Biotemplat. Zum anderen induzieren die Hydroxygruppen die heterogene Keimbildung von ZrbM durch Kondensationsreaktionen zwischen dem Biotemplat und molekularen Zr-Spezies. Somit ist es nun möglich genetisch kontrolliert Zr-basierte Nanomaterialien zu mineralisieren. Im Rahmen dieser Arbeit gelang es nicht nur einzelne Phagen zu mineralisieren, sondern auch dünne homogene Schichten aus ZrbM. Diese ZrbM-Schichten wurden im letzten Teil dieser Arbeit vergleichend zu Phagenschichten und SiO2-Schichten auf die Adhäsion von Staphylococcus aureus (S. aureus) getestet. S. aureus ist ein pathogenes Bakterium, welches zur Bildung von Biofilmen, zum Beispiel auf Implantaten, und dadurch zu einem Implantatverlust bis hin zu lebensbedrohlichen Komplikationen führen kann. Die Biofilmbildung kann effektiv unterbunden werden, indem die Bakterienadhäsion auf Oberflächen verhindert wird. Daher wurde im Rahmen dieser Arbeit untersucht, ob bestimmte chemische Oberflächen, das heißt bestimmte Materialien oder auch bestimmte funktionelle Gruppen, die Bakterienadhäsion unterdrücken können. Die Untersuchung der Bakterienadhäsion auf den verschiedenen Oberflächen ergab, dass auf der Phagenschicht im Vergleich zur SiO2-Schicht und einer Schicht aus ZrbM eine sehr geringe Bakterienadhäsion vorlag. Untersuchungen verschiedener Einflussfaktoren auf die Bakterienadhäsion zeigten, dass die Bakterienadhäsion an der SiO2-Schicht und der ZrbM-Schicht durch die Oberflächenrauigkeit, die Hydrophobizität und die Oberflächenladung beeinflusst werden kann. Bei der Phagenschicht korrelierten weder die Oberflächenladung, noch die Oberflächenrauigkeit und die Hydrophobizität im Vergleich zu den anorganischen Materialoberflächen mit der Bakterienadhäsion. Dies ließ darauf schließen, dass die geringe Bakterienadhäsion auf der Phagenschicht auf die biochemische Zusammensetzung der Hüllproteine, vor allem auf die Abwesenheit spezifischer Bindedomänen (Ligand-Rezeptor-Wechselwirkungen), zurückzuführen ist.Item Open Access Interaction of carbon and nitrogen in iron(Stuttgart : Max-Planck-Institut für Intelligente Systeme (ehemals Max-Planck-Institut für Metallforschung), 2016) Göhring, Holger; Mittemeijer, Eric Jan (Prof. Dr. Ir.)Item Open Access Aluminum-induced crystallization of semiconductor thin films(2015) Qu, Fei; Schmitz, Guido (Prof. Dr.)Thin film materials of the semiconductors, such as silicon (Si), germanium (Ge) or their alloys, are turning into the most promising functional materials in the energy technology. However, the morphologies of these semiconductor thin films must be varied to be suitable for the different applications, e.g. a large-grained layer as the seed layer of thin film solar cells, a porous structure for anode materials of high energy rechargeable lithium (Li) ion batteries. Due to the collective interdiffusion process during the aluminum (Al)-induced crystallization, in this thesis, the suitable morphologies are achieved for the corresponding applications under the different fabrication conditions. A large-grained Si layer can be formed by the crystallization of Si in a porous Al layer, which is obtained by applying a bias voltage. Since the Al grain boundaries are contaminated by e.g. oxygen (O), the diffusion of Si in the Al grain boundaries is retarded. It can lead to a reduction of the nucleation density of Si. At a certain high temperature, a collective diffusion process of Si in Al is activated. Consequently, a large-grained Si layer with (100) texture can be formed. By purposely interrupting the annealing of nanocrystalline Al/amorphous Si (a-Si) bilayers, a porous structure of the crystallized Si can be developed due to the incomplete intermixing of Si and Al. Due to the different dominant diffusion processes of Si in Al at the different annealing temperatures, the most Si diffuses along the different paths in the Al layer, such as triple junction, grain boundary and Al bulk. Therefore, it can develop the different morphologies of the porous Si layers after the selectively etching of Al. By introducing an amorphous Ge interlayer between the crystalline Al and amorphous Si layer, the Al grain boundaries are not essential for the crystallization of the amorphous Si in contrast to the case in Al/Si bilayer system. Si crystallizes continuously on the pre-crystallized Ge seeds which form initially at the original interface of crystalline Al and amorphous Ge. The thermodynamic models to interpret the fundamentals of these different crystallization behaviors of Si are established based on the change of the interface energy between the different phases of the whole system during the crystallization. Using the effective diffusivity, the dominant diffusion process of Si in Al can be investigated to explore the morphological dependence of the crystallized Si layer on the annealing conditions.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 Microstructural changes and intermetallic compound formation in metallic bilayers(Stuttgart : Max-Planck-Institut für Intelligente Systeme (ehemals Max-Planck-Institut für Metallforschung), 2016) Rossi, Paul J.; Mittemeijer, Eric Jan (Prof. Dr. Ir.)This thesis investigates interdiffusion and intermetallic compound (IMC) formation, as well as their effects on the microstructure, in metallic thin-film bilayers. The investigation focuses on bilayers based on the Ag-Sn and Ag-In binary systems, which are technologically important as basis for lead free solders. Due to the enhanced diffusional mechanisms in these systems, diffusion occurs readily even at room and low temperatures. The proceeding interdiffusion eventually leads to IMC formation in the bilayers, allowing for the investigation of the kinetics of IMC formation and the associated microstructural changes at room and low temperatures. The combination of the properties special to thin films with the diffusional mechanisms in the binary Ag-Sn and Ag-In systems leads to interesting effects, such as the dependence of IMC formation on the stacking sequence in the bilayers. The obtained experimental results for both systems could be explained using thermodynamic and kinetic models. Experimental characterization of the bilayers mainly relied on X-ray diffraction (XRD) and electron microscopy. In order to investigate the effect of the deposition process on IMC formation and the microstructure of the bilayers, different physical vapor deposition (PVD) techniques, especially thermal evaporation and magnetron sputtering, were used for the preparation of the bilayers. During investigation of the Ag-Sn system it was found that ambiguity exists among the published crystal structures of the Ag3Sn IMC. Therefore, the crystal structure of Ag3Sn has been reinvestigated using high-resolution XRD in connection with Rietveld refinements.Item Open Access Design of nanostructured vanadium pentoxide scaffolds inspired by natural cuttlebone(2018) Knöller, Andrea; Bill, Joachim (Prof. Dr.)Item Metadata only Internal precipitation of nitrides in iron-based alloys(Stuttgart : Max-Planck-Institut für Intelligente Systeme (ehemals Max-Planck-Institut für Metallforschung), 2016) Steiner, Tobias; Mittemeijer, Eric J. (Prof. Dr. Ir.)X‐ray diffraction has become a standard method of microstructural analysis. However, in systems with a complex microstructure, the interpretation of the measured diffractograms may not be very straightforward. The influence of the precipitation of fine alloying element nitrides and the changes in precipitation morphology that occur upon continued nitriding on the shape and position of XRD peaks have been identified. The thus obtained quantitative model has been applied to a variety of precipitation systems and in general good agreement of predicted values and experimental results is found. The precipitation of finely distributed alloying element nitrides is the main strengthening mechanism in the diffusion zone of nitrided parts. Various alloying elements having an affinity for N show considerably different nitriding behavior. Cr shows a strong N‐affinity and therefore readily precipitates in the presence of N. However, Mo has a weak strength of interaction with N and reacts only slowly. In order to better understand the nitriding behavior of nitrided steels containing both Cr and Mo, the nitriding behavior of ternary Fe‐Cr‐Mo model alloys is investigated. The complex precipitation sequence of ternary mixed Cr-Mo-nitrides has been identified and the role of the Cr/Mo-ratio of the alloy is exposed. X‐ray diffraction has become a standard method of microstructural analysis. However, in systems with a complex microstructure, the interpretation of the measured diffractograms may not be very straightforward. The influence of the precipitation of fine alloying element nitrides and the changes in precipitation morphology that occur upon continued nitriding on the shape and position of XRD peaks have been identified. The thus obtained quantitative model has been applied to a variety of precipitation systems and in general good agreement of predicted values and experimental results is found.Item Open Access Hydrogen transport in thin films : Mg-MgH2 and Ti-TiH2 systems(2018) Hadjixenophontos, EfiHydrogen storage has become progressively important due to increasing energy demand. Magne-sium (Mg/MgH2) is one of the most promising elements of hydrogen uptake, however, the slow kinetics and need for high temperatures during dehydrogenation make this material challenging for mobile applications. Meanwhile, Titanium (Ti/TiH2/TiO2) draws attention due to its catalytic effect in hydrogenation of other metals with higher capacities. A comprehensive way to quantitatively char-acterize the kinetics of hydride formation in both systems (Mg and Ti) is shown here. A technique allowing a large range of pressures and temperatures (room temperature to 300 °C and from 0.05 bar up to 100 bar) is developed successfully. Thin films (50-1000 nm), deposited by ion beam sput-tering (PVD), are used because of their smooth surface and defined structure. In order to study hydrogen transport precisely, X-ray diffraction (XRD), electron microscopy (SEM/FIB/TEM) and electric resistance measurements are used. In the case of Mg, while a Pd coating is used as catalyst, the hydride is formed from the surface towards the substrate and transformation in the morpholo-gy is observed. Parabolic law is followed and the diffusion coefficient of hydrogen in MgH2 is ob-tained at room temperature (2.67 · 10-17 cm2/s). Additionally, a model is created to fit the experi-mental change in resistance during hydrogen loading and shows the changes in the behavior of thicker layers. The interface between Pd/Mg is discussed, since Mg5Pd2 and Mg6Pd are formed at high temperatures and are most dominant over dehydrogenation. However, at room temperature, this interface appears to be more stable. The activation energy of hydrogenation is calculated ex-perimentally from an Arrhenius plot to be equal to Ea = 22.6 ± 2.0 kJ/mol and the pre-factor D0 = 3904 cm2/s. Additional attention is given to magnesium hydride as an anode electrode in Li-ion bat-teries. TEM investigations of thin film electrodes demonstrate the complete lithiation of the mate-rial however, with drastic volume changes, leading to bad reversibility. In Ti the thin oxide layer naturally formed on the surface, appears to play a dominant role in the kinetics of hydrogen transport leading to a linear kinetics. A pressure dependency is observed, while an experimental evaluation of the permeation coefficient in the oxide is also discussed. Important information on the hydrogen transport is obtained in both systems, giving an input for further improvements of such hydrides.Item Open Access Functional nanostructured metal oxide hybrid materials based on M13 phages(2019) Kilper, Stefan; Bill, Joachim (Prof. Dr.)Item Open Access Misfit-layered cobalt oxides for thermoelectric energy conversion(2017) Büttner, Gesine; Weidenkaff, Anke (Prof. Dr.)The conversion of waste heat into electrical current by a thermoelectric converter can significantly contribute to a more sustainable usage of our resources. The p-type misfit-layered [Ca2CoO3-δ][CoO2]1.62 is known for its promising conversion efficiency, which yet needs to be improved significantly for commercial applications. The efficiency of a material increases with the Figure of Merit ZT=σα^2/κ, with Seebeck coefficient α, electrical conductivity σ, and thermal conductivity κ. The aim of this thesis is to provide a better understanding of the electrical and the thermal properties of the complex [Ca2CoO3 δ][CoO2]1.62 and to use this understanding to improve the efficiency of converters. Accordingly, (i) the increase of ZT via cation substitution is shown; (ii) a better understanding of the electrical transport above room temperature is developed; (iii) the effect of stoichiometric defects and secondary phases on the thermoelectric properties is investigated. Finally, (iv) [Ca2CoO3 δ][CoO2]1.62 - CaMn0.97W0.03O3 δ - converters are fabricated and the efficiency is increased by a suitable converter design. More specifically, the unexplored influence of Ru and In substitution on the thermoelectric properties of the polycrystalline [Ca2CoO3 δ][CoO2]1.62 is investigated. While In does not have a positive effect, Ru for Co substitution increases ZT up to 20 %. This increase stems from a strong reduction of the thermal conductivity - which is probably induced by resonance scattering - while the decrease of the power factor α^2 σ is minor. The electrical transport mechanism of pure and Ru-substituted [Ca2CoO3 δ][CoO2]1.62 between room temperature and 800 K so far lacks a coherent theoretical model. Surprisingly, the framework of Anderson localization, which was developed to describe conduction in an impurity band of semiconductors, can be applied to the oxide. The Anderson model assumes that transport happens via charge-carrier hopping in a random Coulomb potential. For [Ca2CoO3 δ][CoO2]1.62, charges are considered to hop between Co sites in the CoO2 layer, while the random potential originates from interactions with the mismatched Ca2CoO3 δ layer. The presence of the ionized Ru atoms further alters the Coulomb potential, which increases the activation energy of the transport behavior. This understanding might contribute to the development of better theoretical models for the prediction of the thermoelectric properties of substituted [Ca2CoO3 δ][CoO2]1.62 compounds. A further improvement of the materials efficiency can be achieved by systematic introduction of stoichiometric defects and impurity phases. Here, the unexplored influence of the Co/Ca ratio on the thermoelectric properties of [Ca2 wCoO3 δ][CoO2]1.62, and the effect of Co3O4 impurity phase are investigated. It is shown that an increasing Co/Ca ratio in the [Ca2 wCoO3 δ][CoO2]1.62 phase leads to a larger figure of merit ZT induced by a strong resistivity drop. The decrease of resistivity stems from additional p-type charge carriers created by the formation of Ca vacancies. The Co3O4 impurity phase increases the thermal conductivity of the composite samples and leads to a reduction of ZT when the volume fraction of the Co3O4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca2 wCoO3 δ][CoO2]1.62 phase. Not only the figures of merit of the materials, but also the design of a thermoelectric converter determines the device efficiency. In a converter, a p-type and a suitable n-type thermoelectric material are connected electrically in series and thermally in parallel. Here, [Ca2 wCoO3 δ][CoO2]1.62 is combined with the n-type CaMn0.97W0.03O3-δ and the device efficiency is improved by a variation of the ratio A_p/A_n of the cross section areas of the legs. The good agreement between the experimental values and the predictions of the compatibility model show the high quality of the fabricated devices and the value of the model for the optimization of the converter design. The adjustment of A_p/A_n improves the power output and the efficiency of the converters, where the best volume and area power densities exceed published high temperature values. The achieved efficiency of 1.08 % at a temperature of 1085 K at the hot side is close to the theoretical expected efficiency and can be further improved via ZT.