Structuring of polymer surface by evaporation of sessile microdrops

In this thesis, we investigated the evaporation of sessile microdroplets on different solid substrates. Three major aspects were studied: the influence of surface hydrophilicity and heterogeneity on the evaporation dynamics for an insoluble solid substrate, the influence of external process parameters and intrinsic material properties on microstructuring of soluble polymer substrates and the influence of an increased area to volume ratio in a microfluidic capillary, when evaporation is hindered. In the first part, the evaporation dynamics of pure sessile water drops on smooth self-assembled monolayers (SAMs) of thiols or disulfides on gold on mica was studied. With increasing surface hydrophilicity the drop stayed pinned longer. Thus, the total evaporation time of a given initial drop volume was shorter, since the drop surface, through which the evaporation occurs, stays longer large. Usually, for a single drop the volume decreased linearly with t1.5, t being the evaporation time, for a diffusion-controlled evaporation process. However, when we measured the total evaporation time, ttot, for multiple droplets with different initial volumes, V0, we found a scaling of the form V0 = attotb. The more hydrophilic the substrate was, the more showed the scaling exponent a tendency to an increased value up to 1.6. This can be attributed to an increasing evaporation rate through a thin water layer in the vicinity of the drop. Under the assumption of a constant temperature at the substrate surface a cooling of the droplet and thus a decreased evaporation rate could be excluded as a reason for the different scaling exponent by simulations performed by F. Schönfeld at the IMM, Mainz. In contrast, for a hairy surface, made of dialkyldisulfide SAMs with different chain lengths and a 1:1 mixture of hydrophilic and hydrophobic end groups (hydroxy versus methyl group), the scaling exponent was found to be ~ 1.4. It increased to ~ 1.5 with increasing hydrophilicity. A reason for this observation can only be speculated: in the case of longer hydrophobic alkyl chains the formation of an air layer between substrate and surface might be favorable. Thus, the heat transport to the substrate might be reduced, leading to a stronger cooling and thus decreased evaporation rate. In the second part, the microstructuring of polystyrene surfaces by drops of toluene, a good solvent, was investigated. For this a novel deposition technique was developed, with which the drop can be deposited with a syringe. The polymer substrate is lying on a motorized table, which picks up the pendant drop by an upward motion until a liquid bridge is formed. A consecutive downward motion of the table after a variable delay, i.e. the contact time between drop and polymer, leads to the deposition of the droplet, which can evaporate. The resulting microstructure is investigated in dependence of the processes parameters, i.e. the approach and the retraction speed of the substrate and the delay between them, and in dependence of the intrinsic material properties, i.e. the molar mass and the type of the polymer/solvent system. The principal equivalence with the microstructuring by the ink-jet technique was demonstrated. For a high approach and retraction speed of 9 mm/s and no delay between them, a concave microtopology was observed. In agreement with the literature, this can be explained by a flow of solvent and the dissolved polymer to the rim of the pinned droplet, where polymer is accumulated. This effect is analogue to the well-known formation of ring-like stains after the evaporation of coffee drops (coffee-stain effect). With decreasing retraction speed down to 10 µm/s the resulting surface topology changes from concave to convex. This can be explained with the increasing dissolution of polymer into the solvent drop prior to the evaporation. If the polymer concentration is high enough, gelation occurs instead of a flow to the rim and the shape of the convex droplet is received. With increasing delay time from below 0 ms to 1s the depth of the concave microwells decreases from 4.6 µm to 3.2 µm. However, a convex surface topology could not be obtained, since for longer delay times the polymer sticks to the tip of the syringe. Thus, by changing the delay time a fine-tuning of the concave structure is accomplished, while by changing the retraction speed a principal change of the microtopolgy can be achieved. We attribute this to an additional flow inside the liquid bridge, which enhanced polymer dissolution. Even if the pendant drop is evaporating about 30 µm above the polymer surface without any contact (non-contact mode), concave structures were observed. Rim heights as high as 33 µm could be generated for exposure times of 20 min. The concave structure exclusively lay above the flat polymer surface outside the structure even after drying. This shows that toluene is taken up permanently. The increasing rim height, rh, with increasing exposure time to the solvent vapor obeys a diffusion law of rh = rh0  tn, with n in the range of 0.46 ~ 0.65. This hints at a non-Fickian swelling process. A detailed analysis showed that the rim height of the concave structure is modulated, unlike for the drop deposition. This is due to the local stress relaxation, which was initiated by the increasing toluene concentration in the extruded polymer surface. By altering the intrinsic material parameters i.e. the polymer molar mass and the polymer/solvent combination, several types of microstructures could be formed. With increasing molar mass from 20.9 kDa to 1.44 MDa the resulting microstructure changed from convex, to a structure with a dimple in the center, to concave, to finally an irregular structure. This observation can be explained if one assumes that the microstructuring is dominated by two opposing effects, a decreasing solubility with increasing polymer molar mass, but an increasing surface tension gradient leading to instabilities of Marangoni-type. Thus, a polymer with a low molar mass close or below the entanglement limit is subject to a high dissolution rate, which leads to fast gelation compared to the evaporation rate. This way a coffee-rim like effect is eliminated early and a convex structure results. For high molar masses the low dissolution rate and the low polymer diffusion might lead to increased surface tension gradients and a typical local pile-up of polymer is found. For intermediate polymer masses around 200 kDa, the dissolution and evaporation rate are comparable and the typical concave microtopology is found. This interpretation was supported by a quantitative estimation of the diffusion coefficient and the evaporation rate. For a different polymer/solvent system, polyethylmethacrylate (PEMA)/ethylacetate (EA), exclusively concave structures were found. Following the statements above this can be interpreted with a lower dissolution rate. At low molar masses the concentration of PEMA in EA most likely never reaches the gelation point. Thus, a concave instead of a convex structure occurs. At the end of this section, the optically properties of such microstructures for a potential application as microlenses are studied with laser scanning confocal microscopy. In the third part, the droplet was confined into a glass microcapillary to avoid evaporation. Since here, due to an increased area to volume ratio, the surface properties of the liquid and the solid walls became important, the influence of the surface hydrophilicity of the wall on the interfacial tension between two immiscible liquid slugs was investigated. For this a novel method for measuring the interfacial tension between the two liquids within the capillary was developed. This technique was demonstrated by measuring the interfacial tensions between slugs of pure water and standard solvents. For toluene, n-hexane and chloroform 36.2, 50.9 and 34.2 mN/m were measured at 20°C, which is in a good agreement with data from the literature. For a slug of hexane in contact with a slug of pure water containing ethanol in a concentration range between 0 and 70 (v/v %), a difference of up to 6 mN/m was found, when compared to commercial ring tensiometry. This discrepancy is still under debate.

The influence of heat treatment on the phase relations in mineral growth systems

ABSTRACT Corundum is one of the most famous gems materials. Different heat treatment methods for enhancement purposes are commonly applied and accepted in the gem market. With this reason, the identification of the natural, unheated corundum is intensively investigated. In this study, aluminium hydroxide minerals and zircon are focused to observe the crystallization and phase change of these minerals during heat treatment procedures. Aluminium hydroxide minerals can be transformed to alumina with the corundum structure by heating. The reaction history of aluminium hydroxide minerals containing corundum was investigated comparing it with diaspore, boehmite, gibbsite and bayerite by TG and DTA methods. These hydroxide minerals were entirely transformed to corundum after heating at 600°C. Zircon inclusions in corundums from Ilakaka, Madagascar, were investigated for the influence of different heat-treatment temperatures on the recovery of their crystalline structure and on possible reactions within and with the host crystals. The host corundum was heated at 500, 800, 1000, 1200, 1400, 1600 and 1800°C. The crystallinity, the trapped pressure, and the decomposition of the zircon inclusions within the host corundum have been investigated by Raman spectroscopy. Radiation-damaged zircon inclusions may be used as an indicator for unheated Ilakaka corundum crystals. They are fully recrystallized after heating at 1000°C influencing the lowering of the 3 Raman band shift, the decreasing of FWHM of the 3 Raman band and the decreasing of the trapped pressure between the inclusion and the host corundum. Under microscopic observation, surface alterations of the inclusions can be firstly seen from transparent into frosted-like appearance at 1400°C. Then, between 1600°C and 1800 °C, the inclusion becomes partly or even completely molten. The decomposition of the zircon inclusion to m-ZrO2 and SiO2-glass phases begins at the rim of the inclusion after heating from 1200°C to 1600°C which can be detected by the surface change, the increase of the 3 Raman band position and the trapped pressure. At 1800°C, the zircon inclusions entirely melt transforming to solid phases during cooling like m-ZrO2 and SiO2-glass accompanied by an increase of pressure between the transformed inclusion and its host.

Spin-crossover in metallomesogens of iron(II)

Covalent grafting mesogenic groups to the coordination cores of the parent mononuclear low-spin and spin-crossover compounds afforded metallomesogenic complexes of iron(II). In comparison with the parent complexes the spin-crossover properties of the alkylated derivatives are substantially modified. The type of the modification was found to be dependent on the properties of the parent system and the nature of the used anion, however, the general tendency is the destabilization of the low-spin state at the favor of spin-crossover or high-spin behavior below 400 K. The structural insight revealed the micro-segregated layered organization. The effect of the alkylation of the parent compounds consists first of all in the change of the lattice to a two-dimensional lamellar one retaining significant intermolecular contacts only within the ionic bilayers. The comprehensive analysis of the structural and thermodynamic data in the homologous series pointed at the mechanism of the interplay between the structural modification on melting and the induced anomalous change of the magnetic properties. A family of one-dimensional spin-crossover polymers was synthesized and characterized using a series of spectroscopic methods, X-ray powder diffraction, magnetic susceptibility measurements and differential scanning calorimetry. The copper analogue of was also synthesized and its crystal structure solved. In comparison with the mononuclear systems, the polymeric mesogens of iron(II) are less sensitive to the glass transition, which was attributed to the moderate concomitant variation of the structure. Nevertheless, the observed increase of the magnetic hysteresis with lengthening of the alkyl substituents was ascribed to the interplay of the structural reorganization of the coordination core due to spin-crossover with the structural delay in the spatial reorganization of the mesogenic substituents. The classification of mononuclear and polymeric metallomesogens according to the interactions between the structural- and the spin-transition and analysis of the data on the reported spin-crossover metallomesogens led to the separation of three types, namely: Type i: systems with coupling between the electronic structure of the iron(II) ions and the mesomorphic behavior of the substance; Type ii: systems where both transitions coexist in the same temperature region but are not coupled due to competition with the dehydration or due to negligible structural transformation; Type iii: systems where both transitions occur in different temperature regions and therefore are uncoupled. Fine-tuning, in particular regarding the temperature at which the spin-transition occurs with hysteresis properties responsible for the memory effect, are still a major challenge towards practical implementation of spin-crossover materials. A possible answer to the problem could be materials in which the spin-crossover transition is coupled with another transition easily controllable by external stimuli. In the present thesis we have shown the viability of the approach realized in the mesogenic systems with coupled phase- and spin-transitions.

Computer simulations of microstructures related to the olivine spinel transition

Tiefherd-Beben, die im oberen Erdmantel in einer Tiefe von ca. 400 km auftreten, werden gewöhnlich mit dem in gleicher Tiefe auftretenden druckabhängigen, polymorphen Phasenübergang von Olivine (α-Phase) zu Spinel (β-Phase) in Verbindung gebracht. Es ist jedoch nach wie vor unklar, wie der Phasenübergang mit dem mechanischen Versagen des Mantelmaterials zusammenhängt. Zur Zeit werden im Wesentlichen zwei Modelle diskutiert, die entweder Mikrostrukturen, die durch den Phasenübergang entstehen, oder aber die rheologischen Veränderungen des Mantelgesteins durch den Phasenübergang dafür verantwortlich machen. Dabei sind Untersuchungen der Olivin→Spinel Umwandlung durch die Unzugänglichkeit des natürlichen Materials vollständig auf theoretische Überlegungen sowie Hochdruck-Experimente und Numerische Simulationen beschränkt. Das zentrale Thema dieser Dissertation war es, ein funktionierendes Computermodell zur Simulation der Mikrostrukturen zu entwickeln, die durch den Phasenübergang entstehen. Des Weiteren wurde das Computer Modell angewandt um die mikrostrukturelle Entwicklung von Spinelkörnern und die Kontrollparameter zu untersuchen. Die Arbeit ist daher in zwei Teile unterteilt: Der erste Teil (Kap. 2 und 3) behandelt die physikalischen Gesetzmäßigkeiten und die prinzipielle Funktionsweise des Computer Modells, das auf der Kombination von Gleichungen zur Errechnung der kinetischen Reaktionsgeschwindigkeit mit Gesetzen der Nichtgleichgewichtsthermodynamik unter nicht-hydostatischen Bedingungen beruht. Das Computermodell erweitert ein Federnetzwerk der Software latte aus dem Programmpaket elle. Der wichtigste Parameter ist dabei die Normalspannung auf der Kornoberfläche von Spinel. Darüber hinaus berücksichtigt das Programm die Latenzwärme der Reaktion, die Oberflächenenergie und die geringe Viskosität von Mantelmaterial als weitere wesentliche Parameter in der Berechnung der Reaktionskinetic. Das Wachstumsverhalten und die fraktale Dimension von errechneten Spinelkörnern ist dabei in guter Übereinstimmung mit Spinelstrukturen aus Hochdruckexperimenten. Im zweiten Teil der Arbeit wird das Computermodell angewandt, um die Entwicklung der Oberflächenstruktur von Spinelkörnern unter verschiedenen Bedigungen zu eruieren. Die sogenannte ’anticrack theory of faulting’, die den katastrophalen Verlauf der Olivine→Spinel Umwandlung in olivinhaltigem Material unter differentieller Spannung durch Spannungskonzentrationen erklärt, wurde anhand des Computermodells untersucht. Der entsprechende Mechanismus konnte dabei nicht bestätigt werden. Stattdessen können Oberflächenstrukturen, die Ähnlichkeiten zu Anticracks aufweisen, durch Unreinheiten des Materials erklärt werden (Kap. 4). Eine Reihe von Simulationen wurde der Herleitung der wichtigsten Kontrollparameter der Reaktion in monomineralischem Olivin gewidmet (Kap. 5 and Kap. 6). Als wichtigste Einflüsse auf die Kornform von Spinel stellten sich dabei die Hauptnormalspannungen auf dem System sowie Heterogenitäten im Wirtsminerals und die Viskosität heraus. Im weiteren Verlauf wurden die Nukleierung und das Wachstum von Spinel in polymineralischen Mineralparagenesen untersucht (Kap. 7). Die Reaktionsgeschwindigkeit der Olivine→Spinel Umwandlung und die Entwicklung von Spinelnetzwerken und Clustern wird durch die Gegenwart nicht-reaktiver Minerale wie Granat oder Pyroxen erheblich beschleunigt. Die Bildung von Spinelnetzwerken hat das Potential, die mechanischen Eigenschaften von Mantelgestein erheblich zu beeinflussen, sei es durch die Bildung potentieller Scherzonen oder durch Gerüstbildung. Dieser Lokalisierungprozess des Spinelwachstums in Mantelgesteinen kann daher ein neues Erklärungsmuster für Tiefbeben darstellen.

Nuclear charge radii of light isotopes based on frequency comb measurements

Optical frequency comb technology has been used in this work for the first time to investigate the nuclear structure of light radioactive isotopes. Therefore, three laser systems were stabilized with different techniques to accurately known optical frequencies and used in two specialized experiments. Absolute transition frequency measurements of lithium and beryllium isotopes were performed with accuracy on the order of 10^(−10). Such a high accuracy is required for the light elements since the nuclear volume effect has only a 10^(−9) contribution to the total transition frequency. For beryllium, the isotope shift was determined with an accuracy that is sufficient to extract information about the proton distribution inside the nucleus. A Doppler-free two-photon spectroscopy on the stable lithium isotopes (6,7)^Li was performed in order to determine the absolute frequency of the 2S → 3S transition. The achieved relative accuracy of 2×10^(−10) is improved by one order of magnitude compared to previous measurements. The results provide an opportunity to determine the nuclear charge radius of the stable and short-lived isotopes in a pure optical way but this requires an improvement of the theoretical calculations by two orders of magnitude. The second experiment presented here was performed at ISOLDE/CERN, where the absolute transition frequencies of the D1 and D2 lines in beryllium ions for the isotopes (7,9,10,11)^Be were measured with an accuracy of about 1 MHz. Therefore, an advanced collinear laser spectroscopy technique involving two counter-propagating frequency-stabilized laser beams with a known absolute frequency was developed. The extracted isotope shifts were combined with recent accurate mass shift calculations and the root-mean square nuclear charge radii of (7,10)^Be and the one-neutron halo nucleus 11^Be were determined. Obtained charge radii are decreasing from 7^Be to 10^Be and increasing again for 11^Be. While the monotone decrease can be explained by a nucleon clustering inside the nucleus, the pronounced increase between 10^Be and 11^Be can be interpreted as a combination of two contributions: the center-of-mass motion of the 10^Be core and a change of intrinsic structure of the core. To disentangle these two contributions, the results from nuclear reaction measurements were used and indicate that the center-of-mass motion is the dominant effect. Additionally, the splitting isotope shift, i.e. the difference in the isotope shifts between the D1 and D2 fine structure transitions, was determined. This shows a good consistency with the theoretical calculations and provides a valuable check of the beryllium experiment.

Who can (not) be Greek? Citizenship, Identity and Belonging among youth of sub-Saharan African background in Athens

‘Who can be Greek?’ This was the question posed to the Greek society for the first time before the implementation of the Act 3838 in March 2010 which gave the right to access the Greek citizenship -under specific preconditions- to all children of legal migrants born or schooled in Greece. This change of the Nationality Code in order to include all those children was coincided by the economic crisis resulting into the rise of xenophobia, racism and extreme-right rhetoric. The outcome was the cancellation of the Act 3838 by the State Council in February 2013. Under this particular framework, the notions of identity and belonging formed among the youth of African background in Athens are explored. The ways those youngsters perceive not only themselves but also their peers, their countries of origin and the country they live in, are crucial elements of their self-identification. Researches have shown that the integration of the second generation is highly connected to their legal and social status. However, integration is a rather complex process, influenced and shaped by many variables and multiple factors. It is not linear; therefore, its outcomes are difficult to be predicted. Yet, I argue that citizenship acquisition facilitates the process as it transforms those children from ‘aliens’ to ‘citizens’. How these youngsters are perceived by the majority society and the State is one of the core questions of the research, focusing on the imposed dual ‘otherness’ they are subject to. On the one hand, they have to deal with the ‘otherness’ originating from the migrant status inherited to them by their parents, and on the other with the ‘otherness’ deriving from their different phenotypic characteristics. Race matters and becomes a means of discrimination against youth of African background who are perceived as inassimilable and ‘forever others’.

Measurement of the elastic electron-proton cross section and separation of the electric and magnetic form factor in the Q 2 range from 0.004 to 1 (GeV/c) 2

The electromagnetic form factors of the proton are fundamental quantities sensitive to the distribution of charge and magnetization inside the proton. Precise knowledge of the form factors, in particular of the charge and magnetization radii provide strong tests for theory in the non-perturbative regime of QCD. However, the existing data at Q^2 below 1 (GeV/c)^2 are not precise enough for a hard test of theoretical predictions.rnrnFor a more precise determination of the form factors, within this work more than 1400 cross sections of the reaction H(e,e′)p were measured at the Mainz Microtron MAMI using the 3-spectrometer-facility of the A1-collaboration. The data were taken in three periods in the years 2006 and 2007 using beam energies of 180, 315, 450, 585, 720 and 855 MeV. They cover the Q^2 region from 0.004 to 1 (GeV/c)^2 with counting rate uncertainties below 0.2% for most of the data points. The relative luminosity of the measurements was determined using one of the spectrometers as a luminosity monitor. The overlapping acceptances of the measurements maximize the internal redundancy of the data and allow, together with several additions to the standard experimental setup, for tight control of systematic uncertainties.rnTo account for the radiative processes, an event generator was developed and implemented in the simulation package of the analysis software which works without peaking approximation by explicitly calculating the Bethe-Heitler and Born Feynman diagrams for each event.rnTo separate the form factors and to determine the radii, the data were analyzed by fitting a wide selection of form factor models directly to the measured cross sections. These fits also determined the absolute normalization of the different data subsets. The validity of this method was tested with extensive simulations. The results were compared to an extraction via the standard Rosenbluth technique.rnrnThe dip structure in G_E that was seen in the analysis of the previous world data shows up in a modified form. When compared to the standard-dipole form factor as a smooth curve, the extracted G_E exhibits a strong change of the slope around 0.1 (GeV/c)^2, and in the magnetic form factor a dip around 0.2 (GeV/c)^2 is found. This may be taken as indications for a pion cloud. For higher Q^2, the fits yield larger values for G_M than previous measurements, in agreement with form factor ratios from recent precise polarized measurements in the Q2 region up to 0.6 (GeV/c)^2.rnrnThe charge and magnetic rms radii are determined as rn⟨r_e⟩=0.879 ± 0.005(stat.) ± 0.004(syst.) ± 0.002(model) ± 0.004(group) fm,rn⟨r_m⟩=0.777 ± 0.013(stat.) ± 0.009(syst.) ± 0.005(model) ± 0.002(group) fm.rnThis charge radius is significantly larger than theoretical predictions and than the radius of the standard dipole. However, it is in agreement with earlier results measured at the Mainz linear accelerator and with determinations from Hydrogen Lamb shift measurements. The extracted magnetic radius is smaller than previous determinations and than the standard-dipole value.

Development of new tools and devices for CMB and foreground data analysis and future experiments

The discovery of the Cosmic Microwave Background (CMB) radiation in 1965 is one of the fundamental milestones supporting the Big Bang theory. The CMB is one of the most important source of information in cosmology. The excellent accuracy of the recent CMB data of WMAP and Planck satellites confirmed the validity of the standard cosmological model and set a new challenge for the data analysis processes and their interpretation. In this thesis we deal with several aspects and useful tools of the data analysis. We focus on their optimization in order to have a complete exploitation of the Planck data and contribute to the final published results. The issues investigated are: the change of coordinates of CMB maps using the HEALPix package, the problem of the aliasing effect in the generation of low resolution maps, the comparison of the Angular Power Spectrum (APS) extraction performances of the optimal QML method, implemented in the code called BolPol, and the pseudo-Cl method, implemented in Cromaster. The QML method has been then applied to the Planck data at large angular scales to extract the CMB APS. The same method has been applied also to analyze the TT parity and the Low Variance anomalies in the Planck maps, showing a consistent deviation from the standard cosmological model, the possible origins for this results have been discussed. The Cromaster code instead has been applied to the 408 MHz and 1.42 GHz surveys focusing on the analysis of the APS of selected regions of the synchrotron emission. The new generation of CMB experiments will be dedicated to polarization measurements, for which are necessary high accuracy devices for separating the polarizations. Here a new technology, called Photonic Crystals, is exploited to develop a new polarization splitter device and its performances are compared to the devices used nowadays.

Investigation of the electric field enhanced PNA-DNA hybridization on Au surface by using surface plasmon field-enhanced fluorescence spectroscopy (SPFS)

Recently, the surface plasmon field-enhanced fluorescence spectroscopy (SPFS) was developed as a kinetic analysis and a detection method with dual- monitoring of the change of reflectivity and fluorescence signal for the interfacial phenomenon. A fundamental study of PNA and DNA interaction at the surface using surface plasmon fluorescence spectroscopy (SPFS) will be investigated in studies. Furthermore, several specific conditions to influence on PNA/DNA hybridization and affinity efficiency by monitoring reflective index changes and fluorescence variation at the same time will be considered. In order to identify the affinity degree of PNA/DNA hybridizaiton at the surface, the association constant (kon) and the dissociation constant (koff) will be obtained by titration experiment of various concentration of target DNA and kinetic investigation. In addition, for more enhancing the hybridization efficiency of PNA/DNA, a study of polarized electric field enhancement system will be introduced and performed in detail. DNA is well-known polyelectrolytes with naturally negative charged molecules in its structure. With polarized electrical treatment, applying DC field to the metal surface, which PNA probe would be immobilized at, negatively charged DNA molecules can be attracted by electromagnetic attraction force and manipulated to the close the surface area, and have more possibility to hybridize with probe PNA molecules by hydrogen bonding each corresponding base sequence. There are several major factors can be influenced on the hybridization efficiency.

Electron spectroscopy of novel charge transfer systems based on polycyclic aromatic hydrocarbons

Organische Ladungstransfersysteme weisen eine Vielfalt von konkurrierenden Wechselwirkungen zwischen Ladungs-, Spin- und Gitterfreiheitsgraden auf. Dies führt zu interessanten physikalischen Eigenschaften, wie metallische Leitfähigkeit, Supraleitung und Magnetismus. Diese Dissertation beschäftigt sich mit der elektronischen Struktur von organischen Ladungstransfersalzen aus drei Material-Familien. Dabei kamen unterschiedliche Photoemissions- und Röntgenspektroskopietechniken zum Einsatz. Die untersuchten Moleküle wurden z.T. im MPI für Polymerforschung synthetisiert. Sie stammen aus der Familie der Coronene (Donor Hexamethoxycoronen HMC und Akzeptor Coronen-hexaon COHON) und Pyrene (Donor Tetra- und Hexamethoxypyren TMP und HMP) im Komplex mit dem klassischen starken Akzeptor Tetracyanoquinodimethan (TCNQ). Als dritte Familie wurden Ladungstransfersalze der k-(BEDT-TTF)2X Familie (X ist ein monovalentes Anion) untersucht. Diese Materialien liegen nahe bei einem Bandbreite-kontrollierten Mottübergang im Phasendiagramm.rnFür Untersuchungen mittels Ultraviolett-Photoelektronenspektroskopie (UPS) wurden UHV-deponierte dünne Filme erzeugt. Dabei kam ein neuer Doppelverdampfer zum Einsatz, welcher speziell für Milligramm-Materialmengen entwickelt wurde. Diese Methode wies im Ladungstransferkomplex im Vergleich mit der reinen Donor- und Akzeptorspezies energetische Verschiebungen von Valenzzuständen im Bereich weniger 100meV nach. Ein wichtiger Aspekt der UPS-Messungen lag im direkten Vergleich mit ab-initio Rechnungen.rnDas Problem der unvermeidbaren Oberflächenverunreinigungen von lösungsgezüchteten 3D-Kristallen wurde durch die Methode Hard-X-ray Photoelectron Spectroscopy (HAXPES) bei Photonenenergien um 6 keV (am Elektronenspeicherring PETRA III in Hamburg) überwunden. Die große mittlere freie Weglänge der Photoelektronen im Bereich von 15 nm resultiert in echter Volumensensitivität. Die ersten HAXPES Experimente an Ladungstransferkomplexen weltweit zeigten große chemische Verschiebungen (mehrere eV). In der Verbindung HMPx-TCNQy ist die N1s-Linie ein Fingerabdruck der Cyanogruppe im TCNQ und zeigt eine Aufspaltung und einen Shift zu höheren Bindungsenergien von bis zu 6 eV mit zunehmendem HMP-Gehalt. Umgekehrt ist die O1s-Linie ein Fingerabdruck der Methoxygruppe in HMP und zeigt eine markante Aufspaltung und eine Verschiebung zu geringeren Bindungsenergien (bis zu etwa 2,5eV chemischer Verschiebung), d.h. eine Größenordnung größer als die im Valenzbereich.rnAls weitere synchrotronstrahlungsbasierte Technik wurde Near-Edge-X-ray-Absorption Fine Structure (NEXAFS) Spektroskopie am Speicherring ANKA Karlsruhe intensiv genutzt. Die mittlere freie Weglänge der niederenergetischen Sekundärelektronen (um 5 nm). Starke Intensitätsvariationen von bestimmten Vorkanten-Resonanzen (als Signatur der unbesetzte Zustandsdichte) zeigen unmittelbar die Änderung der Besetzungszahlen der beteiligten Orbitale in der unmittelbaren Umgebung des angeregten Atoms. Damit war es möglich, präzise die Beteiligung spezifischer Orbitale im Ladungstransfermechanismus nachzuweisen. Im genannten Komplex wird Ladung von den Methoxy-Orbitalen 2e(Pi*) und 6a1(σ*) zu den Cyano-Orbitalen b3g und au(Pi*) und – in geringerem Maße – zum b1g und b2u(σ*) der Cyanogruppe transferiert. Zusätzlich treten kleine energetische Shifts mit unterschiedlichem Vorzeichen für die Donor- und Akzeptor-Resonanzen auf, vergleichbar mit den in UPS beobachteten Shifts.rn

Paleosol-based stratigraphy of late Quaternary deposits from the Po basin, between Bologna and the Po river (Northern Italy)

Stratigraphic studies carried out over the last decades in Italy and elsewhere testify a growing interest in Quaternary deposits and in the influence of climate change on their architecture. The subsurface of the Po Plain, in its topmost portion, is made up of alluvial deposits organized in depositional cycles at different scales. This PhD thesis provides millennial-scale stratigraphic reconstruction of the Late Pleistocene-Holocene deposits beneath the southern Po Plain, based on basin-scale correlation of laterally-extensive buried soil horizons. Far from the aim of characterizing palaeosols from a mineralogical and geochemical point of view, we focused on the physical and stratigraphic significance of these horizons. In the Bologna urban area, which hosts an abundance of stratigraphic data, the correlation between seventeen continuously-cored boreholes led to the identification of five vertically-stacked palaeosol-bounded sequences within the 14C time window. In a wide portion of the alluvial plain north of Bologna, far away from the Apenninic margin and from the Po River, where subsurface stratigraphic architecture is dominated by markedly lenticular sediment bodies, palaeosols revealed to be the only stratigraphic marker of remarkable lateral continuity. These horizons are characterized by peculiar resistance values, which make them easily identifiable via pocket penetration tests. Palaeosols reveal specific geometric relationships with the associated alluvial facies associations, allowing reliable estimates of soil development as a function of alluvial dynamics. With the aid of sixty new radiocarbon dates, a reliable age attribution and likely time intervals of exposure were assigned to each palaeosol. Vertically-stacked palaeosols delimitate short-term depositional cycles, likely related to the major episodes of climatic change of the last 40 ky. Through integration of stratigraphic data with 750 archaeological reports from the Bologna area, the impact of human settlements on depositional and pedogenic processes during the late Holocene was investigated.

Implications of regional fault distribution and kinematics for the uplift of rift flanks around the Rwenzori Mountains, Southwestern Uganda

Das Ziel dieser Arbeit bestand in der Untersuchung der Störungsverteilung und der Störungskinematik im Zusammenhang mit der Hebung der Riftschultern des Rwenzori Gebirges.rnDas Rwenzori Gebirge befindet sich im NNE-SSWbis N-S verlaufenden Albertine Rift, des nördlichsten Segments des westlichen Armes des Ostafrikanischen Grabensystems. Das Albertine Rift besteht aus Becken unterschiedlicher Höhe, die den Lake Albert, Lake Edward, Lake George und Lake Kivu enthalten. Der Rwenzori horst trennt die Becken des Lake Albert und des Lake Edward. Es erstreckt sich 120km in N-S Richtung, sowie 40-50km in E-W Richtung, der h¨ochste Punkt befindet sich 5111 ü. NN. Diese Studie untersucht einen Abschnitt des Rifts zwischen etwa 1°N und 0°30'S Breite sowie 29°30' und 30°30' östlicher Länge ersteckt. Auch die Feldarbeit konzentrierte sich auf dieses Gebiet.rnrnHauptzweck dieser Studie bestand darin, die folgende These auf ihre Richtigkeit zu überprüfen: ’Wenn es im Verlauf der Zeit tatsächlich zu wesentlichen Änderungen in der Störungskinematik kam, dann ist die starke Hebung der Riftflanken im Bereich der Rwenzoris nicht einfach durch Bewegung entlang der Graben-Hauptst¨orungen zu erklären. Vielmehr ist sie ein Resultat des Zusammenspiels mehrerer tektonische Prozesse, die das Spannungsfeld beeinflussen und dadurch Änderungen in der Kinematik hervorrufen.’ Dadurch konzentrierte sich die Studie in erster Linie auf die Störungsanalyse.rnrnDie Kenntnis regionaler Änderungen der Extensionsrichtung ist entscheidend für das Verständnis komplexer Riftsysteme wie dem Ostafrikanischen Graben. Daher bestand der Kern der Untersuchung in der Kartierung von Störungen und der Untersuchung der Störungskinematik. Die Aufnahme strukturgeologischer Daten konzentrierte sich auf die Ugandische Seite des Rifts, und Pal¨aospannungen wurden mit Hilfe von St¨orungsdaten durch Spannungsinversion rekonstruiert.rnDie unterschiedliche Orientierung spr¨oder Strukturen im Gelände, die geometrische Analyse der geologischen Strukturen sowie die Ergebnisse von Mikrostrukturen im Dünnschliff (Kapitel 4) weisen auf verschiedene Spannungsfelder hin, die auf mögliche Änderungen der Extensionsrichtung hinweisen. Die Resultate der Spannungsinversion sprechen für Ab-, Über- und Blattverschiebungen sowie für Schrägüberschiebungen (Kapitel 5). Aus der Orientierung der Abschiebungen gehen zwei verschiedene Extensionsrichtungen hervor: im Wesentlichen NW-SE Extension in fast allen Gebieten, sowie NNE-SSW Extension im östlichen Zentralbereich.rnAus der Analyse von Blattverschiebungen ergaben sich drei unterschiedliche Spannungszustände. Zum Einen NNW-SSE bis N-S Kompression in Verbindung mit ENE-WSW bzw E-W Extension wurde für die nördlichen und die zentralen Ruwenzoris ausgemacht. Ein zweiter Spannungszustand mit WNW-ESE Kompression/NNE-SSW Extension betraf die Zentralen Rwenzoris. Ein dritter Spannungszustand mit NNW-SSE Extension betraf den östlichen Zentralteil der Rwenzoris. Schrägüberschiebungen sind durch dazu schräge Achsen charakterisiert, die für N-S bis NNW-SSE Kompression sprechen und ausschließlich im östlichen Zentralabschnitt auftreten. Überschiebungen, die hauptsächlich in den zentralen und den östlichen Rwenzoris auftreten, sprechen für NE-SW orientierten σ2-Achsen und NW-SE Extension.rnrnEs konnten drei unterschiedliche Spannungseinflüsse identifiziert werden: auf die kollisionsbedingte Bildung eines Überschiebungssystem folgte intra-kratonische Kompression und schließlich extensionskontrollierte Riftbildung. Der Übergang zwischen den beiden letztgenannten Spannungszuständen erfolgte Schrittweise und erzeugte vermutlich lokal begrenzte Transpression und Transtension. Gegenw¨artig wird die Störungskinematik der Region durch ein tensiles Spannungsregime in NW-SE bis N-S Richtung bestimmt.rnrnLokale Spannungsvariationen werden dabei hauptsächlich durch die Interferenzrndes regionalen Spannungsfeldes mit lokalen Hauptst¨orungen verursacht. Weitere Faktoren die zu lokalen Veränderungen des Spannungsfeldes führen können sind unterschiedliche Hebungsgeschwindigkeiten, Blockrotation oder die Interaktion von Riftsegmenten. Um den Einfluß präexistenter Strukturen und anderer Bedingungen auf die Hebung der Rwenzoris zu ermitteln, wurde der Riftprozeß mit Hilfe eines analogen ’Sandbox’-Modells rekonstruiert (Kapitel 6). Da sich die Moho-Diskontinuität im Bereich des Arbeitsgebietes in einer Tiefe von 25 km befindet, aktive Störungen aber nur bis zu einer Tiefe von etwa 20 km beobachtet werden können (Koehn et al. 2008), wurden nur die oberen 25 km im Modell nachbebildet. Untersucht und mit Geländebeobachtungen verglichen wurden sowohl die Reihenfolge, in der Riftsegmente entstehen, als auch die Muster, die sich im Verlauf der Nukleierung und des Wachstums dieser Riftsegmente ausbilden. Das Hauptaugenmerk wurde auf die Entwicklung der beiden Subsegmente gelegt auf denen sich der Lake Albert bzw. der Lake Edward und der Lake George befinden, sowie auf das dazwischenliegende Rwenzori Gebirge. Das Ziel der Untersuchung bestand darin herauszufinden, in welcher Weise das südwärts propagierende Lake Albert-Subsegment mit dem sinistral versetzten nordwärts propagierenden Lake Edward/Lake George-Subsegment interagiert.rnrnVon besonderem Interesse war es, in welcherWeise die Strukturen innerhalb und außerhalb der Rwenzoris durch die Interaktion dieser Riftsegmente beeinflußt wurden. rnrnDrei verschiedene Versuchsreihen mit unterschiedlichen Randbedingungen wurden miteinander verglichen. Abhängig vom vorherrschenden Deformationstyp der Transferzone wurden die Reihen als ’Scherungs-dominiert’, ’Extensions-dominiert’ und als ’Rotations-dominiert’ charakterisiert. Die Beobachtung der 3-dimensionalen strukturellen Entwicklung der Riftsegmente wurde durch die Kombination von Modell-Aufsichten mit Profilschnitten ermöglicht. Von den drei genannten Versuchsreihen entwickelte die ’Rotationsdominierten’ Reihe einen rautenförmiger Block im Tranferbereich der beiden Riftsegmente, der sich um 5−20° im Uhrzeigersinn drehte. DieserWinkel liegt im Bereich des vermuteten Rotationswinkel des Rwenzori-Blocks (5°). Zusammengefasst untersuchen die Sandbox-Versuche den Einfluss präexistenter Strukturen und der Überlappung bzw. Überschneidung zweier interagierender Riftsegmente auf die Entwicklung des Riftsystems. Sie befassen sich darüber hinaus mit der Frage, welchen Einfluss Blockbildung und -rotation auf das lokale Stressfeld haben.

Methane production through anaerobic digestion of dedicated energy crops

Methane yield of ligno-cellulosic substrates (i.e. dedicated energy crops and agricultural residues) may be limited by their composition and structural features. Hence, biomass pre-treatments are envisaged to overcome this constraint. This thesis aimed at: i) assessing biomass and methane yield of dedicated energy crops; ii) evaluating the effects of hydrothermal pre-treatments on methane yield of Arundo; iii) investigating the effects of NaOH pre-treatments and iv) acid pre-treatments on chemical composition, physical structure and methane yield of two dedicated energy crops and one agricultural residue. Three multi-annual species (Arundo, Switchgrass and Sorghum Silk), three sorghum hybrids (Trudan Headless, B133 and S506) and a maize, as reference for AD, were studied in the frame of point i). Results exhibit the remarkable variation in biomass yield, chemical characteristics and potential methane yield. The six species alternative to maize deserve attention in view of a low need of external inputs but necessitate improvements in biodegradability. In the frame of point ii), Arundo was subjected to hydrothermal pre-treatments at different temperature, time and acid catalyst (with and without H2SO4). Pre-treatments determined a variable effect on methane yield: pre-treatments without acid catalyst achieved up to +23% CH4 output, while pre-treatments with H2SO4 catalyst incurred a methanogenic inhibition. Two biomass crops (Arundo and B133) and an agricultural residue (Barley straw) were subject to NaOH and acid pre-treatments, in the frame of point iii) and iv), respectively. Different pre-treatments determined a change of chemical and physical structure and an increase of methane yield: up to +30% and up to +62% CH4 output in Arundo with NaOH and acid pre-treatments, respectively. It is thereby demonstrated that pre-treatments can actually enhance biodegradability and subsequent CH4 output of ligno-cellulosic substrates, although pre-treatment viability needs to be evaluated at the level of full scale biogas plants in a perspective of profitable implementation.

Spectroscopic investigations of functional bulk and thin film Heusler alloys

Functional and smart materials have gained large scientific and practical interest in current research and development. The Heusler alloys form an important class of functional materials used in spintronics, thermoelectrics, and for shape memory alloy applications. An important aspect of functional materials is the adaptability of their physical properties. In this work functional polycrystalline bulk and epitaxial thin film Heusler alloys are characterized by means of spectroscopic investigation methods, X-ray magnetic circular dichroism (XMCD) and energy dispersive X-ray analysis (EDX). With EDX the homogeneity of the samples is studied extensively. For some cases of quaternary compounds, for example Co2(MnxTi1−x)Sn and Co2(Mn0.5Dy0.5)Sn, an interesting phase separation in two nearly pure ternary Heusler phases occurs. For these samples the phase separation leads to an improvement of thermoelectric properties. XMCD as the main investigation method was used to study Co2TiZ (Z = Si, Sn, and Sb), Co2(MnxTi1−x)Si, Co2(MnxTi1−x)Ge, Co2Mn(Ga1−xGex), Co2FeAl, Mn2VAl, and Ni2MnGa Heusler compounds. The element-specific magnetic moments are calculated. Also, the spin-resolved unoccupied density of states is determined, for example giving hints for half-metallic ferromagnetism for some Co-based compounds. The systematic change of the magnetic moments and the shift of the Fermi energy is a proof that Heusler alloys are suitable for a controlled tailoring of physical properties. The comparison of the experimental results with theoretical predictions improves the understanding of complex materials needed to optimize functional Heusler alloys.

Demersal communities in the Mediterranean Sea: a case study of Triglidae (Osteichthyes, Scorpaeniformes) on the conservation and sustainable use of marine resources

An appropriate management of fisheries resources can only be achieved with the continuous supply of information on the structure and biology of populations, in order to predict the temporal fluctuations. This study supports the importance of investigating the bio-ecology of increasingly exploited and poorly known species, such as gurnards (Osteichthyes, Triglidae) from Adriatic Sea (Mediterranean), to quantify their ecological role into marine community. It also focuses on investigate inter and intra-specific structuring factor of Adriatic population. These objectives were achieved by: 1) investigating aspects of the population dynamics; 2) studying the feeding biology through the examination of stomach contents; 3) using sagittal otoliths as potential marker of species life cycle; 4) getting preliminary data on mDNA phylogeny. Gurnards showed a specie-specific “critical size” coinciding with the start of sexual maturity, the tendency to migrate to greater depths, a change of diet from crustaceans to fish and an increase of variety of food items eaten. Distribution of prey items, predator size range and depth distribution were the main dimensions that influence the breadth of trophic niche and the relative difference amongst Adriatic gurnards. Several feeding preferences were individuated and a possible impact among bigger-size gurnards and other commercial fishes (anchovy, gadoids) and Crustacea (such as mantis prawn and shrimps) were to be necessary considered. Otolith studies showed that gurnard species have a very fast growth despite other results in other areas; intra-specific differences and the increase in the variability of otolith shape, sulcus acusticus shape, S:O ratios, sulcus acusticus external crystals arrangement were shown between juveniles and adults and were linked to growth (individual genetic factors) and to environmental conditions (e.g. depth and trophic niche distribution). In order to facilitate correct biological interpretation of data, molecular data were obtained for comparing morphological distance to genetic ones.