Abscheidung und Charakterisierung von Plasmapolymerschichten auf Fluorkohlenstoff- und Siloxan-Basis

In dieser Arbeit wurden Fluorkohlenstoff-basierte und siliziumorganische Plasmapolymerfilme hergestellt und hinsichtlich ihrer strukturellen und funktionalen Eigenschaften untersucht. Beide untersuchten Materialsysteme sind in der Beschichtungstechnologie von großem wissenschaftlichen und anwendungstechnischen Interesse. Die Schichtabscheidung erfolgte mittels plasmachemischer Gasphasenabscheidung (PECVD) an Parallelplattenreaktoren. Bei den Untersuchungen zur Fluorkohlenstoff-Plasmapolymerisation stand die Herstellung ultra-dünner, d. h. weniger als 5 nm dicker Schichten im Vordergrund. Dies wurde durch gepulste Plasmaanregung und Verwendung eines Gasgemisches aus Trifluormethan (CHF3) und Argon realisiert. Die Bindungsstruktur der Schichten wurden in Abhängigkeit der eingespeisten Leistung, die den Fragmentationsgrad der Monomere im Plasma bestimmt, analysiert. Hierzu wurden die Röntgen-Photoelektronenspektroskopie (XPS), Rasterkraftmikroskopie (AFM), Flugzeit-Sekundärionenmassenspektrometrie (ToF-SIMS) und Röntgenreflektometrie (XRR) eingesetzt. Es zeigte sich, dass die abgeschiedenen Schichten ein homogenes Wachstumsverhalten und keine ausgeprägten Interfacebereiche zum Substrat und zur Oberfläche hin aufweisen. Die XPS-Analysen deuten darauf hin, dass Verkettungsreaktionen von CF2-Radikalen im Plasma eine wichtige Rolle für den Schichtbildungsprozess spielen. Weiterhin konnte gezeigt werden, dass der gewählte Beschichtungsprozess eine gezielte Reduzierung der Benetzbarkeit verschiedener Substrate ermöglicht. Dabei genügen Schichtdicken von weniger als 3 nm zur Erreichung eines teflonartigen Oberflächencharakters mit Oberflächenenergien um 20 mN/m. Damit erschließen sich neue Applikationsmöglichkeiten ultra-dünner Fluorkohlenstoffschichten, was anhand eines Beispiels aus dem Bereich der Nanooptik demonstriert wird. Für die siliziumorganischen Schichten unter Verwendung des Monomers Hexamethyldisiloxan (HMDSO) galt es zunächst, diejenigen Prozessparameter zu identifizieren, die ihren organischen bzw. glasartigen Charakter bestimmen. Hierzu wurde der Einfluss von Leistungseintrag und Zugabe von Sauerstoff als Reaktivgas auf die Elementzusammensetzung der Schichten untersucht. Bei niedrigen Plasmaleistungen und Sauerstoffflüssen werden vor allem kohlenstoffreiche Schichten abgeschieden, was auf eine geringere Fragmentierung der Kohlenwasserstoffgruppen zurückgeführt wurde. Es zeigte sich, dass die Variation des Sauerstoffanteils im Prozessgas eine sehr genaue Steuerbarkeit der Schichteigenschaften ermöglicht. Mittels Sekundär-Neutralteilchen-Massenspektrometrie (SNMS) konnte die prozesstechnische Realisierbarkeit und analytische Quantifizierbarkeit von Wechselschichtsystemen aus polymerartigen und glasartigen Lagen demonstriert werden. Aus dem Intensitätsverhältnis von Si:H-Molekülen zu Si-Atomen im SNMS-Spektrum ließ sich der Wasserstoffgehalt bestimmen. Weiterhin konnte gezeigt werden, dass durch Abscheidung von HMDSO-basierten Gradientenschichten eine deutliche Reduzierung von Reibung und Verschleiß bei Elastomerbauteilen erzielt werden kann.

Noble-metal nanoparticles produced with colloidal lithography: fabrication, optical properties and applications

In this work, metal nanoparticles produced by nanosphere lithography were studied in terms of their optical properties (in connection to their plasmon resonances), their potential application in sensing platforms - for thin layer sensing and bio-recognition events -, and for a particular case (the nanocrescents), for enhanced spectroscopy studies. The general preparation procedures introduced early in 2005 by Shumaker-Parry et al. to produce metallic nanocrescents were extended to give rise to more complex (isolated) structures, and also, by combining colloidal monolayer fabrication and plasma etching techniques, to arrays of them. The fabrication methods presented in this work were extended not only to new shapes or arrangements of particles, but included also a targeted surface tailoring of the substrates and the structures, using different thiol and silane compounds as linkers for further attachment of, i.e. polyelectrolyte layers, which allow for a controlled tailoring of their nanoenvironment. The optical properties of the nanocrescents were studied with conventional transmission spectroscopy; a simple multipole model was adapted to explain their behaviour qualitatively. In terms of applications, the results on thin film sensing using these particles show that the crescents present an interesting mode-dependent sensitivity and spatial extension. Parallel to this, the penetrations depths were modeled with two simplified schemes, obtaining good agreement with theory. The multiple modes of the particles with their characteristic decay lengths and sensitivities represent a major improvement for particle-sensing platforms compared to previous single resonance systems. The nanocrescents were also used to alter the emission properties of fluorophores placed close to them. In this work, green emitting dyes were placed at controlled distances from the structures and excited using a pulsed laser emitting in the near infrared. The fluorescence signal obtained in this manner should be connected to a two-photon processes triggered by these structures; obtaining first insight into plasmon-mediated enhancement phenomena. An even simpler and faster approach to produce plasmonic structures than that for the crescents was tested. Metallic nanodiscs and nanoellipses were produced by means of nanosphere lithography, extending a procedure reported in the literature to new shapes and optical properties. The optical properties of these particles were characterized by extinction spectroscopy and compared to results from the literature. Their major advantage is that they present a polarization-dependent response, like the nanocrescents, but are much simpler to fabricate, and the resonances can be tailored in the visible with relative ease. The sensing capabilities of the metallic nanodiscs were explored in the same manner as for the nanocrescents, meaning their response to thin layers and to bio-recognition events on their surface. The sensitivity of these nanostructures to thin films proved to be lower than that of the crescents, though in the same order of magnitude. Experimental information about the near field extension for the Au nanodiscs of different sizes was also extracted from these measurements. Further resonance-tailoring approaches based on electrochemical deposition of metals on the nanodiscs were explored, as a means of modifying plasmon resonances by changing surface properties of the nanoparticles. First results on these experiments would indicate that the deposition of Ag on Au on a submonolayer coverage level can lead to important blue-shifts in the resonances, which would open a simple way to tailor resonances by changing material properties in a local manner.

Optical resonances of sphere-on-plane geometries

The optical resonances of metallic nanoparticles placed at nanometer distances from a metal plane were investigated. At certain wavelengths, these “sphere-on-plane” systems become resonant with the incident electromagnetic field and huge enhancements of the field are predicted localized in the small gaps created between the nanoparticle and the plane. An experimental architecture to fabricate sphere-on-plane systems was successfully achieved in which in addition to the commonly used alkanethiols, polyphenylene dendrimers were used as molecular spacers to separate the metallic nanoparticles from the metal planes. They allow for a defined nanoparticle-plane separation and some often are functionalized with a chromophore core which is therefore positioned exactly in the gap. The metal planes used in the system architecture consisted of evaporated thin films of gold or silver. Evaporated gold or silver films have a smooth interface with their substrate and a rougher top surface. To investigate the influence of surface roughness on the optical response of such a film, two gold films were prepared with a smooth and a rough side which were as similar as possible. Surface plasmons were excited in Kretschmann configuration both on the rough and on the smooth side. Their reflectivity could be well modeled by a single gold film for each individual measurement. The film has to be modeled as two layers with significantly different optical constants. The smooth side, although polycrystalline, had an optical response that was very similar to a monocrystalline surface while for the rough side the standard response of evaporated gold is retrieved. For investigations on thin non-absorbing dielectric films though, this heterogeneity introduces only a negligible error. To determine the resonant wavelength of the sphere-on-plane systems a strategy was developed which is based on multi-wavelength surface plasmon spectroscopy experiments in Kretschmann-configuration. The resonant behavior of the system lead to characteristic changes in the surface plasmon dispersion. A quantitative analysis was performed by calculating the polarisability per unit area /A treating the sphere-on-plane systems as an effective layer. This approach completely avoids the ambiguity in the determination of thickness and optical response of thin films in surface plasmon spectroscopy. Equal area densities of polarisable units yielded identical response irrespective of the thickness of the layer they are distributed in. The parameter range where the evaluation of surface plasmon data in terms of /A is applicable was determined for a typical experimental situation. It was shown that this analysis yields reasonable quantitative agreement with a simple theoretical model of the sphere-on-plane resonators and reproduces the results from standard extinction experiments having a higher information content and significantly increased signal-to-noise ratio. With the objective to acquire a better quantitative understanding of the dependence of the resonance wavelength on the geometry of the sphere-on-plane systems, different systems were fabricated in which the gold nanoparticle size, type of spacer and ambient medium were varied and the resonance wavelength of the system was determined. The gold nanoparticle radius was varied in the range from 10 nm to 80 nm. It could be shown that the polyphenylene dendrimers can be used as molecular spacers to fabricate systems which support gap resonances. The resonance wavelength of the systems could be tuned in the optical region between 550 nm and 800 nm. Based on a simple analytical model, a quantitative analysis was developed to relate the systems’ geometry with the resonant wavelength and surprisingly good agreement of this simple model with the experiment without any adjustable parameters was found. The key feature ascribed to sphere-on-plane systems is a very large electromagnetic field localized in volumes in the nanometer range. Experiments towards a quantitative understanding of the field enhancements taking place in the gap of the sphere-on-plane systems were done by monitoring the increase in fluorescence of a metal-supported monolayer of a dye-loaded dendrimer upon decoration of the surface with nanoparticles. The metal used (gold and silver), the colloid mean size and the surface roughness were varied. Large silver crystallites on evaporated silver surfaces lead to the most pronounced fluorescence enhancements in the order of 104. They constitute a very promising sample architecture for the study of field enhancements.

The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions?

The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions? The collapse of polyions in a poor solvent is a complex system and is an active research subject in the theoretical polyelectrolyte community. The complexity is due to the subtle interplay between hydrophobic effects, electrostatic interactions, entropy elasticity, intrinsic excluded volume as well as specific counter-ion and co-ion properties. Long range Coulomb forces can obscure single molecule properties. The here presented approach is to use just a small amount of screening salt in combination with a very high sample dilution in order to screen intermolecular interaction whereas keeping intramolecular interaction as much as possible (polyelectrolyte concentration cp ≤ 12 mg/L, salt concentration; Cs = 10^-5 mol/L). This is so far not described in literature. During collapse, the polyion is subject to a drastic change in size along with strong reduction of free counterions in solution. Therefore light scattering was utilized to obtain the size of the polyion whereas a conductivity setup was developed to monitor the proceeding of counterion collection by the polyion. Partially quaternized PVP’s below and above the Manning limit were investigated and compared to the collapse of their uncharged precursor. The collapses were induced by an isorefractive solvent/non-solvent mixture consisting of 1-propanol and 2-pentanone, with nearly constant dielectric constant. The solvent quality for the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of electrostatic interaction prior and during polyion collapse. Given that the Manning parameter M for QPVP4.3 is as low as lB / c = 0.6 (lB the Bjerrum length and c the mean contour distance between two charges), no counterion binding should occur. However the Walden product reduces with first addition of non solvent and accelerates when the structural collapse sets in. Since the dielectric constant of the solvent remains virtually constant during the chain collapse, the counterion binding is entirely caused by the reduction in the polyion chain dimension. The collapse is shifted to lower wns with higher degrees of quaternization as the samples QPVP20 and QPVP35 show (M = 2.8 respectively 4.9). The combination of light scattering and conductivity measurement revealed for the first time that polyion chains already collect their counter ions well above the theta-dimension when the dimensions start to shrink. Due to only small amounts of screening salt, strong electrostatic interactions bias dynamic as well as static light scattering measurements. An extended Zimm formula was derived to account for this interaction and to obtain the real chain dimensions. The effective degree of dissociation g could be obtained semi quantitatively using this extrapolated static in combination with conductivity measurements. One can conclude the expansion factor a and the effective degree of ionization of the polyion to be mutually dependent. In the good solvent regime g of QPVP4.3, QPVP20 and QPVP35 exhibited a decreasing value in the order 1 > g4.3 > g20 > g35. The low values of g for QPVP20 and QPVP35 are assumed to be responsible for the prior collapse of the higher quaternized samples. Collapse theory predicts dipole-dipole attraction to increase accordingly and even predicts a collapse in the good solvent regime. This could be exactly observed for the QPVP35 sample. The experimental results were compared to a newly developed theory of uniform spherical collapse induced by concomitant counterion binding developed by M. Muthukumar and A. Kundagrami. The theory agrees qualitatively with the location of the phase boundary as well as the trend of an increasing expansion with an increase of the degree of quaternization. However experimental determined g for the samples QPVP4.3, QPVP20 and QPVP35 decreases linearly with the degree of quaternization whereas this theory predicts an almost constant value.

Proton-conducting copolymers, blends and composites with phosphonic acid as protogenic group

ABSTRACT: In this work, proton conducting copolymers, polymer blends and composites containing phosphonic acid groups have been prepared. Proton conduction mechanisms in these materials are discussed respectively in both, the anhydrous and humidified state. Atom transfer radical copolymerization (ATRCP) of diisopropyl-p-vinylbenzyl phosphonate (DIPVBP) and 4-vinyl pyridine (4VP) is studied for the first time in this work. The kinetic parameters are obtained by using the 1H-NMR online technique. Proton conduction in poly(vinylbenzyl phosphonic acid) (PVBPA) homopolymer and its statistical copolymers with 4-vinyl pyridine (poly(VBPA-stat-4VP)s) are comprehensively studied in both, the “dry” and “wet” state. Effects of temperature, water content and polymer composition on proton conductivities are studied and proton transport mechanisms under various conditions are discussed. The proton conductivity of the polymers is in the range of 10-6-10-8 S/cm in nominally dry state at 150 oC. However, proton conductivity of the polymers increases rapidly with water content in the polymers which can reach 10-2 S/cm at the water uptake of 25% in the polymers. The highest proton conductivity obtained from the polymers can even reach 0.3 S/cm which was measured at 85oC with 80% relative humidity in the measuring atmosphere. Poly(4-vinyl pyridine) was grafted from the surface of SiO2 nanoparticles using ATRP in this work for the first time. Following this approach, silica nanoparticles with a shell of polymeric layer are used as basic particles in a polymeric acidic matrix. The proton conductivities of the composites are studied under both, humidified and dry conditions. In dry state, the conductivity of the composites is in the range of 10-10~10-4 S/cm at 150 oC. While in humid state, the composites show much higher proton conductivity. The highest proton conductivity obtained with the composites is 0.5 S/cm measured at 85oC with 80% relative humidity in the measuring atmosphere. The miscibility of poly (vinyl phosphonic acid) and PEO is studied for the first time in this work and a phase diagram is plotted based on a DSC study and optical microscopy. With this knowledge, homogeneous PVPA/PEO mixtures are prepared as proton-conducting polymer blends. The mobility of phosphonic acid groups and PEO in the blends is determined by 1H-MAS-NMR in temperature dependent measurements. The effect of composition and the role of PEO on proton conduction are discussed.

Unconventional superconductivity of the heavy fermion compound UNi 2 Al 3

The heavy fermion compound UNi2Al3 exhibits the coexistence of superconductivity and magnetic order at low temperatures, stimulating speculations about possible exotic Cooper-pairing interaction in this superconductor. However, the preparation of good quality bulk single crystals of UNi2Al3 has proven to be a non-trivial task due to metallurgical problems, which result in the formation of an UAl2 impurity phase and hence a strongly reduced sample purity. The present work concentrates on the preparation, characterization and electronic properties investigation of UNi2Al3 single crystalline thin film samples. The preparation of thin films was accomplished in a molecular beam epitaxy (MBE) system. (100)-oriented epitaxial thin films of UNi2Al3 were grown on single crystalline YAlO3 substrates cut in (010)- or (112)-direction. The high crystallographic quality of the samples was proved by several characterisation methods, such as X-ray analysis, RHEED and TEM. To study the magnetic structure of epitaxial thin films resonant magnetic x-ray scattering was employed. The magnetic order of thin the film samples, the formation of magnetic domains with different moment directions, and the magnetic correlation length were discussed. The electronic properties of the UNi2Al3 thin films in the normal and superconducting states were investigated by means of transport measurements. A pronounced anisotropy of the temperature dependent resistivity ρ(T) was observed. Moreover, it was found that the temperature of the resistive superconducting transition depends on the current direction, providing evidence for multiband superconductivity in UNi2Al3. The initial slope of the upper critical field H′c2(T) of the thin film samples suggests an unconventional spin-singlet superconducting state, as opposed to bulk single crystal data. To probe the superconducting gap of UNi2Al3 directly by means of tunnelling spectroscopy many planar junctions of different design employing different techniques were prepared. Despite the tunneling regime of the junctions, no features of the superconducting density of state of UNi2Al3 were ever observed. It is assumed that the absence of UNi2Al3 gap features in the tunneling spectra was caused by imperfections of the tunnelling contacts. The superconductivity of UNi2Al3 was probably suppressed just in a degraded surface layer, resulting in tunneling into non superconducting UNi2Al3. However, alternative explanations such as intrinsic pair breaking effects at the interface to the barrier are also possible.

First Ramsey-type mass measurements with ISOLTRAP and design studies of the new PENTATRAP project

Der Einsatz von Penningfallen in der Massenspektrometrie hat zu einem einmaligen Genauigkeitssprung geführt. Dadurch wurden Massenwerte verschiedenster Atome zu wichtigen Eingangsparametern bei immer mehr physikalischen Fragestellungen. Die Massenspektrometrie mit Hilfe von Penningfallen basiert auf der Bestimmung der freien Zyklotronfrequenz eines Ions in einem homogenen Magnetfeld νc=qB/(2πm). Sie wird mit Flugzeitmethode (TOF-ICR) bestimmt, wobei eine relative Massenungenauigkeit δm/m von wenigen 10^-9 bei Nukliden mit Lebensdauern von <500 ms erreicht wird. Dies wurde durch die im Rahmen dieser Arbeit erstmals in der Penningfallen-Massenspektrometrie eingesetzten Ramsey-Methode möglich. Dabei werden zeitlich separierte, oszillierenden Feldern zur resonanten Ionenanregung genutzt, um die Frequenzmessung durch die Flugzeitmethode zu verbessern. Damit wurden am Penningfallenmassenspektrometer ISOLTRAP an ISOLDE/CERN die Massen der Nuklide 26,27Al und 38,39Ca bestimmt. Alle Massen wurden in die „Atomic Mass Evaluation“ eingebettet. Die Massenwerte von 26Al und 38Ca dienten insbesondere zu Tests des Standardmodells. Um mit Massenwerten fundamentale Symmetrien oder die Quantenelektrodynamik (QED) in extremen Feldern zu testen wurde ein neues Penningfallenprojekt (PENTATRAP) für hochpräzise Massenmessungen an hochgeladenen Ionen konzipiert. In dieser Doktorarbeit wurde vornehmlich die Entwicklung der Penningfallen betrieben. Eine Neuerung bei Penningfallenexperimenten ist dabei die permanente Beobachtung des Magnetfeldes B und seiner zeitlichen Fluktuationen durch so genannte „Monitorfallen“.

Pore structure and column efficiency of silica monoliths in high performance liquid chromatography (HPLC)

Five different methods were critically examined to characterize the pore structure of the silica monoliths. The mesopore characterization was performed using: a) the classical BJH method of nitrogen sorption data, which showed overestimated values in the mesopore distribution and was improved by using the NLDFT method, b) the ISEC method implementing the PPM and PNM models, which were especially developed for monolithic silicas, that contrary to the particulate supports, demonstrate the two inflection points in the ISEC curve, enabling the calculation of pore connectivity, a measure for the mass transfer kinetics in the mesopore network, c) the mercury porosimetry using a new recommended mercury contact angle values. rnThe results of the characterization of mesopores of monolithic silica columns by the three methods indicated that all methods were useful with respect to the pore size distribution by volume, but only the ISEC method with implemented PPM and PNM models gave the average pore size and distribution based on the number average and the pore connectivity values.rnThe characterization of the flow-through pore was performed by two different methods: a) the mercury porosimetry, which was used not only for average flow-through pore value estimation, but also the assessment of entrapment. It was found that the mass transfer from the flow-through pores to mesopores was not hindered in case of small sized flow-through pores with a narrow distribution, b) the liquid penetration where the average flow-through pore values were obtained via existing equations and improved by the additional methods developed according to Hagen-Poiseuille rules. The result was that not the flow-through pore size influences the column bock pressure, but the surface area to volume ratio of silica skeleton is most decisive. Thus the monolith with lowest ratio values will be the most permeable. rnThe flow-through pore characterization results obtained by mercury porosimetry and liquid permeability were compared with the ones from imaging and image analysis. All named methods enable a reliable characterization of the flow-through pore diameters for the monolithic silica columns, but special care should be taken about the chosen theoretical model.rnThe measured pore characterization parameters were then linked with the mass transfer properties of monolithic silica columns. As indicated by the ISEC results, no restrictions in mass transfer resistance were noticed in mesopores due to their high connectivity. The mercury porosimetry results also gave evidence that no restrictions occur for mass transfer from flow-through pores to mesopores in the small scaled silica monoliths with narrow distribution. rnThe prediction of the optimum regimes of the pore structural parameters for the given target parameters in HPLC separations was performed. It was found that a low mass transfer resistance in the mesopore volume is achieved when the nominal diameter of the number average size distribution of the mesopores is appr. an order of magnitude larger that the molecular radius of the analyte. The effective diffusion coefficient of an analyte molecule in the mesopore volume is strongly dependent on the value of the nominal pore diameter of the number averaged pore size distribution. The mesopore size has to be adapted to the molecular size of the analyte, in particular for peptides and proteins. rnThe study on flow-through pores of silica monoliths demonstrated that the surface to volume of the skeletons ratio and external porosity are decisive for the column efficiency. The latter is independent from the flow-through pore diameter. The flow-through pore characteristics by direct and indirect approaches were assessed and theoretical column efficiency curves were derived. The study showed that next to the surface to volume ratio, the total porosity and its distribution of the flow-through pores and mesopores have a substantial effect on the column plate number, especially as the extent of adsorption increases. The column efficiency is increasing with decreasing flow through pore diameter, decreasing with external porosity, and increasing with total porosity. Though this tendency has a limit due to heterogeneity of the studied monolithic samples. We found that the maximum efficiency of the studied monolithic research columns could be reached at a skeleton diameter of ~ 0.5 µm. Furthermore when the intention is to maximize the column efficiency, more homogeneous monoliths should be prepared.rn

New sensing platforms based on nanoscopic devices for probing protein-membrane interactions

A novel nanosized and addressable sensing platform based on membrane coated plasmonic particles for detection of protein adsorption using dark field scattering spectroscopy of single particles has been established. To this end, a detailed analysis of the deposition of gold nanorods on differently functionalized substrates is performed in relation to various factors (such as the pH, ionic strength, concentration of colloidal suspension, incubation time) in order to find the optimal conditions for obtaining a homogenous distribution of particles at the desired surface number density. The possibility of successfully draping lipid bilayers over the gold particles immobilized on glass substrates depends on the careful adjustment of parameters such as membrane curvature and adhesion properties and is demonstrated with complementary techniques such as phase imaging AFM, fluorescence microscopy (including FRAP) and single particle spectroscopy. The functionality and sensitivity of the proposed sensing platform is unequivocally certified by the resonance shifts of the plasmonic particles that were individually interrogated with single particle spectroscopy upon the adsorption of streptavidin to biotinylated lipid membranes. This new detection approach that employs particles as nanoscopic reporters for biomolecular interactions insures a highly localized sensitivity that offers the possibility to screen lateral inhomogeneities of native membranes. As an alternative to the 2D array of gold nanorods, short range ordered arrays of nanoholes in optically transparent gold films or regular arrays of truncated tetrahedron shaped particles are built by means of colloidal nanolithography on transparent substrates. Technical issues mainly related to the optimization of the mask deposition conditions are successfully addressed such that extended areas of homogenously nanostructured gold surfaces are achieved. Adsorption of the proteins annexin A1 and prothrombin on multicomponent lipid membranes as well as the hydrolytic activity of the phospholipase PLA2 were investigated with classical techniques such as AFM, ellipsometry and fluorescence microscopy. At first, the issues of lateral phase separation in membranes of various lipid compositions and the dependency of the domains configuration (sizes and shapes) on the membrane content are addressed. It is shown that the tendency for phase segregation of gel and fluid phase lipid mixtures is accentuated in the presence of divalent calcium ions for membranes containing anionic lipids as compared to neutral bilayers. Annexin A1 adsorbs preferentially and irreversibly on preformed phosphatidylserine (PS) enriched lipid domains but, dependent on the PS content of the bilayer, the protein itself may induce clustering of the anionic lipids into areas with high binding affinity. Corroborated evidence from AFM and fluorescence experiments confirm the hypothesis of a specifically increased hydrolytic activity of PLA2 on the highly curved regions of membranes due to a facilitated access of lipase to the cleavage sites of the lipids. The influence of the nanoscale gold surface topography on the adhesion of lipid vesicles is unambiguously demonstrated and this reveals, at least in part, an answer for the controversial question existent in the literature about the behavior of lipid vesicles interacting with bare gold substrates. The possibility of formation monolayers of lipid vesicles on chemically untreated gold substrates decorated with gold nanorods opens new perspectives for biosensing applications that involve the radiative decay engineering of the plasmonic particles.

Reactive halogen compounds in the marine boundary layer: method developments and field measurements

Reactive halogen compounds are known to play an important role in a wide variety of atmospheric processes such as atmospheric oxidation capacity and coastal new particle formation. In this work, novel analytical approaches combining diffusion denuder/impinger sampling techniques with gas chromatographic–mass spectrometric (GC–MS) determination are developed to measure activated chlorine compounds (HOCl and Cl2), activated bromine compounds (HOBr, Br2, BrCl, and BrI), activated iodine compounds (HOI and ICl), and molecular iodine (I2). The denuder/GC–MS methods have been used to field measurements in the marine boundary layer (MBL). High mixing ratios (of the order of 100 ppt) of activated halogen compounds and I2 are observed in the coastal MBL in Ireland, which explains the ozone destruction observed. The emission of I2 is found to correlate inversely with tidal height and correlate positively with the levels of O3 in the surrounding air. In addition the release is found to be dominated by algae species compositions and biomass density, which proves the “hot-spot” hypothesis of atmospheric iodine chemistry. The observations of elevated I2 concentrations substantially support the existence of higher concentrations of littoral iodine oxides and thus the connection to the strong ultra-fine particle formation events in the coastal MBL.

Measurement and modeling of cloud condensation nuclei in continental air

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. Knowledge of the spatial and temporal distribution of CCN in the atmosphere is essential to understand and describe the effects of aerosols in meteorological models. In this study, CCN properties were measured in polluted and pristine air of different continental regions, and the results were parameterized for efficient prediction of CCN concentrations.The continuous-flow CCN counter used for size-resolved measurements of CCN efficiency spectra (activation curves) was calibrated with ammonium sulfate and sodium chloride aerosols for a wide range of water vapor supersaturations (S=0.068% to 1.27%). A comprehensive uncertainty analysis showed that the instrument calibration depends strongly on the applied particle generation techniques, Köhler model calculations, and water activity parameterizations (relative deviations in S up to 25%). Laboratory experiments and a comparison with other CCN instruments confirmed the high accuracy and precision of the calibration and measurement procedures developed and applied in this study.The mean CCN number concentrations (NCCN,S) observed in polluted mega-city air and biomass burning smoke (Beijing and Pearl River Delta, China) ranged from 1000 cm−3 at S=0.068% to 16 000 cm−3 at S=1.27%, which is about two orders of magnitude higher than in pristine air at remote continental sites (Swiss Alps, Amazonian rainforest). Effective average hygroscopicity parameters, κ, describing the influence of chemical composition on the CCN activity of aerosol particles were derived from the measurement data. They varied in the range of 0.3±0.2, were size-dependent, and could be parameterized as a function of organic and inorganic aerosol mass fraction. At low S (≤0.27%), substantial portions of externally mixed CCN-inactive particles with much lower hygroscopicity were observed in polluted air (fresh soot particles with κ≈0.01). Thus, the aerosol particle mixing state needs to be known for highly accurate predictions of NCCN,S. Nevertheless, the observed CCN number concentrations could be efficiently approximated using measured aerosol particle number size distributions and a simple κ-Köhler model with a single proxy for the effective average particle hygroscopicity. The relative deviations between observations and model predictions were on average less than 20% when a constant average value of κ=0.3 was used in conjunction with variable size distribution data. With a constant average size distribution, however, the deviations increased up to 100% and more. The measurement and model results demonstrate that the aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the measurement results and parameterizations presented in this study can be directly implemented in detailed process models as well as in large-scale atmospheric and climate models for efficient description of the CCN activity of atmospheric aerosols.

First measurements of the aSPECT spectrometer

The aSPECT spectrometer has been constructed to measure, with high precision, the integral proton spectrum of the free neutron decay. From this spectrum the neutrino electron angular correlation coefficient a can be inferred. The coefficient a is involved in several Standard Model tests, like the unitarity test of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. aSPECT has been designed to determine the coefficient a with an accuracy better than 3×10−4, that is, one order of magnitude better than the best current accuracy. First measurements with neutron beam with the aSPECT spectrometer were performed in the Forschungsneutronenquelle Heinz Maier-Leibnitz, in Munich. A study of the data taken in this period is presented in this thesis, demonstrating the proof of principle of the spectrometer. However, the observation of situation and time-dependent background instabilities impedes the report of a new value of the coefficient a. A thorough data analysis is carried out to identify sources of these background instabilities in order to improve the aSPECT experiment for future beam times. The investigation indicates that trapped particles are most likely the reason for the background problems. Furthermore, it has been observed that measurements containing less trapped particles provide a-values closer to the currently Particle Data Group value. Based on this findings, different measures are proposed to eliminate potential traps in the spectrometer. Indeed, with the proposed modifications realized for the following beam-times, the observed background instabilities were greatly reduced.

Prozessanalytische Technologien "PAT" zur Optimierung von Wirbelschichtgranulationsprozessen

In der Herstellung fester Darreichungsformen umfasst die Granulierung einen komplexen Teilprozess mit hoher Relevanz für die Qualität des pharmazeutischen Produktes. Die Wirbelschichtgranulierung ist ein spezielles Granulierverfahren, welches die Teilprozesse Mischen, Agglomerieren und Trocknen in einem Gerät vereint. Durch die Kombination mehrerer Prozessstufen unterliegt gerade dieses Verfahren besonderen Anforderungen an ein umfassendes Prozessverständnis. Durch die konsequente Verfolgung des PAT- Ansatzes, welcher im Jahre 2004 durch die amerikanische Zulassungsbehörde (FDA) als Guideline veröffentlicht wurde, wurde der Grundstein für eine kontinuierliche Prozessverbesserung durch erhöhtes Prozessverständnis, für Qualitätserhöhung und Kostenreduktion gegeben. Die vorliegende Arbeit befasste sich mit der Optimierung der Wirbelschicht-Granulationsprozesse von zwei prozesssensiblen Arzneistoffformulierungen, unter Verwendung von PAT. rnFür die Enalapril- Formulierung, einer niedrig dosierten und hochaktiven Arzneistoffrezeptur, wurde herausgefunden, dass durch eine feinere Zerstäubung der Granulierflüssigkeit deutlich größere Granulatkörnchen erhalten werden. Eine Erhöhung der MassRatio verringert die Tröpfchengröße, dies führt zu größeren Granulaten. Sollen Enalapril- Granulate mit einem gewünschten D50-Kornverteilung zwischen 100 und 140 um hergestellt werden, dann muss die MassRatio auf hohem Niveau eingestellt werden. Sollen Enalapril- Granulate mit einem D50- Wert zwischen 80 und 120µm erhalten werden, so muss die MassRatio auf niedrigem Niveau eingestellt sein. Anhand der durchgeführten Untersuchungen konnte gezeigt werden, dass die MassRatio ein wichtiger Parameter ist und zur Steuerung der Partikelgröße der Enalapril- Granulate eingesetzt werden kann; unter der Voraussetzung dass alle anderen Prozessparameter konstant gehalten werden.rnDie Betrachtung der Schnittmengenplots gibt die Möglichkeit geeignete Einstellungen der Prozessparameter bzw. Einflussgrößen zu bestimmen, welche dann zu den gewünschten Granulat- und Tabletteneigenschaften führen. Anhand der Lage und der Größe der Schnittmenge können die Grenzen der Prozessparameter zur Herstellung der Enalapril- Granulate bestimmt werden. Werden die Grenzen bzw. der „Design Space“ der Prozessparameter eingehalten, kann eine hochwertige Produktqualität garantiert werden. rnUm qualitativ hochwertige Enalapril Tabletten mit der gewählten Formulierung herzustellen, sollte die Enalapril- Granulation mit folgenden Prozessparametern durchgeführt werden: niedrige Sprührate, hoher MassRatio, einer Zulufttemperatur von mindestens > 50 °C und einer effektiven Zuluftmenge < 180 Nm³/h. Wird hingegen eine Sprührate von 45 g/min und eine mittlere MassRatio von 4.54 eingestellt, so muss die effektive Zuluftmenge mindestens 200 Nm³/h und die Zulufttemperatur mindestens 60 °C betragen, um eine vorhersagbar hohe Tablettenqualität zu erhalten. Qualität wird in das Arzneimittel bereits während der Herstellung implementiert, indem die Prozessparameter bei der Enalapril- Granulierung innerhalb des „Design Space“ gehalten werden.rnFür die Metformin- Formulierung, einer hoch dosierten aber wenig aktiven Arzneistoffrezeptur wurde herausgefunden, dass sich der Wachstumsmechanismus des Feinanteils der Metformin- Granulate von dem Wachstumsmechanismus der D50- und D90- Kornverteilung unterscheidet. Der Wachstumsmechanismus der Granulate ist abhängig von der Partikelbenetzung durch die versprühten Flüssigkeitströpfchen und vom Größenverhältnis von Partikel zu Sprühtröpfchen. Der Einfluss der MassRatio ist für die D10- Kornverteilung der Granulate vernachlässigbar klein. rnMit Hilfe der Störgrößen- Untersuchungen konnte eine Regeleffizienz der Prozessparameter für eine niedrig dosierte (Enalapril)- und eine hoch dosierte (Metformin) Arzneistoffformulierung erarbeitet werden, wodurch eine weitgehende Automatisierung zur Verringerung von Fehlerquellen durch Nachregelung der Störgrößen ermöglicht wird. Es ergibt sich für die gesamte Prozesskette ein in sich geschlossener PAT- Ansatz. Die Prozessparameter Sprührate und Zuluftmenge erwiesen sich als am besten geeignet. Die Nachregelung mit dem Parameter Zulufttemperatur erwies sich als träge. rnFerner wurden in der Arbeit Herstellverfahren für Granulate und Tabletten für zwei prozesssensible Wirkstoffe entwickelt. Die Robustheit der Herstellverfahren gegenüber Störgrößen konnte demonstriert werden, wodurch die Voraussetzungen für eine Echtzeitfreigabe gemäß dem PAT- Gedanken geschaffen sind. Die Kontrolle der Qualität des Produkts findet nicht am Ende der Produktions- Prozesskette statt, sondern die Kontrolle wird bereits während des Prozesses durchgeführt und basiert auf einem besseren Verständnis des Produktes und des Prozesses. Außerdem wurde durch die konsequente Verfolgung des PAT- Ansatzes die Möglichkeit zur kontinuierlichen Prozessverbesserung, zur Qualitätserhöhung und Kostenreduktion gegeben und damit das ganzheitliche Ziel des PAT- Gedankens erreicht und verwirklicht.rn

Microstructure of epitaxial thin films of the ferromagnetic shape memory alloy Ni 2 MnGa

Gegenstand dieser Arbeit ist die Präparation und die ausführliche Charakterisierung epitaktischer Dünnschicht-Proben der Heusler Verbindung Ni2MnGa. Diese intermetallische Verbindung zeigt einen magnetischen Formgedächtnis-Effekt (MFG), der sowohl im Bezug auf mögliche Anwendungen, als auch im Kontext der Grundlagenforschung äußerst interessant ist. In Einkristallen nahe der Stöchiometrie Ni2MnGa wurden riesige magnetfeldinduzierte Dehnungen von bis zu 10 % nachgewiesen. Der zugrundeliegende Mechanismus basiert auf einer Umverteilung von kristallographischen Zwillings-Varianten, die eine tetragonale oder orthorhombische Symmetrie besitzen. Unter dem Einfluss des Magnetfeldes bewegen sich die Zwillingsgrenzen durch den Kristall, was eine makroskopische Formänderung mit sich bringt. Die somit erzeugten reversiblen Längenänderungen können mit hoher Frequenz geschaltet werden, was Ni2MnGa zu einem vielversprechenden Aktuatorwerkstoff macht. rnDa der Effekt auf einem intrinsischen Prozess beruht, eignen sich Bauteile aus MFG Legierungen zur Integration in Mikrosystemen (z.B. im Bereich der Mikrofluidik). rnrnBislang konnten große magnetfeldinduzierte Dehnungen nur für Einkristalle und Polykristalle mit hoher Porosität („foams") nachgewiesen werden. Um den Effekt für Anwendungen nutzbar zu machen, werden allerdings Konzepte zur Miniaturisierung benötigt. Eine Möglichkeit bieten epitaktische dünne Filme, die im Rahmen dieser Arbeit hergestellt und untersucht werden sollen. Im Fokus stehen dabei die Optimierung der Herstellungsparameter, sowie die Präparation von freitragenden Schichten. Zudem werden verschiedene Konzepte zur Herstellung freistehender Mikrostrukturen erprobt. Mittels Röntgendiffraktometrie konnte die komplizierte Kristallstruktur für verschiedene Wachstumsrichtungen verstanden und die genaue Verteilung der Zwillingsvarianten aufgedeckt werden. In Verbindung mit Mikroskopie-Methoden konnte so die Zwillingsstruktur auf verschiedenen Längenskalen geklärt werden. Die Ergebnisse erklären das Ausbleiben des MFG Effekts in den Proben mit (100) Orientierung. Andererseits wurde für Schichten mit (110) Wachstum eine vielversprechende Mikrostruktur entdeckt, die einen guten Ausgangspunkt für weitere Untersuchungen bietet.rnDurch die spezielle Geometrie der Proben war es möglich, Spektroskopie-Experimente in Transmission durchzuführen. Die Ergebnisse stellen den ersten experimentellen Nachweis der Änderungen in der elektronischen Struktur einer metallischen Verbindung während des martensitischen Phasenübergangs dar. Durch Messen des magnetischen Zirkulardichroismus in der Röntgenabsorption konnten quantitative Aussagen über die magnetischen Momente von Ni und Mn getroffen werden. Die Methode erlaubt überdies die Beiträge von Spin- und Bahn-Moment separat zu bestimmen. Durch winkelabhängige Messungen gelang es, die mikroskopische Ursache der magnetischen Anisotropie aufzuklären. Diese Ergebnisse tragen wesentlich zum Verständnis der komplexen magnetischen und strukturellen Eigenschaften von Ni2MnGa bei.rn

Near-field mediated enhancement effects on plasmonic nanostructures

In dieser Arbeit wird eine detaillierte Untersuchung und Charakterisierung der Zwei-Photonen-induzierten Fluoreszenzverstärkung von organischen Farbstoffen auf plasmonischen Nanostrukturen vorgestellt. Diese Fluoreszenzverstärkung ist insbesondere für hochaufgelöste Fluoreszenzmikroskopie und Einzelmolekülspektroskopie von großer Bedeutung. Durch die Zwei-Photonen-Anregung resultiert eine Begrenzung des Absorptionsprozesses auf das fokale Volumen. In Kombination mit dem elektrischen Nahfeld der Nanostrukturen als Anregungsquelle entsteht eine noch stärkere Verringerung des Anregungsvolumens auf eine Größe unterhalb der Beugungsgrenze. Dies erlaubt die selektive Messung ausgewählter Farbstoffe. Durch die Herstellung der Nanopartikel mittels Kolloidlithografie wird eine definierte, reproduzierbare Geometrie erhalten. Polymermultischichten dienen als Abstandshalter, um die Farbstoffe an einer exakten Distanz zum Metall zu positionieren. Durch die kovalente Anbindung des Farbstoffs an die oberste Schicht wird eine gleichmäßige Verteilung des Farbstoffs in geringer Konzentration erhalten. rnEs wird eine Verstärkung der Fluoreszenz um den Faktor 30 für Farbstoffe auf Goldellipsen detektiert, verglichen mit Farbstoffen außerhalb des Nahfelds. Sichelförmige Nanostrukturen erzeugen eine Verstärkung von 120. Dies belegt, dass das Ausmaß der Fluoreszenzverstärkung entscheidend von der Stärke des elektrischen Nahfelds der Nanostruktur abhängt. Auch das Material der Nanostruktur ist hierbei von Bedeutung. So erzeugen Silberellipsen eine 1,5-fach höhere Fluoreszenzverstärkung als identische Goldellipsen. Distanzabhängige Fluoreszenzmessungen zeigen, dass die Zwei-Photonen-angeregte Fluoreszenzverstärkung an strukturspezifischen Abständen zum Metall maximiert wird. Elliptische Strukturen zeigen ein Maximum bei einem Abstand von 8 nm zum Metall, wohingegen bei sichelförmigen Nanostrukturen die höchste Fluoreszenzintensität bei 12 nm gemessen wird. Bei kleineren Abständen unterliegt der Farbstoff einem starken Löschprozess, sogenanntes Quenching. Dieses konkurriert mit dem Verstärkungsprozess, wodurch es zu einer geringen Nettoverstärkung kommt. Hat die untersuchte Struktur Dimensionen größer als das Auflösungsvermögen des Mikroskops, ist eine direkte Visualisierung des elektrischen Nahfelds der Nanostruktur möglich. rnrnEin weiterer Fokus dieser Arbeit lag auf der Herstellung neuartiger Nanostrukturen durch kolloidlithografische Methoden. Gestapelte Dimere sichelförmiger Nanostrukturen mit exakter vertikaler Ausrichtung und einem Separationsabstand von etwa 10 nm wurden hergestellt. Die räumliche Nähe der beiden Strukturen führt zu einem Kopplungsprozess, der neue optische Resonanzen hervorruft. Diese können als Superpositionen der Plasmonenmoden der einzelnen Sicheln beschrieben werden. Ein Hybridisierungsmodell wird angewandt, um die spektralen Unterschiede zu erklären. Computersimulationen belegen die zugrunde liegende Theorie und erweitern das Modell um experimentell nicht aufgelöste Resonanzen. rnWeiterhin wird ein neuer Herstellungsprozess für sichelförmige Nanostrukturen vorgestellt, der eine präzise Formanpassung ermöglicht. Hierdurch kann die Lage der Plasmonenresonanz exakt justiert werden. Korrelationen der geometrischen Daten mit den Resonanzwellenlängen tragen zum grundlegenden Verständnis der Plasmonenresonanzen bei. Die vorgestellten Resultate wurden mittels Computersimulationen verifiziert. Der Fabrikationsprozess erlaubt die Herstellung von Dimeren sichelförmiger Nanostrukturen in einer Ebene. Durch die räumliche Nähe überlappen die elektrischen Nahfelder, wodurch es zu kopplungs-induzierten Shifts der Plasmonenresonanzen kommt. Der Unterschied zu theoretisch berechneten ungekoppelten Nanosicheln kann auch bei den gegenüberliegenden sichelförmigen Nanostrukturen mit Hilfe des Plasmonenhybridisierungsmodells erklärt werden.