L’assemblage couche-par-couche permet de fabriquer des films multimatériaux aux propriétés variées présentant une structure stratifiée. Ce travail décrit les études structurelles des films multicouches de polyélectrolytes à l’aide de mesures de diffusion de neutrons.L’effet du vieillissement des films a été déterminé par réflectométrie des neutrons. Nous avons observé un léger tassement des films après 5 ans et une forte expansion après 15 ans.Nous avons aussi montré que le substrat et l’air en surface ont une influence sur la structure des couches proches des extrémités des films, conduisant à une structure inhomogène perpendiculairement à la surface.Nous avons finalement étudié la conformation des chaînes de polyélectrolytes dans les films multicouches ; nous avons déterminé que les chaînes de PSS dans des films préparés par trempage ont une conformation en pelotes aplaties, contrairement aux chaînes de polyélectrolytes en solution qui présentent une conformation sphérique. / The Layer-by-Layer assembly allows the build-up of multimaterial films with various properties showing a stratified structure. This work describes the structural strudies of multilayer films of polyelectrolytes with neutron scattering measurements.Ageing effect on films was determined by neutron reflectometry. We observed a slight shrink of the films after 5 years and a strong expansion after 15 years.We also showed that the proximity of the substrate and the air at the surface have an influence on the structure of the layers at the extremities of the films, leading to an inhomogeneous structure perpendicularly to the surface.Finally, we studied the conformation of polyelectrolyte chains in the multilayer films ; we determined that PSS chains in dipped films have a flattened coil conformation, whereas the polyelectrolyte chains in solution have a spherical conformation.

In der vorliegenden Projektarbeit wurde ein erster Design-Vorschlag für eine Superspiegel-Test-Anlage am Ausbildungskernreaktor 2 der TU Dresden erstellt. Mit dieser soll die Reflektivität von Neutronensuperspiegeln bestimmt werden. Die Funktionalität des erarbeiteten Vorschlags ist mit Hilfe der Software McStas überprüft worden. McStas ist ein Monte-Carlo Programm, das Neutronenstrahlen für neutronenoptische Anwendungen simuliert. Basierend auf der Arbeit an einer existierenden Anlage am Paul-Scherrer-Institut, NARZISS, wurde außerdem eine Software entwickelt. Die Software dient der Auswertung der am Instrument gewonnenen Daten.:1. Einleitung 2. Neutronenoptik 2.1. Reflexion und Transmission 2.2. Reflexion an dünnen Schichten 2.3. Superspiegel 2.4. Polarisierende Spiegel 2.5. Monochromatoren 2.6. Detektoren 3. McStas 3.1. Überblick 3.2. Source 3.3. Mirror 3.4. Monitor 4. NARZISS am PSI 4.1. Aufbau 4.2. Justage und Versuchsdurchführung 4.3. Anwendungen am Beispiel eigener Messungen 4.3.1. Neutronensuperspiegel 4.3.2. Wafer 4.4. McStas-Modell NARZISS 5. Simulationen für ein Superspiegeltest-Instrument an der TU Dresden 5.1. Randbedingungen 5.2. Aufbau 5.3. Quelle 5.4. Simulationsergebnisse 5.4.1. Wellenlänge 5.4.2. Kollimation, Divergenz 5.4.3. Abschätzung Messzeit 5.5. Ergebnis und Verbesserungspotentiale 6. NOA - Ein Programm zur Auswertung von NARZISS-Messergebnissen 6.1. Zielstellung 6.2. Architektur 6.3. Berechnungen und Bearbeitungsablauf 6.3.1. Teil: Reflektivität 6.3.2. Teil: Polarisierung 6.4. Ergebnis 7. Zusammenfassung und Ergebnis sowie Ausblick / In the current project there was developed a first design-suggestion for a super-mirror-teststation at the nuclear training reactor Ausbildungskernreaktor 2 at the TU Dresden. It should be used to test the reflectivity of neutron super mirrors. The usability was tested with the software McStas. McStas is a Monte-Carlo ray-tracing simulation tool for neutron optical simulations. Based on the work at an existing reflectometry-station at the Paul-Scherrer-Institut, NARZISS, it was also part of the project to develop a software. The software enables the analysis of the NARZISS data.:1. Einleitung 2. Neutronenoptik 2.1. Reflexion und Transmission 2.2. Reflexion an dünnen Schichten 2.3. Superspiegel 2.4. Polarisierende Spiegel 2.5. Monochromatoren 2.6. Detektoren 3. McStas 3.1. Überblick 3.2. Source 3.3. Mirror 3.4. Monitor 4. NARZISS am PSI 4.1. Aufbau 4.2. Justage und Versuchsdurchführung 4.3. Anwendungen am Beispiel eigener Messungen 4.3.1. Neutronensuperspiegel 4.3.2. Wafer 4.4. McStas-Modell NARZISS 5. Simulationen für ein Superspiegeltest-Instrument an der TU Dresden 5.1. Randbedingungen 5.2. Aufbau 5.3. Quelle 5.4. Simulationsergebnisse 5.4.1. Wellenlänge 5.4.2. Kollimation, Divergenz 5.4.3. Abschätzung Messzeit 5.5. Ergebnis und Verbesserungspotentiale 6. NOA - Ein Programm zur Auswertung von NARZISS-Messergebnissen 6.1. Zielstellung 6.2. Architektur 6.3. Berechnungen und Bearbeitungsablauf 6.3.1. Teil: Reflektivität 6.3.2. Teil: Polarisierung 6.4. Ergebnis 7. Zusammenfassung und Ergebnis sowie Ausblick

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Verankerte Polymere können die Funktionalität einer Oberfläche beeinflussen. Der Schwerpunkt dieser Arbeit liegt auf der Untersuchung von Polymerbürsten aus Polyacrylsäure (PAA) und Poly(N,N-dimethylaminoethyl methacrylat) (PDMAEMA). Auf Oberflächen, die mit PAA Bürsten beschichtet sind, können Proteine im nativen Zustand immobilisiert werden. Für PDMAEMA ist eine Reaktion auf externe Reize bekannt. So kann dessen untere kritische Lösungstemperatur (LCST) zur Einstellung der Hydrophobizität von Oberflächen verwendet werden. Erstmalig im Rahmen dieser Arbeit wurde untersucht, wie sich hydrostatischer Druck von bis zu 1000 bar auf die Funktionalität der verwendeten Polymerbürsten auswirkt. Aus Diblock-Kopolymeren wurden Langmuir-Filme unterschiedlicher Ankerdichte mit der Langmuir-Schäfer Technik auf feste Substrate übertragen. Die Funktionalität der PAA Bürsten wurde vor und nach der Adsorption von Rinderserumalbumin (BSA) in gepufferter D2O-Lösung mit Hilfe der Neutronenreflektometrie (NR) bei 1 bar und 900 bar an der fest-flüssig Grenzfläche untersucht. Es wurden Volumenfraktionsprofile der PAA Bürste und adsorbierten BSA extrahiert, woraus sich eine lineare Abhängigkeit zwischen Ankerdichte und Menge an adsorbiertem Protein feststellen ließ. Erhöhung des hydrostatischen Druckes auf 900 bar veränderte weder die PAA Volumenprofile noch die Immobilisierung von BSA. Die PDMAEMA Bürsten wurden mittels NR bei Temperaturen von 20-60 °C und Drücken von 1-1000 bar untersucht. Zur Analyse der Daten wurde ein neuartiges Dichteprofil-Modell verwendet. Temperaturerhöhung führt zur stetigen Abnahme der Bürstendicke. Dies lässt sich durch den LCST induzierten Phasenübergang der Polymere vom hydrophilen in einen hydrophoben Zustand erklären. Es wurde gefunden, dass eine Erhöhung des hydrostatischen Druckes diesem Prozess entgegenwirkt. Strukturänderungen der Polymerbürsten bei Erhöhung der Temperatur um 10 K ließen sich durch Erhöhung des Druckes um 1000 bar rückgängig machen. / The functionality of an interface can be modified by polymer brushes. The focus of this work is on brushes of either polyacrylic acid (PAA) or poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). PAA brushes provide a soft interface that prevents the denaturation of adsorbed proteins. PDMAEMA is known to respond to external stimuli. The lower critical solution temperature (LCST) of PDMAEMA can be used to tune the hydrophobicity of the interface with temperature. For the first time, the effect of elevated hydrostatic pressure, up to 1000 bar, on the functionality of these systems is investigated. Planar PAA and PDMAEMA brushes are prepared from precursor diblock copolymer Langmuir layers with varied grafting density utilizing the Langmuir-Schäfer transfer technique. For solvent-swollen PAA brushes, neutron reflectivity (NR) measurements are conducted at the solid-liquid interface after incubation in buffered D2O and after the adsorption of bovine serum albumin (BSA) from the aqueous liquid phase at 1 bar and 900 bar. Detailed volume fraction profiles of the PAA brush and adsorbed BSA proteins are extracted. The amount of adsorbed BSA is found to scale linearly with grafting density. An elevated hydrostatic pressure of 900 bar is found to have no impact on the structure of the PAA brush and its capability to bind BSA proteins. The PDMAEMA brushes are investigated by NR at the solid-liquid interface in a temperature range of 20 to 60 °C for hydrostatic pressures from 1 to 1000 bar. A novel theoretical model of the brush density profile is used to fit the experimental NR data. Increasing the temperature causes a continuous decrease of the polymer brush thickness due to a hydrophobic coil to globule transition of the polymer chains when crossing the LCST. Hydrostatic pressure is found to act antagonistic to temperature. The hydrophobic collapse of the PDMAEMA brush caused by a temperature increase of 10 K is counterbalanced by a pressure increase of 1000 bar.

Polymer/inorganic nanoparticle hybrid thin films, primarily composed of functional inorganic nanoparticles, are of great interest to researchers because of their interesting electronic, photonic, and optical properties. In the past two decades, layer-by-layer (LbL) assembly has become one of the most powerful techniques to fabricate such hybrid thin films. This method offers an easy, inexpensive, versatile, and robust fabrication technique for multilayer formation, with precisely controllable nanostructure and tunable properties. In this thesis, various ways to control the structure of hybrid thin films, primarily composed of polyelectrolytes and indium tin oxide (ITO), are the main topics of study. ITO is one of the most widely used conductive transparent oxides (TCOs) for applications such as flat panel displays, photovoltaic cells, and functional windows. In this work, polyethyleneimine (PEI) was used to stabilize the ITO suspensions and improve the film buildup rate during the LbL assembly of poly(sodium 4-styrenesulfonate) (PSS) and ITO. The growth rate was doubled due to the stronger interaction forces between the PSS and PEI-modified ITO layer. The assembly of hybrid films was often initiated by a polyelectrolyte precursor layer, and the characteristics of the precursor layer were found to significantly affect the assembly of the hybrid thin films. The LbL assembly of ITO nanoparticles was realized on several substrates, including cellulose fibers, write-on transparencies, silicon wafers, quartz crystals, and glasses. By coating the cellulose fibers with ITO nanoparticles, a new type of conductive paper was manufactured. By LbL assembly of ITO on write-on transparencies, transparent conductive thin films with conductivity of 10⁻⁴ S/cm and transparency of over 80 % in the visible range were also prepared. As a result of this work on the mechanisms and applications of LbL grown films, the understanding of the LbL assembly of polyelectrolytes and inorganic nanoparticles was significantly extended. In addition to working with ITO nanoparticles, this thesis also demonstrated the ability to grow bicomponent [PEI/SiO₂]n thin films. It was further demonstrated that under the right pH conditions, these films can be grown exponentially (e-LbL), resulting in much thicker films, consisting of mostly the inorganic nanoparticles, in much fewer assembly steps than traditional linearly grown films (l-LbL). These results open the door to new research opportunities for achieving structured nanoparticle thin films, whose functionality depends primarily on the properties of the nanoparticles.

Tunneling phenomenon has been studied since the time of Sir Isaac Newton. In the case of neutron tunneling phenomenon, it is the quantum mechanics wave-particle duality which manifests itself. In this case, particularly, the neutron wave-packet under total reflection condition suffers the so-called frustrated total reflection as known in standard optics. More accurately, this tunneling phenomenon shows itself via sharp dips in the plateau of total reflection. The prerequisite to observe such quantum mechanics phenomenon lies within a thin film Fabry-Perot resonator configuration. This thin film Fabry-Perot resonator geometry consists of two reflecting mirrors separated by a transparent material from a neutron optics viewpoint. In view of the specific neutron scattering properties related to the spin of the neutron wave-packet. As a direct proof, isotopic nickel based thin films Fabry-Perot resonator have been fabricated by depositing thin film of nickel by ion beam sputtering. The vacuum chamber was pumped down to the pressure of 10-8 mbar and deposition was performed at pressure of 2x10-4 mbar. The deposition rate was kept at 1.5 nm / minute and thickness layers were monitored by a calibrated quartz microbalance. Unpolarized neutron reflectometry measurements were carried out at the ORPHEE reactor using the time-of-flight EROS reflectometer. The incidence neutron wavelength varied between 3 – 25 Å. The grazing angle and angular resolution were of the order of 0.8˚ and 0.05 respectively. The software program, a Matlab routine for the simulation of specular X-ray and neutron reflectivity data with matrix technique, was employed to simulate the phenomenon and thereafter the experimentally obtained data and calculated (theoretical) data were compared. From the analysis of the comparison, a conclusion was drawn about the agreement between experimental data and theoretical data. The tunneling phenomenon has been observed in nanostructured isotopic nickel based thin film Fabry-Perot resonator. It manifested itself by the existence of dips, tunneling resonances, in the total reflection plateau due to quasi-bound states in the isotopic nickel based thin film Fabry-Perot resonator. In total, there were 7 tunneling resonances. The full widths at half maximum of these dips were found to decrease with increasing momentum wave vector transfer (Q) and this correlated to the neutron lifetime in the nanostructured isotopic nickel based thin film Fabry-Perot resonator. / Physics / M. Sc. (Physics)

MnSi(111) films were grown on Si(111) substrates by solid phase epitaxy (SPE) and molecular beam epitaxy (MBE) to determine their magnetic structures. A lattice mismatch of -3.1% causes an in-plane tensile strain in the film, which is partially relaxed by misfit dislocations. A correlation between the thickness dependence of the Curie temperature (TC) and strain is hypothesized to be due to the presence of interstitial defects. The in-plane tensile strain leads to an increase in the unit cell volume that results in an increased TC as large as TC = 45 K compared to TC = 29.5 K for bulk MnSi crystals. The epitaxially induced tensile stress in the MnSi thin films creates an easy-plane uniaxial anisotropy. The magnetoelastic coefficient was obtained from superconducting quantum interference device (SQUID) magnetometry measurements combined with transmission electron microscopy (TEM) and x-ray diffraction (XRD) data. The experimental value agrees with the coefficient determined from density functional calculations, which supports the conclusion that the uniaxial anisotropy originates from the magnetoelastic coupling. Interfacial roughness obscured the magnetic structure of the SPE films, which motivated the search for a better method of film growth. MBE grown films displayed much lower interfacial roughness that enabled a determination of the magnetic structure using SQUID and polarized neutron reflectometry (PNR). Out-of-plane magnetic field measurements on MBE grown MnSi(111) thin films on Si(111) substrates show the formation of a helical conical phase with a wavelength of 2?/Q = 13.9 ± 0.1 nm. The presence of both left-handed and right-handed magnetic chiralities is found to be due to the existence of inversion domains that result from the non-centrosymmetric crystal structure of MnSi. The magnetic frustration created at the domain boundaries explains an observed glassy behaviour in the magnetic response of the films. PNR and SQUID measurements of MnSi thin films performed in an in-plane magnetic field show a complex magnetic behaviour. Experimental results combined with theoretical results obtained from a Dzyaloshinskii model with an added easy-plane uniaxial anisotropy reveals the existence of numerous magnetic modulated states that do not exist in bulk MnSi. It is demonstrated in this thesis that modulated chiral magnetic states can be investigated with epitaxially grown MnSi(111) thin films on insulating Si substrates, which offers opportunities to investigate spin-dependent transport in chiral magnetic heterostructures based on this system.

<p> Over the past decade, the development of surface-initiated living polymerization methods has brought a breakthrough to surface modification owing to their control ability. Surface-initiated atom transfer radical polymerization (si-ATRP), as the most popular one, has been widely employed to give novel polymer structures and functionalities to various surfaces for the purposes of tailoring surface properties, introducing new functions, or preparing so-called "smart surfaces", which can respond to external stimuli such as solvent type, pH, temperature, electric and magnetic fields etc. In this thesis, the mechanistic study of the si-ATRP was first carried out through modeling to gain good understanding of si-ATRP. Si-ATRP was then employed to prepare different types of polymer brushes to produce "smart surfaces". </p> <p> The kinetic model was developed using the method of moment. Combined with experimental data, a quantitative analysis was carried out for the si-ATRP mechanism. All information of grafted polymer chains, including active chain concentration, radical concentration, chain length, polydispersity, was illustrated. A new radical termination mechanism, termed as migration-termination, was proposed for si-ATRP. </p> <p> Si-ATRP was then employed to graft poly(oligo(ethylene glycol) methacrylate) (POEGMA) block poly(methyl methacrylate) (PMMA) brushes on silicon wafer surfaces. Simple solvent treatment gave nanoscale patterns via the phase segregation of POEGMA and PMMA segments. Various patterns including spherical aggregates, wormlike aggregates, stripe patterns, perforated layers and complete overlayers, were obtained by adjusting the upper block layer thickness. Furthermore, these nanopatterns had a unique stimuli-responsive property, i.e., switching between different morphologies reversibly after being treated with selective solvents. </p> <p> POEGMA-block-poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes, having two hydrophilic segments, were synthesized by si-ATRP method. A variety of nanopatterns and their stimuli-responsive ability were observed. The adsorption behaviors of fibrinogen on these patterns were thoroughly studied by ellipsometry, water contact angel measurement, AFM and radio labelling method. </p> <p> A novel thermo-responsive copolymer, poly(2-(2-methoxyethoxy)ethyl methacrylate -co-oligo(ethylene glycol) methacrylate) (P(ME02MA-co-OEGMA)), was also grafted onto silicon wafers. Its thermo-responsive behavior and chain conformation in aqueous solution were studied by neutron reflectometry (NR). Both extended and collapsed brushes exhibited good protein adsorption resistance. </p> / Thesis / Doctor of Philosophy (PhD)