Beton wird global als Werkstoff eingesetzt, weist als Natur-verwendendetes Material allerdings unterschiedliche regionale Spezifikationen auf. Hier entsteht ein Spannungsfeld zwischen Universalismus und Partikularismus. Die beim Absäuern offengelegten Sandkörner werden zum ortsbezogenen Naturpigment, die diese Ambivalenz sinnlich erfahrbar machen. Die Werkgruppe präsentiert in ihrer Uniformität ein Bild der Gemeinsam- und Verbundenheit. Gleichzeitig erheben die einzelnen Platten Anspruch auf spezifische, in ihrer Körnung auf partikularer Ebene abgebildete Eigenschaften der Diversität und Einzigartigkeit.

Since mechanical properties of parts in mechanical engineering are influenced in many ways by their surface structure, detailed knowledge of the surface structure is essential for predicting and describing these properties. Tactile and optical measurement methods are well established but cannot always reach every area of a part due to geometric constraints. To enable measurements in these areas, a method utilizing impressions and a laser scanning microscope is proposed. It is easy to use and able to correctly reproduce surface structures of technical surfaces, which is proven by a comparison of original parts and impressions of three surface areas on an example specimen. Two application examples from the domain of fatigue strength tests are shown. The surface structure is measured directly in the notch radius of shaft shoulders and inside hollow shafts made in different manufacturing processes. Utilizing modern optical measurement instruments, the proposed method enables accurate measurements of surface structure in previously inaccessible areas.

In dieser Dissertation wird die Struktur von ultradünnen Schichten auf atomar ebenen Festkörperoberflächen durch die streifende Streuung von Atomen und Molekülen untersucht. Dabei werden Atome mit kinetischen Energien im keV-Bereich unter flachem Einfallswinkel von etwa 1° an der Oberfläche gestreut und mit einem ortsauflösenden Detektor nachgewiesen. Bei hinreichend kleinen Projektilenergien werden Beugungserscheinungen beobachtet, die durch Interferenz von Materiewellen erklärt werden können. Die Auswertung der Intensität der Beugungsreflexe ermöglicht die Bestimmung von Atompositionen. Wird die Probe azimutal verdreht, ändern sich die seitliche Ablenkung der Projektile und die Zahl der während des Streuprozesses an der Oberfläche emittierten Elektronen. Dies wird zur Identifikation von Richtungen mit dichtgepackten Atomketten genutzt und der Vergleich mit Trajektoriensimulationen gestattet Rückschlüsse auf die Atompositionen der obersten Lage. Beim System einer Atomlage SiO2/Mo(112) kann durch mehrere Messmethoden eindeutig zwischen zwei konkurrierenden Strukturmodellen unterschieden und die Atompositionen eines Modells mit hoher Genauigkeit bestätigt werden. Die Adsorption von Sauerstoff auf einer Mo(112)-Oberfläche wird detailliert studiert und für mehrere Überstrukturphasen werden Modelle aufgestellt. Für V2O3/Au(111) kann durch Triangulationsmessungen eine geringfügige Modifikation eines existierenden Strukturmodells abgeleitet werden. Auf einer Cu(001)-Oberfläche werden dünne, kristalline FeO und Fe3O4-Schichten präpariert und untersucht. Die Inkommensurabilität der quadratischen Substrat- und der hexagonalen Adsorbateinheitszelle führt zu komplexen LEED-Mustern, die durch Mehrfachstreuung erklärt werden können. Dies ist auch der Schlüssel zur Erklärung der Beugungsbilder bei Adsorbatstrukturen der chiralen Aminosäure Alanin auf Cu(110) und damit die Grundlage für die Aufstellung eines Strukturmodells für dieses System. / In this thesis the structure of ultrathin films on atomically flat crystal surfaces is investigated by means of grazing scattering of atoms and molecules. Atoms with kinetic energies in the keV regime are scattered from the surface under small angles of incidence of approximately 1° and are detected by means of a position-sensitive detector. For sufficiently small projectile energies diffraction phenomena are observed which can be explained by interference of matter waves. The analysis of the intensities of diffraction spots makes it possible to determine atomic positions. When the sample is rotated azimuthally the deflection of projectiles and the number of emitted electrons during the scattering process at the surface varies. This is used to identify directions with close-packed strings of atoms and comparison with trajectory simulations gives information on atomic positions of the topmost layer. For the system of one atomic layer of SiO2/Mo(112) it can be unambiguously distinguished between two competing structural models. The positions of atoms of one model are confirmed with high accuracy by the use of several methods. The adsorption of oxygen on a Mo(112) surface is studied in detail and for several superstructure phases models are proposed. For the surface of a V2O3 layer on a Au(111) substrate a slight modification of an existing structural model is derived by means of triangulation measurements. On a Cu(001) surface thin crystalline FeO and Fe3O4 films are grown and studied. The incommensurability of the quadratic substrate with the hexagonal adsorbate surface unit cell gives rise to complex pattern for low energy electron diffraction, which can be explained by multiple scattering. This is also the key to the explanation of diffraction images for adsorbate structures of the chiral amino acid alanine on Cu(110) and the basis for developing a structural model for this system.

Die Dissertation beschäftigt sich mit der Bestimmung der Oberflächenstruktur von Oxidkristallen. Die strukturelle Charakterisierung fand mittels der streifenden Streuung schneller Atome und Moleküle statt. Bei dieser Methode werden Atome oder Moleküle mit Energien im keV Bereich unter streifendem Einfall an einer Einkristalloberfläche gestreut. Sie werden unter axialer Gitterführung entlang niedrig-indizierter Kristallrichtungen gestreut und können mittels eines ortsauflösenden Detektors nachgewiesen werden. Bei hinreichend kleinen Energien werden Beugungserscheinungen beobachtet, die auf die Interferenz von Materiewellen zurückzuführen sind. Durch eine Analyse der Streuverteilung der Projektile, können Rückschlüsse auf das Wechselwirkungspotential und somit auf die Struktur der Oberfläche gezogen werden. Durch die Untersuchung der (100)- und (001)-Fläche konnten alle Gitterparameter des Ga2O3-Systems bestimmt werden. Die Messungen an der (100) Fläche lieferten Aufschluss über die Terminierung, für die ein alternatives Strukturmodell entwickelt wurde. Aufbauend auf der Entdeckung der longitudinalen Kohärenz bei der streifenden Streuung von Atomen an der Al2O3(11-20)-Fläche konnten die vorhandenen Messungen erweitert und ein effektives Auswerteprogramm entwickelt werden. Bei Messungen an der Al2O3(0001)-Fläche wurde ebenfalls das Auftreten einer longitudinalen Kohärenz beobachtet. Für beide Flächen wurden die jeweiligen Gitterparameter mit höchster Präzision bestimmt und die Intensitätsverteilung der Streubilder durch ein einfaches Modell beschrieben. Erstmalig in dieser Arbeitsgruppe konnte ein Wechselwirkungspotential für die Streuung von H2-Molekülen an einer KCl(001)-Fläche abgeleitet werden. Der im Experiment beobachtete drastische Unterschied in der Intensitätsmodulation der Beugungsreflexe mit der senkrecht-de Broglie Wellenlänge für gestreute Atome und Moleküle konnte mit Simulationen unter Verwendung des abgeleiteten Wechselwirkungspotentials erklärt werden. / This PhD thesis deals with the investigation of surface structures of oxide crystal surfaces. Therefore, the method of grazing scattering of fast atoms and molecules was applied. The projectiles are scattered with energies in the keV range under grazing incidence from a single crystal surface along low-indexed surface directions. They are recorded with a position sensitive detector. For sufficiently low energies diffraction patterns are observed that can be understood in terms of the interference of matter waves. By analyzing these patterns the interaction potential and in this manner the surface structure can be derived. The investigation of the (100) and (001) surface led to a determination of all lattice parameters of the Ga2O3 system so that it was possible to determine the termination of the (100) surface. An alternative structural model for this termination could be derived. After the discovery of a longithudinal coherence for the grazing scattering process on a Al2O3(11-20) surface, the existing measurements were expanded and an effective evaluation procedure was developed. In measurements on the Al2O3(0001) surface the longithudinal coherence was observed as well. For both surfaces, the lattice parameters could be determined with very high accuracy and the intensity distribution was described by a very simple model. For the first time in this working group the interaction potential for the scattering of H2 molecules from a KCl(001) surface could be deviated. The observed difference in the intensity distribution in dependence of the perpendicular de Broglie wavelength for scattered atoms and molecules could be explained by applying simulations using the deviated interaction potential.

Die vorliegende Arbeit befaßt sich mit der Herstellung und Untersuchung magnetischer MnAs-Schichten auf halbleitenden GaAs-Substraten. Die einkristallinen MnAs-Schichten wurden unter Verwendung der Molekularstrahlepitaxie auf GaAs abgeschieden. Die detaillierte Darstellung des MnAs-Wachstums beschreibt den Einfluß der Herstellungsbedingungen auf die strukturelle Qualität. Eine systematische Analyse der MnAs-Oberflächenstruktur resultiert in einem Phasendiagramm der Rekonstruktionen. Die Keimbildung von MnAs während des Wachstums der ersten Monolagen wird anhand der Ergebnisse einer in-situ-Analyse diskutiert. Dabei kamen komplementär die Reflexionselektronenbeugung und die Reflexionsdifferenzspektroskopie zum Einsatz. Die strukturellen Eigenschaften der MnAs-Schichten wurden mittels Transmissionselektronenmikroskopie analysiert. Eingehende Studien der Grenzfläche zeigen zwei richtungsabhängige Mechanismen des Abbaus der Gitterfehlpassung in dem Heteroepitaxiesystem MnAs/GaAs. Die Diskussion der magnetischen Eigenschaften erfolgte sowohl auf makroskopischer als auch auf mikroskopischer Skala. Die durch Magnetometrie erhaltenen Resultate liefern wichtige Erkenntnisse zum Magnetismus dünner Schichten. Untersuchungen der magnetischen Domänen in MnAs mittels magnetischer Kraftmikroskopie zeigen das komplizierte Wechselspiel zwischen Oberflächentopographie und magnetischer Struktur. Die Abbildung der magnetischen Domänen als Funktion des angelegten magnetischen Feldes gibt Aufschluß über das Magnetisierungsverhalten auf mikroskopischer Skala. / This work investigates the growth and characterization of magnetic MnAs layers on semi-insulating GaAs substrates. The single-crystalline MnAs layers are deposited on GaAs by molecular beam epitaxt. A detailed analysis of the MnAs growth reveals the influence of the growth conditions on the structural quality of the layers. A phase diagram showing four stoichiometry dependent reconstructions is obtained by a systematic analysis of the MnAs surface structure. The nucleation of MnAs during growth of the first monolayers is examined by in-situ reflection electron diffraction and reflectance difference spectroscopy measurements. The structural properties of the MnAs layers are analyzed by transmission electron microscopy. It is found that the lattice mismatch is accommodated at the MnAs/GaAs interface by a coincidence lattice along one direction and by misfit dislocation along the perpendicular direction. The discussion of the magnetic properties covers the macroscopic as well as the microscopic scales. Magnetometry results provide important knowledge about thin film magnetism in MnAs layers. Extensive magnetic force microscopy investigations of the magnetic domains in MnAs illustrate the complicated relationship between surface topography and magnetic structure. Imaging of magnetic domains as a function of the applied magnetic field gives new insights on magnetization behavior on a microscopic scale. The MnAs phase transition at 43° C is investigated by combined X-ray diffraction and magnetization measurements. The MnAs structure changes from the ferromagnetic to the paramagnetic state, accompanied by a crystal structure change from hexagonal to orthorhombic. A detailed analysis of the phase transition provides important information concerning crystal growth and allows optimization of the fabrication conditions.

In this thesis the structure and hydration of small organic and amphipilic compounds adsorbed at the air-liquid interface, have been studied using the nonlinear optical technique Vibrational Sum Frequency Spectroscopy (VSFS). The second order nature of the sum frequency process makes this technique particularly surface sensitive and very suitable for interfacial studies, as molecules at the surface can be distinguished even in the presence of a vast excess of the same molecules in the bulk. Particular emphasis was given to the surface water structure and how it is affected by the presence of small model compounds such as acetic acid and formic acid, and also non-ionic surfactants with sugar based and ethylene oxide based polar headgroups. Understanding the structure of water at these interfaces is of considerable fundamental importance, and here VSFS provided unique information. Upon addition of tiny amounts of these surface active compounds, the ordered surface structure of water was found to be significantly perturbed, as revealed by the changes observed in the characteristic spectroscopic signature of the dangling OH bond of water molecules, which vibrate free in air and are present in the top monolayer. Dramatic differences between the different compounds were also observed in the bonded OH region, providing a valuable insight into the hydration of polar groups at interfaces. Additionally, by employing different polarization combinations of the laser beams involved in the sum frequency process, information about the different water species present at the surface and their average orientation were extracted. In particular an unusual state of water was found with a preferred orientation in a non-donor configuration in close proximity to the hydrophobic region formed by the hydrocarbon tails of the surfactant molecules. The conformation and orientation of the different adsorbates were also characterized, targeting their specific vibrational frequencies. Noteworthy is the orientation of the fluorocarbon chain of ammonium perfluorononanoate (APFN), which in contrast to the hydrocarbon chains of the other surfactant molecules studied, remained constant over a wide range of surface densities. This behaviour was also observed for the anionic headgroup of sodium dodecyl sulphate (SDS). Other interesting findings were the formation of a cyclic dimer bilayer at the surface of concentrated aqueous solutions of acetic acid and the water structuring effect induced by poly(ethylene-oxide) headgroups, in spite of being themselves disordered at the air-liquid interface.

<p>In this thesis the structure and hydration of small organic and amphipilic compounds adsorbed at the air-liquid interface, have been studied using the nonlinear optical technique Vibrational Sum Frequency Spectroscopy (VSFS). The second order nature of the sum frequency process makes this technique particularly surface sensitive and very suitable for interfacial studies, as molecules at the surface can be distinguished even in the presence of a vast excess of the same molecules in the bulk. Particular emphasis was given to the surface water structure and how it is affected by the presence of small model compounds such as acetic acid and formic acid, and also non-ionic surfactants with sugar based and ethylene oxide based polar headgroups. Understanding the structure of water at these interfaces is of considerable fundamental importance, and here VSFS provided unique information. Upon addition of tiny amounts of these surface active compounds, the ordered surface structure of water was found to be significantly perturbed, as revealed by the changes observed in the characteristic spectroscopic signature of the dangling OH bond of water molecules, which vibrate free in air and are present in the top monolayer. Dramatic differences between the different compounds were also observed in the bonded OH region, providing a valuable insight into the hydration of polar groups at interfaces. Additionally, by employing different polarization combinations of the laser beams involved in the sum frequency process, information about the different water species present at the surface and their average orientation were extracted. In particular an unusual state of water was found with a preferred orientation in a non-donor configuration in close proximity to the hydrophobic region formed by the hydrocarbon tails of the surfactant molecules.</p><p>The conformation and orientation of the different adsorbates were also characterized, targeting their specific vibrational frequencies. Noteworthy is the orientation of the fluorocarbon chain of ammonium perfluorononanoate (APFN), which in contrast to the hydrocarbon chains of the other surfactant molecules studied, remained constant over a wide range of surface densities. This behaviour was also observed for the anionic headgroup of sodium dodecyl sulphate (SDS). Other interesting findings were the formation of a cyclic dimer bilayer at the surface of concentrated aqueous solutions of acetic acid and the water structuring effect induced by poly(ethylene-oxide) headgroups, in spite of being themselves disordered at the air-liquid interface.</p>

Les propriétés inattendues des nanoparticules d'or font que le contrôle de leur taille, de leur forme et/ou de leur morphologie devient essentiel pour une application ciblée. Des formes variées de nanoparticules en solution colloïdale ont été synthétisées. L'analyse de ces solutions par spectroscopie UV-Visible montre que les nanoparticules anisotropes ont deux bandes plasmoniques. Aussi, le potentiel zêta mesuré révèle que les solutions sont stables dans les conditions d'étude. La caractérisation par la microscopie électronique en transmission a permis d'observer que leur surface présente différentes orientations cristallographiques. Le dépôt sous potentiel du plomb par voltammétrie cyclique a révélé les sites cristallographiques à la surface de ces nanomatériaux. Ces matériaux présentent des proportions de surface orientée (111), (110) et (100) et de défauts cristallins en accord avec les résultats de microscopie. L'étude électrochimique dans l'électrolyte support montre que la formation des oxydes sur ces nanomatériaux dépend de leur structure. La cinétique de croissance des couches d’oxyde sur les nanobâtonnets d’or dépend fortement du potentiel, du temps de polarisation et de la température. Des différentes formes structurales des nanomatériaux d'or synthétisés et en présence de molécules modèles telles que le glucose et l'acide formique, les nanosphères présentent l'activité la plus forte pour l'oxydation du glucose ; tous les nanomatériaux sont moins actifs pour l'oxydation de l'acide formique. Les analyses par FTIR in situ mettent en évidence la gluconolactone comme intermédiaire de cette réaction et la forte influence de la structure de surface. / Due to the unusual properties of gold nanoparticles, the control of their size, their shape and/or their morphology for a well-targeted application becomes essential. Various shape controlled particles in colloidal solutions were synthesized. The analysis of such solution by UV-visible spectroscopy shows that the anisotropic particles exhibit two surface plasmon resonance bands. In addition, the zeta potential measurements reveal that such solutions are stable in the experimental conditions. It is clearly observed by the transmission electron microscopy characterization of these nanomaterials that their surface has different crystallographic orientations. The under potential deposition (upd) of lead by cyclic voltammetry revealed the surface crystallographic sites which present different ratio of orientated surface (111), (110), (100) and defaults confirming the microscopy results. The cyclic voltammetry in supporting electrolyte shows that the oxides formation on these nanomaterials depends strongly on their structure. On gold nanorods, an extensive study of the kinetic of the oxide layers growth shows that this process is affected by the polarization potential and time as well as temperature. The nanospheres exhibited high activity toward the glucose oxidation, while all the synthesized nanomaterials presented low activity toward the formic acid oxidation. Gluconolactone appears as the main intermediate species during the oxidation of glucose which is a surface structure dependent process.

The adsorption and coadsorption of sulfur and oxygen on the Ir(110) surface was investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). The clean Ir(110) surface forms alternating (331) and (33-1) minifacets, resulting in a mesoscopically rippled surface. Upon chemisorption of sulfur or oxygen and subsequent annealing, the surface structure is changed. In the following, the results concerning sulfur and oxygen adsorption will be summarized before addressing the coadsorption system. Sulfur adsorption: At sulfur coverages of 0.1-0.2 ML, the Ir(110) surface adopts a (1x2) missing-row configuration similar to clean Au(110) and Pt(110). The sulfur-stabilized Ir(110)-(1x2) does not show any evidence for the preference of (111) faceted steps, and consequently does not form a mesoscopic fish-scale pattern. The latter was observed on the (110) surfaces of Au and Pt, and was found to be driven by the preference for (111) step facets. On Ir(110), no such preference seems to exist, since (331) step facets are frequently observed. With respect to the adsorbed sulfur, no extended islands are observed, indicating repulsive adsorbate-adsorbate interactions. At sulfur coverages near 0.5 ML, a p(2x2) structure with p2mg (glide-plane) symmetry is observed. The adsorption site and structural model derived by STM are compatible with an earlier LEED analysis of that structure: S adsorbs in threefold coordinated fcc hollow sites above the (111) facets formed by the non-missing substrate rows. At coverages higher than 0.5 ML, a c(2x4) LEED pattern with additional faint streaks in the [-110] azimuth is observed. STM reveals that the streaks are due to pairs of sulfur atoms (dimers, for brevity) in a second adsorbate layer, that can be desorbed by heating to 1100 K. A structural model is derived on the basis of the STM results, showing the dimer atoms in on-top positions over sulfur atoms of the first adsorbate layer. When the surface is completely covered by the dimers, the surface is saturated at 0.75 ML. Oxygen adsorption: In agreement with earlier reports, oxygen adsorption and subsequent annealing to 700-900 K results in an unreconstructed (1x1) surface, covered by a c(2x2)-O overlayer at 0.5 ML coverage. Coadsorption of oxygen on an S-precovered surface (S-coverage below 0.5 ML) leads to a phase separation of the adsorbates (competitive adsorption). At low coverages, oxygen forms a p(2x2)-O phase, whereas at higher O-coverages a compression into a (1x2)-O phase is observed. Postannealing the (1x2)-O phase at 900 K in vacuum leads to a reduction of the sulfur concentration, indicating sulfur oxidation. Interestingly, the p(2x2)-O phase does not seem to be reactive, according to the AES results. A possible explanation may be that the more densely packed (1x2)-O phase can be regarded as an activated structure. This is also supported by the STM results. At S-coverages above 0.5 ML, the surface is completely poisoned with respect to oxygen adsorption. Nevertheless, heating the sulfur saturated Ir(110)-c(2x4)-S structure in an oxygen atmosphere, the sulfur concentration gradually drops to zero. At intermediate stages of this oxidation process, island formation is observed by STM, but the underlying formation processes remain to be resolved.

This study delves into the syntactic notion of subject relation in Shona with the aim of characterizing and defining it. This is done through analysing data collected from two of the Shona speaking provinces in Zimbabwe, namely, Harare and Masvingo. The data collection procedures involved the tape recording of oral interviews as well as doing selective listening to different speeches. The data were then analysed using the projection principle, noun phrase movement transformational rule as well as the selectional principles established for the subject relation in the other well researched natural languages. The research found out that there is no one single rule that can be used to determine the subject of every possible Shona sentence. One has to make use of all the seven selectional principles established in the well-researched natural languages. The research managed to assess the applicability of the selectional rules in different sentences. The rules were then ranked according to their reliability in determining the subjects of each of the various Shona sentences. It also came to light that the Shona subject relation has a number of sub-categories as a result of the various selectional rules involved in determining them. These were also ranked in a hierarchy of importance as they apply in the language. For instance, whilst some are assigned to their host words at the deep structure or underlying level of syntax, some are assigned at the surface structure level and can be shifted easily. It also emerged that the freedom of the subject relation in the language varies with the sub-category of the relation. It came to light as well that in Shona both noun phrases (NPs) and non-NPs are assigned the subject role. / African Languages / D. Litt. et Phil. (African Languages)