In this Master Thesis work, the effect of pressure on sintering of cemented carbides is investigated. Special focus hasbeen given to the residual porosity after sintering. It is well known that sintering shrinkage depends on binder phasecontent, grain size, temperature and pressure. Thus 4 different cemented carbides grades were selected. The gradeswere pressed into standard products and TRS (Tensile Rupture Strength) rods with two different shrinkage factors.These were then sintered at different pressures and temperatures. Thereafter the impact of pressure on propertiessuch as Density, Coercivity, Porosity and TRS were analyzed. The observations were further supported with Weibullprobability analysis and fracture surface analysis in SEM.It has been shown that there exists a distinct threshold pressure at which significant reduction in porosity occurs forgiven compacted densities. For 3 out of 4 cemented carbide grades it has been observed that P2 sintering pressure issufficient to meet desired product characteristics. The fourth grade required a minimum sintering pressure of P4 toachieve desired quality criteria. Moreover it has been concluded that an increased sintering pressure increasesmaterial strength, as compared to vacuum sintering, thereby reducing the amount of early failures caused by poresduring TRS test.                                    Keywords: Cemented Carbides, Pressurized Sintering, Tungsten carbide, Porosity, Vacuum sintering, TensileRupture Strength, Weibull analysis, Fracture surface analysis.

3D scanning has grown to become an important tool in a wide variety of applications. Still, acquiring high-quality 3D models using scanning technology is a challenging task. In this thesis, we present various ways that reduce the hurdles of existing 3D scanning pipelines with the ultimate goal of bringing this technology closer to the end user. To achieve this goal, we focus on three sub problems of traditional scanning pipelines: First, we present a novel algorithm that can be used to consistently orient the normals of huge point clouds. We achieve this by formulating the orientation problem as a graph-based energy minimization problem and applying out-of core methods. Second, we introduce interactivity into the scanning pipeline by presenting an online surface reconstruction method that produces high-quality semi-regular meshes. The resulting interactive pipeline is highly efficient because it reduces the turn-around between presentation of the final result and possible corrections by the user. Third, we develop a robust method to texture-map semi-regular meshes. This approach is based on a generalization of motorcycle graphs, which partitions arbitrary meshes into quadrilateral patches. These patches then serve as the parametrization domains of the texture atlas. Finally, we present an application from the area of cave science. The application is targeted at quantitatively and objectively assessing a cave's size. To achieve this goal, we present methods to analyze the structure of caves, especially to distinguish chambers from passages.

When approaching a metal surface, the electronic structure of Rydberg atoms or molecules is perturbed by the surface potential and at close enough distances resonant ionisation of the Rydberg electron into the conduction band of the surface can occur. It is possible to interfere in this process and steer the ionisation distance by making use of the polarisability of the Rydberg orbital in the presence of electric fields. The resulting ions from the surface can extracted via electric fields and subsequently detected via well established ion detection schemes. The question of how this charge-transfer process is affected by different properties of the surface (both electronic and structural) represents the main aspect of the work presented in this thesis. At first, the charge transfer of atomic hydrogen Rydberg atoms with a flat gold metal surface is investigated. While such a surface might appear homogeneous, stray fields are present in its vicinity due to local variations in the surface work function. The surface ionisation process as a function of applied electric field is therefore measured experimentally and the results are compared with classical Monte-Carlo simulations (which include stray field effects). This way the possibility to utilize Rydberg states as a probe of the magnitude of such stray fields is demonstrated. To investigate the effect the surface structure can have on the ionisation process, the interaction of Rydberg atoms with surfaces covered by nanoparticles is investigated. Surface ionisation is measured at a 5 nm nanoparticle monolayer surface and it is shown that population transfer between surface- and vacuum-oriented Rydberg states occurs. In addition, results are presented, which suggest a dependence of the ionisation process on the relative size of Rydberg orbital and nanoparticle. Furthermore, charge transfer between a Rydberg state and discrete electronic states at the surface vacuum interface are investigated by performing experiments with a Cu(100) band-gap semiconductor surface. By analysing surface ionisation as a function of collisional velocity ionisation rates can be determined and are subsequently compared with theoretical predictions. The potential of identifying resonant ionisation is thereby demonstrated. Last, a new method to produce 2s atomic hydrogen via mixing of the 2s and 2p state in an electric field is proposed and first experimental results are presented, thus demonstrating viability of the idea. The experiments presented in this thesis represent the most in depth analysis of the charge-transfer process between atomic hydrogen Rydberg states and a range of different surfaces to date. As such, they demonstrate the potential of utilizing the unique properties of Rydberg states and their applicability as surface probes. In addition, these results pave the way for further experiments involving thin films or the phenomenon of quantum reflectivity.

Imaging membrane potential is a promising technique in the elucidation of the interactions of large networks of neurons. The membrane potential in a neuron varies as an action potential, the basic electrical signal of neuronal communication, travels along the length of the cell. Voltage sensitive dyes play a key role by providing an optical readout of the electric field generated across a neuron membrane by the action potential. However, none of the dyes reviewed in Chapter 1 generate sufficient signal change with changes in membrane potential; this sensitivity problem limits the ability of the imaging membrane potential technique to allow the high spatial and temporal resolution necessary for neuronal networks to be better understood. This thesis features two avenues of research that are expected to result in the necessary enhancements to voltage sensitive dyes to improve the signal change. The first avenue is based on the effect of an electric field upon the non-linear optical properties of a porphyrin macromolecule. The encouraging field sensitivity of a previous porphyrin monomer voltage sensor inspired an investigation which identified optimisations to enhance the voltage sensitivity (Chapter 2). The design, synthesis and initial characterisation of optimised porphyrin voltage sensors is detailed in Chapter 3. The second avenue is based on the effect of an electric field upon the rate of intermolecular electron transfer. In a suitably designed dye, the competition between electron transfer and fluorescence, following excitation by incoming light, allows the fluorescence intensity to act as an optical indicator of the electron transfer rate. New dyes were rationally designed and synthesised, as this effect had not been applied to voltage sensitive imaging before the research detailed in Chapter 4. The challenging purification of the new amphiphilic dyes synthesised also inspired research into a novel testing method which does not require amphiphilic dyes (Chapter 5).

Diese Dissertation beschäftigt sich mit der Grenzflächenausbildung von dünnen Tantal- und Titan-basierenden Schichten zu den piezoelektrischen Substratmaterialien Lithiumniobat sowie Lithiumtantalat, als Teil eines Schichtstapels für die Metallisierung akustischer Oberflächenbauelemente. Ziel ist es das grundlegende Verständnis für die chemischen Wechselwirkungen beim Aufwachsen der Schichten, ihrer thermischen und zeitlichen Stabilität sowie ihrer Effekte auf das Schichtwachstum einer Deckschicht bestehend aus Aluminium zu gewinnen. Ein Schwerpunkt war die Präparation der Substratoberflächen hinsichtlich einer Oberflächenreinigung und -modifikation. Zu diesem Zweck wurden neben verschiedenen Standard-Verfahren auch eine eigens angefertigte plasmagestützte Oberflächenbehandlung systematisch analysiert. Auf derart präparierten Substraten fanden im Folgenden die Schichtabscheidung und die Analyse des Schichtwachstums, hauptsächlich mit winkelaufgelöster Photoelektronenspektroskopie, statt. Anhand von thermischen Belastungen sowie zeitlicher Veränderungen der Schichten im Vakuum konnten grundlegende Aussagen zur Stabilität der Grenzflächen gewonnen werden. Zur Komplettierung des Schichtstapels wurden auf ausgewählten Substrat-Schicht Kombinationen das Wachstum von Aluminiumschichten hinsichtlich ihrer unterschiedlicher Texturbildung analysiert und Aussagen zur Relevanz chemischer Ursachen getroffen. / This dissertation addresses the interface formation between thin Tantalum and Titanium based layers onto the piezoelectric substrate materials Lithiumniobate and Lithiumtantalate as part of a metallisation stack for surface acoustic wave devices. The goal is to extend the fundamental knowledge of chemical interactions during layer growth, its thermal and temporal stability plus its effects on the layer growth of an Aluminium cover layer. One focus lies on the preparation of the substrate surfaces for cleaning and modification purpose. For this, besides standard procedures a specially built plasma-based device was systematically evaluated for surface treatment. The following layer deposition was then implemented onto these prepared substrate surfaces and mainly analysed by angle-resolved photoelectron spectroscopy. By the means of thermal load and temporal alteration of the layers in vacuum essential knowledge about the interface stability was gained. For the completion of a whole layer stack selected substrate-layer combinations were covered with Aluminum and its layer growth was analysed with respect to the different formation of texture and its potential chemical cause.

Single-walled carbon nanotubes (SWCNTs) were decorated with metal nanoparticles. Using a complementary analysis with spatially resolved micro-Raman spectroscopy, high resolution transmission electron microscopy, electron diffraction, and tip-enhanced Raman spectroscopy, we show that the SWCNTs form bundles in which smaller diameter SWCNTs are the ones preferentially affected by the presence of Au and Ag nanoparticles. This result is exploited to evaluate the structural organization of SWCNTs with mixed chiralities in bundles, leading us to postulate that smaller diameter SWCNTs surround larger ones. We found that this effect occurs for very distinct scenarios including SWCNTs both in nanometer thin films and in field effect transistor configurations at the wafer-level, suggesting a universal phenomenon for SWCNTs deposited from dispersions. / Einwandige Kohlenstoffnanoröhren (SWCNTs) wurden mit Metallnanopartikeln dekoriert. Nach Anwendung von ortsauflösender Raman-Mikroskopie und -Spektroskopie, Transmissionselektronenmikroskopie, Elektronenbeugung und spitzenverstärkter Ramanspektroskopie wird festgestellt, dass sich aus den SWCNTs fasrige Bündel formen, wobei die analytischen Signaturen der SWCNTs mit kleinerem Durchmesser stärker von der Präsenz der Gold- und Silbernanopartikel beeinflusst werden als die der größeren. Dieses Resultat kann damit erklärt werden, dass in der Struktur solcher Bündel SWCNTs mit kleinerem Durchmesser außen und SWCNTs mit größerem Durchmesser innen zu liegen kommen. Wir konnten diesen Effekt für verschiedene Szenarien nachweisen: i) für SWCNTs in nanometerdünnen ungeordneten Filmen und ii) für SWCNTs, ausgerichtet zwischen Elektroden in der Geometrie eines Feldeffekttransistors. Diese Feststellung legt nahe, dass es sich um ein universelles Phänomen für aus flüssigen Dispersionen abgeschiedene SWCNTs handelt. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful technique for the analysis of organic surfaces and interfaces for many innovative technologies. However, despite recent developments, there are still many issues and challenges hindering the robust, validated use of ToF-SIMS for quantitative measurement. These include: the lack of metrology and fundamental understanding for the use of novel cluster primary ion beams such as C60ⁿ⁺ and Ar₂₀₀₀⁺; the need for validated and robust measurement protocols for difficult samples, such as those with significant micron scale surface topography; the lack of guidance on novel data analysis methods including multivariate analysis which have the potential to simplify many time-consuming and intensive analyses in industry; and the need to establish best practice to improve the accuracy of measurements. This thesis describes research undertaken to address the above challenges. Sample topography and field effects were evaluated experimentally using model conducting and insulating fibres and compared with computer simulations to provide recommendation to diagnose and reduce the effects. Two popular multivariate methods, principal component analysis (PCA) and multivariate curve resolution (MCR), were explored using mixed organic systems consisting of a simple polymer blend and complex hair fibres treated with a multi-component formulation to evaluate different multivariate and data preprocessing methods for the optimal identification, localisation and quantification of the chemical components. Finally, cluster ion beams C60ⁿ⁺ and Ar_500-2500⁺ were evaluated on an inorganic surface and an organic delta layer reference material respectively to elucidate the fundamental metrology of cluster ion sputtering and pave the way for their use in organic depth profiling. These studies provide the essential metrological foundation to address frontier issues in surface and nanoanalysis and extend the measurement capabilities of ToF-SIMS.

Predictive models of structures containing frictional joints presently suffer from poor descriptions of interface behaviour at the joints. This thesis aims to address this shortfall by furthering the physical understanding of parameters affecting interface behaviour such as friction and contact stiffness. Aspects of friction and contact stiffness relevant to the characterisation of fretting joints are investigated by a combined modelling and experimental approach. Friction and wear behaviour in gross-slip fretting are investigated by in-line and rotational fretting tests. New 3D topography parameters are found to be useful in the analysis of surfaces during fretting. Wear-scar shape is found to be dependent on material. A phenomenon whereby friction increases during the gross-slip phase of individual cycles is found to be due to wear-scar interaction primarily through the interference of local features distributed over the contact area. These features are similar in size to the applied fretting stroke. A simple model to explain the behaviour is put forward which shows that wear-scar shape determines the form of the friction variation. A finite-element (FE) model of the interaction of an elastic-plastic asperity junction is used to predict sliding friction coefficients. The modelling differs from previous work by: permitting greater asperity overlaps, enforcing an interface shear strength, and allowing material failure. The results are also used to predict friction coefficients for a stochastic rough surface. The magnitudes of the predicted friction coefficients are generally representative of experimental measurements. Results suggest that friction arises from both plasticity and tangential interface adhesion. Contact stiffness is studied for both fretting and non-fretting. A technique to isolate the true interface stiffness from results derived from load-deflection data is developed by comparing experimental and FE results. In the fretting wear case, comparison of tangential contact stiffness results in the literature with FE results reveals an interface whose compliance dominates the response to the extent that stiffness is proportional to contact area. In fretting tests such as this, wear debris is thought to be a factor contributing to high interface compliance. Non-fretting experiments performed here show that, at higher pressures, interface domination is reduced as the contact approaches the smooth case. Experiments are performed where contact stiffness is measured simultaneously by both ultrasound and digital image correlation. The effect of normal and tangential loading upon the contact stiffness (normal and tangential) is investigated. Experimental evidence showing that ultrasound measures an ‘unloading’ stiffness while DIC measures a ‘loading’ stiffness is obtained for the case of tangential loading where the ‘DIC stiffness’ decreases with increasing tangential load whereas the ‘ultrasound stiffness’ remains approximately constant. On average, ultrasound gives magnitudes 3.5 and 2.5 times stiffer than the DIC results for the normal and tangential stiffness cases, respectively. The difference in magnitudes can largely be physically explained, and is relatively small considering the significant differences between the techniques. Therefore, both methods can claim to give valid measurements of contact stiffness – though each has its own limitations which are outlined herein.

Surface catalysed reactions play an important role in chemical productions. Developments of catalyst requiring high activity whilst improving on product selectivity can potentially have a profound effect in the chemical industry. Traditional catalyst modifications were focused on tuning the size, shape and foreign metal doping to form well defined metal nanoparticles of unique functionalities. Here, we show new approach to engineering of metal nanocatalysts via a subsurface approach can modify the chemisorption strength of adsorbates on the surface. Carbon modified nanoparticles were synthesised using glucose to stabilise Pd nanoparticles at a molecular level. Upon heat treatment, the carbonised glucose encapsulated the Pd nanoparticles with carbon atoms take residence in the octahedral holes (15 at.%). These materials were tested in liquid phase stereoselective hydrogenations of 3-hexyn-1-ol and 4-octyne. The former has importance in the fragrance industry towards the production of leaf fragrance alcohol. It was shown for the first time that the geometrically and electronically modified Pd with interstitial carbon atoms reduced the adsorption energy of alkenes, ultimately leading to higher reaction selectivity. Boron modified Pd nanoparticles was synthesised using BH₃.THF in the liquid phase. The material possess high B interstitial saturation (20 at.%), which can be synthesised for the first time below 100°C. These materials were tested in the liquid phase selective hydrogenation of various alkynes and 2-chloronitrobenzene, of which the latter has importance in the pesticides industry. Kinetic modelling on the hydrogenation of 4-octyne suggests these subsurface occupied B does play a pivotal role on increasing the reaction selectivity, as removal of these species lead to decreased selectivity. Au nanoparticles were synthesised and characterised using H¹³COOH NMR. The new liquid NMR characterisation method is successfully applied to examine the chemisorption strength of metal nanoparticles. An attempt to synthesise PVP capped B modified Pd nanoparticles with the above NMR characterisation was investigated. It is believed the examples of subsurface atom modifications as shown here may offer future catalyst developments in this area.

This thesis is concerned with the chemical modification of polymers in the preparation of a library of materials which exhibit altered surface properties as a result of the surface chemical functionality, with particular emphasis on the development of materials that control biofouling and are antibacterial. Chemical modification of crosslinked polystyrene, in film and microsphere form, was carried out by carbene insertion followed by diazonium coupling. This provided access to a collection of materials with varying surface chemistry, whilst the bulk properties of the polystyrene substrates were maintained. Synthesis of the diaryldiazo and the diazonium salts used to perform the surface modifications is described, as well as the preparation and characterisation of the materials. Analysis of the ability of the materials to adsorb and bind the protein bovine serum albumin (BSA) is presented with data obtained from two methods of observation. Quartz Crystal Microbalance with Dissipation (QCM-D) and a protein assay based on the change in optical density of a BSA/PBS solution are used to demonstrate how the specific surface chemistry of the materials influences the ability to adsorb and bind protein. The behaviour of the materials was time dependent and was rationalised with respect to the surface water contact angle and the calculated parameters polar surface area and % polar surface area of the functional groups added to the surfaces. Finally, penicillin loaded materials were prepared and their antibacterial activity was tested against E. coli and S. aureus, demonstrating that the antibiotic is still active from within the polystyrene scaffold.