<p>A thorough investigation was performed on the behaviour of Ni, Fe and Cu oxides dissolved in cryolite melts, and the solubility of these species was measured as a function of alumina content, NaF/AlF₃ molar ratio (CR) and temperature. Predominance area diagrams showing the solid phases containing Ni, Fe and Cu, respectively, as a function of the partial oxygen pressure and the alumina activity at 1020 ^oC were constructed. These diagrams were based on present emf and solubility measurements.</p><p>The interpretations of the solubility measurements for the oxides of Ni and Fe gaveconclusive and consistent results. The oxides of Ni and Fe exhibit decreasing solubility with decreasing temperature and with increasing alumina concentration. The Ni(II) concentration decreased from 0.32 wt% in cryolite to 0.003 wt% in alumina-saturated melts, while that of Fe(II) decreased from 4.17 to 0.32 wt% in similar melts. FeO and NiO are stable solid phases at low alumina concentrations, while FeAl₂O₄ and NiAl₂O₄ are stable at high concentrations. The alumina concentrations corresponding to the points of coexistence between FeO and FeAl₂O₄ and between NiO and NiAl₂O₄ were determined to be 5.03 and 3.0 wt% Al₂O₃, respectively, corresponding to the following Gibbs energy of formation from the oxide compounds,∆G⁰_fNiAl2o4 = –28.6 ± 2 kJ/mol and ∆G⁰_{f FeAl2O4} = –17.6 ± 0.5 kJ/mol.</p><p>The solubilities of FeAl₂O₄ and NiAl₂O₄as a function of the CR were investigated in alumina-saturated melts at 1020 ^oC. For both compounds a maximum solubility was found at CR ~5, being 0.008 wt% Ni(II) and 0.62 wt% Fe(II). The results are discussed with respect to the species present in solution. Both Fe(II) and Ni(II) dissolve as fluorides with different numbers of associated “NaF’s”. Ni(II) seems to form Na₃NiF₅ in melts with molar ratios 2 to 12, while Fe(II) is present as NaFeF₃ in acidic (CR 3–10) melts and as Na₃FeF₅and probably some Na₄FeF₆ in basic melts (CR > 3).</p><p>The solubility of both Cu oxidation states Cu(I) and Cu(II) decreases with decreasing temperature. The solubilities of Cu(I) initially decreased with increasing alumina concentration, showing a minimum at a certain alumina concentration followed by an increase. The solubilities were 0.36 wt% Cu(I) and 0.92 wt% Cu(II) in cryolite, and 0.30wt% Cu(I) and 0.45 wt% Cu(II) in alumina-saturated cryolite at 1020 ^oC.</p><p>At 1020 ^oC the solubilities of Cu₂O and CuO were little influenced when changing the CR from 3 to 8 in alumina-saturated melts (~0.30 wt% Cu(I) and ~0.45 wt% Cu(II)), but there was an upward trend for CR < 3. Solubility measurements for CuO in alumina-saturated melts at CR 3.0 to 1.2 clearly showed that the saturation concentration is dependent on both temperature and melt composition.</p><p>Copper ions in solution show a complex behaviour, since they form fluorides and oxycomplexes simultaneously. The extent of co-existence of Cu(I) and Cu(II) in the same melt is also considerable, and it is depending on the alumina activity in the melt. According to thermodynamics the stable copper oxide phases at high alumina activities are the aluminates CuAlO₂ and CuAl₂O₄. However, no clear changes in the solubilities were found for the points of coexistence between Cu₂O and CuAlO₂ and CuO and CuAl₂O₄, respectively, as was the case for Ni(II) and Fe(II). Although there are uncertainties regarding the thermodynamic data available for the formation of copper aluminates, models for the dissolution mechanisms and for the species present in the melt are suggested. Cu(I) seems to form mainly CuF at low alumina contents, while Na₅CuO₃ dominates at higher alumina concentrations. Likewise, Cu(II) seems to form CuF₂, but the concentration of CuF₂ decreases with increasing alumina content. The species that gave the best fit for the cupric oxy-complexes was Na₁₆CuO₉, and the amount increased with increasing alumina content.</p><p>Cermet anodes were prepared with a NiFe₂O₄-based oxide phase mixed with a ~20 wt% copper-rich metal phase. The electrical conductivity for these materials was measured as a function of temperature, showing semiconductor behaviour in the temperature range from room temperature to 1050 ^oC. The highest electrical conductivity measured was ~30 S/cm at 1000 ^oC, which is on the low side for use as an anode material for aluminium production.</p><p>Three cermet anodes were tested by electrolysis for 48 hours. After the experiments the anodes were examined with SEM. There was no metal phase present in the outer 100 µm of the anode, not even pores were observed that could indicate where the metal grains had been. A copper-rich phase was found in one case ~2 mm from the outer surface, and it is believed that copper diffuses out of the anode.</p><p>The cermet anodes dissolved slowly in the electrolyte during electrolysis. The steady state concentrations of Fe and Cu in the electrolyte were below the saturation concentrations, while the concentration of Ni was 3 - 4 times above saturation. The dissolution of the anode does not fit a first order mass-transport model, but it can probably be explained by a controlled dissolution mechanism with some additional disintegration/spalling of the anode material. Further work is needed to draw a firm conclusion. In general, correct solubility data for the anode constituents are needed to make a proper evaluation of various anode materials. Perhaps the first order mass-transport model agrees for some materials, but based on the present results it seems untenable for cermet materials made of NiFe₂O₄ with a copper-rich metal phase.</p><p>The solubilities of the oxides of Ni(II) and Fe(III) are very low for the alumina-saturated melt used during electrolysis, which make them promising candidates for inert anodes. However, if nickel aluminate, which is an insulator, is formed and deposited on the anode surface, it is a cause of concern. Fe(II) aluminate is not expected to form on the anode surface, since Fe(III) is the stable oxidation state in the presence of oxygen gas. However, solid Fe(II) aluminate may be formed in the bulk of the electrolyte where the partial oxygen pressure is lower.</p>

<p>The work presented in this thesis is concerned with the microstructure of zinc oxide varistor materials used in surge protecting devices. This class of material has been characterised with special emphasis on the functional microstructure and the development of the microstructure during sintering. Several different techniques have been used for the analysis, especially scanning electron microscopy (SEM) in combination with electron beam-induced current (EBIC) analysis and <i>in-situ</i> studies of heat-treatment experiments and transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectrometry (EDS) and electron holography. </p><p>Detailed TEM analyses using primarily centred dark-field imaging of grain boundaries, especially triple and multiple grain junctions, were used to reveal the morphological differences between the various Bi₂O₃ phases. The triple and multiple grain junctions were found to exhibit distinct differences in morphology, which could be attributed the difference in structure of the crystalline Bi₂O₃ polymorphs present in the junctions. </p><p>Electrical measurements were performed on individual ZnO/ZnO grain boundaries using EBIC in the SEM. The EBIC signal was found to depend strongly on the geometric properties of the interface and also on the symmetry of the depletion region at the interface. A symmetric double Schottky barrier was never observed in the experiments, but instead barriers with clear asymmetry in the depletion region. Experimental results together with computer simulations show that reasonably small differences in the deep donor concentrations between grains could be responsible for this effect.</p><p>Electron holography in the TEM was used to image the electrostatic potential variation across individual ZnO/ZnO interfaces. The sign of the interface charge, the barrier height (about 0.8 eV) and the depletion region width (100 to 150 nm) were determined from holography data. Asymmetries of the depletion region were also found with this technique. </p><p>The full sintering process of doped ZnO powder granules was studied <i>in-situ</i> in the environmental SEM. The densification and grain growth processes were studied through the sintering cycle. The formation of a functional microstructure in ZnO varistor materials was found to depend strongly on the total pressure.</p>

<p>Electrical transport properties of nanoparticle gold films made by the gas evaporation method were analysed using resistivity measurements. Low temperature electrical transport measurements showed a cross-over from a temperature range dominated by inelastic scattering to a temperature range dominated by elastic scattering, presumably by grain boundaries. This cross-over shifted towards lower temperatures with increasing grain size. </p><p>High temperature in-situ electrical transport measurements were carried out in isothermal annealing experiments. Four types of samples, prepared at different deposition rates, were analysed. Samples prepared at low deposition rate displayed a higher thermal stability than samples prepared at high deposition rate. A relaxation model was fitted to the in-situ electrical transport data. The model included an activation energy, which was found to increase with increasing annealing temperature for all samples, thus pointing at the presence of pinning mechanisms in the samples.</p><p>Optical properties of nanoparticle gold films were investigated in the 0.3 < λ < 12.5 µm wavelength range. A model taking grain boundary scattering into account was successfully fitted to the experimental data and it was shown that the infrared reflectance decreased with decreasing grain size as a consequence of increased grain boundary scattering.</p><p>Nanoparticle tin-doped indium oxide films were made by spin-coating a dispersion containing the nanoparticles onto a substrate. The tin-doped indium oxide particles were prepared by a wet-chemical method. Optical properties were investigated in the 0.3 < λ < 30 µm wavelength range by reflectance and transmittance measurements. Effective medium theory was employed in the analyses of the optical data and information regarding film porosity and charge carrier concentration and mobility within the individual nanoparticles was obtained. It was found that ionized impurity scattering of the conduction electrons dominates within the particles. The temperature-dependent film resistivity was found to be governed by insulating barriers between clusters containing a large number of nanoparticles, thereby giving a negative temperature coefficient of resistivity.</p>

<p>This work focuses on the surface and interfacial characterisation of silane films of a non-organofunctional silane, 1,2-bis(triethoxysilyl)ethane (BTSE), and an organofunctional silane, γ-mercaptopropyltrimethoxysilane (γ-MPS), deposited on Al, Zn and Al-43.4Zn-1.6Si (AlZn) alloy coated steel. Furthermore, a tribological study of a vegetable oil coupled to an aluminium surface pre-treated with γ-MPS is presented and, finally, the tribological response of thin organic coatings exposed to a sliding contact as evaluated by surface analysis is discussed. The main analyses techniques used were time-of-flight secondary ion mass spectrometry (ToF-SIMS), Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). </p><p>The results presented in this thesis show that the combination of ToF-SIMS, AES and XPS analysis can be used in order to obtain useful and complementary information regarding the surface and interface characteristics of silane films and organic coatings deposited on metal substrates.</p><p>The major result regarding the silane films is that the silane film composition/structure is not dependent of pH-value during deposition or type of metal substrate. The presence of Si-O-Me ion fragments in the ToF-SIMS spectra is a strong indication that a chemical interaction between the silane film and the metal substrate exists. Furthermore, it has been shown that it is possible to bond a vegetable oil to a thiol functionalised aluminium surface and to produce a coating thick enough to obtain desired friction and wear characteristics. Finally, the use of ToF-SIMS analysis makes it possible to distinguish between mechanical and tribochemical wear mechanisms.</p>

<p>WC/Co cemented carbide is a composite material for highly demanding wear applications. The unique combination of hardness (from the WC-phase) and toughness (from the binder Co) gives a material especially suitable for rock drilling. This thesis, investigates the deterioration and wear of these cemented carbide buttons and the correlation to different rock types.</p><p>To better understand the nature of the wear of the cemented carbide buttons, the counter surface –the rock- has also been studied. A range of important rock types has been investigated with respect to hardness distribution and scratch response in a micro scale and friction properties when slid against cemented carbides. </p><p>The cemented carbide may deteriorate due to a number of mechanisms. The effect of fatigue in the structure was studied in TEM and particle erosion response was used to probe the corresponding mechanical degradation. </p><p>Further, homing cross sectioning has been developed and used as a new technique to investigate the presence of weak zones in the surface layer of a drill button. It was found that rock penetration into this layer is a very common mechanism, with profound implications for the nature of the wear. </p><p>High resolution scanning electron microscopy has been extensively used to map the deterioration and wear of numerous drill buttons, worn against different rock types in different kinds of drilling applications. Finally, the collected data on the surface damage, the reptile skin formation, the rock intrusion and the properties of the rock are assembled into a new view of the deterioration and wear of cemented carbide in rock drilling. </p>

<p>For a long time spectrophotometry has been a powerful method of determining optical material properties. Since the technique measures the parameters of interest, reflectance and transmittance, it is in general easy to use and interpret. Certain materials, such as miniature structures or scattering materials, must be given a more careful analysis to avoid incorrect interpretation. General solutions to measurement challenges for thick scattering samples and anisotropically scattering samples are presented.</p><p>Thorough knowledge about the components of a spectrophotometer gives a solid base which is necessary when trying to design or modify an instrument for the characterisation of miniature components. Focusing optics and pinhole apertures are two methods investigated for studying samples on a millimeter scale. Focusing optics retain a high intensity but might cause internal reflection. Pinhole apertures are easy to build into a sample holder, but they will reduce light intensity which can give problems with signal to noise ratio. Using a microscope as a focusing lens system permits the measurement of samples of a size down to the order of ten micrometers. However, absolute measurements are difficult due to the strong focusing properties of the microscope.</p><p>Translucent sheets are of interest for daylighting applications, a growing field in today's energy-conscious society. If sunlight is to be used for indoor illumination it is preferable to make it diffuse. By using Transparent Refractive Index Matched Micro (TRIMM) particles in a transparent polymer sheet, it is possible to obtain high transmittance in combination with tailorability of the scattering profile. Such sheets have been characterised experimentally, as well as by Monte Carlo raytracing simulations. The good agreement between simulation and experiment shows that this type of simulation can be used in the materials design process. A more theoretical study of patterns in multiple Mie scattering has been carried out using the Monte Carlo program developed for characterisation of the TRIMM particle sheets.</p>

<p>Recent developments in thin film synthesis of diamond have facilitated a host of new technical applications. These are motivated by the many attractive properties of diamond, for example high hardness, chemical inertness, transparency and heat conductivity. Unfortunately, these properties also make it difficult to fashion complex geometries. Other problems are the severely limited choice of suitable substrate materials and large surface roughness. To reduce these complications, a technology denoted <i>replication and bodybuilding</i> has been developed. The basic principle is to grow the diamond film onto a mold and then build a mechanical support on top of the diamond film. Then the mold is removed. Thereby, a diamond surface with the desired 3D geometry and the same surface roughness as the mold is created.</p><p>Three potential applications for devices built using the replication and bodybuilding concept have been explored. <i>Grinding tools for hard materials</i> have proved superior to conventional technology in rate of removal as well as in resulting surface finish. Diamond surfaces have also been crafted into <i>ultra-durable dies for injection molding</i> of hard particle reinforced polymers. Initial testing of an <i>abrasive diamond device</i>, intended to make CMP processes more economical and easier to control has successfully been carried out.</p><p>Diamond and diamond-like carbon is well-known for being “low-friction materials”, but are here demonstrated to actually be “high-friction materials” with the ability to disguise themselves in certain environments, most notably with the aid of water molecules. The mechanisms involved in these variations have been investigated. Using NEXAFS it is shown that high friction sliding is accompanied by changes in the material structure. These changes are induced by surface roughness as well as by strong adhesive forces.</p><p>Highly hydrogenated carbon coatings, on the other hand, affording super-low friction coefficients (<0.01) under certain circumstances, will suffer an increase in friction in the presence of water.</p>

<p>Electro-acoustic devices such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices have been in commercial use for over 60 years and can be found in applications ranging from specialised scientific and military equipment to consumer products, such as mobile telephones, TV and radio receivers, etc. Today by far the largest market for electro-acoustic devices is the telecommunication industry which annually consumes approximately three billion acoustic wave filters for frequency control alone.</p><p>The development of new materials and technologies for electro-acoustic devices has gained a substantial and growing interest from both academic and industrial research communities in recent years due to the enormous growth in the telecommunication industry and other forms of wireless data communication. One of the bigger issues has been to replace the single crystalline substrates with thin film piezoelectric materials deposited by reactive sputtering. This would not only reduce the manufacturing costs but will also enable high frequency of operation and a wider choice of substrate materials. However, in order to obtain the material properties required for the intended application a detailed theoretical description of the reactive sputtering process is necessary since the texture and other functional properties of the piezoelectric material are extremely sensitive to the process parameters in addition to the structure of the underlying material.</p><p>This thesis studies the reactive sputtering process and its application for the fabrication of thin film electro-acoustic devices. The aim has been to gain a further insight into the process and make use of this knowledge to improve the fabrication of electro-acoustic devices. In this work modelling of the reactive sputtering process has been improved by studying certain fundamental aspects of the process and in particular the dynamics of the processes taking place during sputtering both at the target and the substrate surfaces. Consequently, highly textured thin piezoelectric aluminium nitride films have been synthesized and thin film bulk acoustic resonators (FBAR) operating in the GHz range have been fabricated and studied.</p>

<p>The aim of this thesis was to develop wear resistant physical vapour deposited coatings of TiB₂ as well as multilayers of Cr/CrN. The correlation between deposition parameters and fundamental coating properties such as microstructure, composition, residual stress and hardness has been investigated. Finally, the influence of these properties on the coating behaviour in tribological applications has been evaluated.</p><p>It is shown that the use of electron bombardment of the growing coating during d.c. magnetron sputtering is beneficial for the growth of superhard TiB₂ coatings. Furthermore, electron bombardment results in TiB₂ coatings with significantly lower residual stresses than coatings deposited using ion bombardment. The low stresses in these coatings open up the possibility to deposit thicker PVD coatings, as confirmed in this thesis.</p><p>In addition, the use of TiB₂ coatings in tribological contacts against aluminium proved to be superior to many other commercial coatings used today, with respect to wear resistance, anti galling properties and a low friction.</p><p>Finally, a model is proposed which explains the observation that the abrasive wear resistance of multilayered Cr/CrN coatings can outperform that of the individual constituents. The model was found to satisfactory predict experimental data.</p>

<p>Direct semiconductor wafer bonding has emerged as a technology to meet the demand foradditional flexibility in materials integration. The applications are found in microelectronics, optoelectronics and micromechanics. For instance, wafer bonding is used to produce silicon-on-insulator (SOI) wafers. Wafer bonding is also interesting to use for combining dissimilar semiconductors, such as Si and InP, with different dictated optical, electronic and mechanicalproperties. This enables a completely new freedom in the design of components and systems, e.g. for high performance optoelectronic integrated circuits (OEIC). Although wafer bonding has proved to be a useful and versatile tool, the high temperature annealing that is needed to achieve reliable properties sometimes hampers its applicability. Therefore, low temperature wafer bonding procedures may further qualify this technology.</p><p>In the present thesis, low temperature wafer bonding procedures using oxygen plasma surface activation have been studied. A specially designed fixture was adopted enabling <i>in situ </i>oxygen plasma wafer bonding. Oxygen plasma surface activation was seen to indeed yield high Si-Si bonding-strength at low temperatures. Here, the optimisation of the plasma parameters was shown to be the key to improved results. Furthermore, dependence of wafer bonded Si p-n junctions on the annealing temperature was investigated. InP-to-Si wafer bonding is also presented within this thesis. High temperature annealing was seen to induce severe material degradation. However, using oxygen plasma assisted wafer bonding reliable InP-to-Si integration was achieved already at low temperature, thereby circumventing the problems associated with the lattice and thermal mismatch that exist between these materials. As a result, low temperature InP-based epitaxial-layer transferring to Si could be presented. Finally, high-quality SiO2 insulator on InP and Si was realised at low temperatures.</p><p>It is concluded that low temperature oxygen plasma assisted wafer bonding is an interesting approach to integrate dissimilar materials, for a wide range of applications.</p>