<p>A new NO_x sensor for high-temperature applications has been developed and thouroghly characterised. The sensor layers are a mixed oxide of CoO, MgO and MgO₂ deposited by thermal evaporation with a porous platinum gate on top, deposited by thermal evaporation or sputtering. The sensitivity and selectivity of the sensor is promising and is shown to depend upon the ratio between Co and Mg in the film and a number of competing mechanisms are shown to take place on the sensor surface. Response and recovery of the device is still slow and there are some drift, which are suggested to be due to a restructuring sensor surface during operation that was found by SEM-studies. Finally,the oxide surface has been characterized by XPS and a novel process for deposition of the sensor layers by lift-off technique has been developed.</p>

<p>The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries.</p><p>The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).</p>

<p>In powder metallurgy research field, Direct Metal Laser Sintering (DMLS) and Metal Powder Starch Consolidation (MPSC) are relatively new rapid forming techniques to fabricate complex and near net-shaped components. The working principles of DMLS are to melt and fuse metal powder layer by layer in computer controlled systems to pile up components like three dimensional printing. It has been for instance extensively used for mould inserts, die parts, and functional metal prototypes. Another, less explored method, starch consolidation is a pressureless direct casting method which consists principally of mixing powder slurry, casting into moulds, consolidation, drying, and sintering. With a strong focus on both methods, the study here combines several strong material technology sectors; powder, rapid forming, mechanical property testing and surface technology. It covers the processing chain from green body preparation, optimization of</p><p>sintering, nitriding, post sinter heat treatment, to modeling and assessment of material behaviour for end-user applications. An iron based powder and a high vanadium high speed steel powder with low and high carbon contents were used in the DMLS and MPSC processes, respectively. The overall aim of the study is to synthesize near net-shaped powder-based components, to characterize pores and microstructure, and to establish a fundamental understanding of failure mechanisms of powder based materials in bending fatigue, thermal fatigue and wear.</p><p>The study showed the DMLS and MPSC technologies could produce shaped components with a multi-phased structure, controllable nitriding depth and high relative densities in a range of 97 - 99.7 %. Materials' heterogeneity and porosity have detrimental influence on mechanical properties, especially on crack initiation and subsequent propagation.</p>

<p>The function of titanium- and nickel-silicides is to lower the series resistance and contact resistivity in gate, source and drain contacts of an integrated circuit transistor. </p><p>With decreasing dimensions, the low resistivity C54 TiSi₂ is not formed and stays in its high resistivity phase C49. It was found that a layer of niobium interposed between titanium and silicon, which is supposed to promote the C54 phase, led to the formation of the high resistivity C40 (Ti,Nb)Si₂ in both small and large contacts. </p><p>Increased interest in Si_1-xGe_x layers led to the inclusion of the Ni-Si-Ge system in this project. The interaction between nickel and poly-Si_0.42Ge_0.58 was found to be different from nickel and poly-silicon in the meaning of the phases formed during high temperature annealing. High-resistivity NiSi₂ was formed at 750°C, but nickel and Si_0.42Ge_0.58 formed no disilicide. A massive out-diffusion of germanium from the NiSi_1-uGe_u resulted in agglomeration at lower temperatures than for NiSi. This was ascribed to the larger enthalpy of formation for nickel reacting with silicon than with germanium. Ternary phase diagrams, with and without the disilicide phase, were calculated. According to the tie lines, NiSi_1-uGe_u will be in thermodynamic equilibrium with Si_1-xGe_x when u is smaller than x. This was confirmed experimentally, where a balanced germanium concentration in NiSi_1-uGe_u and Si_1-xGe_x, stabilized the germanosilicide. When nickel interacted with strained and relaxed silicon-germanium it was established that a strained substrate led to a morphologically unstable NiSi_1-uGe_u. The germanosilicide was highly textured on both (001) and (111) substrates. The texturing was explained by the absence of Ni(SiGe)₂ which forced NiSiGe to reorient so as not to resemble a digermanosilicide at the film/substrate interface. NiSi_0.82Ge_0.18 formed on p⁺-Si_0.82Ge_0.18 in CBKs grew laterally under the SiO₂, defining the contact hole. The contact resistivity extracted by 3D modelling was 5×10^-8 Ωcm².</p>

<p>This thesis comprises tribological studies of extremely well-defined surfaces of different designs. Both low-friction and high-friction surfaces were manufactured and experimentally evaluated.</p><p>In the low-friction studies, lithography and anisotropic etching of silicon was first used as a texturing technique. The textured surfaces were subsequently PVD coated with TiN or DLC to achieve tribologically relevant interfaces. The results showed that under starved lubricated conditions, fine surface textures lowered the coefficient of friction and the wear rate. It was shown that also the orientation of the texture is of major importance for the lubricating function.</p><p>Further, a novel embossing technique was developed, permitting texturing of steel and other materials. A micro mechanically designed diamond tool was used to emboss steel surfaces. The roller/piston contact from a hydraulic motor was simulated and introduction of an embossed texture on the piston decreased the level and the fluctuation of the friction. The effect of the texture was here similar to the effect of an additional polish step. However, in general it is not an easy task to substantially improve a boundary lubricated contact by introducing a texture. </p><p>Studies of high friction surfaces were performed on micro mechanically designed diamond surfaces equipped with sharp pyramids or ridges. Just as theory predicts, the coefficient of friction was dependent on the shape of the ploughing bodies, but not on the counter material or the load. The tested surfaces resulted in static coefficients of friction between 1.1 and 1.6, depending on surface design and orientation. These are extremely high values, and therefore very interesting for practical applications requiring a high static friction.</p><p>Conclusively, the present thesis shows that it is possible to design and produce surfaces both for improved lubrication in sliding contact and for substantially improved high friction performance in static contacts.</p>

Theoretical studies of point defect interactions and structural stability of compounds have been performed using density functional theory. The defect-related properties, such as activation energy of diffusion, electronic and magnetic structure of selected materials have been studied. The major part of the present work is devoted to a very important material for semiconductor industry, GaAs. The formation energies of intrinsic point defects and the solution energies of 3d transitions in GaAs have been calculated from first principles. Based on the calculated energies, we analysed the site preference of defects in the crystal. The tendency of defects to form clusters has been investigated for the intrinsic defects as well as for impurities in GaAs. The magnetic moment of 3d impurities has been calculated as a function of the chemical environment. The possibility of increasing the Curie temperature in (Ga,Mn)As by co-doping it with Cr impurities has been examined on the basis of calculated total energy difference between the disordered local moment and the ferromagnetically ordered spin configurations. We found that, in order to reach the highest critical temperature, GaAs should be separately doped with either Cr or Mn impurities. Also, we have shown that diffusion barrier of interstitial Mn depends on the charge state of this impurity in (Ga, Mn)As. The formation of defect complexes between interstitial and substitutional Mn atoms, and their influence on the value of diffusion barrier for interstitial Mn, has been studied. The pair interactions energies between interstitial oxygen atoms in hcp Zr, Hf and Ti have been calculated using first principles. Based on the calculated energies, the oxygen ordering structures in IVB transition metal solid solutions have been explained. A prediction of nitrogen ordering in Hf-N solid solution has been made. The thermodynamic description of intermetallic compounds in the Zr-Sn binary system has been obtained. The conclusion has been made that Zr substitution on the Sn sites takes place in the Zr4Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound. The influence of pressure on the phase stability in the Fe-Si system has been investigated. We have found instability of the hcp Fe0.9Si0.1 random alloy with respect to the decomposition onto the Si-poor hcp Fe alloy and the B2 FeSi under high pressure. The tendency of this decomposition becomes stronger with increasing the applied pressure. / QC 20100624

The function of titanium- and nickel-silicides is to lower the series resistance and contact resistivity in gate, source and drain contacts of an integrated circuit transistor. With decreasing dimensions, the low resistivity C54 TiSi2 is not formed and stays in its high resistivity phase C49. It was found that a layer of niobium interposed between titanium and silicon, which is supposed to promote the C54 phase, led to the formation of the high resistivity C40 (Ti,Nb)Si2 in both small and large contacts. Increased interest in Si1-xGex layers led to the inclusion of the Ni-Si-Ge system in this project. The interaction between nickel and poly-Si0.42Ge0.58 was found to be different from nickel and poly-silicon in the meaning of the phases formed during high temperature annealing. High-resistivity NiSi2 was formed at 750°C, but nickel and Si0.42Ge0.58 formed no disilicide. A massive out-diffusion of germanium from the NiSi1-uGeu resulted in agglomeration at lower temperatures than for NiSi. This was ascribed to the larger enthalpy of formation for nickel reacting with silicon than with germanium. Ternary phase diagrams, with and without the disilicide phase, were calculated. According to the tie lines, NiSi1-uGeu will be in thermodynamic equilibrium with Si1-xGex when u is smaller than x. This was confirmed experimentally, where a balanced germanium concentration in NiSi1-uGeu and Si1-xGex, stabilized the germanosilicide. When nickel interacted with strained and relaxed silicon-germanium it was established that a strained substrate led to a morphologically unstable NiSi1-uGeu. The germanosilicide was highly textured on both (001) and (111) substrates. The texturing was explained by the absence of Ni(SiGe)2 which forced NiSiGe to reorient so as not to resemble a digermanosilicide at the film/substrate interface. NiSi0.82Ge0.18 formed on p+-Si0.82Ge0.18 in CBKs grew laterally under the SiO2, defining the contact hole. The contact resistivity extracted by 3D modelling was 5×10-8 Ωcm2.

This thesis comprises tribological studies of extremely well-defined surfaces of different designs. Both low-friction and high-friction surfaces were manufactured and experimentally evaluated. In the low-friction studies, lithography and anisotropic etching of silicon was first used as a texturing technique. The textured surfaces were subsequently PVD coated with TiN or DLC to achieve tribologically relevant interfaces. The results showed that under starved lubricated conditions, fine surface textures lowered the coefficient of friction and the wear rate. It was shown that also the orientation of the texture is of major importance for the lubricating function. Further, a novel embossing technique was developed, permitting texturing of steel and other materials. A micro mechanically designed diamond tool was used to emboss steel surfaces. The roller/piston contact from a hydraulic motor was simulated and introduction of an embossed texture on the piston decreased the level and the fluctuation of the friction. The effect of the texture was here similar to the effect of an additional polish step. However, in general it is not an easy task to substantially improve a boundary lubricated contact by introducing a texture. Studies of high friction surfaces were performed on micro mechanically designed diamond surfaces equipped with sharp pyramids or ridges. Just as theory predicts, the coefficient of friction was dependent on the shape of the ploughing bodies, but not on the counter material or the load. The tested surfaces resulted in static coefficients of friction between 1.1 and 1.6, depending on surface design and orientation. These are extremely high values, and therefore very interesting for practical applications requiring a high static friction. Conclusively, the present thesis shows that it is possible to design and produce surfaces both for improved lubrication in sliding contact and for substantially improved high friction performance in static contacts.

Synthesis, nuclear structure, and magnetic properties of the perovskites: Nd0.7-xMgxSr0.3MnO3 (x=0.0, 0.1), Nd0.6Mg0.1Sr0.3Mn1-zMgzO3 (z=0.1, 0.2), LaCr1-yMnyO3 (y=0.0, 0.1, 0.2, 0.3) and La1-xNdxFe0.5Cr0.5O3 (x=0.1, 0.15, 0.2) have been studied. The structure of the samples was investigated by X-ray and Neutron powder diffraction and the magnetic properties were investigated by magnetization measurements using SQUID-magnetometry. All compounds have orthorhombic structure with spacegroup Pnma (No. 62). The compounds which had the composition Nd0.7Sr0.3Mn1-yMgyO3 by preparation, were found to attain the composition Nd0.7-xMgxSr0.3MnO3 and Nd0.6Mg0.1Sr0.3Mn1-zMgzO3. The x=0.0 and 0.1 compounds order in a pure ferromagnetic structure at about 200 K, but the Mn moments become slightly tilted and attain an antiferromagnetic component below 20 K. A ferromagnetic Nd moment also appears at low temperatures. The compounds with Mg substitution y=0.2 and 0.3 do not exhibit long range magnetic order, but local ferromagnetic correlations among the Mn moments appear below 200 K. At low temperature, also a local antiferromagnetic ordering of the Nd magnetic moments occurs. In these compounds, the Mn3+/Mn4+ ratio is reduced so that the double exchange interaction is suppressed and the antiferromagnetic superexchange interaction favoured. The samples of composition LaCr1-yMnyO3 have orthorhombic structure at room temperature and below. The magnetic properties of the system are markedly affected by Mn-substitution. The parent compound LaCrO3 is a pure G-type antiferromagnet with Néel temperature 290 K. With incresing Mn-substitution, a ferromagnetic component developes in the ordered phase bcause of canting of the magnetic moments. The degree of canting increases with increasing Mn-substitution and the magnitude of the antiferromagnetic component of the moment decreases. The system La1-xNdxFe0.5Cr0.5O3 has the same antiferromagnetic G-type structure as LaCrO3, but orders already at temperatures above 400 K and develops only a very weak ferromagnetic component of the magnetic moment at low temperatures.

Magnetic properties of diluted magnetic semiconductors and magnetic metallic multilayers are investigated by SQUID magnetometry. By doping GaAs with magnetic Mn2+ ions under well defined growth conditions, one obtains a diluted magnetic semiconductor, (Ga,Mn)As, in which the randomly-distributed magnetic ions act as acceptor centers. At high enough dopant and hole concentration a carrier-induced ferromagnetic state results between the magnetic ions. Due to peculiarities of the growth process sizable amounts of donor defects, such as Mn interstitials and As antisites, are also introduced into the GaAs host. The magnetic properties of (Ga,Mn)As are altered by the presence of such defects through the compensation effect of the holes. The Mn interstitials are thermally unstable above a certain threshold temperature and therefore their concentration can be controlled by post-growth annealing. The influence of the interfaces on the magnetic moment of FeNi/V and FeNi/Co superlattices has been studied. A decrease of the `FeNi' magnetic moment at the interfaces is observed for FeNi/V superlattices while in case of FeNi/Co an enhanced magnetic moment is obtained at the interfaces. Changes of the interlayer exchange coupling have been studied in a series of Fe/V(Fe) multilayers in which the V spacer was alloyed with small amounts of Fe. The dynamic magnetic properties of discontinuous metal-insulator multilayers of Ni81Fe19/Al2O3 have been investigated. By varying the thickness of the insulator the system exhibits a superferromagnetic, a 3d spin-glass-like and a superparamagnetic behavior.