<p>SiGe thin film alloys are the subject of intense interest in semiconductor research. The extent of bond length dependence upon alloy composition in these materials is a subject of some debate in the literature. This work details our Si and Ge K-edge extended x-ray absorption fine structure (EXAFS) measurements on a selection of strained and relaxed single crystal SiGe alloys. Constrained, simultaneous fits to the EXAFS of multiple spectra from both Si and Ge K-edges were performed in order to extract quantitative data for bond lengths and co-ordination numbers.</p> <p>The first analysis was performed solely using EXAFS spectra from relaxed alloys grown on Si. The results indicate that first shell bonding in relaxed SiGe alloys adheres to a weakly mixed Pauling-Vegard regime, showing detectable composition dependence (bond length change of 0.03 A over the full composition range). In the</p> <p>notation of the CT theory of Thorpe and co-workers <em>(Phys. Rev. </em>B 46,15872 (1992)), the topological rigidity parameter, a** is found to be 0.70+0.09 -0.03</p> <p>The results are compared to other theoretical and experimental results, and alternate models to the CT theory are explored. Ordering effects in the co-ordination numbers are also evaluated.</p> <p>The second analysis was performed on a small range of complimentary strained and relaxed samples, to investigate the hypothesis that strained SiGe alloys on Si(100) have shorter bond lengths than relaxed samples. The results of the analysis suggest that strain accommodation is at least partly accomplished by bond length contraction.</p> <p>Finally, the Appendix details a complimentary project in near-edge x-ray absorption fine structure measurements of SiGe alloys. Specifically, a strain-induced polarisation dependence in the Si K-edge spectra of SiGe films is explored with measurements of a large range of samples. The results indicate that the source of the polarisation is not yet fully understood.</p> / Master of Engineering (ME)

Slagsegheten hos stål är komplext beroende av ett antal olika parametrar, som i olika grad påverkar varandra. Många betydande och viktiga ledtrådar har hittats som förhoppningsvis kan ge en bredare förståelse varför slagsegheten varierar och varför den inte alltid uppnås i nuvarande process. Studien har utförts på kalldragna sömlösa rör, med stålsort EN 10305-1. Projektet innefattar ett antal olika produkt specifikationer med olika dimensioner, med lite olika kemiska sammansättning. På grund av slagseghetskraven på industriella produkter var det viktigt att utvärdera vilka parametrar som påverkar. En utvärdering gjordes dels av resultat från slagseghetsprovning efter påverkande processer, och dels från utvärdering av stålets mikrostruktur. Förutom dimension och kemisk sammansättning, varierar processlinjens faktorer. Den första processen som påverkar är kalldragningen som i denna studie har haft reduktioner mellan 15% och 31%. Avspänningsglödgningens temperatur påverkar även, där temperaturerna 525 oC, 575 oC och 600 oC är de som använts på produkterna i projektet. Vissa av projektets produkter har även normaliserats, och resultaten tyder på att detta är en mycket viktig process om man ser till slagseghet. Målsättningen var att får fram omslagskurvor vid olika tillstånd av stålet. Utifrån dessa tillsammans med utvärdering av stålets mikrostruktur och kemisk sammansättning kunde flera diskussioner föras. Den viktiga slutledningen som kunde dras var att inga faktorer är ensam avgörande för slagsegheten i den här studien. Den kemiska sammansättningen påverkar ihop med processlinjens olika faktorer. Man bör ligga på en temperatur för avspänningsglödgning över 550 oC. Projektet visar även på att större dimensioner påverkar slagsegheten negativt. Två viktiga felmarginaler kan ha påverkat resultaten i projektet, dels positionen för vart anvisningen görs på provstaven i förhållande till rören och dels användandet av en praxis som beräknar resultat från provning med reducerade provstavar. En undersökning av dessa felmarginaler gjordes, och resultaten var tydliga. En mer noggrann provuttagning bör göras, och man bör vara mer försiktig vid användandet av praxisen.

<p>Slagsegheten hos stål är komplext beroende av ett antal olika parametrar, som i olika grad påverkar varandra.</p><p>Många betydande och viktiga ledtrådar har hittats som förhoppningsvis kan ge en bredare förståelse varför slagsegheten varierar och varför den inte alltid uppnås i nuvarande process.</p><p>Studien har utförts på kalldragna sömlösa rör, med stålsort EN 10305-1. Projektet innefattar ett antal olika produkt specifikationer med olika dimensioner, med lite olika kemiska sammansättning. På grund av slagseghetskraven på industriella produkter var det viktigt att utvärdera vilka parametrar som påverkar. En utvärdering gjordes dels av resultat från slagseghetsprovning efter påverkande processer, och dels från utvärdering av stålets mikrostruktur.</p><p>Förutom dimension och kemisk sammansättning, varierar processlinjens faktorer. Den första processen som påverkar är kalldragningen som i denna studie har haft reduktioner mellan 15% och 31%. Avspänningsglödgningens temperatur påverkar även, där temperaturerna 525 oC, 575 oC och 600 oC är de som använts på produkterna i projektet. Vissa av projektets produkter har även normaliserats, och resultaten tyder på att detta är en mycket viktig process om man ser till slagseghet.</p><p>Målsättningen var att får fram omslagskurvor vid olika tillstånd av stålet. Utifrån dessa tillsammans med utvärdering av stålets mikrostruktur och kemisk sammansättning kunde flera diskussioner föras.</p><p>Den viktiga slutledningen som kunde dras var att inga faktorer är ensam avgörande för slagsegheten i den här studien. Den kemiska sammansättningen påverkar ihop med processlinjens olika faktorer. Man bör ligga på en temperatur för avspänningsglödgning över 550 oC. Projektet visar även på att större dimensioner påverkar slagsegheten negativt.</p><p>Två viktiga felmarginaler kan ha påverkat resultaten i projektet, dels positionen för vart anvisningen görs på provstaven i förhållande till rören och dels användandet av en praxis som beräknar resultat från provning med reducerade provstavar. En undersökning av dessa felmarginaler gjordes, och resultaten var tydliga. En mer noggrann provuttagning bör göras, och man bör vara mer försiktig vid användandet av praxisen.</p>

<p>Regarding the use of material, modern lightweight car bodies are becoming more and more complex than previous constructions. The materials nowadays are used for a more specific field of application and more high strength steels are used and also other materials like aluminium, stainless steel, reinforced polymers are used more frequent. The joining of these materials often requires new or modified joining processes. The aim with this thesis is concerned with the development of simulation models of the joining process as well as mechanical properties of self piercing riveted (SPR) joints and pierce nut joints. In both of these joining methods problems occur when introducing more high strength steel sheets. For SPR, fractures occur in the rivet, and for pierce nut the thread will be damaged.</p><p>Since both the SPR process and the pierce nut process expose the material for plastic deformation up to 150%, correct material properties for very large strain and a simulation program that could handle this was required. With the commercial finite element program Deform2D an axi-symmetric model has been built for the SPR process and the pierce nut process. Because of the computational time, 3D simulations were only used where it was necessary. The developed 3D models use the commercial finite element program ABAQUS-Explicit. All simulation models have been verified with satisfactory agreement to experimental results.</p><p>For SPR, an axi-symmetric simulation model was used for evaluating and optimising the setting process in the stainless steel sheets EN1.4301, HyTens 800 and HyTens 1200. Subsequently, 3D models were used for predicting the mechanical properties of new SPR joints that have showed reduced risk for rivet cracking. In pierce nut simulations, nuts with hardness 8 and 10 have been set in the high strength steel sheet DP600. An axi-symmetric simulation model was used for centred nut setting and two different simulation models in 3D were used to evaluate eccentric nut setting and torque resistance.</p><p>This work resulted in more knowledge about the fracture risk in the rivet and how to reduce it. The strain and stress, which was used as fracture indicators, were reduced to the half with modifications of the rivet and the die geometry. Mechanical property simulations in shear and peel load resulted in satisfactory results for new SPR joints that have showed reduced fracture risk during rivet setting. New die and rivet designs can be developed effectively by combining the process and mechanical property simulations.</p><p>For a pierce nut joint in high strength steel sheets (1.5mm DP600), the simulations show that the cutting of the sheet in combination with eccentric setting over the die causes the thread damage. The thread damage can be avoided by changing the dimension of the nut or by increasing the strength of the nut material. The simulation models can also be used to develop new nut and die geometries for future applications.</p>

<p>The aim of the present work was to clarify the mechanisms of hydrogen removal during vacuum degassing. The main reason for this was because the primary source of hydrogen pick-up in steel-making is the moisture in the furnace atmosphere and the raw material charged into the ladle furnace. Previous studies showed that the presence of hydroxyl ions in the ladle slag results in hydrogen transfer from the slag back into the steel bath. The main focus of this thesis was therefore to gain deeper knowledge of the ladle slag and its properties. For this purpose a number of slag compositions were examined in order to clarify whether these slags were single liquids at 1858 K. 14 out of 27 compositions in the Al₂O₃ CaO MgO SiO₂system was completely melted. These results were in disagreement with the existing phase diagrams.</p><p>Water solubility measurements were carried out by employing a thermo gravimetric technique. The temperature was found to have negligible effect on the water solubilities. The experimental results showed that the water capacity values varied between 1x10³and 2x10³ in the majority of the composition range. However, for compositions close to CaO saturation the water capacity value could reach higher than 3x10³. The experimental determined water capacity was further used to develop a water capacity model for the quaternary slag system Al₂O₃CaO MgO SiO₂. The model was constructed by considering the affects of the binary interactions between the cations in the slag on the capacity of capturing hydroxyl ions. The model calculations agreed well with the experimental results as well as with the literature data.</p><p>An attempt was made to develop a preliminary process model for dehydrogenation by using the results from CFD calculation. For this purpose industrial sampling was made during vacuum treatment. The hydrogen concentrations decreases fast in the initial stages of the degassing, but is slowed down in the final stage. The model calculations fit the initial stage of the dehydrogenation process well. In the final stage of the process the predicted values are somewhat lower than the plant data. The results from the model prediction showed that a dynamic process model could be satisfactorily constructed using the results from CFD calculation.</p><p>The present work aimed at determining how big impact hydroxyl ions in the slag have on the final hydrogen concentration in the liquid steel. It was found that the effect is of less importance regarding the final concentration of the metal after the degassing treatment.</p>

<p>Lead chalcogenides and tin chalcogenides and their alloys are IV−VI family semiconductors with unique material properties compared with similar semiconductors. For instance, Pb<i>Y </i>(<i>Y </i>= S, Se, and Te) are narrow-gap semiconductors with anomalous negative pressure coefficient and positive temperature coefficient. It is known that this behavior is related with the symmetry of wave functions in first Brillouin zone L-point, which moves the edges of valence band maximum and conduction band minimum towards each other with pressure increasing. SnTe has opposite behavior since its wavefunction symmetry is different from Pb<i>Y</i>. Therefore, by alloying PbTe and SnTe one can change and control the band gap energy and its pressure or temperature dependence. These chalcogenides alloys have therefore a huge potential in industrial low-wavelength applications and have been attracted the attention of researchers.</p><p>This thesis comprises theoretical studies of Pb<i>Y</i>, Sn<i>Y</i> (<i>Y </i>= S, Se and Te) and the Pb₁−<i>x</i>Sn<i>x</i>Te alloys (<i>x</i>= 0.00, 0.25, 0.50, 0.75, and 1.00) by means of a first-principles calculation, using the full-potential linearized augmented plane waves method and the local density approximation.</p><p>The optical properties of Pb₁−<i>x</i>Sn<i>x</i>Te alloys are investigated in terms of the dielectric function <i>ε</i>(<i>ω</i>) = ε₁(<i>ω</i>) + <i>iε</i><i>2</i><i>(ω</i>). We find strong optical response in the 0.5–2.0 eV region arising from optical absorption around the LW-line of the Brillouin zone. The calculated linear optical response functions agree well with measured spectra from ellipsometry spectroscopy performed by the Laboratory of Applied Optics, Linköping University. The calculations of the electronic band-edges of the binary PbY and SnY compounds, show similar electronic structure and density-of-states, but there are differences of the symmetry of the band-edge states at and near the Brillouin zone L-point. PbY have a band gap of E<i>g</i><i> </i>0.15−0.30 eV. However, SnY are zero-gap semiconductors<i> E</i><i>g</i> = 0 if the spin-orbit interaction is excluded. The reason for this is that the lowest conduction band and the uppermost valence band cross along the LW line. When including in Pb<i>Y</i>. Although Pb<i>Y</i> and Sn<i>Y </i>have different band-edge physics at their respective equilibrium lattice constants, the change of the band-edges with respect to cell volume is qualitatively the same for all six chalcogenides. The calculations show that the symmetry of band edge at the L-point changes when lattice constant varies and this change affects the pressure coefficient. the spin-orbit interaction a gap <i>E</i><i>g</i><i> </i>≈ 0.2 eV is created, and hence this gap is induced by the spin-orbit interaction. At the L-point, the conduction-band state is a symmetric state and the valence-band state is antisymmetric thereby the L-point pressure coefficient ⁺₄L−₄Lp<i>E</i><i>g</i>∂∂/)L( in SnY is a positive quantity. In contrast to Sn<i>Y</i>, the Pb<i>Y</i> compounds have a band gap both when spin-orbit coupling is excluded and included; this gap is at the L-point, and the conduction-band state has and the valence-band state has symmetry, and thereby this band edge yields the characteristic negative pressure coefficient ⁺₄L−₄Lp<i>E</i><i>g</i>∂∂/)L(</p>

No description available.

<p>[Missing page 58]</p> / Doctor of Philosophy (PhD)

<p>Austenite growth in the intercritical annealing of ternary (Fe-C-Mn) and quaternary (Fe-C-Mn-Si) dual phase steels is studied. The growth process is modelled assuming local equilibrium at austenite/ferrite interfaces and diffusion control. An isothermal anneal starting with a ferrite-pearlite mixture is examined. Growth proceeds in four stages: (1) austenite nucleation from pearlite (which is not examined); (2) attainment of uniform carbon activity within each austenite particle; (3) attainment of uniform carbon activity over large distances in the material (e.g., 100 (mu)m); and (4) austenite growth controlled by diffusion of alloying element(s) in ferrite. The last stage is the only stage where significant alloying element partitioning occurs. This leads to the centre of each austenite particle retaining its initial alloying element concentration while the rim is enriched or depleted in alloying element depending on the value of the alloying element diffusion coefficient. This non-uniform concentration profile is associated with the end of austenite growth and results in a volume fraction greater than the equilibrium volume fraction. Full equilibration of the austenite does not occur in practical time periods. The preceding description applies to all cases treated. Material initially homogeneous with respect to alloying elements was examined: (1) for a planar geometry; (2) for a spherical geometry; and (3) with different size particles. A material initially non-uniform with respect to alloy element (e.g., having an initial sinusoidal fluctuation of alloying element) was examined for the case of: (1) a wavelength comparable with spacing between austenite particles; and (2) longer wavelengths. The assumption that local equilibrium established in short times (100 s) was verified with Scanning Transmission Electron Microscope (STEM) observations. STEM and microprobe analysis data also qualitatively verified predicted Mn concentration profiles for long (50 h) anneals. Volume fractions predicted were in reasonable agreement with observed and published volume fraction data.</p> / Doctor of Philosophy (PhD)

<p>Lattice disorder produced by heavy ion implantation of cadmium sulphide crystals at 50 K and 300 K has been investigated using Transmission Electron Microscopy (TEM) and Rutherford Backscattering (RBS)/- Channeling techniques.</p> <p>TEM observations of Bi⁺, Ar⁺ and Ne⁺ implanted samples showed that two types of dislocation loops were produced, type I with a Burgers vector b= 1/2 <0001> and type II with a Burgers vector b = 1/3' <1120>. Type II loops were nearly twice as large in size and two to three times greater in number density then type I loops. The large loops of type II were predominantly vacancy loops. Both types of loops lie predominantly in the {1100} and {1120} prism planes. The loop size and number density increased with increasing energy deposited into elastic collisions. For increasing ion dose the loop size increased while the number density decreased.</p> <p>In-situ measurements of the lattice disorder have been made using the RBS/ channeling technique with 0.6 MeV to 2.8 MeV He⁺ channeled along the a- and c-axes of the CdS crystals. The amount of disorder was measured in terms of the areal density of cadmium scattering centers (ND), and the minimum dechanneling yield (xmin) . Measured Nd values were found to be two orders of magnitude lower than theoretical prediction and the Xmin values were about an order of magnitude higher than those calculated assuming randomly displaced scattering centers. The disorder was greater measured along the c-axis than along the a-axis. It was also greater at 300 K than at 50 K. These observations suggest that the lattice distortion is greater in the direction perpendicular to the c-axis. It was also found that Nd increased with increasing E₀, while Xmin values were energy independent over the energy range investigated. These results and the rapid increase in Nd values observed when the crystal is tilted slightly away from the channeling direction ('Off-Axis' measurements) are consistent with the presence of dislocation loops as observed by the TEM.</p> / Doctor of Philosophy (PhD)