[pt] O processo de galvanização por imersão a quente é uma técnica industrial largamente utilizada para proteger componentes de aço expostos à corrosão ambiental. Este processo envolve reações complexas, cujos mecanismos ainda são motivo de debate. A boa performance do revestimento está diretamente relacionada com as fases intermetálicas presentes no revestimento final. Assim, o entendimento do mecanismo de nucleação e crescimento das fases durante a etapa de tratamento térmico contribui para a melhoria do processo, principalmente para redução de custos e desenvolvimento de novos produtos. No presente trabalho, a técnica MAXIM (Materials X-rays Imaging) foi utilizada para identificar as fases presentes em amostras galvanizadas submetidas a diferentes tratamentos. Um difratômetro equipado com um sistema de colimação e detecção formado por uma placa contendo microcanais (Micro-Channel Plate, MCP) situada em frente à uma câmera CCD, permite a obtenção de uma imagem de raios-X. Com esta técnica pode-se identificar a origem posicional do feixe difratado com resolução de cerca de 12mm. Foram realizados dois tipos de experimentos: (1) experimentos, à temperatura ambiente, que consistiam na observação de amostras galvanizadas previamente tratadas (2) experimentos de tratamento térmico in situ, onde a evolução das fases pode ser acompanhada em tempo real. Pode- se concluir que a técnica MAXIM, acoplada ao forno de tratamento térmico in situ, é um método eficiente de observar a distribuição e evolução das fases presentes nas amostras galvanizadas e galvannealed. Este técnica é sensível o suficiente para detectar a evolução das fases com boa resolução espacial. / [en] Galvannealing is an important commercial processing technique used to protect steel components exposed to corrosive environments. This process involves a number of complex reactions and their precise mechanisms are still a matter of debate. The good performance of the coating is closely related to the Fe-Zn intermetallic phases present in the coating. The understanding of the mechanisms for phase nucleation and growth during the galvannealing process is, therefore, essential to help improving current processes, mainly for cost reduction and new products development. In the present study, the MAXIM (MAterials Xrays Imaging) technique was used to identify the phases present in previously galvanized steel samples subjected to different annealing conditions. A diffractometer equipped with a novel imaging system comprising a micro-channel plate (MCP) in front of a CCD detector was used. This setup allows positionresolved X-ray diffraction investigation of materials, with a resolution of 12mm. The experiments involved two sets of conditions; (1) experiments based on the observation, at room temperature, of previously galvannealed samples. (2) in-situ annealing experiments, where the phase evolution was recorded in real time. It can be concluded that MAXIM, coupled to in-situ annealing, provides a useful method for observing the phase evolution and distribution in galvanized/galvannealed samples. The method is sensitive enough to detect the time/temperature evolution of these phases, with good spatial resolution.

Le travail présenté dans cette thèse a pour objectif d’étudier le dopage p des nanofils de ZnO par deux procédés différents : in-situ (durant la croissance) et ex-situ par diffusion des impuretés dans les nanofils à partir d’une phase gazeuse. Les nanofils de ZnO étudiés ont été élaborés par MOCVD et caractérisés par différentes techniques : MEB, MET, EDX, XPS, nano-Auger, DRX, SIMS, Sonde atomique tomographique, Raman, PL et I(V). Les tentatives de dopage ex-situ n’ont pas permis aux dopants (arsenic, phosphore et antimoine) de diffuser et de s’incorporer dans la matrice de ZnO. Ces derniers sont restés en surface. Néanmoins, ce procédé a mis en évidence l’importance du traitement de surface des nanofils, avec un recuit sous zinc, afin de réduire d'une part les défauts associés à la surface très réactive de ZnO, et d'autre part de diminuer la densité d’impuretés résiduelle de type n, condition préliminaire à l’incorporation de dopants de type p électriquement actifs. Concernant le dopage in-situ des nanofils de ZnO, le dopant (azote) s’incorpore plus facilement dans la matrice ZnO atteignant une concentration de l’ordre de 1020 at.cm-3. Les analyses de μ-Raman et de μ-PL montrent que l’azote est reparti de façon inhomogène le long des fils. Si les mesures optiques confirment la présence d'accepteurs dans le matériau après dopage, les mesures électriques révèlent toutefois que la conduction des fils dopés azote restent de type n. / The work presented in this thesis aims to study the p-doping of ZnO nanowires by two different methods: in-situ (during growth) and ex-situ by diffusion of impurities in the nanowires from a gas phase. ZnO nanowires were prepared by MOCVD and characterized by different techniques: SEM, TEM, EDX, XPS, nano-Auger, XRD, SIMS, atom probe tomography, Raman, PL and I (V). The ex-situ doping attempts have not allowed the dopants (arsenic, phosphorus and antimony) to be diffused and incorporated into the ZnO matrix. They still remained on the surface. However, this process has highlighted the importance of nanowire surface annealing treatment with zinc, in order to reduce i) the density of surface related defects, and ii) the density of residual impurities n-type. This is a precondition for the incorporation of electrically active p-type dopants. For in-situ doping of ZnO nanowires, the dopant (nitrogen) is incorporated more easily into the ZnO matrix, reaching a concentration of about 1020 at.cm-3. Analyses of μ-Raman and μ-PL show that nitrogen atoms are inhomogeneously incorporated along the nanowires. If optical measurements confirm the presence of acceptors in the material after doping, the electrical measurements show, however, that nitrogen doped nanowires remain n-type.

Philosophiae Doctor - PhD / In this thesis we report on the metal-mediated-thermally induced changes of the structural and optical properties of hydrogenated amorphous silicon deposited by hot-wire CVD, where aluminium and nickel were used to induce crystallization. The metal-coated amorphous silicon was subjected to a thermal annealing regime of between 150 and 520°C. The structural measurements, obtained by Raman spectroscopy, show partial crystallization occurring at 350 °C. At the higher annealing temperatures of 450°C and 520°C complete crystallization occurs. Reflection and transmission measurements in the UV-visible range were then used to extract the optical properties. By adopting the effective medium approximation a single optical model could be constructed that could successfully model material that was in different structural phases, irrespective of metal contamination. Changes in the absorption of the material in various stages of transition were confirmed with a directly measured absorption technique, and the modelled absorption closely followed the same trends This study forms part of the larger overall solar cell research project, of which the primary aim is to eventually develop a silicon solar panel that optimises the characteristics for best performance. / South Africa

Philosophiae Doctor - PhD / Antimicrobial peptides (AMPs) play a key role in the innate immune response. They can be ubiquitously found in a wide range of eukaryotes including mammals, amphibians, insects, plants, and protozoa. In lower organisms, AMPs function merely as antibiotics by permeabilizing cell membranes and lysing invading microbes. Prediction of antimicrobial peptides is important because experimental methods used in characterizing AMPs are costly, time consuming and resource intensive and identification of AMPs in insects can serve as a template for the design of novel antibiotic. In order to fulfil this, firstly, data on antimicrobial peptides is extracted from UniProt, manually curated and stored into a centralized database called dragon antimicrobial peptide database (DAMPD). Secondly, based on the curated data, models to predict antimicrobial peptides are created using support vector machine with optimized hyperparameters. In particular, global optimization methods such as grid search, pattern search and derivative-free methods are utilised to optimize the SVM hyperparameters. These models are useful in characterizing unknown antimicrobial peptides. Finally, a webserver is created that will be used to predict antimicrobial peptides in haemotophagous insects such as Glossina morsitan and Anopheles gambiae. / South Africa

Philosophiae Doctor - PhD / The limited supply of fossil hydrocarbon resources and the negative impact of CO2 emission on the global environment dictate the increasing usage of renewable energy sources. Concentrating solar power (CSP) systems are the most likely candidate for providing the majority of the renewable energy. For efficient photo-thermal conversion, these systems require spectrally selective solar absorber surfaces with high solar absorbance in the solar spectrum region and low thermal emittance in the infrared region. In this thesis, a spectrally selective AlxOy/Pt/AlxOy multilayer solar absorber was designed and deposited onto copper substrate using electron beam evaporation at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit the multilayer solar absorber coatings. The optical constants measured using spectroscopic ellipsometry, showed that both AlxOy layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance ~ 0.94±0.01 and low thermal emittance ~ 0.06 ± 0.01 at 82oC.The structural and optical properties of the coatings were investigated. It was found that the stratification of the coatings consists of a semitransparent middle Pt layer sandwiched between two layers of AlxOy. The top and bottom AlxOy layers were nonstoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of AlxOy. The surface roughness of the stack was found to be comparable to the inter-particle distance. To study the thermal stability of the multilayer solar absorber coatings, the samples were annealed at different temperatures for different duration in air. The results showed changes in morphology, structure, composition, and optical properties depend on both temperature and duration of annealing. The XRD pattern showed that the intensity of Pt decreased with increasing annealing temperature and therefore, disappeared at high temperature. With increasing annealing temperature, an increase in the size of Pt particles was observed from SEM. The AlxOy/Pt/AlxOy multilayer solar absorber coatings deposited onto Cu substrate were found to be thermally stable up to 500oC in air for 2 h with good spectral selectivity of 0.951/0.09. At 600oC and 700oC, the spectral selectivity decreased to 0.92/0.10 and 0.846/0.11 respectively, which is attributed to the diffusion of Cu and formation of CuO and Cu2O phases. Long term thermal stability study showed that the coatings were thermally stable in air up to 450oC for 24 h. To elucidate the degradation mechanism beyond 500oC, HI-ERDA has been used to study depth-dependent atomic concentration profiles. These measurements revealed outward diffusion of the copper substrate towards the surface and therefore, the decrease in the constituents of the coating. Hence, to prevent copper from diffusing towards the coatings, a thin Tantalum (Ta) layer was deposited between the base AlxOy layer and the copper substrate.The effect of a thin Ta layer on the thermal stability of AlxOy/Pt/AlxOy multilayer solar absorber coatings was investigated. The Cu/Ta/AlxOy/Pt/AlxOy multilayer solar absorber coatings were found to be thermally stable up to 700oC in air for 2 h with good spectral selectivity of 0.937/0.10. At 800oC, the spectral selectivity decreased to 0.870/0.12, which is attributed to the diffusion of Cu and formation of CuO phase. The formation of CuO phase was confirmed by XRD, EDS and Raman spectroscopy. Long term thermal stability study showed that the coatings were thermally stable in air up to 550oC for 24 h. Therefore, the Cu/Ta/AlxOy/Pt/AlxOy spectrally selective solar absorber coatings can be used for high temperature solar-thermal applications.

The operational scheduling at coal handling facilities is of the utmost importance to ensure that the coal consuming processes are supplied with a constant feed of good quality coal. Although the Sasol Coal Handling Facility (CHF) were not designed to perform coal blending during the coal handling process, CHF has to blend the different sources to ensure that the quality of the feed supplied is of a stable nature. As a result, the operation of the plant has become an extremely complex process. Consequently, human intelligence is no longer sufficient to perform coal handling scheduling and therefore a scheduling model is required to ensure optimal plant operation and optimal downstream process performance. After various attempts to solve the scheduling model optimally, i.e. with exact solution methods, it was found that it is not possible to accurately model the complexities of CHF in such a way that the currently available exact solvers can solve it in an acceptable operational time. Various alternative solution approaches are compared, in terms of solution quality and execution speed, using a simplified version of the CHF scheduling problem. This investigation indicates that the Simulated Annealing (SA) metaheuristic is the most efficient solution method to provide approximate solutions. The metaheuristic solution approach allows one to model the typical sequential thoughts of a control room operator and sequential operating procedures. Thus far, these sequential rules could not be modelled in the simultaneous equation environment required for exact solution methods. An SA metaheuristic is developed to solve the practical scheduling model. A novel SA approach is applied where, instead of the actual solution being used for neighbourhood solution representation, the neighbours are indirectly represented by the rules used to generate neighbourhood solutions. It is also found that the initial temperature should not be a fixed value, but should be a multiple of the objective function value of the initial solution. An inverse arctan-based cooling schedule function outperforms traditional cooling schedules as it provides the required diversification and intensification behaviour of the SA. The scheduling model solves within 45 seconds and provides good, practically executable results. The metaheuristic approach to scheduling is therefore successful as the plant complexities and intricate operational philosophies can be accurately modelled using the sequential nature of programming languages and provides good approximate optimal solutions in a short solution time. Tests done with live CHF data indicate that the metaheuristic solution outperforms the current scheduling methodologies applied in the business. The implementation of the scheduler will lead to a more stable factory feed, which will increase production yields and therefore increase company profits. By reducing the amount of coal re-handling (in terms of throw-outs and load-backs at mine bunkers), the scheduler will reduce the coal handling facility’s annual operating cost by approximately R4.6 million (ZAR). Furthermore, the approaches discussed in this document can be applied to any continuous product scheduling environment. Additional information available on a CD stored at Level 3 of the Merensky Library. / Dissertation (MEng (Industrial Engineering))--University of Pretoria, 2011. / Industrial and Systems Engineering / unrestricted

The progress in device performance of modern microelectronic technology is mainly driven by down-scaling. In the near future, this road will probably reach a point where physical limits make even more down-scaling impossible. The substitution of single components materialwise over the last decades, like high-k dielectrics or metal gates, has been a suitable approach to foster performance improvements. In this scheme, the integration of high-mobility III-V compound semiconductors as channel materials into Si technology is a promising route to follow for the next one or two device generations. III-V integration, today, is conventionally performed by using techniques like molecular beam epitaxy or wafer bonding which utilize solid phase crystallization but suffer to strain due to the lattice mismatch between III-V compounds and Si. An alternative approach using sequential ion beam implantation in combination with a subsequent flash lamp annealing is presented in this work. Using this technique, nanocrystals from various III-V compounds have been successfully integrated into bulk Si and Ge as well as into thin Si layers which used either SOI substrates or were grown by plasma-enhanced chemical vapour deposition. The III-V compounds which have been fabricated are GaP, GaAs, GaSb, InP, InAs, GaSb and InxGa1-xAs with variable composition. The structural properties of these nanocrystals have been investigated by Rutherford backscattering, scanning electron microscopy and transmission electron microscopy, including bright-field, dark-field, high-resolution, high-angle annular dark-field and scanning mode imaging, electron-dispersive x-ray spectroscopy and energy-filtered element mapping. Furthermore, Raman spectroscopy and X-ray diffraction have been performed to characterise the nanocrystals optically. In Raman spectroscopy, the characteristic transversal and longitudinal optical phonon modes of the different III-V compounds have been observed. These signals proof that the nanocrystals have formed by the combination of ion implantation and flash lamp annealing. Additionally, the appearance of the typical phonon modes of the respective substrate materials verifies recrystallization of the substrate by the flash lamp after amorphisation during implantation. In the bulk Si samples, the nanocrystals have a circular or rectangular lateral shape and they are randomly distributed at the surface. Their cross-section has either a hemispherical or triangular shape. In bulk Ge, there are two types of precipitates: one at the surface with arbitrary shape and another one buried with circular shape. For the thin film samples, the lateral shape of the nanocrystals is more or less arbitrary and they feature a block-like cross-section which is limited in height by the Si layer thickness. Regarding crystalline quality, the nanocrystals in all samples are mainly single-crystalline with only a few number of stacking faults. However, the crystalline quality in the bulk samples is slightly better than in the thin films. The X-ray diffraction measurements display the (111), (220) and (311) Bragg peaks for InAs and GaAs as well as for the InxGa1-xAs where the peaks shift with increasing In content from GaAs towards InAs. The underlying formation mechanism is identified as liquid phase epitaxy. Hereby, the ion implantation leads to an amorphisation of the substrate material which is then molten by the subsequent flash lamp annealing. This yields a homogeneous distribution of the implanted elements within the melt due to their strongly increased diffusivity in the liquid phase. Afterwards, the substrate material starts to recrystallize at first and an enrichment of the melt with group-III and group-V elements takes place due to segregation. When the temperature is low enough, the III-V compound semiconductor starts to crystallize using the recrystallized substrate material as a template for epitaxial growth. In order to gain control over the lateral nanocrystal distribution, an implantation mask of either aluminium or nickel is introduced. Using this mask, only small areas of the samples are implanted. After flash lamp treatment, nanocrystals form only in these small areas, which allows precise positioning of them. An optimal implantation window size with an edge length of around 300nm has been determined to obtain one nanocrystal per implanted area. During an additional experiment, the preparation of Si nanowires using electron beam lithography and reactive ion etching has been conducted. Hereby, two different processes have been investigated; one using a ZEP resist, a lift-off step and a Ni hard mask and another one using a hydrogen silsesquioxane resist which is used directly as a mask for etching. The HSQ-based process turned out to yield Si nanowires of better quality. Combining both, the masked implantation and the Si nanowire fabrication, it might be possible to integrate a single III-V nanocrystal into a Si nanowire to produce a III-V-in-Si-nanowire structure for electrical testing. / Der Fortschritt in der Leistungsfähigkeit der Bauelemente moderner Mikroelektroniktechnologie wird hauptsächlich durch das Skalieren vorangetrieben. In naher Zukunft wird dieser Weg wahrscheinlich einen Punkt erreichen, an dem physikalische Grenzen weiteres Herunterskalieren unmöglich machen. Der Austausch einzelner Teile auf Materialebene, wie Hoch-Epsilon-Dielektrika oder Metall-Gate-Elektroden, war während der letzten Jahrzehnte ein geeigneter Ansatz, um die Leistungsverbesserung voranzubringen. Nach diesem Schema ist die Integration von III-V-Verbindungshalbleiter mit hoher Mobilität ein vielversprechender Weg, dem man für die nächsten ein oder zwei Bauelementgenerationen folgen kann. Heutzutage erfolgt die III-V-Integration konventionell mit Verfahren wie der Molekularstrahlepitaxie oder dem Waferbonden, welche die Festphasenkristallisation nutzen, die aber aufgrund der Gitterfehlanpassung zwischen III-V-Verbindungen und Silizium an Verspannungen leiden. In dieser Arbeit wird ein alternativer Ansatz präsentiert, welcher die sequenzielle Ionenstrahlimplantation in Verbindung mit einer darauffolgenden Blitzlampentemperung ausnutzt. Mit Hilfe dieses Verfahrens wurden Nanokristalle verschiedener III-V-Verbindungshalbleiter erfolgreich in Bulksilizium- und -germaniumsubstrate sowie in dünne Siliziumschichten integriert. Für die dünnen Schichten wurden hierbei entweder SOI-Substrate verwendet oder sie wurden mittels plasmagestützer chemischer Gasphasenabscheidung gewachsen. Die hergestellten III-V-Verbindungen umfassen GaP, GaAs, GaSb, InP, InAs, InSb und InxGa1-xAs mit veränderbarer Zusammensetzung. Die strukturellen Eigenschaften dieser Nanokristalle wurden mit Rutherford-Rückstreu-Spektroskopie, Rasterelektronenmikroskopie und Transmissionselektronenmikroskopie untersucht. Bei der Transmissionelektronenmikroskopie wurden die Hellfeld-, Dunkelfeld-, hochauflösenden, “high-angle annular dark-field” und Rasteraufnahmemodi sowie die energiedispersive Röntgenspektroskopie und die energiegefilterte Elementabbildung eingesetzt. Darüber hinaus wurden Ramanspektroskopie- und Röntgenbeugungsmessungen durchgeführt, um die Nanokristalle optisch zu charakterisieren. Mittels Ramanspektroskopie wurden die charakteristischen transversal- und longitudinal-optischen Phononenmoden der verschiedenen III-V-Verbindungen beobachtet. Diese Signale beweisen, dass sich unter Verwendung der Kombination von Ionenstrahlimplantation und Blitzlampentemperung Nanokristalle bilden. Weiterhin zeigt das Vorhandensein der typischen Phononenmoden der jeweiligen Substratmaterialien, dass die Substrate aufgrund der Blitzlampentemperung rekristallisiert sind, nachdem sie durch Ionenimplantation amorphisiert wurden. In den Bulksiliziumproben besitzen die Nanokristalle eine kreisförmige oder rechteckige Kontur und sind in zufälliger Anordnung an der Oberfläche verteilt. Ihr Querschnitt zeigt entweder eine Halbkugel- oder dreieckige Form. Im Bulkgermanium gibt es zwei Arten von Ausscheidungen: eine mit willkürlicher Form an der Oberfläche und eine andere, vergrabene mit sphärischer Form. Betrachtet man die Proben mit den dünnen Schichten, ist die laterale Form der Nanokristalle mehr oder weniger willkürlich und sie zeigen einen blockähnlichen Querschnitt, welcher in der Höhe durch die Siliziumschichtdicke begrenzt ist. Bezüglich der Kristallqualität sind die Nanokristalle in allen Proben mehrheitlich einkristallin und weisen nur eine geringe Anzahl an Stapelfehlern auf. Jedoch ist die Kristallqualität in den Bulkmaterialien ein wenig besser als in den dünnen Schichten. Die Röntgenbeugungsmessungen zeigen die (111), (220) und (311) Bragg-Reflexe des InAs und GaAs sowie des InxGa1-xAs, wobei sich hier die Signalpositionen mit steigendem Gehalt an Indium von GaAs zu InAs verschieben. Als zugrundeliegender Bildungsmechanismus wurde die Flüssigphasenepitaxie identifiziert. Hierbei führt die Ionenstrahlimplantation zu einer Amorphisierung des Substratmaterials, welches dann durch die anschließende Blitzlampentemperung aufgeschmolzen wird. Daraus resultiert eine homogene Verteilung der implantierten Elemente in der Schmelze, da diese eine stark erhöhte Diffusivität in der flüssigen Phase aufweisen. Danach beginnt zuerst das Substratmaterial zu rekristallisieren und es kommt aufgrund von Segregationseffekten zu einer Anreicherung der Schmelze mit den Gruppe-III- und Gruppe-V-Elementen. Wenn die Temperatur niedrig genug ist, beginnt auch der III-V-Verbindungshalbleiter zu kristallisieren, wobei er das rekristallisierte Substratmaterial als Grundlage für ein epitaktisches Wachstum nutzt. In der Absicht Kontrolle über die laterale Verteilung der Nanokristalle zu erhalten, wurde eine Implantationsmaske aus Aluminium beziehungsweise Nickel eingeführt. Durch die Benutzung einer solchen Maske wurden nur kleine Bereiche der Proben implantiert. Nach der Blitzlampentemperung werden nur in diesen kleinen Bereichen Nanokristalle gebildet, was eine genaue Positionierung dieser erlaubt. Es wurde eine optimale Implantationsfenstergröße mit einer Kantenlänge von ungefähr 300 nm ermittelt, damit sich nur ein Nanokristall pro implantierten Bereich bildet. Während eines zusätzlichen Experiments wurde die Präparation von Siliziumnanodrähten mit Hilfe von Elektronenstrahllithografie und reaktivem Ionenätzen durchgeführt. Hierbei wurden zwei verschiedene Prozesse getestet: einer, welcher einen ZEP-Lack, einen Lift-off-Schritt und eine Nickelhartmaske nutzt, und ein anderer, welcher einen HSQ-Lack verwendet, der wiederum direkt als Maske für die Ätzung dient. Es stellte sich heraus, dass der HSQ-basierte Prozess Siliziumnanodrähte von höherer Qualität liefert. Kombiniert man beides, die maskierte Implantation und die Siliziumnanodrahtherstellung, miteinander, sollte es möglich sein, einzelne III-V-Nanokristalle in einen Siliziumnanodraht zu integrieren, um eine III-V-in-Siliziumnanodrahtstruktur zu fertigen, welche für elektrische Messungen geeignet ist.

La réalisation des jonctions ultra-minces et fortement dopées est un enjeu majeur pour la continuité de la miniaturisation des dispositifs microélectroniques. Les techniques de production en termes d'implantation ionique et de recuit d'activation doivent évoluer afin de répondre aux exigences du marché de la microélectronique. Le travail de recherche de cette thèse s’inscrit dans le cadre du projet ALDIP (Activation Laser de Dopants implantés par Immersion Plasma) et a pour objectif l’étude et le contrôle du procédé laser pour la réalisation des jonctions ultra-minces sur silicium (cristallin ou préamorphisé par implantation ionique) dopé au bore. En effet, le contrôle in situ du processus de recuit laser s'avère indispensable pour l'industrialisation de ce procédé qui jusqu'au là a fait l'objet de plusieurs études de recherche. Ainsi, le travail réalisé durant cette thèse a permis de mettre en place une méthode de contrôle, in situ, qui a été calibrée afin de la rendre accessible par le milieu industriel. Il s'agit de la méthode RRT (Réflectivité Résolue en Temps). Pour mener ce travail de thèse à terme, nous avons utilisé deux dispositifs expérimentaux comportant chacun un laser UV impulsionnel nanoseconde, un système optique d’homogénéisation et un dispositif RRT. Par ailleurs, plusieurs techniques de caractérisation ex situ ont été employées (TOF-SIMS, MEB, ...) notamment dans l’objectif de calibrer la méthode RRT. Ce travail expérimental a été couplé à une étude de simulation numérique qui a permis de mieux comprendre les paramètres clés du recuit laser et qui s’est souvent avérée en bon accord avec les résultats expérimentaux obtenus. / The realization of highly-doped ultra-shallow junctions became a key point for the reduction of microelectronic devices. Production techniques (implantation and activation annealing) must evolve to meet the market requirements of microelectronics. This job takes part of the ALDIP (Laser Activation of Dopants implanted by Plasma Immersion) project and it is focused on the study and control of the laser process for the realization of ultra-shallow junctions. The in situ control of laser annealing process is indispensable for the industrialization of this technique, which until then was the subject of several research studies. Thus, the work done during this thesis has permitted to set up a control method, in situ, which was calibrated to make it accessible to the industry. This experimental device is based on the RRT method (Time Resolved Reflectivity). In order to carry this work forward, we used two experimental systems based on the RRT method with two different nanosecond laser pulses (UV) and a homogenizer system. In addition, several ex situ characterization techniques were used notably for the purpose of calibrating the RRT method. This experimental work has been coupled with a numerical simulation study which provided a better understanding of the key parameters of the laser annealing. This comparison has often proved to be in a good agreement with experimental results.

Routing problems are ones of the most famous members of the group of the classical optimalization combinatorial problems. Travelling salesman problem and problems derived from it have been attracting mathematics and analysts, since they were firstly formulated, and accelerating a development of new methods and approaches that can be used for a wide range of another real-life problems. This thesis aims to demonstrate an usefulness and a flexibility of shown metaheristic methods. Results are compared with outputs of alternative algorithms or known optimal solutions where it is possible. To fulfill this goal the VBA application has been developed. The results of experiments are presented and the application is decribed in a second part of this thesis. A reader should be sufficiently instructed which way he could choose to solve similar types of problems

The aim of the current thesis was to investigate the preparation of MnSi film on Si substrates. The preparation process includes room temperature sputtering Mn films with different thicknesses and flash-lamp annealing with different energy density (annealing temperature). Systematic investigations on their structural, electrical, magnetic, and magneto-transport properties were performed. The key findings are summarized below: Thin films with the B20-MnSi phase on Si(100) substrates were fabricated for the first time. They exhibit magnetic skyrmion behaviour. In comparison with Si(111) substrates, Si(100) substrates are more preferred from the practical application point of view. The nucleation of B20-MnSi on Si(100) is believed to be triggered by the fast solid-state phase reaction between Mn and Si via ms-range flash-lamp annealing. Compared with the corresponding bulk material, our films show an increased Curie temperature of around 43 K. The magnetic and transport measurements reveal that skyrmions in B20-MnSi on Si(100) made by sub-seconds solid-state reaction are stable within much broader field and temperature windows than bulk MnSi. The parasitic MnSi1.7 phase can be further minimized or eliminated by optimizing the annealing conditions, the quality of the deposited Mn film, and its interface with the Si substrate. Our work demonstrates a promising route for the fabrication of B20-type transition metal silicides for integrated and/or hybrid spintronic applications on Si(100) wafers, which are more preferable for industry applications. The growth of MnSi films on Si(111) substrates has been widely realized by solid phase epitaxy or molecular beam epitaxy since the lattice mismatch and symmetry fit better. One problem is the parasitic MnSi1.7 phase. By controlling the reaction parameters using strongly non-equilibrium flash lamp annealing, we have achieved full control over the phase formation of Mn-silicides in thin films from single-phase B20-MnSi or MnSi1.7 to mixed phases. The obtained films are highly textured and reveal sharp interfaces to the Si substrate. The obtained B20-MnSi films exhibits a high Curie temperature of 41 K. The skyrmion phase can be stabilized over broad temperature and magnetic field ranges. We propose flash-lamp-annealing-induced transient reaction as a general approach for phase separation in transition-metal silicides and germanides and for growth of B20-type films with enhanced topological stability. By comparing the magnetic properties of MnSi films grown on both Si(111) and Si(100) substrates by ourselves and by others in literature, we found one common feature. It is the increased Curie temperature of around 41-43 K for all MnSi films. It is much higher than 29.5 K for bulk MnSi. We try to understand the puzzling Curie temperature widely reported in MnSi films. We have prepared MnSi films with a large variation regarding their thickness, crystallinity, strain and phase separation. Particularly, polycrystalline MnSi films on Si(100) and textured MnSi films on Si(111), both with different mixture ratio with MnSi1.7 have been grown and systematically characterized. Surprisingly, all obtained MnSi films exhibit a high Curie temperature at around 43 K. The skyrmion phase has also been detected in these films. However, we find no correlation between the increased Curie temperate and the film thickness, strain, lattice volume or the mixture with MnSi1.7. Our work has not provided a conclusive picture for this question, but is rather calling a revisit, especially to the effect by the interface, stoichiometry and point defects. Further studies are essential to understand the B20 transition-metal silicide/germanides films and therefore to utilize them for spintronic applications.:Contents Abstract iii Kurzfassung v 1. Introduction 1 1.1 B20 compounds and magnetic skyrmions 1 1.2 B20 MnSi with magnetic Skyrmions 8 1.2.1 Crystallization process 10 1.2.2 Phase diagram of Mn-Si binary compounds 13 1.2.3 Bulk B20-MnSi 14 1.2.4 B20-MnSi thin film 18 1.2.5 B20-MnSi nanowire 25 1.3 Fast annealing method 27 1.4 Objectives and the structure of the thesis 30 2. Experiment 32 2.1 Sample preparation 32 2.1.1 DC magnetron sputtering 32 2.1.2 Sub-second annealing 35 2.2 Structure characterization: X-ray diffraction 40 2.3 Property characterization 41 2.3.1 Magnetic properties 41 2.3.2 Magneto-transport properties 44 3. B20-MnSi films grown on Si(100) substrates with magnetic skyrmion signature 46 3.1 Introduction 46 3.2 Experiment 47 3.3 Results and Discussions 48 3.4 Conclusions 56 4. Phase selection in Mn-Si alloys by fast solid-state reaction with enhanced skyrmion stability 57 4.1 Introduction 57 4.2 Experiment 59 4.3 Results 61 4.3.1 MnSi and MnSi1.7 phase reaction 61 4.3.2 Magnetic Skyrmion 68 4.3.3 Discussion 76 4.4 Conclusion 78 5. On the Curie temperature of MnSi films 80 5.1 Introduction 80 5.2 Experiment 82 5.3 Results 83 5.4 Conclusion 89 6. Summary and outlook 90 6.1 Summary 90 6.2 Outlook 91 6.2.1 Film thickness effect on formation of (111)-textured B20-MnSi 91 6.2.2 MnSi1.7% influence on Skyrmion stability 96 6.2.3 Preparation of other transition-metal monosilicides and germanides 98 Acknowledgement 99 References 101 Publication list 117 Curriculum Vitae 119 Erklärung 120