La LIBS (Laser Induced Breakdown Spectroscopy) est une technique d'analyse élémentaire basée sur l'exploitation du spectre d'émission optique issu de l'ablation laser d'un échantillon. Aujourd'hui, la LIBS ne s'est pas encore imposée comme une technique de choix pour la majorité des applications comme c'est le cas pour les techniques de plasma à couplage inductif. L'une des principales raisons à cela est la difficulté à fournir des mesures quantitatives justes. Il existe donc aujourd'hui une nécessité de mieux comprendre et caractériser les plasmas et les phénomènes issus de l'interaction laser-Matière sur tout type de matériaux pour améliorer les performances de cette technique analytique. Cette interaction laser/matière étant, de plus, spécifique au type de matériau analysé, il est indispensable d'étudier ces effets sur une vaste gamme de matériaux. Deux types d'échantillons ont donc été utilisés pour étudier les plasmas LIBS: des matériaux contenant des terres rares et des matériaux plastiques. Les travaux réalisés sur les terres rares ont permis de sélectionner des raies d'analyse « disponibles », c'est-À-Dire sans interférences spectrales provenant des autres éléments de cette famille et suffisamment sensibles pour réaliser une analyse quantitative. Cette étude a mis en avant le fait que les effets de matrice dus à la quantité de terres rares et à la nature de l'échantillon sont importants. Ces effets de matrice sont propres à chaque élément et à chaque matrice, ils sont donc à prendre en considération pour toute analyse LIBS d'un échantillon contenant plusieurs terres rares. Si l'accumulation d'un grand nombre de terres rares a un effet significatif sur le signal d'un de ces analytes, leurs présences en nombre et quantité limitée (2 à 4) donnent un effet compensable par étalonnage interne. Dans le cadre de l'analyse LIBS des matériaux plastiques, une étude détaillée du signal en utilisant différentes conditions de plasma a été réalisée. L'analyse quantitative s'est portée sur plusieurs éléments dont certains difficiles à exciter comme le brome et le chlore. Grâce à l'utilisation d'une atmosphère contrôlée d'hélium, la détection des halogènes employés comme retardateurs de flamme dans les plastiques, a été possible. Un important effet de matrice a été observé à 266 nm en comparaison avec les résultats obtenus à 532 nm. Cependant, ces différences marquées à 266 nm ont permis la discrimination des quatre familles de polymères étudiées. En présence d'hélium, des différences significatives ont été obtenues pour les rapports C2/He et CN/He. En les traçant l'un en fonction de l'autre, il est ainsi possible de discriminer les différents types de plastiques étudiés / The LIBS (Laser Induced Breakdown Spectroscopy) technique is an elemental analysis technique based on the use of the optical emission spectrum from a sample of laser ablation. Today, LIBS has not emerged as a technique of choice for the majority of applications, as is the case for inductive coupled plasma techniques. One of the main reasons for this is the difficulty in providing accurate quantitative measurements. So there is now a need to better understand and characterize plasmas and phenomena from laser-Matter interaction on all types of materials to improve the performance of this analytical technique. This laser/material interaction is specific to the type of material analyzed, so it is essential to study these effects on a wide range of materials. Two types of samples have been used to study LIBS plasmas: materials containing rare earths and plastics. Work on rare earths were used to select the analytical lines free of spectral interference from other elements of this family and sensitive enough to carry out a quantitative analysis. This study highlighted the fact that the matrix effects due to the amount of rare earth and nature of the sample are important. These matrix effects are unique to each element and matrix, so they are to be considered in all LIBS analysis of a sample containing several rare earths. If the accumulation of a large number of rare earths (i.e 12) has a significant effect on the signal of the analytes, the effect of a limited number (i.e. 2 to 4) could be compensated by use on an internal standard. In the context of the LIBS analysis of plastic materials, a detailed study of the signal using different plasma conditions was performed. The quantitative analysis was focused on several elements, including bromine and chlorine which are difficult to excite. Through the use of a controlled atmosphere of helium, the detection of halogens used as flame retardants in plastics was significantly improved. An important matrix effect was observed at 266 nm in comparison with the results obtained at 532 nm. However, these differences at 266 nm allowed the discrimination of four families of polymers studied. In the presence of helium, significant differences were obtained for the C2 / He and CN / He ratios. This criteria was found to be relevant for the discrimination between the different types of plastics studied

Philosophiae Doctor - PhD / The results of the multivariate analyses suggest that most of the variation in the composition of the samples was of an intra-sample nature, illustrating large scale patchiness in foraminiferal distribution. There were, however, definite differences between communities around Robben Island and in St Helena Bay, and least variation was found between the control and pipeline sites, and between the stations of each site. When the trace metal concentrations and the percentage nitrogen increased, the richness, diversity and abundance of foraminifera tended to decrease. Sediment grain size positively affected abundance but negatively affected diversity and richness. In both areas mean grain size did not, however, appear to play a very large role in influencing diversity. Cadmium, copper, chromium, the percentage nitrogen and the mean grain size were identified as the most important variables influencing the community structure by the BIOENV BEST routine in PRIMER. The trace metals and percentage nitrogen only had negative effects on the diversity and abundance as well as on the abundance of the dominant genera, whereas the mean grain size had variable effects. / South Africa

Au travers de nos sens, nous pouvons appréhender la complexité des stimuli du milieu environnant. Dans le règne animal, il existe deux systèmes de lecture de l’information: l’un analytique et l’autre synthétique. Quels facteurs favorisent chacun de ces modes de perception? Perdurent-ils au cours de la vie? Varient-ils d'une espèce à l'autre? Ces questions ont été adressées en partie conjointement chez l’Homme adulte et le lapin nouveau-né, dans le cadre général de la perception d’odeurs issues de mélanges d'odorants plus ou moins complexes (2-6 odorants), et notamment de mélanges accords.Premièrement, nos résultats soulignent, chez l’Homme, que la sensibilité individuelle (seuils de détection) module la perception d'un mélange accord binaire. Deuxièmement, l’expérience répétée des constituants de ce mélange favorise sa perception analytique, chez l’Homme comme le lapereau, alors que l’expérience du même mélange favorise sa perception synthétique seulement chez le lapereau. Troisièmement, chez les deux espèces, un même mélange complexe de six odorants semble engendrer la perception d'une configuration (propre à la notion d'accord), ce qui n'est pas le cas de tout mélange de complexité comparable. Les lapereaux présentent, par ailleurs, des capacités d’analyse de ce mélange plus prononcées. Enfin, une étude prospective, par IRMf, des corrélats neurophysiologiques liés à chacune de ces perceptions a été réalisée chez l’Homme. / Through our senses, we can grasp the complexity of the stimuli that arise from our surroundings. Within the animal kingdom, two systems of information processing exist: one elemental and the other configural. Which factors promote each of these types of perception? Do they persist across lifespan? Do they vary from one species to another? In part, these issues were addressed simultaneously in human adults and newborn rabbits, within the general framework of odour mixture perception (more or less complex: 2-6 odorants), including the perception of blending mixtures.Firstly, our results highlight that in humans individual sensitivity (detection thresholds) modulates the perception of a binary blending mixture. Secondly, repeated experience with the components of a mixture promotes the elemental perception of the mixture both in humans and rabbits, while experience of the mixture promotes its configural perception only in rabbits. Thirdly, in both species, a same complex mixture of six odorants seems to trigger the perception of a configuration (specific to the blending effect); this is however not the case of any mixture of similar complexity. Besides, newborn rabbits display more pronounced elemental skills for this mixture. Finally, a prospective fMRI study was conducted in humans to investigate the neurophysiological correlates of these two modes of perception.The present findings confirm that the olfactory system can work both configurally and elementally, sometimes in the same way for similar mixtures in individuals from different species, and at different stages of development. This dual activity of the olfactory system is modulated by factors inherent to individuals and to mixtures themselves.

Le traitement thermique est une méthode appropriée pour la valorisation d'essences européennes peu durables. Les modifications chimiques en résultant confèrent au bois une meilleure stabilité dimensionnelle et durabilité aux attaques fongiques, alors que les propriétés mécaniques diminuent plus ou moins. Le verrou actuel de ce procédé reste la grande difficulté à produire à l'échelle industrielle un produit de qualité constante (durabilité, stabilité dimensionnelle, couleur). Ces difficultés sont dues à l'hétérogénéité du matériau et des conditions de traitement réalisé généralement par convexion. La mise au point d'un pilote de traitement thermique par conduction permettant une mesure en dynamique de la perte de masse a été réalisée pour optimiser la conduite du traitement, mieux comprendre les réactions de thermodégradation et développer un outil de contrôle de la qualité du bois traité. Les résultats obtenus, réalisés dans des conditions de traitement proches des conditions industrielles, indiquent un effet important de l'essence de bois traitée sur les cinétiques de perte de masse observées, les feuillus étant généralement plus sensibles à la thermodégradation que les résineux. Il a ensuite été établi une forte corrélation entre le niveau de thermodégradation du bois estimé à partir de sa perte de masse et l'augmentation de sa durabilité aux champignons basidiomycètes. L'analyse fine et la compréhension des mécanismes réactionnels intervenant durant le traitement ont permis de mettre en évidence un lien direct entre la composition élémentaire du bois et la perte de masse due aux réactions de thermodégradation, permettant également de prédire la durabilité aux attaques fongiques. Le taux de carbone, d'oxygène ou encore le rapport O/C peuvent de ce fait être considérés comme des marqueurs pertinents permettant de contrôler la qualité du bois traité thermiquement. / Thermal treatment has been used to improve properties of non durable European species. Chemical modification of some of the wood components provides improved dimensional stability and biological performance against decay fungi while mechanical properties such as modulus of rupture are reduced. Quality control of commercially made thermally treated wood is one of the major road blocks of its industrial development. The variability inherent within a wood species and between wood species, density and chemical compositions variation combined with the heat treatment parameters such as temperature duration and levels contribute to the production of heterogeneous heat treated wood. The development of a heat treatment process by conduction which monitors the weight changes during the process will facilitate and help in controlling, in understanding and predicting the properties of heat treated wood. Data collected from a pilot study of heat treated wood using conditions similar to commercial process show that hardwood species were more susceptible to thermal degradation as compared to softwood. It was also established that wood chemical composition is directly connected to the percent of weight loss due to thermodegradation, allowing the use of chemical composition to predict fungi durability. Carbon and oxygen contents and/or oxygen to carbon ratio of heat treated wood can be therefore used as valuable markers to develop quality control assessment of heat treated wood.

La spectroscopie sur plasma induit par laser (LIBS) est une technique d'analyse élémentaire couplant l'ablation laser dans le cas des échantillons solides, à la spectroscopie d'émission atomique. Malgré de nombreux avantages qui en font une technique de plus en plus attractive, la spectroscopie LIBS n'est pas encore reconnue comme méthode d'analyse quantitative. En effet, les problèmes d'hétérogénéité des échantillons, d'effets matrice, d'auto-absorption des raies d'émission et surtout de manque de répétabilité participent à la dégradation des performances analytiques de la spectroscopie LIBS. Dans le but de faire évoluer la technique, ces travaux de thèse consistent à réaliser un cas particulier de démonstration de l'évaluation des performances analytiques d'un système LIBS de laboratoire en intégrant des notions de qualité. L'exemple porte ici sur l'analyse d'échantillons d'aciers certifiés. Une première étude concerne le déroulement de l'optimisation du système pour l'analyse quantitative. L'effet des différents paramètres expérimentaux sur le signal LIBS étant complexe, un protocole méthodique est indispensable. Une étude paramétrique est donc ici proposée en vue de déterminer les conditions expérimentales les plus propices à l'analyse quantitative. Une fois optimisée, la méthode LIBS est ensuite caractérisée grâce aux principes classiques de la validation de méthode. La justesse ainsi que la fidélité de la méthode sont évaluées dans des conditions de répétabilité et de précision intermédiaire. Cette dernière étude montre des résultats prometteurs pour la technique. L'application d'une carte de contrôle montre néanmoins un manque de stabilité du système de laboratoire et permet d'enclencher des actions correctives en vue d'améliorer ses performances analytiques. / Laser-Induced Breakdown Spectroscopy (LIBS) is an elemental analytical technique which combines laser ablation with atomic emission spectroscopy. LIBS spectroscopy has many advantages but is not recognized as a fully quantitative method. Indeed, the problem of samples' heterogeneity, matrix effects, self-absorption of emission lines and the lack of repeatability deteriorate the analytical performances of LIBS. In order to improve this technique, the work presented in this thesis includes an example of analytical performances evaluation with the use of quality notions of a laboratory LIBS system. The method is here specially applied to the analysis of certified steel samples. A first study deals with the optimization of the LIBS system for the quantitative analysis. As the effect of the different experimental parameters on LIBS signal is complex, a methodical protocol is necessary. Here, a parametric study is proposed to determine the experimental conditions suitable for quantitative analysis. Once optimized, the LIBS method is then characterized with basics of method validation. The trueness and the precision of the method are evaluated in conditions of repeatability and intermediate precision. This study shows promising results for LIBS technique. The application of a control chart reveals however an instability of the laboratory system and enables to introduce corrective actions to improve its analytical performances.

Le contrôle des procédés représente un enjeu majeur pour les industries chimiques et pétrochimiques afin de garantir la qualité des produits, le contrôle des coûts, le maintien de la productivité et la maîtrise des risques. L'analyse menée directement au coeur des procédés constitue la voie la plus efficace. Cependant, dans la majorité des applications, les analyses élémentaires sont réalisées essentiellement en laboratoire et très rarement en ligne, par la mise en oeuvre de différentes technologies, le plus souvent lourdes et onéreuses. Ce travail de thèse s'inscrit dans le cadre d'un grand projet d'innovation qui couvre le champ de l'analyse élémentaire en ligne, domaine actuellement peu étudié. La technique d'analyse retenue est la spectrométrie LIBS en raison de sa rapidité et de son application à tout état de la matière sans préparation d'échantillon, ce qui lui offre un fort potentiel pour l'analyse en ligne. Cette technique est investiguée afin de réaliser des analyses en ligne d'éléments présents dans des matrices liquides : saumures, huiles silicone et produits pétroliers. L'optimisation des différents paramètres de mesure est réalisée et une approche d'optimisation s'appuyant sur un plan d'expériences est proposée. Différents modes d'échantillonnage de liquide et plusieurs montages LIBS sont étudiés afin de répondre aux problématiques évoquées. Enfin, une transposition au monde industriel est présentée avec le suivi du soufre en ligne dans des produits pétroliers sur un pilote industriel. Les résultats sont encourageants, mais la stabilité perfectible des mesures dans le temps implique d'explorer de nouvelles pistes d'amélioration / Process control is a major challenge for chemical and petrochemical industries so as to ensure product quality, cost control, sustainable productivity and risk management. To do so, carrying out the analysis directly at the core of the process is the most efficient way. However, for most applications, elemental analyzes are mainly performed in the laboratory and rarely on-line, which requires the implementation of different technologies, usually complex and expensive. This work is part of a large innovative project that covers the field of on-line elemental analysis, a research area still understudied to this day. The analytical technique selected here is the Laser Induced Breakdown Spectroscopy. Indeed, its speed and its capability to analyze all states of matter without sample preparation, gives it a great potential for on-line analysis. This technique is investigated in order to achieve on-line analysis of elements contained in various liquid matrices: brines, silicone oils and petroleum products. The optimization of different measurement parameters is performed, including an experimental design based approach. Different liquid sampling configurations and several LIBS setups are designed in order to tackle the issues encountered. Finally, a transposition to the industrial world is presented through on-line monitoring of sulfur in petroleum products on an industrial pilot process. The results are promising, but improving the stability of measurements over time still requires further research

The presented diploma thesis deals with the elemental composition of hard tissues – human and murine jaws studied by laser-induced plasma spectroscopy (LIBS). Samples of human teeth contained a disease called ankylosis and the difference in elemental composition of healthy and diseased tissue was observed to localize ankylosis in the tooth. When evaluating the map of the spatial distribution of phosphorus and calcium, a decrease in the concentration of these elements in the ankylosis infected area was observed. Furthermore, murine jaws containing lead were analyzed. When assessing the spatial distribution of lead in tissue, it was found that lead was incorporated in murine teeth in the enamel at the tip of the incisor and molars. In conclusion, LIBS method achieved good results considering the detection of the elemental distribution of hard tissues. It enables to differentiate parts of the tooth in terms of elemental composition and tissue hardness and also to detect changes in the matrix caused by a disease or bioaccumulation of heavy metals.

<div> Challenges in the semiconductor industry have resulted in the discovery of a plethora of promising materials and devices such as the III-Vs (InGaAs, GaSb, GaN/InGaN) and 2D materials (Transition-metal dichalcogenides [TMDs]) with wide-ranging applications from logic devices, optoelectronics to biomedical devices. Performance of these devices suffer significantly from scattering processes such as polar-optical phonons (POP), charged impurities and remote phonon scattering. These scattering mechanisms are long-ranged, and a quantitative description of such devices require non-local scattering calculations that are computationally expensive. Though there have been extensive studies on coherent transport in these materials, simulations are scarce with scattering and virtually non-existent with non-local scattering. </div><div> </div><div>In this work, these scattering mechanisms with full non-locality are treated rigorously within the Non-Equilibrium Green's function (NEGF) formalism. Impact of non-locality on charge transport is assessed for GaSb/InAs nanowire TFETs highlighting the underestimation of scattering with local approximations. Phonon, impurity scattering, and structural disorders lead to exponentially decaying density of states known as Urbach tails/band tails. Impact of such scattering mechanisms on the band tail is studied in detail for several bulk and confined III-V devices (GaAs, InAs, GaSb and GaN) showing good agreement with existing experimental data. A systematic study of the dependence of Urbach tails with dielectric environment (oxides, charged impurities) is performed for single and multilayered 2D TMDs (MoS2, WS2 and WSe2) providing guideline values for researchers. </div><div><br></div><div>Often, empirical local approximations (ELA) are used in the literature to capture these non-local scattering processes. A comparison against ELA highlight the need for non-local scattering. A physics-based local approximation model is developed that captures the essential physics and is computationally feasible.</div>

<div>With the transistor dimensions scaling down to a few atoms, quantum phenomena - like quantum tunneling and entanglement - will dictate the operation and performance of the next generation of electronic devices, post-CMOS era. While quantum tunneling limits the scaling of the conventional transistor, Tunneling Field Effect Transistor (TFET) employs band-to-band tunneling for the device operation. This mechanism can reduce the sub-threshold swing (S.S.) beyond the Boltzmann's limit, which is fundamentally limited to 60 mV/dec in a conventional Si-based metal-oxide-semiconductor field-effect transistor (MOSFET). A smaller S.S. ensures TFET operation at a lower supply voltage and, therefore, at lesser power compared to the conventional Si-based MOSFET.</div><div><br></div><div>However, the low transmission probability of the band-to-band tunneling mechanism limits the ON-current of a TFET. This can be improved by reducing the body thickness of the devices i.e., using 2-Dimensional (2D) materials or by utilizing heterojunction designs. In this thesis, two promising methods are proposed to increase the ON-current; one for the 2D material TFETs, and another for the III-V heterojunction TFETs.</div><div><br></div><div>Maximizing the ON-current in a 2D material TFET by determining an optimum channel thickness, using compact models, is presented. A compact model is derived from rigorous atomistic quantum transport simulations. A new doping profile is proposed for the III-V triple heterojunction TFET to achieve a high ON-current. The optimized ON-current is 325 uA/um at a supply voltage of 0.3 V. The device design is optimized by atomistic quantum transport simulations for a body thickness of 12 nm, which is experimentally feasible.</div><div> </div><div>However, increasing the device's body thickness increases the atomistic quantum transport simulation time. The simulation of a device with a body thickness of over 12 nm is computationally intensive. Therefore, approximate methods like the mode-space approach are employed to reduce the simulation time. In this thesis, the development of the mode-space approximation in modeling the triple heterojunction TFET is also documented.</div><div><br></div><div>In addition to the TFETs, quantum computing is an emerging field that utilizes quantum phenomena to facilitate information processing. An extra chapter is devoted to the electronic structure calculations of the Si:P delta-doped layer, using the empirical tight-binding method. The calculations agree with angle-resolved photoemission spectroscopy (ARPES) measurements. The Si:P delta-doped layer is extensively used as contacts in the Phosphorus donor-based quantum computing systems. Understanding its electronic structure paves the way towards the scaling of Phosphorus donor-based quantum computing devices in the future.</div>

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / This study reports the synthesis and characterization of cobalt oxide nanoparticles using a microwave technique and chemical precipitation with oxidation method. Cobalt complexes were prepared using carboxylic acids (acetic acid, heptanoic acid, and stearic acid) as ligands. The complexes were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Elemental analyses (EA). Cobalt oxide nanoparticles were synthesized from the complexes via a microwave-assisted technique. A precipitation oxidation preparation reaction was used varying different parameters like pH, time, oxidising agent, heating method and cobalt precursor. The use of the cobalt nitrate and cobalt acetate as cobalt precursors resulted in spherical and cubic nanoparticles respectively. Cobalt precursors containing a longer hydrocarbon chain length, for instance cobalt heptanoate, did not yield cobalt oxide nanoparticles with the precipitation oxidation reaction due non- solubility of the complex. Using cobalt acetate as precursor, an increase in the pH from 7.91 to 10.18 caused the cobalt oxide nanoparticles shape to become well defined cubes with a narrower size range and CoOOH needles formed when the pH was further increased to 12.26. The optimum pH of 10.18 yielded cubic cobalt oxide particles having an average size of 25.45 nm with a standard deviation of 6.12. The nanoparticle size decreased from 35.70 nm to 4.45 nm when the oxygen oxidant was replaced with hydrogen peroxide. Conventional heating with a hotplate yielded nanoparticles with a more homogenous shape and size than microwave heating. The size of the nanoparticles increased from 22.81 nm to 25.45 nm when reaction time changed from 16 hours to72 hours.