Mott insulators are a family of materials in which strong electron-electron interactions induce an unconventional insulating state in the system that would otherwise behave as an electrical conductor according to the non-interacting band theory. In particular, the nature of the Mott metal-insulator transition (MIT) has been the subject of intense research interest because it can involve a complicated interplay between magnetic and electronic properties. In some Mott systems, Mott transitions occur in the one-step process, from an antiferromagnetic insulator (AFI) to a paramagnetic metal phase (PMM), while in other Mott systems a two-step transition with an intermediate antiferromagnetic metal (AFM) phase can be observed. Since 2015, the muon spin relaxation (𝜇SR) group at Columbia University started systematic 𝜇SR studies on a series of Mott systems, including one-step transition Mott systems 𝑅𝐸NiO₃ and V₂O₃, as well as two-step transition Mott systems Ba(Co, Ni)S₂, Ni(S, Se)₂ and (La, Sr)VO₃. This dissertation first introduces the comprehensive 𝜇SR research on multiple families of Mott systems conducted by our 𝜇SR group, including 𝑅𝐸NiO₃, V₂O₃, and BaCoS₂. Then the 𝜇SR experimental findings on the Mott system NiS₂₋ₓSeₓ will be presented, which is the most extensively studied material in this thesis. The NiS₂₋ₓSeₓ system is of particular interest because there is a large region of intermediate AFM state emerging between AFI and PMM states with Se doping, making it an ideal platform to provide information on static magnetism in the AFM state and thus can help us better understand the evolution of magnetic NiS₂₋ₓSeₓ, with our key findings being: (1) The AFM state of the NiS₂₋ₓSeₓ system shows significantly random spin correlations, and the magnetic order is suppressed by a gradual reduction of the ordered moment size, with a nearly full ordered volume fraction until very close to the AFM-PMM boundary. (2) No signature of dynamic critical behavior was observed in the thermal phase transition, indicating a first-order thermal phase transition. The next part of this dissertation presents our computational simulations on the NiS₂₋ₓSeₓ system. Dipolar field simulations have shown that only the combination of easy axis randomization and Ni moment dilution in NiS₂ can lead to the internal field distribution corresponding to the observed 𝜇SR spectrum in the AFM region. Also, this picture could qualitatively explain the neutron and muon results consistently, thus reconciling the seemingly contradicting experimental results by 𝜇SR and the previous neutron scattering studies shown in the AFM region. Furthermore, we propose a percolation model that can capture both the charge and spin connections of the interpenetrating percolating spin and charge networks in the NiS₂₋ₓSeₓsystem, which raises the possibility of "compromising metallicity and magnetic order" in the two-step Mott transition evolving AFI to AFM to PMM states in NiS₂₋ₓSeₓ.

Nitrogen-doped carbon materials have garnered much interest due to their abilities to behave as electrocatalysts for reactions important in energy production (oxygen reduction) and biosensing (hydrogen peroxide reduction). Here, we demonstrate fabrication methods and determine electrocatalytic properties of nitrogen-doped screen-printed carbon (N-SPCE) electrodes. Nitrogen doping of graphite was achieved through a simple soft-nitriding technique which was then used in lab-formulated screen-printing inks to prepare N-SPCEs. N-SPCEs displayed good electrocatalytic activity, reproducibility and long term stability towards the electrochemical reduction of hydrogen peroxide. N-SPCEs exhibited a wide linear range (20 µM to 5.3 mM), reasonable limit of detection of 2.5 µM, with an applied potential of -0.4 V (vs. Ag/AgCl). We also demonstrate that nitrided-graphite can similarly be used as a platform for the deposition of electrocatalytic platinum nanoparticles, resulting in Pt-N-SPCEs with a lower limit of detection (0.4 µM) and better sensitivity (0.52 µA cm-2 µM-1) towards H2O2 reduction.

L’objet de cette thèse est d’étudier le dopage ex-situ de nanofils semiconducteurs IV pour des applications en électronique, spintronique ou encore thermoélectricité. Deux techniques de dopage ont été explorées : l’implantation par faisceaux d’ions et le Spin-On-Doping (SOD).L’implantation d’ions Mn a été testée dans les nanofils de Ge avec l’objectif de synthétiser un matériau semi-conducteur ferromagnétique dilué. Une concentration en Mn de quelques pourcents peut être atteinte sans amorphisation du fil ni formation de précipités, ce qui est très encourageant. Lors d’expériences d’implantation réalisées in situ dans un microscope électronique en transmission, une forte exaltation de la pulvérisation sous irradiation électronique a été constatée.La technique SOD consiste à faire diffuser thermiquement les impuretés de type p ou n contenues une résine de type HSQ (Hydrogen silsesquioxane) qui enrobe les nanofils. Le recuit de la HSQ (dopée ou non) engendre une modification structurale des nanofils (bien que cette technique soit considérée comme non destructive). Lors du recuit, une transformation partielle de la phase diamant 3C vers la phase hexagonale 2H, a en effet été observée dans les nanofils de Si et de Ge, au-delà de 500 et 400°C respectivement. Les paramètres essentiels de la transformation de phase sont la contrainte de cisaillement résultant de la densification de la résine et le budget thermique. Les nanofils de Ge deviennent amorphes au-delà de 650°C, ce qui interdit en pratique leur dopage par SOD.Les caractérisations électriques ont été réalisées sur des nanofils de Si réalisés par gravure ionique réactive sur substrats orientés (111) et contactés en matrice ou individuellement. Pour le contactage de nanofils uniques en configuration NW-FET (nanowire field effect transistors), un procédé technologique basé sur la lithographie électronique a dû être développé. Les difficultés à surmonter étaient relatives à la faible longueur des nanofils. Diverses techniques de caractérisation ont été mises en œuvre (I-V en configuration verticale ou horizontale de type TLM (Transient Linear Measurement), SSRM (scanning spreading resistance microscopy), EBIC (electron beam induced current). Les mesures collectives concernent des ensembles de nanofils de type p enrobés dans une résine qu’elle soit dopante ou non. Pour observer un courant notable dans la structure, un recuit est nécessaire. Au-delà d’une température de recuit de 600°C, une polarisation négative du substrat induit un comportement conforme au mécanisme SCLC (space charge limited current) attendu pour des nanofils faiblement dopés enrobés dans une matrice isolante. En positif, on observe une caractéristique I(V) ohmique et une densité de courant jusqu’à 500 fois plus élevée dans les nanofils que dans le substrat. Ce comportement pourrait être dû à l’influence des états d’interface provenant de la technique de gravure. Cette hypothèse est confortée par le fait qu’après recuit à 900°C, le courant en direct s’explique en considérant dans les fils un dopage proche de celui du substrat, et surtout par l’observation en SSRM d’une couche conductrice interfaciale entre fils et HSQ. Elle permet aussi d’interpréter les mesures sous pointes faites sur les fils de type n. Le mode de transport SCLC a également été observé pour des nanofils individuels contactés sous pointe ou par lithographie. Ces mesures n’ont pas mis directement en évidence l’influence de la transformation de phase.Le dopage de type n ou p par SOD s’avère efficace après recuit à 900°C. Dans ce cas, les comportements observés, contacts ohmiques et jonctions p-n, peuvent être interprétés plus simplement en considérant des niveaux de dopage supérieurs à 3×10¹⁶ cm⁻³ en type p et 2×10¹⁶ cm⁻³ en type n. Ces valeurs déduites des résistivités mesurées sont sans doute très sous-estimées puisque la mobilité dans les fils est sans doute inférieure à celle du volume. / This thesis aims at studying the ex-situ doping of semiconducting nanowires (NWs) for applications in electronics, spintronics or thermoelectricity. Two widely used techniques have been envisaged: ion beam implantation and Spin-On-Doping (SOD).The ion beam implantation of Mn ions has been tested in Ge NWs in an attempt to form a 1D diluted magnetic semiconductor structure. A Mn concentration of few percents can be achieved without amorphization of the nanowire nor clustering, what is very promizing. During implantation done in situ in a transmission electron microscope, a strong enhancement of the sputtering under electron irradiation has been observed.The doping by SOD results from the thermal diffusion of p-type or n-type impurities contained in a HSQ (Hydrogen silsesquioxane) resist in which the NWs are embedded. The curing of the HSQ resist (doped or not) leads to a structural modification of nanowires (while SOD is generally assumed to be non-destructive). As a result of the annealing, a partial transformation of the 3C diamond phase towards the 2H hexagonal phase is observed in Si and Ge nanowires, above 500 et 400°C respectively. The main parameters of that phase transformation are the shear stress due to the HSQ densification and the thermal budget. Ge NWs are found to turn to amorphous above 650°C, what renders SOD practically unusable for Ge NWs. Two methods are currently used for the fabrication of nanowires, the VLS (vapor-liquid-solid) growth and reactive ion etching of (111) Si wafers. For practical reasons, etched NWs were used for the study of their electrical properties.The electrical characterizations were done on arrays of Si NWs embedded in a HSQ matrix or on single NWs. For contacting single NWs in the NW-FET(nanowire field effect transistors) configuration , a process based on electron beam lithography has been developed. The issues to be solved were related to the low length of NWs. Various measurement techniques were used: I-V in two tips or TLM (Transient Linear Measurement) arrangement, SSRM (scanning spreading resistance microscopy), EBIC (electron beam induced current). Collective measurements were done on arrays of p-type NWs embedded in a HSQ resist, doped or not. It was firstly observed that an annealing is needed to observe a noticeable current in the structure. Above an annealing temperature of 600°C, for a negative bias applied to the substrate, the observed behavior can be described by the SCLC (space charge limited current) mechanism expected for poorly doped NWs in an isolating matrix, while a positive bias applied to the substrate results in an ohmic characteristic and in a current density up to 500 times higher in the NWs than in the substrate. This unexpectedly high intensity in direct bias may be attributed to electrically active surface states resulting from the etching process. This hypothesis is conforted by the fact that an annealing at 900°C (without extra doping) the measured intensity can be explained by assuming the same doping level in NWS than in the substrate. In addition, an interfacial conductive between resist and nanowires can be observed by SSRM. These interfacial states can be also involved for understanding the measurements done on n-type NWS. The SCLC mechanism of transport has been also observed for single NWs contacted by tips or by lithographied contacts. These measurements were not able to evidence the effect of the phase transformation on the electrical properties.P-type and n-type doping by SOD becomes effective after annealing at 900°C. After doping, ohmic or rectifying behaviours on p-type substrate are observed as expected. That renders more easy the interpretation of results, by assuming doping levels in the NWs of 3×10¹⁶ cm⁻³ and 2×10¹⁶ cm⁻³ for p-type and n-type respectively. These values as deduced from resistivities are probably very underestimated as the mobilities in NW are probably much lower than in the bulk.

Bien que l’effet psychotrope des antidépresseurs soit bien connu, afin de corriger les conséquences du stress et de renforcer la confiance en soi, de nombreux autres effets pharmacologiques, notamment périphériques, doivent encore être approfondis. Les antidépresseurs inhibiteurs de la recapture de la sérotonine (ISRS) peuvent avoir un effet bénéfique sur la performance physique en participant à une réparation et à une croissance plus rapides des muscles. Il a récemment été démontré que la sérotonine était impliquée dans la récupération de la force musculaire chez un modèle murin de myopathie de Duchenne (Gurel et al., 2015). Les antidépresseurs tels que les inhibiteurs sélectifs de la recapture de la sérotonine (ISRS) sont largement utilisés pour traiter divers troubles de la santé mentale, tels que la dépression modérée à sévère et l’anxiété. Les deux symptômes contribuent à l’insomnie, à la perte d’appétit, au manque de motivation et à une fatigue physique accrue. Ces symptômes peuvent nuire aux performances physiques des athlètes, en particulier de ceux qui développent des habiletés et des techniques spécifiques à un sport, reçoivent des volumes d’entraînement plus importants à différentes intensités et participent à des compétitions plus fréquentes. Par conséquent, les athlètes peuvent utiliser des médicaments qui renforcent la motivation et / ou améliorent la condition physique générale en réduisant les symptômes dépressifs. L'utilisation d'antidépresseurs n'est pas encore interdite dans les sports d'élite. Des rapports récents sur le dopage associé aux ISRS montrent une tendance croissante de son utilisation chez les athlètes en bonne santé. La consommation d'antidépresseurs chez les athlètes a augmenté dans différents sports au cours de la dernière décennie, notamment les sports d'endurance.. Notre projet doit donc permettre de caractériser les conséquences d'un traitement chronique par ISRS sur les performances physiques chez la souris et de mettre en évidence le ou les mécanismes impliqués, en particulier la variation du shunt métabolique sérotonine / kynurénine, ainsi que les modifications de biomarqueurs, variations potentiellement utilisables chez l'homme dans la lutte contre le dopage.Nous aimerions élucider notre travail de recherche dans les articles suivants:Article 1: Nous avons étudié les effets de l'exercice et de la fluoxétine seuls ou en association avec un traitement prolongé à la fluoxétine (18 mg / kg / jour) et un exercice physique d'endurance (six semaines) chez la souris mâle BalbC / j, sur tapis roulant. Nous avons ensuite évalué l'activité neurocomportementale, les marqueurs musculaires du stress oxydatif et les modifications du métabolisme du tryptophane dans les tissus plasmatiques, musculaires et cérébraux des souris BalbC / J. En général, nous nous sommes concentrés sur la vitesse aérobie la plus élevée, le temps d’endurance jusqu’à l’épuisement, la force musculaire des membres antérieurs en saisissant un mesureur de force, des tests neurocomportementaux tels que le test en champ ouvert et élevé et le labyrinthe, l’activité enzymatique mitochondriale (activité du citrate synthase et du cytochrome C oxydase) dans le muscle gastrocnémien. , marqueur de stress oxydant tel que le test DHE (Dihydroéthidium) et DCF-DA (Dichlorofluorscine diacétate).Article 2: Nous avons étudié les effets de l’exercice et de la fluoxétine seule ou les effets combinés d’un traitement prolongé à la fluoxétine (18 mg / kg / jour) et d’un exercice d’endurance physique (six semaines) chez la souris mâle BalbC / j, sur tapis roulant. / As much as the psychotropic effect of antidepressants is well known, correcting the consequences of stress and boosting self-confidence, so many other pharmacological effects, peripheral in particular, remain to be deepened. Serotonin reuptake inhibitor antidepressants (SSRIs) may have a beneficial effect on physical performance by participating in faster muscle repair and growth. It has recently been shown that serotonin was involved in the recovery of muscle strength in a mouse model of Duchenne myopathy (Gurel et al., 2015).Antidepressants such as selective serotonin reuptake inhibitors (SSRIs) are widely used to treat various mental health disorders, such as moderate-to-severe depression and anxiety. Both symptoms contribute to insomnia, loss of appetite, lack of motivation and increased physical fatigue. These symptoms can impair physical performances for athletes, more specifically for those who develop sport-specific skills and techniques, receive higher training volumes at various intensities, and participate in more frequent competitions. Therefore athletes may use drugs that enhance motivation and/or improve overall fitness by reducing depressive symptoms. The use of antidepressants is not yet forbidden in elite sports. Recent reports on doping associated with SSRIs show an increasing trend of its usage among healthy athletes. The antidepressants intake among athletes has increased in different sports over the last decade, especially endurance sports. The antidepressants Bupropion and Amineptine were removed from the list of banned substances.Our project must therefore make it possible to characterize the consequences of chronic treatment with SSRIs on the physical performance in mice and to highlight the mechanism (s) involved, in particular the variation of the serotonin / kynurenine metabolic shunt, as well as the modifications of biomarkers, potentially usable variations in humans in the fight against doping.We would like to elucidate our research work in the following articles:Article 1: We studied the effects of exercise and fluoxetine alone or in combination of long-term fluoxetine treatment (18mg/kg/day) and endurance physical exercise (six weeks) in male balbC/j mice, on animal treadmill. Subsequently we evaluated neurobehavioral activity, muscle markers of oxidative stress, and changes in tryptophan metabolism in plasma, muscle and brain tissues in the BalbC/J mice. Generally we focused on the highest aerobic velocity, endurance time until exhaustion, forelimb muscle strength by gripping strength meter, neurobehavioral tests such as open field and elevated plus maze test, mitochondrial enzyme activity (Citrate synthase and cytochrome-C oxidase activity) in gastrocnemius muscle, oxidative stress marker such as DHE (Dihydroethidium) and DCF-DA (Dichlorofluorscine di-acetate)test.Article 2: We studied the effects of exercise and fluoxetine alone or combinative effects of long-term fluoxetine treatment (18mg/kg/day) and endurance physical exercise (six weeks) in male balbC/j mice, on animal treadmill. After the mentioned exercise protocol we focused on changes in tryptophan (TRP) metabolism in plasma, muscle and brain tissues in the BalbC/J mice. To confirm the metabolomic, we also studied the KP related enzyme related genes and proteins by the modern required materials and methods. We correlated the result of article1 with the metabolites level of kynurenine pathway of tryptophan metabolism. We studied the expression of transcriptor factor PGC1α level in muscle which is induced by physical exercise(Agudelo et al., 2014). PGC1α subsequently induce the expression of kynurenine aminotransferase 1 and 2 (KAT1 and KAT2) in skeletal muscles, which convert kynurenine (KYN) to kynurenic acid (KYNA). Conversion of kynurenine to kynurenic acid decrease the level of kynurenine and quinolinic acid an NMDA receptor agonist and a neurotoxic compound.

Au cours de cette thèse, j’ai étudié la possibilité et les avantages d’utiliser des contacts nanométriques au-dessous de 1 µm. Des simulations analytiques et numériques ont montré que ces contacts nanométriques sont avantageux pour les cellules en silicium cristallin comme ils peuvent entrainer une résistance ohmique négligeable. Mon travail expérimental était focalisé sur le développement de ces contacts en utilisant des nanoparticules de polystyrène comme un masque. En utilisant la technique de floating transfert pour déposer les nanosphères, une monocouche dense de nanoparticules s’est formée. Cela nécessite une gravure par plasma de O2 afin de réduire la zone de couverture des NPs. Cette gravure était faite et étudiée en utilisant la technique de plasmas matriciels distribués à résonance cyclotronique électronique (MD-ECR). Une variété de techniques de créations de trous nanométriques était développée et testée dans des structures de couches minces et silicium cristallin. Des trous nanométriques étaient formés dans la couche de passivation, de SiO2 thermique, du silicium cristallin pour former des contacts nanométriques dopés. Un dopage local de bore était fait, à travers ces trous nanométriques par diffusion thermique et implantation ionique. En faisant la diffusion, le dopage local était observé par CP-AFM en mesurant des courbes de courant-tension à l’intérieur et à l’extérieur des zones dopées et en détectant des cellules solaires nanométriques. Par contre le processus de dopage local par implantation ionique a besoin d’être améliorer afin d’obtenir un résultat similaire à celui de diffusion. / The use of point contacts has made the Passivated Emitter and Rear Cell design one of the most efficient monocrystalline-silicon photovoltaic cell designs in production. The main feature of such solar cell is that the rear surface is partially contacted by periodic openings in a dielectric film that provides surface passivation. However, a trade-off between ohmic losses and surface recombination is found. Due to the technology used to locally open the contacts in the passivation layer, the distance between neighboring contacts is on the order of hundreds of microns, introducing a significant series resistance.In this work, I explore the possibility and potential advantages of using nanoscale contact openings with a pitch between 300 nm to 10 µm. Analytic and numerical simulations done during the course of this thesis have shown that such nanoscale contacts would result in negligible ohmic losses while still keeping the surface recombination velocity Seff,rear at an acceptable level, as long as the recombination velocity at the contact (Scont) is in the range from 103-105 cm/s. To achieve such contacts in a potentially cost-reducing way, my experimental work has focused on the use of polystyrene nanospheres as a sacrificial mask.The thesis is therefore divided into three sections. The first section develops and explores processes to enable the formation of such contacts using various nanosphere dispersion, thin-film deposition, and layer etching processes. The second section describes a test device using a thin-film amorphous silicon NIP diode to explore the electrical properties of the point contacts. Finally, the third section considers the application of such point contacts on crystalline silicon by exploring localized doping through the nanoholes formed.In the first section, I have explored using polystyrene nanoparticles (NPs) as a patterning mask. The first two tested NPs deposition techniques (spray-coating, spin-coating) give poorly controlled distributions of nanospheres on the surface, but with very low values of coverage. The third tested NPs deposition technique (floating transfer technique) provided a closely-packed monolayer of NPs on the surface; this process was more repeatable but necessitated an additional O2 plasma step to reduce the coverage area of the sphere. This was performed using matrix distributed electron cyclotron resonance (MD-ECR) in order to etch the NPs by performing a detailed study.The NPs have been used in two ways; by using them as a direct deposition mask or by depositing a secondary etching mask layer on top of them.In the second section of this thesis, I have tested the nanoholes as electrical point-contacts in thin-film a-Si:H devices. For low-diffusion length technologies such as thin-film silicon, the distance between contacts must be in the order of few hundred nanometers. Using spin coated 100 nm NPs of polystyrene as a sacrificial deposition mask, I could form randomly spaced contacts with an average spacing of a few hundred nanometers. A set of NIP a-Si:H solar cells, using RF-PECVD, have been deposited on the back reflector substrates formed with metallic layers covered with dielectrics having nanoholes. Their electrical characteristics were compared to the same cells done with and without a complete dielectric layer. These structures allowed me to verify that good electrical contact through the nanoholes was possible, but no enhanced performance was observed.In the third section of this thesis, I investigate the use of such nanoholes in crystalline silicon technology by the formation of passivated contacts through the nanoholes. Boron doping by both thermal diffusion and ion implantation techniques were investigated. A thermally grown oxide layer with holes was used as the doping barrier. These samples were characterized, after removing the oxide layer, by secondary electron microscopy (SEM) and conductive probe atomic force microscopy (CP-AFM).

Title: Nutritional supplements as permitted doping Objectives: The main goal of this thesis is to find out for what specific reasons users of additional resources are willing to invest their money in the purchase of supplements, and also what is the decisive factor in choosing a particular type of product. Methods: To find out the knowledge of people sports at a professional or amateur level in the field of nutritional supplements, the method of questionnaire sociological survey was used. This method was used in order to determine the awareness of athletes about this topic, their possible influence by advertising or product prices, and also to ensure the complete anonymity of respondents. Results: This thesis describes the topic of nutritional supplements among athletes across all possible sports. We have found that the sports population has a very good overview of nutritional supplements, but at the same time it does not give as much of the right balance of their food. Keywords: sport, management, marketing, nutritional supplements, doping, prohibited substances

No description available.

Supercapacitor is the best potential candidate of the energy storage system due to the superior charge or discharge efficiency, high power density (>10 kW kg-1), and long cycling life. Porous carbon materials as the promising electrode material have been widely used in supercapacitor. In fact, conventional porous carbon supercapacitor electrodes cannot fulfil the growing demand of high energy and power densities of supercapacitor. A large number of studies show that nitrogen doping can change the surface electronic structure of carbon materials, thus significantly improving the electrochemical properties. In addition to, the pore structure and morphology of carbon materials have great influence on the electrochemical performance. In this work, we firstly fabricated nitrogen-doped porous carbon nanotubes by using a simple mixed salts (NaCl/ZnCl2) activation strategy. The as-obtained porous carbon nanotubes exhibited excellent electrochemical performance in supercapacitor. Furthermore, two- dimension nitrogen-doping porous nanosheets were prepared by a salt template-assisted monomer deposition method. In this study, by optimizing the synthesis conditions, the as-obtained carbon nanosheets showed a high specific capacitance of 277 F g-1 at 1 A g-1 and excellent cycle stability retained 91 % after 10,000 cycles. / College of Engineering, Science and Technology / M. Tech.( Civil and Chemical Engineering

The metamagnetic transition from an antiferromagnetic (AF) to the ferromagnetic (FM) state in FeRh alloys and the accompanying magnetocaloric effect (MCE) have been investigated with a particular attention to the sample preparation routes. Direct measurements of the adiabatic temperature change show that the MCE in FeRh remains partly reversible despite the hysteresis and exceeds the effect in the benchmark material Gd by 15 %. The AF−FM transition is strongly affected by the microstructure that is formed depending on the heat treatment parameters. This can explain the discrepancy in the reported data over 80 years of research. The effect on the magnetic properties is found to originate from the interaction of the major α'-phase with the secondary γ-phase that has been typically ignored for its negligible magnetic contribution. The nominal composition of the magnetic α'-phase is found to differ from the actual one for binary and substituted FeRh alloys. The elements can be redistributed within the two phases in such a way, that the actual amount of the doping element in the α'-phase that experiences the AF−FM transition is greatly reduced. This demonstrates the significance of microstructural studies, especially when comparing experimental results with theoretical calculations and developing routes to tune and optimize the magnetocaloric properties of materials.

No description available.