Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices.

L'hydrate de méthane est un cristal non-stœchiométrique dans lequel les molécules d'eau forment des cages liées par liaison hydrogène qui piégent des molécules de méthane. Des ressources abondantes en hydrate de méthane peuvent être trouvées sur Terre, en particulier dans les roches poreuses minérales (par exemple, l'argile, le permafrost, les fonds marins, etc.). Pour cette raison, la compréhension de la thermodynamique et de la cinétique de formation de l'hydrate de méthane confiné dans des milieux poreux suscite beaucoup d'attention. Dans cette thèse, nous combinons la modélisation moléculaire et des approches théoriques pour déterminer la thermodynamique et la cinétique de formation de l'hydrate de méthane confiné dans des milieux poreux. Tout d'abord, l'état de l'art en matière de thermodynamique et de cinétique de formation de l'hydrate de méthane est présenté. Deuxièmement, différentes stratégies de simulation moléculaire, y compris des calculs d'énergie libre utilisant l'approche de la molécule d'Einstein, la méthode de coexistence directe et la technique textit{hyperparallel tempering}, sont utilisées pour évaluer la stabilité de l'hydrate de méthane à différentes températures et pressions. Troisièmement, parmi ces stratégies, la méthode de coexistence directe est choisie pour déterminer le déplacement du point de fusion lors du confinement dans des pores, $Delta T_m = T_m^{pore} - T_m^{bulk} $ où $ T_m^{pore}$ et $T_m^{bulk}$ sont les températures de fusion d'hydrate de méthane non confiné et confiné. Nous avons constaté que le confinement diminue la température de fusion, $T_m^{pore} < T_m^{bulk} $. Le changement de température de fusion en utilisant la méthode de la coexistence directe est cohérent avec l'équation de Gibbs-Thompson qui prédit que le décalage de la température de fusion dépend linéairement de l'inverse de la taille des pores, $Delta T_m/T_m^{bulk} sim k_{GT}/ D_p$. La validité quantitative de cette équation thermodynamique classique pour décrire de tels effets de confinement et de surface est également abordée. Les tensions de surface des interfaces hydrate-substrat et eau-substrat sont déterminées à l'aide de la dynamique moléculaire pour valider quantitativement l'équation de Gibbs-Thompson. Des simulations de dynamique moléculaire sont également effectuées pour déterminer les propriétés thermodynamiques importantes de l'hydrate de méthane non confiné et confiné: (a) conductivité thermique $lambda$ en utilisant le formalisme de Green-Kubo et la fonction d'autocorrélation du flux thermique; (b) expansion thermique $alpha_P$ et compressibilité isotherme $kappa_T$. Enfin, des conclusions et perspectives pour des travaux futurs sont présentées. / Methane hydrate is a non-stoichiometric crystal in which water molecules form hydrogen-bonded cages that entrap methane molecules. Abundant methane hydrate resources can be found on Earth, especially trapped in mineral porous rocks (e.g., clay, permafrost, seafloor, etc.). For this reason, understanding the thermodynamics and formation kinetics of methane hydrate confined in porous media is receiving a great deal of attention. In this thesis, we combine computer modeling and theoretical approaches to determine the thermodynamics and formation kinetics of methane hydrate confined in porous media. First, the state-of-the-art on the thermodynamics and formation kinetics of methane hydrate is presented. Second, different molecular simulation strategies, including free energy calculations using the Einstein molecule approach, the direct coexistence method, and the hyperparallel tempering technique, are used to assess the phase stability of bulk methane hydrate at various temperatures and pressures. Third, among these strategies, the direct coexistence method is chosen to determine the shift in melting point upon confinement in pores, $Delta T_m = T_{m}^{pore} - T_{m}^{bulk}$ where $T_m^{pore}$ and $T_m^{bulk}$ are the melting temperatures of bulk and confined methane hydrate. We found that confinement decreases the melting temperature, $T_m^{pore}<T_m^{bulk}$. The shift in melting temperature using the direct coexistence method is consistent with the Gibbs-Thompson equation which predicts that the shift in melting temperature linearly depends on the reciprocal of pore width, i.e., $Delta T_m/T_m^{bulk} sim k_{GB}/D_p$. The quantitative validity of this classical thermodynamic equation to describe such confinement and surface effects is also addressed. The surface tensions of methane hydrate-substrate and liquid water-substrate interfaces are determined using molecular dynamics to quantitatively validate the Gibbs-Thompson equation. Molecular dynamics simulations are also performed to determine important thermodynamic properties of bulk and confined methane hydrate: (a) thermal conductivity $lambda$ using the Green-Kubo formalism and the autocorrelation function of the heat-flux and (b) the thermal expansion $alpha_P$ and isothermal compressibility $kappa_T$. Finally, some conclusions and perspectives for future work are given.

Le dioxyde d'uranium irradié (UO2), combustible nucléaire des réacteurs à eau pressurisée, contient deux populations de cavités saturées par des gaz de fission : i. des cavités intergranulaires plutôt lenticulaires, dont la taille varie de quelques dizaines à plusieurs centaines de nanomètres, ii. des cavités intragranulaires plutôt sphériques, dont la taille est de l'ordre du nanomètre. Des travaux récents ont montré qu'il existe un effet de surface à l'échelle des cavités nanométriques qui modifie le comportement élastique effectif du combustible. Ce travail vise à proposer un modèle micromécanique analytique capable de tenir compte de cette microstructure hétérogène ainsi que de l'effet de surface afin de décrire le comportement élastique macroscopique de l'UO2 irradié. La démarche mise en oeuvre est fondée sur une modélisation multi-échelles et s'appuie sur des techniques d'homogénéisation en mécanique des matériaux. L'UO2 irradié est décrit comme un matériau poreux contenant des nanocavités sphériques (cavités intragranulaires) et sphéroïdales (cavités intergranulaires), sous pression et orientées aléatoirement. L'effet de surface présent à l'échelle nanométrique est pris en compte via un modèle d'interface imparfaite cohérente entre la matrice et les cavités. Un modèle original fondé sur l'approche par motifs morphologiques représentatifs a été développé afin de décrire le comportement élastique effectif de ce milieu hétérogène. Le modèle analytique proposé repose sur des hypothèses simplificatrices dont la pertinence est évaluée à partir de simulations numériques par éléments finis qui s'appuient sur une formulation spécifique afin de tenir compte de la présence d'interfaces imparfaites cohérentes. / The irradiated uranium dioxide (UO2), which is the nuclear fuel of pressurized water reactors, contains two populations of cavities saturated by fission gaz: i. intergranular cavities almost lenticular in shape whose size ranges between few tens to several hundred nanometers, ii. intragranular cavities, almost spherical in shape whose size is of the order of the nanometer. Recent studies have shown the existence of a surface effect at the scale of nanometric cavities, which influences the effective elastic behavior of the nuclear fuel. In this work, an analytical micromechanical model, which is able to take into account this heterogeneous microstructure and the surface effect at the nanometric scale, is proposed to describe the macroscopic behavior of the irradiated UO2. The approach is based on a multiscale modeling and homogenization techniques in mechanics of materials. The irradiated UO2 is described as a porous media, which contains pressurized spherical nanocavities (intragranular cavities) and randomly oriented pressurized spheroidal cavities (intergranular cavities). The surface effect is taken into account with imperfect coherent interfaces between the matrix and the cavities. A novel model based on the morphologically representative pattern approach has been developed to describe the effective elastic behavior of this heterogeneous medium. The proposed model relies on assumptions whose relevance is evaluated with finite element simulations which require a specific formulation to take into account the imperfect coherent interfaces.

Ces travaux de thèse ont pour but l'élaboration de matrices poreuses sol-gel pour une applications de détections des composés organiques microbiens, ce-ci a des fins d'identifications bactériennes.Les travaux se sont articulés autour des la synthèse et l'optimisation du matériaux d'une part puis de l'analyse des composés organiques volatiles (COV) microbiens d'autre part. Cette analyse a été envisagé selon deux voies. La première était une approche globale des profils olfactifs microbiens. La seconde était une approche ciblée des COV cibles d’importance majeur.La synthèse du matériau a été mené par voie sol-gel, les études caractéristiques ont été effectué par manométrie d'azote et diffraction des rayons X aux petits angles.La détection microbienne, via notre matériaux sol-gel, s'effectue par transduction optique. Les spectrométries d'Absorbance ou de Fluorescence ont été envisagées en mode directe (sans molécules sondes) ou en mode indirect (avec molécules sondes). / 989/5000The purpose of this thesis is to develop sol-gel porous matrices for microbial detection of microbial organic compounds for bacterial identification.The work revolved around the synthesis and optimization of materials on the one hand and then the analysis of volatile organic compounds (VOCs) on the other hand. This analysis was considered in two ways. The first was a global approach to microbial olfactory profiles. The second was a targeted approach to target VOCs of major importance.The synthesis of the material was carried out by sol-gel, the characteristic studies were carried out by nitrogen manometry and X-ray diffraction at small angles.Microbial detection, via our sol-gel material, is carried out by optical transduction. The Absorbance or Fluorescence spectrometries were considered in direct mode (without probe molecules) or in indirect mode (with probe molecules)

Cette thèse de doctorat aborde de nouvelles conceptions de films à base de résines d’ester de cyanate (CER) en présence de liquides ioniques (LIs) en tant qu'agents multifonctionnels : catalyseurs, agents de modification réactifs, renforts ou agents porogènes. Les liquides ioniques de structures et de concentrations variables accélèrent de manière significative la polycyclotrimérisation du dicyanate d’ester de bisphenol E, en l'absence de tout solvant organique supplémentaire ou additif. Les réseaux de polycyanurates resultants dopés avec des liquides ioniques aprotiques peuvent constituer des matériaux prometteurs pour la production de structures photosensibles. De tels systèmes nanocomposites permettent la séparation, larécupération et le recyclage aisés des LIs par simple extraction, ce qui permet finalement l'obtention de films nanoporeux thermostables. Les caractéristiques de la porosité de ces matériaux dépendent de la concentration des LIs dans les précurseurs CERs. Les LIs protoniques contenant des groupements fonctionnels >NH et -OH, indépendamment de leurmasse molaire, de la structure chimique du cation et de l'anion, sont incorporés chimiquement dans le réseau polycyanurate. Ainsi, les matériaux hybrides obtenus avec des fragments de liquides ioniques pourraient fournir d’excellents candidats pour des recherches futures sur les ionomères et les nanocomposites. / This PhD thesis addresses new designs of cyanate ester resin (CER) films in the presence of ionic liquids as multifunctional agents: catalysts, reactive modifiers, fillers or porogens. It should be emphasized that ionic liquids (ILs) of varying structures and concentrations significantly accelerate the polycyclotrimerization of dicyanate ester of bisphenol E, in the absence of any additional organic solvent or additive. The resulting polycyanurate networks doped with aprotic ionic liquids can be promising materials for producing photosensitive structures. Such nanocomposite systems allow for easier separation, recovery, and recycling of ILs by mere extraction, which eventually affords thermally stable nanoporous films. The porosity features of these materials depend on the concentration of ILs in the CER precursors.Protic ILs containing functional >NH and -OH groups, regardless of molar mass, chemical structure of cation and anion, chemically incorporate into the polycyanurate network, thus the resulting hybrid materials with fragments of ionic liquids could provide excellent candidates for future research in ionomers and nanocomposites.

Le confinement de la matière condensée dans un milieu nanoporeux peut induire à l'échelle nanométrique des changements structurels ou dynamiques drastiques qui conduisent finalement aux propriétés originales. Le confinement des polyélectrolytes, qui sont des polymères porteurs d'une charge électrique, présente un intérêt particulier. Dans ce projet, des membranes d'alumine nanoporeuse auto-ordonnée (nPAAMs), dont les paramètres structuraux sont réglés par la synthèse, ont été choisies comme milieu de confinement et des approches expérimentales ont été proposées pour étudier le confinement d'un polyélectrolyte fort (PE), polystyrène-sulfonate de sodium. Une partie importante de ce travail a été consacrée à la caractérisation des charges structurales et superficielles des nPAAMs. La structure et la composition du nPAAM sont caractérisées par la combinaison de la microscopie électronique à balayage et de la diffusion neutronique à petit angle (SANS). Une stratégie détaillée est proposée pour mesurer les nPAAM dans des conditions optimales en raison de leur forme anisotrope et de leur pouvoir de diffusion élevé ainsi que des informations sur leur composition chimique. La charge superficielle de la membrane a été déterminée par des mesures de potentiel d’écoulement. La charge de la paroi du pore peut être ajustée à une charge positive ou négative et l'étendue des interactions électrostatiques peut être ajustée, ce qui permet d'adapter le milieu aux études de confinement électrostatique. Le comportement de perméation et l'adsorption du polyélectrolyte à l'intérieur des pores sont étudiés par SANS en combinaison avec des mesures de perméabilité. La cinétique de l'adsorption est obtenue par le potentiel d’écoulement et la possibilité d'utiliser la réflectivité neutronique pour ces études est proposée. Ce travail fournit des approches expérimentales sur la caractérisation de l'PE en milieu confiné. / The confinement of condensed matter in nanoporous medium can induce at the nanoscale drastic structural or dynamical changes that ultimately lead to original properties. Of a specific interest is the confinement of polyelectrolytes that are polymers carrying an electrical charge. In this project, self-ordered nanoporous alumina membranes (nPAAMs), whose structural parameters are tuned through the synthesis, have been chosen as a confining medium and experimental approaches have been proposed to study the confinement of a strong polyelectrolyte (PE), sodium polystyrene-sulfonate . An important part of this work has been devoted to the structural and surface charge characterization of nPAAMs. The nPAAM’s structure and composition are characterized by combining scanning electron microscopy and small angle neutron scattering (SANS). A detail strategy is proposed for measuring the nPAAMs under optimal conditions due to their anisotropic shape and high scattering power and information on their chemical composition. The membrane’s surface charge has been determined by streaming potential measurements. The pore’s wall charge can be adjusted to positive or negative charge and the extent of the electrostatic interactions can be tuned, tailoring the medium for electrostatic confinement studies. The permeation behavior and the adsorption of the polyelectrolyte inside the pores is studied by SANS combined with flow measurements. The kinetics of the adsorption is accessed by streaming potential and the possibility to use of neutron reflectivity for such studies is proposed. This work provides experimental approaches insight into the characterization of PE under confinement.

In this doctoral project, a relatively new form of carbon material, with unique narrow pore size distribution around 7 Å and with uniform structure, has been electrochemically characterised using the single particle microelectrode technique. The carbon has been used as electrode material for supercapacitors. This type of capacitors is used as high power energy buffers in hybrid vehicles and for stationary power backup. The principle for the microelectrode technique consists of connecting a carbon particle with a carbon fibre by means of a micromanipulator. The single particle and carbon fibre together form a microelectrode. Combination of this technique with electroanalytical methods such as cyclic voltammetry and potential step measurements allows for the survey of electrochemical phenomena and for the determination of ion transport parameters inside the nanopores. A mathematical model based on Fick’s second law, for diffusion of ions inside the nanopores at non steady state, was used for the determination of effective diffusion coefficients (Deff). The coefficients were calculated from an asymptotic solution of Fick’s equation, applied for a thin layer adjacent to the external surface of the carbon particles and valid for the current response in a short time region. Another asymptotic solution was obtained, using spherical geometry and valid for the current response in a long time region. In this doctoral work, the carbon particles have been exposed to potential cycling, which mimics that of large electrodes during operation of a double layer capacitor. The potential-current response, E-I, for the nanoporous carbon, shows a pure capacitive behaviour between –0.5 V and 0.1 V vs. the Hg|HgO reference electrode. The detection of the faradaic processes beyond these potentials was possible by lowering of the voltammometric sweep rate. The electrochemical processes occurring at positive and at negative potential were investigated separately. Cyclic voltammometric measurements showed that the chemisorption of hydroxyl groups, occurring between 0.1 and 0.3 V, leads to a mild oxidation of the carbon structure, resulting in surface groups containing an oxygen atom at a specific carbon site (e.g., phenolic or quinine type). These oxygen-containing surface groups caused an increase of the specific capacitance, which remained constant throughout a number of voltammometric cycles. The Deff decreased on the other hand with the number of cycles. The Deff decreases also with the positive potential. The evaluation of Deff indicates adsorption of hydroxyl groups and an increase of the effective tortuosity of the pore system. The oxidation of the carbon particles, between 0 and 0.5 V, leads to more extensive oxidation and to surface groups containing two oxygen atoms at a single carbon site, followed by formation of carbonate ions. The oxygen-containing surface groups and carbonate ions formed at these potentials do not contribute to the specific capacitance and drastically retard or obstruct the ion transport inside the nanopores. At negative potentials the carbon particles show a dominantly capacitive behaviour. The faradaic processes taking place below –0.5 V vs. Hg|HgO reference electrode are generation and adsorption of hydrogen. These processes do not perturb significantly the electrochemical and ion transport properties of the nanoporous carbon particles. It was found that hydrogen generation occurs at –0.5 V vs. Hg|HgO and that two hydrogen oxidation processes take place at positive potentials. The results indicate that the weakly adsorbed hydrogen undergoes oxidation between 0 and 0.1 V and that the strongly adsorbed hydrogen is oxidised at more positive potentials. The single particle technique was adapted for the determination of diffusion coefficients of an organic electrolyte. The different size of the anions and cations caused different transport characteristics at negative and positive potentials. Slow cycling was found important for ion penetration inside the nanopores and for the evaluation of the effective diffusion coefficients. The effective diffusion coefficients for the nanoporous carbon using aqueous 6M KOH and 0.1M TEABF4 in acetonitrile were estimated to 1.4 (±0.8).10-9 cm2 s-1 and 1.3 (±0.4) 10-8 cm2 s-1, respectively.

För att undersöka skillnad i prestationsförmåga mellan celler sensiterade med växtextraktsbaserad färg, och celler sensiterademed ruteniumkomplex-baserad färg, samt huruvida presskraften påverkar en cells prestationsförmåga, tillverkades icke-slutna fotoelektrokemiska färg-sensiterade solceller med tunnfilmsfotoelektroder av pressad, nanoporös titandioxid. Cellerna pressades med tre olika presskrafter och sensiterades med växtextraktsfärg från rödkål, rödbeta, viol och henna, samt en ruteniumkomplex-baserad färg som fick utgöra kontrollbetingelse. För varje cell uppmättes IPCE- och iV-värde och motsvarande fyllnadsgrad (fill factor) och dessa jämfördes. Ingen signifikant skillnad kunde fastställas mellan celler pressade med olika presstryck. Bland cellerna sensiterade med växtextraktbaserad färg presterade rödbeta bäst. Cellen med högst effektivitet hade fyllnadsgraden 70%. Emellertid uppvisade de växtfärgade cellerna genomgående sämre effektivitet än de rutenium-sensiterade och fotoströmmarna var mycket låga. IPCE-värdena var allmännt låga: den bäst presterande cellen hade ett IPCE-värde på något över 0,06 i våglängdsintervallet 440-470 nm. En förklaring till detta är de övriga ämnen som förutom pigment återfinns i de växtbaserade färgerna. Dessa hindrar pigmentmättnad och förhindrar att växtfärgen når ruteniumfärgens intensitet. En annan anledning består i svårigheten att passa ihop energinivåerna i cellens elektrolyt-halvledarsystem med energinivåerna hos pigmentet i växtfärgen. / Non-sealed photoelectrochemical dye sensitised solar cells (DSSC) with pressed nanoporous TiO2 thin film photoelectrodes were manufactured for the purposes of finding out whether plant extractbased dye sensitised cells can perform as well as ruthenium complex-based dye sensitised cells and whether the pressing force affects the cell performance. The cells were pressed with three different pressing forces and sensitised with plant extracts from red cabbage, beetroot, violet and henna, as well as with a ruthenium complex-based dye for comparison. The IPCE and iV values and the corresponding fill factors of the cells were evaluated and compared. No significant difference between the cells pressed with different pressing forces could be established. Among the plant extract-based dye sensitised cells the ones sensitised with beetroot extract performed best. The cell that achieved the highest efficiency had a fill factor of 70%. Compared to the ruthenium-sensitised cells the overall performance of the plant dye sensitised cells were very poor and the produced photocurrents very low. The IPCE values were generally low: one of the best-performing cells had an IPCE value of slightly over 0.06 in the 440-470 nm wavelength ranges. One reason for this is that it is difficult to obtain a plant extract dye as intense and deep in colour as ruthenium complex-based dyes, since pigment saturation is obstructed by the presence of other chemical compounds in the plant extracts. Another is that it is a delicate and difficult matter to match the energy levels in the electrolyte-semiconductor system with the energy levels of the pigments in the plant extract dye.

The overall focus of this thesis is on the development and understanding of nanoporous layered silicates and membranes, particularly for potential applications in gas separations. Nanoporous layered materials are a rapidly growing area of interest, and include materials such as layered zeolites, porous layered oxides, layered aluminophosphates, and porous graphenes. They possess unique transport properties that may be advantageous for membrane and thin film applications. These materials also have very different chemistry from 3-D porous materials due to the existence of a large, chemically active, external surface area. This feature also necessitates the development of innovative strategies to process these materials into membranes and thin films with high performance.

Environmental separation processes such as removal of heavy metals from aqueous solutions, electrosorption in groundwater remediation, and capacitive desalination, as well as energy storage in supercapacitors, are based on the electrical double layer (EDL) formation within nanoporous carbon materials. This research is focused on the nano-scale phenomena of EDL formation inside the confined space of nanopores. The electrosorption behavior of nanoporous carbon materials was characterized by measuring the double-layer capacitance using cyclic voltammetry. The presence of micropores results in the occurrence of EDL overlapping, corresponding to a considerable loss of the double-layer capacitance. Hence, pore size distribution plays an important role in determining the double-layer capacitance. EDL formation has significant influence on ion transport and sorption inside nanopores. The data obtained by simple diffusion and electrochemically-aided diffusion experiments demonstrated the size-exclusion effects on pore accessibility by ions. A larger ion-exclusion volume prevents larger ions from penetrating inside the pores. Batch equilibrium electrosorption experiments using nanoporous carbon materials showed that selective electrosorption, imposed by the difference in the size of hydrated ions, occurs in a competitive environment. Molecular modeling based on Monte Carlo methods was developed to simulate the EDL formation in a slit-type nanopore. Simulation results indicated that the competition in asymmetries of ion charge and size not only determines the screening of surface charge but also affects the electrolyte distribution within charged pores. In a mixture of electrolytes, the charge/size competitive effects can dominate pore accessibility. Multivalent counterions with large size have the energetic advantage of screening surface charge. On the other hand, small monovalent counterions present a ¡§size affinity¡¨ to access the pores. Therefore, electrosorption selectivity of counterions with different properties is a result of a counterbalance between minimization of potential energy and size-exclusion effects. Manipulation of electrosorption selectivity to separate ions could in principle be achieved via tuning the EDL formation inside the pores. The findings of the thesis have several significant implications for the development of advanced techniques for selective separation of ions in environmental systems and energy storage.