Two-dimensional (2D) layered hexagonal boron nitride (h-BN) has become a very popular material in nanoelectronics in recent years because of its extraordinary chemical stability and thermal conductivity [1]. Recently, h-BN is also commonly used as a dielectric material [2], and research in this area is still in its early stages. The commonly used methods for fabricating h-BN include mechanical exfoliation and chemical vapor deposition (CVD). CVD is a recognized industry-compatible method for producing large-area h-BN. However, studies have shown that multilayer h-BN grown by CVD is polycrystalline and contains multiple local defects [3]. These defects and inhomogeneity cannot be avoided and lead to small amounts of atom-wide amorphous regions that have weak dielectric strength [3]. Although the general characteristics of h-BN prepared by these two fabrication methods can be learned from different works in the literature, it is difficult to study the quality of h-BN without systematically comparing the differences between the two growth methods under the same experimental conditions and with large number of samples. This also makes it difficult for researchers to choose the best-quality h-BN. In this work, the morphological characteristics and electrical properties of mechanically exfoliated h-BN and CVD-grown h-BN from different sources have been compared under different conditions. Commercially available h-BN flakes mechanically exfoliated from NIMS h-BN bulk crystal show no leakage current at electrical fields up to 25.9 MV/cm, and above this applied electrical force, the size of the conductive spots is extremely small (1.99 ± 1.81 nm2). On the contrary, “monolayer” CVD-grown h-BN samples from Graphene Supermarket were shown to be amorphous in ~20% of their area, which makes them appear discontinuous from an electrical point of view, plus they contain large thickness fluctuations up to 6 layers. Moreover, in nanoelectronic measurements collected with a conductive atomic force microscope (CAFM) working in vacuum, mechanically exfoliated h-BN showed better electrical homogeneity and presented later dielectric breakdown compared to the h-BN samples fabricated by the CVD method.

Wide bandgap semiconductor visible light-emitting diodes (LED) development has spawned the prestigious Nobel Prize in Physics in 2014. Building upon this success, the scope of research has expanded to ultrawide bandgap semiconductors, which possess immense potential in the realm of deep ultraviolet (DUV) photonics. These materials have gained attention for their applicability in various areas, including public sterilization, solar-blind DUV communication, and real-time monitoring. Leveraging on the unique ultrawide tunable bandgap property, highly crystalline capability, and robust behavior, group III-Oxide and III-Nitride semiconductors were employed for sensitive DUV photodetector (PD) and efficient DUV emission, respectively. The primary research are as follows: • III-Oxide heteroepitaxial growth optimization: The influences of substrate temperature, laser energy, and oxygen pressure for the Ga2O3 growth are systematically investigated. Furthermore, the doping capability, multi-phase availability, and bandgap tunability are demonstrated. • Flexible Ga2O3 film growth and electronic devices: Flexible Mica substrate is employed to epitaxially grow κ-phase Ga2O3 thin film. The fabricated flexible PD has an Iphoton/Idark ratio of over 107 under DUV luminescence. The fatigue test performed with 1-3 cm bending radii and 10,000 bending cycles exhibits the robust flexibility of the demonstrated DUV PD. • Transferable Ga2O3 membrane for vertical electronics: Mica as a Ga2O3 growth platform enables the large-scale transfer of ultra-thin Ga2O3 membrane from mica to arbitrary tape due to the weak interfacial bond energy. A vertical and self-powered PD is demonstrated with a responsivity of 17 mA/W under DUV illumination and 0 V bias. • Interfacial mismatch engineering for freestanding Ga2O3 membrane: Looking beyond the hetero-mismatch and engineering the interfacial thermal strain between Si-doped Ga2O3 and AlN could result in the exfoliation of freestanding ultrathin Ga2O3 membrane, allowing vertical device configuration and preferable thermal management. The exfoliation mechanism has been clarified and vertical DUV PD with high on/off ratio is demonstrated. • Efficient III-Nitride LEDs: Buried polarization-induced tunneling junction is employed to suppress electron overflow and simultaneously enhance hole injection. Furthermore, monolithic integration of DUV and visible LEDs is proposed and demonstrated by deliberately cascading DUV and visible active regions, which could replace the current integration technique in the sterilization system.

Heavy metals, oxyanions (NO3-, PO4-), pharmaceuticals, and dyes in aquatic environments are inevitable economic and health concerns. Ingestion of these contaminants, even in trace amounts, causes long and short-term serious threats to human health. Conventional pollutant mitigation strategies can be costly or ineffective. Due to high efficiency, simplicity, low price, adsorbent reuse, and pollutant (e.g., phosphates) recovery, adsorption has been widely used for wastewater purification. Many efficient, environmentally compatible, and cost-effective sorbents have been successfully applied in environmental remediation. Chapter I is about characterization of graphene-coated pinewood biochar hybrids and evaluation of their copper removal performances. Here, we synthesized three types of pinewood biochar-graphene composites consisting of three different graphene precursors and compared their aqueous Cu2+ removal performances against raw pinewood biochar. To the best of our knowledge, no previous work has characterized the copper decontamination by graphene-biochar hybrids. Chapter II is about thermally- and chemically-treated lignite adsorbents for phosphate remediation. We engineered a cost efficient lignite system with co-precipitated Ca2+/Mg2+ followed by pyrolysis at 600 ⁰C to remediate aqueous phosphates. Micro-sized surface deposited oxide/hydroxide/carbonate particles promoted phosphate uptake of Ca2+/Mg2+-modified-lignite by 31 and 72 times, compared to thermally treated lignite (w/o a chemical treatment) and the raw lignite, respectively. The exhausted adsorbent can act as a slow-release fertilizer, which is comparable with commercial phosphate fertilizers. Chapter III is about synthesis of activated lignite [A-L], Ca2+-modified lignite [Ca-L], and Fe3O4 nanoparticle-loaded activated lignite (Fe3O4-A-L) for phosphate remediation. Even though A-L has a very high surface area (2854 m2/g), it did not achieve much phosphate sorption. Ca-L phosphate uptake was highest due to the high concentrations of surface deposited CaCO3, CaO, and Ca(OH)2. A pH-independent (from pH 5 to 9) phosphate removal was reported by highly basic Ca-L. However, the Ca2+ leaching was highest at pH 5. Precipitation of Ca2+ phosphates/hydrophosphates is the major phosphate removal mechanism of Ca-L. Fe3O4 and Fe2O3 sites of Fe3O4-A-L enhanced phosphate adsorption capacity, 8-fold versus A-L (67.6 mg/g vs 8.0 mg/g at 25 ºC). Fe3O4-A-L remediated phosphates via inner-sphere surface complexation and precipitation.

Hybrid organic-inorganic nanocomposites have received considerable attention during the last five years due to their unexpected properties. This work incorporated nanodispersed organically modified montmorillonite clay into polydicyclopentadiene resin matrices. Montmorillonite consists of 1 nm platelet sheets with a 2:1 structure, consisting of an alumina octahedral layer sandwiched between two silica tetrahedral layers. The relative weak forces between platelets allow small molecules like water, solvents and monomers as well as polymers, to enter into the interlayer spacings between the platelet sheets. In-situ polymerization of highly delaminated clay/dicyclopentadiene(DCPD) dispersions was used to prepare clay/polydicyclopentadiene (polyDCPD) nanocomposites. Highly delaminated composites were characterized using X-ray diffraction, X-ray scattering and high resolution TEM. Composites with 0.5-1 weight percent of clay had higher Tg values and flexural moduli. The flow properties of the organically-modified montmorillonite/DCPD liquid dispersions were examined using a co-rotating viscometer. The dispersions with clay concentrations higher than 0.5wt% clay in DCPD showed thixotropic flow behavior. Small angle neutron scattering (SANS) experiments were performed to obtain anisotropic scattering of highly delaminated clay in DCPD due to the orientation of clay platelets and tactoids in the shear field. No anisotropic scattering was observed. The reason for this unexpected result is not yet understood. Highly delaminated organically-modified clay composites were examined using small angle neutron scattering (SANS) and ultra small angle neutron scattering (USANS). The SANS data from 0.5, 1 and 2wt% clay/polyDCPD composites with 2 different types of clay were fitted to the stacked disk model. The average number of clay layers per tactoid was predicted by fitting the experimental data to the stacked disk model. Extensive high-resolution TEM analyses were performed on the same samples to obtain the average numbers of clay layers per tactoid. Two finite element models, one for the intercalated clay/polyDCPD nanocomposite and one for the exfoliated clay/polyDCPD nanocomposite, were developed. The effects of these different dispersion geometries for seven platelets in the polyDCPD matrix on the stress distributions were examined. The exfoliated platelet model showed reduced deformations and uniform stress distributions. The highest stress concentrations were found on the platelets? surfaces and where platelets were in close proximity.

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Cette thèse démontre le potentiel dont dispose l’exfoliation en phase liquide du graphite dans le but d’obtenir des feuillets de graphène dispersés dans un solvant organique. Ainsi le mécanisme d’exfoliation a été étudié en profondeur, en particulier, l’influence de plusieurs paramètres (température, puissance et solvants). Le choix de ses paramètres se montre crucial dans le contrôle du procédé, et pour l’obtention des feuillets de graphène ayant une taille ciblée. Il est donc possible de fabriquer des nano-feuillets de quelques dizaines de nanomètre qui en plus possèdent des propriétés de photoluminescence.Dans le but de comprendre le mécanisme d’exfoliation en phase liquide assistée par des molécules, une nouvelle approche a été mise au point : l’approche supramoléculaire. Cette approche se base sur l’utilisation de surfactants d’un nouveau type. En effet, les molécules sélectionnées possèdent une longue chaine alkyle. Cette chaine s’adsorbe sur la surface du graphène et permet de stabiliser les feuillets lors de l’exfoliation. L’influence de la taille de la chaine alkyle de ces molécules lors de l’exfoliation a été vérifiée. De plus, ces molécules ont été équipées de différentes fonctions supramoléculaires afin qu’elles puissent former des dimères sur la surface du graphène. L’ajout de ces molécules augmente non seulement le rendement d’exfoliation mais aussi le nombre de mono-feuillets présents dans ces dispersions. Ces dispersions présentent des propriétés conductrices lorsqu’elles sont déposées sur des substrats. Une nouvelles méthode de déposition a été mise au point afin d’améliorer et d’augmenter la conductivité mais aussi le pourcentage de transparence. / This thesis demonstrates the potential of exfoliation of the graphite in the liquid phase in order to obtain graphene sheets dispersed in an organic solvent. Thus the exfoliation mechanism has been studied, in particular, the influence of several parameters (temperature, power and solvents). The choice of parameters is actually crucial for the control of the process, and to obtain graphene sheets having a targeted size. It is therefore possible to manufacture nanosheets of several tens of nanometers, which in addition exhibit photoluminescence properties.In order to understand the exfoliation mechanism in liquid phase assisted by molecules, a new approach has been developed: the supramolecular approach. This approach is based on using a new type of surfactant. Indeed, the selected molecules carry a long alkyl chain. This chain is adsorbed on the surface of graphene and can stabilize the sheets during exfoliation. The influence of the size of the alkyl chain of these molecules during exfoliation was verified. Furthermore, these molecules have been equipped with various supramolecular functions, which can form dimers on the surface of graphene. The addition of these molecules not only increases exfoliation performance but also the number of mono-layers present in these dispersions. These dispersions have conductive properties when deposited on substrates. A new deposition method was developed to enhance and increase conductivity but also the percentage of transparency.

Le lait est produit par les cellules épithéliales mammaires (CEM). La quantité de lait produit est déterminée par le nombre de CEM et leur activité métabolique. Le nombre de CEM dépend de l’équilibre entre la prolifération cellulaire et l’apoptose. Le processus d’exfoliation, défini comme le décrochage des CEM de l’épithélium mammaire et leur évacuation dans le lait, a été proposé comme participant aussi à la régulation du nombre de CEM. Les objectifs de cette thèse étaient d’identifier les mécanismes biologiques impliqués dans la régulation de ce processus et d’étudier son rôle dans la régulation du nombre de CEM et son influence sur la production laitière. Nos résultats montrent qu’une partie des CEM est exfoliée entre deux traites consécutives.Cependant, la majorité des CEM sont exfoliées au moment de la traite suite à la contraction des cellules myoépithéliales et à la perte d’intégrité de l’épithélium induites par la décharge d’ocytocine. Le cortisol, au contraire, participerait à la restauration de l’intégrité de l’épithélium mammaire après la fin de la traite et limiterait l’exfoliation. Nous avons montré que les variations du taux d’exfoliation étaient opposées aux variations de production laitière dans le cas d’une restriction alimentaire et après la fin d’un traitement à l’hormone de croissance mais pas dans le cas d’un changement de fourrage, de l’inhibition de la prolactine et pendant un traitement à l’hormone de croissance. Le processus d’exfoliation des CEM participe donc à la régulation de la production laitière mais pas de façon systématique. / Milk is synthesized by mammary epithelial cells (MEC). Milk yield is determined by the number of MEC in the mammary gland and the metabolic activity of these cells. It is well known that MEC number depends on the balance between cell proliferation and apoptosis. The MEC exfoliation process, defined as the shedding of MEC from the mammary epithelium into milk, is another process that might participate in the regulation of MEC number in the udder and thus in milk yield variations. The aims of this thesis were to identify the mechanisms that regulate the exfoliation process and to study the potential role of this process in regulating the number of MEC and milk yield.Our results showed that some MEC are exfoliated between milkings. Most of the MEC are, however, exfoliated during milking as a consequence of the myoepithelial cell contraction and the disruption of mammary epithelium integrity, both of which are caused by milking-induced oxytocin release. Cortisol may play a role in limiting MEC exfoliation by restoring mammary epithelium integrity after milking. We showed that the exfoliation process participates in regulating milk yield during feed restriction and after a treatment with bovine growth hormone but did not participate in regulating milk yield when forage in the ration was changed, when prolactin secretion was inhibited, or during a treatment with bovine growth hormone. These results suggest that the MEC exfoliation process likely participates in regulating milk yield but not systematically.

Depuis la découverte des propriétés physiques et électroniques du graphène, un très grand nombre de méthodes visant à produire et modifier chimiquement le graphène ont été développées afin d'étendre et améliorer ses capacités en vue de futures applications. Les travaux réalisés au cours de cette thèse ont portés sur une méthode exfoliation du graphite en phase liquide assistée d'une réaction de cycloaddition réversible. Cette approche repose sur la réaction de Diels-Alder entre le graphite et un diène masqué très réactif, et se révèle être très efficace dans des solvants organiques volatils qui ne permettent pas l'exfoliation directe du graphite. L'introduction de groupements fonctionnels sur le diène a permis de moduler les propriétés de surface de films de graphène, ainsi que de post-fonctionnaliser les feuillets de graphène afin d'apporter une plus-value au matériau. / Since the discovery of the exciting properties of graphene, many techniques to produce and chemically modify graphene have been developed in order to expand and improve its properties in view of future applications. The study presented in this thesis focus on a process for the chemically-assisted exfoliation of graphite based on a reversible cycloaddition reaction. It relies on the Diels-Alder reaction between graphite and highly reactive masked diene, and it is effective even in solvents that are otherwise ineffective for exfoliation of graphite. Furthermore, it is possible to introduce functional groups on the diene, thereby enabling the tuning of the surface properties of graphene, as well as the post-functionalization of graphene sheets.

Sa conductivité électronique ou encore sa transparence optique sont autant de propriétés physico-chimiques singulières du graphène qui expliquent le nombre accru de méthodes d’exfoliation de précurseurs graphitiques développées pour l’obtention de ce matériau. Pour palier à l’utilisation d’un oxyde de graphite/graphène caractérisé par une chimie de surface mal maitrisée, des graphites fluorés, de cristallinité mais aussi de concentration en fluor variables, ont été préparés par fluoration de graphite sous fluor moléculaire pur après optimisation des paramètres. Les précurseurs, que ce soit par fluoration dynamique ou statique, ainsi obtenus ont été caractérisés finement : diffraction des rayons X, spectroscopies IR et Raman et leur texture sondée par Microscopie Electronique à Balayage et à Transmission. Suite à cela, trois méthodes d’exfoliation ont été mises en place, basées sur des mécanismes différents : i) une exfoliation par choc thermique, déjà connue mais dont les mécanismes de décomposition ont été affinés dans cette étude, ii) une exfoliation en voie liquide, avec l’utilisation pour la première fois d’un graphite fluoré pour la synthèse de graphène fluoré multi feuillets par voie électrochimique pulsée, et enfin iii) une méthode originale, peu conventionnelle, basée sur l’interaction laser femtoseconde/graphite hautement fluoré pour induire des mécanismes de réduction contrôlée, et surtout d’exfoliation de la matrice. Ces méthodes ont permis de mettre en évidence l’intérêt de la présence de fluor dans la course actuelle pour la synthèse de graphène, et ont montré l’obtention de matériaux graphéniques,possédant une fonction résiduelle fluorée intéressante pour certaines applications. / Its electronic conductivity or its optical transparency are unequaled physicochemicalproperties of graphene which explain the increased number of exfoliation methods based ongraphitic precursors to obtain this material. To overcome the use of a graphite/graphene oxidecharacterized by a poorly controlled surface chemistry, graphite fluorides, with variablecrystallinity and also fluorine concentration, were prepared by fluorination of graphite under puremolecular fluorine atmosphere after optimization of the process parameters. The obtainedprecursors, whether by dynamic or static fluorination, were characterized : X-Ray diffraction, FTIRand Raman spectroscopies for the structure, and their texture probed by Scanning andTransmission Electron Microscopy. After that, three methods of exfoliation were developed, basedon different mechanisms: i) a thermal shock, already known but decomposition mechanisms wererefined in this study, ii) an exfoliation within liquid medium by pulsed electrochemical treatment,using for the first time a fluorinated graphite for the synthesis of few-layered fluorinated grapheneand finally iii) an unconventional method, based on the interaction between femtosecond laser andhighly fluorinated graphite to induce mechanisms like controlled reduction, and especially for thisstudy exfoliation of the matrix. These methods have permit to highlight the interest of fluorine inthe current race for the synthesis of graphene, and have shown the production of graphenematerials, having an interesting fluorinated residual functionalization for some applications.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.