L'objectif de cette thèse a consisté à étudier des procédés de fabrication de couches de diffusion de gaz (GDL) en silicium poreux appliqués à l'intégration de micropiles à combustible de type PEMFC sur plaquette de silicium. Deux types de couches ont été étudiés : sur surface plane (2D) et sur surface texturée (3D). Les couches de diffusion de gaz ont été réalisées par l'anodisation de silicium de type N fortement résistif. Une localisation des motifs poreux a été obtenue par ouverture d'un masque en polysilicium sur oxyde thermique de silicium. Seules les GDL 2D entièrement macroporeuses assuraient un débit d'hydrogène compatible avec les objectifs de fabrication d'une micropile prototype. Le prototype a permis de valider la compabilité de la couche de diffusion de gaz avec les étapes d'empilement des couches actives constitutive de la micropile. Son fonctionnement nous a permis d'atteindre une densité de puissance de 250 mW/cm². / This thesis work deals with porous silicon gas diffusion layer (GDL) fabrication process. The aim was to integrate this GDL into proton exchange membrane micro fuel cells (PEMFC). Consequently, the GDL must be localized in specific wafer areas. We have also developed 2D and 3D structures. To produce a GDL, we have anodized low doped N type silicon subrates. thus, we have fabricated macroporous GDL and double layer structures made up of a mesaporous layer on a macroporous one. Patterning of the GDL has been obtained through a hard mask (polysilicon on top of a silicon oxide layer) or using a localized doping. We have concluded this work by achieving micro fuel cell prototypes with macroporous silicon gas diffusion layers. After validation of micro PEMFC active layer mechanical stacking, we have measured a maximum power density of about 250 mW/cm².

L’analyse de la fonction systolique longitudinale par speckletracking permet d’analyser les mouvements de déformations du myocarde ainsi que la fonction systolique longitudinale ventriculaire gauche. Le Strain Longitudinal Global (SLG) est le paramètre le plus étudié en cardiologie et s’intéresse aux déformations du grand axe du ventricule gauche. Il n’existe pas de données sur le SLG chez les patients atteints d’une pathologie cérébrale aiguë placés sous ventilation mécanique, alors que les cardiopathies de stress ont été largement décrites dans ce contexte. Nous avons évalué le SLG chez des patients atteints d’hémorragie sous-arachnoïdienne par rupture d’anévrysme. Il existait plus de 30% de cardiopathies de stress évaluée par le SLG, alors que la fraction d’éjection ventriculaire gauche était normale. Chez les patients traumatisés crâniens, nous avons observé une absence de cardiopathies de stress, avec un SLG conservé. Néanmoins nous ne pouvons exclure que les anomalies constatées sont liées aux variations des conditions de charge secondaires à la ventilation mécanique. Nous avons testé l’effet de la ventilation mécanique invasive après anesthésie générale au bloc opératoire sur le SLG, ainsi que les effets du lever de jambe passif. Au décours de l’anesthésie générale, il existe une altération modeste mais significative du SLG. Après une épreuve de lever de jambe passif, l’altération du SLG est persistante. En conclusion, les altérations du SLG témoignant d’une cardiopathie de stress, sont spécifiques en neuroréanimation, mais l’analyse du SLG doit prendre en compte les variations rapides de conditions de charge. / .Speckle-tracking echography allows the analysis of left ventricular strain movements and longitudinal systolic function. Global Longitudinal Strain (GLS) is the most studied parameter in cardiology and provides data regarding strain movements of the left ventricle in the long axis. There are no data regarding SLG in neurocritical care patients undergoing invasive mechanical ventilation, although stress cardiomyopathy has been numerously described in this context. We have studied GLS in patients with aneurysmal subarachnoid haemorrhage. We identified over 30% of stress cardiomyopathy with GLS along with preserved left ventricular ejection fraction. In patients with traumatic brain injury, GLS was preserved implying the absence of stress cardiomyopathy. However, we could not rule out that GLS alterations were the consequences of the variations in the loading conditions of the left ventricle, because of mechanical ventilation. We tested these effects in patients undergoing invasive mechanical ventilation with general anaesthesia in the operating room. We also tested the effects of passive leg raising. After general anaesthesia, we witnessed a moderate but significant GLS impairment. After a passive leg raising test, GLS impairment was still present. In definite, GLS’s modifications are specific of the neurocritical care setting and imply the existence of stress cardiomyopathy, but GLS analysis must consider rapid modifications of the loading conditions.

Graphene, the thinnest material with a stable 2D structure, is a potential alternative for silicon-based electronics. However, zero band gap of graphene causes a poor on-off ratio of current thus making it unsuitable for logic operations. This problem prompted scientists to find other suitable 2D materials. Creating vacancy defects or synthesizing hybrid 2D planar interfaces with other 2D materials, is also quite promising for modifying graphene properties. Experimental productions of these materials lead to the formation of possible defects and impurities with significant influence in device properties. Hence, a detailed understanding of the effects of impurities and defects on the properties of 2D systems is quite important. In this thesis, detailed studies have been done on the effects of impurities and defects on graphene, hybrid graphene/h-BN and graphene/graphane structures, silicene and transition metal dichalcogenides (TMDs) by ab-initio density functional theory (DFT). We have also looked into the possibilities of realizing magnetic nanostructures, trapped at the vacancy defects in graphene, at the reconstructed edges of graphene nanoribbons, at the planar hybrid h-BN graphene structures, and in graphene/graphane interfaces. A thorough investigation of diffusion of Fe adatoms and clusters by ab-initio molecular dynamics simulations have been carried out along with the study of their magnetic properties. It has been shown that the formation of Fe clusters at the vacancy sites is quite robust. We have also demonstrated that the quasiperiodic 3D heterostructures of graphene and h-BN are more stable than their regular counterpart and certain configurations can open up a band gap. Using our extensive studies on defects, we have shown that defect states occur in the gap region of TMDs and they have a strong signature in optical absorption spectra. Defects in silicene and graphene cause an increase in scattering and hence an increase in local currents, which may be detrimental for electronic devices. Last but not the least, defects in graphene can also be used to facilitate gas sensing of molecules as well as and local site selective fluorination.

An analysis of 2D object packing algorithms, created by foreign authors, and commercial two-dimensional stock packing software packages was performed in this work; also methods’ advantages and disadvantages were pointed out. A model of two-dimensional rectangular object packing into stock was formed, and the software solving 2D object packing problems was created according to this model. The tests proved that the suggested method is effective and beneficial.

In this thesis the layered, two-dimensional material MoTe2 is examined experimentally for its optoelectronic properties, using a field effect transistor device configuration. MoTe2 experiences a strong light matter interaction, which is highly dependent on the conditions of the measurement, and the wavelength of light used. Light is able to: produce a photocurrent in MoTe2, desorb adsorbates from the surface, and even controllably thin by a single layer at a time. A theoretical study on MoTe2 also provides insights on the source of some of these interesting light matter interactions. MoTe2 is found to be a fast and responsive photodetector when illuminated with red laser light in ambient conditions, with increases in current stemming from the photovoltaic effect. Due to the generated charge carriers from the photovoltaic effect, conductivity can increase by increasing the Fermi energy of the material, or by a photogating effect where excited charges are trapped and behave as an artificial gate for the field effect transistor. The mechanisms of charge trapping are experimentally investigated due to their prevalence in the photodetection mechanisms. A theoretical study points towards the existence of two types of trap states, in not just MoTe2 but all transition metal dichalcogenides, with shallow traps closer to the valence band edge (τ ~ 500 s) and deeper traps (τ ~ 1000 s), further away from the valence band edge. MoTe2, under the effects of higher energy photons from blue and green lasers, showed different photocurrent mechanisms to red light. From the increased energy of the photons, photo-desorption of adsorbates on the surface of MoTe2 occurred causing a decrease in the overall current, in a rarely seen photocurrent mechanism. Again, both shallow and deep traps are evident from the experimental measurements, with the shallow traps being removed when illuminated by higher energy photons. Finally, a humidity assisted photochemical layer-by-layer etching process was developed with an in-situ Raman spectroscopy system, able to thin MoTe2 by a single layer at a time with 200 nm spatial resolution. MoTe2 FETs were created with thinned channels to examine the effect of the thinning technique on optoelectronic properties. Some improvement in optoelectronic performance (higher responsivity, higher mobility) was seen for the thinned channel devices, with great improvement observed for monolayer MoTe2.

High frequency wave propagation is well described even at caustics by Gaussian beams and the complex eikonal equation. In contrast to the real eikonal equation, the complex eikonal equation is elliptic and not well posed as an initial value problem. We develop a new model that approximates the 2D complex eikonal equation but is well posed as an initial value problem. This model consists of a coupled system of partial and ordinary differential equations. We prove that there exists a local solution to this new system by a Picard iteration method and show uniqueness under certain constraints. Different numerical approximations are then developed based on direct finite difference approximations or the method of characteristics. Numerical simulations with a variety of velocity profiles are presented and compared with solutions to the corresponding Helmholtz equation. / text

La compréhension des mécanismes cellulaires et moléculaires qui sont mis en jeu au moment de la croissance et la maturation pré-ovulatoire induite par la LH, permettra de définir des marqueurs de qualité et de maturité du follicule destiné à ovuler, et ainsi de mieux anticiper le moment de l’ovulation. L’objectif majeur de cette thèse était d’identifier certain des facteurs régulateur impliqués dans la maturation folliculaire par deux approches globales d’analyse protéomique et transcriptomique. La première étude a permis d’établir pour la première fois les cartes protéiques du liquide folliculaire équin et canin. Les analyses comparatives des liquides folliculaires provenant de différents stades physiologiques n’ont montré, dans nos conditions expérimentales, que peu de différences. Nos résultats obtenus dans la deuxième étude indiquent que les différentes méthodes enrichissement du liquide folliculaire peuvent améliorer, pour certaines de manière conséquente, la résolution des gels 2D-PAGE. Notre étude transcriptomique globale a révélé un groupe de gènes différentiellement exprimés dans les cellules folliculaires aux différents stades étudiés. Ces gènes sont potentiellement impliqués pendant le développement folliculaire dans l’espèce équine. Les deux approches (protéomique et transcriptomique) que nous avons utilisées au cours de ce travail sont complémentaires car la connaissance des gènes exprimés par les cellules folliculaires peuvent permettre d’identifier certains gènes codant pour des protéines sécrétoires retrouvées dans le liquide folliculaire. / An understanding of the cellular and molecular mechanisms involved in the growth and maturation of the preovulatory follicle induced by LH, will help us to understand and identify the markers of quality and maturity of the follicle destined to ovulate, and better anticipate the time of ovulation. The main objective of this thesis was to identify some regulatory factors involved in follicle maturation using two global approaches: proteomic and transcriptomic analysis. The first study established for the first time the protein map of equine and canine follicular fluids. The comparative analyses of follicular fluid from different physiological stages were shown little or no difference in our experimental conditions. Results obtained with the second study suggested that between depletion and enrichement methods, the enriched follicular fluid can improve for some consistent manner, the resolution of 2D-PAGE gels. Our global transcriptomic study revealed a group of genes differentially expressed in follicular cells at different physiological stages. These genes are potentially involved during follicle development in the equine species. The two approaches (proteomic and transcriptomic) that we used in this work are complementary, as the knowledge of genes expressed by follicle cells can help to identify some genes coding for secretory proteins secreted in follicular fluid.

Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, Pós-Graduação em Geociências Aplicadas, 2016. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2017-05-02T17:14:17Z No. of bitstreams: 1 2016_UmbertoJoséTravagliaFilho.pdf: 4405139 bytes, checksum: e286c5da82e172b958605cb778ceff3c (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2017-05-08T21:15:52Z (GMT) No. of bitstreams: 1 2016_UmbertoJoséTravagliaFilho.pdf: 4405139 bytes, checksum: e286c5da82e172b958605cb778ceff3c (MD5) / Made available in DSpace on 2017-05-08T21:15:52Z (GMT). No. of bitstreams: 1 2016_UmbertoJoséTravagliaFilho.pdf: 4405139 bytes, checksum: e286c5da82e172b958605cb778ceff3c (MD5) Previous issue date: 2017-05-08 / Devido ao aumento no número de levantamentos de campo utilizando o Método Eletromagnético no Domínio do Tempo (TDEM), novos programas para processamento deste método foram desenvolvidos. Com o objetivo de contribuir com a aplicação do método, foi desenvolvido o programa ImagEM – programa de modelagem 2D para dados TDEM. O ImagEM possui sub-rotinas para realizar o pré-processamento, processamento (inversão simplificada por meio do método da secante) e imageamento dos perfis do campo secundário, das linhas de contorno da resistividade e da seção da resistividade pela profundidade para dados terrestres e aéreos, além da modelagem do alvo (mergulho, direção e profundidade). Os mapas podem ser obtidos pelo método de Krigagem, ou do Inverso da Distância Ponderada. Nesta tese são apresentados três artigos. No primeiro artigo, foram aplicados dados sintéticos para modelos de duas e três camadas, com a resistividade variando entre 10 e 100 Ω•m e profundidade variando entre 100 e 400m. No segundo artigo, os dados coletados com o equipamento PROTEM (Geonics) foram submetidos ao programa. A área desta coleta foi o complexo Cristalino em Carajás - PA, a inversão recuperou os valores de resistividade que variam entre 1.104 e 2.104 Ω•m e profundidade entre 50 e 400m. Também foi possível descrever as feições das regiões condutivas e a mudança em sua direção. No último artigo, foram utilizados os dados Aeroeletromagnéticos (AEM), sobre a Bacia de San Pedro (EUA), obtidos pelo GEOTEM nas três componentes (x, y e z). Aplicando a transformada de Hilbert sobre as três componentes foi possível calcular o Envelope de Energia. Por meio da razão entre a componente Bz e o Envelope de Energia foi possível avaliar os picos de energia e estimar o mergulho, a profundidade e a direção (strike) do alvo. Estes resultados foram modelados utilizando a função RDI (Resistivity Depth Image) que apresenta uma imagem da resistividade pela profundidade descrita também pelo programa. Estas informações trouxeram mais detalhes para se realizar a modelagem da subsuperfície condutiva. / Due to the increase of field surveys using Time Domain Electromagnetic Methods (TDEM), new algorithms for data processing have been developed. In order to contribute to the use of TDEM, the program ImagEM - 2D modeling program for TDEM data was developed. The ImagEM has subroutines to execute pre-processing, processing (simplified inversion through the secant method) and imaging of secondary field profiles of resistivity contour lines and depth section resistivity for ground and air data, beyond the target modeling (dip, direction and depth). Maps can be obtained through the methods of Kriging, or Inverse Distance Square. This thesis presents three articles. The first article was applied to synthetic data models with two and three layers, with resistivity ranging from 10 to 100 Ω.m and depth ranging between 100 and 400m. In the second article the program was submitted to data collected in Carajás using the PROTEM equipment (Geonics), the inversion routine recovered the resistivity values ranging from 1.104 and 2.104 Ω.m and depth values from 50 to 400m. Also, it was possible to describe the features of conductive regions and the change in its direction. In the last article we use airborne electromagnetic data (AEM) from the Basin of San Pedro (USA), obtained by GEOTEM with three components (x, y and z). Applying a Hilbert transform on the three component data, it was possible to calculate the energy envelope. Through the ratio of Bz and the Energy Envelope component it was possible to evaluate the energy peaks and estimate the dip, depth and direction (strike) of the target, these results were confronted with section of RDI also described by the program. These data brought more information to carry out the modeling of the conductive subsurface.

Two-dimensional (2D) materials show novel electronic, optical and chemical properties and have great potential in devices such as field-effect transistors (FET), photodetectors and gas sensors. This thesis focuses on scanning tunneling microscopy and spectroscopy (STM/STS) investigation of interfaces and defects 2D transition metal dichalcogenides (TMDCs). The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). By properly choosing the growth condition, Sub-10 nm TiSe2 flakes were successfully obtained. A 2 × 2 charge density wave (CDW) was clearly observed on these ultrathin flakes by scanning tunneling microscopy (STM). Accurate CDW phase transition temperature was measured by transport measurements. This work opens up a new approach to synthesize TMDCs. The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface under electrical stressing. We have observed nonlinear area evolution and growth from triangular to hexagonal driven by STM subjected electrical stressing. Our simulations of monolayer island evolution using phase-field modeling and first-principles calculations are in good agreement with our experimental observations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing. The third part of the thesis focuses on point defects in 2D PtSe2. We observed five types of distinct defects from STM topography images and measured the local density of states (LDOS) of those defects from scanning tunneling spectroscopy (STS). We identified the types and characteristics of these defects with the first-principles calculations. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials. / Doctor of Philosophy / Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted more and more attentions. When the thickness of a layered material thinned to one or few atoms, it shows interesting properties different from its bulk phase. Due to the reduced dimensionality, interfaces and defects in 2D materials will significantly affect the electronic property and chemical activity. However, such nanometer scale features are several orders of magnitude smaller than the wavelength of visible light, which is the limit of resolution for optical microscope. Scanning tunneling microscope (STM) is widely used in study of 2D materials not only because it can provide the topography and local electronic information at atomic scale, but also because of the possibility of directly fabricate atomic scale structure on the surface. The first part of the thesis focuses on the synthesis of 2D TiSe2 with chemical vapor transport (CVT). TiSe2 belongs to the transition metal dichalcogenides (TMDCs) family, showing a sandwiched layered structure. When the temperature goes down to 200K, a 2 × 2 superlattice called charge density wave (CDW) will show up, which is clearly observed in our STM images. The second part of the thesis focuses on monolayer vacancy islands growing on TiSe2 surface controlled by electrical stressing. During continuous STM scanning, we have observed nonlinear area growth of the vacancy islands. The shape of those islands transfers from triangular to hexagonal. We successfully simulated such growth using phase-field modeling and first-principles calculations. The results could be potentially important for device reliability in systems containing ultrathin TMDCs and related 2D materials subject to electrical stressing. The third part of the thesis focuses on defects in 2D PtSe2. We observed five types of distinct defects in our STM topography images. By comparing them with DFT-calculated simulation images, we identified the types and characteristics of these defects. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering in few-layer 1T-PtSe2 and other related 2D materials.

The emergence of monolayer two-dimensional (2D) materials revolutionizes the strategies of advancing the modern technologies. Semiconducting 2D materials such as MoS2, WS2, MoSe2, and WSe2 especially act as a propeller aiming to accelerate and expand the research of catalyst, battery, and electronics. Hydrogen evolution reaction (HER) is fundamentally important for various electrochemical processes, such as fuel cells and H2 production, particularly for the replacement of precious metal catalysts, Pt. Plus, the needs of energy storage and the emphatic requirements of fast charging are rising with the advancement of microprocessor technologies. The bulk form MoS2 is a poor HER catalyst and shows negligible capacitance, however, monolayer MoS2 exhibits extraordinary performance in both HER and energy storing capability. Through a modified top-down process to isolate individual monolayer flakes of MoS2 incorporating with a one-step direct printing technique the exposed surface area can be maximized and immediately exploited as a catalyst for stably producing H2 in both acidic and basic solutions and even at extreme radiative environments. Furthermore, individual monolayer MoS2 flakes can as well be collected and stored as a powder form which remain the free-standing quality giving rise to the significance of creating 3D monolayer flakes containing inks for inkjet printing which results in an enhanced capacitance in supercapacitors. In addition, the advancement of the miniaturization of silicon transistors is approaching the inevitable physical limits in the gating channel because of the short channel effect which is the primary concern to cease Moore’s law. Monolayer semiconductors offer dangling-bonds-free atomically thin and flat surface which is desirable as channel materials in transistors. Although the mass producibility of top-down process provides promising prospect in catalyst and battery applications the control of the uniform thickness on a large scale is extremely difficult. Chemical vapor deposition (CVD) and sapphire wafer is one of the most reliable bottom-up processes for the mass production of wafer-scale 2D semiconducting films in the manufacturing lines with the lowest costs and highest throughputs. An approach of epitaxially growing single-crystal 2D semiconducting films is elucidated to achieve the state-of-the-art crystallographical and electrical uniformity on 2-inch sapphire wafers.