Abstract The development and advancement of microelectronics industry is very drastically. So, the key to create new technology of process and it's costs can be cut by simulating the performance of these equipments. The reactor of chemical vapor deposition (CVD) is important to semiconductor production process.. This research use numerical method to study the process parameters of low-pressure chemical vapor deposition (LPCVD) of Tungsten (W).In this simulation, the CVD reactor modeling are constructed and discreditzed by using the implicit finite volume method. The grids are arranged in a staggered manner for the discretization of the governing equations. Then, the SIMPLE-type algorithm will be used to solve all of the discretized algebra equations. In this research, the reactor is an single wafer and cold-wall system. The nozzle position is adjustable from 100 to 250mm.The nozzle-to-wafer distance is adjustable by changing the height from 30 to 120mm.The temperature and pressure in the reactor system can be setup with susceptor temperature 300~600 and pressure 0.5~8Torr. The results show that the flow in the reactor may depend on the flow rate and nozzle position. An effective means to avoid unstable is to reduce the susceptor temperature and system pressure due to the effects of buoyancy force and recirculation.

Chemical vapor deposition is a process that enables the deposition of thin films material with a high degree of thickness control, composition and film quality. In an ultra-high vacuum environment (UHV), films of high purity and controlled crystal structure can be achieved. The control of the crystal structure is achieved thanks to reduced contamination, e.g. oxygen, which allows the grown film to align itself with the underlying substrate. The film purity is also ensured by the reduced amount of contaminants present in the UHV environment. This master’s thesis discusses the design and construction of a cold wall reactor using a pyrolytic graphite heater encased in a thin layer of pyrolytic boron nitride, and an Oerlikon-Leybold Turbovac 361 turbomolecular pump. This heater is shown to achieve temperatures greater than 1200°C, as well as reach pressures in the 10-10 Torr range. Graphene growth on copper is discussed as well as the ultra-high vacuum annealing of graphene devices on boron nitride substrates. The graphene growth experiments coupled with this system’s annealing capabilities demonstrate the functionality and versatility of this type of chemical vapor deposition system. / text

Une étude expérimentale sur la faisabilité du procédé de dessalement par congélation sur les parois d'un tube cylindrique est présentée. Le procédé se décompose en deux étapes essentielles : la cristallisation suivie par le ressuage. Les cristallisations sont conduites à partir d'une solution stagnante ou agitée par un bullage d'air. Les paramètres opératoires clés sont la rampe de refroidissement et la salinité de l’eau traitée. Leur effet sur la salinité de la glace produite a été quantifié, dans les deux modes de fonctionnement, statique et agité. Le dispositif expérimental permet également de contrôler le gradient thermique à travers la couche de solution pour les cristallisations effectuées en statique. L'absence de gradient thermique et donc de courant de convection mène à des couches de glace très contaminées en sels. Les résultats combinant la cristallisation et le ressuage montrent que dans tous les cas, on peut obtenir de l'eau potable mais avec un rendement plus élevé et une durée réduite si la cristallisation a lieu en mode dynamique. Les conditions opératoires optimales sont proposées. La modélisation des transferts de matière et de chaleur à travers les couches de glace et de solution en régime diffusionnel et convectif a permis d’interpréter l’influence des paramètres opératoires des cristallisations opérées sans agitation. Enfin, l’évaluation économique du procédé complet de dessalement, basées sur des points de fonctionnement expérimentaux, indique que la consommation énergétique d’une petite installation pourrait être très faible en utilisant une machine frigorifique idéale fonctionnant entre l’unité de ressuage et l’unité de congélation. / An experimental study on the feasibility of sea water desalination by indirect freezing is presented. The whole process of desalination involves a freezing step, followed by a purification of the ice layer by sweating. Crystallization is led from quiescent solution or from agitated solution by air bubbling. The key operating parameters are the cooling rate, and solution salinity. Their effect on ice purity has been quantified in the static and agitated modes. The experimental setup enables as well the control of temperature gradient through the solution when the freezing step is conducted in the static mode. In the absence of temperature gradient and consequently the absence of convection currents, the ice layers formed are very contaminated in salts. The results combining crystallization and sweating show that in all cases, we can obtain drinking water, but with high yield and reduced process time when the crystallization is led in agitated mode. The optimal operating conditions are presented. The modelling of mass and heat transfers in the two phases in the diffusional and convective regimes has enabled the interpretation of the influence of operating parameters of crystallizations operated without agitation. At last, the economic evaluation of the whole desalination process, based on experimental operating points, indicates that energetic consumption of a small scale unit maybe low when using an ideal refrigerating machine which works between the sweating and the crystallization unities.

abstract: Chemical Vapor Deposition (CVD) is the most widely used method to grow large-scale single layer graphene. However, a systematic experimental study of the relationship between growth parameters and graphene film morphology, especially in the industrially preferred cold wall CVD, has not been undertaken previously. This research endeavored to address this and provide comprehensive insight into the growth physics of graphene on supported solid and liquid Cu films using cold wall CVD. A multi-chamber UHV system was customized and transformed into a cold wall CVD system to perform experiments. The versatile growth process was completely custom-automated by controlling the process parameters with LabVIEW. Graphene growth was explored on solid electrodeposited, recrystallized and thin sputter deposited Cu films as well as on liquid Cu supported on W/Mo refractory substrates under ambient pressure using Ar, H₂ and CH₄ mixtures. The results indicate that graphene grown on Cu films using cold wall CVD follows a classical two-dimensional nucleation and growth mechanism. The nucleation density decreases and average size of graphene crystallites increases with increasing dilution of the CH₄/H₂ mixture by Ar, decrease in total flow rate and decrease in CH₄:H₂ ratio at a fixed substrate temperature and chamber pressure. Thus, the resulting morphological changes correspond with those that would be expected if the precursor deposition rate was varied at a fixed substrate temperature for physical deposition using thermal evaporation. The evolution of graphene crystallite boundary morphology with decreasing effective C deposition rate indicates the effect of edge diffusion of C atoms along the crystallite boundaries, in addition to H₂ etching, on graphene crystallite shape. The roles of temperature gradient, chamber pressure and rapid thermal heating in C precursor-rich environment on graphene growth morphology on thin sputtered Cu films were explained. The growth mechanisms of graphene on substrates annealed under reducing and non-reducing environment were explained from the scaling functions of graphene island size distribution in the pre-coalescence regime. It is anticipated that applying the pre-coalescence size distribution method presented in this work to other 2D material systems may be useful for elucidating atomistic mechanisms of film growth that are otherwise difficult to obtain. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018

This work deals with spatially-evolving supersonic turbulent boundary layers over adiabatic and cold walls at M∞ = 2 and up to Re0 ≈ 2600 using 3 different SGS models. The numerical methodology is based on high-order split-centered scheme to discretize the convective fluxes of the Navier-Stokes equations . For the adiabatic case, it is demonstrated that all SGS models require a comparable minimum grid-refinement in order to capture accurately the near-wall-turbulence. Overall, the models exhibit correct behavior when predictiong the dynamic properties, but show different performances for the temperature distribution in the near-wall region. For the isothermal case, it is found that the compressibility effects are not enhanced due to the wall cooling. As expected, the total temperature fluctuations are not negligible in the near-wall region. The study shows that the anti-correlation linking both velocity and temperature fields, derived from the Morkovin's hypothesis, is not satisfied.

Ce travail vise à étudier un procédé de traitement d'eaux usées industrielles par cristallisation en milieu fondu sur paroi froide. Deux effluents modèles sont choisis : un mélange eau/acétone et un mélange eau/acide propanoïque. Dans un premier temps, l'équilibre solide-liquide du mélange est étudié pour connaitre les limites de l'étude en température et en concentration. Le procédé de traitement de l'eau est alors conduit, selon un mode opératoire précis. Deux modes de fonctionnement sont mis en œuvre, un mode statique et un mode dynamique avec une circulation en boucle de la solution. La concentration en impuretés dans la glace est analysée après chaque cycle de congélation. L'étude paramétrique, conduite suivant un plan d'expériences, a mis en avant les effets importants de la concentration initiale de la solution et de la rampe de refroidissement. La microstructure de la glace est également analysée par microscopie en chambre froide pour interpréter les mécanismes d'incorporation d'impuretés au sein de la glace. Les inclusions de liquide sont sous la forme de poches de solution à faible vitesse de croissance et sont localisées dans les joints de grain à plus forte vitesse. Enfin, la modélisation du procédé fonctionnant en mode statique, par les éléments finis et en 2D axisymétrique avec frontière mobile, montre la présence de mouvements de convection. En mode dynamique, l'hydrodynamique de l'écoulement dans l'espace annulaire est décrite par une modélisation 3D prenant en compte la position de l'entrée et de la sortie. Les résultats démontrent la faisabilité du procédé et permettent des avancées significatives dans la compréhension des phénomènes mis en jeu / This work aims to study a process of industrial wastewater treatment by melt crystallization on a cold wall. Two effluent model solutions are chosen: water/acetone and water/propionic acid binary mixtures. First, the solid liquid phase diagrams are determined experimentally in order to delimit the operating range of temperature and concentration. Then, a parametric study of the wastewater treatment process by freezing is performed, by means of an experimental design, for two working modes, static mode and dynamic mode by adding a recirculation loop, respectively. The impurity concentration in the ice is analyzed after each freezing cycle. The process requires applying very precise conditions and the ice concentration mainly depends on the initial solution concentration and on the applied cooling rate. The ice microstructure is also characterized by optical microscopy in a cold chamber and gives insights into the mechanism of impurity incorporation: the liquid inclusions are localized under the form of solution pockets at low growth rate or between the polycrystals at higher growth rate. Lastly, 2D axisymmetric modelling of the process in static mode, based on finite elements and taking into account the moving boundary, shows the presence of buoyancy loops in relation with the density dependence of the solution with temperature. In dynamic mode, the hydrodynamics in the annular space is described by a 3D model to account for the positions of the inlet and outlet pipes. All the results demonstrate the process feasibility and allow better understanding of the occurring phenomena

Cette thèse traite des transferts pariétaux dans les écoulements turbulents supersoniques via la simulation des grandes échelles turbulentes. Des couches limites adiabatique et refroidie évoluant à Mach M∞ = 2 et à Reynolds Re0 ≈ 2600 sont considérées. Les simulations numériques utilisent un schéma split-centered d’ordre élevé pour la discrétisation des flux convectifs. Les résultats obtenus sont comparés aux simulations numériques directes (DNS) disponibles dans la littérature. Plusieurs modèles de sous-maille ont été testés et validés. Il a été montré que ces modèles exigent un minimum de raffinement de maillage afin de capturer les structures les plus énergétiques présentes en proche paroi. Les modèles montrent des performances différentes pour la distribution de la température à la paroi. Pour le cas d’une paroi refroidie, les fluctuations de température totale ne sont pas négligeables dans la région proche-paroi. Et l’anticorrélation (u’, T’) se basant sur l’hypothèse de Morkovin n’est pas satisfaite. / This work deals with spatially-evolving supersonic turbulent boundary layers over adiabatic and cold walls at M∞ = 2 and up to Re0 ≈ 2600 using 3 different SGS models. The numerical methodology is based on high-order split-centered scheme to discretize the convective fluxes of the Navier-Stokes equations . For the adiabatic case, it is demonstrated that all SGS models require a comparable minimum grid-refinement in order to capture accurately the near-wall-turbulence. Overall, the models exhibit correct behavior when predictiong the dynamic properties, but show different performances for the temperature distribution in the near-wall region. For the isothermal case, it is found that the compressibility effects are not enhanced due to the wall cooling. As expected, the total temperature fluctuations are not negligible in the near-wall region. The study shows that the anti-correlation linking both velocity and temperature fields, derived from the Morkovin's hypothesis, is not satisfied.

Turbulent boundary layers approximating those found on the NASA Orion Multi-Purpose Crew Vehicle (MPCV) thermal protection system during atmospheric reentry from the International Space Station have been studied by direct numerical simulation, with the ultimate goal of reducing aerothermodynamic heating prediction uncertainty. Simulations were performed using a new, well-verified, openly available Fourier/B-spline pseudospectral code called Suzerain equipped with a ``slow growth'' spatiotemporal homogenization approximation recently developed by Topalian et al. A first study aimed to reduce turbulence-driven heating prediction uncertainty by providing high-quality data suitable for calibrating Reynolds-averaged Navier--Stokes turbulence models to address the atypical boundary layer characteristics found in such reentry problems. The two data sets generated were Ma[approximate symbol] 0.9 and 1.15 homogenized boundary layers possessing Re[subscript theta, approximate symbol] 382 and 531, respectively. Edge-to-wall temperature ratios, T[subscript e]/T[subscript w], were close to 4.15 and wall blowing velocities, v[subscript w, superscript plus symbol]= v[subscript w]/u[subscript tau], were about 8 x 10-3 . The favorable pressure gradients had Pohlhausen parameters between 25 and 42. Skin frictions coefficients around 6 x10-3 and Nusselt numbers under 22 were observed. Near-wall vorticity fluctuations show qualitatively different profiles than observed by Spalart (J. Fluid Mech. 187 (1988)) or Guarini et al. (J. Fluid Mech. 414 (2000)). Small or negative displacement effects are evident. Uncertainty estimates and Favre-averaged equation budgets are provided. A second study aimed to reduce transition-driven uncertainty by determining where on the thermal protection system surface the boundary layer could sustain turbulence. Local boundary layer conditions were extracted from a laminar flow solution over the MPCV which included the bow shock, aerothermochemistry, heat shield surface curvature, and ablation. That information, as a function of leeward distance from the stagnation point, was approximated by Re[subscript theta], Ma[subscript e], [mathematical equation], v[subscript w, superscript plus sign], and T[subscript e]/T[subscript w] along with perfect gas assumptions. Homogenized turbulent boundary layers were initialized at those local conditions and evolved until either stationarity, implying the conditions could sustain turbulence, or relaminarization, implying the conditions could not. Fully turbulent fields relaminarized subject to conditions 4.134 m and 3.199 m leeward of the stagnation point. However, different initial conditions produced long-lived fluctuations at leeward position 2.299 m. Locations more than 1.389 m leeward of the stagnation point are predicted to sustain turbulence in this scenario. / text