This work is focused on thermodynamic modelling of isobaric vapour-liquid-liquid equilibrium (VLLE) (homogeneous) and (heterogeneous) for binary, ternary and quaternary systems. This work uses data for organic/aqueous systems; historically these mixtures were used in the production of penicillin and were required to be separated by continuous fractional distillation. Modelling of the separation required phase equilibrium data to be available so that predictions could be made for equilibrium stage temperatures, vapour compositions, liquid compositions and any phase splitting occurring in the liquid phase. Relevant data became available in the literature and work has been carried out to use relevant theories in correlating and predicting as was originally required in the distillation equilibrium stage modelling. All the modelling carried out was at atmospheric pressure. The modelling has been done using an Equation of State, specifically Peng Robinson Styrjek Vera (PRSV), combined with the activity coefficient model UNIversal QUAsi Chemical (UNIQUAC) through Wong Sandler mixing rules (WSMR). The success of all correlations and predictions was justified by minimizing the value of the Absolute Average Deviation (AAD) as defined within the thesis. Initially the integral Area Method and a method called Tangent Plane Intersection (TPI) were used in the prediction of liquid-liquid equilibrium (LLE) binary systems. This work used a modified 2-point search, suggested a 3-point search and has successfully applied both of these methods to predict VLLE for binary systems. It was discovered through the application of the TPI on ternary VLLE systems that the method was strongly sensitive to initial values. This work suggested and tested a Systematic Initial Generator (SIG) to provide the TPI method with realistic initial values close to the real solution and has demonstrated the viability of the SIG on improving the accuracy of the TPI results for the ternary systems investigated. In parallel with the TPI another method the Tangent Plane Distance Function (TPDF) was also investigated. This method is based on the minimisation of Gibbs free energy function related to the Gibbs energy surface. This method consistently showed it was capable of predicting VLLE for both ternary and quaternary systems as demonstrated throughout this work. The TPDF method was found to be computationally faster and less sensitive to the initial values. Some of the methods investigated in this work were also found to be applicable as phase predictors and it was discovered that the TPDF and the SIG methods were successful in predicting the phase regions; however the TPI method failed in identifying the 2 phase region. Applying the techniques described to newly available quaternary data has identified the strengths and weaknesses of the methods. This work has expanded the existing knowledge and developed a reliable model for design, operation and optimisation of the phase equilibria required for prediction in many separation processes. Currently available modelling simulation packages are variable in their predictions and sometimes yield unsatisfactory predictions. Many of the current uses of VLLE models are particularly focused on Hydrocarbon/Water systems at high pressure. The work described in this thesis has demonstrated that an EOS with suitable mixing rules can model and predict data for polar organic liquids at atmospheric and below atmospheric pressure and offers the advantage of using the same modelling equations for both phases.

Reflux condensation occurs in a vertical tube when there is an upward core flow of vapour (or gas-vapour mixture) and a downward flow of the liquid film. The understanding of this condensation configuration is crucial in the design of reflux condensers and in loss-of-coolant safety analyses in nuclear power plant steam generators. A range of modelling approaches exists for co-current film condensation from gas-vapour mixtures in parallel-plate channels and tubes. These methods are based on marching from the inlet down the tube and do not apply to the reflux condensation. In this research, however, a two-dimensional two-phase model was developed that solves the steady, full elliptic governing equations in both the film and the gas-vapour core flow on a non-orthogonal mesh that dynamically adapts to the phase interface. Gas-vapour shear and heat and mass transfer at the interface were accounted for fundamentally. This modelling is a big step ahead of current capabilities by removing the limitations of previous reflux condensation models which inherently cannot account for the detailed local balances of shear, mass, and heat transfer at the phase interface. The model was developed and applied for co-current and counter-current flows in vertical parallel-plate channels, followed by vertical tubes. In each stage, the model results were compared against the available experimental and numerical data for validation purposes. A wide range of boundary conditions and geometries have been studied to examine the details of co-current and counter-current condensation phenomena. Velocity, temperature, pressure, and gas mass fraction profiles along with the axial variation of various parameters such as local Nusselt number, film thickness, interface and centre-line temperature and gas mass fraction are presented in parametric studies. / February 2017

La capture du carbone de combustion implique le transport de gaz riches en CO2 a haute temperature. Cette etude vise a preciser les facteurs controlant l'oxydation d'alliages chromino-formeurs dans ces environnements. Des alliages modeles Fe–Cr et Fe–Cr–Ni ont ainsi ete exposes a des melanges Ar–CO2–H2O a 650 et 800 °C, et les produits de reaction examines a l'aide de techniques de metallographie conventionnelles. La precipitation de carbures sous des couches d'oxyde indique une sursaturation en carbone a l'interface metal/oxyde, par rapport a l'atmosphere exterieure. Sur la base d'un modele d'equilibre thermodynamique local, les vitesses de carburation et fractions volumiques de precipites mesurees sont utilisees pour evaluer l'influence de la composition de l'oxyde et de la presence d'H2O dans le gaz sur le transport du carbone. En analysant la depletion en chrome dans l'alliage sous-jacent, nous montrons que la carburation limitee sous une couche de chromine n'altere pas la stabilite de l'oxyde. L'evolution morphologique des nodules d'oxydes riches en fer formes a la suite de la rupture localisee de la chromine est mise en relation avec la capacite de l'alliage a fournir du chrome a l'interface metal/oxyde. L'application de modeles de germination-croissance aux cinetiques de developement de nodules permet d'evaluer la resistance des couches de chromine via des frequences de germination determinees a partir des taux de recouvrement de nodules et des gains de masse des echantillons. Nous examinons enfin l'importance relative de la germination et de la croissance des nodules dans le controle de la performance globale des alliages en fonction de la temperature de reaction. / Materials to convey hot CO2-rich gases are needed in carbon capture technologies currently being developed. This work is aimed at investigating the factors controlling the oxidation of chromia-forming alloys in these atmospheres. To do so, model Fe–Cr and Fe–Cr–Ni alloys were exposed to Ar–CO2–H2O gas mixtures at 650 and 800 °C,and the reaction products examined using conventional metallography techniques. Carbide precipitation beneath oxide scales reflects a carbon supersaturation at the metal/oxide interface relative to the external atmosphere: as a gradient of oxygen potential is established across the growing scale, an elevated carbon activity results at the interface if the scale transmits carbon. On the basis of a local equilibrium model, measured carburisation rates and precipitate volume fractions were used to evaluate the influence of oxide composition and of the presence of H2O in the gas on carbon uptake/transport in the scales. Limited carburisation beneath Cr2O3 scales was shown by means of an analysis of subscale chromium depletion not to alter the oxide stability. The morphological evolution of Fe-rich oxide nodules formed as a result of localised Cr2O3 failure was studied in relation to the alloy ability to supply chromium to the metal/oxide interface. Application of nucleation-growth models to the kinetics of nodule development allowed the resistance of Cr2O3 scales to be evaluated in terms of nodule nucleation rates determined from experimental nodule surface coverages and specimen weight gains. The relative importance of nodule nucleation and growth in determining the overall alloy performance as a function of reaction temperature is discussed.

Cette thèse s'intéresse aux liens entre l'évolution du contenu en eau de l'atmosphère et la formation des précipitations. L'objectif général des travaux qui y sont présentés est d'améliorer la compréhension des mécanismes de formation des précipitations en se basant sur des mesures de vapeur d’eau effectuées principalement par GPS. Une étude statistique originale effectuée à partir de 5 années de mesures (GPS, pluviomètre et capteurs météorologiques au sol, situés sur le campus des Cézeaux, Clermont-Ferrand) a permis de mettre en évidence qu'en moyenne l'augmentation du contenu intégré en vapeur d'eau (IWV) est un précurseur de la formation des pluies, et que les variations de l'humidité dans la colonne atmosphérique toute entière sont pour l'essentiel découplées de celles observées à la surface. En effet, contrairement à l'humidité au sol, l'IWV atteint son maximum en moyenne 20 minutes avant le pic de précipitations. Cela semble indiquer que lorsque les précipitations commencent la condensation devient prépondérante à l'échelle de la colonne atmosphérique toute entière tandis qu'au niveau du sol il y a une forte évaporation. L'étude détaillée des précipitations convectives qui se sont produites sous le vent des Vosges le 18 Juillet 2007 (période d'observation intensive 9a de la campagne Convective and Orographically- induced Precipitation Study - COPS), a permis de mettre en évidence l'apport essentiel du GPS pour l'étude des précipitations convectives dans une région de moyenne montagne. En effet, grâce à une utilisation combinée de mesures radar à haute résolution, d'analyses de surface et de stations GPS (permettant d’observer des structures du champ de vapeur d’eau à petite échelle et haute résolution temporelle, à 2D et 3D), nous avons montré que l'accumulation d'humidité précédait de plusieurs heures l'initiation de la convection et que le déclenchement convectif est favorisé par la convergence du flux d'humidité. Cette dernière est associée à une convergence du vent dans les basses couches, ce qui entraîne un important transport vertical de la vapeur d'eau, observé grâce à la tomographie GPS. La direction du vent en amont du relief s'est révélée contrôler pour beaucoup la localisation des zones de convergence. Le forçage local dû à l'orographie à petite échelle (< 5km) a également été mis en évidence, en complétant les observations par des résultats de simulations numériques à haute résolution. / This thesis focuses on the links between the evolution of atmospheric water vapour content and precipitation formation. The general goal of the works presented is to improve the understanding of the precipitation formation mechanisms using water vapour measurements, primarily made by GPS. An original statistical study based on 5 years of data (from GPS, rain gauge, and other meteorological probes collocated on a platform in Clermont-Ferrand, France) shows that the increase of integrated water vapour amount (IWV) is, on average, a precursor for rain formation. We also show that the IWV evolution is primarily disconnected from the variations in water vapour mixing ratio measured at the surface. Indeed, unlike moisture at the surface, the IWV reaches its maximum on average 20 minutes before the precipitation peak. This could indicate that the condensation dominates in the whole column, while at the surface there is a strong evaporation. The detailed study of convective precipitations which occurred on 18th of July 2007 (Intensive Operation Period 9a of the Convective and Orographically- induced Precipitation Study COPS) on the lee side of the Vosges Mountains shows the significant contribution of GPS measurement for the study of convective precipitations in mountainous areas. Indeed, Thanks to a synergic use of radars, surface meteorological analysis and GPS receivers (which allow the observation of small scale water vapour field features, with a high temporal resolution), we show that the moisture accumulation occurs several hours before convective initiation and we also show that the triggering of the convection is favoured by moisture flux convergence (MFC). This MFC is associated with surface wind convergence leading to a substantial vertical transport of water vapour, which is observed by the GPS tomography. The wind direction on the windward side of the mountains appears to control the location of this convergence zone. The role of local forcing due to small scale orography (< 5km) is also shown, complementing the observations by the results from high resolution numerical model simulations.

La première partie de ce travail présente une nouvelle méthode qui permet de détermination rapidement de la température et de la concentration en fer d'un plasma d'arc MAG utilisé dans la technologie de soudage par plasma. Le plasma est un mélange [Ar-CO2] en présence de fer, avec un rapport molaire entre Ar et CO2 constant de 82%-18%. La seconde partie s'intéresse au rayonnement d'un plasma d'argon utilisé dans la technologie soudage GTAW et pouvant conduire à des dangers photobiologique. Dans le chapitre 1, le contexte et la motivation de ce travail sont présentés. Les travaux déjà effectués et publiés dans ces deux axes scientifiques sont passés en revue. Dans le chapitre 2, les compositions à l'équilibre sont calculées par la méthode de la minimisation de l'énergie libre de Gibbs. Les densités et fonctions de partitions obtenues pour chaque espèces présente dans le plasma sont ensuite utilisées pour déterminer les pertes radiatives des plasmas [Ar-CO2]-Fe via la méthode du coefficient d'émission net (CEN). Cette estimation des pertes ne peut se faire sans le calcul préalable du coefficient d'absorption spectral que nous avons réalisé finement par la méthode " raie par raie ". Tous les mécanismes radiatifs prédominants dans le plasma ont été pris en compte: continua atomique et moléculaire, raies atomiques et moléculaires. Cette partie constitue la base de cette étude sur laquelle se fonde notre nouvelle méthode de diagnostic destinée à déterminer à la fois la température et la concentration en fer d'un plasma d'arc de soudage. Le chapitre 3 est dédié à l'étude expérimentale d'un plasma d'arc MAG constituée d'une analyse spectroscopique permettant de remonter au profil de température et tester l'hypothèse de l'Équilibre Thermodynamique Local. La température d'excitation est obtenue par la méthode de Boltzmann tandis que la mesure d'élargissement de Stark pour les raies de fer et d'argon permet de remonter à la température et la densité des électrons. / This PhD thesis introduces a method that allows the fast determination of temperature and iron concentration for MAG-P Arc. The MAG-P Arc is in fact [Ar-CO2]-Fe mixtures, with a constant molar ratio between Ar and CO2 [82%Ar-18%CO2]. In a second time, this thesis presents a study of the optical radiation associated to photobiological hazards for argon GTAW Arc. In chapter 1, the background and motivation of this work is introduced. The previous works published in this field are reviewed. In chapter 2, the equilibrium compositions are calculated firstly using the minimization of Gibbs free energy. Then the radiative properties of [Ar-CO2]-Fe plasmas are obtained in the frame of the net emission coefficient (NEC) approach, using the accurate "line by line" method. All significant radiative contribution mechanisms are taken into account in the calculation. This study will constitute a groundwork to build the diagnostic method that allows determination of temperature and iron concentration profiles in welding arc. In chapter 3, spectroscopic investigation of the LTE hypothesis across the MAG-P Arc is made. Excitation temperature is obtained with Boltzmann plot method while iron and argon lines Stark broadening measurements are used to get electron temperature and electron density. LTE hypothesis validity across the arc is discussed considering the agreement between the two temperatures, the electron density and iron content. Results show supporting evidence for the main part of the plasma, along radial and axial directions. Discrepancies occur only at the fringe of the arc, where the two temperatures differ by more than 2000 K. In chapter 4, a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase is introduced. This method consists in measuring the plasma spectral radiation of the arc with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570-590 nm and 606-627 nm respectively; calculating theoretically the dependence of the absolute emissivity e570-590 nm and relative emissivity e570-590 nm/e607-627 nm versus the plasma temperature and the iron concentration. This method has also been validated for a layer of plasma by adopting other existing diagnostics such as Stark broadening, which demonstrates the effectiveness of this new method. In chapter 5, a theoretical investigation of the UV (180-400 nm), UVA (315-400 nm) and blue light (300-700 nm) radiation associated with the photobiological hazards to workers for argon GTAW arcs is presented. The radiative properties of argon plasma are calculated for the three spectral regions, and a two-dimensional model of a GTAW arc is then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment. Finally, a general conculsion is given in chapter 6.

Les aérosols fins ont un impact environnemental primordial. Ils influencent notamment la santé, ont un impact sur la visibilité et le climat. Les Aérosols Organiques Secondaires (AOS) représentent une fraction importante des aérosols fins. Les AOS résultent de la conversion d'espèces gazeuses, formées au cours de l'oxydation des composés organiques volatils (COV), en particules par des processus de nucléation et/ou condensation sur des aérosols préexistants. L'oxydation gazeuse des COV implique une myriade de composés secondaires intermédiaires pouvant participer à la formation d'AOS. Les AOS regroupent ainsi une très grande variété d'espèces. Afin d'étudier la formation d'AOS, il est nécessaire de développer des schémas chimiques décrivant explicitement la formation des composés secondaires. Le LISA a développé en collaboration avec le NCAR (National Center of Atmospheric Research) un générateur de schémas chimiques d'oxydation des composés organiques volatils : le GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere). Ce travail vise à tester (i) la fiabilité de GECKO-A à reproduire les concentrations d'AOS observées lors d'expériences en chambre de simulation atmosphérique (CSA) et (ii) la sensibilité de la formation d'AOS aux paramètres physico-chimiques tels que les pressions de vapeur saturante, effets de parois des CSA ou encore aux constantes cinétiques de réaction. Afin d'évaluer la pertinence des schémas chimiques générés avec GECKO-A, le modèle a été confronté à des expériences effectuées en CSA visant à évaluer la formation d'AOS. Le paramètre clé du partitionnement des composés organiques semi-volatils est la pression de vapeur saturante (Pvap) des espèces. Les trois méthodes considérées comme les plus fiables disponibles dans la littérature ont été implémentées dans GECKO-A afin de tester la sensibilité de la formation d'AOS à l'estimation des Pvap. Les pressions de vapeur saturantes estimées par les différentes méthodes présentent des valeurs très différentes s'étalant sur plusieurs ordres de grandeur. Malgré ces divergences marquées, la concentration et la spéciation simulées pour l'AOS s'avèrent en définitive peu sensibles à la méthode utilisée pour estimer les pressions de vapeur. Aucune méthode d'estimation de Pvap n'a par ailleurs permis de réconcilier les concentrations modélisées et observées. La concentration d'AOS demeure systématiquement surestimée de l'ordre d'un facteur 2. L'absorption des composés organiques gazeux semi-volatils sur les murs d'une chambre de simulation atmosphérique a ensuite été étudiée. L'intégration de ce processus dans le modèle conduit à diminuer de façon importante les concentrations simulées en AOS, jusqu'à un facteur 2. En outre, les rendements simulés après implémentation de ce processus apparaissent en bon accord avec les rendements mesurés en CSA. L'hypothèse d'une mauvaise représentation de certains processus en phase gazeuse a également été testée via des tests de sensibilité. En particulier, la sensibilité de la formation d'AOS aux constantes de réactions entre les COV et le radical OH a été explorée. Le système a montré une grande sensibilité à la variabilité des constantes cinétiques de réaction des COV avec le radical OH, que ce soit au niveau de l'estimation de la constante cinétique ou au niveau de la détermination du site d'attaque du radical OH. La sensibilité à l'estimation des constantes de décomposition des radicaux alkoxyles a également été testée. Cette étude n'a en revanche montré que peu d'effets sur le rendement en AOS formé / Fine aerosols have an important impact on health, visibility and climate. Secondary Organic Aerosols (SOA) represent an important fraction of fine aerosol composition. SOA are formed by nucleation or condensation onto pre-existing particles of gaseous species formed during the oxidation of emitted volatile organic compounds (VOC). VOC oxidation implies a huge number of secondary intermediates which are potentially involved in SOA formation. In order to study SOA formation, it is necessary to develop chemical schemes describing explicitly the formation and condensation of the gaseous secondary intermediates. The LISA has thus developed in collaboration with NCAR (National Center of Atmospheric Research) a generator of explicit chemical schemes : GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere). This work aims at testing (i) the reliability of GECKO-A to simulate observed SOA concentrations in Atmospheric Simulation Chamber (ASC) and (ii) exploring the SOA sensitivity to physico-chemical parameters such as saturation vapour pressures, chamber walls effects or kinetics rate constants. In order to assess GECKO-A's chemical schemes, the model has been confronted to chamber experiments performed to study SOA. Saturation vapour pressure (Pvap) is the key parameter controlling the gas/particles partitioning of organic compounds The three Pvap estimation methods considered as the more reliable in the literature have been implemented in GECKO-A. Pvap estimated by the three methods differs highly, up to several orders of magnitude. Despite of these discrepancies, simulated SOA concentration and speciation show a low sensitivity to the method used to estimate the Pvap. Moreover, none of the methods were able to make the model fit the observations. SOA concentration is systematically overestimated of a factor 2. Semi volatile organic compounds deposition on a chamber walls has been investigated. The implementation of this process in the model leads to a significant decrease of the simulated SOA concentrations, up to factor of 2. Simulated SOA yields are in good agreement with measured SOA yields. The hypothesis of a misrepresentation of some gaseous processes has then been investigated through sensitivity tests. SOA formation sensitivity to COV+ OH reactions rate constants has been explored. Results exhibited a high sensitivity to the rate constants estimations (regarding the rate constants values estimation, as well as the determination of the OH attack sites). The estimated alkoxy radicals decomposition rate constants have also been tested. This test showed however no significant impact on the simulated SOA yields

This work mainly investigates the use of aerosol assisted chemical vapour deposition (AACVD) process to fabricate thin film materials for energy efficient glazing and thin film solar cells applications. Ga-doped ZnO thin films were firstly deposited onto glass substrates by AACVD of zinc and gallium acetylacetonates in methanol. After optimizing the doping concentration, film thickness and heating temperature, ZnO:Ga coatings with high visible transparency (> 80 %) and infrared reflection (up to 48.9 % at 2500 nm) were obtained, which is close to the optical requirements for commercial energy saving glazing. Pyramid-shaped and plate-shaped zinc oxides films were then deposited on glass substrates by AACVD of zinc-acetate-dihydrate, acetic acid and deionized water in methanol. These surface-textured ZnO films exhibited good visible transparency (~70 %), low sheet resistance (~60 Ω sq-1) and ultra large haze factor (up to 98.5 %), which is the most hazy ZnO ever reported and can be potentially used as the front contact in thin-film solar cells. Finally, uniform compact CH3NH3PbI3 perovskite films with high phase purity and micron-sized pinhole-free grains were deposited on glass substrates by a novel two-step and three-step sequential AACVD process. In conclusion, AACVD shows a great potential for the scalable fabrication of ZnO-based and organometallic halide-based thin film materials.

This work investigates the use of the novel electric field assisted chemical vapour deposition (EACVD) process in the production of titanium dioxide thin films for photocatalytic applications on glass substrate. This work looks into the interaction of applied electric fields with the precursor species during the aerosol assisted chemical vapour deposition (AACVD) and atmospheric pressure chemical vapour deposition (APCVD) reaction of Titanium isopropoxide (TTIP) and Titanium (IV) Chloride (TiCl4) with different solvents. The electric field was generated by applying a potential difference between two fluorine-doped tin oxide glass sheets. The electric field was varied between 0 – 3000 Vm-1. The deposited films were analysed and characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, UV-vis spectroscopy, water-contact angles and resazurin photcatalytic testing. It was observed that the application of electric fields produced changes in the morphology, particle size, growth rate, crystal orientation and crystal phases. Generally, films produced under the influence of the electric fields showed higher photo-activity than films produced in absence of electric fields. The deposited films produced from the electric field assisted aerosol chemical vapour deposition (EAACVD) showed higher photo-activity with applied AC electric fields than with applied DC electric fields. Likewise, they showed higher photo-activity than the deposited films produced from the electric field assisted atmospheric pressure chemical vapour deposition (EAAPCVD) with applied AC electric fields. The results obtained were explained by the interaction mechanisms between the electric fields and the precursor species, which differ depending on the CVD technique used. Although titanium dioxide photo-activity is comprised by a combination of factors, it was observed that an optimum can be obtained by varying both experimental conditions and field strength. In particular, optimum results were obtained for deposited films which showed long-shaped particles, reduced particle size and high preferential orientation in the anatase (004) plane. Electric field assisted chemical vapour deposition (EACVD) shows a great potential for the improvement of commercial products available in the market such as self-cleaning and antibacterial surfaces.

Solid state synthesis of layered, rotationally disordered intergrowths consisting of rock salt (MX) and hexagonal (TX2) constituents in various sequences [(MX)1+δ]m[TX2]n is carried out by developing structural and compositional prototypes of the desired product, using fine control of the elemental reactants and then annealing at low temperature to facilitate self-assembly. (M = Sn, La, Eu; T = V, Mo.) The remarkable rotational disorder in these systems - in contrast to traditional misfits - and their proven applications in thermal, electrical and thermoelectric disciplines make them a useful group of materials for demonstrating control of reaction pathways of solid state reactions using low temperatures and short times. The synthesized materials are structurally characterized using X-ray diffraction (XRD), X-ray reflectivity (XRR), and Scanning Transmission Electron Microscopy (STEM). Electrical characterization is carried out on patterned samples using the Van der Pauw method of resistivity and the Hall effect method. Composition of the samples is determined using wavelength dispersive electron probe microanalysis (EPMA). Time domain thermoreflectance is used to determine the cross plane thermal conductivity. The family of [(SnSe)1.05]m(MoSe2)n (m = n = 1, 2, 3, 4), which possess the same composition but different unit cell thicknesses, shows that there is no correlation between c-axis unit cell thickness and cross plane thermal conductivity. The family of structural isomers [(SnSe)1.05]4[MoSe2]4, [(SnSe)1.05]3[MoSe2]3[(SnSe)1.05]1[MoSe2]1, [(SnSe)1.05]3[MoSe2]2[(SnSe)1.05]1[MoSe2]2, [(SnSe)1.05]2[MoSe2]3[(SnSe)1.05]2[MoSe2]1,[(SnSe)1.05]2[MoSe2]1[(SnSe)1.05]1[MoSe2]2[(SnSe)1.05]1[MoSe2]1 and [(SnSe)1.05]2[MoSe2]2[(SnSe)1.05]1[MoSe2]1[(SnSe)1.05]1[MoSe2]1 have the same c-axis lattice thickness and absolute composition but have different numbers of [(SnSe)1.05]/[MoSe2] interfaces. Thermal conductivity studies carried out on these showed no correlation with the interface density. (LaSe1-x)1.17(VSe2-y)n (n = 2, 3, 4) feature a family of compounds that self-assemble at higher than usual temperatures. They form non-stoichiometric moieties with unique structural proclivities including La vacancies and V interstitials compared to other ferecrystals or previous misfits. The designable electrical properties show evidence of charge transfer. (EuSe)1+δ(VSe2)n (n = 1, 2, 3) is a family of materials that complements the investigation of Ln-based ferecrystals. They show evidence of multiple M oxidation states. These compounds highlight the use of rational design of structure and composition to tune properties. This dissertation includes previously published and unpublished co-authored material. / 10000-01-01

The production of large area, high quality two-dimensional (2D) materials using chemical vapour deposition (CVD) has been an important and difficult topic in contemporary materials science research, after the discovery of the diverse and extraordinary properties exhibited by these materials. This thesis mainly focuses on the CVD synthesis of two 2D materials; bilayer graphene and monolayer tungsten disulphide (WS2). Various factors influencing the growth of each material were studied in order to understand how they affect the quality, uniformity, and size of the 2D films produced. Following this, these materials were combined to fabricate 2D vertical heterostructures, which were then spectroscopically examined and characterised. By conducting ambient pressure CVD growth with a flat support, it was found that high uniform bilayer graphene could be grown on the centimetre scale. The flat support provides for the consistent delivery of precursor to the copper catalyst for graphene growth. These results provide important insights not only into the upscaling of CVD methods for growing large area, high quality graphene and but also in how to transfer the product onto flexible substrates for potential applications as a transparent conducting electrode. Monolayer WS2 is of interest for use in optoelectronic devices due to its direct bandgap and high photoluminescence (PL) intensity. This thesis shows how the controlled addition of hydrogen into the CVD growth of WS2 can lead to separately distributed domains or centimetre scale continuous monolayer films at ambient pressure without the need for seed molecules, specially prepared substrates or low pressure vacuum systems. This CVD reaction is simple and efficient, ideal for mass-production of large area monolayer WS2. Subsequent studies showed that hexagonal domains of monolayer WS2 can have discrete segmentation in their PL emission intensity, forming symmetric patterns with alternating bright and dark regions. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. These results provide important insights into the spatially varying properties of these CVD-grown TMDs materials, which may be important for their effective implementation in fast photo sensors and optical switches. Finally, by introducing a novel non-aqueous transfer method, it was possible to create vertical stacks of mixed 2D layers containing a strained monolayer of WS2, boron nitride, and graphene. Stronger interactions between WS2 on graphene was found when swapping water for IPA, likely resulting from reduced contamination between the layers associated with aqueous impurities. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, a result which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with large area coverage and controllable thickness on the atomic level.