Thin films of GeTe₂ were deposited on glass substrates using RF magnetron sputtering with various hydrogen flow rates in the growth chamber. Transmission data of deposited films were taken and used to determine optical constants: refractive index (n), extinction coefficient (κ), and absorption coefficient (α)) and the energies: E₀₄, E₀₃, Tauc band gap E[subscript]Tauc and Urbach energy E[subscript]U. An increase of these energies was observed with increasing hydrogen flow rate. This increase is interpreted on the basis of the density of state model proposed by Mott and Davis. An increase of network disorder due to the inclusion of hydrogen into the GeTe₂ thin films was determined from the B[superscript]1/2 parameter, Urbach energy and full width at half maximum of Raman vibrational modes. The crystallization process induced by thermal annealing on GeTe₂ was studied. X-ray diffraction measurements were performed and the results suggest that crystallization of GeTe₂ occurs via a phase separation into Te and GeTe crystalline phases. This observation is in agreement with a previous report. The crystallization temperature increases with the addition of hydrogen. This increase is explained in terms of dangling bonds. A large change (approximately 60 percent decrease) of the optical transmission occurs after the phase change from amorphous to crystalline. This decrease is interpreted as a result of the observed phase separation.

In this thesis methodological developments have been made for the description of flexible conjugated dyes in room temperature spectrum calculations. The methods in question target increased accuracy and efficiency by combining classical molecular dynamics (MD) simulations with time-dependent response theory spectrum calculations. For absorption and fluorescence spectroscopies a form of conformational averaging is used, where the final spectrum is obtained as an average of spectra calculated for geometries extracted from ground and excited state MD simulations. For infrared and Raman spectroscopies averaged spectra are calculated based on individual spectra, obtained for zero-temperature optimized molecular structures, weighted by conformational statistics from MD trajectories. Statistics for structural properties are also used in both cases to gain additional information about the systems, allowing more efficient utilization of computational resources. As it is essential that the molecular mechanics description of the system is highly accurate for methods of this nature to be effective, high quality force field parameters have been derived, describing the molecules of interest in either the MM3 or CHARMM force fields. These methods have been employed in the study of three systems. The first is a platinum(II) actylide chromophore used in optical power limiting materials, for which a ultraviolet/visible absorption spectrum has been calculated. The second is a family of molecular probes called luminescent conjugated oligothiophenes, used to detect and characterize amyloid proteins, for which both absorption and fluorescence spectra have been calculated. Finally, infrared and Raman spectra have been calculated for a group of branched oligothiophenes used in organic solar cells. In addition, solvation effects have been studied for conjugated poly\-eletrolytes in water, resulting in the development of two solvation models suitable for this class of molecules. The first uses a quantum meachanics/molecular mechanics (QM/MM) description, in which the solute mole\-cule is described using accurate quantum mechanical methods while the surrounding water molecules are described using point charges and polarizable point dipoles. The second discards the water entirely and removes the ionic groups of the solute. The QM/MM model provides highly accurate results while the cut-down model gives results of slightly lower quality but at a much reduced computational cost. Finally, a study of protein-dye interactions has been performed, with the goal of explaining changes in the luminescence properties of the LCO chromophores when in the presence of amyloid proteins. Results were less than conclusive.

Die Schwingungsspektroskopie, besonders die Raman-Spektroskopie, stellt ein wichtiges Werkzeug für Untersuchungen von Biomineralien dar. Raman-Spektroskopie wurde zur Untersuchung der organischen und anorganischen Bestandteile von Schwammskeletten eingesetzt. Die Raman-Spektroskopie trug auch zur Charakterisierung von biomimetischen Silikat-Präzipitaten bei. Durch ortsaufgelöste Raman-Spektroskopie konnte erstmalig die Verteilung von organischem Material in den extrahierten Silikatzellwänden von Kieselalgen nachgewiesen werden. Die ortsaufgelöste Raman-Spektroskopie wurde ebenfalls zur Untersuchung des SERS-Effekts an Zellwänden von Kieselalgen an die Silber-Nanopartikel gekoppelt waren eingesetzt.

This dissertation presents subwavelength optics with focus on the theory and applications of subwavelength apertures in a metal film. Two main issues regarding the optics with subwavelength apertures are investigated. As the first issue, the extraordinary optical transmission (EOT) through a single hole in a metallic waveguide is presented. A total transmission through a single subwavelength aperture is theoretically predicted for a perfect electric conductor regardless of the aperture size, without relying on aperture arrays and surface corrugations as presented in previous works. The waveguide EOT is then applied to boost the optical throughput of an apertured near-field scanning optical microscope (NSOM) probe. Using a new structure for the apertured NSOM probe which allows for waveguide EOT, the optical throughput and the damage threshold are boosted by 100× and 40× as compared to a conventional structure, and the experimental findings are backed-up by comprehensive finite-difference time-domain (FDTD) simulations. Single fluorescent molecules are scanned using the EOT apertured NSOM probe, and a spatial resolution of 62 nm is achieved. As the second issue, subwavelength apertures are found useful for optical trapping. A small dielectric particle can significantly change the optical transmission through an aperture by dielectric loading, and subsequently, a large optical force is induced which favors trapping. A self-induced back-action (SIBA) optical trap is designed using a circular nanohole in a gold film. Trapping of 50 nm polystyrene particle is experimentally achieved, which is not possible using a conventional single beam optical tweezers. The circular nanohole SIBA trap works beyond the perturbative regime, as proven by FDTD simulations and a Maxwell stress tensor analysis. We further improve the nanohole trapping using a double-nanohole, which is more sensitive for small dielectric changes due to the intense local field enhancement between its two sharp tips. A single 12 nm silica sphere is experimentally trapped using the double-nanohole, as the smallest trapped dielectric particle reported. We also achieve the trapping of a single protein – a bovine serum albumin (BSA) protein with a hydrodynamic radius of 3.4 nm in the folded form. The trapped BSA is also unfolded by the large optical force, as confirmed by experiments with changing optical power and changing pH. The high signal-to-noise ratio of 33 in monitoring single protein trapping and unfolding shows a tremendous potential for using the double-nanohole as a sensor for protein binding events at a single molecule level. / Graduate

The study of two pharmaceutically active systems that each display polymorphism has provided a platform upon which to develop and apply solid-state NMR techniques in order to increase the understanding of the solid-state structure of small organic molecules. The multidisciplinary approach adopted has highlighted the advantages of solid-state NMR as a non-invasive probe of molecular conformation and crystallographic packing.Carbon-13 CP/MAS spectra of the two polymorphs of BRL55834 - a fluorinated benzopyran derivative - immediately suggest the presence of one and three molecules in the asymmetric unit. A lack of crystals suitable for single-crystal XRD has catalysed the application of high-power powder X-ray diffraction studies. Subsequent attempts at structure solution using Genetic Algorithm techniques are showing preliminary results that reinforce predictions made from solid-state NMR. Novel triple-channel techniques have aided assignment and resolution of die complex (^13)C CP/MAS spectra. Enrichment of the (^15)N site appears to have resulted in the formation of a new polymorph. Techniques for the analysis of detection Units have been developed using solid-state Raman spectroscopy and chemometric analysis. The aminoxanthine derivative, BRL61063, provides interesting inter-form variations in molecular disorder, solid-state packing, and hydrogen bonding. A previously basic understanding of the single-crystal XRD data has been further evaluated through the course of this Ph.D. and solid-state NMR spectral editing techniques have been developed and applied to identify these phenomena. Recrystallisation studies have produced two samples that appear to exist in an intermediate state between the rigid and mobile structural limits. Temperature variation causes interesting changes in the relaxation characteristics and natural abundance (^15)N and (^13)C CP/MAS spectra. Residual dipolar coupling effects vary in their manifestation within the (^13)C CP/MAS spectra of the polymorphic systems studied and comparison with the literature yields important information regarding molecular conformation. Nitrogen-15 enrichment and operation at higher magnetic field have been applied to reduce these second order effects. Finally, some distance has been travelled along the path towards decoupling (^14)N. Future development of this technique holds potential for resolution enhancement in the solid state spectra of most naturally occurring, nitrogen-containing molecules.

Mars is one of the best candidates among planetary bodies for supporting life. The presence of water in the form of ice and atmospheric vapour together with the availability of biogenic elements and energy are indicators of the possibility of hosting life as we know it. The occurrence of permanently frozen ground – permafrost, is a common phenomenon on Mars and it shows multiple morphological analogies with terrestrial permafrost. Despite the extreme inhospitable conditions, highly diverse microbial communities inhabit terrestrial permafrost in large numbers. Among these are methanogenic archaea, which are anaerobic chemotrophic microorganisms that meet many of the metabolic and physiological requirements for survival on the martian subsurface. Moreover, methanogens from Siberian permafrost are extremely resistant against different types of physiological stresses as well as simulated martian thermo-physical and subsurface conditions, making them promising model organisms for potential life on Mars. The main aims of this investigation are to assess the survival of methanogenic archaea under Mars conditions, focusing on methanogens from Siberian permafrost, and to characterize their biosignatures by means of Raman spectroscopy, a powerful technology for microbial identification that will be used in the ExoMars mission. For this purpose, methanogens from Siberian permafrost and non-permafrost habitats were subjected to simulated martian desiccation by exposure to an ultra-low subfreezing temperature (-80ºC) and to Mars regolith (S-MRS and P-MRS) and atmospheric analogues. They were also exposed to different concentrations of perchlorate, a strong oxidant found in martian soils. Moreover, the biosignatures of methanogens were characterized at the single-cell level using confocal Raman microspectroscopy (CRM). The results showed survival and methane production in all methanogenic strains under simulated martian desiccation. After exposure to subfreezing temperatures, Siberian permafrost strains had a faster metabolic recovery, whereas the membranes of non-permafrost methanogens remained intact to a greater extent. The strain Methanosarcina soligelidi SMA-21 from Siberian permafrost showed significantly higher methane production rates than all other strains after the exposure to martian soil and atmospheric analogues, and all strains survived the presence of perchlorate at the concentration on Mars. Furthermore, CRM analyses revealed remarkable differences in the overall chemical composition of permafrost and non-permafrost strains of methanogens, regardless of their phylogenetic relationship. The convergence of the chemical composition in non-sister permafrost strains may be the consequence of adaptations to the environment, and could explain their greater resistance compared to the non-permafrost strains. As part of this study, Raman spectroscopy was evaluated as an analytical technique for remote detection of methanogens embedded in a mineral matrix. This thesis contributes to the understanding of the survival limits of methanogenic archaea under simulated martian conditions to further assess the hypothetical existence of life similar to methanogens on the martian subsurface. In addition, the overall chemical composition of methanogens was characterized for the first time by means of confocal Raman microspectroscopy, with potential implications for astrobiological research. / Der Mars ist unter allen Planeten derjenige, der aufgrund verschiedener Faktoren am wahrscheinlichsten Leben ermöglichen kann. Das Vorhandensein von Wasser in Form von Eis und atmosphärischem Dampf zusammen mit der Verfügbarkeit biogener Elemente sowie Energie sind Indikatoren für die Möglichkeit, Leben, wie wir es kennen, zu beherbergen. Das Auftreten von dauerhaft gefrorenen Böden, oder auch Permafrost, ist ein verbreitetes Phänomen auf dem Mars. Dabei zeigen sich vielfältige morphologische Analogien zum terrestrischen Permafrost. Permafrostgebiete auf der Erde, welche trotz extremer, Bedingungen durch eine große Zahl und Vielfalt mikrobieller Gemeinschaften besiedelt sind, sind hinsichtlich möglicher Habitate auf dem Mars die vielversprechendste Analogie. Die meisten methanogenen Archaeen sind anaerobe, chemolithotrophe Mikroorganismen, die auf der Marsoberfläche viele der metabolischen und physiologischen Erfordernisse zum Überleben vorfinden. Methanogene Archaeen aus dem sibirischen Permafrost sind zudem extrem resistent gegenüber unterschiedlichen Formen von physiologischem Stress sowie simulierten thermo-physikalischen Marsbedingungen. Die Hauptziele dieser Untersuchung bestehen darin, das Überleben der methanogenen Archaeen unter Marsbedingungen zu beurteilen, wobei der Fokus auf methanogenen Archaeen aus dem sibirischen Permafrost liegt, sowie deren Biosignaturen mit Hilfe der Raman-Spektroskopie zu charakterisieren, einer starken Technologie zur mikrobiellen Identifikation, welche bei der ExoMars-Mission zum Einsatz kommen wird. Zu diesem Zweck wurden methanogene Archaeen aus dem sibirischen Permafrost sowie aus Nicht-Permafrost-Habitaten in Simulationen Marsbedingungen ausgesetzt, wie Austrocknung durch Langzeitversuche bei ultraniedrigen Temperaturen unter dem Gefrierpunkt (-80ºC), Mars-analogen Mineralien (S-MRS und P-MRS) sowie einer Marsatmosphäre. Weiterhin wurden die Kulturen verschiedenen Konzentrationen von Magnesiumperchlorat, einem starken Oxidant, der im Marsboden nachgewiesenen wurde, ausgesetzt. Ferner wurden die Biosignaturen einzelner Zellen der methanogenen Archaeen mit Hilfe der konfokalen Raman-Mikrospektroskopie (CRM) charakterisiert. Die Ergebnisse zeigten für alle untersuchten methanogenen Stämme Überleben und Methanbildung, nachdem diese simulierten Austrocknungsbedingungen ausgesetzt worden waren. Nach Versuchen mit Temperaturen unter dem Gefrierpunkt zeigten die Stämme aus dem sibirischen Permafrost eine schnellere Wiederaufnahme der Stoffwechseltätigkeit, wohingegen bei den Referenzorganismen aus Nicht-Permafrost-Habitaten die Zell¬membranen im größeren Ausmaß intakt blieben. Der Stamm Methanosarcina soligelidi SMA-21 aus dem sibirischen Permafrost zeigte nach dem Belastungstest mit Marsboden und Mars-analoger Atmosphäre signifikant höhere Methanbildungsraten. Zudem überlebten alle untersuchten Stämme die Zugabe von Magnesiumperchlorat in der entsprechenden Konzentration, die auf dem Mars vorkommt. Weiterhin konnten durch die Raman-Spektroskopie beachtliche Unterschiede in der chemischen Zusammensetzung zwischen methanogenen Archaeen aus Permafrost- und Nicht-Permafrost-Habitaten, trotz ihrer phylogenetischen Verwandtschaft, ermittelt werden. Die Konvergenz der chemischen Zusammensetzung der Permafrost-Stämme könnte das Resultat ihrer Anpassung an die Umgebung sein, was auch die Unterschiede hinsichtlich ihrer Resistenz verglichen mit Nicht-Permafrost-Stämmen erklären könnte. Als Teil dieser Studie wurde die Raman-Spektroskopie als Analyse-Technik zur Ferndetektion von methanogenen Archaeen, welche in eine Mineral-Matrix eingebettet sind, evaluiert. Diese Dissertation trägt zu einem besseren Verständnis hinsichtlich der Grenzen für ein Überleben von methanogenen Archaeen unter simulierten Marsbedingungen bei und damit zu einer Beurteilung der Hypothese, ob es ähnliches Leben unter der Marsoberfläche geben könnte. Darüber hinaus wurde erstmalig die chemische Zusammensetzung von methanogenen Archaeen mit Hilfe der Raman-Mikrospektroskopie charakterisiert. Dieser Technologie kommt eine wesentliche Bedeutung für weitere Forschungstätigkeit in der Astrobiologie zu.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on March 23, 2010). Thesis advisor: Dr. Mengshi Lin. Includes bibliographical references.

One of the most important events in the history of life is the evolution of the complex, eukaryotic cell. The eukaryotes are complex organisms with membrane-bound intracellular structures, and they include a variety of both single-celled and multicellular organisms: plants, animals, fungi and various protists. The evolutionary origin of this group may be studied by direct evidence of past life: fossils. The oldest traces of eukaryotes have appeared by 2.4 billion years ago (Ga), and have additionally diversified in the period around 1.8 Ga. The Mesoproterozoic Era (1.6-1 Ga) is characterised by the first evidence of the appearance complex unicellular microfossils, as well as innovative morphologies, and the evolution of sexual reproduction and multicellularity. For a better understanding of the early eukaryotic evolution and diversification patterns, a part of this thesis has focused on the microfossil records from various time periods and geographic locations. Examination of microfossil morphology, cell wall microstructure and biochemical properties, reflect their intracellular complexity and function, and allow reconstructions of their life cycle, as well as observing the evolutionary pattern of change from Mesoproterozoic, to Cambrian-Ordovician transition. Several case studies included assemblages deriving from Mesoproterozoic, Neoproterozoic and early Paleozoic time intervals that show disparate morphotypes and innovative features indicative of algal clades. The Mesoproterozoic Ruyang Group in northern China has yielded a diverse microfossil assemblage that provides important clues about the diversification of different eukaryotic groups. Furthermore these microfossils contributed an additional evidence for the emergence of the crown group Eukarya by 1.7-1.4 Ga. In another part of this thesis, examination of wall microstructure and chemical properties via Raman spectroscopy has been used to assess the biological affinities of various Neoproterozoic problematic carbonaceous compression fossils. Studies on the early Phanerozoic (c. 545-485 Ma) assemblages from Estonia reconstructed patterns of the early radiations of phytoplankton and its evolutionary innovations. A continuing theme in this thesis has been using a combination of evidence of microfossils’ fine-scale morphology, ecology and chemical properties to determine their function in life, in addition to their systematic position. / Palaeobiology and diversification of Proterozoic-Cambrian photosynthetic eukaryotes

Si le graphène est un candidat prometteur pour de nombreuses applications, il reste des questions fondamentales à résoudre. Les objectifs de cette thèse visent à obtenir une crois- sance de graphène de haute qualité, à développer de nouveaux concepts de transfert pour réaliser de nouveaux dispositifs tout en contrôlant la formation de défauts dans sa struc- ture. Nous avons été en mesure d'augmenter la surface d'une monocouche polycristalline de graphène d'une échelle de quelques centimètres à celle d'une plaquette de silicium sans changer de chambre CVD. D'autre part, nous avons démontré une méthode permettant de diminuer la densité de nucléation et ainsi d'obtenir du graphène monocristallin de quelques centaines de microns. Concernant la réalisation de nouveaux dispositifs, nous avons obtenu des circuits à base de graphène polycristallin empilés par transferts successifs où la région de bicouche artificielle se comporte comme un bicouche intrinsèque. Nous avons également développé une nouvelle méthode pour suspendre le graphène à l'échelle macroscopique sur des supports en piliers. Dans un tel système, les contraintes dans le graphène restent in- férieures à 0,2%. Par la suite une méthode de dépôt d'électrodes par voie sèche a été développée pour éviter toute dégradation du graphène. Ce processus de transfert a été amélioré pour atteindre des tailles de substrats allant jusqu'à 4 pouces pour le silicium et le saphir. Il a été enfin utilisé comme électrode transparente d'une LED à puits quantiques pour remplacer des électrodes Ni / Au . Nous avons mis au point des procédés de création sélective de défauts sur le graphène. Tout d'abord des défauts ont été induits chimiquement de façon contrôlable et ont été analysés par spectroscopie Raman et microscopie électronique en transmission qui ont révélé un mécanisme en deux étapes de formation de défauts dans la structure de graphène. Nous avons également étudié l'effet des défauts chargés adsorbés sur la surface du graphène sans former de liaisons avec lui. Contrairement à la littérature où les particules chargées sont déposées a posteriori, les nanoparticules chargées étaient présentes pendant la croissance sur cuivre. Nous interprétons l'existence d'une bande de phonons D' très intense devant celle de la D, et encore jamais signalée avec la présence de ces nanoparticules / Though graphene is strong candidate to make various applications, still there are issues that need to be resolved. The purpose of this thesis is to grow high quality graphene and transfer it to make new graphene based devices and to engineer defects into graphene structure. We have been able to increase the growth polycrystalline monolayer graphene from few centimeter scale to wafer scale without changing the CVD chamber. At the same time, we have demonstrated a method to decrease the nucleation density which allows us to grow large single crystal graphene from few to hundreds of micrometer. Concerning new design of graphene based devices, the polycrystalline graphene was trans- ferred to create artificial bilayer crossbars where the bilayer region behaved like naturally grown bilayer graphene. We have also developed a novel method of suspending graphene in macroscopic scale in pillared surface. In such a system, the strain in graphene is found to be less than 0.2%. Thereafter a completely dry method of depositing electrodes was developed which prevents damaging of graphene. The scale and process of transferring graphene was improved to different substrates such as 4 inch Si and sapphire substrates. It was used as transparent electrode to in a quantum well LED to replace the Ni/Au electrodes. We have been able to engineer defects into graphene. Firstly defects were induced in a controllable way using chemical method and were analyzed using Raman spectroscopy and Transmission Electron Microscopy which revealed a two step mechanism of defect formation in the graphene structure. We have also studied the effect of charged defects which adsorb onto the graphene surface without forming bonds with it. Unlike in literature where charged particles were deposited onto graphene, here the charged nano particles were present dur- ing the growth process in the copper foil. We believe that due to these nano particles, the intensity of D' phonon is greatly enhanced. Such anomalously higher intensity of D' band compared to D band has not been reported before

Cette thèse porte sur l’optimisation d’un procédé de croissance, reproductible et contrôlé, d’une monocouche de graphène sur la face –Si du carbure de silicium (SiC (0001)) par sublimation sous faible pression d’argon (10 mbars). Au vue de la littérature, cette croissance à faible pression reste un challenge. Différentes techniques complémentaires telles que la spectroscopie Raman, la microscopie à force atomique, la microscopie à effet tunnel et des mesures d’effet Hall ont été menées afin de valider la croissance de la monocouche et d’en étudier sa morphologie de surface ainsi que ses propriétés structurales et électroniques. L’ensemble des résultats obtenus démontre le contrôle de la croissance d’une monocouche de graphène homogène, continue et de grande taille (6x6mm²). Plus de 50 échantillons monocouches ont été synthétisés pendant la thèse démontrant ainsi un procédé reproductible dans un bâti de croissance prototype de la société montpelliéraine Annealsys. Un mécanisme de croissance en bord de marche et la présence de marches et de terrasses a pu être mis en évidence alors que la littérature rapporte des difficultés à optimiser des procédés de croissance à basse pression d’argon. L’effet de la vitesse de montée en température a également été étudié dans le but de contrôler la morphologie du SiC de façon à pouvoir évaluer l’impact de la largeur des marches sur les propriétés électroniques du graphène. La largeur des marches obtenue (10 µm) permettront des mesures originales de transport, localisées sur une marche.Le procédé robuste et reproductible développé a permis différentes études approfondies sur ce graphène épitaxié. Sur la face-Si du SiC croît d’abord une couche tampon liée de manière covalente au SiC. Une deuxième couche tampon croît sous la première qui devient alors du graphène. Le peu de résultats présents dans la littérature nous a conduit à étudier cette couche d’interface entre le graphène et le SiC. A partir d’un nombre important de mesures par spectroscopie Raman, la signature de cette couche tampon a pu être obtenue. Un spectre Raman inhomogène de celle-ci a été mis en évidence. Pour aller plus loin, nous avons mis en œuvre deux techniques d’exfoliation du graphène pour avoir accès à la couche tampon sur SiC. Les signatures Raman des couches tampon couvertes ou non de graphène ont été analysées et comparées. Deux résultats majeurs sont à souligner : (i) l’aire du signal Raman de la couche tampon augmente après le retrait du graphène et (ii) deux pics fins sont observés seulement sur le spectre du graphène épitaxié. Ces résultats démontrent l’existence d’un couplage entre le graphène et la couche tampon.La dernière partie de ce travail de thèse concerne les propriétés électriques de ces monocouches de graphène sur SiC. Contrairement au classique dopage n du graphène épitaxié sur SiC (0001), un dopage résiduel de type p a été mesuré et attribué à un effet de l’environnement. Les impuretés chargées présentes à la surface des échantillons pourraient être à l’origine de flaques d’électrons et de trous (puddles) réparties à la surface des échantillons et responsables de leur dopage inhomogène. Ces fluctuations de potentiel ont été estimées en ajustant les données expérimentales à partir d‘un modèle mettant en jeu deux types de porteurs. De plus, nous avons pu mettre en évidence un changement de dopage d’un type p à n sous vide et sous illumination UV. La désorption d’absorbants chargés pourrait expliquer ce changement. Ces résultats démontrent une possible modulation des propriétés électriques de nos échantillons par un facteur externe tel que l’exposition aux UV. / This manuscript presents a work aiming to optimize a reproducible and controlled growth process of a monolayer graphene on Si-face of SiC (SiC (0001)) by sublimation under low argon pressure, i.e. 10 mbar. This low pressure process is challenging regarding the results in the literature. Various complementary techniques as optical microscopy, Raman spectroscopy, atomic force microscope, scanning tunneling microscope, and Hall Effect measurements have been performed on the samples in order to validate the monolayer graphene growth and investigate their surface morphology, their structural and electronic properties. All the results obtained from these measurements confirm the control of homogeneous, continuous and large-size (6×6 mm²) monolayer graphene from our optimized growth process. More than 50 monolayers graphene were produced during this thesis, validating a reproducible process in a prototype furnace developed by Annealsys, local company in Montpellier. The step-flow growth mode which encourages the formation of step-terrace surface structures is obtained under this unclassical growth condition contrary as established in the literature. Moreover, we have investigated the effect of the temperature ramp on the SiC morphology to evaluate the impact of the width of the terraces on electronic properties of graphene. Samples with terraces larger than 10 µm have been obtained allowing original transport measurements localized on only one terrace.Thanks to the reproducibility of our optimized growth process, further characterization studies on epitaxial graphene were investigated. The first carbon layer grown on SiC (0001) is a buffer layer covalently linked to SiC. Then a second buffer layer grows under the first one that becomes graphene. This well-known buffer layer at graphene / SiC (0001) interface has been investigated in this thesis to complete the poor literature on this topic. Statistically buffer Raman signatures have been obtained and compared to the literature demonstrating an inhomogeneous buffer layer. Furthermore, we have developed two graphene transfer techniques aiming to exfoliate graphene layer and leave behind only the buffer layer on the sample surface. The Raman signatures of buffer layer in these two cases (with or without graphene coverage) have been compared. We believe the evidenced evolution could be related to the coupling between graphene and buffer layer. Two major results illustrate this coupling: (i) the Raman signature of buffer layer increases in integrated intensity after the graphene transfer and (ii) two fines peaks are observed only in epitaxial graphene spectra and not in uncovered buffer layer spectra.The last part of this work concerns the electrical properties of monolayer graphene on SiC (0001). Contrary to the typical n-type doping of epitaxial graphene, the low p-type residual Hall concentration observed in our samples has been related to the atmospheric effect. More precisely, the charged impurities deposited on the sample surface could lead to the formation of electron-hole puddles, resulting in an inhomogeneous doping. The potential fluctuation has been estimated by fitting the experimental data using a model of two types of charges. Moreover, we have shown that the doping type change from p-type to n-type under vacuum condition or under UV illumination. This could be explained by desorption of the charged absorbents during the pumping or UV illumination. These results demonstrate the possibility of tuning the electrical properties of our samples by external factor such as UV light.