In dieser Arbeit wurden einerseits die elektronischen Eigenschaften von Graphenen und andererseits die Verwendung von Graphenen und Kohlenstoff-basierten Hybridmaterialien als transparente Elektroden untersucht. Entsprechend ist der erste, umfangreichere Teil der Arbeit Grundlagen-orientiert und fokussiert auf die elektrostatische Wechselwirkung zwischen Graphen und dem Substrat Glimmer. Der zweite, kleinere Teil befasst sich mit der Entwicklung leitfähiger Tinten auf der Basis von Graphenen und anderen Kohlenstoff-basierten Hybridmaterialien für Anwendungen in der druckbaren Elektronik, insbesondere für die Herstellung transparenter Elektroden. Graphen auf Glimmer ist ein sehr wohldefiniertes System, in dem das Graphen über mehrere Quadratmikrometer atomar flach ist. Schichtdickenabhängige Variationen des Oberflächenpotentials von einzel- und mehrlagigen Graphenen auf Glimmer wurden mittels Kelvin Probe Rasterkraftmikroskopie untersucht. Damit konnte die elektrostatische Abschirmlänge von Graphen auf Glimmer bestimmt werden. Lokale Variationen des Oberflächenpotentials innerhalb einer Graphenlage, verursacht durch eingeschlossene Wasserschichten zwischen Graphen und Glimmer, wurden mit Rasterkraftmikroskopie, elektrostatischer Rasterkraftmikroskopie und der Raman-Spektroskopie untersucht. Dies ermöglichte es, die Dotierung von Graphen durch eingeschlossene Wasserschichten zu quantifizieren. Außerdem wurde gezeigt, dass Graphen auf molekular modifiziertem Glimmer lokal auf der Nano-Skala dehnbar ist. Dabei wurde der Glimmer durch das Aufbringen von dendronisierten Polymeren verschiedener Generationen auf Nanometer-Skala modifiziert. Dies eröffnet neue Möglichkeiten, die lokalen elektronischen Eigenschaften von Graphen durch Dehnung zu kontrollieren.Schließlich wurden Kohlenstoff-basierte leitfähige Tinten hergestellt, daraus transparente Elektroden hergestellt, und die Formulierungen der Tinten für das Drucken auf Plastiksubstrate optimiert. / This work focusses on the electronic properties of graphene on the one hand, and on the application of graphenes and other carbon-based hybrid materials for transparent electrodes on the other hand. Accordingly, the first part of the work, which is the larger one, is of fundamental nature and focusses on the electronic interaction between graphene and mica as a substrate. The second, smaller part deals with the design of novel conductive inks based on graphene and other carbon-based hybrid materials for applications in printed electronics, in particular for the production of transparent electrodes. Graphene on mica is a very well defined system, which provides atomically flat graphene extending over several square micrometers. Layer-dependent surface potential variations of single and few layered graphenes on mica were probed with Kelvin Probe Force Microscopy. This allowed to estimate the screening length of graphene on mica. Local variations of the surface electrostatic potential above single layer graphene, originating from confined fluid interfacial monolayers of water between the mica and the graphene, were monitored with Scanning Force Microscopy, Electrostatic Scanning Force Microscopy and Raman spectroscopy. This allowed to quantify the doping of graphene by the confined water layers. Exfoliation of graphene onto adsorbed nanostructures on mica allowed to control the strain of graphene at the nano-scale. Nanostructuring was achieved by first coating mica with submonolayers of dendronized polymers of different generations and subsequently depositing graphene. This approach provides new opportunities for the control of the electronic properties of graphene by strain.Finally, novel conducting carbon-based inks were designed and transparent electrodes were fabricated therefrom. The formulations of the inks were optimized for printing on plastic substrates.

Depuis près d'un demi-siècle, l'industrie de la microélectronique a prospéré grâce à la miniaturisation des transistors Si CMOS. Cependant, la course à la miniaturisation se heurtera dans les prochaines années à des barrières physiques incontournables. Ainsi, de nombreux travaux technologiques sont en cours de réalisation sur les technologies émergentes et avancées. Ces technologies, notamment le graphène et la CMOS FD-SOI, représentent de grandes opportunités dans le domaine de la microélectronique, et notamment pour la conception de circuits radiofréquences et millimétriques. En outre, avec l'évolution croissante des objets et services connectés, les chercheurs travaillent intensivement sur les systèmes sans fil de cinquième génération (5G). La demande de débit de donnés et le besoin de spectre ont motivé l'utilisation de fréquences millimétriques. Par conséquent, la recherche 5G est confrontée par un ensemble de défis. L'un des défis majeurs de la 5G est la réduction de la consommation d'énergie. En fait, l'efficacité énergétique est directement liée à la fiabilité et au coût des systèmes de communication. L'amplificateur de puissance est l’élément le plus consommateur d'énergie, et l'un des blocs les plus critiques des émetteurs-récepteurs radio. Ainsi, la recherche dans ce domaine est cruciale pour les systèmes de communication de la prochaine génération. Par conséquent, l'objectif de cette thèse est d'étudier et de concevoir des amplificateurs de puissance sur les technologies émergentes et avancées pour les applications 5G. / For nearly half a century, the microelectronics industry has flourished based on the scaling of the silicon CMOS transistor technology. However, the race to transistor miniaturization encounters inevitable physical barriers. Thus, many technological works are under way for the realization of future transistors on emerging and advanced technologies. These technologies, notably the graphene and the CMOS FD-SOI, represent great opportunities for research in the fields of microelectronics, and especially for the design of radiofrequency and millimeter circuits. Besides, with the rising evolution of wireless devices and services, researchers are intensively working on the fifth generation (5G) wireless systems. The demand for high speed data and the need for more spectrum, have motivated the use of millimeter wave carrier frequencies. Therefore, the 5G research is faced with an evolving set of challenges. One of the major challenges of the next generation communication technology is reducing energy consumption. In fact, the power efficiency is directly related to the reliability and cost of the communication systems. It is widely known that the radiofrequency power amplifier is the most power consuming component in the radio transceivers, and is also one of the most critical building blocks in radio front-end. Therefore, research in this area is crucial for next generation communication systems. Consequently, the objective of this thesis is to study and design power amplifiers on emerging and advanced technologies for 5G applications.

The surface-specific technique of vibrational sum frequency spectroscopy (VSFS) can provide vibrational information about chemical bonds at surfaces and interfaces. Two photons, of visible and infrared frequency, are spatially and temporally overlapped at a surface/interface to produce a photon at the sum frequency (SF) of the two input photons. As well as this process only being allowed in non-centrosymmetric media (i.e. VSFS is surface/interface specific), the SF process is enhanced when the IR beam is resonant with vibrational resonances. Broadband VSFS has been used in this project to study surfaces of two distinct classes of materials, namely graphene and polymers. Firstly, broadband VSFS was used to investigate the heating polymeric thin films using a home-built heated sample cell. The cell was tested using self-assembled monolayers (SAMs) of 1-octadecanethiol (ODT) grown on gold substrates. It was subsequently used to investigate thin films of poly(methyl methacrylate) (PMMA) of four different thicknesses and two different molecular weights that were spin-coated onto gold substrates. It was shown that the monolayers of ODT become disordered upon heating and solidified to incorporate the disorder introduced by the heating process. The PMMA films were also shown to become more disordered as a function of temperature. Secondly, broadband VSFS was used to investigate modified graphene, motivated by the fact that modifications to pristine graphene, be it intentional (i.e. functionalisation) or unintentional (i.e. contamination), cause the properties of graphene to change. This project focused on studying hydrogenated graphene, N-methylbenzamide functionalised graphene and contamination on commercial graphene. A method for calculating the number of hydrogen atoms in a hydrogen island was developed. VSF spectra of CH stretches in N-methylbenzamide functionalised graphene were obtained. Residues on commercially bought graphene were detected using VSFS and RAIRS. These residues were assigned to PMMA that remained on the CVD graphene by the process of transferring the CVD graphene from the copper foil on which it was grown onto the gold substrates.

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

Les copolymères à bloc (BCP) ont la propriété particulière de s’auto-assembler en structures périodiques. Ces macromolécules en association avec la photolithographie est un candidat prometteur à utiliser comme technique alternative pour les patterning avancé de très haute résolution. De cette façon, la réduction des circuits intégrés peut être maintenue. Les BCPs avec une forte incompatibilité chimique entre les deux blocs présentent une valeur élevée du paramètre d’interaction de Flory-Huggins χ. La théorie des BCPs prédit des caractéristiques périodiques de seulement quelques nanomètres avec des BCPs à haut valeur d’interaction.Cette thèse présente un dispositif expérimental en vue du développement d’une lithographie à BCPs de deuxième génération en utilisant le polystyrène-bloc polydiméthylsiloxane (PS-b-PDMS), contre le polystyrène-bloc-Polydi(méthyle méthacrylate) (PS-b-PMMA) à faible valeur de χ. Sur ce sujet, la cinétique d’auto-assemblage d’un PS-b-PDMS avec une valeur du paramètre de segregation χN élevée a été amélioré avec le mélange de plastifiants sélectifs au bloc PS. L’auto-assemblage sur des grandes surfaces a été alors prouvé par un recuit thermique rapide (~ 30 s). Comme une preuve de concept de la lithographie, certains masques PS-b-PDMS testés ont été transférés sur Si, où des caractéristiques allant jusqu’à 25 nm ont été atteintes.Le principe de la lithographie par BCP a également été utilisé pour montrer la structuration de matériaux 2D. Par exemple, le graphène présente un besoin réel de structuration en nanostructures très étroites afin d’ouvrir un gap entre la bande de valence et la bande conduction pour modifier ses propriétés électriques par confinement quantique.Un bas Le PS-b-PDMS a été utilisé pour patterner avec de tailles caractéristiques de 10 nm. Le BCP est déposé par centrifugation et recuit directement sur le graphène.L’auto-assemblage sur de grandes surfaces (1 cm²) est réalisé en quelques minutes et le masque est ensuite transféré vers le graphène par gravure plasma à base d’oxygène, où dans une seule étape la matrice PS est éliminé, les cylindres PDMS oxydés et le graphène gravé. De grandes surfaces de nanorubans de 11 nm de largeur (GNR) ont été fabriquées par la lithographie de l’auto-assemblage du PS-b-PDMS. Un nettoyage au plasma H2 a également été effectué afin d’éliminer les contaminants organiques apparaissant lors des étapes de fabrication. Des techniques différentes pour l’analyse du carbone telles que la spectroscopie photoélectronique de rayons X, la spectroscopie Raman et la microscopie à force atomique ont été utilisées pour montrer la haute qualité des GNR.La caractérisation électrique des GNRs tels que la mobilité et l’ouverture du gap dans le graphène ont également été mesurés pour confirmer le comportement électronique des nanorubans de graphène. Des valeurs de l’ordre de 150 cm²/V s et 30 meV ont été mesurées. L’ensemble de la procédure expérimentale a été réalisé dans le cadre des réglèmentations de salles blanches pour la microélectronique, puis les processus d’auto-assemblage des BCPs proposés sont évolutifs et peu coûteux et sont bien adaptés pour être intégrés aux techniques existantes de fabrication de semi-conducteurs. / The Block copolymers (BCPs) have the particular property of self-assemble into ordered periodical structures. These macromolecules in association with the classic photolithography, is a promising candidate to be used as an alternative technique for the advanced patterning. This way, the downsizing of the integrated circuits can be kept up. BCPs with high chemical incompatibility between their blocks exhibit a high value of the Flory-Huggins interaction parameter χ. The BCP theory predicts periodical features sizes with high-χ; BCPs of only few nanometers.The BCP lithography principe was also used to show the patterning of 2D materials. For exemple, graphene present a real needs of patterning into very narrow nanostructures to open up a bandgap to switch its electrical properties by quantum confinement. A low χN PS-b-PDMS was used to pattern ~ 10 nm features. BCP is spin-coated and annealed directly on graphene. Self-assembly on large surfaces (1 cm²) is achieved in few minutes and the mask is then transferred on graphene by oxygen-based plasma etching, where in a single step will eliminate the PS matrix, oxidized the PDMS cylinders and etch the graphene. Large surfaces of 11nm-width Graphen nanoribbons (GNRs) were fabricated by the self-assembly of PS-b-PDMS. Dry H2 plasma cleaning was also performed to remove organic contaminants appearing during the fabrication steps. Different analysis techniques of carbon such as Raman and X-ray photoelectron spectroscopy and atomic force microscopy were used to show the high chemical quality of the GNRs.Electrical characterization of the GNRs such as mobility and the bandgap openingin graphene were measured also to confirm the electronic behavior of the graphene nanoribbons. Values of the order of 150 cm²/V s and 30 meV were measured. The entire procedure was realized under microelectronics clean room requirement, then, the BCP self-assembly processes proposed are scalable and low cost, and is well-suited for integration with existing semiconductor fabrication techniques.The lithographical procedure developed in this investigation could also be generalized to fabricate different graphene nanostructures such as graphene nanomeshes or quantum dots that could be envisaged for other applications in functional devices. GNRs on large surfaces are expect to find a broad ranges of applications, in the fields of electrochemical and bioanalysis.

"There is plenty of room at the bottom." This bold and prophetic statement from Nobel laureate Richard Feynman back in 1950s at Cal Tech launched the Nano Age and predicted, quite accurately, the explosion in nanoscience and nanotechnology. Now this is a fast developing area in both science and technology. Many think this would bring the greatest technological revolution in the history of mankind. To understand electronic and optical properties of nanostructures, the following problems have been studied. In particular, intensity of mid-infrared light transmitted through a metallic diffraction grating has been theoretically studied. It has been shown that for s-polarized light the enhancement of the transmitted light is much stronger than for p-polarized light. By tuning the parameters of the diffraction grating enhancement can be increased by a few orders of magnitude. The spatial distribution of the transmitted light is highly nonuniform with very sharp peaks, which have the spatial widths about 10 nm. Furthermore, under the ultra fast response in nanostructures, the following two related goals have been proved: (a) the two-photon coherent control allows one to dynamically control electron emission from randomly rough surfaces, which is localized within a few nanometers. (b) the photoelectron emission from metal nanostructures in the strong-field (quasistationary) regime allows coherent control with extremely high contrast, suitable for nanoelectronics applications. To investigate the electron transport properties of two dimensional carbon called graphene, a localization of an electron in a graphene quantum dot with a sharp boundary has been considered. It has been found that if the parameters of the confinement potential satisfy a special condition then the electron can be strongly localized in such quantum dot. Also the energy spectra of an electron in a graphene quantum ring has been analyzed. Furthermore, it has been shown that in a double dot system some energy states becomes strongly localized with an infinite trapping time. Such states are achieved only at one value of the inter-dot separation. Also a periodic array of quantum dots in graphene have been considered. In this case the states with infinitely large trapping time are realized at all values of inter-dot separation smaller than some critical value.

It has been predicted that gold, aluminum, and copper do not fundamentally change the graphene band structure when they are in close proximity to graphene, but merely increase the doping. My data confirms this prediction, as well as explores other consequences of the metal/graphene interface. First, I present a technique to fabricate thin oxide barriers between graphene and aluminum and copper to create tunnel junctions and directly probe graphene in close proximity to a metal. I map the differential conductance of the junctions versus tunnel probe and back gate voltage, and observe mesoscopic fluctuations in the conductance that are directly related to the graphene density of states. I develop a simple theory of tunneling into graphene to extract experimental numbers, such as the doping level of the graphene, and take into account the electrostatic gating of graphene by the tunneling probe. Next, results of measurements in magnetic fields will also be discussed, including evidence for incompressible states in the Quantum Hall regime wherein an electron is forced to tunnel between a localized state and an extended state that is connected to the lead. The physics of this system is similar to that encountered in Single Electron Transistors, and some work in this area will be reviewed. Finally, another possible method of understanding the interface between a metal and graphene through transport is presented. By depositing disconnected gold islands on graphene, I am able to measure resonances in the bias dependent differential resistance, that I connect to interactions between the graphene and gold islands.

The graphene moiré superstructure formed on Ru(0001) (g/Ru(0001)) has shown the potential as a template to self-assemble super-lattices of metal nanoparticles as model catalysts. To explore the possibility of rational catalyst design on g/Ru(0001), detailed density functional theory (DFT) calculations have been performed to investigate the adsorption and diffusion of Rh and Au adatoms on g/Ru(0001). The consequences of different hopping rates for cluster nucleation have been explored by performing Monte Carlo-based statistical analysis, which suggests that diffusing species other than adatoms need to be taken into account to develop an accurate description of cluster nucleation and growth on this surface. DFT calculations have also been carried out to investigate the adsorption and diffusion of 18 4d (Y-Ag) and 5d (La-Au) transition metal adatoms on g/Ru(0001). Given the necessity to study larger diffusing species than adatoms, DFT calculations have been performed to study the adsorption and diffusion of Rh and Au dimers and trimers on g/Ru(0001). It was shown that the mobility of Rh clusters decreases with the increase of cluster size, while for Au, dimers diffuse faster than monomers and trimers on the moiré surface. We then used a genetic algorithm combined with DFT calculations to predict the lowest energy structure of a Au8 cluster on g/Ru(0001). Our prediction leads us to propose that Au clusters aggregates through Oswald ripening with Au dimer being the major diffusing species. Finally, we examined the morphology of a Cu19 cluster on g/Cu(111) using MD simulations with COMB3 potential. We also studied the mobility of Cu clusters on g/Cu(111) at elevated temperatures. The analysis suggests that g/Cu(111) may not be a suitable substrate for the formation and growth of isolated Cu clusters. All these calculation results have provided us a better understanding and useful insights into the nucleation and growth mechanism of metal clusters on graphene moiré.

This dissertation research is focused on first principles studies of graphene and single organic molecules for nanoelectronics applications. These nanosized objects attracted considerable interest from the scientific community due to their promise to serve as building blocks of nanoelectronic devices with low power consumption, high stability, rich functionality, scalability, and unique potentials for device integration. Both graphene electronics and molecular electronics pursue the same goal by using two different approaches: top-down approach for graphene devices scaling to smaller and smaller dimensions, and bottom-up approach for single molecule devices. One of the goals of this PhD research is to apply first-principles density functional theory (DFT) to study graphene/metal and molecule/metal contacts at atomic level. In addition, the DFT-based approach allowed us to predict the electronic characteristics of single molecular devices. The ideal and defective graphene/metal interfaces in weak and strong coupling regimes were systematically studied to aid experimentalists in understanding graphene growth. In addition, a theory of resonant charge transport in molecular tunnel junctions has been developed. The first part of this dissertation is devoted to the study of atomic, electronic, electric, and thermal properties of molecular tunnel junctions. After describing the model and justifying the approximations that have been made, the theory of resonant charge transport is introduced to explain the nature of current rectification within a chemically asymmetric molecule. The interaction of the tunneling charges (electrons and holes) with the electron density of the metal electrodes, which in classical physics is described using the notion of an image potential, are taken into account at the quantum-mechanical level within the tight binding formalism. The amount of energy released onto a molecule by tunneling electrons and holes in the form of thermal vibration excitations is related to the reorganization energy of the molecule, which is also responsible for an effective broadening of molecular levels. It was also predicted that due to the asymmetry of electron and hole resonant energy levels with respect to the Fermi energy of the electrodes, the Joule heating released from the metallic electrodes is also non-symmetric and can be used for the experimental determination of the type of charge carriers contributing to the molecular conductance. In the second part of the dissertation research ideal and defective graphene/metal interfaces are studied in weak and strong interface coupling regimes. The theoretical predictions suggest that the interface coupling may be controlled by depositing an extra metallic layer on top of the graphene. DFT calculations were performed to evaluate the stability of a surface nickel carbide, and to study graphene/carbide phase coexistence at initial stages of graphene growth on Ni(111) substrate at low growth temperatures. Point defects in graphene were also investigated by DFT, which showed that the defect formation energy is reduced due to interfacial interactions with the substrate, the effect being more pronounced in chemisorbed graphene on Ni(111) substrate than in physisorbed graphene on Cu(111) substrate. Our findings are correlated with recent experiments that demonstrated the local etching of transfered graphene by metal substrate imperfections. Both graphene and molecular electronics components of the PhD dissertation research were conducted in close collaboration with several experimental groups at the University of South Florida, Brookhaven National Laboratory, University of Chicago, and Arizona State University.

Graphene, a honeycomb lattice of sp2-bonded carbon atoms, has received considerable attention in the scientific community due to its unique electronic properties. Distinct symmetries of the graphene wave functions lead to unusual quantum properties, such as a unique half-integer quantum Hall effect. As an added consequence of these symmetries, back-scattering in graphene is strongly prohibited leading to long coherence lengths of carriers. These charge carriers at low energy exhibit linear energy-momentum dispersion, much like neutrinos. Thus, carriers in graphene can be described as massless Dirac fermions. Graphene grown epitaxially on semiconducting substrates offers the possibility of large-scale production and deterministic patterning of graphene for nanoelectronics. In this work, epitaxial graphene is created on SiC(0001) by annealing in vacuum. Sequential scanning tunneling microscopy (STM) and spectroscopy (STS) are performed in ultrahigh vacuum at a temperature of 4.2 K and 300 K. These atomic-scale studies address the growth, interfacial properties, stacking order, and quasiparticle coherence in epitaxial graphene. STM topographic images show the atomic structure of successive graphene layers on the SiC substrate, as well as the character of defects and adatoms within and below the graphene plane. STS differential conductance (dI/dV) maps provide spatially and energy resolved snapshots of the local density of states. Such maps clearly show that scattering from atomic defects in graphene gives rise to energy-dependent standing wave patterns. We derive the carrier energy dispersion of epitaxial graphene from these data sets by quantifying the dominant wave vectors of the standing waves for each tunneling bias.