The thesis contains two parts. Part 1 describes the investigations on graphene and contains five sections. Section 1, gives a brief overview of graphene and other nanocarbons. The other four sections deal with various aspects of single-layer and few-layer graphene such as functionalization and solubilization, surface properties and gas adsorption, molecular charge transfer interaction and some properties and applications. Section 2 describes covalent and noncovalent functionalization and solubilization of few-layer graphene samples prepared by different methods as well as of single-walled carbon nanotubes (SWNTs). It includes covalent functionalization of graphene with organometallic reagents, noncovalent functionalization of graphene and SWNTs with surfactants as well as large aromatic molecules, and exfoliation of few-layer graphene by a water-soluble coronene carboxylate. Section 3 deals with surface properties and gas adsorption (mainly H2 and CO2) of few-layer graphenes. It is found that graphene samples with high surface area can adsorb even more than 3 wt% of H2 at high pressure which makes it promising material for gas-storage applications. Section 4 describes the molecular charge-transfer interaction of single and few-layered graphenes and SWNTs with different electron-donor and -acceptor molecules probed by both ITC measurements and Raman spectroscopy. Electron–acceptor molecules interact more strongly with graphene and SWNTs than the -donor molecules and nature of interaction of metallic SWNTs are different than the as-prepared ones. A Raman study of the interaction of single-layer graphene, prepared by micromechanical cleavage as well as chemical route, with an electron donor molecule such as tetrathiofulvalene (TTF) and an electron acceptor molecule such as tetracyanoethylene (TCNE) is examined. In Section 5, some properties and applications of graphene are discussed. These include fluorescence quenching phenomena observed with few-layer graphene samples on two fluorescent molecules such as coronene and perylene derivatives. Fabrication of a sensing device as well as of FETs prepared from doped and undoped few-layer and single-layer graphene samples forms part of this section. Part 2 of the thesis includes a brief introduction of hybrid open-framework material and synthesis, characterization and crystal structure of various open-framework metal carboxylates, starting with different transition and main group metals. The carboxylic acids used to form these frameworks vary such as simple aliphatic amino acids such as beta-alanine and aspartic acid or simple aliphatic hydroxyl carboxylic acid such as malic acid in its chiral and achiral forms or five-membered heterocyclic aromatic acid, such as imidazole dicarboxylic acid.

The control of environmental pollution, particularly in wastewater treatment, is one of the major concerns of the 21st century. Among the currently available pollution control technologies, photocatalysis is one of the most promising and efficient approaches to the reduction of pollutants. Graphene, a carbon nanomaterial with specific physical and chemical properties, has been reported as a promising potential new catalyst material in this field. A Bi2WO6 photocatalyst modified with graphene oxide was synthesized in a two-step hydrothermal process. Compared with pure Bi2WO6, the modified photocatalyst with 1.2 wt% graphene oxide improved photoactivity during the degradation of rhodamine-B (RhB) dye pollutant, by facilitating the dissociation of photogenerated excitons, which in turn results in more O2- radicals. XRD characterization showed that the modification of Bi2WO6 with graphene oxide does not affect its structure or morphology. The adsorption properties of graphene also contribute to the improvement of photoactivity. Other parameters such as catalyst dosage, temperature and solution pH are studied, with the aim to improve the efficiency of RhB removal.

Par delà ses applications largement distribuées pour le stockage de l’information binaire, la spintronique vise le traitement Booléen de l’information. Des dispositifs de logique de spin (spin-FETs et portes logiques de spin) sont envisagés en se basant sur la propagation et la manipulation de porteurs polarisés en spin injectés dans un canal latéral depuis un contact magnétique. En dépit de deux décennies de recherche active, l’efficacité des dispositifs (notamment en termes de longueur de propagation du spin et d’amplitude du signal de spin) est toujours limitée quand le canal latéral est un métal ou un semi-conducteur conventionnel : la mise en évidence d’un medium adapté est nécessaire.Le transport dépendant du spin dans le graphène a été étudié dans le cadre de cette thèse. Dans un premier temps, l'impact et la structure de barrières tunnel de haute qualité déposées sur le graphène, nécessaires pour l'injection efficace de l'information de spin, ont été étudiés. A partir de ces résultats, des dispositifs complets d'injection, transport et détection de spin basés sur un feuillet de graphène épitaxié ainsi que sur une bicouche de graphène exfoliée ont alors été construits. Enfin, des mesures de transport du spin dans ces dispositifs ont été effectuées, puis analysées via les modèles classiques de drift/diffusion. Les forts signaux obtenus (gamme du MΩ), en validant l'existence d'un support capable de transporter le spin avec une très forte efficacité sur des distances macroscopiques (jusqu’à 200 µm), ouvrent la voie à une implémentation des concepts de traitement de l'information de spin. / Beyond its widely distributed applications for binary data storage, spintronics aims Boolean information processing. Spin logic devices (spin-FETs and spin logic gates) are envisioned through the propagation and the manipulation of a spin-polarized carriers injected into a lateral channel from a magnetic contact. In spite of two decades of active research, the devices efficiency (in particular in terms of spin propagation length and spin signal amplitude) is still limited when the lateral channel is made of conventional metals or semiconductors: a suitable host still lacks. Spin-dependant transport in graphene is investigated in this thesis. At first, the impact of the growth and on the structure of high quality tunnel barriers deposited on graphene, required to obtain an efficient injection of the spin information, has been studied. From these results, complete devices for spins injection, transport and detection based on an epitaxial graphene sheet and also on an exfoliated bilayer graphene flake were built. Finally, measurements of spin transport in these devices were carried, and then analyzed through classical drift/diffusion models. The strong signals obtained (MΩ range), by validating the existence of a substrate able to carry the spin information with a very large efficiency on macroscopic distances (up to 200 µm), open the way for the implementation of spin processing concepts.

In less than a decade of research, graphene has earned a long list of superlatives to its name and is expected to have applications in various fields such as electronics, photonics, optoelectronics, materials, biology and chemistry. Graphene has also attracted a lot of attention because its properties can be engineered either via intrinsic changes or by modification of its environment. Raman spectroscopy has become an ideal characterization method to obtain qualitative and quantitative information on these changes. This thesis investigates the possibility to change, supplement and monitor the electonic and optical properties as well as the chemical reactivity of graphene. It is achieved by i) substrate effect, ii) introduction of defects in the structure of graphene and iii) the combination of graphene with other two- dimensional crystals such as hexagonal boron nitride (h-BN) and transition metal dichacolgenides. In particular, the experimental work presented here describes: I - The influence of the type of substrate on the Raman intensity of graphene. This work leads to the calculation of the Raman scattering efficiency of graphene after CaF2 is found to be a suitable substrate for this kind of study in contrast to Si/SiOx that strongly modulates the Raman intensities. The G peak scattering efficiency is found to be about 200 x 10-5 m-1 Sr-1 at 2.4 eV while that of the 2D peak is one order of magnitude higher, confirming the resonant nature of the 2D peak Raman scattering process. II - An attractive method to produce large (up to several hundreds of microns across) and high quality graphene by anodic bonding. This cheap, fast and solvent-free method also allows introduction of vacancy like defects in the samples in a relatively controllable way. III - The Raman signatures of several types of defect such as sp3 sites, vacancies and substitutional atoms. For low defect concentration (stage 1) the intensitiy ratio I(D)/I(D') is constant and is 13 for sp3 sites, 9 for substitutional atoms and 7 for vacancies. This signature is explained using the local activation model recently proposed to model the amorphization trajectory of graphene with containing vacancy-like defects. IV - Controlled modification of graphene through mild oxygen plasma. The influence of sp3 sites on monolayer and bilayer graphene's electrical properties are discussed. In the case of bilayer under controlled conditions, it is possible to modify only the top layer. This may lead to decoupling between the two layers, which could explain the good mobility measured for this system. The possiblity to use such system as a sensor is discussed. V - The characteristic Raman signature of aligned graphene/h-BN superlattices. The Raman spectrum shows strong changes in perfectly aligned superlattices, which could be attributed to the reconstruction of the Dirac spectrum. VI - A prototype photovoltaic cell made of a graphene and tungsten disulphide (WS2) heterostructure with an external quantum efficiency of about 30%. The beneficial combination of an excellent absorption in WS2 atomically thin films due to the presence of van Hove singularities and graphene used as a transparent, flexible and conductive electrode is demonstrated.

Plasmon resonances have attracted a lot of recent research interest for their potential applications, including bio-sensing, sub-wavelength optics, negative refractive index metamaterials and their ability to produce massively enhanced electromagnetic fields. Localised surface plasmon resonances (LSPR) in metallic nanostructures can offer large electromagnetic field enhancements, and nanometre-scale localisation of electric fields. Their resonance wavelengths and properties can be tuned by variation of the nanostructure geometry and are sensitive to environmental refractive index. Coupling of localised plasmon resonances can: Create new hybrid modes that cannot be supported by individual nanostructures, overcome some of the limitations of individual LSPR, and open up possibilities for new applications and active control of plasmon resonances. This thesis contains results from samples exploiting near-field, far-field and resistive coupling of localised plasmon resonances to create novel resonance modes that may make them suitable for important applications. Firstly results are presented from samples exhibiting strong collective plasmon resonances at normal incidence, which could be used to improve the spatial resolution of, miniaturise and add new functionality to highly sensitive surface plasmon resonance based approaches to bio-sensing. A very high bio-sensing figure of merit is calculated for the nanostructure arrays fabricated. Results are also presented from samples designed to produce the highest quality factor resonances possible when excited with light at grazing incidence. The highest resonance quality factors measured were conservatively estimated to be >210, which to our knowledge are the highest values of quality factor measured in diffraction coupled arrays at the resonance wavelengths around 1.5 μm. Evidence for the existence of a presently largely unrecognised resistive coupling mechanism is also presented from an array of gold nanostripes covered with a graphene layer. If further work is successful, this could allow extremely rapid modulation of theoptical properties of a plasmonic array by application of gate voltage to the graphenelayer. Finally an improvement to the fabrication procedure for established near-field coupled composite plasmonic nanostructures that create a cascaded electromagnetic field enhancement effect is presented.

Linear and nonlinear microwave properties of chemical vapor deposition (CVD)-grown graphene are characterized by incorporating a coplanar waveguide (CPW) transmission-line test structure. The intrinsic linear transport properties (S-parameters) of the graphene sample are measured and extracted via a deembedding procedure and then fitted with an equivalent circuit model up to 10 GHz. A statistical uncertainty analysis based on multiple measurements is implemented to esti- mate the error of the extracted graphene linear parameters as well. Nonlinear properties (second- and third-order harmonics as a function of fundamental input power) of the sample are also measured with a fundamental input signal of 1 GHz. Clear harmonics generated from graphene are observed, while no obvious fundamental power saturation is seen. The measured nonlinearity is applied in a graphene patch antenna case study to understand its influence on potential applications in terms of third-order intermodulation levels.

Phonon properties of AB (Bernal) stacked bilayer graphene (BLG) with various types of defects have been investigated theoretically. Forced Vibrational (FV) method has been employed to compute the phonon modes of disordered BLG. A downward linear shift of E2g mode frequencies has been observed with an increasing amount of defect concentration. Moreover, two identical E2g peaks have been observed in PDOS of the bilayer system where the individual layer contains 12C and 13C atoms respectively. From computed typical mode patterns of in-plane K-point optical mode phonons, it has been noticed that phonons become strongly localized around a few nanometers area at the presence of defects and localized modes increase with the increasing amount of defect concentration. The edge effect on the localized phonon modes has also been discussed for bilayer armchair graphene nanoribbons (BiAGNRs). The impact of defects on the phonon conduction properties has also been studied for BiAGNRs. My investigated results can be convenient to study the thermal conductivity and electron-phonon interaction of bilayer graphene-based nanodevices and to interpret the Raman and infrared spectra of disordered system.

In electronic flat bands the electron kinetic energy is quenched and dominated by interaction and correlated states can emerge. These many-body collective modes are not only interesting enigmas to solve, but may also lead to real-life applications. This thesis studies correlated states in graphene, a tunable system that can be programmed by ex- ternal parameters such as electric field. Two types of graphene flat bands are examined. One, highly degenerate and discreet Landau levels created by external magnetic field. Two, moirè flat bands created by relative crystalline twist between graphene layers. Correlated states are studied with transport measurements. The results were measured in dual-gated graphite/Boron nitride encapsulated graphene heterostructures with very low disorder. The high quality of the heterostructure is showcased by ballistic electron optics including nega- tive refraction across a gate-defined pn junction. In the first type of flat band — a partially filled Landau level — the competition of electrons solid states and fractional quantum Hall liquid manifests as reentrant quantum Hall effect, with a valley and spin hierarchy unique to graphene. Alternatively, in the flat bands arising from moiré superlattices, we explore two tuning knobs of correlated states. In twisted bilayer graphene, the band width are tuned by changing interlayer hybridization via pressure. The resulting superconducting and correlated insulator states can be restored outside of a narrow range of twist angles near 1.1 degrees. New fermi surfaces also form at commensurate fillings of the flat band with reduced degeneracy. In twisted monolayer-bilayer graphene, we find extraordinary level of control and tunability because of the low symmetry. With perpendicular electric field, the system can alternate among correlated metallic and insulating states, as well as topological magnetic states. The magnetization direction can be switched purely with electrostatic doping at zero magnetic field.

Understanding the deformation mechanism in nanocomposites is critical to realizing a host of next-generation technologies like stretchable electronics, three-dimensional multifunctional surfaces, and nanoscale machines. Graphene’s unparalleled mechanical strength and stability – owing to its two-dimensional geometry, high intrinsic strength, and Young’s modulus – have opened up new opportunities to engineer composites of higher strength-to-weight ratios for various practical applications. The ability of graphene (Gr) to act as a strength enhancer depends on the interface interactions and the composite’s microstructure. Here we demonstrate a microstructure design of Cu-Gr-Cu nanolaminate that enhances the composite’s load-bearing capacity, improves the composite’s strength, and reduces its coefficient of friction. The mechanical and frictional properties of Cu-Gr-Cu nanolaminate were probed using the nanoindenter. A series of nanoindentations performed on Cu-Gr-Cu nanolaminate exhibit an effective yield strength of 320 MPa and effective flow strength of 0•.5 GPa. Scratch tests performed on the free surface of the Cu-Gr-Cu nanolaminate show a considerable decrease in the coefficient of friction from 0.3 to 0.2. The cantilever bending test performed on Cu-Gr-Cu nanolaminate showed an increase in flow strength and strain hardening compared to Cu-Cu. The enhancement in the mechanical and friction properties of Cu-Gr-Cu nanolaminate suggests a build-up of dislocations at the Cu-Graphene interface. FEA simulations of the nanoindentation on Cu-Gr-Cu nanolaminate confirm the effectiveness of graphene as a barrier to plastic deformation. The pile-up of dislocations at the Cu-Graphene interface implies large plastic strain gradients near the interface. We developed a strain gradient plasticity computational model of the beam bending experimental system based upon Gudmundson’s higher-order theory and implemented it as a user element in ABAQUS. A set of material parameters is identified that reproduce the experimental for

The synthesis of transition metal dichalcogenides (TMDs) are crucial to realization of their real-world applications in electronic, optoelectronic and chemical devices. However, the fabrication yield in terms of material quality, crystal size, defect density are poorly controlled. In this work, by employing the up-to-date stack-and-transfer and nano fabrication techniques, synthetic TMDs that obtained from different growth methods with various crystal qualities were studied. In most of the cases, better crystals with lower defect densities and larger crystal domain sizes are preferred. Self-flux method was developed to obtain better quality crystals comparing to the traditional chemical vapor transport, as characterized by lower defect densities. BN encapsulating graphene device platform was utilized and TMDs monolayers with different defect densities was inserted in between the BN/graphene interface, where intrinsic defects from the TMDs disturbed the electronic environment of graphene. With the better TMD crystal insertion, we obtain much better electrical performed device in terms of hysteresis, FWHM of Dirac peak and electron mobility. This device also showed advantage in quantum transport measurements . On the other hand, the presence of defects are not always undesired, especially when it comes to serve as electrocatalysts, in which most of the reactions take place at vacancy sites. However, similar to most of the MoS2 electronic devices, forming barrier-free metal semiconductor contact is the major challenge. We develop a platform that contact resistance could be monitored simultaneously with electrochemical activity. In this platform, the total device resistance is significantly reduced before electrochemical reaction happens while the intrinsic catalytic activity of the MoS₂ can be extracted. With this platform, we found the intrinsic catalytic activity of MoS₂ strongly correlated to H-coverage on its surface. By adding molecular mediator into electrolytes, H-coverage and the resulting HER activity was enhanced via “Catch and Release” mechanism. Molecular simulation was performed to support our experimental results.