Graphene, as a recently discovered carbon allotrope, possesses with it many outstanding properties ranging from high electrical conductivity to great mechanical strength. Single layer graphene can be prepared by mechanical cleavage of graphite or by a more sophisticated method, CVD. However, the scale-up process for these preparation techniques is still unconvincing. Solution-processed graphene from exfoliation of graphite oxide on the other hand provides an alternative prospect resulting in the formation of graphene nanoplatelets (GNPs), which can be readily manipulated to tailor-suit various application demands. The main aim of the thesis is to explore the possibility and availability of this versatile method to produce graphene nanoplatelet and its composites with good all-round performance in energy and bioanalytical applications. A range of physical and chemical characterisation techniques were utilised including SEM, TEM, AFM, XPS, XRD, DLS, FTIR, Raman and UV-Vis spectroscopy in order to investigate the structural and chemical information of the graphene-based materials prepared. Functionalisation of graphene oxide with polyelectrolyte polymer could facilitate deposition of platinum nanoparticles in the formation of Pt-GNPs composites. The resultant composite was employed for bioanalytical application in the detection of an important neurotransmitter, glutamate, based on glutamate oxidase enzyme. The performance of Pt-GNPs based glutamate sensor exhibited enhanced sensitivity and prolonged stability compared to the sensors based on Pt decorated diamond or glassy carbon electrodes. The significant interfering effect from concomitant electrochemically active biological compounds associated with Pt-GNPs electrode however could be alleviated via opting for Prussian blue deposited GNPs electrode instead. The oppositely charged Pt-GNPs due to different functionalising polymers were also subject to self-assembly, which was enabled by the electrostatic interaction of the opposite charges of Pt-GNPs. The self-assembled film showed enhanced mechanical stability than the conventional drop-casted film and provided reasonably good activity towards oxidation of hydrogen peroxide. Three-component composite of graphene, nanodiamond and polyaniline was prepared via in-situ polymerisation for usage as an electrode material in electrochemical capacitors ("supercapacitors"). The addition of graphene was shown to significantly enhance specific capacitance while nanodiamond could improve the stability of the electrode by strengthening the polymer core. Another approach to produce a supercapacitor was via electrodeposition of nickel and cobalt hydroxides on graphene oxide film corporated with bicarbonate salt. The film was then subject to thermal reduction of GO and expansion of graphene layers within the film was observed. This leavening process enhanced the surface area of graphene film and thus the higher specific capacitance was obtained. The decoration of nickel and cobalt hydroxides onto the film also boosted the specific capacitance further however the poor cycling stability of the heated film still remained an issue. Graphene nanoplatelets were also used as a support for electrodeposition of Pt nanoparticles for methanol oxidation in acidic media. The preferential phase of the Pt deposited and large surface area of graphene in comparison to other carbon supports studied led to good catalytic activity being observed.

In this thesis, two-dimensional materials such as graphene are tested for their suitability for opto-electronic applications using terahertz time domain spectroscopy (THz-TDS). This ultrafast all-optical technique can probe the response of novel materials to photoexcitation, and yield information about the dynamics of the material systems. Graphene grown by chemical vapour deposition (CVD) is studied using optical-pump THz-probe time domain spectroscopy in a variety of gaseous environments in Chapter 4. The photoconductivity response of graphene grown by CVD is found to vary dramatically depending on which atmospheric gases are present. Adsorption of these gases can open a local bandgap in the material, allowing stimulated emission of THz radiation across the gap. Semiconducting equivalents to graphene, molybdenum disulphide (MoS₂) and tungsten diselenide (WSe₂), grown by CVD, are investigated in Chapter 5. These members of the transition metal dichalcogenide family show sub-picosecond responses to photoexcitation, suggesting promise for use in high-speed THz devices. In Chapter 6, an alternative production route to CVD is studied. Liquid-phase exfoliation offers fast, easy production of few-layer materials. THz spectroscopy reveals that the dynamics of these materials after photoexcitation are remarkably similar to those in CVD-grown materials, offering the potential of cheaper materials for future devices. Finally in Chapter 7, it is shown that carbon nanotubes can be used to make ultrafast THz devices. Unaligned, semiconducting single walled carbon nanotubes can be photoexcited to produce an ultrafast, dynamic THz polariser. The work in this thesis demonstrates the potential for these novel materials in future opto-electronic applications. THz spectroscopy is shown to be an important tool for the characterisation of new materials, providing information that can be used to understand the dynamics of materials, and improve production methods.

In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were successfully synthesized with chemical vapor deposition over both Cu and Si (with surface oxide) substrates. These synthetic graphene films were characterized with thorough microscopic and spectrometric tools and also in terms of electrical device performance. Graphene growth with a simple chemo thermal route was also explored for understanding the growth mechanisms. The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficient at cleaning surface contaminants and thus allowing for the formation of large area homogeneous strictly monolayer graphene film over Cu substrate. Chemical vapor deposition is the most generally used method for graphene mass production and integration. There is also interest in growing graphene directly from organic molecular adsorbents on a substrate. Few studies exist. These procedures require multiple step reactions, and the graphene quality is limited due to small grain sizes. Therefore, a significantly simple route has been demonstrated. This involves organic solvent molecules adsorbed on a Cu surface, which is then annealed in a hydrogen atmosphere in order to ensure direct formation of graphene on a clean Cu substrate. The influence of temperature, pressure and gas flow rate on the one-step chemo thermal synthesis route has been investigated systematically. The temperature-dependent study provides an insight into the growth kinetics, and supplies thermodynamic information such as the activation energy, Ea, for graphene synthesis from acetone, isopropanol and ethanol. Also, these studies highlight the role of hydrogen radicals for graphene formation. In addition, an improved understanding of the role of hydrogen is also provided in terms of graphene formation from adsorbed organic solvents (e.g., in comparison to conventional thermal chemical vapor deposition). Graphene synthesis with chemical vapor deposition directly over Si wafer with surface oxide (Si/SiOx ) has proven challenging in terms of large area and uniform layer number. The direct growth of graphene over Si/SiO x substrate becomes attractive because it is free of an undesirable transfer procedure, necessity for synthesis over metal substrate, which causes breakage, contamination and time consumption. To obtain homogeneous graphene growth, a local equilibrium chemical environment has been established with a facile confinement CVD approach, inwhich two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises facetted grains despite initially nucleating as round islands. Upon clustering these grains facet to minimize their energy, which leads to faceting in polygonal forms because the system tends to ideally form hexagons (the lowest energy form). This is much like the hexagonal cells in a beehive honeycomb which require the minimum wax. This process also results in a near minimal total grain boundary length per unit area. This fact, along with the high quality of the resultant graphene is reflected in its electrical performance which is highly comparable with graphene formed over other substrates, including Cu. In addition the graphene growth is self-terminating, which enables the wide parameter window for easy control. This chemical vapor deposition approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates which suffer from transfer. Moreover, this growth path shall be applicable for direct synthesis of other two dimensional materials and their Van der Waals hetero-structures. / Im Zuge dieser Doktorarbeit wurden großflächige und homogene Graphen-Monolagen mittels chemischer Gasphasenabscheidung auf Kupfer- (Cu) und Silizium-(Si) Substraten erfolgreich synthetisiert. Solche monolagigen Graphenschichten wurden mithilfe mikroskopischer und spektrometrischer Methoden gründlich charakterisiert. Außerdem wurde der Wachstumsmechanismus von Graphen anhand eines chemo-thermischen Verfahrens untersucht. Die Bildung von homogenen Graphenschichten auf Cu erfordert eine sehr saubere Substratoberfläche, weshalb verschiedene Substratvorbehandlungen und dessen Einfluss auf die Substratoberfläche angestellt wurden. Vier Vorbehandlungsarten von Cu-Substraten wurden untersucht: Abwischen mit organischen Lösungsmitteln, Atzen mit Eisen-(III)-Chloridlösung, Wärmebehandlung an Luft zur Erzeugung von Cu-Oxiden und Wärmebehandlung an Luft mit anschließender Wasserstoffreduktion. Von diesen Vorbehandlungen ist die zuletzt genannte Methode für die anschließende Abscheidung einer großflächigen Graphen-Mono-lage am effektivsten. Die chemische Gasphasenabscheidung ist die am meisten verwendete Methode zur Massenproduktion von Graphen. Es besteht aber auch Interesse an alternativen Methoden, die Graphen direkt aus organischen, auf einem Substrat adsorbierten Molekülen, synthetisieren konnen. Jedoch gibt es derzeit nur wenige Studien zu derartigen alternativen Methoden. Solche Prozessrouten erfordern mehrstufige Reaktionen, welche wiederrum die Qualität der erzeugten Graphenschicht limitieren, da nur kleine Korngrößen erreicht werden konnen. Daher wurde in dieser Arbeit ein deutlich einfacherer Weg entwickelt. Es handelt sich dabei um ein Verfahren, bei dem auf einer Cu-Substratoberfläche adsorbierte, organische Lösungsmittelmoleküle in einer Wasserstoffatmosphäre geglüht werden, um eine direkte Bildung von Graphen auf einem sauberen Cu-Substrat zu gewahrleisten.Der Einfluss von Temperatur, Druck und Gasfluss auf diesen einstufigen chemothermischen Syntheseweg wurde systematisch untersucht. Die temperaturabhängigen Untersuchungen liefern einen Einblick in die Wachstumskinetik und thermodynamische Größen, wie zum Beispiel die Aktivierungsenergie Ea, für die Synthese von Graphen aus Aceton, Isopropanol oder Ethanol. Diese Studien untersuchen außerdem die Rolle von Wasserstoffradikalen auf die Graphensynthese. Weiterhin wurde ein verbessertes Verständnis der Rolle von Wasserstoff auf die Graphen-synthese aus adsorbierten, organischen Lösungsmitteln erlangt (beispielsweise im Vergleich zur konventionellen thermischen Gasphasenabscheidung). Die direkte Graphensynthese mittels chemischer Gasphasenabscheidung auf Si-Substraten mit einer Oxidschicht (Si/SiOx ) ist extrem anspruchsvoll in Bezug auf die großflächige und einheitliche Abscheidung (Lagenanzahl) von Graphen-Monolagen. Das direkte Wachstum von Graphen auf Si/SiOx -Substrat ist interessant, da es frei von unerwünschten Übertragungsverfahren ist und kein Metall-substrat erfordert, welche die erzeugten Graphenschichten brechen lassen können. Um ein homogenes Graphenwachstum zu erzielen wurde durch den Kontakt zweier Si-Wafer, mit ihren Oxidflachen zueinander zeigend, eine lokale Umgebung im chemischen Gleichgewicht erzeugt. Diese Konfiguration der Si-Wafer ist nötig, um eine einheitliche Graphen-Monolage bilden zu können. Eine gründliche Untersuchung des abgeschiedenen Materials zeigt, dass trotz der anfänglichen Keimbildung von runden Inseln facettierte Körner erzeugt werden. Aufgrund der Bestrebung der Graphenkörner ihre (Oberflächen-) Energie zu minimieren, wird eine Facettierung der Körner in polygonaler Form erzeugt, was darin begründet liegt, dass das System idealerweise eine Anordnung von hexagonal geformten Körnern erzeugen würde (niedrigster Energiezustand). Der Prozess ist vergleichbar mit der sechseckigen Zellstruktur einer Bienenstockwabe, welche ein Minimum an Wachs erfordert. Dieser Prozess führt auch zu einer nahezu minimalen Gesamtkorn-grenzlänge pro Flächeneinheit. Diese Tatsache zusammen mit der hohen Qualität der resultierenden Graphenschicht spiegelt sich auch in dessen elektrischer Leistungsfähigkeit wider, die in hohem Maße mit der auf anderen Substraten gebildeten Graphenschichten (inklusive Cu-Substrate) vergleichbar ist. Darüber hinaus ist das Graphenwachstum selbstabschliessend, wodurch ein großes Parameterfenster für eine einfache und kontrollierte Synthese eröffnet wird. Dieser Ansatz zur chemischen Gasphasenabscheidung von Graphen auf Si- Substraten ist leicht skalierbar und gegenüber der Abscheidung auf Metallsubstraten konkurrenzfähig, da keine Substratübertragung notig ist. Darüber hinaus ist dieser Prozess auch für die direkte Synthese anderer zweidimensionalen Materialien und deren Van-der-Waals-Heterostrukturen anwendbar.

In low dimensional systems, electron correlation effects can often be enhanced. This can be vital since these effects not only play an important role in the study of many-electron physics, but are also useful in designing new materials for various applications. Since its isolation from graphite in 2004, graphene, a two dimensional sheet of carbon atoms, has drawn considerable interest due to its remarkable properties. In the past few years, research has moved on from single to bi-, dual- and multi-layer graphene systems, each displaying their own multitudes of intriguing properties. In particular, multi-layer systems that are electronically decoupled, but still coupled via the long-range Coulomb interaction, are very fascinating as they provide an opportunities to study phenomena like excitonic condensates, non-zero band gaps and van der Waals (vdW) interactions. In this thesis, I shall discuss our recent work on two different physical aspects of dual- layer graphene systems under uniaxial strain. Firstly, I shall present results on the vdW correlation energy evaluated, within the Random Phase Approximation, at zero temperature between two undoped graphene layers separated by a finite distance. The correlation energy is obtained for three anisotropic models with variations in the strength of the effective coupling constant. We find that the vdW interaction energy increases with increasing anisotropy and the many-body contributions to the correlation energy are non-negligible. In the second part, I shall talk about the formation of inter-layer electron-hole (excitonic) pairings, caused by the inter-layer Coulomb interaction between two uniaxially strained graphene sheets which are appropriately doped with electrons/holes and our studies of the dependence of strain on the effective interaction. We find that strain, in combination with precise control of the initial momentum can effectively overcome the suppression due to inter-layer screening effects.

Graphene, the world's first truly two-dimensional material, is unique for having an electronic structure described by an effective Lorentz invariant theory. One important consequence is that the ratio or Coulomb energy to kinetic energy is a constant, depending only on conditions within the lattice rather than on the average charge density as in a typical Galilean invariant material. Given this unusual property, a natural question would be how do phenomena, such as screening of a Coulomb impurity, happen in graphene? Moreover, how does the addition of uniaxial strain enhance or diminish this behavior? Here I discuss our work to calculate the charge density distribution in a lattice of strained graphene under the effect of an external Coulomb impurity. Graphene can have its band structure significantly altered by the application of uniaxial strain. Two cases are here explored: relatively weak strain at some finite chemical potential, and extreme strain with zero chemical potential. In the first system, the strain induces elliptic Dirac cones, engendering some inherent directionality to graphene's electronic properties that did not exist before. This anisotropy manifests itself in the polarization function, and so too in the screening charge density. A finite chemical potential in this case is necessary for any screening to take place in graphene since, without it, there are no electron states near the Fermi level to polarize. Both in the strained and unstrained case, decaying oscillations known as Friedel oscillations are observed. The result of strain is a multifaceted anisotropy of the charge distribution: the amplitude, frequency, and the position of the first peak in the oscillations are each varied depending on the direction one observes. In the second system, extreme strain in graphene leads to a merging of Dirac cones, yielding a transition to a new energy spectrum. This band structure is unusual in that it becomes quadratic along the direction of strain while remaining linear along the perpendicular. We evaluate the screening response to a Coulomb impurity in this case at zero chemical potential, and yet long-range distribution tails are still observed. The result is a very exotic charge distribution, in which the radial distribution of charge and the angular distribution are highly coupled, and at various distances, both screening and anti-screening regions are observed around the impurity. The anti-screening regions are local, and the net induced charge density still satisfies the accepted model of screening.

Catalysis is one of the pillars of the chemical industry. While the use of catalyst is typically recognized in the automobile industry, their impact is more widespread as; catalysts are used in the synthesis of 80% of the US commercial chemicals. Despite the improved selectivity provided by catalyst, process inefficiencies still threaten the sustainability of a number of synthesis methods, especially in the pharmaceutical industry. Recyclable solid supported catalysts offer a unique opportunity to address these inefficiencies. Such systems coupled with continuous synthesis techniques, have the potential to significantly reduce the waste to desired product ratio (E-factor) of the production techniques. This research focuses developing sustainable processes to synthesize organic molecules by using continuous synthesis methods. In doing so, solid supported metal catalyst systems were identified, developed, and implemented to assist in the formation of carbon-carbon bonds. Newly developed systems, which utilized metal nanoparticles, showed reactivity and recyclability, comparable to commercially available catalyst. Nanoparticles are emerging as useful materials in a wide variety of applications including catalysis. These applications include pharmaceutical processes by which complex and useful organic molecules can be prepared. As such, an effective and scalable synthesis method is required for the preparation of nanoparticle catalysts with significant control of the particle size, uniform dispersion, and even distribution of nanoparticles when deposited on the surface of a solid support. This project describes the production of palladium nanoparticles on a variety of solid supports and the evaluation of these nanoparticles for cross coupling reactions. This report highlights novel synthesis techniques used in the formation of palladium nanoparticles using traditional batch reactions. The procedures developed for the batch formation of palladium nanoparticles on different solid supports, such as graphene and carbon nanotubes, are initially described. The major drawbacks of these methods are discussed, including limited scalability, variation of nanoparticle characteristics from batch to batch, and technical challenges associated with efficient heating of samples. Furthermore, the necessary conditions and critical parameters to convert the batch synthesis of solid supported palladium nanoparticles to a continuous flow process are presented. This strategy not only alleviates the challenges associated with the robust preparation of the material and the limitations of scalability, but also showcases a new continuous reactor capable of efficient and direct heating of the reaction mixture under microwave irradiation. This strategy was further used in the synthesis of zinc oxide nanoparticles. Particles synthesized using this strategy as well as traditional synthesis methods, were evaluated in the context industrially relevant applications.

Zinc Oxide (ZnO) is one of the most extensively studied semiconductors because of its unique properties, namely, its wide band gap (3.37 eV) and high excitation binding energy (60 meV). These properties make ZnO a promising material for uses in a broad range of applications including sensors, catalysis and optoelectronic devices. The presented research covers a broad spectrum of these interesting nanomaterials, from their synthesis and characterization to their use as photocatalyts. A new synthetic approach for producing morphology controlled ZnO nanostructures was developed using microwave irradiation (MWI). The rapid decomposition of zinc acetate in the presence of a mixture of oleic acid (OAC) and oleylamine (OAM) results in the formation of hexagonal ZnO nanopyramids and ZnO rods of varying aspect ratios. The factors that influence the morphology of these ZnO nanostructures were investigated. Using ligand exchange, the ZnO nanostructures can be dispersed in aqueous medium, thus allowing their use as photocatalysts for the degradation of malachite green dye in water. Photocatalytic activity is studied as a function of morphology; and, the ZnO nanorods show enhanced photocatalytic activity for the degradation of the dye compared to hexagonal ZnO nanopyramids. After demonstrating the catalytic activity of these ZnO nanostructures, various ways to enhance photocatalytic activity were studied by modification of this MWI method. Photocatalytic activity is enhanced through band gap modulation and the reduction of electron-hole recombination. Several approaches were studied, which included the incorporation of Au nanoparticles, N-doping of ZnO, supporting ZnO nanostructures on reduced graphene oxide (RGO), and supporting N-doped ZnO on N-doped RGO. ZnO-based nanostructures were studied systematically through the entire process from synthesis and characterization to their use as photocatalysis. This allows for a thorough understanding of the parameters that impact these processes and their unique photocatalytic properties.

Exciting periods of scientific research are often associated with discoveries of novel materials. Such period was brought about by the successful preparation of graphene which is a 2D allotrope of carbon with remarkable electronic, optical and mechanical properties. Functional graphene-based nanocomposites have great promise for applications in various fields such as energy conversion, opteoelectronics, solar cells, sensing, catalysis and biomedicine. Herein, microwave and laser-assisted synthetic approaches were developed for decorating graphene with various semiconductor, metallic or magnetic nanostructures of controlled size and shape. We developed a scalable microwave irradiation method for the synthesis of graphene decorated with CdSe nanocrystals of controlled size, shape and crystalline structure. The efficient quenching of photoluminescence from the CdSe nanocrystals by graphene has been explored. The results provide a new approach for exploring the size-tunable optical properties of CdSe nanocrystals supported on graphene which could have important implications for energy conversion applications. We also extended this approach to the synthesis of Au-ceria-graphene nanocomposites. The synthesis is facilely conducted at mild conditions using ethylenediamine as a solvent. Results reveal significant CO conversion percentages between 60-70% at ambient temperatures. Au nanostructures have received significant attention because of the feasibility to tune their optical properties by changing size or shape. The coupling of the photothermal effects of these Au nanostructures of controlled size and shape with GO nanosheets dispersed in water is demonstrated. Our results indicate that the enhanced photothermal energy conversion of the Au-GO suspensions could to lead to a remarkable increase in the heating efficiency of the laser-induced melting and size reduction of Au nanostructures. The Au-graphene nanocomposites are potential materials for photothermolysis, thermochemical and thermomechanical applications. We developed a facile method for decorating graphene with magnetite nanocrystals of various shapes (namely, spheres, cubes and prisms) by the microwave-assisted-reduction of iron acetylacetonate in benzyl ether. The shape control was achieved by tuning the mole ratio between the oleic acid and the oleyamine. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, UV-Vis and PL spectroscopy, powder X-ray diffraction, XPS and Raman spectroscopy.

Dynamic atomistic description of bio-inorganic interfaces represents a challenging problem for contemporary computational chemistry. A detailed analysis of processes occurring on the interface between biomolecule and inorganic material can help our understanding of various processes, ranging from chromatography and protein separation to protein immobilization techniques and their effect on enzyme activity or protein conformational stability. High complexity of bio- inorganic interfaces prevents detailed investigation using accurate, but computationally demanding ab initio methods. Since reliable empirical potentials are not available for these systems, the aim of this work is to develop force fields based on ab initio data as well as a general methodology for parameterization of such force fields. Our potential fitting procedure was carried out in an automated fashion based on molecular dynamics simulation. The resulting potentials were applied for investigation of inorganic material's influence on polypeptide conformations.

In last two years, the proposal to create artificial graphene in standard semiconducting 2D systems via surface patterning has emerged. This way, an alternative system would be created, allowing us to study phenomena related to Dirac-type particles in a fully carbon free system. The main idea of the concept assumes the creation of an additional potential in a quantum well by nanopatterning of the specimen surface or by using local electrodes. The additionally introduced modulation can transform the conventional (i.e. parabolic) energy dispersion into separated minibands with possible appearance of Dirac cones. In the theoretical part, we introduce four basic criteria that estimate appropriate technological parameters and the required experimental conditions. Experimentally, we study the cyclotron resonance of prepared heterostructures AlGaAs/GaAs with induced hexagonal potential via the etching lateral holes. The observed multi-mode resonance response is discussed with respect to the expected appearance of Dirac cones.