Devices were developed to explore the perturbation of graphene using high-frequency signals. Two kinds of effects were studied: the interaction of graphene with surface acoustic waves (SAWs) and the propagation of picosecond pulses. The coupling of graphene with SAWs was first studied using flip-chip devices, which employed an evanescent field extending across the gap between the chips. A later design directly integrated layers of graphene grown by chemical vapour deposition (CVD) on piezoelectric 5ubstrates, containing interdigital transducers (IDTs) for SAW generation and detection. Graphene devices were characterised using Raman spectroscopy and atomic force microscopy; the electronic properties of CVD-graphene were investigated by performing magnetoresistance measurements. The measurements of the acoustically-generated current in the direct-coupling devices closely followed the SAW response of the IDTs, demonstrating the acousto-electric effect in graphene for the first time . . In a second class of devices, graphene was transferred to a quartz substrate, and, using on-chip waveguides, integrated with photoconductive switches capable of generating and detecting sub-picosecond pulses, which allow studying THz-frequency transmission in the system. Pulses containing frequency components of up to 2.5 THz were generated in these devices. The demonstration of the acousto-electric effect in graphene paves the way for SAW-based charge manipulation in graphene, such as singleelectron transport. The propagation of picosecond pulses in graphene could be used to further investigate the properties of graphene in the terahertz-frequency range.

During the last decade, the requirement of medical, food and environmental analysis for fast, reliable and inexpensive screening methods has given rise to increasing interest in the field of disposable amperometric biosensors. Screen-printed carbon electrodes (SPCE) are the most attractive basis for the construction of such devices as they combine good electrochemical properties with low manufacturing cost. However, effective immobilisation of enzymes on the surface of SPCE is difficult due to the inert nature of the carbon material. This thesis shows that poly(ethyleimine) (PE!) deposited onto the screen-printed carbon surface can be used as a universal and versatile platform for the multipoint electrostatic adsorption of various enzymes. Such electrostatic immobilisation can be significantly stabilised by biomimetic condensation of silicic acid which reinforces the PEI-enzyme complexes through gentle, non-covalent concreting of the polymeric backbone with silica. Another important problem in the assembly of amperometric biosensors on the basis of SPCE is the signal generation since many redox reactions which govern the sensitivity of an amperometric biosensor, e.g. oxidation of hydrogen peroxide, proceed with difficulty on the screen-printed carbon surface. In order to address this issue, simple cost-effective techniques for doping SPCE with redox mediators, cobalt phthalocyanine and Prussian Blue, have been developed. When applied to PEI-modified electrodes these techniques allowed the construction of amperometric biosensors sensitive to glucose, acetylcholine or organophosphate inhibitors.

The dimensional scaling of CMOS technology is approaching its fundamental limits and alternate device architectures and more functional channel materials ensuring superior operation al sub l0mm length scales are required to realise post CMOS applications. Among the quest for alternate materials. carbon based nanostructures such as 1•0 carbon nanotubes and graphene nanoribbons are considered as one of the many possible candidates. Demonstration of these one dimensional graphitic prototypes in microelectronic industry are strongly hindered by several factors such as the difficulty in controlling band gap. precise positioning and manufacturing on wafer scale, controlling carrier type and carrier concentration. deposition of CMOS compatible gate di electric and formation of low resistive contacts. Amongst these. an absence of a finite band gap and issues in controlling carrier concentration in graphene presents a major challenge for this material to be considered in logic devices. Moreover. both carbon nanotubes and graphene nanoribbons exhibit a diameter/width dependent band gap. At the nanoscale however. estimating the band gap both from experiment and theory is fraught with difficulties related to the underlying assumptions. Hence an accurate theoretical prediction of the performance of these material in future microelectronic devices is essential at this point since the International Technology Road map for Semiconductors (ITRS) -2011 edition strongly recommends carbon based nanostructures as an alternate channel material al for post CMOS logic applications. Also the technology requires novel band gap engineering techniques and doping g strategies without destruction of the intrinsic properties to enable application of graphene in various sectors such as microelectronics. photonics, photovoltaics and biosensors. In this thesis. suitable device geometries of such carbon based materials and their performance evaluation using realistic band gap values is investigated. Zig-zag nanotubes in the diameter range 0.55 - 1.26nm are considered in the study. Both MOSFET and tunnel FET device geometrics arc considered, but more focus is given To the tunnel-FET considering its energy efficient operation. The evaluation is made using non-equilibrium Greens function based numerical simulation with band gap values which have been calculated from the slate of an many-body perturbation theory GW method by P.Umari el al. Comparison of on-off ratio. device delay and saturation current in nanotube tunnel FETs reveals a considerable difference from previous evaluations made in the literature. Analysis reveals that. among the semiconducting zig-zag chiralities considered here, (11,0) nanotube devices in the tunnel FET configuration exhibits the best on-off ratio. device delay and saturation current which meets the ITRS-20Il requirement of low-operating power technology for 2020. Comparison of nanotube tunnel FETs with graphene nanoribbon tunnel FETs reveals that nanotube FETs deliver high on-off ratio and saturation current and exhibit comparable device delay. Among the considered families of nanoribbons, a l6AGNR exhibits best on -off ratio and device delay which operates within the future ITRS requirement. An atomic level investigation of the fundamental properties of a new type of metalgraphene system fanned by intercalation of gold atoms in epitaxial graphene is also presented. The effects of gold deposition on monolayer graphene (MG) epitaxied on SiC (0001) substrate are examined via Scanning Tunneling Microscopy (STM) and Spectroscopy (STS). Gold atoms exhibit mainly two types of self- assembly process below the graphene layer and the resulting gold-graphene systems exhibits contrasting electronic properties from each other. Insertion of a monolayer of gold below the monolayer graphene opens up a 100meV band gap in the electronic spectrum of graphene and creates a finite p-doping in graphene. While gold atoms intercalated in the form of atomic clusters shows negligible doping effect. Finally, signatures of a superlattice structure composed of a quasiperiodic arrangement of atomic gold clusters below an epitaxied graphene layer are examined Using dispersive Raman spectroscopy. The gold- graphene system exhibits a laser excitation energy dependant red shift of the 2D mode as compared to pristine epitaxial graphene. The phonon dispersion in pristine and gold intercalated graphene are mapped using experimentally observed Raman signatures and third-nearest neighbour (3NN) tight binding band structure model. This reveals that the observed behaviour is caused by modifications of the phonon. dispersion rather than changes in electronic structure. The intercalated gold atoms are found to restore the phonon band structure of epitaxial graphene towards that of free standing graphene.

A spray deposition manufacturing route has been developed for the fabrication of carbon nano-structured and micro-structured energy storage devices in a thin film format, with controlled film thickness, homogeneous film surface morphology and high electrochemical performance for both supercapacitors and lithium ion battery anodes. Three types of low cost commercially available carbon materials (graphite, activated carbon and carbon black) have been investigated, and electrodes characterised in terms of surface morphology, surface chemistry, microstructure and electrochemical properties. By using ball milling, CO₂ activation and adding suitable carbon conductive additives, nano-graphite-based film electrodes (one meter long and ~ 3 µm thickness) have been fabricated, with excellent ion transport and low electrical resistance (< 1.8 Ω). Specific capacitance of 110 F/g at a scan rate of 100 mV/s in 1 M H₂SO₄ was achieved. The high rate performance of activated carbon-based electrodes ( ~2 µm thickness) has been enhanced by reducing the contact resistance of electrode/current collector interface and building a well-interconnected and hierachical meso/macro-porous structure. A specific capacitance of over 120 F/g at a scan rate of 600 mV/s or 20 A/g current density in 1 M H₂SO₄ was achieved. The performance of carbon black-based electrodes (~4 µm thickness) in different electrolytes has been studied in both two- and three-electrode cells. High specific capacitances of 260 F/g at 1 A/g was achieved in 6 M KOH, together with energy and power densities of 21 kW/kg and 18 Wh/kg in 1 M Na₂SO₄. Finally, graphite-based electrodes for rechargeable lithium-ion batteries have also been fabricated with controlled film thickness from ~ 900 nm to ~ 40 µm and 98% capacity retention of 371 mA/g after 20 cycles. Spray deposition has been demonstrated to have the potential for scalability in the manufacture of carbon-based thin film electrodes with competitive properties.

DNA origami is a method for constructing 2-dimensional nanostructures with arbitrary shapes, by folding a long piece of viral genomic DNA into an extended pattern (Rothemund, 2006). In this thesis DNA origami nanostructures that in- corporate active transport are developed, by combining rectangular DNA origami tiles with either synthetic DNA motors, or the protein motor F1-ATPase. The transport of an autonomous, unidirectional, and processive 'burnt-bridges' DNA motor across an extended linear track anchored to a DNA origami tile is demonstrated. Ensemble fluorescence measurements are used to characterise motor transport, and are compared to a simple deterministic model of stepping. The motor moves 100 nm along a track at 0.1 nms-1 Atomic force microscopy (AFM) is used to study the transport of individual motor molecules along the track with single-step resolution. A DNA origami track for a 'two-foot' DNA motor is also developed, and is characterised by AFM and ensemble fluorescence measurements. The burnt-bridges DNA motor is then directed through a track network with either 1 or 3 bifurcations. Ensemble fluorescence measurements demonstrate that the path taken can be controlled by the addition of external control strands, or pre-programmed into the motor. A method for attaching the rotary motor protein F1-ATPase to DNA origami tiles is developed. Different bulk and single-molecule methods for demonstrat- ing protein binding are explored. Single-molecule observations of rotation of the protein motor on a DNA origami substrate are made, and are of equivalent data quality to existing techniques.

This thesis presents a time-resolved incoherent anti-Stokes Raman spectroscopy (TRIARS) study of the D- G- and G'-band phonon population dynamics in single-walled carbon nanotubes (SWCNTs). The purpose of this study is to explore the mechanisms which control the decay of non-equilibrium.

Carbon nanoparticles constitute a class of important materials that have uses in many different fields. This thesis focuses on the synthesis and surface modification of different carbon nanoparticles and each novel nanomaterial is demonstrated to have a specific sensing application. Carbon blacks play a significant role in the research that is presented herein. Emperor 2000, a commercial bulk-produced carbon black available from Cabot Corporation, is the starting material for many of the investigations. The surface of Emperor 2000 is shown to be susceptible to physisorption, through π-π stacking. These interactions are exploited to append pyrene-based compounds onto the surface of the carbon nanoparticles. This methodology results in carbon nanoparticles with surface boronic acid functionality that is demonstrated to be affective in the electrochemical detection of catecholic caffeic acid. Emperor 2000 carbon nanoparticles are commercially produced with phenylsulphonic acid functional groups on the surface. This functionality is subjected to synthetic methods to obtain carbon nanoparticles with extremely hydrohphobic character, which are demonstrated as important substrates for probing lipophilic redox systems and lipid character under different experimental conditions. Fluorescent carbon nanodots (C-dots) are another important form of carbon nanoparticle. Herein, the facile synthesis of C-dots that possess intrinsic pyridine functionality is described. These nanodots exhibit two-photon fluorescence that is exhibited both in solution and in HeLa cells. The nanodots are demonstrated to have the potential to be developed into nanomedicines and biocompatible scaffolds for new drug delivery mechanisms. These straightforward synthesis, modification, and application methods demonstrate the effectiveness and the versatility of carbon nanoparticles. This class of nanomaterial is generally outclassed by modern and more fashionable carbon nanotubes and graphene-based systems. However, carbon nanoparticles are more cost effective and readily available carbon-based nanomaterials that can be used for a wide range of applications.

This thesis details the preparation and subsequent characterisation of novel nanostructured porous materials with tuneable porosity. The main focus is the development of inorganic and carbonaceous porous materials for catalysis, templating and gas storage applications. Three distinct methods of synthesis are investigated, namely: (i) hydrothermal synthesis of zeotype aluminosilicates, (ii) nanocasting techniques for templated carbons and (iii) sol-gel processes, with/without metal salt 'porogen', to carbon aerogels. Post-synthesis modification methods for carbonaceous materials include supercritical carbon dioxide mediated incorporation of palladium nanoparticles into zeolite templated carbons and chemical activation for carbon aerogels resulting in enhanced textural properties. Chapter 1: Provides the foundation and background to the main themes of nanostructured porous materials investigated in this work. Information about fundamental properties and applications is emphasised. Chapter 2: Gives a brief background of techniques used for characterisation of the porous materials generated in this research programme. Gas sorption techniques used to probe hydrogen storage and carbon dioxide uptake are also presented. Chapter 3: Describes stepwise experimental techniques followed in the preparation of various porous materials. The chapter also describes the instrumentation used in these techniques. Chapter 4 - 7: Each chapter reports a separate but sequential area of research in which appropriate additional theory and background is provided with associated literature review. This is followed by a results and discussion section, with a concluding summary for each chapter. Chapter 4: Details the synthesis of ordered mesoporous aluminosilicates, which exhibit some zeolitisation, prepared from a recipe conventionally used for the synthesis of microporous zeolite SEA. The porosity of the aluminosilicates is modified by simple washing and/or refluxing (in water) of either on the as-synthesised mesophase or the calcined material. The aluminosilicates have excellent hydrothermal stability and strong acidity and thus combine the best properties from mesoporous materials and zeolites. Chapter 5: Describes the preparation of zeolite templated carbons (ZTC) generated as replicas of zeolite Y via a hard template nanocasting process. In order to enhance hydrogen storage, the ZTCs are impregnated with Palladium nanoparticles using supercritical carbon dioxide solvent, scC02, as environmentally benign reaction media. The Pd-doped ZTCs exhibit enhanced hydrogen storage due to optimised (with respect to metal content and particle size) incorporation of Pd. Chapter 6: A two-step process for the generation of zeolite template carbons (ZTCs) was investigated. In this case the nanocasting technique involves liquid impregnation of zeolite 13X with furfuryl alcohol followed by chemical vapour deposition (CVD) of ethylene at variable CVD temperatures. The two-step process was a successful attempt to optimise the replication of the zeolite structure in the carbons. The ZTCs had very high surface area and excellent mechanical stability, and achieved the highest hydrogen storage capacity (7.3 wt% at 77 K and 20 bar) ever reported for any carbon material. Chapter 7: Organic Sol-gel chemistry is explored in the formation of carbon aerogels via conventional methods involving the use of resorcinolformaldehyde resins and melamine-formaldehyde with or without metal salt as a porogen and subcritical drying. Chemical activation is used to modify the porosity of aerogels for potential applications in carbon dioxide uptake. Chapter 8: A brief overall conclusion to this research work is presented together with recommendations for future research.

M.Tech. (Chemistry, Faculty of Applied and Computer Science), Vaal University of Technology. / Complexes of alkyldithiocarbamate and thiuram have been extensively explored for various applications in the medical field. Thiuram and dithiocarbamate ligands were used to prepared complexes of cobalt and copper. The high abundance of sulfur in these ligands has resulted to be the preferred complexes for the synthesis of metal sulfide nanoparticles. All the prepared complexes were characterized using techniques such as IR and 1HNMR spectroscopy, elemental analysis, and thermogravimetric analysis. All the spectra data obtained were consistent with the coordination of the ligands through sulfur atom to the metal ion. The thermogravimetric analysis of all complexes decomposed to form metal sulfide, which really confirmed that all the complexes could be used to metal sulfide nanoparticles. All the prepared complexes were used to synthesize MxSy nanoparticles. The metal sulfide nanoparticles were successful prepared by thermal decomposition of the single-source precursor in hexadecylamine solution. The reaction parameter such as the concentration (1.0, 0.5, 0.25 and 0.125 g), reaction temperature (80, 130, 200, 250 °C) and the time (5, 10, 15, 20, 25 and 30) of the reactionwere varied to see their effect on the preparation of the nanoparticles. The prepared metal sulfide nanoparticles were characterized using techniques such as UV spectroscopy, photoluminescence spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The concentration was found to have a profound effect in size and shape of the prepared nanoparticles. The nanoparticles prepared at various concentrations were dominated by sphere with an average size of 2-30 nm. The XRD pattern confirmed that the composition is not affected by the temperature. Thetemperature has a dramatic effect in size, shape and the stoichiometry of the reaction. This was confirmed by an increase in size as the temperature was increased, with the exception of cobalt sulfide nanoparticles that decrease in size while temperature was increase. The XRD pattern showed different composition as the temperature was varied. Time of the reaction was found to affect the particles size of the nanoparticle. The sizes of the nanoparticles were increase as the time of the reaction was prolonged.

Au cours des dernières décennies, en raison de sa stabilité́ chimique et thermique exceptionnelle associée à son caractère isolant, le nitrure de bore hexagonal sous forme de nanofeuillets (BNNSs) trouve un grand intérêt dans de nombreuses applications. En effet, il est sérieusement envisagé l’utilisation de ces nanomatériaux comme support de graphene ou pour la fabrication d’hétérostructures horizontales utilisables dans le domaine de la microélectronique pour des applications de nouvelle génération. Il existe deux grandes voies de synthèse de ces nanostructures 2D de h-BN, par dépôt chimique en phase vapeur (CVD), ou par exfoliation d’un monocristal. Dans le but de préparer des BNNS de grande qualité́ chimique et cristalline, notre groupe propose une nouvelle stratégie de synthèse en associant la voie polymère précéramique (PDC) à des techniques de frittage, par Spark Plasma Sintering (SPS) et Hot Isostatic Pressing (HIP). Premièrement, le comportement thermique du précurseur précéramique, le polyborazilène (PBN) a été étudié en conditions dynamiques in-situ. Il a ainsi été mis en évidence, le rôle bénéfique du promoteur de cristallisation (Li3N) sur la qualité cristalline du matériau final. Cependant, une étape de frittage complémentaire reste obligatoire pour parfaire la structuration cristalline du h-BN. Premièrement, un procédé́ de frittage par SPS a été mis en œuvre. Dans cette étude, ont été particulièrement étudiés l’influence de la température de frittage (1200-1950°C) ainsi que la teneur en promoteur de cristallisation (0-10% mass.) sur la qualité cristalline du matériau final. Après optimisation des conditions de synthèse, des pastilles de h-BN composées d’une grande quantité de plaquettes monocristallines de taille d’environ 200 μm2 ont été obtenues. Les caractérisations de ces monocristaux attestent d'une haute qualité́ chimique et cristalline, même si des impuretés, sans doutes dues à l’environnement en graphite dans le SPS, sont détectées par cathodoluminescence. Enfin, des mesures physiques montrent que les BNNSs préparés présentent une constante diélectrique intéressante de 3,9, associée à une résistance diélectrique correcte de 0,53 V/nm. Afin d’augmenter encore la taille des monocristaux préparés, un second procédé́ de frittage, par HIP, a été étudié́. Cette autre combinaison originale conduit alors à des monocristaux de h-BN significativement plus gros (jusqu’à 2000 μm de taille latérale), transparents, incolores et très faciles à exfolier. Ainsi cette nouvelle association de la synthèse de PBN par voie PDCs et du procédé́ de céramisation par HIP nous semble une voie des plus prometteuses pour générer de grands monocristaux de h-BN et des nanofeuillets susceptibles de supporter des hétérostructures à base de graphène. / In the past decades, due to their exceptional chemical and thermal stabilities together with their electrical insulation properties, hexagonal boron nitride nanosheets (BNNSs) have become a promising support substrate for graphene and promoted the incentive of various van der Waals heterostructures. For such applications, BNNSs are generally obtained by Chemical Vapor Deposition (CVD) or exfoliation. In order to achieve high quality and large BNNSs, our group has proposed a novel synthesis strategy based on the Polymer Derived Ceramics (PDCs) route combined with sintering techniques: Spark Plasma Sintering (SPS) or Hot Isostatic Pressing (HIP). Since hexagonal boron nitride (h-BN) crystallization is a key point in the synthesis of high quality BNNSs, efforts have been led to understand the beneficial role of a promotor of crystallization (Li3N), adopting a suitable in situ dynamic approach. It has been established that Li3N does improve the crystallization level of the product, and lower the transformation temperatures from polyborazylene to h-BN. Then, we have further investigate the influence of the SPS sintering temperature (1200-1950°C) and of the crystal promoter content (Li3N, 0-10 wt.%) on BN growth. The tested SPS parameters strongly modify the size of the resulting h-BN flakes. For an optimal Li3N concentration of 5 wt.%, h-BN flakes larger than 200 μm2 (average flake area) have been obtained. A high degree of crystallinity and purity have been achieved, even if the very-sensitive cathodoluminescence technic indicated traces of impurities, probably due to surrounding graphite parts of the SPS. Few-layered BNNSs have been successfully isolated, through exfoliation process. As a final application purpose, further physical measurements have confirmed that SPS derived h-BN exhibits an interesting dielectric constant of 3.9 associated with a dielectric strength of 0.53 V/nm. Due to a very high compact character of SPS-derivative h-BN crystals, the post-exfoliation step is made very difficult, resulting in BNNSs of tens of microns lateral size. Therefore, we have studied another sintering procedure by HIP for the ceramization process. Through this combination, we aim to promote the size of h-BN single crystals, leading to larger size exfoliated BNNSs. Characterizations from bulk crystals to BNNSs have been carried out in three aspects: morphology, lattice structure and chemical composition. This novel attempt has provided us transparent and colorless h-BN single crystals with large lateral size, up to 2000 μm. Besides, BNNSs with high purity have also been confirmed. HIP, as a new ceramization process of PDCs, has to be considered as a promising way to obtain large h-BN single crystals and nanosheets for supporting graphene and 2D heterostructures.