Graphene is essentially a monolayer of sp2 bonded carbon atoms, arranged in a honeycomb lattice. Graphene has in recent years attracted phenomenal interest from researchers in materials science, condensed matter physics, and electronics since its first demonstration in 2004. The importance of graphene research was epitomised by the Nobel prize for physics being awarded to pioneers of the field in 2010. The main topic of this research was the development of epitaxial graphene on silicon carbide (SiC) substrates. The substrate inferred processability of epitaxial graphene enables graphene devices to be fabricated on full wafers using standard semiconductor processing techniques. Biosensor research is a rapidly expanding field. The major driver comes from the healthcare industry but there are also applications for biosensors in the food quality appraisal and environmental monitoring industries. The key advantages of electrochemical biosensors over competing sensor technologies are the low cost of mass production, and ability to make sensors into small compact systems. Smaller, portable sensors allow for the development of point-ofcare medical devices, which can be crucial in fast diagnosis and long-term monitoring of diseases. Graphene channel resistor devices have been fabricated using electron beam lithography and a successfully developed contact metallisation scheme - using Titanium / Gold contacts. The metal-graphene contacts have been characterised using XPS and electrical current-voltage measurements. The graphene channel device has been used as the basis of an electrochemical sensor for human chorionic gonadotropin (hCG), an indicator of pregnancy - which has also been linked to increased risk of several cancers. The immunosensor developed is a promising tool for point-of-care detection of hCG, due to its excellent detection capability, simplicity of fabrication, low-cost, high sensitivity and selectivity.

In the present thesis, research work to tackle challenges such as large-scale integration, selectivity and low efficiency around different types of nanocarbon based sensors is performed. The findings of these studies are given in the form of peer-reviewed publications and conclusions with future recommendations proposed as a summary. The work focuses on three key sensors types, gas sensors, biosensors and photodetectors. The first key aspect is dielectrophoretic (DEP) deposition of nitrogen doped single-walled carbon nanotubes (N-SWCNTs) and it is used as a route to large-scale assembly of increased reactivity, and thus selectivity, gas sensors. Furthermore, suspended SWCNTs and few layer graphene (FLG) devices are fabricated through a novel process which results in increased surface area transducers and low resistance SWCNTs based devices. Moreover, biosensors face similar challenges to gas sensors with the addition that their selectivity needs to be engineered through the formation of a biomimetic interface due to the nature of the analytes they are destined to investigate. Non-covalent functionalization of graphene using self-assembled phospholipid membranes delivered in a controlled and precise manner by dip-pen nanolithography (DPN) was demonstrated together with a high-speed fabrication process of bioassays onto patterned CVD graphene using a parallel tips system. Lastly, for the case of photodetectors, a SWCNT – nanoplasmonic system is proposed as a solution to the major issue of low quantum efficiency in low dimensionality materials. First, the performance of various geometries and arrangements of Au nanoparticles is explored by transferring a micromechanically exfoliated graphene flake onto them and studying the Raman enhancement that arises due to uncoupled and coupled near-fields. An increase of graphene Raman signal of 103 was observed for the areas suspended between two closely spaced dimers as a result of strong near field coupling when the polarisation of the incident light is parallel to the nanostructures axis. A large-scale integration of SWCNTs positioned in between the dimers using DEP is performed as a demonstration of the scalability of the system.

Made available in DSpace on 2015-05-14T12:14:06Z (GMT). No. of bitstreams: 1 ArquivoTotalMarcio.pdf: 781183 bytes, checksum: 74353c8a0d88a7ead0ba65e66e3b2738 (MD5) Previous issue date: 2013-07-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Currently, the study of the physical properties of nanomaterials has been a vast field of study in Condensed Matter Physics and Materials Science and Engineering. Such objects have various applications like making electronic devices smaller and more efficient, for example. Carbon nanotubes are an interesting class in this regard due to their experimental synthesis and theoretical description well established in the literature. A carbon nanotube can be viewed as a rolled up graphene sheet. In 2002, Kral and Sadeghpoura investigated the rotation of nanotubes by applying lasers. Motivated by this achievement, in this work we focus the description of the dynamics of the charge carriers in a spinning nanotube , but this time also considering a magnetic field . For this, we begin with an effective Dirac Hamiltonian for massless fermions, as done for the case of graphene, but in this case using coordinates z and f.The vector potentials associated to the magnetic field and to rotation(Coriolis field) enter Dirac equation via the usual minimal coupling.The Coriolis vector potential comes from the idea of the Aharonov-Carmi, an "rotational"analog the celebrated Aharonov-Bohm effect. Finally, we analyze the influence of the presence of the field and the rotation in the energy spectrum. / Atualmente, o estudo de propriedades físicas de nanomateriais têm sido um vasto campo de estudoem Física da Matéria Condensada e em Ciência e Engenharia de Materiais. Tais objetos possuemdiversas aplicações, como a fabricação de dispositivos eletrônicos menores e mais eficientes, porexemplo. Nanotubos de Carbono constituem uma classe interessante neste contexto, devido às suaspossibilidades de síntese experimental e descrição teórica bem estabelecida na literatura. Umnanotubo de carbono pode ser visto como uma folha de Grafeno enrolada.Em 2002, Kral e Sadeghpoura investigaram a rotação de nanotubos pela aplicação de lasers.Motivados por tal realização, neste trabalho nos preocupamos em tentar descrever a dinâmica dosportadores de carga num nanotubo girante, mas desta vez considerando também um campomagnético..Para tal, partiremos de um hamiltoniano efetivo de Dirac para férmions sem massa,talcomo feito para o caso do Grafeno, mas neste caso com o uso de coordenadas z e φ. Inserimos ocampo e a rotação via acoplamento mínimo, utilizando um potencial vetor associado ao campomagnético e um potencial vetor associado à rotação. Mostraremos que este último advém da ideiado efeito Aharonov-Carmi , um análogo rotacional do célebre efeito Aharonov-Bohm.Por fim, analisamos a influência da presença do campo e da rotação no espectro de energia.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O grafeno à definido como uma estrutura cristalina bidimensional, formada por uma rede hexagonal de Ãtomos de carbono, e devido Ãs suas propriedades eletrÃnicas e estruturais, existe um enorme interesse em investigar as propriedades fÃsicas de materiais originados da modificaÃÃo quÃmica do grafeno. AlÃm disso, o grafeno à a base para todos os alÃtropos de carbono com estrutura grafÃtica (hibridizaÃÃo sp2), podendo ser envolvido de forma esfÃrica, formando os fulerenos (0D), enrolado em uma estrutura cilÃndrica conhecida como nanotubos de carbono (1D), ou empilhado, gerando assim, o grafite (3D), ou cortado em fitas gerando os "ribbons" (1D). Dentre esses materiais derivados do grafeno, destacam-se os que sÃo sintetizados a partir da oxidaÃÃo da folha de grafeno, chamados de Ãxido de grafeno (OG). Esse trabalho foi direcionado à preparaÃÃo de amostras de nanoestruturas de carbono e a realizaÃÃo de medidas de Microscopia de Varredura por Sonda (SPM), tendo como finalidade, uma melhor compreensÃo da morfologia e das propriedades fÃsicas desses materiais. Em especÃfico, o escopo desse trabalho foi estudar as caracterÃsticas morfolÃgicas de Nanotubos de carbono e as propriedades eletrostÃticas do grafeno com o uso das tÃcnicas de SPM. Para isso, analisou-se o comportamento mecÃnico de Nanotubos de carbono quando sujeitos a compressÃes radiais usando uma ponta de AFM e os resultados foram, entÃo, comparados com resultados conhecidos na literatura. No que diz respeito ao grafeno, foram realizadas medidas de AFM (Microscopia de ForÃa AtÃmica), EFM (Microscopia de ForÃa ElÃtrica) e Espectroscopia Raman em amostras de grafeno puro, grafeno tratado com Ãcido nÃtrico e Ãxido de grafeno. Os resultados foram, entÃo, discutidos e comparados entre si. As amostras de grafeno foram obtidas a partir do mÃtodo de esfoliaÃÃo mecÃnica do grafite e as medidas realizadas em atmosfera ambiente. Dessa forma, os resultados mostraram que o tratamento com Ãcido nÃtrico, resultou no desvio no pico da banda G no grafeno e, tambÃm, ocasionou uma mudanÃa no comportamento eletrostÃtico nas bordas da amostra, quando comparado ao grafeno puro. / Graphene is dened as one-dimensional crystal structure, formed by a hexagonal network of carbon atoms,and due to the in unique structural and electronic properties, there is a great interest in investigating the physical properties of materials obtained from the chemical modication of graphene. Furthermore, graphene is the basic structural framework for all allotropes of carbon structure graphitic (hybridization sp2) and may be curled in a spherical shape, forming fullerenes (0D), rolled up into a cylindrical structure known as carbon nanotubes (1D), stacked, thus generating graphite (3D) and cut into stripes thus forming graphene nanoribbons. Among these materials derived from graphene, those that are synthesized from the oxidation of the graphene sheet, called graphene oxide (GO) are set apart. This work was focused to sample preparation of carbon nanostructures and their caracterization by means of Scanning Probe Microscopies (SPM) aiming to get a better understanding of the morphology and physical properties of these materials. In particular, the goal of this study was to investigate the morphological characteristics of CNTs and the electrostatic properties of graphene using SPM techniques. For this, we analyzed the mechanical behavior of carbon nanotubes when subjected to a radial compression by using AFM tip and the results were compared with those reported in the literature. Regardig the graphene we measured by AFM (Atomic Force Microscopy), EFM (Electric Force Microscopy) and Raman spectroscopy in pristine graphene, graphene treated with nitric oxide and graphene oxide, and the results were discussed and compared to each other. The graphene samples were obtained by using the exfoliation method of graphite and mechanical measurements performed in ambient atmosphere. The results showed that treatment with nitric acid resulted in peak shift of G band in graphene and also caused a change in the electrostatic behavior of edges of the sample when compared to pristine graphene.

Graphene, a one-atom thick sheet of carbon, is the thinnest, strongest and most electrically conductive material ever discovered. Alongside carbon nanotubes it is part of the group of nanocarbons whose unique properties have sparked huge interest in possible applications, including electronic devices, solar cells and biosensors. Doping of these materials allows for the modification of their optical and electronic properties,which is crucial to realising these applications. Studying the properties of these doped materials at atomic resolution and finding controllable and industrially scalable routes to doping, such as low energy ion implantation, are thus essential if they are to becomethe materials of the future. In this thesis, highly localised optical enhancements in metal doped graphene are studied using energy-filtered transmission electron microscopy in a monochromated and aberration corrected electron microscope. The ideal conditions for imaging the low energy loss region of graphene using EFTEM are discussed and new methods to compensate for image artifacts when using this technique at high resolution are presented. Density functional theory is used to reveal new visible spectrum plasmon excitations in the electron energy loss spectra of boron and nitrogen doped nanocarbons. Atomic resolution scanning transmission electron microscopy and nanoscale electron energy loss spectroscopy are used to investigate controllable and defect-free substitutional doping of suspended graphene films through low energy ion implantation. Computational methods for filtering high angle annular dark field images are shown and software for the automated processing and spectroscopic analysis of these images is developed.

M-Tech. (Department of Chemistry, Faculty of Applied and Computer Science), Vaal University of Technology. / The commercial flake graphite was prepared into functionalized graphite oxide (GO) by adopted chemical treatment. After the exfoliation and intercalation of graphite into functionalized graphene oxide that formed stable colloidal dispersion in polar aprotic solvent, the reduction process was undertaken by continuous stirring with hydrazine hydrate in a microwave at 35 oC for two hours. The reduced material was characterized by X-ray diffraction (XRD), attenuated total reflectance (ATR) FT-IR, Ultra-violet visible (UV-vis), atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman microscopy and magnified optical microscopy that confirm the oxidation of graphite and reduction of graphene oxide into graphene sheets. Carbon nanomaterials were synthesized from Co-Sn, Co-Sr and Co-Zn as catalysts supported on Al2O3, CaCO3 and MgO. The as-prepared nanomaterials were characterized by thermogravimetric and derivative thermogravimetric analysis (TGA & DTA), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and the transmission electron microscopy. The intensity ratios (ID/IG) of the D- and G- bands were found to be the same that is averagely at 0.83. The TGA & DTA curves have shown Co-Sn/Al had significant weight loss, Co-Sr/Mg weight loss and decomposition, Co-Sr/Al decomposition and Co-Zn/Mg weight loss. However these weight losses were not significant. The EDS analysis showed all elements which took part in the reaction confirming the success of each synthesis. The SEM images show carbon nanotubes only on samples that have been synthesized on MgO as confirmed by TEM images. Finally the XRD showed some characteristic peaks at desired peaks except that they were other peaks attributed to impurities and armophous carbon. It was also observed that Co-Sn/Ca and Co-Sn/Mg XRD curves showed broad peaks at theta = 24.3o & 42.6o and theta = 23.9o & 43.1o respectively which are lattice structure characteristic peaks.

Composites based on ICP with conductive (SWCNT and Te) and insulating fillers (TiO2 and CuO and insulating polymers with conducting fillers (rGO, modified rGO, and SWCNT) were prepared and their thermoelectric properties were investigated. Attempts to enhance the thermoelectric properties of PEOT:PSS composites did not bring about a significant change. But, the attempts to modify rGO brought about a considerable improvement in the thermoelectric properties. At the end, the use of SWCNT provided the maximum ZT in case of insulating polymer composites. Eventually, SEBS/4 wt% SWCNT with a ZT of 0.0017 and SBS/0.5 wt% SWCNT with a ZT 6  10-6 stood out as the best p-type and n-type thermoelectric material, respectively, in this work. This success paved the way to build 2 modules of thermoelectric generators which generated a maximum potential of 93.2 mV at a temperature difference of 40 K.