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The aim of this research was to demonstrate a high current and stable field emission (FE) source based on carbon nanotubes (CNTs) and electron multiplier microchannel plate (MCP) and design efficient field emitters. In recent years various CNT based FE devices have been demonstrated including field emission displays, x-ray source and many more. However to use CNTs as source in high powered microwave (HPM) devices higher and stable current in the range of few milli-amperes to amperes is required. To achieve such high current we developed a novel technique of introducing a MCP between CNT cathode and anode. MCP is an array of electron multipliers; it operates by avalanche multiplication of secondary electrons, which are generated when electrons strike channel walls of MCP. FE current from CNTs is enhanced due to avalanche multiplication of secondary electrons and in addition MCP also protects CNTs from irreversible damage during vacuum arcing. Conventional MCP is not suitable for this purpose due to the lower secondary emission properties of their materials. To achieve higher and stable currents we have designed and fabricated a unique ceramic MCP consisting of high SEY materials. The MCP was fabricated utilizing optimum design parameters, which include channel dimensions and material properties obtained from charged particle optics (CPO) simulation. Child Langmuir law, which gives the optimum current density from an electron source, was taken into account during the system design and experiments. Each MCP channel consisted of MgO coated CNTs which was chosen from various material systems due to its very high SEY. With MCP inserted between CNT cathode and anode stable and higher emission current was achieved. It was ~25 times higher than without MCP. A brighter emission image was also evidenced due to enhanced emission current. The obtained results are a significant technological advance and this research holds promise for electron source in new generation lightweight, efficient and compact microwave devices for telecommunications in satellites or space applications. As part of this work novel emitters consisting of multistage geometry with improved FE properties were was also developed.

Plasma sprayed aluminum oxide ceramic coating is widely used due to its outstanding wear, corrosion, and thermal shock resistance. But porosity is the integral feature in the plasma sprayed coating which exponentially degrades its properties. In this study, process maps were developed to obtain Al2O3-CNT composite coatings with the highest density (i.e. lowest porosity) and improved mechanical and wear properties. Process map is defined as a set of relationships that correlates large number of plasma processing parameters to the coating properties. Carbon nanotubes (CNTs) were added as reinforcement to Al2O3 coating to improve the fracture toughness and wear resistance. Two novel powder processing approaches viz spray drying and chemical vapor growth were adopted to disperse CNTs in Al2O3 powder. The degree of CNT dispersion via chemical vapor deposition (CVD) was superior to spray drying but CVD could not synthesize powder in large amount. Hence optimization of plasma processing parameters and process map development was limited to spray dried Al2O3 powder containing 0, 4 and 8 wt. % CNTs. An empirical model using Pareto diagram was developed to link plasma processing parameters with the porosity of coating. Splat morphology as a function of plasma processing parameter was also studied to understand its effect on mechanical properties. Addition of a mere 1.5 wt. % CNTs via CVD technique showed ~27% and ~24% increase in the elastic modulus and fracture toughness respectively. Improved toughness was attributed to combined effect of lower porosity and uniform dispersion of CNTs which promoted the toughening by CNT bridging, crack deflection and strong CNT/Al2O3 interface. Al2O3-8 wt. % CNT coating synthesized using spray dried powder showed 73% improvement in the fracture toughness when porosity reduced from 4.7% to 3.0%. Wear resistance of all coatings at room and elevated temperatures (573 K, 873 K) showed improvement with CNT addition and decreased porosity. Such behavior was due to improved mechanical properties, protective film formation due to tribochemical reaction, and CNT bridging between the splats. Finally, process maps correlating porosity content, CNT content, mechanical properties, and wear properties were developed.

In the current age of fast-depleting conventional energy sources, top priority is given to exploring non-conventional energy sources, designing highly efficient energy storage systems and converting existing machines/instruments/devices into energy-efficient ones. ‘Energy efficiency’ is one of the important challenges for today’s scientific and research community, worldwide. In line with this demand, the current research was focused on developing two highly energy-efficient devices – field emitters and Li-ion batteries, using beneficial properties of carbon nanotubes (CNT). Interface-engineered, directly grown CNTs were used as cathode in field emitters, while similar structure was applied as anode in Li-ion batteries. Interface engineering was found to offer minimum resistance to electron flow and strong bonding with the substrate. Both field emitters and Li-ion battery anodes were benefitted from these advantages, demonstrating high energy efficiency. Field emitter, developed during this research, could be characterized by low turn-on field, high emission current, very high field enhancement factor and extremely good stability during long-run. Further, application of 3-dimensional design to these field emitters resulted in achieving one of the highest emission current densities reported so far. The 3-D field emitter registered 27 times increase in current density, as compared to their 2-D counterparts. These achievements were further followed by adding new functionalities, transparency and flexibility, to field emitters, keeping in view of current demand for flexible displays. A CNT-graphene hybrid structure showed appreciable emission, along with very good transparency and flexibility. Li-ion battery anodes, prepared using the interface-engineered CNTs, have offered 140% increment in capacity, as compared to conventional graphite anodes. Further, it has shown very good rate capability and an exceptional ‘zero capacity degradation’ during long cycle operation. Enhanced safety and charge transfer mechanism of this novel anode structure could be explained from structural characterization. In an attempt to progress further, CNTs were coated with ultrathin alumina by atomic layer deposition technique. These alumina-coated CNT anodes offered much higher capacity and an exceptional rate capability, with very low capacity degradation in higher current densities. These highly energy efficient CNT based anodes are expected to enhance capacities of future Li-ion batteries.

Despite the tremendous application potentials of carbon nanotubes (CNTs) proposed by researchers in the last two decades, efficient experimental techniques and methods are still in need for controllable production of CNTs in large scale, and for conclusive characterizations of their properties in order to apply CNTs in high accuracy engineering. In this dissertation, horizontally well-aligned high quality single-walled carbon nanotubes (SWCNTs) have been successfully synthesized on St-cut quartz substrate by chemical vapor deposition (CVD). Effective radial moduli (Eradial) of these straight SWCNTs have been measured by using well-calibrated tapping mode and contact mode atomic force microscopy (AFM). It was found that the measured Eradial decreased from 57 to 9 GPa as the diameter of the SWCNTs increased from 0.92 to 1.91 nm. The experimental results were consistent with the recently reported theoretical simulation data. The method used in this mechanical property test can be easily applied to measure the mechanical properties of other low-dimension nanostructures, such as nanowires and nanodots. The characterized sample is also an ideal platform for electrochemical tests. The electrochemical activities of redox probes Fe(CN)63-/4-, Ru(NH3)63+, Ru(bpy)32+ and protein cytochrome c have been studied on these pristine thin films by using aligned SWCNTs as working electrodes. A simple and high performance electrochemical sensor was fabricated. Flow sensing capability of the device has been tested for detecting neurotransmitter dopamine at physiological conditions with the presence of Bovine serum albumin. Good sensitivity, fast response, high stability and anti-fouling capability were observed. Therefore, the fabricated sensor showed great potential for sensing applications in complicated solution.

Orientador: Marcos Akira D'Ávila / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-26T18:13:53Z (GMT). No. of bitstreams: 1 Nascimento_AnaFlavia_M.pdf: 2761959 bytes, checksum: 7c55b1346515739af95a22eec2db0ae2 (MD5) Previous issue date: 2015 / Resumo: Este trabalho teve como objetivo a obtenção, por eletrofiação, de mantas de fibras de poli(fluoreto de vinilideno) (PVDF) sob tratamento com plasma e dispersão de nanotubo de carbono (NTC). O plasma possui a característica de tornar a superfície da manta de PVDF hidrofílica, que pode favorecer a adesão de NTC na superfície da fibra. O NTC utilizado foi previamente funcionalizado, com a presença de grupo carboxílico na superfície do tubo para que houvesse melhor afinidade entre ele e a superfície do PVDF, além disso, foi utilizado surfactante na dispersão aquosa de NTC para que se pudesse obter sua melhor distribuição e dispersão. A análise de MEV foi utilizada para estudar a morfologia das fibras, DSC para determinar a porcentagem de cristalinidade das amostras, FTIR e DRX para identificar as fases cristalinas presentes. Verificou-se pelo ensaio de condutividade elétrica que mantas tratadas com nanotubo de carbono apresentaram-se condutivas. O material obtido apresentou flexibilidade mesmo após os tratamentos com plasma e dispersão de NTC, e condutividade elétrica. A potencial aplicação em componentes eletrônicos se deve ao significativo aumento de condutividade elétrica quando a manta foi tratada em dispersão de NTC, além dos resultados mostrarem a presença de fase beta do PVDF nessas amostras. Isso se deve a uma boa distribuição e dispersão de NTC funcionalizado na estrutura superficial das fibras eletrofiadas / Abstract: In this work, fiber mats of poly(vinylidene fluoride) (PVDF) were prepared by electrospinning and suffered plasma surface treatment and immersion on carbon nanotube (CNT) dispersion. Plasma treatment can change the surface mat properties, became it through hydrophilic, which may be easier the adhesion of CNT on fiber surface. The CNT were functionalized with carboxylic group on the tube surface to became with better affinity between the nanotube and the PVDF surface, besides, surfactant was used in the CNT water dispersion to take it in a better distribution and dispersion. SEM analysis was done to evaluate the fibers morphology, DSC was to determine the samples crystallinity percentage, FTIR and XRD were to identify the crystalline phases. It was possible to ensure the conductivity at mats treated with carbon nanotubes through electrical conductivity essay. The polymeric mat showed flexibility even after the plasma and dispersion CNT treatments, besides electrical conductivity. Electronic components potential application is due to significant increase of electrical conductivity after the mat treatments, besides the results showed beta phase of PVDF in these samples. This is because of good distribution and dispersion of functionalized CNT on the surface structure of electrospun fibers / Mestrado / Materiais e Processos de Fabricação / Mestra em Engenharia Mecânica

O óxido nítrico além de poluidor ambiental, também desempenha diversas funções no organismo, por exemplo, trata-se de uma molécula sinalizadora em diversos processos metabólicos. Por causa disso, a detecção de NO é uma importante ferramenta para a medicina. Assim, existe um significante interesse tanto da indústria como da medicina no desenvolvimento de novos materiais que possam detectar oxido nítrico Os Nanotubos de Carbono de Paredes Múltiplas, intensivamente explorados desde sua descoberta em 1991, são considerados promissores em diversas aplicações devido a sua estrutura única e a possibilidade de realizar modificações as quais influenciam suas propriedades físicas e químicas. Já o ouro, conhecido por sua baixa atividade catalíca quando utilizado na forma cristalina, começou a ter seu poder catalítico explorado a partir de 1985, quando descobriu-se que, se utilizado na forma de pequenas partículas, este comporta-se mais como átomos individuais e torna-se mais catalítico que o ouro cristalino. Assim, o objetivo deste trabalho foi promover a funcionalização dos nanotubos de carbono, o que pode ser confirmado por MEV, FTIR e RAMAN, e, a partir dos grupos funcionais gerados, ancorar nanoparticulas de ouro em suas paredes, a fim de otimizar as propriedades catalíticas do material. O material gerado foi caracterizado morfologicamente e estruturalmente por MEV-FEG, EDX, Raio-X, RAMAN e UV-vis. Já a caracterização eletroquímica foi feita por voltametria cíclica frente ao K4[Fe(CN)6], com o qual foi possível mostrar um aumento na densidade de corrente de pico, o deslocamento do potencial de pico para valores menos positivos e também a diminuição do sobrepotencial, quando comparados o sensor Náfion®/AuNP/MWCNT/GC com o Náfion®/GC, Náfion®/MWCNT/GC e Náfion®/Ouro. O eletrodo proposto foi utilizado na determinação de Óxido Nítrico, em tampão PBS pH 4,4, utilizando a técnica de voltametria de pulso diferencial. A metodologia proposta apresentou um limite de detecção de 2,4x10-10 mol L-1 e um limite de quantificação de 7,9x10-10 mol L-1. Assim, este trabalho mostrou a potencialidade de utilização do eletrodo Náfion®/AuNP/MWCNT/GC como sensor eletroquímico para detecção e quantificação de óxido nítrico. / Nitric oxide (NO) is an environmental polluter, which also plays several roles in the body, for example, as a signaling molecule for many metabolic processes. Because this, detecting NO is an important tool in medicine. As a result, there was significant interest in both industry and medicine in developing new materials that can detect NO. Multiwall carbon nanotubes, that have been intensively explored since its discovery in 1991, are considered promising in many applications due to its unique structure and because it can be easily modified in order to tuning their physical and chemical properties. But the interest in using gold as the catalytic material appeared only in 1985, when was discovered that small particles form of gold behaves as individual atoms and it are more catalytic that crystalline gold. In this way, the objectives of this study were promoted the functionalization of carbon nanotubes - which could be confirmed by SEM, FTIR, Raman - and, with the functional groups generated, anchoring gold nanoparticles in their walls, in order to improve the catalytic properties of such material. The developed material was morphologically and structurally characterized by FEG-SEM, EDX, X-ray, Raman and UV-vis. As well, the electrochemical characterization was performed by cyclic voltammetry in K4[Fe(CN)6] solution. When Nafion®/AuNP/MWCNT/GC sensor was compared with Náfion®/GC, Náfion®/MWCNT/GC and Náfion®/Gold, its show an increase in current density peak, the peak potential displacement to less positive values and also decreased potential difference between the cathodic and anodic peak. The proposed electrode was used in the determination of nitric oxide in PBS buffer pH 4.4, which showed a detection limit of 2,4x10-10 mol L-1 and a quantification limit of 7,9x10-10 mol L-1 using the differential pulse voltammetry. Thus, this study demonstrated the potential use of Nafion®/AuNP/MWCNT/GC electrode as an electrochemical sensor in the nitric oxide detection and quantification.

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This diploma thesis deals with monitoring the properties of concrete with carbon nanoparticles. The theoretical part describes properties of nanoparticles, their dosing and dispersion. In the practical part of the diploma thesis the physico-mechanical properties of the concrete with the addition of carbon nanotubes were determined after 7 and 28 days of aging. The frost resistance test was then determined after 100 cycles. All results were compared with the reference samples.

This dissertation presents a unique concept for a device architecture named the nanotube (NT) architecture, which is capable of higher drive current compared to the Gate-All-Around Nanowire architecture when applied to heterostructure Tunnel Field Effect Transistors. Through the use of inner/outer core-shell gates, heterostructure NT TFET leverages physically larger tunneling area thus achieving higher driver current (ION) and saving real estates by eliminating arraying requirement. We discuss the physics of p-type (Silicon/Indium Arsenide) and n-type (Silicon/Germanium hetero-structure) based TFETs. Numerical TCAD simulations have shown that NT TFETs have 5x and 1.6 x higher normalized ION when compared to GAA NW TFET for p and n-type TFETs, respectively. This is due to the availability of larger tunneling junction cross sectional area, and lower Shockley-Reed-Hall recombination, while achieving sub 60 mV/dec performance for more than 5 orders of magnitude of drain current, thus enabling scaling down of Vdd to 0.5 V. This dissertation also introduces a novel thin-film-transistors architecture that is named the Wavy Channel (WC) architecture, which allows for extending device width by integrating vertical fin-like substrate corrugations giving rise to up to 50% larger device width, without occupying extra chip area. The novel architecture shows 2x higher output drive current per unit chip area when compared to conventional planar architecture. The current increase is attributed to both the extra device width and 50% enhancement in field effect mobility due to electrostatic gating effects. Digital circuits are fabricated to demonstrate the potential of integrating WC TFT based circuits. WC inverters have shown 2× the peak-to-peak output voltage for the same input, and ~2× the operation frequency of the planar inverters for the same peak-to-peak output voltage. WC NAND circuits have shown 2× higher peak-to-peak output voltage, and 3× lower high-to-low propagation delay times when compared to their planar counterparts. WC NOR circuits have shown 70% higher peak-to-peak output voltage, over their planar counterparts. Finally, a WC based pass transistor logic multiplexer circuit is demonstrated, which has shown more than 5× faster high-to-low propagation delay compared to its planar counterpart at a similar peak-to-peak output voltage.