With more and more integration of analog and RF circuits in scaled CMOS technologies, process variation is playing a critical role which makes it difficult to achieve all the performance specifications across all the process corners. Moreover, at scaled technology nodes, due to lower voltage and current handling capabilities of the devices, they suffer from reliability issues that reduce the overall lifetime of the system. Finally, traditional static style of designing analog and RF circuits does not result in optimal performance of the system. A new design paradigm is emerging toward digitally assisted analog and RF circuits and systems aiming to leverage digital correction and calibration techniques to detect and compensate for the manufacturing imperfections and improve the analog and RF performance offering a high level of integration. The objective of the proposed research is to design digital friendly and performance tunable adaptive analog/RF circuits and systems with digital enhancement techniques for higher performance, better process variation tolerance, and more reliable operation and developing strategy for testing the proposed adaptive systems. An adaptation framework is developed for process variation tolerant RF systems which has two parts – optimized test stimulus driven diagnosis of individual modules and power optimal system level tuning. Another direct tuning approach is developed and demonstrated on a carbon nanotube based analog circuit. An adaptive switched mode power amplifier is designed which is more digital-intensive in nature and has higher efficiency, improved reliability and better process resiliency. Finally, a testing strategy for adaptive RF systems is shown which reduces test time and test cost compared to traditional testing.

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composite fibers were made using various processing methods such as conventional solution spinning, gel spinning, and bi-component gel spinning. The detailed characterization exhibited that the smaller and longer CNT will reinforce polymer matrix mostly in tensile strength and modulus, respectively. Gel spinning combined with CNT also showed the promising potential of PAN/CNT composite fiber as precursor fiber of the next generation carbon fiber. High resolution transmission electron microscopy showed the highly ordered PAN crystal layer on the CNT, which attributed to the enhanced physical properties. The subsequent carbonization study revealed that carbonized PAN/CNT fibers have at least 50% higher tensile strength and modulus as compared to those of carbonized PAN fibers. Electrical conductivity of CNT containing carbon fiber was also 50% higher than that of carbonized PAN fiber. In order to have carbon fiber with high tensile strength, the smaller diameter precursor fiber is preferable. Bi-component gel spinning produced 1-2 µm precursor fiber, resulting in ~1 µm carbon fiber. The tensile strength of the carbonized bi-component fiber (islands fibers) is as high as 6 GPa with tensile modulus of ~500 GPa. Further processing optimization may lead to the next generation carbon fiber.

The graphitic nature, continuous structure, and high mechanical properties of carbon nanotubes (CNTs) make them good candidate for reinforcing polymer fiber. The different types of CNTs including single-wall carbon nanotubes (SWNTs), few-wall carbon nanotubes (FWNTs), and multi-wall carbon nanotubes (MWNTs), and carbon nanofibers (CNFs) differ in terms of their diameter and number of graphitic walls. The desire has been to increase the concentration of CNTs as much as possible to make next generation multi-functional materials. The work in this thesis is mainly focused on MWNT and CNF reinforced polyacrylonitrile (PAN) composite fibers, and SWNT, FWNT, and MWNT reinforced poly(etherketone) (PEK) composite fibers. To the best of our knowledge, this is the first study to report the spinning of 20% MWNT or 30% CNF reinforced polymer fiber spun using conventional fiber spinning. Also, this is the first study to report the PEK/CNT composite fibers. The fibers were characterized for their thermal, tensile, mechanical, and dynamic mechanical properties. The fiber structure and morphology was studied using WAXD and SEM. The effect of two-stage heat drawing, sonication time for CNF dispersion, fiber drying temperature, and molecular weight of PAN was also studied. Other challenges associated with processing high concentrations of solutions for making composite fibers have been identified and reported. The effect of CNT diameter and concentration on fiber spinnability and electrical conductivity of composite fiber have also been studied. This work suggests that CNT diameter controls the maximum possible concentration of CNTs in a composite fiber. The results show that by properly choosing the type of CNT, length of CNTs, dispersion of CNTs, fiber spinning method, fiber draw ratio, and type of polymer, one can get electrically conducting fibers with wide range of conductivities for different applications. The PEK based control and composite fibers possess high thermal stability with almost no weight loss up to 500 degree C and negligible thermal shrinkage up to 200 degree C. The PEK based fibers showed high toughness which surpassed many of the high-performance fibers like Kevlar(R) and Zylon(R). The 10% FWNT containing fiber is unique in terms of high electrical conductivity and high toughness. The CNT based fibers may be used as structural material, fire-barrier/protection textile, electrode for electrochemical capacitor or fuel cells, and as a template for directional growth of tissues.

This report details work toward the fabrication of a single-electron transistor created from a single-walled carbon nanotube (SWNT). Specifically discussed is a method for growing carbon nanotubes (CNTs) via carbon vapor deposition (CVD). The growth is catalyzed by a solution of 0.02g Fe(NO3)3·9H2O, 0.005g MoO2(acac)2, and 0.015g of alumina particles in 15mL methanol. SWNT diameter ranges from 0.6 to 3.0 nm. Also discussed is a method to control nanotube growth location by patterning samples with small islands of catalyst. A novel “maskless” photolithographic process is used to focus light from a lightweight commercial digital projector through a microscope. Catalyst islands created by this method are approximately 400 μm2 in area.

Au cours de ces dernières années, le développement des capteurs de gaz a connu un essor grandissant pour des applications industrielles, militaires et environnementales afin d’assurer la sécurité et la protection contre les gaz nocifs et toxiques. Ces applications demandent des capteurs sensibles, sélectifs, à faible consommation d’énergie et à faible coût. Le travail de thèse présenté dans ce manuscrit, s’inscrit dans ce contexte. Il a pour objectif la réalisation d’un capteur hyperfréquence à base de nanotubes de carbone et fabriqué par technologie jet d’encre. Le principe de fonctionnement du capteur repose sur la caractérisation en fréquence d’un résonateur RF, dont un élément est sensible grâce aux nanotubes de carbone, à la présence d’un gaz environnant. Le manuscrit aborde l’ensemble des étapes nécessaires à la réalisation du capteur, à savoir : la conception des dispositifs de test, s’appuyant sur une étude théorique de leur comportement, la caractérisation des matériaux utilisées, la fabrication sur un substrat flexible par une technique d’impression jet d’encre et enfin la caractérisation du capteur de gaz en termes de comportement en fréquence et de sensibilité en présence de gaz. / In recent years, the development of gas sensors has grown rapidly for industrial, military and environmental applications to ensure safety and protection against harmful and toxic gases. These applications require sensitive, selective, low power and low cost sensors. The thesis work presented in this manuscript fits into this context. Its objective is the realization of a microwave sensor based on carbon nanotubes and manufactured by inkjet technology. The operating principle of the sensor is based on the frequency characterization of an RF resonator, one element of which is sensitive, thanks to the carbon nanotubes, to the presence of a surrounding gas. The manuscript addresses all the steps necessary for the realization of the sensor, namely: the design of the test devices, based on a theoretical study of their behavior, the characterization of the materials used, the fabrication on a flexible substrate by inkjet printing technique and finally the characterization of the gas sensor in terms of frequency behavior and sensitivity in the presence of gas.

Measurement of all the mechanical properties of carbon nanotubes is extremely difficult because of its small size. In the present work, all the five transverse isotropic properties of single wall carbon nanotubes (SWCNTs) and double wall carbon nanotubes are estimated through molecular structural mechanics for different chirality, length and assumed thickness. Armchair, zigzag & chiral SWCNTs and polychiral DWCNTs are considered for the analysis. Longitudinal and lateral Young’s modulus; longitudinal and lateral Poisson’s ratio and shear modulus are estimated for 1080 SWCNTs and 1170 polychiral DWCNTs. Effect of temperature on all the properties of SWCNT are investigated. Modal characterization of SWCNT is carried out in base fixed condition and different mode shapes viz. axial, torsion and bending mode shapes are identified based on the effective mass. Once the transverse isotropic properties of SWCNTs are estimated, these are used to estimate the transverse isotropic properties of nanocomposites embedded with SWCNT agglomerates. During the manufacturing of nanocomposite, SWCNT agglomerates are formed due to sticking of number of SWCNTs. Parametric studies are carried out to see the effect of SWCNT length on the properties of nanocomposite. Empirical formulae for all the transverse isotropic properties of SWCNT at room temperature and elevated temperature; frequency of SWCNT are derived. Empirical formulae for polychiral DWCNT transverse isotropic properties are estimated. Input for these empirical formulae are the length, chirality and assumed thickness. Empirical formulae were also derived for nanocomposite embedded with different number of SWCNTs having different chirality. The derived empirical formulae were validated with available analytical and experimental results for some sample cases.

ALENCAR, Rafael Silva. Estudo de fônons em nanotubos de carbono e dissulfeto de molibdênio: efeito do acoplamento entre camadas. 2016. 116 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2016. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2016-07-04T18:55:57Z No. of bitstreams: 1 2016_tese_rsalencar.pdf: 15208196 bytes, checksum: 0879a7d3b08f7d02d899e3d78888e828 (MD5) / Approved for entry into archive by Edvander Pires (edvanderpires@gmail.com) on 2016-07-04T18:56:56Z (GMT) No. of bitstreams: 1 2016_tese_rsalencar.pdf: 15208196 bytes, checksum: 0879a7d3b08f7d02d899e3d78888e828 (MD5) / Made available in DSpace on 2016-07-04T18:56:56Z (GMT). No. of bitstreams: 1 2016_tese_rsalencar.pdf: 15208196 bytes, checksum: 0879a7d3b08f7d02d899e3d78888e828 (MD5) Previous issue date: 2016 / In this work we present the studies on Double (DWCNTs) and Triple Wall Carbon Nanotubes, on molybdenum disulfide in the bulk form and on few layer of MoS_2 under hydrostatic high pressure conditions. Theoretical calculations were performed in collaboration to support the experimental results. For the DWCNTs samples, changes in the G-band frequency vs. pressure plot and the disappearance of the radial breathing modes (RBM) between 2 GPa and 5 GPa indicate the beginning and ending of the radial collapse of the nanotubes. Theoretical calculations based on Density-Functional Tight-Binding (DFTB) shown that the collapse pressure (P_c) for DWCNTs follows a d^{-3}_{in} law, in excellent agreement with the experimental results. The P_c dependence on number of tube-walls and on the inter-wall distance is also investigated. For the TWCNTs samples, pressure screening effects are observed for the innermost tubes of TWCNTs similar to what has been already found for DWCNTs. However, using the RBM pressure coefficients in conjunction with the histogram of the diameter distribution, we were able to separate the RBM Raman contribution related to the intermediate tubes of TWCNTs from that related to the inner tubes of DWCNTs. By combining Raman spectroscopy and high pressure measurements, it was possible to identify these two categories of inner tubes even if the two tubes exhibit the same diameters, since their pressure response is different. Furthermore, it was possible to observe similar RBM profiles of the innermost tubes of TWCNTs using different resonance laser energies but also under different pressure conditions. This is attributed to changes in the electronic transition energies caused by small pressure-induced deformations. Theoretical calculations based on ab initio were performed for support the experimental results. By using Raman spectroscopy, it was possible to estimate the displacement of the optical energy levels with pressure. For the exfoliated MoS_2 samples, we studied the effect of the stacking on the E^1_{2g} and A_{1g} vibrational modes at high pressures. New components for both modes were observed with increasing pressure. It was also observed that the pressure coefficient of the E^1_{2g} mode decreases exponentially with MoS_2 thickness is increased, differently of the A_{1g} mode and the new components, which do not present a significant dependence on the variation of the number of layers. These results were attributed to deformations in the MoS_2 structure induced by a biaxial strain (dependent on the number of layers), resulting from the deformation of the SiO_2 substrate. Such adhesion decreases with the increasing of the MoS_2 thickness due to the increasing on the unbinding regions between MoS_2 and SiO_2. As result, a higher pressure is needed to improve the adhesion and consequently, a higher pressure is required to achieve the biaxial strain. For the MoS_2 microcrystalline powder, except for the B_{1u}, E^2_{2g}, E_{1g}, E^1_{2g} and A_{1g} modes, the behavior of all other modes was studied for the first time in high pressure conditions. For all modes, a linear variation of the Raman frequency and positive pressure coefficient was observed. Moreover, the differences in the behavior of the intensity profiles of the A_{1g}, 2LA(M) and A_{2u} modes in resonance and off-resonance were attributed to variations in the energy of direct optical transitions induced by pressure. / Nesta Tese apresentamos os estudos de espectroscopia Raman em condições extremas de pressão hidrostática realizados em nanotubos de carbono de parede dupla (DWCNTs) e tripla (TWCNTs), em dissulfeto de molibdênio na forma bulk e em poucas camadas. Cálculos teóricos foram usados para dar suporte aos resultados experimentais. Para as amostras de DWCNTs, as mudanças no coeficiente de pressão da banda G e o desaparecimento dos modos de respiração radial (RBMs) entre 2 GPa e 5 GPa foram interpretados como um indicativo do início e fim do colapso radial dos nanotubos de carbono (CNTs). Os cálculos teóricos usando Tight-Binding baseado no Funcional da Densidade (DFTB) mostraram que a pressão de colapso (P_c) para os DWCNTs segue uma lei de potência do tipo d^{-3}_{in}, em excelente acordo com os resultados experimentais. A dependência de P_c em relação ao número de paredes do tubo, como também a distância inter-paredes também foram investigadas. Para a amostra contendo TWCNTs, através da análise dos coeficientes de pressão dos modos RBMs em conjunto com o histograma da distribuição de diâmetros da amostra, foi possível separarmos as contribuições dos RBMs nos espectros Raman relacionados aos tubos internos dos TWCNTs e DWCNTs, embora possuam a mesma distribuição de diâmetro, a resposta das propriedades vibracionais à pressão são diferentes. Adicionalmente, foi possível observar perfis de intensidades semelhantes para os modos RBMs dos tubos mais internos dos TWCNTs usando diferentes energias de LASER, mas sob diferentes condições de pressão. Atribuímos este resultado à mudanças nas energias de transições eletrônicas causadas por pequenas deformações estruturais nos nanotubos induzidas pela pressão. Cálculos teóricos baseados em ab initio foram realizados para dar suporte às interpretações dos resultados experimentais. Para as amostras de MoS_2 esfoliadas, estudamos o efeito do empilhamento nos modos vibracionais E^1_{2g} e A_{1g} em altas pressões. Novas componentes para esses modos foram observadas com o aumento da pressão. Foi também observado que o coeficiente de pressão do modo E^1_{2g} diminui exponencialmente com o aumento do número de camadas, diferentemente do modo A_{1g} e das novas componentes, que não apresentam uma dependência significativa com a variação da espessura do MoS_2. Atribuímos estes resultados às deformações estruturais do MoS_2 induzidas por uma tensão biaxial (dependente da adesão entre SiO_2 e MoS_2) resultante da deformação do substrato de SiO_2. O aumento do número de camadas diminui a adesão entre o MoS_2 e o SiO_2 devido ao aumento da porcentagem de regiões em não-contato com o substrato, e como consequência, uma pressão mais elevada é necessária para aumentar a adesão, resultando no aumento da pressão para deformar a estrutura do MoS_2. Para o pó microcristalino de MoS2, com exceção dos modos B_{1u}, E^2_{2g}, E1g, E^1_{2g} e A_{1g}, o comportamento de todos os outros modos foi também estudado em condições de altas pressões hidrostáticas. Todos os modos apresentaram uma variação linear de suas frequências Raman com a pressão e coeficientes de pressão positivos. Além disso, as diferenças no comportamento dos perfis de intensidade dos modos A_{1g}, 2LA(M) e A_{2u} em ressonância e fora de ressonância foram interpretados como sendo devido às variações nas energias das transições ópticas direta induzidas pela pressão.

Este trabalho traz a aplicação de alta pressão e alta pressão/temperatura (4.0 GPa e 400º C), em amostras de nanotubos de carbono de paredes múltiplas (NTCPM) comerciais para a obtenção de amostras compactas. Os NTCPM foram funcionalizados com ácido nítrico e ácido nítrico/ácido sulfúrico e, também foram usados nanotubos de carbono dopados com nitrogênio. Foram também processadas amostras contendo nanotubos de carbono de paredes múltiplas incorporados em matriz de zircônia obtida pelo método sol-gel. Para aplicação da alta pressão foi usado um sistema com câmaras do tipo toroidal, utilizando grafite como meio transmissor de pressão. Foram obtidas amostras macroscópicas autossuportadas e com resistência ao manuseio principalmente nas amostras de nanotubos de carbono funcionalizados com ácido nítrico/ácido sulfúrico incorporados em zircônia. Para a caracterização das amostras foram utilizadas as técnicas de Microscopia Eletrônica de Transmissão, Espectroscopia Raman, Difração de Raios X e isotermas de adsorção/dessorção de nitrogênio com as quais foi possível determinar que mesmo após a aplicação de alta pressão/temperatura os nanotubos de carbono não sofrem significativas modificações na sua estrutura e nas suas propriedades morfológicas e texturais, confirmando então que os NTCPM mantém suas características originais, apresentando condições para aplicações em dispositivos. As amostras macroscópicas contendo nanotubos de carbono de paredes múltiplas incorporados em zircônia apresentaram ainda resistência à carga de milhares de vezes o seu peso e comportamento de materiais semi-condutores. / This work presents the application of high pressure and/or high pressure/temperature (4.0 GPa and 400 ° C), on different samples of commercial multi-walled carbon nanotube (MWCNT) to obtain compacted samples. MWCNT were functionalized with nitric acid and nitric acid/sulfuric acid, and also carbon nanotubes doped with nitrogen. MWCNT incorporated in a zirconia matrix obtained by sol-gel method were also processed. For high pressure application it was used a system with the toroidal-type chamber, using graphite as a pressure transmitting medium. Self-supported macroscopic samples were obtained, easy to handle, especially in samples of functionalized carbon nanotubes with nitric and sulfuric acid and also incorporated in zirconia. To characterize the samples it was used Transmission Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nitrogen adsoption/desorption isotherms and it was determined that even after application of high pressure/temperature carbon nanotubes do not suffer significant changes in their structure and in their morphological and textural properties, confirming that the CNT keeps its original characteristics and providing conditions for device applications. The macroscopic samples containing MWCNT incorporated in zirconia also exhibited resistance to load of thousands times its own weight and behavior like semiconductor materials.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this work we use the Density Functional Theory (DFT) to analyze the influence of a water environment in the interaction between amino acids and a semiconductor carbon nanotube (CNT). To the study of the interaction in vacuum we use both an ab initio and a parameterized tight-binding method. To the study of the same interactions in water we performed finite temperature (300 K) molecular dynamics calculations, using the parameterized tight-binding method. The selected amino acids have different hydrophobicity and polarity indexes. Our study shows that for the neutral amino acids, a direct relationship between the variation in the bonding distances and the hydrophobicity indexes when changing from vacuum to water environments, with the hydrophobic (hydrophilic) amino acids getting nearer (farther) of the carbon nanotube. The change in the binding energies, when going from the vacuum to the water environments, shows an inverse relationship with the polarity, with the amino acids that have more polar (nonpolar) side chains showing lower (greater) variations in the binding energies. We also analyze the variations in the binding energies in vacuum and water for the neutral and zwitterionic forms of glicine. We show that the zwitterionic form is more stable in the polar environment of water, whereas the neutral form is more stable in vacuum. / Neste trabalho utilizamos a teoria do funcional da densidade (DFT) para analisar a influência de um meio solvente, a água, na interação de aminoácidos com um nanotubo de carbono (CNT) semicondutor. Para o estudo das interações no vácuo utilizamos tanto um método ab-initio quanto um método tight binding parametrizado. Os estudos destas mesmas interações (CNT-aminoácidos) no meio aquoso foram realizados empregando o método de dinâmica molecular a uma temperatura de 300 K usando o método tight binding parametrizado. Os aminoácidos selecionados para o estudo tinham diferentes valores de índice de hidrofobicidade e de polaridade. Nossos resultados mostram que para a forma neutra destes aminoácidos, há uma relação direta entre a variação da distância da ligação, do vácuo em relação a água, e o índice de hidrofobicidade com os aminoácidos mais hidrofóbicos (hidrofílicos) se aproximando (afastando) do nanotubo de carbono. A variação da energia de ligação, quando se passa do vácuo para o ambiente aquoso, apresenta uma relação inversa com a polaridade, com os aminoácidos que possuem a cadeia lateral mais polares (menos polares) apresentado os menores (maiores) variações na energia de ligação. Analisamos ainda as variações na energia de ligação no vácuo e na água para o aminoácido glicina em relação as suas possíveis formas elétricas: neutra e como íon dipolar (zwiteri onica). Mostramos que a forma zwiteriônica é mais estável no ambiente polar da água, enquanto a forma neutra apresenta maior estabilidade no vácuo.

Este trabalho traz a aplicação de alta pressão e alta pressão/temperatura (4.0 GPa e 400º C), em amostras de nanotubos de carbono de paredes múltiplas (NTCPM) comerciais para a obtenção de amostras compactas. Os NTCPM foram funcionalizados com ácido nítrico e ácido nítrico/ácido sulfúrico e, também foram usados nanotubos de carbono dopados com nitrogênio. Foram também processadas amostras contendo nanotubos de carbono de paredes múltiplas incorporados em matriz de zircônia obtida pelo método sol-gel. Para aplicação da alta pressão foi usado um sistema com câmaras do tipo toroidal, utilizando grafite como meio transmissor de pressão. Foram obtidas amostras macroscópicas autossuportadas e com resistência ao manuseio principalmente nas amostras de nanotubos de carbono funcionalizados com ácido nítrico/ácido sulfúrico incorporados em zircônia. Para a caracterização das amostras foram utilizadas as técnicas de Microscopia Eletrônica de Transmissão, Espectroscopia Raman, Difração de Raios X e isotermas de adsorção/dessorção de nitrogênio com as quais foi possível determinar que mesmo após a aplicação de alta pressão/temperatura os nanotubos de carbono não sofrem significativas modificações na sua estrutura e nas suas propriedades morfológicas e texturais, confirmando então que os NTCPM mantém suas características originais, apresentando condições para aplicações em dispositivos. As amostras macroscópicas contendo nanotubos de carbono de paredes múltiplas incorporados em zircônia apresentaram ainda resistência à carga de milhares de vezes o seu peso e comportamento de materiais semi-condutores. / This work presents the application of high pressure and/or high pressure/temperature (4.0 GPa and 400 ° C), on different samples of commercial multi-walled carbon nanotube (MWCNT) to obtain compacted samples. MWCNT were functionalized with nitric acid and nitric acid/sulfuric acid, and also carbon nanotubes doped with nitrogen. MWCNT incorporated in a zirconia matrix obtained by sol-gel method were also processed. For high pressure application it was used a system with the toroidal-type chamber, using graphite as a pressure transmitting medium. Self-supported macroscopic samples were obtained, easy to handle, especially in samples of functionalized carbon nanotubes with nitric and sulfuric acid and also incorporated in zirconia. To characterize the samples it was used Transmission Electron Microscopy, Raman Spectroscopy, X-ray diffraction and nitrogen adsoption/desorption isotherms and it was determined that even after application of high pressure/temperature carbon nanotubes do not suffer significant changes in their structure and in their morphological and textural properties, confirming that the CNT keeps its original characteristics and providing conditions for device applications. The macroscopic samples containing MWCNT incorporated in zirconia also exhibited resistance to load of thousands times its own weight and behavior like semiconductor materials.