Dissertations / Theses on the topic 'SWCNH'

The aim of this research is to fabricate an electrically conducting, smooth, continuous and sensitive nanofiber using tri-block copolymer PS-b-PDMS-b-PS and SWCNTs by electrospinning. The electronic nanofibers may be utilized for effective biosensing applications. The SWCNTs have been of great interest to researchers because of their exceptional electrical, mechanical, and thermal properties. The nanoscale diameter, high aspect ratio, and low density make them an ideal reinforcing candidate for novel nanocomposite material. Electrically conducting fibers are prepared by electrospinning a solution of PS, PS-b- PDMS-b-PS and functionalized SWCNTs using solvent DMF. The fibers formed have an average diameter and height of 5 and 4 μm respectively. These fibers are characterized by SEM, AFM, and optical microscopy. The electrical characterization of a single fiber shows an almost linear graph of current vs. voltage using the Kelvin Sensing method. This linear graph exemplifies the conducting nature of the fiber. Future work includes preparing nanofibers decorated with functional groups and binding with specific type of enzyme or protein to study their I-V behavior. This approach or method can be utilized for bio-sensing activities, especially for the detection of various antibodies and protein molecules.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 27).
Lithium-ion batteries are commonly used in portable electronics, and the rapid growth of mobile technology calls for an improvement in battery capabilities. Reducing the particle size of electrode materials in synthesis is an important strategy for improving their rate capability and power density (which is the capacity at high rates). Using biological materials as a template during synthesis allows us to achieve this, improving synthesis methods. Utilizing biological materials makes it possible to synthesize nano-scale particles, and using the M13 virus has shown to be an early solution. The addition of conductive material, such as single-walled carbon nanotubes (SWCNT or CNT), also improves the conductivity of the electrode, further improving the battery's rate capabilities (Lee et al., 2009). In this study, our goal is to improve the conductivity of the LIB battery cathode using M13-carbon nanotube complexes.
by Melanie Chantal Adams.
S.B.

We have investigated single-walled carbon nanotube (SWCNT) networks wrapped with the cationic surfactant sodium dodecyl-benzenesulfonate (SBDS) as promising candidates for water detection. This is the first time that the humidity behavior of endohedral Li-doped (Li@) and undoped SWCNTs/SDBS has been shown. We identified a strong and almost monotonic decrease in resistance as humidity increased from 11 to 97%. Sensitivities varied between −3 and 65% in the entire humidity range. Electrical characterization, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) analysis revealed that a combination of the electron donor behavior of the water molecules with Poole-Frenkel conduction accounted for the resistive humidity response in the Li@SWCNT/SDBS and undoped SWCNT/SDBS networks. We found that Li@SWCNTs boosted the semiconducting character in mixtures of metallic/semiconducting SWCNT beams. Moreover, electrical characterization of the sensor suggested that endohedral Li doping produced SWCNT beams with high concentration of semiconducting tubes. We also investigated how frequency influenced film humidity sensing behavior and how this behavior of SWCNT/SDBS films depended on temperature from 20 to 80 ∘ C. The present results will certainly aid design and optimization of SWCNT films with different dopants for humidity or gas sensing in general.

Single wall carbon nanotubes (SWCNTs) show a variety of unparalleled properties such as high electrical and thermal conductivity, high specific surface area (SSA) and a large stiffness under axial loads. One of the major challenges in tapping the vast potential of SWCNTs is to fabricate nanotube based macrostructures that retain the unique properties of nanotubes. Pristine SWCNT aerogels are highly porous, isotropic structures of nanotubes mediated via van der Waals (VDW) interactions at junctions. The mechanical behavior of such aerogels is examined in several experimental studies. However, it is necessary to supplement these studies with insights from simulations in order to develop a fundamental understanding of deformation behavior of SWCNT aerogels. In this study, the mechanical behavior of SWCNT networks is studied using a multi-scale modeling approach. The mechanics of an individual nanotube and interactions between few nanotubes are modeled using molecular dynamics (MD) simulations. The results from atomistic simulations are used to inform meso-scale and continuum scale finite element (FE) models. The deformation mechanism of pristine SWCNT networks under large compressive strain is deduced from insights offered by meso-scale simulations. It is found that the elasticity of such networks is governed by the bending deformation of nanotubes while the plastic deformation is governed by the VDW interactions between nanotubes. The stress response of the material in the elastic regime is dictated by the VDW stresses on nanotubes while in the plastic regime, both the VDW and axial deformation stresses on nanotubes drive the overall stress response. In this study, the elastic behavior of a random SWCNT network with any set of junction stiffness and network density is also investigated using FE simulations. It is found that the elastic deformation of such networks can be governed either by the deformation of the nanotubes (bending, axial compression) or deformation of the junctions. The junction stiffness and the network density determine the network deformation mode. The results of the FE study are also applicable to any stiff fiber network.

Poly[lactic co-glycolic] acid (PLGA) is a biocompatible polymer commonly used in the field of tissue engineering, but its mechanical properties tend to be less than ideal for most orthopedic applications. Five PLGA composites, reinforced with 0 to 1% nonfunctionalized single-walled carbon nanotubes, were prepared and tested for tensile strength. In order to achieve consistent nanotube dispersions, sodium dodecyl sulfate was incorporated as a surfactant. The polymer scaffold fabrication methods were successful at creating suitable samples for tensile testing. After the tests were performed, scanning electron microscope images were taken to examine the fractured edges and determine the cause of failure. Analysis of fractured surfaces indicated good nanotube dispersions in all composite samples, and an increase in tensile strength, with respect to the control (0.532 MPa), was found for composites at the 0.07% nanotube and 0.09% nanotube concentrations (0.570 MPa and 0.643 MPa respectively). Total length at failure decreased as carbon nanotube concentration increased. This experiment showed a promising trend toward increasing the mechanical properties of PLGA/carbon nanotube composites and represented a prospective foundation for future research.

Fabrication of SWCNT-PMMA and Activated Charcoal- PMMA composites was carried out by the compression moulding technique. Then Mechanical and Electrical properties of the composites were investigated. The morphological studies of composites showed a) good dispersion of fillers and b) good interaction between fillers and matrix. Electrical conductivity of SWCNT-PMMA composites was increased by 9 orders of magnitude (at 0.8 % volume fraction of SWCNT) and that of AC-PMMA composites increased by 16 orders of magnitude (at 17 % volume fraction of AC). The percolation threshold of both composites turned out to be lower compared to the theoretical values. A significant improvement in mechanical properties was obtained ??? particularly in AC-PMMA composites which showed a 400 % improvement in Vickers microhardness ??? raising the polymer matrix abrasion property literally to that of Aluminium alloys (Dobrazanski et al 2006). In conclusion, it is to be noted that Activated Charcoal - PMMA composites have a great potential for cost effective conducting polymer composite production by the use of cheap filler: In addition, the compression moulding technique shows good potential for cost effective fabricating technique for amorphous polymers with high electrical and mechanical properties.

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O tratamento químico de nanotubos de carbono (NTC) é necessário para aprimorar suas propriedades, aplicações e remover impurezas. O tratamento, com ácidos fortes como H2SO4 e HNO3 tem sido a alternativa mais utilizada. A mistura desses ácidos fortes produz espécies eletrofílica NO2+, íon nitrônio, que é um potencial agente oxidante, cuja concentração depende da proporção da mistura H2SO4:HNO3. Neste trabalho, a interação entre o íon nitrônio e o nanotubo de carbono de camada única (SWCNT, do inglês Single-Walled Carbon Nanotube) foi explorado experimental e computacionalmente. Experimentalmente a solução H2SO4:HNO3 foi analisada em proporções diferentes (1:1, 2:1, 5:2, 3:1, 4:1, 5:1, 6:1, 7:1 e 8:1 v/v) e a concentração de íon nitrônio foi obtida utilizando-se uma curva analítica construída com uma solução padrão de NO2BF4 em H2SO4. Todas as espécies na mistura ácida foram caracterizadas por espectroscopia Raman. Os resultados mostraram que a concentração do íon nitrônio na mistura ácida varia de 0 até 4,53 mol/L. As misturas 2:1, 5:2 e 3:1 foram então utilizadas para a oxidação química de SWCNT por 4, 8 e 12 horas. As amostras finais foram analisadas por espectroscopia Raman, análise termogravimétrica (TG) e espectroscopia de raios X por dispersão de energia (EDS). Dentre os resultados, foram observados por meio da espectroscopia Raman uma alta desordem estrutural no sistema após a oxidação, com significativas mudanças nos modos de respiração radial (RBM), como o desaparecimento de bandas de tubos com pequenos diâmetros, além do aumento dada razão ID/IG de 0,027 para 0,59 em tubos oxidados com a mistura 3:1. As análises TG mostraram um aumento na temperatura de decomposição dos tubos em, pelo menos, 30ºC se comparado às amostras padrão, sugerindo um significativo grau de oxidação. Os resultados de EDS apontaram um aumento considerável na quantidade de oxigênio, passando de 7% para 20%, aumentando com o aumento do tempo de reação e com a concentração do íon nitrônio. Computacionalmente a interação entre o íon nitrônio e o SWCNT foi estudada através de cálculos de mecânica quântica. Foram analisados modelos do tipo armchair (5,5), sendo um tubo perfeito (P) e dois outros contendo defeitos do tipo Stone-Wales (SW) e monovacância (V1) para modelar regiões distintas na superfície do nanotubo. Para os modelos P e SW, o grupo funcional éter (COC) foi obtido como um produto principal, com um epóxido (CCO) encontrado como um intermediário de reação. As barreiras de energia livre de Gibbs foram de 31,7 kcal.mol-1 (P) e 37,8 kcal.mol-1 (SW) em solução aquosa à 298,15 K e 1 atm. O mecanismo envolvendo o modelo V leva à obtenção de uma carbonila (CO) como produto principal, formado espontaneamente através da adsorção do íon NO2+. O mecanismo de alta energia também foi descrito no modelo V, passando por um estado de transição, caracterizado como um anel do tipo oxaziridina. Através deste caminho um grupamento do tipo alcóxido (CO-) é formado inicialmente e reage com um carbono vizinho, produzindo um grupo funcional do tipo éter (COC). A energia livre de Gibbs de ativação foi de 4,5 e 11,2 kcal.mol-1 para primeiro (CO-) e segundo (COC) passos, respectivamente. Os resultados reportados sugerem o início da oxidação em meio ácido através da região de vacância, com primeira oxidação levando a uma carbonila, seguida das reações nos defeitos topológicos (P e SW) na superfície com a formação de um éter (COC) como principal produto.
The chemical treatment of carbon nanotubes (CNT) is necessary to improve their properties, applications and to remove impurities. Treatments with strong acids as H2SO4 and HNO3 is the mostly used alternative. The mixture of these strong acids produces the electrophilic species NO2+, the nitronium ion that is a potential oxidizing with concentration depending on the H2SO4:HNO3 proportion. In this work the interaction between the nitronium ion and a single-walled carbon nanotube (SWCNT) was explored experimentally e theoretically. Experimentally, the H2SO4:HNO3 solution was analyzed at different proportions (1:1, 2:1, 5:2, 3:1, 4:1, 5:1, 6:1, 7:1 and 8:1 v/v) and the nitronium ion concentration obtained using a calibration plot constructed from a standard solution of NO2BF4 in H2SO4. All the species in the acid mixture were characterized by Raman spectroscopy. The results showed that the concentration of nitronium ion in the acid mixtures varied from 0 to 4.53 mol/L. The mixtures 2:1, 5:2 and 3:1 were then used for the chemical oxidation of single-walled CNT for 4, 8 and 12 hours. The final samples were analyzed by Raman spectroscopy, thermal gravimetric analysis (TGA) and energy dispersive X-ray spectroscopy (EDS). It was observed by Raman spectroscopy a higher structural disorder in the system after the oxidation, with significant changes in RBM modes, such as disappearance of bands of small diameter tubes, and in the ID/IG ratio, which increases from 0.027 until 0.59 to CNT oxidized with 3:1 mixture. The TGA showed an increase in the temperature of the tube decomposition of at least 30ºC relative to the pristine form, suggesting a significant oxidation degree. The EDS data point to considerable increase of the oxygen amount from 7% to at least 20%, increasing with the reaction time and nitronium ion concentration. Theoretically the interaction between nitronium ion and SWCNT was studied by quantum mechanical calculations. In addition to the pristine (P) form of an armchair (5,5) SWCNT, two other species containing Stone-Wales (SW) and mono-vacancy (V1) defects were considered in order to model the distinct defective regions on the carbon nanotube surface. For the P and SW regions, the ether (COC) functional group was predicted as the main product, with an epoxide (CCO) found as a reactive intermediate. The Gibbs free energy barriers were predicted to be 31.7 (P) and 37.8 kcal mol-1 (SW) in aqueous solution at 298.15 K and 1 atm. The mechanism involving the V1 region leads to the carbonyl group (CO) as the main product, which is formed spontaneously upon NO2+ adsorption without energy barrier. A higher energy mechanism was also described for V1 region, passing through a transition state characterized as an oxaziridine-like ring. Through this pathway an alkoxy (CO-) is firstly formed and reacts with the neighbor carbon yielding the ether (COC) functional group. The activation Gibbs free energies were 4.5 and 11.2 kcal mol-1 for the first (CO- formation) and second (COC formation) steps, respectively. The results reported here suggest that at the beginning of oxidation in acid medium, the vacancy regions (V) are firstly oxidized leading to the carbonyl (CO) functional groups, followed by reactions at the topological defective parts (P and SW) of the tube surface where the ether (COC) function is the main product.

L’objectif final de la thèse est l'impression de la couche photo-active ternaire d'une cellule solaire organique en utilisant deux approches: l'une concerne l'apport de nanotubes de carbone (SWCNT) pour améliorer les propriétés de transport, l'autre concerne la préparation de mélanges ternaires de matériaux pour contrôler la couleur des cellules. Les encres pour la couche active incluant des SWCNT fonctionnalisés sont composées d’un donneur d'électron (polymère) (poly(3-hexylthiophène), [P3HT]) et d’un accepteur d'électron ( [6,6]-phényl C61-butyrique ester méthylique d'acide [PCBM]) et ont été développées pour la fabrication de cellules inversées. Ces cellules sont réalisées sur substrats de verre pour l'optimisation de leurs performances, puis sur substrats plastiques pour les applications. Diverses couches d'interfaces ont été testées, qui incluent l'oxyde de zinc (ZnO, couches obtenues par pulvérisation ionique (IBS) ou à partir de solutions de nanoparticules) pour la couche de transport d'électrons et le PEDOT:PSS, le P3MEET, le V2O5 et le MoO3 pour la couche de transport de trous. Des essais ont été effectués avec et sans CNT afin d’étudier leur impact sur les performances. Des résultats similaires sont obtenus dans les deux cas. Il était attendu que les CNT améliorent les performances, ce qui n’a pas été observé pour le moment. Des travaux supplémentaires sont donc nécessaires au niveau de la formulation de la couche active.Avec trois polymères de couleur rouge (P3HT), bleu (B1) et vert (G1), nous avons préparé des mélanges ternaires efficaces permettant l'obtention de couleurs jusque là indisponibles . Nous avons fait une étude sur le piégeage et les mécanismes de diodes parallèles associés aux mélanges. En général, nous avons constaté que les mélanges ternaires de polymères bleu et vert peuvent être décrits par une mécanisme de diodes parallèles, sans entrainer de perte de performances, ce qui n'est pas possible pour les systèmes P3HT:B1 :PCBM et P3HT:G1:PCBM qui se piègent mutuellement. L’objectif final du projet est l'impression de la couche photo-active ternaire d'une cellule solaire organique, composites ternaires (polymère:polymères:acceptor) ou dopés avec les SWCNT. Cette étape nécessite encore des développements futurs
Two approaches were followed to achieve increased control over properties of the photo-active layer (PAL) in solution processed polymer solar cells. This was accomplished by either (1) the addition of functionalized single-walled carbon nanotubes (SWCNTs) to improve the charge transport properties of the device or (2) the realization of dual donor polymer ternary blends to achieve colour-tuned devices.In the first component of the study, P3HT:PC61BM blends were doped with SWCNTs with the ambition to improve the morphology and charge transport within the PAL. The SWCNTs were functionalized with alkyl chains to increase their dispersive properties in solution, increase their interaction with the P3HT polymer matrix, and to disrupt the metallic characteristic of the tubes, which ensures that the incorporated SWCNTs are primarily semi-conducting. P3HT:PCBM:CNT composite films were characterized and prepared for use as the photoactive layer within the inverted solar cell. The CNT doping acts to increase order within the active layer and improve the active layer’s charge transport properties (conductivity) as well as showed some promise to increase the stability of the device. The goal is that improved charge transport will allow high level PSC performance as the active layer thickness and area is increased, which is an important consideration for large-area inkjet printing. The use of ternary blends (two donor polymers with a fullerene acceptor) in bulk-heterojunction (BHJ) photovoltaic devices was investigated as a future means to colour-tune ink-jet printed PSCs. The study involved the blending of two of the three chosen donor polymers [red (P3HT), blue (B1), and green (G1)] with PC61BM. Through EQE measurements, it was shown that even devices with blends exhibiting poor efficiencies, caused by traps, both polymers contributed to the PV effect. However, traps were avoided to create a parallel-like BHJ when two polymers were chosen with suitable physical compatibility (harmonious solid state mixing), and appropriate HOMO-HOMO energy band alignment. The parallel diode model was used to describe the PV circuit of devices with the B1:G1:PC61BM ternary blend

Avec le logiciel AIMPRO, qui fournit une modélisation quantique basée sur la théorie de fonctionnelle de densité, on étudie plusieurs exemples importants de la faiblesse des interactions intermoléculaires dans les nanomatériaux de carbone. Au niveau mécanique quantique, nos calculs donnent une compréhension fiable et améliorée du rôle et de la fonction des interactions intermoléculaires faibles, ce qui ne peut pas être prédit par des méthodes conventionnelles comme les potentiels interatomiques classiques. Premièrement, on étudie l’interaction entre le brome physisorbé sur les nanomatériaux de carbone (graphène, graphite, nanotubes de carbone simple [SWCNT] et double [DWCNT] parois). Pour le graphène, nous trouvons une nouvelle forme de Br2, à notre connaissance jamais présentée dans la littérature, où la molécule se trouve perpendiculaire à la feuille de graphène avec un dipôle fort. La bromation ouvre un gap de petite taille (86 meV) dans la structuré de bande électronique et dope fortement le graphène. Dans le graphite, Br2 reste parallèle aux couches de carbone avec un transfert de charge moins fort et sans dipôle moléculaire. À plus haute concentration, la formation de chaînes de polybromure est thermodynamiquement favorisée, mais n’a pas lieu spontanément à cause d’une barrière d’activation appréciable (27,01 kJ / mol). Avec les nanotubes monoparoi, le Br2 reste perpendiculaire à la surface du tube, comme observé avec le graphène; dans les fagots, le Br2 s'intercale comme dans le graphite. Les spectres Raman sont enregistrés afin de vérifier ce résultat. Dans la deuxième partie, on étudie des interactions d’empilement de type π-π entre le benzène d’une part, les chaînes oligomères de PPV d’autre part, avec des nanomatériaux de carbone. Pour le dimère du benzène, nous avons réussi à reproduire les structures stables trouvées par ailleurs via des calculs de plus haut niveau de théorie ; pour le benzène sur le graphène ou sur les SWCNTs, l'empilement est de type AB comme dans le graphite. L'orientation de l’interaction dans le cas PPV / PPV est différente de celle obtenue dans le cas PPV / nanotube ou PPV / graphène. Dans le premier cas des plans moléculaires sont orthogonaux, semblable à un empilement de PPV ou d'autres hydrocarbures aromatiques polycycliques. Dans les autres cas, l’axe de la chaîne de PPV se trouve parallèle au plan du graphène comme à l’axe des nanotubes, ce qui est attribué à des effets d'empilement π-π. L'analyse des fonctions d’onde près du niveau de Fermi suggère qu’il y a peu de couplage électronique entre PPV et SWCNTs. La différence d’interaction prévue entre PPV et nanotubes semi-conducteurs ou métalliques suggère une nouvelle conception de composites PPV-SWCNT pour les dispositifs électroluminescents organiques
This thesis uses the ab initio density functional modeling programme AIMPRO to study several important examples of weak intermolecular interactions in carbon nanomaterials. At the quantum mechanical level, our calculations give a reliable and improved understanding of the role and feature of weak intermolecular interactions, which cannot be accurately predicted by conventional methods such as classical interatomic potentials. First, the geometry and binding of bromine physisorbed on carbon nanomaterials (graphene, graphite and single walled nanotubes) is studied. In graphene, we find a new Br2 form which is reported for the first time in this thesis, where the molecule sits perpendicular to the graphene sheet with an extremely strong molecular dipole. Bromination opens a small (86- meV) band gap and strongly dopes the graphene. In graphite Br2 is stable parallel to the carbon layers with less charge transfer and no molecular dipole. At higher Br2 concentrations polybromide chain structures are thermodynamically favoured, but will not occur spontaneously due to an appreciable formation barrier (27. 01 kJ/mol). For single walled nanotubes Br2 lies perpendicular to the tube surface similar to graphene, while in bundles Br2 intercalates similar to graphite. Experimental Raman spectra are recorded to verify this result. We next study π-π stacking interactions between benzene and PPV oligomer chains with various carbon nanomaterials. For the benzene dimer we successfully reproduce high level theory stable structures, and for benzene on graphene and SWCNTs, the stacking arrangement matches AB- stacking in graphite. The orientation of the interaction between PPV/PPV is different from PPV/nanotube or PPV/graphene. In the former the molecular planes are orthogonal, similar to the crystal packing in PPV, as well as in other polyaromatic hydrocarbons. In the others the PPV plane lies (axially) parallel to the substrates, attributed to π-π stacking effects. Wavefunction analysis suggests very little electronic coupling between the PPV and SWCNTs near to the Fermi level. Predicted differences in interaction between PPV and semi-conducting or metallic tubes suggest a new route to experimental ultraefficient composite PPV-SWCNT organic light emitting device design

Single-walled carbon nanotubes (SWNTs) are nowadays one of the most investigated materials and the realization of ordered SWNT structures is of fundamental importance for the improvement of many technological fields, from the non-linear optics to the realization of transistor, to the assembly of gas sensing devices. A SWNT is formed by rolling a graphene sheet into a seamless cylinder with a diameter on the nanometer scale. The individual SWNTs are joined each other and assembled into bundles by Van der Waals forces. Guest molecules can potentially interact with SWNTs via the outer surfaces of bundles, the inside of the tubes and /or the interstitial channels between the tubes in a bundle. These different situations are expected to play an important role in tuning the guest molecule/SWNT interaction during gas adsorption and/or desorption, and have been investigated theoretically and experimentally using different approaches. In particular, the interaction between gaseous molecules and SWNTs has been investigated from different point of view, including gas storage and gas detection through modification of electronic and thermal properties or through modification of the field emission properties. Compared with conventional solid-state sensors, that typically operate at temperatures over 200 °C, and conducting polymers-based sensors, that provide only limited sensitivity, sensing devices assembled with single-wall nanotubes can exhibit high sensitivity and fast response time at room temperature. Due to the high surface area of nanotubes, a little amount of nanotube material can provide many sites for gas interaction. The accessibility of these sites depends on the status of aggregation of the nanotubes. Our preliminary studies suggested that the sensitivity of a nanotube-based device can be optimized controlling the organization of the SWNTs. Ordered bundles of SWNTs exhibit indeed a sensitivity double with respect to that of a disordered deposit. This is likely due to the enhancement of surface area for organized SWNT systems with respect to randomly placed SWNT bundles. Hence, aligned nanotubes can serve as a very efficient material for use in gas detection. Directionality of SWNT can be obtained directly during the synthesis process, or after manipulation of dispersed nanotubes, by mean of several methods, such as filtration/deposition from suspension in strong magnetic fields, field emission, electrophoresis or dielectrophoretical processes. In particular the use of electric fields to move, position and align SWNTs has been reported in recent papers and the results indicate that both the electrophoresis (EP) and dielectrophoresis (DEP) routes have potential advantages for arranging nanotubes in controlled systems. Beyond the sensitivity, another severe constraint for gas detection is the time either for the reset of the sensor after exposure to the gas, either for the acceleration of the response itself. Since practical applications can be severely limited by slow absorption/desorption processes, we felt it worthwhile to investigate in a systematic way some physical parameters affecting the sensor response. In this thesis we present a study of NH3 ,NOx and H2 detection using organized SWNTs as sensing material and an innovative procedure to improve the time response of the sensor by applying a back gate voltage. Moreover study on gas detection and gas storage were done using QCM sensor.

The extraordinary properties of the single wall carbon nanotubes (SWCNTs) have stimulated an enormous amount of research towards the realization of SWCNT-based products for different applications ranging form nanocomposites to nanoelectronics. Their high charge mobility, exceedingly good current-carrying capacities and ability to be either semiconducting or metallic render them ideal building blocks for nanoelectronics. For nanoelectronic applications, either individual or parallel aligned SWCNTs are advantageous. Moreover, closely packed arrays of parallel SWCNTs are required in order to sustain the relatively large currents found in high frequency devices. Two key areas still require further development before the realization of large-scale nanoelectronics. They are the reproducible control of the nanotubes spatial position/orientation and chiral management. In terms of nanotube orientation, different techniques have been demonstrated for the fabrication of horizontally aligned SWCNTs with either post synthesis routes (e.g. dielectrophoresis and Langmuir-Blodgett approach) or direct growth (e.g. chemical vapor deposition (CVD)). The low temperature of the production process, allowing the formation of aligned nanotubes on pretty much any substrate, is the main advantage of the post synthesis routes, while the poor levels of reproducibility and spatial control, and the limited quality of the aligned tubes due to the inherently required process steps are limitations. The simplicity, up-scalability, along with the reproducible growth of clean high quality SWCNTs with well-controlled spatial, orientation and length, make CVD the most promising for producing dense horizontally well-aligned SWCNTs. These CVD techniques suffer some drawbacks, namely, that because they are synthesized using catalyst particles (metals or non-metals) the catalyst material can contaminate the tubes and affect their intrinsic properties. Thus, the catalyst-free synthesis of aligned SWNT is very desirable. This thesis comprises detailed and systematic experimental investigations in to the fabrication of horizontally aligned SWCNTs using both post growth (Dielectrophoresis) and direct growth (CVD) methods. Both catalyst-assisted and catalyst-free SWCNTs are synthesized by CVD. While metallic nanoparticles nucleate and grow SWCNTs, opened and activated fullerene structures are used for all carbon catalyst-free growth of single wall and double wall carbon nanotubes. The systematic studies allow for a detailed understanding of the growth mechanisms of catalyst and catalyst-free grown SWCNTs to be elucidated. The data significantly advances our understanding of horizontally aligned carbon nanotubes by both post synthesis alignment as well as directly as-synthesized routes. Indeed, the knowledge enables such tubes to be grown in high yield and with a high degree of special control. It is shown, for the first time, how one can grow horizontally aligned carbon nanotubes in crossbar configurations in a single step and with bespoke crossing angles. In addition, the transport properties of the aligned tubes at room temperature are also investigated through the fabrication of devices based on these tubes
Die außergewöhnlichen Eigenschaften von einwandigen Kohlenstoffnanoröhren (engl. single wall carbon nanotubes, SWCNTs) haben bemerkenswerte Forschungsaktivitäten zur Verwirklichung von auf SWCNTs basierenden Anwendungen für verschiedene Bereiche, die von Nanokompositen bis hin zur Nanoelektronik reichen, stimuliert. Ihre hohe Ladungsträgermobilität und die außerordentlichen hohen Ladungsdichten, die in SWCNTs erreicht werden können sowie ihre Eigenschaft, entweder halbleitend oder metallisch zu sein, machen sie zu idealen Konstituenten von nanoelektronischen Schaltkreisen. Für Anwendungen in der Nanoelektronik sind entweder einzelne oder parallel angeordnete SWCNTs vorteilhaft. Darüber hinaus sind dicht gepackte Anordnungen von SWCNTs erforderlich, um die relativ hohen Ströme in Hochfrequenzbauelementen zu transportieren. Für eine erfolgreiche Realisierung von großskaligen nanoelektronischen Bauteilen, die auf SWCNTs basieren, sind noch zwei enorm wichtige Kernprobleme zu lösen, die weitere Forschungsanstrengungen erfordern: die reproduzierbare und verlässliche Kontrolle der räumlichen Positionierung und Orientierung der Nanoröhren sowie die Kontrolle der Chiralität der einzelnen SWCNTs. Hinsichtlich der Orientierung der Nanoröhren kann die horizontal parallele Ausrichtung von SWCNTs mit verschiedenen Techniken erreicht werden. Diese setzen entweder nach dem eigentlichen Wachstum der Röhren ein (Post-Synthese-Methoden wie z.B. Dielektrophorese oder Langmuir-Blodgett-Techniken) oder erreichen direkt während des Wachstums (z.B. durch Chemical-Vapor-Deposition-Methoden (CVD)) die parallele Anordnung. Durch die niedrigen Prozesstemperaturen, die während des Herstellungsprozesses erforderlich sind, erlauben die nach der eigentlichen Synthese stattfindenden Ausrichtungsmethoden die parallele Anordnung von Nanoröhren auf nahezu jedem Substrat, jedoch stellen die geringe Reproduzierbarkeit dieser Prozesse, die schwierige Kontrollierbarkeit der räumlichen Anordnung und die limitierte Qualität der ausgerichteten Röhren aufgrund der erforderlichen Prozessschritte natürliche Beschränkungen dieser Techniken dar. Die einfache Durchführung und ihre Skalierbarkeit, zusammen mit dem reproduzierbaren Wachstum qualitativ sehr hochwertiger SWCNTs mit hoher Kontrolle von räumlicher Anordnung, Orientierung und Länge machen die CVD-Methode zur erfolgversprechendsten Technik für die Herstellung von dichtgepackten hochparallelen horizontalen Anordnungen von SWCNTs. Diese CVD-Ansätze weisen jedoch auch einige Nachteile auf, die in den bei der Synthese verwendeten Katalysatorpartikeln (metallisch oder nicht-metallisch) begründet liegen, da das Katalysatormaterial die Röhren kontaminieren und dadurch ihre intrinsischen Eigenschaften beeinflussen kann. Daher ist eine katalysatorfreie Synthesemethode für ausgerichtete SWCNTs ein höchst erstrebenswertes Ziel. Die vorliegende Arbeit beschreibt detaillierte und systematische experimentelle Untersuchungen zur Herstellung von horizontalen, parallel ausgerichteten Anordnungen von SWCNTs unter Verwendung von Methoden, die sowohl nach dem eigentlichen Wachstum der Nanoröhren (Dielektrophorese) als auch während des Wachstums ansetzen (CVD). Bei den CVD-Methoden werden sowohl solche, die auf der Verwendung von Katalysatoren basieren, als auch katalysatorfreie Techniken verwendet. Während metallische Nanopartikel den Ausgangspunkt für das Wachstum von SWCNTs darstellen, werden geöffnete und aktivierte Fullerenstrukturen verwendet, um das katalysatorfreie Wachstum von reinen ein- oder mehrwandigen Nanoröhren zu erreichen. Die systematischen Untersuchungen ermöglichen ein tiefgehendes Verständnis der Wachstumsmechanismen von SWCNTs, die unter Verwendung von Katalysatoren oder katalysatorfrei erzeugt synthetisiert wurden. Die erzielten Ergebnisse erhöhen in einem hohen Maß das Verständnis der Herstellung von horizontal parallel angeordneten Nanoröhren, die durch Post-Synthese-Methoden oder direkt während des Wachstumsprozesses ausgerichtet wurden. Die erzielten Einsichten erlauben die Herstellung solcher Strukturen mit hoher Ausbeute und mit einem hohen Maß an räumlicher Kontrolle der Anordnung. Zum ersten Male kann ein Verfahren präsentiert werden, mit dem horizontal parallel angeordnete Nanoröhren in gekreuzten Strukturen mit wohldefinierten Kreuzungswinkeln hergestellt werden können. Zusätzlich werden die Transporteigenschaften von parallel ausgerichteten Nanoröhren bei Raumtemperatur, durch die Herstellung von auf den dargestellten Strukturen basierenden Bauelementen, untersucht

Single-walled carbon nanotubes (SWCNTs) are new forms of carbon nanostructure that have exhibited important physical and chemical properties with a wide range of future applications including microelectronic devices, nanoscale transistors, catalyst supports, biosensors, reinforcement materials, medical chemistry, etc. Up to now, many versatile methods have been used for SWNCT synthesis. These methods can produce SWCNT besides many by-products such as amorphous carbon, fullerenes, nanocrystalline graphite and multi-walled carbon nanotubes. For the exploration of the physical properties of SWNCT and to investigate the possibilities of chemical functionalization it is advantageous to work with a material that is as pure as possible. The work presented here is focused on in situ purification of SWCNT soot synthesized by a large-scale (i.e., production rate of ~100 g h[superscript -1]) induction thermal plasma process. The main objectives of this research are: 1) to get rid of amorphous carbon impurities from SWCNT soot produced in the induction thermal plasma system, 2) to study the effect of oxidizing gas flow rate (i.e. oxygen) and temperature on the purification process. The methodology used in this experimental design is based on gas-phase thermal oxidation of synthesized SWCNT soot. The experimental apparatus can be divided in to two parts as follows: 1) synthesis system which consists of a flow type reactor equipped with a high frequency plasma torch operated at 3 MHz along with quenching and filtration systems 2) purification system which consists of an oven and a gas heater used to control the temperature of oxidizing gases, and a filtration system where thermal oxidation of the synthesized soot takes place. SWCNT soot was synthesized by an induction thermal plasma process using a mixture of carbon black (Raven 860 ultra) as a carbon source and nickel (Ni), cobalt (Co) and yttrium oxide (Y[subscript 2]O[subscript 3]) as catalysts. A series of preliminary experimental tests was conducted to evaluate the process ability to purify SWCNT soot in situ using a gas-phase thermal oxidation process. In these tests, temperature measurements along the filtration system were carried out during synthesis and purification processes. Two types of oxidizing gases (i.e., air and oxygen) were injected into the filtration system and the purified samples were characterized by different powerful techniques such as high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and Raman spectroscopy. The results indicated that in situ removal of amorphous carbon from SWCNT soot synthesized by induction thermal plasma can be successfully achieved (a purity of more than 60 wt% of SWCNTs was achieved). Moreover thermal oxidation of the soot causes a narrower distribution of tube diameters in the purified sample. Overall, the findings of this study are relevant to the purification process technology of SWCNTs and future research is proposed to fully understand the reaction mechanism of SWCNT soot by oxygen. Based in the results of this work, additional work using a modification of the filtration system (i.e., collection chamber and filter tubes) should be performed in order to get rid of other carbonaceous impurities. Different gases can be also introduced in to the filtration system to improved the purification process and extend it for removal of catalysts particles. Our findings reveal that the present synthesis system has a capability for functionalization of tubes in situ. Therefore according to the type of functional groups which are desired to be attached to the tubes, proper gases can be injected into the filtration system.

In the present study the interaction of Hydrogen Sulfide with inside and outside single-wall carbon nanotube of (5,0) and (5,5) was investigated. This study was conducted using DFT at B3LYP/6-31G* level of theory. Computational calculations were performed in the gaseous phase in Gaussian 09. The geometry of all molecules under investigation was determined by optimizing all geometrical variables without any symmetry constraints. The harmonic frequencies were computed from analytical derivatives for all species in order to define the minimum-energy structures. The adsorption energies, the thermodynamic properties, HOMO-LUMO energy gaps and partial charges of the interacting atoms were also studied during two rotation kinds of H2S molecules vertical and horizontal to the main axes of nanotube. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35161

This dissertation involves the study of epitaxial behavior of one-dimensional nanomaterials like single-walled carbon nanotubes and Indium Arsenide nanowires grown on metallic catalyst surfaces. It has been previously observed in our novel microplasma based CVD growth of SWCNTs on Ni-Fe bimetallic nanoparticles that changes in the metal catalyst composition was accompanied by variations in the average metal-metal bond lengths of the nanoparticle and that in turn, affected nanotube chirality distributions. In this dissertation, we have developed a very simplistic model of the metal catalyst in order to explain the nanotube growth of specific nanotube chiralities on various Ni-Fe catalyst surfaces. The metal catalyst model is a two-dimensional flat surface with varying metal-metal bond lengths and comprising of constituent metal atoms. The effect of the composition change was modeled as a change in the bond length of the model catalyst surface and density functional theory based calculations were used to study specific nanotube caps. Our results indicated that nanotube caps like (8,4) and (6,5) show enhanced binding with increased metal-metal bond lengths in the nanoparticle in excellent agreement with the experimental observations. Later, we used this epitaxial nucleation model and combined with a previously proposed chirality-dependent growth rate model to explore better catalysts that will preferentially grow an enhanced chirality distribution of metallic nanotubes. From our DFT calculations and other geometrical considerations for nanotube growth, we demonstrated that the pure Ni0.5Cu0.5 metal nanoparticles and its lattice-strained surfaces can serve as a promising catalyst for enhanced growth of metallic nanotubes. Finally, we extended this model of epitaxial growth to study the growth of,andoriented nanowires on gold metal nanoparticles where a faster growth rate ofnanowires was previously observed in experiments on shaped nanoparticles than that on spherical nanoparticles. The DFT calculations indicated an enhanced growth selectivity of theoriented nanowires on the Au(111) surfaces. However, the DFT results also show that theandNWs will preferentially grow on the Au(100) surface than on the Au(100) surface. The epitaxial model based DFT calculations of nanotube and nanowire growth on metal catalyst surfaces presented in this dissertation, provide a deep insight into their epitaxial growth mechansims and, can be easily exploited to layout better design principles of synthesizing catalysts that helps in growing these one-dimensional nanomaterials with desired material properties.

Crucial features in gas sensors for environmental monitoring are the gas sensitivity in the low ppb range and the ability to discriminate variations of a certain polluting gas from other interfering gases. Monitoring of ammonia gas concentrations is mandatory to reduce the hazard for human health and vegetation determined by the widespread use of ammonia derivatives as agricultural nitrogen fertilizers, industrial production and traffic. In particular, ammonia, besides being a toxic molecule is one of the main precursors of secondary fine particulate matter (PM10, PM2.5). Ammonia could hence be used as a local marker of secondary fine particulate formation, allowing indirect control of particulate emission sources. In spite of this urgency, the detection of NH3 concentrations in urban areas with chemiresistor gas sensors (CGSs) has been so far widely overlooked, since the average levels are usually low, i.e. in the 20-30 ppb range, while the CGSs are generally tested by exposure to ammonia in the ppm range. Carbon nanotubes (CNTs), discovered more than 20 years ago, are well known and studied systems for many applications, among which (of course) gas sensing. With respect to commercial electrochemical sensors (mostly based on metal oxide materials), CNTs show a higher physical and chemical stability, better transport of charge to the electrodes and a wide range of possible hybrid architectures and operational features, among which the operation at room temperature, that make them unique materials for gas detection. The main goal of this thesis is to increase the sensitivity to [NH3] and to lower the detection limit (DL), exploring sample preparation strategies of low-cost single walled carbon nanotubes (SWCNT)-based gas sensors operating at room temperature, considering also the response to other interfering gases. Furthermore, effects of metal oxide nanoparticles functionalization and gas response of hybrid layers have been also investigated.

Die vorliegende Dissertation behandelt das Zusammenspiel von effizienten aktiven Lasermedien und neuartigen sättigbaren Absorbern, welche auf den Kohlenstoff-Nanostrukturen Graphen und den einwandigen Kohlenstoff Nanoröhren (SWCNTs) basieren. Die aktiven Lasermedien decken den Spektralbereich von 1,0 Mikrometer bis 2,1 Mikrometer ab, d.h. eine ganze Oktave, und nutzen die laseraktiven Ionen des Ytterbiums, Chroms und Thuliums. In dieser Arbeit werden die auf Graphen und SWCNT basierenden sättigbaren Absorber hinsichtlich ihres einer Anregung folgenden Relaxationsverhaltens, ihrer von der Fluenz abhängigen Transmission und ihres Sättigungs- verhaltens bei hohen Fluenzen untersucht. Eine vorangestellte Einführung der optischen Eigenschaften von Graphen und SWCNTs wird gegeben und die Modelle zur Beschreibung realer Proben werden aus theoretischen Modellvorstellungen hergeleitet. Die sättigbaren Absorber basierend auf Graphen und SWCNTs werden untereinander und mit klassischen halbleitenden sättigbaren Absorbern verglichen. Diese Arbeit zeigt ferner die Erzeugung ultrakurzer Pulse verschiedener Laser mit diesen neuartigen sättigbaren Absorbern basierend auf Kohlenstoff Nanostrukturen. Die erhaltenen Pulse werden mittels Spektrometrie, Autokorrelation, Radiofrequenz- und partiell FROG-Messungen charakterisiert, und der zugrunde liegende Pulsformungsmechanismus, sowie die Stabilität gegen das Güteschalten werden diskutiert.
This thesis addresses the interplay of highly efficient active laser media and novel saturable absorbers based on the carbon nanostructures graphene and single-walled carbon nanotubes (SWCNTs). The active laser media cover the spectral region from 1.0 micron up to 2.1 micron, i.e. a whole octave, and apply ytterbium, chromium and thulium as active lasing ions. Within this work, the saturable absorbers based on SWCNTs and graphene are characterized with respect to their relaxation behaviour after excitation, and with respect to their fluence-dependent transmission and saturation. A precedent introduction of the general optical properties of graphene and SWCNTs is presented as well and the models to describe real samples experimentally are deduced from theoretical model conceptions. The saturable absorbers based on graphene and SWCNTs are compared to each other and to classical semiconducting saturable absorbers. This thesis further presents the generation of ultrashort laser pulses applying these novel carbon nanostructure based saturable absorbers in different lasers. The obtained pulses are characterized by spectrometry, autocorrelation, radio-frequency measurements and partially by FROG measurements. Additionally, the underlying pulse formation process and the Q-switching stability are discussed.

This thesis comprises detailed experimental and theoretical investigations of the transport properties of one-dimensional nanostructures. Most of the work is dedicated to the exploration of the fascinating effects occurring in single wall carbon nanotubes (SWCNT). These particular nanostructures gained an overwhelming interest in the past two decades due to its outstanding electronic and mechanical features. We have investigated the properties of a novel family of carbon nanostructures, named here as Y-shaped rings. The studies show that they present very interesting quantum interference effects. A high structural stability under tensile strain and elevated temperatures is observed. Within the semi-classical potential adopted, the critical strain values of structure rupture lie in the same range of their pristine SWCNT counterparts. This is directly verified by the first observations of these ring-like structures in a transmission electron microscopy. A merging process of asymmetric into symmetric rings is investigated in-situ under electron beam irradiation at high temperatures. The electronic properties of these systems are theoretically studied using Monte Carlo simulations and environment dependent tight-binding calculations. From our results, we address the possibility of double-slit like interference processes of counter-propagating electron waves in the ring-like structures. The nature of well defined, sharp peaks in the density of states are determined as the discrete eigenenergies of the central loop part. Furthermore, the formation and dispersion of standing waves inside the ring is shown to originate from the quantum-dot like confinement of each branch between the leads. The obtained dispersion relation is shown to be the same occurring in purely one-dimensional quantum dots of similar geometries. Furthermore, Fabry-Perot-like interferences are observed. We established at the IFW a bottom-up processing route to fabricate nanotube based electronic devices. The SWCNTs are grown by chemical vapor deposition and we present a detailed study of the different approaches to obtain individual nanotubes suitable for a successful integration into electronic devices. Wet-chemistry and ultra-thin films as well as ferritin were employed as catalyst particles in the growth of SWCNT samples. By adjusting the optimized process parameters, we can control the obtained yield from thick nanotube forests down to just a couple of free-standing individual SWCNTs. The nanotubes are localized, contacted by standard e-beam lithography and characterized at ambient- as well as liquid helium temperatures. We usually obtain quite transparent contacts and the devices exhibit metallic or a mixed metallic/semiconducting behavior. The well-known memory effect upon gate voltage sweeping as well as single electron tunneling in the Coulomb blockade regime are addressed.

Les propriétés des nanotubes de carbone monoparois (SWCNTs) dépendent fortement de leur structure atomique. La croissance sélective en structure des SWCNTs est donc un objectif clé à atteindre pour les applications potentielles de ces matériaux uniques. Dans le travail présenté dans ce manuscrit, nous proposons une nouvelle méthode originale alliant chimie de coordination et chimie des surfaces, pour la croissance de SWCNTs par décomposition chimique en phase vapeur, à partir de pré­ curseurs de catalyseurs variés synthétisés par voie chimique.L 'étude approfondie de ce procédé est présenté pour trois systèmes métalliques de précurseurs (Fe, NiFe, NiCr), issus de la famille du bleu de Prusse. Une caractérisation détaillée des précurseurs, catalyseurs, et des SWCNTs synthétisés a permis de mettre en évidence des effets de la composition du catalyseur sur les phénomènes de croissance.Une étude comparative de microscopie électronique en transmission et de spectroscopie Raman pour la détermination de la distribution de diamètre des échantillons de SWCNTs obtenus a été effectuée, mettant en lumière l 'importance primordiale du recours à des caractérisations croisées pour l 'évaluation de la sélectivité des croissances.Enfin, d'autres pistes de précurseurs de catalyseurs synthétisés par voie chimique sont explorées. Des résultats préliminaires sur deux systèmes bimétalliques de précurseurs issus de la famille des « cyanosols » (FePd) , et de celle des polyoxometallates (CoW) sont présentés, soulignant leur intérêt pour la compréhension des mécanismes complexes de croissance des SWCNTs
The work presented in this manuscript is focused on the study of single-walled carbon nanotube (S WCNT) growth by chemical vapor deposition, through the tuning of catalyst nanoparticle composition. The properties of S WCNTs strongly depend on their atomic structure, making structurally selective growth essential for future applications. Here we present a new and original method combining surface chemistry and coordination chemistry, for S CNT growth using a wide range of mono- and bimetallic catalyst systems, formed by the reduction of chemically synthesized catalyst precursors.A thorough study of this process is presented for three metallic precursor systems (Fe, NiFe, NiC), derived from the Prussian blue compound family. An extensive characterization of the precursors, ca­ -talysts, and the resulting S CNTs has allowed to evidence effects of catalyst composition on growth phenomena.We also show the importance of cross-characterization of SWCNT growth samples, through a comparative study between TEM, and Raman spectroscopy for diameter distribution assessment of our growth samples, and on diameter-sorted SWCNT samples.Preliminary results on the use of cyanosols and polyoxomet alates for SWCNT growth with additional bimetallic catalyst systems (FePd , and CoW) are also presented , highlighting the rich potential of inorganic chemistry and coordination chemistry in the field of SWCNT growth

Since their discoveries, carbon nanotubes have been widely studied, but mostly in the forms of 1D individual carbon nanotube (CNT). From practical application point of view, it is highly desirable to produce carbon nanotubes in large scales. This has resulted in a new class of carbon nanotube material, called the vertically aligned carbon nanotube arrays (VA-CNTs). To date, our ability to design and model this complex material is still limited. The classical molecular mechanics methods used to model individual CNTs are not applicable to the modeling of VA-CNT structures due to the significant computational efforts required. This research is to develop efficient structural mechanics approaches to design, model and characterize the mechanical responses of the VA-CNTs. The structural beam and shell mechanics are generally applicable to the well aligned VA-CNTs prepared by template synthesis while the structural solid elements are more applicable to much complex, super-long VA-CNTs from template-free synthesis. VA-CNTs are also highly “tunable” from the structure standpoint. The architectures and geometric parameters of the VA-CNTs have been thoroughly examined, including tube configuration, tube diameter, tube height, nanotube array density, tube distribution pattern, among many other factors. Overall, the structural mechanics approaches are simple and robust methods for design and characterization of these novel carbon nanomaterials

碩士
國立臺灣大學
化學研究所
106
The study on molecular electronic properties is based on Metal-Molecule-Metal (MMM) junctions. Common method for fabricating MMM junctions such as focused ion/electron beam-induced deposition (FIBD/FEBID) is not ideal due to metal-halo which may result in short circuit. Herein, Pt-SWCNT (single-walled carbon nanotube)-Pt platforms were fabricated by thermal scanning probe lithography (t-SPL). T-SPL uses heated probe to define the pattern. A dedicated t-SPL instrument is NanoFrazor which is thermal atomic force microscopy probe. First, two-layer polymers were spin coated on wafer which has been deposited SWCNTs. The base layer is polymethylglutarimide (PMGI) and top layer is polyphthalaldehyde (PPA). The probe of NanoFrazor can be heated to 1000 0C. When the hot probe is brought into contact with surface, PPA decomposes and evaporates locally. Therefore, we pattern the both ends of SWCNT for electrodes. The time of this process is about 1-3 minutes. Next, using developer to dissolve the bare PMGI. Subsequently, deposit Pt by physical vapor deposition (PVD) and then lift off unwanted region of Pt. This study focuses on fabrication of Pt-SWCNT-Pt platforms by t-SPL technique. (1) To scan the SWCNT which under the two-layer polymers by AFM, decreasing the concentration of PPA for thinner film; however, low concentration of PPA result in the PMGI being over-etching. The 20 nm PMGI and 20 nm PPA are appropriate conditions. (2) The resistivity of Pt wire is 4.11 X 10–6 Ωcm which is lower than that fabricated by FIBD/FEBID. (3) The resistance of Pt-SWCNT-Pt is 9.5 kΩ which consistent with previous work. Furthermore, the IETS (inelastic electron tunnelling spectroscopy) signal of SWCNT are detected.

abstract: Dye sensitized solar cells (DSSCs) are the third generation solar cells expected to outperform the first two generations of solar cells with their advantages of comparative higher efficiency and lower manufacturing costs. The manufacturing cost of Dye sensitized solar cells is one fifth of the conventional silicon solar cell. However, DSSCs have problems of low conversion efficiency, stability and reliability. Some effective approaches are required to improve their performance. This paper projects the work related to assessment and verification of the repeatability of the semi-automated fabrication process. Changes were introduced in to the fabrication process to enhance the efficiency and stability. The sealant step in the fabrication process was remodeled to a newer version with an improvement in efficiency from 11% to 11.8%. Sputtering was performed on counter electrode in 30 seconds intervals. Cells were fabricated to assess the performance & time dependent characteristics from EIS experiments. Series resistance increased three times in sputtered Pt electrode as compared to standard platinum electrode. This resulted in the degradation of conductive surface on glass electrode due to heavy bombardment of ions. The second phase of the project work relates to the incorporation of SWCNT on the TiO2 electrode and its effect on the cell efficiency. Different weight loadings (0.1 wt %, 0.2 wt%, 0.4 wt %) of SWCNTs were prepared and mixed with the commercial TiO2 paste and ethanol solvent. The TiO2-SWCNT layer was coated on the electrode using screen-printing technique. Both open circuit voltage and photocurrent were found to have measurable dependence on the TiO2 layer loading. Photo voltage ranged from ~0.73 V to ~0.43 V and photocurrent from ~8 to ~33 mA depending on weight percent loading. This behavior is due to aggregation of particles and most TiO2 aggregate particles are not connected to SWCNT. Transparency loss was observed leading to saturation in the photo current and limiting the light absorption within the TiO2 film.
Dissertation/Thesis
M.S.Tech Technology 2011

碩士
國立清華大學
動力機械工程學系
106
Thermoelectric cooler (TEC) is a device which converts electrical energy into heat energy. The primary principle of the TEC is the Peltier effect. Thermoelectric cooler is a sandwich structure consisting of many different materials. When a direct current is applied, thermal stress and thermal deformation are unavoidably produced in the TEC due to the temperature gradient. Moreover, due to the mismatch of thermal expansion coefficient between component materials of the TEC, the TEC may be out of work after an extended period of practice. In this thesis, two sets of three dimensional digital image correlation (3D-DIC) systems were adopted to measure the deformation of two different TECs, i.e. TEC_A and TEC_B, of 127 pairs of p-type and n-type semiconductors with and without the heat sink, respectively. Strains of the TEC under different currents were measured, and the quality of the TEC was investigated by the strain and temperature distributions. Results showed that the strain becomes higher as the current increased. The quality of TEC_B was also found better based on results of the strain distribution. To enhance the cooling effect, single-walled carbon nanotube (SWCNT) was used to coat on the surface of the heat sink, and the cooling effect of the heat sink was found successfully improved. The strain of the TEC is smaller when the SWCNT heat sink was added, and the overall temperature distribution was also decreased. In the future, it is possible to use the SWCNT heat sink to replace the cooling fan for TECs under low and medium current. In addition to increase the service life of TECs, cost and the vibration produced from the cooling fan can also be reduced.

碩士
國立臺灣大學
化學研究所
107
The Metal–Molecule–Metal (MMM) junctions are widely utilized to measure the electrical properties of single molecules and constructed mostly by break-junction and electromigration method in literature precedents. However, the size of gap and target molecules are different, and the attachment is constructed on the basis of chemical adsorption, resulting in the instability of device. To fix these issues, single single-walled carbon nanotube (single SWCNT) replaces metal as electrode material due to its nano diameter where we envisaged to form covalent bond with molecule in construction of MMM junction. Compared with SWCNT branches, single SWCNT forms one bond with molecule. However, it is challenging that the carbon nanotubes are prone to form carbon branches in organic solvents and water. Therefore, we introduced single-strand DNA in SWCNT solution to suppress the aggregation of SWCNT by the strong π-π interaction between single-strand DNA and single SWCNT, improving the ratio of single SWCNT to 87% significantly. Also, we modified the fabrication using thermal scanning probe lithography (t-SPL) and photoresist with better yield. The molecular junction with Pt–single SWCNT–Pt is therefore constructed and the temperature-dependent resistance of single SWCNT can be obtained. Also, the D band, G band (C–C vibration in sp2-hybridized graphene) and G’ band (duplicated band from D band) of single SWCNT can be observed in inelastic electron tunneling spectroscopy (IETS). Our effort involves DNA-assisted dispersion of single SWCNT, modification of t-SPL, focusing on the electrical properties of single SWCNT and identification of single SWCNT in IETS. This research manifests a systematic, rational approach to obtain the characterization of single SWCNT, which is beneficial for further applications such as Pt–SWCNT–molecule–SWCNT–Pt molecular junction.

碩士
國立雲林科技大學
電子工程系
106
The non-enzymatic glucose sensor was successfully prepared in this research which the single-wall carbon nanotubes (SWCNTs) were wrapped with Nafion to enhance the sensitivity of sensor based on the copper(I) oxide (Cu2O) surface modification of zinc oxide nanorod (ZnO NR)/Graphene composites on ITO glass. The experimental procedure of this research has four steps: First, the different sputtering time was used to deposit the ZnO seed layer, and then will be synthesis ZnO NR by hydrothermal. The morphology of ZnO NR was checked by scanning electron microscope (SEM). Secondly, the optimal cupreous time of Cu2O on the ZnO NR would be verified by electrochemistry with the different concentration of glucose. Thirdly, the SWCNTs wrapped with Nafion was dropped to Cu2O /ZnO NR to increase the catching ability of the glucose and checked by electrochemistry. Lastly, graphene would be prepared on the ITO glass and then fabricated the Cu2O surface modification of ZnO NR/Graphene composites. In the electrochemistry measurement, 0.1M NaOH was used as the electrolyte, and there were four concentrations of glucose: 0, 100, 150 and 200 mg dL-1. The electrochemical characteristics of the sensors were investigated by cyclic voltammetry (CV). The results showed the modified electrodes of Cu2O/ZnO NR had a linear response to glucose concentration and the maximum concentration could reach to 200 mg/dL with the sensitivity of 0.6207 μA mg-1 dL cm-2(about 11.17 μA mM-1 cm-2). Because the SWCNTs wrapped with Nafion could enhance the capturing ability of glucose checked by the CVs curve of electrochemistry. Since, the modified electrodes of SWCNT/Cu2O/ZnO NR has the optimal linear range from 0 to 200 mg/dL and good sensitivity of 16.1 μA mg-1 dL cm-2(289.8 μA mM-1 cm-2). Anyway, the SWCNTs wrapped with Nafion could increase the sensitivity of glucose sensor. The chronoamperometry (CA) is a precision real time response of the glucose sensor. So the graphene was fabricated on the ITO glass to adhesive on the SWCNTs/Cu2O/ZnO NR/Graphene composites as the glucose sensor, then the sensor would be tested by the CA method with the increasing the glucose concentration. The calibration curve of glucose sensor has two linear ranges: 0-5.556 and 5.556-11.111 mM and have the sensitivity of 466.1 and 203.1 μA mM-1 cm-2, respectively. The addition of graphene could increase the sensitivity at low concentration and reduce the response time (< 2 s) for the SWCNTs/Cu2O/ZnO NR glucose sensor.

In the first part, a new analytical approach, within the extended finite element (XFEM) framework, is proposed to compute Strain Energy Release Rates (SERRs) directly from Irwin's integral. Crack tip enrichment functions in XFEM allow for evaluation of integral quantities in closed form (for some crack configurations studied) and therefore results in an accurate and efficient method. The effects of high order enrichments, mesh refinement and the integration limits of Irwin's integral are examined in benchmark numerical examples. The results indicate that high order enrichment functions have significant effect on the convergence, in particular when the integral limits are finite. When the integral limits tend to zero, simpler SERR expressions are obtained and high order terms vanish. Nonetheless, these terms contribute indirectly via coefficients of first order terms. The analytical formulation is then extended to cracks in arbitrary orientations. Several benchmark examples are investigated including off-center cracks, inclined cracks and crack growth problems. On all these problems, the method is shown to work well, giving accurate results. Moreover, due to its analytical nature, no special postprocessing is required which leads to a fast approach to obtain Strain Energy Release Rates. Thus it is concluded that this method may provide a good alternative to the popular J-integral method. In the second part of the thesis, the stress-strain behavior of short single walled carbon nanotube (SWCNT) aggregates is investigated by a novel incremental constrained minimization approach. An AIREBO potential is used to model the interactions within and between CNTs. The idea is to homogenously disperse SWCNTs in the computational cell at random positions and orientations following spherical uniform distributions, and incrementally deform the cell while restraining the movement of atoms at the ends of nanotubes. The stress-strain response of the system is obtained in each loading direction and it is shown to converge to an isotropic behavior (a similar response in all directions) as the number of CNTs in the system increases. In addition, it is shown that the Young's modulus of the system increases linearly with the CNT aggregates density and the method agrees well with results obtained from molecular dynamics simulations running at near zero degrees kelvin, which are obtained at only a fraction of the CPU time required for MD methods.

Well dispersed aqueous suspensions containing single-walled carbon nanotubes (SWCNTs) from bulk powders were prepared with surfactant and without surfactant by acid functionalization. SWCNT coated electrodes were then prepared from the SWCNT aqueous suspensions using various methods to create uniform nanoporous networks of SWCNTs on various substrates and stainless steel (SST) current collectors for use as ultracapacitor electrodes. Drop coating, high voltage electro-spraying (HVES), inkjet printing, and electrophoretic deposition (EPD) methods were evaluated. Optical and scanning electron microscope images were used to evaluate the SWCNT dispersion quality of the various electrodes. Ultimately an EPD process was established which reliably produced uniform SWCNT nanoporous networks on SST substrates. The prepared SWCNT coated electrodes were characterized using cyclic voltammetry and their capacitance was determined. A correlation between extended EPD processing times, EPD processing temperatures, and electrode capacitance was quantified. Optimum EPD processing occurs where linear capacitance gains were observed for processing times less than 10 minutes. At processing times between 10 – 60 minutes a non-linear relationship demonstrated diminishing capacitance gains with extended EPD processing times. Likewise, optimum EPD processing occurs when the processing temperature of the SWCNT suspension is raised above room temperature. At processing temperatures from 45°C to 60°C an increase in capacitance was observed over the room temperature (22°C) electrodes processed for the same durations. Conversely, for processing temperatures less than room temperature, at 5°C, a decrease in capacitance was observed. It was also observed that SWCNT electrodes processed at 60°C processing temperatures resulted in 4 times the capacitance of 5°C electrodes for the same processing times, when the durations were 8 minutes or less. For samples with raised processing temperatures the time dependent capacitance gains were observed to be significantly diminished beyond 10 minute processing times. The SWCNT network thickness was also correlated to EPD processing temperature and capacitance. A linear relationship was identified between the SWCNT network thickness and the capacitance of the electrode. It was also observed that elevated processing temperatures increase the EPD deposition rate of SWCNTs, produce thicker SWCNT networks, and thus create electrodes with higher capacitance than electrodes processed at lower EPD processing temperatures. EPD of SWCNTs was demonstrated in this work to be an effective method for the fabrication of SWCNT ultracapacitor electrodes. Characterization of the process determined that optimal EPD processing occurs within the first 10 minutes of processing time and that elevated processing temperatures yield higher SWCNT deposition rates and higher capacitance values. In this work the addition of SWCNT nanoporous networks to SST electrodes resulted in increases in capacitance of up to 398 times the capacitance of the uncoated SST electrodes yielding a single 1cm2 electrode with a capacitance of 91mF and representing an estimated specific capacitance for the processed SWCNT material of 45.78F/g.

The extraordinary properties of the single wall carbon nanotubes (SWCNTs) have stimulated an enormous amount of research towards the realization of SWCNT-based products for different applications ranging form nanocomposites to nanoelectronics. Their high charge mobility, exceedingly good current-carrying capacities and ability to be either semiconducting or metallic render them ideal building blocks for nanoelectronics. For nanoelectronic applications, either individual or parallel aligned SWCNTs are advantageous. Moreover, closely packed arrays of parallel SWCNTs are required in order to sustain the relatively large currents found in high frequency devices. Two key areas still require further development before the realization of large-scale nanoelectronics. They are the reproducible control of the nanotubes spatial position/orientation and chiral management. In terms of nanotube orientation, different techniques have been demonstrated for the fabrication of horizontally aligned SWCNTs with either post synthesis routes (e.g. dielectrophoresis and Langmuir-Blodgett approach) or direct growth (e.g. chemical vapor deposition (CVD)). The low temperature of the production process, allowing the formation of aligned nanotubes on pretty much any substrate, is the main advantage of the post synthesis routes, while the poor levels of reproducibility and spatial control, and the limited quality of the aligned tubes due to the inherently required process steps are limitations. The simplicity, up-scalability, along with the reproducible growth of clean high quality SWCNTs with well-controlled spatial, orientation and length, make CVD the most promising for producing dense horizontally well-aligned SWCNTs. These CVD techniques suffer some drawbacks, namely, that because they are synthesized using catalyst particles (metals or non-metals) the catalyst material can contaminate the tubes and affect their intrinsic properties. Thus, the catalyst-free synthesis of aligned SWNT is very desirable. This thesis comprises detailed and systematic experimental investigations in to the fabrication of horizontally aligned SWCNTs using both post growth (Dielectrophoresis) and direct growth (CVD) methods. Both catalyst-assisted and catalyst-free SWCNTs are synthesized by CVD. While metallic nanoparticles nucleate and grow SWCNTs, opened and activated fullerene structures are used for all carbon catalyst-free growth of single wall and double wall carbon nanotubes. The systematic studies allow for a detailed understanding of the growth mechanisms of catalyst and catalyst-free grown SWCNTs to be elucidated. The data significantly advances our understanding of horizontally aligned carbon nanotubes by both post synthesis alignment as well as directly as-synthesized routes. Indeed, the knowledge enables such tubes to be grown in high yield and with a high degree of special control. It is shown, for the first time, how one can grow horizontally aligned carbon nanotubes in crossbar configurations in a single step and with bespoke crossing angles. In addition, the transport properties of the aligned tubes at room temperature are also investigated through the fabrication of devices based on these tubes.:Introduction ……………………………………………………………….…………… 11 1 Carbon nanotubes basics ……………………………………………………. 15 1.1 sp2 hybridization …………………………………………………….……… 16 1.2 Graphene basics ………………………………………………………...… 16 1.3 Single wall carbon nanotubes Basics …………………………… 18 1.4 Synthesis of single wall carbon nanotubes ………………… 24 1.4.1 Arc discharge ………………………………………………… 24 1.4.2 Laser ablation ……………………………………………… 24 1.4.3 Chemical vapor deposition …………………………… 25 1.4.4 The as-produced carbon nanotubes …………… 25 1.5 Potential applications of single wall carbon nanotubes 26 1.6 Challenges face single wall carbon nanotubes ………… 27 2 Horizontally aligned single wall carbon nanotubes: a review of fabrication and characterization ………………………………………………… 29 2.1 Introduction …………………………………………...………………………………………… 29 2.2 The requisites of horizontally aligned single wall carbon nanotubes 31 2.3 Characterization of Horizontally aligned single wall carbon nanotubes 32 2.3.1 Electron microscopy …………………………………………………………… 32 2.3.2 Scanning probe microscopy ……………………………………...…………… 34 2.3.3 Spectroscopy ……………………………………………………………………… 35 2.4 Fabrication of horizontally aligned single wall carbon nanotubes ……… 36 2.4.1 Dielectrophoresis (Growth-then-place) …………………….…………… 36 2.4.2 Chemical vapor deposition (Growth-in-place) ………...…………… 40 2.5 Transistor performance from horizontally aligned single wall carbon nanotubes ……… 67 2.5.1 Field effect transistor ……………….…………...………………………….…… 67 2.5.2 Thin film transistor …………………………….…...…………………….……… 68 3 Dielelectrophoretic deposition of single wall carbon nanotubes 69 3.1 Deposition of single wall carbon nanotubes in between metallic electrodes ………………… 69 3.1.1 Dispersion of single wall carbon nanotubes ………………………… 69 3.1.2 Dielectrophoretic alignment of single wall carbon nanotubes 70 3.2 CNTFET topographical characterization …………..………………………..……… 70 3.3 Dielectrophoresis advantages and drawbacks ………………………….....……… 72 4 Growth of catalyst-assisted horizontally aligned single wall carbon nanotubes …..………..... 75 4.1 Experimental procedure ….………………………………………………………...……… 76 4.1.1 ST-cut quartz substrates preparation ……………………….....……… 76 4.1.2 Catalyst solutions preparation ……………………………........……… 76 4.1.3 Growth of single wall carbon nanotubes ……………………………… 77 4.1.4 Single wall carbon nanotubes transfer into silicon substrates 78 4.2 Substrate thermal treatment ………………………………………………..........……… 79 4.3 Formed catalyst nanoparticles ………………………………………………...……… 82 4.4 As-grown single wall carbon nanotubes ………………...……………..…………… 84 4.5 Transferred single wall carbon nanotubes ………………...………….……...…… 91 4.6 Chapter summary ………………………………………………...…………………………… 92 5 Growth of catalyst-free horizontally aligned single wall carbon nanotubes … 93 5.1 Experimental procedure ………………………………………………………………….… 94 5.1.1 Different fullerene-based structure ……………………...……………… 94 5.1.2 Pre-treatment of fullerene structures …………………………...…….. 95 5.1.3 Growth of catalyst-free single wall carbon nanotubes ………… 96 5.2 Different fullerene structures nucleate the growth of single wall carbon nanotubes …… 97 5.3 C60 nucleated aligned single wall carbon nanotubes .……………...………… 98 5.3.1 Orientation of the as-grown nanotubes …………………………..… 98 5.3.2 Yield of the grown nanotubes ……………………………………………… 99 5.3.3 Activated sp2 caps ……………………………………………………...……….… 103 5.3.4 Type of the grown nanotubes …………………………………...………… 106 5.3.5 Growth mechanism of carbon nanotubes nucleated from fullerene … 109 6 Electrical characterization of the aligned single wall carbon nanotubes ……… 113 6.1 Device fabrication …………………………………………………………………..…………… 114 6.1.1 FET fabrication over the dielectrophoretic deposited carbon nanotubes … 114 6.1.2 Fabrication of the CVD grown nanotubes based device …………114 6.2 Electrical characterization of dielectrophoretic deposited single wall carbon nanotubes 115 6.2.1 I-V characteristics of the dielectrophoretic deposited nanotubes 115 6.2.2 Defect detection ………………………………………………………………..…… 117 6.3 Electrical characterization of the CVD grown nanotubes ……………………… 120 6.3.1 IV-Characteristics of the metal-assisted single wall carbon nanotubes ……… 120 6.3.2 Electrical behaviour of the catalyst-free single wall carbon nanotubes …………122 7 Conclusions and outlook ……………..……………………..………………………… 125 Appendix ……..……………………………………..………………………….……………. 129 Bibliography …...…………………………………..………………………….……………. 133 List of figures ….…………………………………..………………………….……………. 143 Glossary …………..…………………………………..………………………….……………. 147 Publications ………………………………………..………………………….……………. 149 Curriculum vitae ……………………………………..………………..…………………. 153 Acknowledgment ……..…………………………………..…..…………………………. 155 Declaration …………………………………………………..…..…………………………. 157
Die außergewöhnlichen Eigenschaften von einwandigen Kohlenstoffnanoröhren (engl. single wall carbon nanotubes, SWCNTs) haben bemerkenswerte Forschungsaktivitäten zur Verwirklichung von auf SWCNTs basierenden Anwendungen für verschiedene Bereiche, die von Nanokompositen bis hin zur Nanoelektronik reichen, stimuliert. Ihre hohe Ladungsträgermobilität und die außerordentlichen hohen Ladungsdichten, die in SWCNTs erreicht werden können sowie ihre Eigenschaft, entweder halbleitend oder metallisch zu sein, machen sie zu idealen Konstituenten von nanoelektronischen Schaltkreisen. Für Anwendungen in der Nanoelektronik sind entweder einzelne oder parallel angeordnete SWCNTs vorteilhaft. Darüber hinaus sind dicht gepackte Anordnungen von SWCNTs erforderlich, um die relativ hohen Ströme in Hochfrequenzbauelementen zu transportieren. Für eine erfolgreiche Realisierung von großskaligen nanoelektronischen Bauteilen, die auf SWCNTs basieren, sind noch zwei enorm wichtige Kernprobleme zu lösen, die weitere Forschungsanstrengungen erfordern: die reproduzierbare und verlässliche Kontrolle der räumlichen Positionierung und Orientierung der Nanoröhren sowie die Kontrolle der Chiralität der einzelnen SWCNTs. Hinsichtlich der Orientierung der Nanoröhren kann die horizontal parallele Ausrichtung von SWCNTs mit verschiedenen Techniken erreicht werden. Diese setzen entweder nach dem eigentlichen Wachstum der Röhren ein (Post-Synthese-Methoden wie z.B. Dielektrophorese oder Langmuir-Blodgett-Techniken) oder erreichen direkt während des Wachstums (z.B. durch Chemical-Vapor-Deposition-Methoden (CVD)) die parallele Anordnung. Durch die niedrigen Prozesstemperaturen, die während des Herstellungsprozesses erforderlich sind, erlauben die nach der eigentlichen Synthese stattfindenden Ausrichtungsmethoden die parallele Anordnung von Nanoröhren auf nahezu jedem Substrat, jedoch stellen die geringe Reproduzierbarkeit dieser Prozesse, die schwierige Kontrollierbarkeit der räumlichen Anordnung und die limitierte Qualität der ausgerichteten Röhren aufgrund der erforderlichen Prozessschritte natürliche Beschränkungen dieser Techniken dar. Die einfache Durchführung und ihre Skalierbarkeit, zusammen mit dem reproduzierbaren Wachstum qualitativ sehr hochwertiger SWCNTs mit hoher Kontrolle von räumlicher Anordnung, Orientierung und Länge machen die CVD-Methode zur erfolgversprechendsten Technik für die Herstellung von dichtgepackten hochparallelen horizontalen Anordnungen von SWCNTs. Diese CVD-Ansätze weisen jedoch auch einige Nachteile auf, die in den bei der Synthese verwendeten Katalysatorpartikeln (metallisch oder nicht-metallisch) begründet liegen, da das Katalysatormaterial die Röhren kontaminieren und dadurch ihre intrinsischen Eigenschaften beeinflussen kann. Daher ist eine katalysatorfreie Synthesemethode für ausgerichtete SWCNTs ein höchst erstrebenswertes Ziel. Die vorliegende Arbeit beschreibt detaillierte und systematische experimentelle Untersuchungen zur Herstellung von horizontalen, parallel ausgerichteten Anordnungen von SWCNTs unter Verwendung von Methoden, die sowohl nach dem eigentlichen Wachstum der Nanoröhren (Dielektrophorese) als auch während des Wachstums ansetzen (CVD). Bei den CVD-Methoden werden sowohl solche, die auf der Verwendung von Katalysatoren basieren, als auch katalysatorfreie Techniken verwendet. Während metallische Nanopartikel den Ausgangspunkt für das Wachstum von SWCNTs darstellen, werden geöffnete und aktivierte Fullerenstrukturen verwendet, um das katalysatorfreie Wachstum von reinen ein- oder mehrwandigen Nanoröhren zu erreichen. Die systematischen Untersuchungen ermöglichen ein tiefgehendes Verständnis der Wachstumsmechanismen von SWCNTs, die unter Verwendung von Katalysatoren oder katalysatorfrei erzeugt synthetisiert wurden. Die erzielten Ergebnisse erhöhen in einem hohen Maß das Verständnis der Herstellung von horizontal parallel angeordneten Nanoröhren, die durch Post-Synthese-Methoden oder direkt während des Wachstumsprozesses ausgerichtet wurden. Die erzielten Einsichten erlauben die Herstellung solcher Strukturen mit hoher Ausbeute und mit einem hohen Maß an räumlicher Kontrolle der Anordnung. Zum ersten Male kann ein Verfahren präsentiert werden, mit dem horizontal parallel angeordnete Nanoröhren in gekreuzten Strukturen mit wohldefinierten Kreuzungswinkeln hergestellt werden können. Zusätzlich werden die Transporteigenschaften von parallel ausgerichteten Nanoröhren bei Raumtemperatur, durch die Herstellung von auf den dargestellten Strukturen basierenden Bauelementen, untersucht.:Introduction ……………………………………………………………….…………… 11 1 Carbon nanotubes basics ……………………………………………………. 15 1.1 sp2 hybridization …………………………………………………….……… 16 1.2 Graphene basics ………………………………………………………...… 16 1.3 Single wall carbon nanotubes Basics …………………………… 18 1.4 Synthesis of single wall carbon nanotubes ………………… 24 1.4.1 Arc discharge ………………………………………………… 24 1.4.2 Laser ablation ……………………………………………… 24 1.4.3 Chemical vapor deposition …………………………… 25 1.4.4 The as-produced carbon nanotubes …………… 25 1.5 Potential applications of single wall carbon nanotubes 26 1.6 Challenges face single wall carbon nanotubes ………… 27 2 Horizontally aligned single wall carbon nanotubes: a review of fabrication and characterization ………………………………………………… 29 2.1 Introduction …………………………………………...………………………………………… 29 2.2 The requisites of horizontally aligned single wall carbon nanotubes 31 2.3 Characterization of Horizontally aligned single wall carbon nanotubes 32 2.3.1 Electron microscopy …………………………………………………………… 32 2.3.2 Scanning probe microscopy ……………………………………...…………… 34 2.3.3 Spectroscopy ……………………………………………………………………… 35 2.4 Fabrication of horizontally aligned single wall carbon nanotubes ……… 36 2.4.1 Dielectrophoresis (Growth-then-place) …………………….…………… 36 2.4.2 Chemical vapor deposition (Growth-in-place) ………...…………… 40 2.5 Transistor performance from horizontally aligned single wall carbon nanotubes ……… 67 2.5.1 Field effect transistor ……………….…………...………………………….…… 67 2.5.2 Thin film transistor …………………………….…...…………………….……… 68 3 Dielelectrophoretic deposition of single wall carbon nanotubes 69 3.1 Deposition of single wall carbon nanotubes in between metallic electrodes ………………… 69 3.1.1 Dispersion of single wall carbon nanotubes ………………………… 69 3.1.2 Dielectrophoretic alignment of single wall carbon nanotubes 70 3.2 CNTFET topographical characterization …………..………………………..……… 70 3.3 Dielectrophoresis advantages and drawbacks ………………………….....……… 72 4 Growth of catalyst-assisted horizontally aligned single wall carbon nanotubes …..………..... 75 4.1 Experimental procedure ….………………………………………………………...……… 76 4.1.1 ST-cut quartz substrates preparation ……………………….....……… 76 4.1.2 Catalyst solutions preparation ……………………………........……… 76 4.1.3 Growth of single wall carbon nanotubes ……………………………… 77 4.1.4 Single wall carbon nanotubes transfer into silicon substrates 78 4.2 Substrate thermal treatment ………………………………………………..........……… 79 4.3 Formed catalyst nanoparticles ………………………………………………...……… 82 4.4 As-grown single wall carbon nanotubes ………………...……………..…………… 84 4.5 Transferred single wall carbon nanotubes ………………...………….……...…… 91 4.6 Chapter summary ………………………………………………...…………………………… 92 5 Growth of catalyst-free horizontally aligned single wall carbon nanotubes … 93 5.1 Experimental procedure ………………………………………………………………….… 94 5.1.1 Different fullerene-based structure ……………………...……………… 94 5.1.2 Pre-treatment of fullerene structures …………………………...…….. 95 5.1.3 Growth of catalyst-free single wall carbon nanotubes ………… 96 5.2 Different fullerene structures nucleate the growth of single wall carbon nanotubes …… 97 5.3 C60 nucleated aligned single wall carbon nanotubes .……………...………… 98 5.3.1 Orientation of the as-grown nanotubes …………………………..… 98 5.3.2 Yield of the grown nanotubes ……………………………………………… 99 5.3.3 Activated sp2 caps ……………………………………………………...……….… 103 5.3.4 Type of the grown nanotubes …………………………………...………… 106 5.3.5 Growth mechanism of carbon nanotubes nucleated from fullerene … 109 6 Electrical characterization of the aligned single wall carbon nanotubes ……… 113 6.1 Device fabrication …………………………………………………………………..…………… 114 6.1.1 FET fabrication over the dielectrophoretic deposited carbon nanotubes … 114 6.1.2 Fabrication of the CVD grown nanotubes based device …………114 6.2 Electrical characterization of dielectrophoretic deposited single wall carbon nanotubes 115 6.2.1 I-V characteristics of the dielectrophoretic deposited nanotubes 115 6.2.2 Defect detection ………………………………………………………………..…… 117 6.3 Electrical characterization of the CVD grown nanotubes ……………………… 120 6.3.1 IV-Characteristics of the metal-assisted single wall carbon nanotubes ……… 120 6.3.2 Electrical behaviour of the catalyst-free single wall carbon nanotubes …………122 7 Conclusions and outlook ……………..……………………..………………………… 125 Appendix ……..……………………………………..………………………….……………. 129 Bibliography …...…………………………………..………………………….……………. 133 List of figures ….…………………………………..………………………….……………. 143 Glossary …………..…………………………………..………………………….……………. 147 Publications ………………………………………..………………………….……………. 149 Curriculum vitae ……………………………………..………………..…………………. 153 Acknowledgment ……..…………………………………..…..…………………………. 155 Declaration …………………………………………………..…..…………………………. 157

博士
靜宜大學
應用化學系
100
ABSTRACT(PartI) A study sensing carbon monoxide (CO) was performed with ZnO-CuO and Pt/ZnO-CuO. These materials were characterized by temperature-programmed reduction (TPR), high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). Composite materials of ZnO-CuO were found to have an active sensing center, the sensor response was obtained for optimized ratio of ZnO and CuO (1:1 weight ratio) yielded highest response of 1.28 (Rco/Rair) for 1000 ppm of CO at room temperature; the response and recovery times were found to be 41 and 86 s, respectively. However, loading 1:1 ZnO-CuO with 0.4% Pt boosted sensor response to 2.64 (Rco/Rair) for 1000 ppm CO concentration. The sensor responses were calculated for CO concentrations of 100 to 1000 ppm with 0.4% Pt/ZnO-CuO. Both the response and recovery times were found to be 81 s. A mechanism for CO sensor response was put forward with reference to CO adsorption and desorption. ABSTRACT(PartII) Gas sensitive nanostructured hybrid films were synthesized via microwave assisted sol-gel route using Polyoxyethylened (80) sorbitan monooleate (TWEEN 80) and tetraethyl orthosilicate (TEOS). TWEEN 80 and TEOS were used as organic and inorganic precursors respectively. FT-IR spectra of the TWEEN 80/TEOS nanohybrid material revealed the formation of organic- inorganic networks between TWEEN 80 and TEOS. XRD spectra and micrographs showed the formation of TWEEN 80/TEOS amorphous nano hybrid film like structures. Surface roughness was measured using an AFM was 1150 nm and measured film thicknesses were between 18-20 µm. 1 % SWCNT (single walled carbon nanotube)/TTH (Tween 80/TEOS nano hybrids) named as 1 % CNT/TTH, CNT/TTH sensor response for 30 to 100 ppb NO concentrations was R2 = 0.9958. Hybrid films have showed better sensor response and faster response time (t90; 290 s). Using Material Studio software, the adsorption phenomena were explained to that of NO gas sensing property.

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.

Different carbon nanostructures have different properties and different applications. It is needed to synthesize good quality and also on large scale. From the point of industrial applications, highly productive and low cost synthesis method is very essential. Research has been done extensively on the intrinsic and individual properties of both single walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWC-NTs) in the range of nanometer to micrometer length scale. The important question is how the properties change beyond this length scale and if they are used in group in the form of an array instead of the individual carbon nanotubes (CNTs). Some applications require large current output, large energy production etc. For such kind of applications, it becomes essential to use CNTs in large number in the form of arrays or array, instead of using large numbers of CNTs in individual level. Future nanotechnology scope requires large scale application using the very rich intrinsic properties of the CNTs and nanomaterials. Keeping these problems and challenges in front, this thesis work is devoted to the research of the large scale synthesis of mm long MWCNTs, having different morphology and studies on various physical properties of MWCNTs in the form of arrays. Synthesis of mm long aligned and buckled MWCNTs have been reported for the first time. Generally buckled CNTs were obtained by compressing the straight CNTs. Apart from this, different morphologies like, aligned straight, helical or coiled CNTs are also synthesized. Resistance of the individual CNT increases with the increase in length. Resistance versus length of an array of CNT also shows similar behaviour. The thermal conductivity of CNT array is observed to decrease with the increase of array diameter (diameter �100 µm). There are few reports of the similar behaviour with the experiments done on small diameter CNT arrays (diameter �100 nm). From these observations, it seems that in the arrays of CNT, their intrinsic individual property is preserved though the magnitudes are different. The conductance measurements done on buckled CNT array by compressing it to apply uniaxial strain, shows the conductance oscillation. This conductance oscillation seems to be originating from the band gap change due to strain when the CNTs bend during compression. Recent research focuses on the arrays of CNT as they can carry large current of the order of several milliamperes that make the arrays suitable in nanoscale electronics and in controlling macroscopic devices such as light emitting diodes and electromotors. Regarding this aspect, a part of this thesis work is devoted on the application of CNT array to field effect transistor (FET) and study of thermoelectric power generation using CNT arrays. The entire thesis is based on the works discussed above. It has been organized as follows: Chapter 1 deals with introduction about the different carbon nanostructures and different synthesis methods. A brief introduction about the different current-voltage (IV) characteristics of SWCNTs and MWCNTs, length and diameter dependence and effect of the mode of contacts, are given. Some applications of the array of CNTs like buckling effect on compression, stretching of CNT into the form of rope, and conduction change on compression are discussed. Application of CNT as FET, as a thermometer, and thermoelectric effect of CNT are discussed. The electromechanical effect of CNT is also discussed briefly. Chapter 2 deals with experimental setup for synthesis of different morphologies of carbon nanostructures. The samples are characterized using common characterization techniques like, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. A brief introduction about Raman Spectroscopy of CNT is given. Chapter 3 reports the unusual IV characteristics and breakdown of long CNT arrays. The current carrying ability and the threshold voltage as a function of array diameter are reported. The effect of the ambient like temperature and pressure are discussed. Chapter 4 deals with theoretical models to analyze the IV characteristics reported in Chapter 3. It has been shown that a set of classical equations are applicable to quantum structures and the band gap can be evaluated. Chapter 5 describes with application of CNT arrays as temperature sensors. It has been shown that CNT arrays of suitable diameters are used as temperature sensors after calibration. Chapter 6 reports the high current FET application of CNT arrays. Effects of temperature and ambient pressure are discussed. The type of the majority charge carrier is determined. Chapter 7 deals with application of CNT arrays as thermoelectric power generator to get large thermoelectric current. Effects of different array diameter are discussed. Modulation of thermoemf with gate voltage is discussed. The type of the majority charge carrier is determined. Chapter 8 reports the effect of compressive strain on buckled MWCNT arrays. Conductance is measured during the compression of the array. Quantum electromechanical conductance oscillation is observed. The structural changes are observed with SEM. Raman spectroscopic study supports the explanation of the effect. Chapter 9 provides the conclusion and overall summary of the thesis.

Single-Walled Carbon Nanotube (SWCNT) based Very Large Scale Integrated circuit (VLSI) interconnect is one of the emerging technologies, and has the potential to overcome the thermal issues persisting even with the advanced copper based interconnect. This is because of it’s promising electrical and thermal transport properties. It can be stated that thermal energy transport in SWCNTs is highly anisotropic due to the quasi one dimensionality, and like in other allotropes of carbon, phonons are the dominant energy carriers of heat conduction. In case of conventional interconnect materials, copper and aluminium, although their thermal conductivity varies over orders of magnitude at temperatures below100 K, near room temperature and above they have almost constant value. On the other hand, the reported experimental studies on suspended metallic SWCNTs illustrate a wide variation of the longitudinal lattice thermal conductivity (κl) with respect to the temperature(T)and the tube length(L)at low, room and high temperatures. Physics based analytical formulation of κl of metallic SWCNT as a function of L and T is essential to efficiently quantify this emerging technology’s impact on the rising thermal management issues of Integrated Circuits. In this work, a physics based diameter independent analytical model for κl of metallic SWCNT is addressed as a function of Lover a wide range of T. Heat conduction in metallic SWCNTs is governed by three resistive phonon scattering processes; second order three phonon Umklapp scattering, mass difference scattering and boundary scattering. For this study, all the above processes are considered, and the effective mode dependent relaxation time is determined by the Matthiessen’s rule. Phonon Boltzmann transport equation under the single mode relaxation time approximation is employed to derive the non-equilibrium distribution function. The heat flux as a function of temperature gradient is obtained from this non-equilibrium distribution function. Based on the Fourier’s definition of thermal conductivity, κl of metallic SWCNT is formulated and the Debye approximations are used to arrive at analytical model. The model developed is validated against both the low and high temperature experimental investigations. At low temperatures, thermal resistance of metallic SWCNT is due to phonon-boundary scattering process, while at high temperatures it is governed by three phonon Umklapp scattering process. It is understood that apart from form factor due to mass difference scattering, boundary scattering also plays the key role in determining the peak value. At room temperature, κl of metallic SWCNT is found to be an order of magnitude higher than that of most of metals. The reason can be attributed to the fact that both sound velocity and Debye temperature which have direct effect on the phonon transport in a solid, are reasonably higher in SWCNTs. Though Umk lapp processes reduce the κl steeper than 1/T beyond room-temperature, it’s magnitude is round1000 W/m/K upto 800 K for various tube lengths, which confirms that this novel material is indeed an efficient conductor of heat also, at room-temperature and above.

Due to the aggressive downscaling of the CMOS technology, power and current densities are increasing inside the chip. The limiting current conduction capacity(106 Acm−2)and thermal conductivity(201Wm−1K−1 for Al and 400 Wm−1K−1 for Cu) of the existing interconnects materials has given rise to different electro-thermal issues such a shot-spot formation, electromigration, etc. Exploration of new materials with high thermal conductivity and current conduction has thus attracted much attention for future integrated circuit technology. Among all the elemental materials, carbon nanomaterials (graphene and carbon nanotube) possess exceptionally high thermal (600-7000 Wm−1K−1) and current( ~108 -109 Acm−2)conduction properties at room temperature, which makes them potential candidate for interconnect materials. At the same time development of efficient energy harvesting techniques are also becoming important for future wireless autonomous devices. The excess heat generated at the hot-spot location could be used to drive an electronic circuit through a suitable thermoelectric generator. As the See beck coefficient of graphene is reported to be the highest among all elementary semiconductors, exploration of thermoelectric properties of graphene is very important. This thesis investigates the electrothermal and thermoelectric properties of metallic single walled carbon nanotube (SWCNT) and single layer graphene (SLG) for their possible applications in thermal management in next generation integrated circuits. A closed form analytical solution of Joule-heating equation in metallic SWCNTs is thus proposed by considering a temperature dependent lattice thermal conductivity (κ) on the basis of three-phonon Umklapp, mass-difference and boundary scattering phenomena. The solution of which gives the temperature profile over the SWCNT length and hence the location of hot-spot(created due to the self-heating inside the chip) can be predicted. This self-heating phenomenon is further extended to estimate the electromigration performance and mean-time-to-failure of metallic SWCNTs. It is shown that metallic SWCNTs are less prone to electromigration. To analyze the electro-thermal effects in a suspended SLG, a physics-based flexural phonon dominated thermal conductivity model is developed, which shows that κ follows a T1.5 and T−2 law at lower(<300 K) and higher temperature respectively in the absence of isotopes(C13 atoms). However in the presence of isotopic impurity, the behavior of κ sharply deviates from T−2 at higher temperatures. The proposed model of κ is found to be in excellent match with the available experimental data over a wide range of temperatures and can be utilized for an efficient electro-thermal analysis of encased/supported graphene. By considering the interaction of electron with in-plane and flexural phonons in a doped SLG sheet, a physics-based electrical conductance(σ) model of SLG under self-heating effect is also discussed that particularly exhibits the variation of electrical resistance with temperature at different current levels and matches well with the available experimental data. To investigate the thermoelectric performance of a SLG sheet, analytical models for See beck effect coefficient (SB) and specific heat (Cph) are developed, which are found to be in good agreement with the experimental data. Using those analytical models, it is predicted that one can achieve a thermoelectric figure of merit(ZT) of ~ 0.62 at room temperature by adding isotopic impurities(C13 atoms) in a degenerate SLG. Such prediction shows the immense potential of graphene in waste-heat recovery applications. Those models for σ, κ, SB and Cph are further used to determine the time evolution of temperature distribution along suspended SLG sheet through a transient analysis of Joule-heating equation under the Thomson effect. The proposed methodology can be extended to analyze the graphene heat-spreader theory and interconnects and graphene based thermoelectrics.