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dc.contributor.authorSnowdon, Monika 15:36:07 (GMT)
dc.description.abstractThis manuscript details the achievements and the scientific evidence for the alignment of single-walled carbon nanotubes for field-effect transistor applications. There has been immense growth in the semiconducting industry over the last 60 years as it moves towards smaller and faster devices. This growth corresponds with Moore's law's predictions that the number of transistors in a chip duplicates approximately every two years. However, the functionality of devices is compromised as they become smaller in size. The manipulation of nanomaterials can contribute novel solutions by providing information on the chemical-physical properties needed to address the challenges of smaller dimensions to develop higher-performance electronics. This dissertation reports on the efforts to replace traditional silicon field-effect transistors (FETs) with single-walled carbon nanotubes (SWNTs), motivated by the need to overcome some of the problems that SWNTs present before they can be integrated into devices. The main difficulty for satisfactory integration arises from the tendency of SWNTs to configure in several ways, resulting in unreliable carrier transport. The project's main goal was to optimize an aligning method and select tube conformations with the desirable semiconducting properties. The alignment relay technique (ART) was developed for the simultaneous alignment and sorting of SWNTs. This method applies a liquid crystal aligned monolayer of SWNT iptycene-tweezers to an oxidized surface. The main research objective was to develop the extent of ART and to explore those ramifications. Additionally, prior to this work, no devices had been manufactured with this technique, ART's effectiveness was unknown. Therefore, the study also extended towards device fabrication to prove that transistors can be made with ART. First, to increase SWNT alignment, the ART was modified to include a sonication treatment, which boosted the degree of alignment up to 80%, but with a 10x decrease in density. The average nanotube lengths were more consistent across the surface and increased from 0.8 to 1.7 µm. Extensive Raman spectroscopic analysis concluded a preference for 1.6 nm-diameter SWNTs. The ART was combined with other popular nano-surface deposition techniques such as Layer-by-Layer and Langmuir-Blodgett to augment the density of SWNTs on the surface. These combinations were hypothesized to increase the density of the aligned SWNTs; however, the results showed bundles of tubes adhering to the silica surface, rather than keeping with the orientation set by the ART. Consequently, additional surface molecules were added to fill gaps in the iptycene monolayer, which increased SWNT density by up to 10% on silica. Second, another form of iptycene-tweezer was synthesized using carboxylic acids, and this new molecule enabled better nanotube adherence to alumina surfaces than silica ones. Both alumina and gold surfaces were attempted with standard ART, and their surfaces were also treated with other molecules to fill in any gaps in order to increase the alignment and density of the SWNTs on the surface. The additional molecules were ineffective on gold but increased the SWNT density by up to 16% on alumina. Third, ART had only been explored with a single batch of SWNTs. Here, various SWNT batches were investigated, along with multi-walled carbon nanotubes (MWNTs), graphene nanoribbons (GNRs), and nanowires (NWs), to explore the extent of this new alignment method. Only SWNTs in the diameter range of 1.4-1.8 nm were effective using the existing parameters. The MWNTs and NWs did not work as the diameters are too large to effectively bind with the iptycene tweezer. The GNRs did not bind as they have a planar structure that is a mismatch for the concave structure of the iptycene tweezers. Lastly, top-gate and bottom-gate transistors were fabricated and tested using both electron beam lithography and photolithography. The ART nanotubes tested in a vacuum as a top-gate can achieve an ION/IOFF of 106 with 10 cm2/Vs mobility. Although greater ION/IOFF and mobility values have been shown for CNTFETs, this work presents the first evidence that functioning devices are possible when using ART, and lays the ground work for the successors of this research. Résumé La fabrication des semi-conducteurs est une énorme industrie qui s’est largement développée au cours des soixante dernières années, évoluant selon les prédictions de la loi de Moore. Cependant, la miniaturisation des appareils électroniques compromet leur infaillibilité. La recherche et la manipulation des nanomatériaux apportent de nouvelles solutions à ce défi. Le domaine des nanotechnologies étudie les propriétés physico-chimiques des semi-conducteurs et permet de surmonter les problèmes liés à cette miniaturisation afin de développer des produits électroniques aux performances optimales. Un problème à résoudre est celui de la réduction de taille des transistors, un composant majeur des appareils électroniques tels que les ordinateurs et cellulaires, qui influe sur leur transport, puissance et intégration. Une solution pour surmonter certains de ces problèmes est d’utiliser les nanotubes de carbone monofeuillets (SWNT, single-walled carbon nanotubes). Cette thèse décrit une voie de recherche visant à remplacer les transistors traditionnels en silicium avec des transistors faits de SWNTs, car certains problèmes empêchant leur utilisation dans les appareils électroniques. La difficulté principale pour l’intégration satisfaisante provient de la tendance des SWNTs à se configurer de plusieurs manières, ce qui entraîne des propriétés semi-conductrices incohérentes. L'objectif primordial du projet était d'optimiser une méthode d'alignement et de sélectionner des conformations de tubes présentant les propriétés semi-conductrices souhaitables. Afin d’améliorer l’alignement des SWNTs, le Alignment Relay Technique (ART) a été développé. Cette technique a pour but d’aligner et en même temps sélecter les SWNTs. La technique se base sur les propriétés des cristaux liquides pour l’alignement, et sur des molécules iptycènes qui peuvent interagir avec les SWNTs et les adhèrent à la surface. Ce projet a pour but d’optimiser l'ART à travers différentes modifications à sa méthodologie. Des techniques de sonication, layer-by-layer, et Langmuir-Blodgett sont étudiées. La sonication peut augmenter l’alignement des nanotubes sur la surface par presque 80%, au prix d’une moindre densité de tubes en surface. L’ajout de molécules additionnelles en surface est également exploré, ainsi qu’une variation de l’iptycène original contenant un segment d’acide carboxylique. Cette version de l’ART démontre une préférence pour les surfaces d’Al2O3 au lieu de SiO2. L’utilisation d’une surface d’or a aussi été investiguée, mais n’est pas montrée d’efficacité. Aussi, des investigations ont lieu en utilisant d’abord des nanotubes de carbone multifeuillets (MWNTs), des nanofils, et nanorubans de carbone. En outre, des transistors ont aussi été fabriqués avec les SWNTs alignés par ART en utilisant la photolithographie et la lithographie par faisceau d'électrons. Les résultats démontrent un ION/IOFF de 106 et une mobilité de 10 cm2/Vs. En résumé, ce manuscrit détaille les réalisations et les preuves scientifiques de l'alignement de nanotubes de carbone à paroi unique appliqué aux transistors.en
dc.publisherUniversity of Waterlooen
dc.subjectsingle-walled carbon nanotubesen
dc.subjectliquid crystal relayen
dc.titleMethods of the Alignment-Relay Technique for Nanosystems: Optimization and Innovationen
dc.typeDoctoral Thesisen
dc.pendingfalse (Nanotechnology)en of Waterlooen
uws-etd.degreeDoctor of Philosophyen
uws-etd.embargo.terms1 yearen
uws.contributor.advisorSchipper, Derek
uws.contributor.affiliation1Faculty of Scienceen

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