<p>Carbon nanomaterials have a wide range of promising and exciting applications. One of the most heavily investigated carbon nanomaterial in recent history has been the carbon nanotube. The intense interest in carbon nanotubes can be attributed to the many exceptional characteristics which give them great potential to revolutionize modern mechanical, optical and electronic technologies. However, controlling these characteristics in a scalable fashion has been extremely difficult. Although some progress has been made in controlling the quality, diameter distribution and other characteristics of carbon nanotube samples, several issues still remain. The two major challenges which have stood in the way of their mainstream application are controlling their orientation and their electronic characteristics. Developing and understanding a Chemical Vapor Deposition based carbon nanotube synthesis method has been the major focus of the research presented here. Although several methods were investigated, including the so-called "fast-heating, slow-cooling" and large feeding gas flowrate methods, it was ultimately found that high-quality, perfectly aligned carbon nanotubes from a variety of metal catalysts could be grown on quartz substrates. Furthermore, it was found that using MeOH could selectively etch small-diameter metallic carbon nanotubes, which ultimately led to the productions of perfectly aligned single-walled carbon nanotube samples consisting almost entirely of semiconducting carbon nanotubes. Thiophene was utilized to investigate and support the hypothesized role of MeOH in producing these selectively gown semiconducting carbon nanotube samples. Additionally, this sulfur-containing compound was used for the first time to demonstrate a two-fold density enhancement in surface grown carbon nanotube samples. This method for selectively producing perfectly aligned semiconducting carbon nanotubes represents a major step towards the integration of carbon nanotubes into mainstream applications.</p><p>Although extremely useful in a variety of technologies, carbon nanotubes have proven impractical for use in H₂ storage applications. As such, microporous carbons have been heavily investigated for such ends. Microporous carbons have distinguished themselves as excellent candidates for H₂ storage media. They are lightweight and have a net-capacity of almost 100%, meaning that nearly all of the H₂ stored in these materials is easily recoverable for use in devices. However, developing a microporous carbon with the appropriately small pore diameters (~1nm), large pore volumes (>1cm<super>3</super>) and large surface areas (&#8805;3000m<super>2</super>/g) has proven exceedingly difficult. Furthermore, maintaining the ideal graphitic pore structure has also been an unresolved issue in many production means. Several microporous carbon synthesis methods were investigated herein, including inorganic and organically templated production schemes. Ultimately, thermally treating poly (etherether ketone) in CO₂ and steam environments was found to produce large surface area porous carbons (&#8805;3000m<super>2</super>/g) with the appropriately small pore diameters (<3nm) and large pore volumes (>1cm<super>3</super>) necessary for optimized storage of H2. Furthermore, the surface chemistry of these pores was found to be graphitic. As a result of these ideal conditions, these porous carbons were found to store ~5.8wt.% H₂ at 77K and 40bar. This represents one of the most promising materials presently under investigation by the United States Department of Energy H₂ Sorption Center of Excellence. </p><p>The success of both of these materials demonstrates the diversity and promise of carbon nanomaterials. It is hoped that these materials will be further developed and will continue to revolutionize a variety of vital technologies.</p> / Dissertation

Synthetic single-walled metal oxide (aluminosilicate) nanotubes (SWNTs) are emerging materials for a number of applications involving molecular transport and adsorption due to their unique pore structure, high surface reactivity, and controllable dimensions. In this thesis, I discuss the potential for employing SWNTs in next generation separation platforms based upon recent progress on synthesis, interior modification, molecular diffusion properties, transport modeling and composite membrane preparation of metal oxide SWNTs. First, I describe the structure, synthesis, and characterization of the SWNTs. Thereafter, chemical modification of the nanotube interior is described as a means for tuning the nanotube properties for molecular separations. Interior functionalization of SWNTs (e.g. carbon nanotubes and metal oxide nanotubes) is a long-standing challenge in nanomaterials science. After controlled dehydration and dehydroxylation of the SWNTs, I then demonstrate that the SWNT inner surface can be functionalized with various organic groups of practical interest via solid-liquid heterogeneous reactions. Finally, I describe a mass transport modeling and measurements for composite membranes composed of SWNTs as fillers. This work demonstrates the use of SWNTs for novel scalable separation units from both a nanoscale and a macroscale point of view.

Gold nanoshells, a material generally composed of a core of silica surrounded by a thin shell of gold, are of great interest due to their unique and tunable optical properties. By varying the shell thickness and core size, the absorption and scattering properties are greatly enhanced. The nanoshells can be made to absorb or scatter light at various regions across the electromagnetic spectrum, from visible to the near infrared. The ability to tune the optical properties of nanoshells allows for their potential use in many different areas of research such as optical imaging, tumor ablation, drug delivery, and solar energy conversion. The research in this thesis focused on the synthesis and characterization of two novel gold nanoshell materials containing thermally-responsive, organic-inorganic hybrid layers. One type of material was based on a two-layer particle with a thermally responsive hybrid core of N-isopropylacrylamide (NIPAM) copolymerized with 3-(trimethoxysilyl)propyl methacrylate (MPS) that was then coated with a thin layer of gold. The second material was a three-layer particle with a silica core, a thermally responsive copolymer of NIPAM and MPS middle layer and an outer shell of gold. Various techniques were used to characterize both materials. Transmission electron microscopy (TEM) was used to image the particles and dynamic light scattering (DLS) was used to determine particle size and the temperature response. Additionally, UV-Vis spectroscopy was used to characterize the optical properties as a function of temperature.

Central to the implementation of colloidal nanomaterials in commercial applications is the development of high throughput synthesis strategies for technologically relevant materials. Solution based synthesis approaches provide the controllability, high throughput, and scalability needed to meet commercial demand. A flow through supercritical fluid reactor was used to synthesize silicon nanowires in high yield with production rates of ~45 mg/hr. The high temperature and high pressure of the supercritical medium facilitated the decomposition of monophenylsilane and seeded growth of silicon nanowires by gold seeds. Crystalline nanowires with diameters of ~25 nm and lengths greater than 20 [micrometers] were routinely synthesized. Accumulation of nanowires in the reactor resulted in deposition of a conformal amorphous shell on the crystalline surface of the wire. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy were used to determine the shell composition. The shell was identified as polyphenylsilane formed by polymerization of the silicon precursor monophenylsilane. A post synthesis etch was developed to remove the shell while still maintaining the integrity of the crystalline silicon nanowire core. Subsequent surface passivation was achieved through thermal hydrosilylation with a terminal alkene. The development colloidal nanomaterials into commercial applications also requires simple and robust bottom-up assembly strategies to facilitate device fabrication. A Langmuir-Blodgett trough was used to assemble continuous monolayers of hexagonally ordered spherical nanocrystals over areas greater than 1 cm². Patterned monolayers and multilayers of FePt nanocrystals were printed onto substrates using pre-patterned polydimethylsiloxane (PDMS) stamps and a modified Langmuir Schaefer transfer technique. Patterned features, including micrometer-size circles, lines, and squares, could be printed using this approach. The magnetic properties of the printed nanocrystal films were also measured using magnetic force microscopy (MFM). Room temperature MFM could detect a remanent (permanent) magnetization from multilayers (>3 nanocrystals thick) films of chemically-ordered L1₀ FePt nanocrystals. Grazing incidence small angle X-ray scattering was used to quantitatively characterize the grain size, crystal structure, lattice disorder, and edge-to-edge spacing of the nanocrystal films prepared on the Langmuir-Blodgett trough both on the air-water interface and after transfer. / text

A series of hybrid component based on reactive polyhedral oligomeric silsesquioxane(POSS) precusors and its reactive copolymers of PGMA were synthesized and utilized to nanobuild in epoxy. Reactive POSS and copolymer dispersed in homogenous in matrix, overcomed POSS-POSS interaction, which resulted in macroscale phase separation. The nanocomposites obtained were analyzed by Scanning electron microscopy, Transmission electron microscopy, X-ray scattering and dynamic mechanical. An analogue of POSS (denoted as POSSMOCA) was synthesized via addition reaction, which had reactive amino group bonding into epoxy network and improved the thermostability, because of the structural silicon, nitrogen and halogen. Epoxy/polyhedral oligomeric silsesquioxanes (POSS) hybrid composites were prepared from prereaction between trifunctional silanol POSS-OH and diglycidyl ether of bisphenol A (DGEBA) via silanol and the oxirane group. Reactive POSS-PGMA was polymerized via Reversible addition-fragmentation transfer polymerization. It was easy to tail the compatibility of the epoxide block copolymer with a step-growth polymerized matrix, to form nanostructure via reaction with PGMA segements. In the case of inert POSS-PMMA copolymers modified epoxy, topology of copolymer defined the final morphology and interaction between epoxy and them, because of directional hydrogen bonding and dilution effect. Tg of different epoxide conversion, obeyed of Gordon-Taylor equation and Kwei equation, k which reflected the interaction of modifier and DGEBA/MEDA and epoxy/amine oligomers, was consistent of the rheology and dynamic results.

Au nanoparticles are increasingly being used in biological applications. Their use is of interest based upon their unique properties that are achieved at the nanoscale, which includes strong optical absorbances that are size and aggregation state dependent. Such absorbances can be used in sensitive chemical/biological detection schemes where bioligands can be directly attached to the nanoparticle surface using facile methods. Unfortunately, a number of complications persist that prevent their wide-scale use. These limitations include minimal nanoparticle stability in biological-based media of high ionic strength, unknown surface functionalization effects using simple biomolecules, and determining the binding motifs of the ligands to the nanoparticle surface. This situation can be further complicated when employing shaped materials where crystallographic facets can alter the binding potential of the bioligands. We have attempted to address these issues using traditional nanoparticle functionalization techniques that are able to be characterized using readily available analytical methods. By exploiting the optical properties of Au nanomaterials, we have been able to determine the solution stability of Au nanorods in a buffered medium and site-specifically functionalized Au nanomaterials of two different shapes: spheres and rods. Such abilities are hypothesized to be intrinsic to the bioligand once bound to the surface of the materials. Our studies have focused mainly on simple amino acids that have demonstrated unique assembly abilities for the materials in solution, resulting in the formation of specific patterns. The applications for such capabilities can range from the use of the materials as sensitive biochemical sensors to their directed assembly for use as device components.

Silicon nanowires are a nanostructure consisting of elongated crystals of silicon. Like many nanostructures, silicon nanowires have properties that change with size. In particular, silicon nanowires have a band-gap that is tuneable with the diameter of the nanowire. They tend to absorb a large portion of the light incident upon them and they form a highly textured surface when grown on an otherwise flat substrate. These properties indicate silicon nanowires are good candidates for use in solar cells. Nanostructured silicon, in the form of nanocrystalline silicon, has been used to produce thin film solar cells. Solar cells produced using silicon nanowires could combine the properties of the silicon nanowires with the low material costs and good stability of nanocrystalline based solar cells. This thesis describes the process of optimisation of silicon nanowire growth on a plasma enhanced chemical vapour deposition system. This optimised growth of silicon nanowires is then used to demonstrate a prototype solar cell using silicon nanowires and amorphous silicon. Several steps had to be accomplished to reach this goal. The growth of silicon nanowires was optimised through a number of steps to produce a high density film covering a substrate. Developments were made to the standard deposition technique and it was found that by using pulsed plasma enhanced chemical vapour deposition the density of nanowire growth could be improved. Of a range of catalysts trialled, gold and tin were found to be the most effective catalysts for the growth of silicon nanowires. A range of substrates was investigated and the nanowires were found to grow with high density on transparent conductive oxide coated glass substrates, which would allow light to reach the nanowires when they were used as part of a solar cell. The silicon nanowires were combined with doped and intrinsic amorphous silicon layers with the aim to create thin film photovoltaic devices. Several device designs using silicon nanowires were investigated. The variant that showed the highest efficiency used doped silicon nanowires as a p-layer which was coated with intrinsic and n-type amorphous silicon. By the characterisation and optimisation of the silicon nanowires, a prototype silicon nanowire solar cell was produced. The analysis of these prototype thin film devices, and the nanowires themselves, indicated that silicon nanowires are a promising material for photovoltaic applications.

The focus of this thesis is on using mechanical strain to tailor the electronic properties of graphene. The first half covers the electro-mechanical coupling for graphene in different configurations, namely a hexagonal Y-junction, various shaped bubbles on different substrates, and with kirigami cuts. For all of these cases, a novel combination of tight-binding electronic structure calculations and molecular dynamics is utilized to demonstrate how mechanical loading and deformation impacts the resulting electronic structure and transport. For the Y-junction, a quasi-uniform pseudo magnetic field induced by strain restricts transport to Landau-level and edge-state-assisted resonant tunneling. For the bubbles, the shape and the nature of the substrate emerge as decisive factors determining the effectiveness of the nanoscale pseudo magnetic field tailoring in graphene. Finally, for the kirigami, it is shown that the yield and fracture strains of graphene, a well-known brittle material, can be enhanced by a factor of more than three using the kirigami structure, while also leading to significant enhancements in the localized pseudo magnetic fields. The second part of the thesis focuses on dissipation mechanisms in graphene nanomechanical resonators. Thermalization in nonlinear systems is a central concept in statistical mechanics and has been extensively studied theoretically since the seminal work of Fermi, Pasta, and Ulam (FPU). Using molecular dynamics and continuum modeling of a ring-down setup, it is shown that thermalization due to nonlinear mode coupling intrinsically limits the quality factor of nanomechanical graphene drums and turns them into potential test beds for FPU physics. The relationship between thermalization rate, radius, temperature and prestrain is explored and investigated.

Made available in DSpace on 2014-06-11T19:32:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-03Bitstream added on 2014-06-13T19:21:28Z : No. of bitstreams: 1 costa_rm_dr_bauru.pdf: 1098183 bytes, checksum: 25def17b0af877f4604042281b271f05 (MD5) / Neste trabalho nós reportamos a síntese, caracterização, adsorção e propriedades dos materiais nomeados de octa[3-(2-amino-1,3,4-tiadiazol)propil]silsesquioxano (ATD-SSQ), octa[3-(3-amino-1,2,4-triazol)propil]silsesquioxano (ATZ-SSQ), octa[3-94-amino-2-mercaptopirimidina)propil]silsesquioxano (4-MCP-SSQ), octa[3-(2-mercaptopirimidina)propil]silsesquioxano (MCP-SSQ) e octa[3-(tioureia)propil]silsesquioxano (TIOU-SSQ). As isotermas de adsorção do M'X IND. 2'(M = Cu(II),Ni(II); X ='Cl POT.-', 'Br POT.-') para ATD-SSQ, ATZ-SSQ, 4MCP-SSQ e TIOU-SSQ. Foram estudadas em solução aquosa e etanólica a 25ºC. As adsorções em solução de etanol foram mais altas que em solução aquosa devido a alta polaridade da água, com maior força de solvatação do soluto e sítios básicos na superfície. As isotermas de adsorção de Cu'Cl IND. 2', Cu'Br IND. 2' e Ni'Cl IND. 2', em soluções etanólica e aquosa foram executadas usando o método da batelada. As condições de equilíbrio foram observadas em um tempo abaixo de 20min para todos os nanomateriais. Os resultados obtidos em experimentos de fluxo usando o método de coluna, demonstraram uma recuperação de 100% dos íons metálicos adsorvidos em uma coluna empacotada com 2g de nanomaterial, usando mL de HCl 1 mol 'L POT. -1' como solução eluente. A sorção-desorção dos íons metálicos possibilitou o desenvolvimento de um método para pré-concentração e determinação de íons metálicos a nível traço em etanol comercial, usado como combustível para automóveis. Os valores determinados pelo método recomendado para as usinas 1, 2 e 3 indicaram uma quantidade de cobre de 51,60 e 78 mg 'L POT. -1', e de ferro de 2, 15, e 3 mg 'L POT. -1', respectivamente. O ATZ-SSQ também foi testado para a determinação (em fluxo usando a técnica de coluna) dos íons metálicos presentes em águas naturais. Estes valores obtidos foram... / In this work we report on the synthesis, characterization, adsorption and properties of the nanomaterials named octa[3-(2-amino-1,3,4-tiadiazole)propyl]silsesquioxane (ATD-SSQ), octakis[3-(3-amino-1,2,4-triazole)propyl]silsesquioxane (ATZ-SSQ), octakis[3-94-amino-2-mercaptopirimidine)propyl]silsesquioxane (4-MCP-SSQ), octakis[3-(2-mercaptopirimidina)propyl]silsesquioxano (MCP-SSQ) e octakis[3-(thioureia)propyl]silsesquioxane (TIOU-SSQ). The isotherms of M'X IND. 2'(M = Cu(II),Ni(II); X ='Cl POT.-', 'Br POT.-') para ATD-SSQ, ATZ-SSQ, 4MCP-SSQ e TIOU-SSQ. Were studied in ethanol and aqueous solutions at 298K. Adsorptions from ethanol solutions were higher than those from aqueous solutions due to the higher polarity of water, which can more strongly solvate the solute and the basic sites on the surface. The adsorption isotherms for Cu'Cl IND. 2', Cu'Br IND. 2' and Ni'Cl IND. 2' from ethanol and aqueous solutions were performed by using the batchwise method. The equilibrium condition is reached at time lower than 20 min for all nanomaterials, ATD-SSQ, ATZ-SSQ, 4MCP-SSQ, MCP-SSQ and TIOU-SSQ. The results obtained in the flow using a column experiments, showed a recovery of the 100% of the metal ions adsorbed in a column packed with 2g of the nanomaterial, using 5 mL of 1.0 mol 'L POT. -1' HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a method for preconcentration and determination of metal ions at trace level in commercial ethanol, used as fuel for car engines. The values determined by recommended method for plants 1, 2 and 3 indicated an amount of copper of 51, 60, and 78 'L POT. -1', and of iron of 2, 15, and 3mg 'L POT. -1', resoectuvely. The ATZ-SSQ was also tested for the determination (in flow using a column technique) of the metal ions present in natural waters. These values are very close... (Complete abstract click electronic access below)

abstract: Zinc oxide (ZnO) has attracted much interest during last decades as a functional material. Furthermore, ZnO is a potential material for transparent conducting oxide material competing with indium tin oxide (ITO), graphene, and carbon nanotube film. It has been known as a conductive material when doped with elements such as indium, gallium and aluminum. The solubility of those dopant elements in ZnO is still debatable; but, it is necessary to find alternative conducting materials when their form is film or nanostructure for display devices. This is a consequence of the ever increasing price of indium. In addition, a new generation solar cell (nanostructured or hybrid photovoltaics) requires compatible materials which are capable of free standing on substrates without seed or buffer layers and have the ability introduce electrons or holes pathway without blocking towards electrodes. The nanostructures for solar cells using inorganic materials such as silicon (Si), titanium oxide (TiO2), and ZnO have been an interesting topic for research in solar cell community in order to overcome the limitation of efficiency for organic solar cells. This dissertation is a study of the rational solution-based synthesis of 1-dimentional ZnO nanomaterial and its solar cell applications. These results have implications in cost effective and uniform nanomanufacturing for the next generation solar cells application by controlling growth condition and by doping transition metal element in solution. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012