Download or read book Rapid Thermal Chemical Vapour Deposition Synthesis of Carbon Nanotubes and Their Wafer Scale Integration Into FET and Sensor Processes written by Iñigo Martín Fernández and published by . This book was released on 2010 with total page 215 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Carbon Nanotubes for Thermal Interface Materials in Microelectronic Packaging written by Wei Lin and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As the integration scale of transistors/devices in a chip/system keeps increasing, effective cooling has become more and more important in microelectronics. To address the thermal dissipation issue, one important solution is to develop thermal interface materials with higher performance. Carbon nanotubes, given their high intrinsic thermal and mechanical properties, and their high thermal and chemical stabilities, have received extensive attention from both academia and industry as a candidate for high-performance thermal interface materials.\r : The thesis is devoted to addressing some challenges related to the potential application of carbon nanotubes as thermal interface materials in microelectronics. These challenges include: 1) controlled synthesis of vertically aligned carbon nanotubes on various bulk substrates via chemical vapor deposition and the fundamental understanding involved; 2) development of a scalable annealing process to improve the intrinsic properties of synthesized carbon nanotubes; 3) development of a state-of-art assembling process to effectively implement high-quality vertically aligned carbon nanotubes into a flip-chip assembly; 4) a reliable thermal measurement of intrinsic thermal transport property of vertically aligned carbon nanotube films; 5) improvement of interfacial thermal transport between carbon nanotubes and other materials.\r : The major achievements are summarized.\r : 1. Based on the fundamental understanding of catalytic chemical vapor deposition processes and the growth mechanism of carbon nanotube, fast synthesis of high-quality vertically aligned carbon nanotubes on various bulk substrates (e.g., copper, quartz, silicon, aluminum oxide, etc.) has been successfully achieved. The synthesis of vertically aligned carbon nanotubes on the bulk copper substrate by the thermal chemical vapor deposition process has set a world record. In order to functionalize the synthesized carbon nanotubes while maintaining their good vertical alignment, an in situ functionalization process has for the first time been demonstrated. The in situ functionalization renders the vertically aligned carbon nanotubes a proper chemical reactivity for forming chemical bonding with other substrate materials such as gold and silicon.\r : 2. An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes. Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of ~35% and ~65%, respectively, in tensile strength (~0.8 GPa) and modulus (~90 GPa) during tensile testing; an ~20% improvement in electrical conductivity (~80000 S m−1) was also reported. The mechanism of the microwave response of CNTs was discussed. Such an microwave annealing process has been extended to the preparation of reduced graphene oxide.\r : 3. Based on the fundamental understanding of interfacial thermal transport and surface chemistry of metals and carbon nanotubes, two major transfer/assembling processes have been developed: molecular bonding and metal bonding. Effective improvement of the interfacial thermal transport has been achieved by the interfacial bonding.\r : 4. The thermal diffusivity of vertically aligned carbon nanotube (VACNT, multi-walled) films was measured by a laser flash technique, and shown to be ~30 mm2 s−1 along the tube-alignment direction. The calculated thermal conductivities of the VACNT film and the individual CNTs are ~27 and ~540 W m−1 K−1, respectively. The technique was verified to be reliable although a proper sampling procedure is critical. A systematic parametric study of the effects of defects, buckling, tip-to-tip contacts, packing density, and tube-tube interaction on the thermal diffusivity was carried out. Defects and buckling decreased the thermal diffusivity dramatically. An increased packing density was beneficial in increasing the collective thermal conductivity of the VACNT film; however, the increased tube-tube interaction in dense VACNT films decreased the thermal conductivity of the individual CNTs. The tip-to-tip contact resistance was shown to be ~1×10−7 m2 K W−1. The study will shed light on the potential application of VACNTs as thermal interface materials in microelectronic packaging.\r : 5. A combined process of in situ functionalization and microwave curing has been developed to effective enhance the interface between carbon nanotubes and the epoxy matrix. Effective medium theory has been used to analyze the interfacial thermal resistance between carbon nanotubes and polymer matrix, and that between graphite nanoplatlets and polymer matrix.
Download or read book Carbon Nanotube Synthesis Device Fabrication and Circuit Design for Digital Logic Applications written by Albert Lin and published by Stanford University. This book was released on 2010 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon Nanotube Field Effect Transistor (CNFET) technology has received a lot of attention in the past few years as a promising extension to silicon-CMOS for future digital logic integrated circuits. While recent research has advanced CNFET technology past many important milestones, robust and scalable solutions must be developed to realize the full potential of CNFETs. Thus, this thesis aims to develop a suite of techniques, spanning from material synthesis to circuit solutions, compatible with very-large-scale integration (VLSI). Specifically, to enable the real-world engineering of carbon nanotube integrated circuits, this thesis presents (1) wafer-scale aligned CNT growth, (2) wafer-scale CNT Transfer, (3) wafer-scale device and circuit fabrication techniques, and (4) ACCNT, a VLSI-compatible circuit design solution to surmounting the problem of metallic CNTs. These techniques culminated in the successful demonstration of CNT transistors, inverters, and NAND logic gates on a wafer scale. Furthermore, this thesis sheds light on important design considerations for the demonstration of a simple CNT "computer" and suggests a few critical directions for future work in the field of carbon nanotube technology. In contributing the above, this thesis hopes to propel carbon nanotube technology forward towards the vision of robust, large-scale integrated circuits using high-density carbon nanotubes.
Download or read book Development of Carbon Nanotube based Gas and Vapour Sensors and Supramolecular Chemistry of Carbon Nano materials written by Lee John Hubble and published by . This book was released on 2009 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: [Truncated abstract] The scientific endeavours described within this thesis attempt to create novel solutions to current scientific, commercial and industrial downfalls, and contribute to the advancement of technologies in these areas. This has been achieved through the application of theoretical and experimental principles, entrenched in the domains of chemistry and physics, which have been harnessed to assist in the transformation from nanoscience to nanotechnology. These solutions range from unique supramolecular systems capable of selective-diameter enrichment of single-walled carbon nanotubes (SWCNTs), to the fabrication of low-cost, potentially remote deployable carbon nanotube-based gas and vapour sensors, and expand right through to the development of water-soluble fluoroionophoric sensors and manipulations of a molecular form of carbon in constructing all-carbon nano-architectures. For the advancement and successful integration of carbon nanotubes (CNTs) into commercial processes, the advent of scalable separation protocols based on their electronic properties is required. SWCNTs have been successfully solubilised using water-soluble p-phosphonated calix[n]arenes (n = 4, 6, 8) and 'extended arm' upper rim functionalised (benzyl, phenyl) p-sulfonated calix[8]arenes. Selective SWCNT diameter solubilisation has been demonstrated and subsequent preferential enrichment of SWCNTs with semiconducting or metallic electronic properties has been achieved. In addition, semiconducting nanotube-enriched supernatants (liquid) have been utilised to fabricate on/off field effect transistors (FET). These water-soluble supramolecular systems can be incorporated into post-growth purification protocols, with direct implications in areas such as carbon nano-electronics and device fabrication. In the current global environment there is a heightened level of public and governmental disquiet due to the reality of impending terrorist attacks. This is compounded by the inherent ease of manufacture and effectiveness of specific chemical warfare agents (CWAs) used in small-scale terrorist operations. ... Additional all-carbon structures are described with the formation of rings of helical SWCNT bundles through post-growth SWCNT modifications, and a variety of fibrous all-carbon structures, most notably novel square-geometry carbon nano-fibres (CNFs), through catalytic-chemical vapour deposition (C-CVD) synthesis strategies. The current requirement for entirely water-soluble fluorescent sensors is routinely documented in the literature. The autofluorescence properties of p-phenyl-sulfonated calix[8]arene are characterised and this water-soluble cavitand is surveyed as a metal cation sensor candidate. This particular system was found to exhibit a change in fluorescence response when exposed to divalent metal cations, and interactions with [UO2]2+, Pb2+, Co2+, and Cu2+ ions are discussed in detail. The system is characterised through a variety of analytical techniques to yield sensor calibration data, degradation characteristics, pH sensitivity and suitability as a 'small molecule' drug-carrier.
Download or read book Investigation Into the Growth Mechanisms of Carbon Nanotubes Formed Using Thermal Chemical Vapour Deposition written by William Murray Whyte and published by . This book was released on 2011 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Hybrid Nanomaterials written by Rafael Vargas-Bernal and published by BoD – Books on Demand. This book was released on 2020-06-10 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two of the hottest research topics today are hybrid nanomaterials and flexible electronics. As such, this book covers both topics with chapters written by experts from across the globe. Chapters address hybrid nanomaterials, electronic transport in black phosphorus, three-dimensional nanocarbon hybrids, hybrid ion exchangers, pressure-sensitive adhesives for flexible electronics, simulation and modeling of transistors, smart manufacturing technologies, and inorganic semiconductors.
Download or read book New Approaches to Scaled up Carbon Nanotube Synthesis and Nanotube based Metal Composites and Sensors written by Amit Goyal and published by . This book was released on 2007 with total page 255 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first phase of the work presented in this dissertation is the development of a scaleable process for the cost-effective synthesis of single walled carbon nanotubes (SWNTs) by thermally-induced catalytic chemical vapor deposition (CVD). With the goal of understanding the growth mechanism and optimize the synthesis process, the effect of CVD and catalyst parameters on nanotube formation was investigated in detail. It was found that nucleation and growth of SWNTs occurred within a few seconds of the introduction of the carbon source, carbon monoxide, at temperatures above 675°C over a Co-Mo/MgO catalyst/support system, resulting in the formation of high quality thinly bundled SWNTs with a narrow individual nanotube diameter distribution. A simple kinetic model is proposed to explain the observed growth and exit gas (CO2) concentration data. A scaled up run using fluidized bed reactor is performed to demonstrate large SWNTs production. In the second phase of the research performed some of the CVD parameters optimized for the synthesis of pure nanotubes were used to infiltrate SWNTs as well as multiwalled carbon nanotubes (MWNTs) into catalyst precursor filled iron and aluminum matrices, respectively, to directly fabricate metal-nanotube composites. Two carbon sources, carbon monoxide and acetylene were used for the synthesis of SWNTs and MWNTs, respectively. The yield strength of iron-carbon nanotube composites showed substantial enhancement of up to 45% and 36 % with 1 wt % of infiltrated SWNTs and MWNTs, respectively, relative to that of similarly treated pure iron samples of the same piece density without carbon nanotubes. Vickers hardness measurements showed an increase of 74% and 96% for iron composites filled with SWNTs and MWNTs, respectively. The use of a mixed feed of CO and acetylene resulted in carbide-free fabrication of the nanocomposites. A reaction mechanism supporting the observed carbide-free growth is also presented. In the third phase of the research performed, a SWNT fabrication protocol using CVD growth or electrophoretic deposition was employed for integrating nanotubes as biosensor and chemical gas sensor probes. For biosensor probes, vertically aligned SWNTs were grown or deposited on metal interconnects (Cr/Co), at precise locations, which were patterned on quartz substrates using photo- and e-beam Iithogrpahy to make electrical connections to each SWNT/bundle individually. Gas sensor probes were fabricated using individually suspended SWNTs contacted by Cr/Au pads as source and drain field effect transistor components for the monitoring of NO2 vapors. The adsorption of an electron donating gas such as NO2 on the SWNT sidewalls shifts the Fermi level of the p-type semiconducting nanotubes, consequently changing their electrical conductivity. Experimental results showed that sensor response to NO2 (at 10-300 ppm levels) was of the order of a few seconds at 100 ppm, and was reversible and reproducible. Recovery of the sensor response was achieved by heating the sensors at 120 °C for a period of 10-12 hours indicating physisorption of the NO2 molecules on the nanotube sidewalls.
Download or read book Carbon Nanotubes for Interconnects written by Aida Todri-Sanial and published by Springer. This book was released on 2016-07-09 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a single-source reference on the use of carbon nanotubes (CNTs) as interconnect material for horizontal, on-chip and 3D interconnects. The authors demonstrate the uses of bundles of CNTs, as innovative conducting material to fabricate interconnect through-silicon vias (TSVs), in order to improve the performance, reliability and integration of 3D integrated circuits (ICs). This book will be first to provide a coherent overview of exploiting carbon nanotubes for 3D interconnects covering aspects from processing, modeling, simulation, characterization and applications. Coverage also includes a thorough presentation of the application of CNTs as horizontal on-chip interconnects which can potentially revolutionize the nanoelectronics industry. This book is a must-read for anyone interested in the state-of-the-art on exploiting carbon nanotubes for interconnects for both 2D and 3D integrated circuits.
Download or read book Carbon Nanotubes and Related Structures written by Dirk M. Guldi and published by John Wiley & Sons. This book was released on 2010-01-26 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by the most prominent experts and pioneers in the field, this ready reference combines fundamental research, recent breakthroughs and real-life applications in one well-organized treatise. As such, both newcomers and established researchers will find here a wide range of current methods for producing and characterizing carbon nanotubes using imaging as well as spectroscopic techniques. One major part of this thorough overview is devoted to the controlled chemical functionalization of carbon nanotubes, covering intriguing applications in photovoltaics, organic electronics and materials design. The latest research on novel carbon-derived structures, such as graphene, nanoonions and carbon pea pods, round off the book.
Download or read book Wafer scale Alignment of Semiconducting Carbon Nanotubes from Solution written by Katherine Rose Jinkins and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon nanotubes are unique one-dimensional materials that exhibit extraordinary properties, including high stability, large elastic modulus, and exceptional charge and thermal transport, making them promising candidates for future mechanical, optical, and electronic devices. Electrical measurements of individual nanotubes have demonstrated room-temperature ballistic conductance and 3× higher current density than state-of-the-art Si field-effect transistors (FETs). While these results are exciting; to achieve the high on-current required for future carbon nanotube technologies to become viable, electronic devices must incorporate multiple nanotubes aligned in parallel. Alignment is especially critical to minimize sheet resistance and reduce charge carrier scattering in devices. However, the alignment of carbon nanotubes at intermediate packing densities in a scalable technique has plagued the electronics community for decades. In this work, we develop, explore, and elucidate three possible solutions to this long-standing challenge. First, we elucidate the mechanism of the floating evaporative self-assembly (FESA) technique, in which stripes of aligned nanotubes are deposited onto substrates by dosing a carbon nanotube ink at a water/substrate interface. We track the key interfaces directly at the substrate during FESA and show that the nanotube alignment occurs from the buried ink/water interface. We also demonstrate improved control over the bandwidth and band spacing of aligned carbon nanotubes and align nanotubes across a 2.5 × 2.5 cm2 substrate, an important step towards high-volume production. Ultimately, though, FESA cannot yield uniform, continuous films of aligned nanotubes over the wafer-scale, so other techniques are explored. We use the understanding gained toward the FESA mechanism to develop another alignment technique, tangential flow interfacial self-assembly (TaFISA), to fabricate uniform films of highly aligned carbon nanotubes for short channel FETs. In this process, we demonstrate that an ink/water interface can induce liquid crystal assembly of carbon nanotubes. Flowing this two-dimensional nematic assembly of nanotubes, globally aligns the nanotubes. By translating a substrate through this flowing ink/water interface, uniform films of highly aligned (within ±5.7°) nanotubes are deposited across 10 cm wide substrates. Due to the underlying lyotropic liquid crystal phenomena, the nanotube ordering improves with increasing concentration and decreasing temperature. The exceptional alignment leads to excellent FET performance with high on-state current density averaging 520 [mu]A [mu]m−1 at a V[DS] of -0.6 V. We also perform a more detailed investigation of experimental parameters that can affect the interfacial assembly, including nanotube ink solvent, substrate surface water contact angle, and modification of the water subphase. We also study the effect of shear on nanotube ink, without the ink/water interface as used in the FESA and TaFISA technique. We elucidate the effect of shear rate on nanotube alignment and find that the alignment increases with increasing shear rate following a power law dependence. We also demonstrate control over the nanotube packing density by tailoring the carbon nanotube ink concentration and ink volume. FETs are fabricated with their charge transport direction parallel and perpendicular to the alignment. The parallel FETs exhibit 7× faster charge carrier mobility of 101 cm2 V−1 s−1, while also simultaneously displaying high on/off ratio of 105. Deposition conditions are extensively optimized to enable alignment within a ± 27° window at nearly ideal packing density of 50 nanotubes [mu]m−1 over large-area 10 × 10 cm2 substrates. These quasi-aligned films are promising candidates for long-channel FETs (e.g., in displays, sensors, and flexible electronics), where some misalignment is necessary to allow charge percolation. We additionally report our work utilizing solution-based shear to fabricate ultrathin films of aligned cellulose nanocrystals. Cellulose nanocrystals (CNC) exhibit excellent mechanical and piezoelectric properties, making this material attractive for use in high-performance coatings. Toward this goal, we use confined shear-based alignment to fabricate ultrathin films of aligned CNC. The shear rate is varied from 19 to 19000 s−1 to improve the half-width at half-maximum of the spread in CNC alignment from 130 to 30°. The CNC solution volume and concentration are both used to independently control the film height.
Download or read book Growth and Electrical Properties of Chemical Vapour Deposited Low Dimensional Sp2 Carbons written by Yee Yuan Tan and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the growth of Sp2 carbon materials - namely graphene and carbon nanotube (CNT) materials using a chemical vapour deposition (CVD) process. A novel CVD process tool based on a photothermal process (PT-CVD) that differs from standard thermal CVD has been developed. This thesis reports the investigations into the properties of the deposited carbon nanomaterials and applications that exploit their electronic properties. The first investigation is into the growth of vertically aligned MWCNT forests. Growth of CNTs at 370°C by a one-step PT-CVD method was demonstrated. The growth rate can reach ~ 1.3 um/min, which is faster than most other reported thermal CVD methods. The use of bimetallic catalyst (Fe/Ti) and the use of rapid thermal process are the keys to this process. AFM topography studies showed that the fast top-down heating mode of the PT-CVD leads to the formation of a Fe/Ti uniform solid solution, which is believed to improve the CNT growth. These CNTs are composed of a few layer crystalline graphene sheets with a 5-6 nm diameter. Raman scattering provides supporting evidence that the as-grown CNTs are of high quality, better than some CNTs grown at higher temperatures by traditional CVD methods. CVD growth of graphene was investigated using Cu foils as substrate, with the field- effect in the graphene subsequently demonstrated by transferring it to a back-gate bottom contact transistor arrangement using poly-4-vinyl-phenol gate dielectric as an alternative to oxide based insulators. This graphene transistor showed a simple, inexpensive fabrication method that is completely compatible to large scale fabrication of organic devices, to demonstrate a field effect hole mobility of 37 cm2/ Vs. Despite the mobility being lower than that found in exfoliated graphene, it demonstrates the potential of a graphene based all carbon transistor for large area electronics. The fabrication and electrical performance of a 3 terminal graphene device is further reported. This device displayed characteristics similar to a p-type graphene FET. While past investigations of distortion and saturation in transfer characteristics of graphene FET indicated that metal-graphene interaction may be the controlling mechanism, this device operation is based on the design of transferring graphene onto a Diamond-like- carbon DLC/p-Si heterostructure with Si as the back contact and with the DLC acting as the dielectric support in contact to graphene. Thus, this provided a mechanism for the DLC/p-Si heterojunction to moderate the I-V characteristics of this device, resulting in a p-type only conduction process in graphene that is also saturable. Following the work on using conventional thermal CVD (T-CVD) for graphene growth, we demonstrated the possibility of using the PT-CVD to develop a graphene growth process. It is found that the non-thermal equilibrium nature of PT -CVD process resulted in a much shorter duration in both heating up and cooling down, thus allows the reduction of the overall growth time for graphene. The choice of performing growth on Ni also allows for the alleviation of hydrogen blister damage that is commonly encountered during growth on Cu substrates. To characterize the film's electrical and optical properties, pristine PT -CVD grown graphene was used as the transparent electrode material in an organic photovoltaic devices (OPV) and is found to be comparable to that reported using pristine graphene prepared by conventional CVD.
Download or read book On the Synthesis of Carbon Nanotubes from Waste Solid Hydrocarbons written by Chuanwei Zhuo and published by . This book was released on 2014 with total page 353 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. They consist of coaxial tubular graphene sheets, with diameters in the order of nanometers (1 × 10−9 m) and lengths in the order of micrometers (1 × 10−6 m). The latter can now be extended into the order of meters. Carbon nanotubes (CNTs) have been studied for more than 20 years. CNTs possess superior electrical, mechanical, thermal, chemical, and structural properties, which make their potential applications nowadays overwhelmingly widespread. Now entering into the growth phase of product life cycle, increasing usage of CNTs in commercial products is part of the beginning of the nano-technological revolution. Expanding markets for CNTs' large volume applications place ever-increasing demands on lowering their production costs to the level acceptable by the end-user applications. It is estimated that the mass application of CNTs will be facilitated only when the price of CNTs approaches that of conductive carbon black. The synthesis of CNTs involves three elements: the carbonaceous feedstocks (raw materials), the catalysts, and the necessary process power consumption. Therefore, they jointly contribute to the major operation expenditures in CNT synthesis/production. Current technologies for large-scale production of CNTs (either chemical vapor deposition, CVD, or combustion synthesis) require intensive consumption of premium feedstocks and catalysts, and the CVD process requires high energy consumption. Therefore, there is a pressing need for resource-benign and energy-benign, cost-effective nano-manufacturing processes. In the search for sustainable alternatives, it would be prudent to explore renewable and/or replenishable low-cost feedstocks, such as those found in municipal, industrial, and agricultural recycling streams. In the search for low cost catalysts, stainless steels have been proposed as cost-effective dual purpose substrates and catalysts, as they contain transition metals (iron, nickel, etc.) which are well-documented to be effective catalysts for CNT growth. In this doctoral dissertation, the feasibility of utilizing municipal / industrial / agriculture wastes as carbon sources for CNTs has been examined and proven. It was also found that the effluents of the CNT synthesis process can also serve as gaseous fuels for "clean" power production, which can then be used for energy self-sustaining CNT synthesis. Besides, a facile catalyst pre-treatment has been developed to activate stainless steel based substrate/catalyst for efficient CNT growth. Finally, the efforts of CO2 on the pyrolyzate gases and on the CNT co-generation were also investigated.
Download or read book Synthesis of Carbon Nanotubes by Chemical Vapor Deposition and Processing of Epoxy Nanocomposites written by and published by . This book was released on 2006 with total page 399 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon nanotubes (CNT) constitute a new class of materials discovered in 1991 by Sumio Iijima that present unusual mechanical, electrical and thermal properties. Chemical Vapor Deposition (CVD) is the most promising synthesis route for producing large quantities of carbon nanotubes at a low cost. The first part of this thesis focuses on surface synthesis of high purity aligned carbon nanotubes using the CVD technique. High purity single wall and multi wall carbon nanotubes were grown using different substrates and catalysts. The substrates include non porous silicon substrates, porous silicon substrates, stainless steel substrates, stainless steel wires, and silicon cantilevers. The catalysts include molybdenum supported cobalt and alumina supported iron liquid catalysts, and iron and molybdenum catalysts deposited using e-beam evaporation and photolithographic techniques. Vertically aligned single wall and multi wall carbon nanotube forests were grown using the Easy Tube nanofurnace based on the CVD mechanism. The maximum length of the nanotubes grown was almost one millimeter and the diameters ranged from 1 to 100 nanometers. The nanotubes have a large surface area to volume ratio and a high electrochemical sensitivity. These properties may be useful for many applications such as reinforcing polymer composites, drug delivery, biomedical implants, neural imaging, development of biosensors for cancer detection, and other medical applications such as sensing and treating disorders like Epilepsy, Parkinson's disease, and Alzheimer's disease. Since nanotubes are proposed to be used for many biomedical applications, it becomes very important to understand the hazards of nanotubes and nanotechnology. Hence this thesis also presents a short overview of the toxicity of nanotubes. Carbon nanotube and nanofiber reinforced polymer composites have received tremendous amount of attention due to their interesting mechanical, electrical and thermal properties and potential applications. These composites potentially offer high stiffness, high strength, low electrical resistivity, dimensional stability, and light weight. Harnessing the unique physical properties of carbon nanostructures in materials applications has yet to be fully realized. The second part of this thesis mainly deals with improving the properties of composites using carbon nanofibers as fillers in an epoxy matrix. The single most important factor influencing use of carbon nanofibers as reinforcing fibers in polymer composites is their ability to effectively transfer the applied load in the matrix. The effective utilization of nanofibers in composites for structural applications depends strongly on the ability to disperse the nanofibers homogeneously in the matrix without damaging them. To be successfully used for enhancing the properties of composites, good interfacial bonding is required to achieve load transfer across the nanofiber-polymer interface. Hence, two main problems which arise in improving the properties are poor dispersion of the fibers in the composite and weak bonding between fibers and the matrix. These problems are attacked in this thesis by mechanical and chemical means. Solvent free functionalization, controlled sonication, high speed shear mixing at elevated temperatures, and high pressure casting are used to exfoliate the nanofibers in the epoxy. Pyrograf and CleanTech carbon nanofibers, which are similar to large diameter multi-wall carbon nanotubes, were used as filler materials in processing of composites. Incorporating 5 percentage by weight Pyrograf carbon nanofibers resulted in improvement of stiffness of the composite by about 45 percentage by weight and incorporating 5 percentage by weight CleanTech carbon nanofibers resulted in improvement of stiffness of the composite by 20 percentage by weight when compared to plain epoxy with out any nanofibers.
Download or read book Carbon Nanotube Synthesis for Microsystems Applications written by Erik Oscar Sunden and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Modern day engineering systems research presently lacks techniques to exploit the unique properties of many nanomaterials; coupled with this challenge exists the need to interface these nanomaterials with microscale and macroscale platforms. A nanomaterial of particular interest is the carbon nanotube (CNT), due to its enhanced physical properties. In addition to varied electrical properties, the CNT has demonstrated high thermal conductivity and tensile strength compared to conventional fiber materials. CNTs are beginning to see commercial applications in areas in which sufficient study has been dedicated. While a large part of the worldwide focus of CNT research has been in synthesis, an equally important area of research lies in CNT integration processes. The unique and useful properties of many nanostructured materials will never be realized in mainstream manufacturing processes and commercial applications without the proper exploration of integration methods such as those detailed in this thesis. The primary motivation for the research detailed in this thesis has been to develop CNT synthesis processing techniques that allow for novel interfacing methods between carbon nanotubes and eventual applications. In this study, an investigation was performed to look at several approaches to integrating CNTs into micro-electromechanical systems (MEMS). Synthesis of CNTs was studied in two different settings. Synthesis was first performed, directly on the microsystem, via a global scale chemical vapor deposition (CVD) process. Secondly, synthesis was performed directly onto a microsystem device via localized resistive heating. Following synthesis, the application of atomically layered, protective coatings was then investigated. Integration methods were then investigated to allow for CNT transfer to microsystem applications incapable of withstanding synthesis temperatures. The developed integration methods were evaluated by creating functional microscale electrical circuits in flexible substrates via hot emboss imprint lithography. Lastly, post synthesis processing methods were used to create micropatterned cell guidance substrates as well as neuronal stimulating substrates.
Download or read book Carbon Nanotubes written by Charan Masarapu and published by ProQuest. This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation covers several diverse and novel aspects of carbon nanotubes (CNTs) related to synthesis, properties and perspective applications in devices. Growth of CNTs on electrically conductive substrates is promising for many applications. However, the lack of complete knowledge of the substrate effects on the CNT growth poses many technical challenges. The mechanism for the growth of aligned multiwall carbon nanotubes (MWNTs) directly on chemically treated stainless steel (type 304) using a chemical vapor deposition process (CVD) is unveiled through detailed X-ray photoelectron spectroscopy (XPS) analysis. It is found that the CNTs prefer to grow on the enriched surface of iron oxides obtained by the chemical treatment rather than on the passive chromium oxide films generally present on the surface of the as-received stainless steel substrates. According to the XPS peak fitting results, to obtain high density aligned MWNTs, the ratio of iron oxide to chromium oxide on the surface of stainless steel should be much greater than one. Based on this growth mechanism, for the first time, site selective MWNT synthesis on stainless substrate is demonstrated. This kind of controlled CNT growth on conducting substrate results in very promising, diverse applications of CNTs in futuristic nanodevices. Understanding the physical properties of MWNTs, such as the specific heat at low temperature, leads to developing more efficient CNT based temperature sensors and thermal devices. In this regard, the specific heat of an aligned bulk MWNT sample peeled from SiO 2 substrate is measured from 300 K to 1.8 K. The dimensional behavior of the specific heat curve at different temperature ranges is accurately analyzed. Interestingly, a T 2 dependence of the specific heat is observed below 5 K, suggesting a nuclear hyperfine component pertaining to the Schottky effect. This effect arises from the magnetic impurities in the MWNTs, whose presence is confirmed by thermogravimetric analysis and microscopy observations. The final goal of synthesizing the CNTs is for a purposeful application, where the properties of the CNTs can be effectively utilized. CNTs are excellent field emitters and have good high temperature stability. A field emission diode for high temperature operation with aligned MWNTs synthesized on SiO 2 substrate is demonstrated for the first time. The diode showed stable performance from 25 °C all the way up to 300 °C, without any significant change in the diode parameters both in the forward and reverse bias. Such kind of diode is very useful in electronic devices employed in extreme temperature environments for down-hole drilling, seismographic and space applications. CNTs have attracted a lot of attention as electrode materials in electrochemical energy storage devices due to their porous structure and high surface area. The success of the aligned MWNT synthesis directly on the conducting substrate stainless steel provided the opportunity to test the MWNTs as anode material in rechargeable lithium ion battery. The assembled cell showed amazing performance at a high charge-discharge rate (1C rate) with a marked increase in the specific capacitance with continuous charge-discharge cycling. The increase in the specific capacitance with cycling is attributed to the combined effect of the gradual MWNT structural changes and the contribution of the stainless steel substrate which is actually acting as a current collector in Li ion intercalation process. An increase in the specific capacitance with cycling means the lifetime of the battery increases with usage which is extraordinary for any electronic device powered by rechargeable lithium ion batteries. Electrochemical power sources that offer high energy and power densities and can also withstand a harsh temperature environment have become extremely desirable in applications ranging from hybrid electric vehicles to military weapons. In this regard, a supercapacitor coin cell with singlewall carbon nanotube (SWNT) film electrodes and polypropylene carbonate organic electrolyte is assembled and tested in the temperature range from 25 °C to 100 °C. Repeated electrochemical measurements - cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge discharge, performed at 25 °C and 100 °C with continuous heating and cooling showed very consistent performance without any cell degradation. Cyclic voltammograms displayed ideal capacitive behavior even at a significant scan rate of 1000 mV/s at 25 °C and 100 °C. The ability of the cell to undergo several tens of thousands of galvanostatic charge-discharge cycles at 100 °C and still work normally when cooled back to 25 °C is highly exceptional. Also, the cell is able to withstand current densities as high as 100 A/g during the galvanostatic charge-discharge yielding eminent power densities. The charge-discharge study at 25 °C with a current density of 20 A/g up to 264700 cycles showed excellent capacitance stability. The usage of such a supercapacitor potentially enables far-reaching advances in back-up energy storage and high pulse power applications. (Abstract shortened by UMI.).
Download or read book Growth of Carbon Nanotubes on Patterned Silicon Wafer by Thermal Chemical Vapor Deposition CVD written by Chiu-Hui Wang and published by . This book was released on 2005 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since Iijima discovered carbon nanotubes in 1991, its excellent mechanical, chemical, and other properties attract many scientists do related researches. In order to apply it into different fields successfully, how to grow up uniformed and quality carbon nanotubes become an important issue. In this thesis, carbon nanotubes are grown up on the patterned silicon wafer by thermal chemical vapor deposition. Adjust the processing conditions which include temperature, gas flow, catalyst thickness and time in each experiment to find out the better recipe for growing carbon nanotubes. The Scanning electron microscopy (SEM) and atomic force microscope (AFM) images present the best conditions in this experiment are: 700°C reaction temperature, 10 minutes pretreatment, less than 6 nm catalyst thickness, and short reaction time.
Download or read book Synthesis of Carbon Nanotubes by Catalytic Chemical Vapor Deposition written by GuiPing Dai and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: As a new carbon material in the twenty-first century, carbon nanotubes (CNTs) have excellent optical, electrical, magnetic, thermal, chemical, and mechanical properties. There are many synthesis methods to produce CNTs. Compared with other methods, chemical vapor deposition (CVD) is the most effective method that has broad prospects for large-scale control of CNTs in recent years due to its simple equipment, simple operation, and lower cost. In order to gain a comprehensive understanding of the controlling parameters about the formation of CNTs, this chapter reviews the latest progress in the preparation of CNTs by CVD from three of the most important influencing factors: carbon sources, catalysts, and substrates. Among them, the catalyst is the most influential factor for the morphology, structure, and properties of CNTs. It should be pointed out that many growth factors can control the particle size distribution, composition, and structure of the catalysts, such as catalyst substrate, metal transition components added, calcination temperature, etc.
