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1
Wiley, Benjamin J. "Synthesis of silver nanostructures with controlled shapes and properties /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9923.
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Jin, Kewang. "Fabrication and characterization of 1D oxide nanostructures /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20JIN.
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Akinyeye, Richard Odunayo. "Nanostructured polypyrrole impedimetric sensors for anthropogenic organic pollutants." Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5301_1248150815.
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The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.
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Srivastava, Devesh. "Fabrication of nanostructures and nanostructure based interfaces for biosensor application." Diss., Connect to online resource - MSU authorized users, 2008.
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Bude, Romain. "Synthèses et caractérisations de matériaux thermoélectriques nanostructurés." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC032/document.
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Les marchés de la thermoélectricité sont en pleine expansion avec l’intérêt croissant pour la récupération d’énergie thermique ou encore pour la gestion de la température de composants électroniques. En dépit de ses nombreux avantages, le développement de cette technologie est freiné par les performances des matériaux. Une voie d’amélioration identifiée est leur nanostructuration afin d’en diminuer la conductivité thermique de réseau.Dans ce travail de thèse, cette voie est appliquée au tellurure de bismuth, matériau connu pour posséder les meilleures performances autour de la température ambiante. Les matériaux sont obtenus par synthèse de nanoparticules en solution avant d’être mis en forme par pressage à chaud.Une première étude est réalisée sur la recherche d’un optimum de la taille de grain dans le massif. On montre que le contrôle des conditions de synthèse permet le contrôle des dimensions des nanoparticules. Par ailleurs, les analyses structurales et fonctionnelles des massifs après densification montrent que la variation de la taille initiale des particules permet le contrôle de la microstructure et des propriétés detransport des massifs.Une seconde étude porte sur la recherche d’un optimum en composition des matériaux Bi2Te3-xSex. Les analyses morphologiques mettent en évidence une structure complexe et particulière, laissant apparaitre la présence de trois phases dans les massifs.Les matériaux obtenus par cette méthode de synthèse possèdent a priori des propriétés de transport anisotropes. La caractérisation de leurs performances thermoélectriques est donc difficile. Plusieurs techniques de caractérisation sont mises en oeuvre afin de mieux connaitre leurs conductivités thermiques. Celles-ci sont faibles, ce qui montre l’intérêt de l’approche. Toutefois, leur conductivité électrique est plus basse que leurs homologues obtenus par des techniques plus conventionnelles. On montre néanmoins que l’optimisation des conditions de synthèse des particules entrant dans la composition des massifs alliés permet d’améliorer leurs propriétés électriques et donc leurs performances thermoélectriquesThe global thermoelectric markets are in expansion with a growing interest for the energy harvesting or the thermal management of electronic components. Despite numerous advantages, this technology development is limited by the materials performances. A way to improve them is to use nanostructures in order to decrease the lattice thermal conductivity.In this work, this approach is applied to bismuth telluride, material well known for its high performance around room temperature. Materials are obtained from solution synthesis of nanoparticles before hot press compaction.A first study focuses on the determination of an optimal grain size in the bulk materials. It is shown that control over the synthesis parameters allows control on the size of nanoparticles.Moreover, structural and physical analyses on the bulks after sintering show that the change of thesynthesis parameters allows control over the microstructure and thermoelectric properties of the bulks.A second study is based on the study of an optimal composition of Bi2Te3-xSex materials. Morphological analysis show a specific and complex structure with three phases in the bulks.It is postulated that these materials should have anisotropic transport properties. Consequently, their characterizations are difficult. Different characterization techniques are used in order to have a better understanding of their thermal conductivities. Thermal conductivity of the bulks is found low which confirm the interest of this approach. However the electrical conductivity is lower than the one of the materials obtained by more conventional methods. We show that the synthesis parameters of the particles can be optimized to increase the thermoelectric performances of the bulk materials
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Kulkarni, Dhaval Deepak. "Interface properties of carbon nanostructures and nanocomposite materials." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49092.
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Two different interfaces were the focus of study: 1) the interface between disordered amorphous carbon and inorganic materials (metal nanostructures and silicon), and 2) the interface between partially ordered graphene (graphene oxide) and synthetic polymer matrix. Specifically, the uniqueness of this study can be summarized through the following novel findings, fabrication processes, and characterization techniques:
• A simple and efficient process for faster, greener, less-expensive, and highly localized transformation of amorphous carbon nanostructures into graphitic nanostructures using low temperature heat and light treatments was developed for the fabrication of low-resistance interfaces between carbon nanomaterials and inorganic metal surfaces.
• A new protocol for high resolution mapping the charge distribution and electronic properties of nanoscale chemically heterogeneous domains on non-homogeneous surfaces such as graphene oxide was established.
• High strength laminated mechanical nanocomposites based on high interfacial stress transfer between polymer matrices and large area, flat, and non-wrinkled graphene oxide sheets were suggested and demonstrated.
• Scanning Thermal Twist Microscopy – a thermal microscopy based technique was developed and demonstrated for characterizing the thermal properties of homogeneous and heterogeneous interfaces with nanoscale spatial resolution and high thermal sensitivity unachievable using traditional techniques.
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Botos, Ákos. "Inorganic materials in hollow carbon nanostructures." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31915/.
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The interactions of metal-containing molecules and nanoparticles (NPs) with the interior of hollow graphitic carbon nanostructures (CNs) were investigated and their chemical transformations in the nanoscale channels of CNs appraised. The gas phase insertion of Group VI metal hexacarbonyl complexes (M(CO)6, M=Cr, Mo, W) into CNs was successfully developed and optimised to provide good filling rates as confirmed by transition electron microscopy (TEM). Infrared (IR) and Raman spectroscopy demonstrated that Group VI M(CO)6 complexes with greater polarisability exhibit stronger van der Waals interactions with the interior of single walled carbon nanotubes (SWNTs). The synthesis of metal based NPs inside graphitised carbon nanofibers (GNFs) by the in situ transformation of the encapsulated M(CO)6 precursor molecules was successfully achieved and it was demonstrated that GNFs can act as a source of oxygen in these reactions. The nanotube filling methodology was applied for the multi-step synthesis of new inorganic materials inside CNs by the controlled reactions of M(CO)6, I2 and H2S. This approach yielded unusual van der Waals hybrid materials such as “tube inside a tube” and other hybrid structures of MoS2 and GNFs. In SWNTs, with significantly narrower diameters than GNFs or multi-walled carbon nanotubes (MWNTs), metal complexes form unique 1D arrays of octahedral [M6I14]2- clusters with the nanotube acting as a nanocontainer and a poly-cation balancing the charge of the guest-clusters. The iodides of Mo and W were effectively converted into extremely thin MS2 nanoribbons (NRs) within SWNTs, providing a new more efficient route to the hybrid inorganic nanostructures. In MWNTs, the [Mo6Ii8Ia2Ia a4/2] clusters are packed in a hexagonal pattern to optimise filling of the void, and when reacted with H2S they provide a range of multi-layered MS2NRs with their widths controlled by the internal diameter of the host nanotube.
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Ganash, Entesar. "Modelling nanostructures with circularly birefringent materials." Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5815/.
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In this work, we have modelled multilayer magneto-photonic nanostructures in one dimension which display circular birefringence. Starting from Maxwell's equations, we have derived the 4 × 4 transfer matrix for these media. This is used to calculate optical and magneto-optical properties when the structure is deposited on an isotropic transparent substrate. For a transparent substrate it is important to include the effect of multiple incoherent back reflections in the substrate; therefore, the calculations were adapted to consider such reflections for both thick finite isotropic and circularly birefringent substrates. The results show the significant contribution of incoherent back reflections on the magneto-optical Kerr effects. We have reanalysed Sato's modulation method including incoherent back reflections in the substrate. We have derived exact and approximate Faraday rotation formulae for a circularly birefringent film on a circularly birefringent substrate; and a circularly birefringent cavity structure.
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Nonnenmann, Stephen Sommers Spanier Jonathan. "Integrated non-planar ferroelectric nanostructures /." Philadelphia, Pa. : Drexel University, 2010. http://hdl.handle.net/1860/3260.
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Langdo, Thomas Andrew 1974. "Selective SiGe nanostructures." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8450.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references (p. 206-215).
Selective epitaxial growth (SEG) of SiGe on patterned SiO2/Si substrates by ultra-high vacuum chemical vapor deposition (UHVCVD) shows promise for the fabrication of novel SiGe microelectronic structures. This work explores selective growth conditions in the SiH2Cl2/SiH4/GeH4/H2 system between 650-850⁰C, without the addition of C12 or HC1, on substrates patterned by both conventional and interferometric lithography. We have achieved several important milestones for the fabrication of vertical MOSFETs by selective growth in 100 nm SiO2 features patterned by interferometric lithography. We have observed excellent selectivity to SiO2 masks with SiH2C12 at 750⁰C, perfect epitaxial Si filling of SiO2 features, the facet morphology during growth, and the effects of n-type doping on selective growth. We have also fabricated extremely sharp p-n diode doping profiles. With the above accomplishments we have demonstrated the feasibility of vertical MOSFET fabrication through selective epitaxial growth. To realize the advantages of advanced MOSFET designs on silicon-on-insulator (SOI) substrates, we have developed a facet-free raised source/drain process utilizing moderate n-type doping of Si selective growth and <110>-oriented vertical SiO2 sidewalls. However, to improve SiO2 spacer dimension fidelity and eliminate Si substrate overetching, a novel SiO2/Si3N4 spacer process was developed. The keys to the SiO2/Si3N4 spacer process are removal of the Si3N4 layer prior to growth and increased Si ELO growth by moderate in situ n-type doping. This process has wide ranging application to both SOI and bulk Si technologies for fabrication of low-resistance contacts in advanced devices.
(cont.) By a combination of interferometric lithography Si/SiO2 substrate patterning and Ge selective epitaxial growth, we have demonstrated threading dislocation blocking at the oxide sidewall which shows promise for dislocation filtering and the fabrication of low defect density Ge on Si for III-V device integration. Defects at the Ge film surface only arise at the merging of epitaxial lateral overgrowth (ELO) fronts from neighboring holes. These results confirm that epitaxial necking can be used to reduce threading dislocation density in any lattice-mismatched systems where dislocations are not parallel to growth directions. Investigation of Ge selective growth in micron-sized SiO2 features by plan-view TEM shows that substrate patterning on the order of microns is insufficient to filter dislocations in a large mismatch system ([epsilon] > 2%). Ge p-i-n photodetectors were selectively grown in micron-sized SiO2/Si features to correlate materials properties with electrical characteristics. For chemical protection and compatibility with Si microelectronics, Ge photodetector regions were capped with a thin n+ Si layer. Photodetectors fabricated on unpatterned substrates demonstrated leakage currents comparable to published results on Ge on Si photodetectors while leakage currents were noticeably degraded in devices grown on patterned substrates.
by Thomas Andrew Langdo.
Ph.D.
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Chang, Sehoon. "Organic/inorganic hybrid nanostructures for chemical plasmonic sensors." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39545.
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The work presented in this dissertation suggests novel design of chemical plasmonic sensors which have been developed based on Localized Surface Plasmon Resonance (LSPR), and Surface-enhanced Raman scattering (SERS) phenomena. The goal of the study is to understand the SERS phenomena for 3D hybrid (organic/inorganic) templates and to design of the templates for trace-level detection of selected chemical analytes relevant to liquid explosives and hazardous chemicals. The key design criteria for the development of the SERS templates are utilizing selective polymeric nanocoatings within cylindrical nanopores for promoting selective adsorption of chemical analyte molecules, maximizing specific surface area, and optimizing concentration of hot spots with efficient light interaction inside nanochannels. The organic/inorganic hybrid templates are optimized through a comprehensive understanding of the LSPR properties of the gold nanoparticles, gold nanorods, interaction of light with highly porous alumina template, and the choice of physical and chemical attributes of the selective coating.
Furthermore, novel method to assemble silver nanoparticles in 3D as the active SERS-active substrate has been demonstrated by uniform, in situ growth of silver nanoparticles from electroless deposited silver seeds excluding any adhesive polymer layer on template. This approach can be the optimal for SERS sensing applications because it is not necessary to separate the Raman bands of the polyelectrolyte binding layer from those of the desired analyte. The fabrication method is an efficient, simple and fast way to assemble nanoparticles into 3D nanostructures.
Addressable Raman markers from silver nanowire crossbars with silver nanoparticles are also introduced and studied. Assembly of silver nanowire crossbar structure is achieved by simple, double-step capillary transfer lithography. The on/off SERS properties can be observed on silver nanowire crossbars with silver nanoparticles depending on the exact location and orientation of decorated silver nanoparticles nearby silver nanowire crossbars.
As an alternative approach for the template-assisted nanostructure design, porous alumina membrane (PAM) can be utilized as a sacrificial template for the fabrication of the nanotube structure. The study seeks to investigate the design aspects of polymeric/inorganic hybrid nanotube structures with plasmonic properties, which can be dynamically tuned by external stimuli such as pH.
This research suggests several different organic/inorganic nanostructure assemblies by various template-assisted techniques. The polymeric/inorganic hybrid nanostructures including SERS property, pH responsive characteristics, and large surface area will enable us to understand and design the novel chemical plasmonic sensors.
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Yiu, Wing-ching James. "Synthesis of one-dimensional tungsten oxide nano-structures by thermal evaporation." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B32047770.
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Marceau, Ross K. W. "Design in light alloys by understanding solute clustering processes during the early stages of age hardening in Al-Cu-Mg alloys." Connect to full text, 2008. http://ses.library.usyd.edu.au/handle/2123/4008.
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Thesis (Ph. D.)--University of Sydney, 2008.Title from title screen (viewed Jan 07, 2009). Includes two published articles co-authored with others. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Australina Key Centre for Microscopy and Microanalysis, Electron Microscope Unit, Faculty of Science. Includes bibliographical references. Also available in print form.
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Schönherr, Piet. "Growth and characterisation of quantum materials nanostructures." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:7dca792e-4236-4d19-aa59-7c9c3cb5d0e4.
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The three key areas of this thesis are crystal synthesis strategies, growth mechanisms, and new types of quantum materials nanowires. The highlights are introduction of a new catalyst (TiO2) for nanowire growth and application to Bi2Se3, Bi2Te3, SnO2, and Ge nanowires; demonstration of step-flow growth, a new growth mechanism, for Bi2Te3 sub-micron belts; and the characterisation of the first quasi-one dimensional topological insulator (orthorhombic Sb-doped Bi2Se3) and topological Dirac semimetal nanowires (Cd3As2). Research into new materials has been one of the driving forces that have contributed to the progress of civilisation from the Bronze Age four thousand years ago to the age of the semiconductor in the 20th century. At the turn to the 21st century novel materials, so-called quantum materials, started to emerge. The fundamental theories for the description of their properties were established at the beginning of the 20th century but expanded significantly during the last three decades based, for example, on a new interpretation of electronic states by topological invariants. Hence, topological insulator (TI) materials such as mercury-telluride are one manifestation of a quantum material. In theory, TIs are characterised by an insulating interior and a surface with spin-momentum locked conduction. In real crystals, however, the bulk can be conducting due to crystal imperfections. Nanowires suppress this bulk contribution inherently by their high surface-to-volume ratio. Additionally, trace impurity elements can be inserted into the crystal to decrease the conductance further. These optimised TI nanowires could provide building blocks for future electronic nanodevices such as transistors and sensors. Initial synthesis efforts using vapour transport techniques and electronic transport studies showed that TI nanowires hold the promise of reduced bulk contribution. This thesis expands the current knowledge on synthesis strategies, crystal growth mechanisms, and new types of quantum materials nanowires. Traditionally, gold catalyst nanoparticles were used to grow TI nanowires. We demonstrate that they are suitable to produce large amounts of nanowires but have undesired side-effects. If a metaloxide catalyst nanoparticle is used instead, quality and even quantity are significantly improved. This synthesis strategy was used to produce a new TI which is built from chains of atoms and not from atomic layers as in case of previously known TIs. The growth of large nanowires with a layered crystal structure leads to step-flowgrowth, an intriguing phenomenon in the growth mechanism: New layers grow on top of previous layers with a single growth frontmoving fromthe root to the tip. These wires are ideal for further electronic characterisation that requires large samples. The nanowire growth of tin-oxide will also be discussed, a side project that arose from my growth studies, which is useful for sensor applications. Under certain conditions it forms tree-like structures in a single synthesis step. All of the aforementioned growth studies are carried out at atmospheric pressure. A separate growth study is carried out in ultra-high vacuum to assess the transferability of the growth process towards the cleanliness requirements of the semiconductor industry. If two quantum materials are joined together, exotic physics may emerge at the interface. One of the goals of TI research is the experimental observation of Majorana fermions, exotic particles which are their ownantiparticles with potential applications in quantum computing that may appear in superconductor/TI hybrid structures. We have synthesised such structures and initial characterisation suggests that the resistivity increases when they are cooled below the critical temperature of the superconductor. Beyond TIs, a new type of quantum material, called a topological Dirac semimetal, opens new realms of exotic physics to be discovered. Nanowires are grownfroma material which has recently been discovered to be a topological Dirac semimetal. Their growth mechanism is characterised and an extremely high electron mobility at room temperature is measured. The contribution of this thesis to the field is summarised in Fig. 1. Its core is the study of the growth mechanism of quantum materials which will be vital for future development of applications and fundamental research.
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Yin, Jinsong. "Self-assembly of ordered nanostructures." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19116.
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Zhang, Jin. "Mechanical behaviours of piezoelectric nanostructures." Thesis, Swansea University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678635.
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The objective of this thesis is to present a modelling and simulation study for the mechanics of PNs with an emphasis placed on the unique features of PNs due to the piezoelectric and small scale effects.
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Lin, Keng-Chu. "NOVEL TITANIA NANOSTRUCTURES FOR PHOTOVOLTAIC APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1372856925.
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Chan, Vanessa Zee-Haye 1973. "Ceramic nanostructures for block copolymers." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9132.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000.Vita.
Includes bibliographical references (leaves 224-234).
The field of nanotechnology has received burgeoning interest in recent years as the characteristic dimensions for many applications (such as integrated circuits and magnetic storage media) become smaller and smaller. In this work, block copolymers are harnessed in order to produce both porous and relief nanostructures. The interest in using these materials is due to the unique morphologies that block copolymers form and the fact that these nanostructures do so by self assembly. With careful selection of the relative volume fraction and phases, nanostructures with highly ordered and complex pore structures with a vast range of different symmetries can be produced; structures that are not attainable by more conventional processing techniques such as lithography. In this thesis, we have produced porous and relief ceramic nanostructures from self-assembling (template free) block copolymer precursors using a one-step, room temperature technique. To accomplish this, a silicon containing block copolymer system was used where upon exposure to an oxidation process the material undergoes two steps 1) the selective removal of the hydrocarbon block and 2) the formation of a ceramic from the inorganic containing block, resulting in nanoporous and nanorelief ceramics. These structures have potential to be used at temperatures far above the T 8 of traditional nanoporous or nanorelief polymers. By choosing the appropriate morphologies and parent block copolymers, 30 nanostructured ceramics with interfacial areas of-40 m2/g, masks for one-step lithography with a density of-5 x 1011 dots/cm2 or templates for the next generation of nanomagnets can be produced. In addition to these applications, it is envisioned that these structures can be used as photonic band gap materials, high temperature membranes and low dielectric constant materials. Specifically, the formation of both nanoporous and nanorelief structures from an ABA triblock copolymer system of poly(pentamethyldisilylstyrene) P(PMDSS) with polyisoprene was studied. The focus of this thesis is on the oxidation of the double gyroid and ''inverse" double gyroid morphologies using either ozone/uv and oxygen plasma techniques. By transmission electron microscopy (TEM) and atomic force microscopy (AFM), it is shown that the PI can be preferentially removed by oxidation resulting in a nanoporous material in the case of the double gyroid morphology and a nanorelief material in the case of the inverse double gyroid morphology. Oxidation of the P(PMDSS) homopolymer was also studied chemically using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier Transform Infra-red Spectroscopy (FTIR), Rutherford Backscattering Spectrometry (RBS) and Forward recoil Spectrometry (FRES) and morphologically by AFM. Through these chemical analysis techniques, it is demonstrated that the ozone + uv and uv only oxidation processes converts thin films of P(PMDSS) to a ceramic, specifically silicon oxycarbide, that is far more stable than the parent homopolymer.
by Vanessa Zee-Haye Chan.
Ph.D.
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Liu, Frank Ph D. Massachusetts Institute of Technology. "Exchange bias in patterned nanostructures." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103268.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 119-127).
Exchange bias between a ferromagnet (FM) and antiferromagnet (AFM), which is utilized to pin the magnetization of a FM into a fixed direction in space, is essential in commonly used electronic components such as magnetic recording heads and magnetic memory cells, as well as novel magnetic logic and memory devices. However, the exchange bias effect has been optimized in materials and used in devices for decades without a good scientific understanding, both due to lack of nanoscale research and conflicted results from differences in fabrication and feature size. In this thesis, we present a special fabrication method that produces exchange bias reliably and consistently. We also show the results of both experimental and simulated investigation of the properties of exchange biased nanostructures such as domain formation, magnetostatic interactions, and response to field-driven switching. -A fabrication method for creating locally exchange biased nanostructures is first developed. By etching back a predeposited FM film, and regrowing a thin FM layer and then the AFM film, this hybrid method combines the benefits of a clean interface produced using subtractive methods and the scalability produced using additive methods. Its consistency is analyzed through vibrating sample magnetometry (VSM) and scanning electron microscopy (SEM). Next, the fabrication method is applied to an array of nanodots with varying ion beam etch durations and dot diameters, demonstrating a reduced exchange bias for small diameters, and no significant change in exchange bias unless the ion beam etch duration exceeded 30s. Based on the consistency of this method, new device-like patterns were fabricated both experimentally and by modeling, in which a grating of AFM stripes was exchange biased with a continuous FM film. Competing magnetic interactions were found in the modeling, and produced extraordinary hysteresis loop shapes in the experimental samples. Next, a grating of AFM stripes was exchange biased with a 900 offset grating of FM stripes using the same fabrication method, which simulates an array of individual magnetic devices. A different set of competing magnetic interactions was found, and the feature sizes of the FM and AFM components were demonstrated to tune these interactions and thus the switching behavior of such devices. Exchange bias of materials with perpendicular magnetic anisotropy (PMA) was attempted by exchange coupling a PMA FM material with an in-plane FM material, which in turn exchange couples with the AFM material. However, the magnitude of the exchange bias was found to be negligible when compared to the coercivity of the PMA material.
by Frank Liu.
Ph. D.
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John, Kannan John Mohanraj <1985>. "Luminophores and Carbon nanostructures: towards new functional materials." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4773/.
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In the scenario of depleting fossil fuels, finding new energy technologies and conserving conventional energy resources have become essential to sustain modern civilization. While renewable energies are on the rise, considerable interest has been turned also to reduce energy consumption of conventional devices and appliances, which are often not yet optimized for this purpose. Modern nanotechnology provides a platform to build such devices by using nanomaterials showing exceptional physico-chemical properties. In particular, carbon materials (fullerenes, carbon nanotubes, graphene etc.), which show high thermal and electrical conductivity, aspect ratio, shear strength and chemical/mechanical resistance, are quite promising for a wide range of applications. However, the problem of solubility often hampers their handling and industrial utilization. These limitations can be mitigated by functionalizing carbon nanostructures, either covalently or non covalently, with organic or inorganic compounds. The exo- and endohedral functionalization of carbon nanotubes (CNTs) with organic/inorganic moieties to produce luminescent materials with desired properties are the main focus of this doctoral work. These hybrids have been thoroughly designed and characterized with chemical, microscopic and photophysical analyses. All the materials based on carbon nanostructures described in this thesis are innovative examples of photoactive and luminescent hybrids, and their morphological and photophysical properties help understanding the nature of interactions between the active units. This may prompt the design and fabrication of new functional materials for applications in the fields of optoelectronics and photovoltaics.
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Tong, Wing-yun. "Organic optoelectronic materials optical properties and 1D nanostructure fabrication /." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38574597.
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Dalmases, Solé Mariona. "Design of novel compositionally controlled hybrid and ternary nanostructures." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/666576.
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The size/shape dependent and unique physical and chemical properties presented by nanostructured materials have attracted great attention in several fields such as energy harvesting, optoelectronics and biomedicine, among others. Even though binary semiconductors have been some of the most studied systems until now, ternary and quaternary semiconductors have started to stand out due to the wide variety of compositions and, as a result, of properties they offer. The importance of hybrid nanomaterials is growing as well: the association of more than one material in the same nanostructure usually allows the preservation or even, the enhancement, of the different properties of the preliminary materials and combines them with the new ones originated from the interaction between the two domains.
This thesis is focused on the design of novel compositionally controlled hybrid and ternary nanostructures based on low toxic materials.
Firstly, a simple procedure at room temperature is reported for the synthesis of hybrid and ternary nanostructures of Ag-Au-Se and Ag-Au-S. The method consists in the reaction between pre-synthesised Ag2Se/Ag2S nanoparticles (NPs) and a Au(III) precursor. The reaction time, the concentration of gold solution, the surfactant nature and the Ag:Au ratio are the four key parameters that allow the control of the final product.
Regarding the Ag-Au-Se system, Au-Ag2Se hybrid nanoparticles (HNPs), Au-Ag3AuSe2 HNPs and Ag3AuSe2 NPs were successfully synthesised. In addition, Au-Ag3AuSe2 HNPs were tested as thermoelectric material, obtaining an improved response in comparison with the binary material (Ag2Se). The potential of Ag3AuSe2 NPs as Computed Tomography contrast agents was also tested, obtaining promising results in this field.
Concerning to the analogous system with sulphur, the higher miscibility of Au and S offers a more complex ternary diagram, with two ternary materials with different stoichiometries: Ag3AuS2 and AgAuS. A gradual transformation of Ag2S to Au2S was achievable by the proposed method, with the possibility of isolating Au-Ag2S HNPs, Au-Ag3AuS2 HNPs, Au-AgAuS HNPs, Au-Au2S HNPs and hollow Au2S NPs.
Secondly, another ternary system was studied: Ag-Cu-S. Even though this system also presents two different ternary materials (Ag3CuS2 and AgCuS), the direct hot injection method proposed here only allows the formation of the AgCuS stoichiometry. Two different mechanisms are reported, depending on the precursor of copper used in the synthesis. The
material was thermoelectrically characterized as well, but without showing a proper performance.
Thirdly, four novel nanostructures based on Cu-Pt-Se are described. They were synthesised by a reaction at high temperature between pre-synthesised Cu2-xSe NPs and a Pt(II) precursor. The nanomaterials were thoroughly structurally and morphologically characterized to study the impact of the Pt:Cu ratio in the final product. The larger the amount of platinum in the structure, the more efficient diffusion of the element occurs through the Cu-Se lattice, with the consequent and slow spell of selenium until its totality.
Finally, hybrophilic hybrid inorganic-organic nanocomposites formed by inorganic NPs (Au, Ag, Ag3AuSe2 i Au@Fe3O4) and a highly fluorescent low molecular weight Au(I) metallogelator are presented. Their coupling is mainly based on aurophilic/metallophilic interactions between atoms in the surface of the NPs and Au(I) atoms from the complex. Additionally, the Ag and Au nanocomposites were characterized by Raman Spectroscopy. It is well known that when a molecule is strongly coupled to a plasmonic nanoparticle, the intensity of the Raman peaks of the molecule are intensified. This phenomenon is known as Surface-Enhanced Raman Spectroscopy (SERS) and could be observed in both materials.
In summary, in this thesis five hybrid and ternary nanostructured systems, based on low toxic materials, have been synthesised, characterized and studied, following the aim of investigate alternative materials, which, in a future, could be applied in energy conversion and biomedicine fields.En els últims anys, els materials ternaris i híbrids han començat a sorgir gràcies al gran ventall de composicions i, per tant, de propietats que ofereixen i que els donen la possibilitat d’aplicar-se en diversos camps, com ara l’emmagatzematge d’energia, l’optoelectrònica o la biomedicina. Aquesta tesis està centrada en el disseny de noves nanoestructures ternàries i híbrides basades en materials amb una toxicitat baixa. En primer lloc, s’ha descrit un procediment simple a temperatura ambient per la síntesi de nanoestructures ternàries i híbrides d’Ag-Au-Se i d’Ag-Au-S que consisteix en la reacció entre nanopartícules d’Ag2Se i Ag2S sintetitzades prèviament i un precursor d’Au(III). El temps de reacció, la concentració del precursor d’or, la naturalesa del tensioactiu i la relació Ag:Au són els quatre paràmetres clau que permeten el control del producte final. Addicionalment, dos compostos del sistema Ag-Au-Se van ser caracteritzats termoelèctricament i com a agents de contrast en tomografia computada. En segon lloc, s’ha estudiat un altre sistema ternari, format per Ag-Cu-S. El mètode d’injecció en calent proposat en aquesta tesi permet la formació del material amb estequiometria AgCuS. El material va ser caracteritzat termoelèctricament, tot i que no mostra resultats satisfactoris degut a la seva baixa conductivitat elèctrica. En tercer lloc, es presenten quatre nanoestructures noves basades en Cu, Pt i Se, sintetitzades mitjançant una reacció a alta temperatura entre NPs de Cu2-xSe sintetitzades prèviament i un precursor de Pt(II). L’impacte de la relació Pt:Cu utilitzada en la síntesi en el producte final va ser estudiada. A mesura que la quantitat de platí augmenta en l’estructura, aquest es va introduint més eficientment en la xarxa cristal·lina del semiconductor de coure i seleni, expulsant gradual i lentament el seleni fins a la totalitat, augmentant així el caràcter metàl·lic de les nanoestructures finals. Finalment, es descriuen uns compostos híbrids hidrofílics, formats a partir de NPs inorgàniques (Au, Ag, Ag3AuSe2 i Au@Fe3O4) i un complex d’Au(I) de baix pes molecular i altament fluorescent. El seu acoblament està basat, essencialment, en interaccions aurofíliques/metal·lofíques entre els àtoms de la superfície de la nanopartícula i els àtoms d’Au(I) del complex.
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Bergman, Kathryn N. "Biomineralization of inorganic nanostructures using protein surfaces." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22674.
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Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Tsukruk, Vladimir; Committee Member: Kalaitzidou, Kyriaki; Committee Member: Valeria Milam.
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Cho, Joungmo. "Computational studies of reacting flows with applications in nanoscale materials synthesis." Amherst, Mass. : University of Massachusetts Amherst, 2009. http://scholarworks.umass.edu/dissertations/AAI3372259/.
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Gu, Hongwei. "Synthesis & application of biofunctional nanostructures /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CHEM%202004%20GU.
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Zhao, Xin. "Field emission study of carbon nanostructures." W&M ScholarWorks, 2006. https://scholarworks.wm.edu/etd/1539623508.
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Recently, carbon nanosheets (CNS), a novel nanostructure, were developed in our laboratory as a field emission source for high emission current. to characterize, understand and improve the field emission properties of CNS, a ultra-high vacuum surface analysis system was customized to conduct relevant experimental research in four distinct areas. The system includes Auger electron spectroscopy (AES), field emission energy spectroscopy (FEES), field emission I-V testing, and thermal desorption spectroscopy (TDS). Firstly, commercial Mo single tips were studied to calibrate the customized system. AES and FEES experiments indicate that a pyramidal nanotip of Ca and O elements formed on the Mo tip surface by field induced surface diffusion. Secondly, field emission I-V testing on CNS indicates that the field emission properties of pristine nanosheets are impacted by adsorbates. For instance, in pristine samples, field emission sources can be built up instantaneously and be characterized by prominent noise levels and significant current variations. However, when CNS are processed via conditioning (run at high current), their emission properties are greatly improved and stabilized. Furthermore, only H2 desorbed from the conditioned CNS, which indicates that only H adsorbates affect emission. Thirdly, the TDS study on nanosheets revealed that the predominant locations of H residing in CNS are sp2 hybridized C on surface and bulk. Fourthly, a fabricating process was developed to coat low work function ZrC on nanosheets for field emission enhancement. The carbide triple-peak in the AES spectra indicated that Zr carbide formed, but oxygen was not completely removed. The Zr(CxOy) coating was dispersed as nanobeads on the CNS surface. Although the work function was reduced, the coated CNS emission properties were not improved due to an increased beta factor. Further analysis suggest that for low emission current (10 uA), thermal, ionic or electronic transition effects may occur, which differently affect the field emission process.
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Anand, Aman Roberts James Andrew. "Studying interactions of gas molecules with nanomaterials loaded in a microwave resonant cavity." [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-4009.
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Yiu, Wing-ching James, and 姚穎貞. "Synthesis of one-dimensional tungsten oxide nano-structures by thermalevaporation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B32047770.
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Smith, Nathan. "Characterisation of zinc oxide nanostructures." Thesis, Swansea University, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678399.
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Yeh, Wei-Ming. "Pattern collapse in lithographic nanostructures: quantifying photoresist nanostructure behavior and novel methods for collapse mitigation." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47696.
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The Microelectronics industry has continuously pushed the limit of critical dimensions to sub-20 nm. One of the challenges is pattern collapse, caused by unbalanced capillary forces during the final rinse and drying process. The use of surfactants offers a convenient method to reduce capillary forces but causes another deformation issue. This thesis work focuses on alternative approaches that are compatible with lithographic processes to mitigate pattern collapse. First, an e-beam lithography pattern with a series of varying line and space widths has been specifically designed in order to quantitatively study pattern collapse behavior. This pattern generates increasing stress in the pairs of resist lines as one moves across the pattern array and eventually a sufficiently small space value (critical space, S1c) is reached in each array such that the stress applied to the resist exceeds the critical stress (σc) required for pattern bending and subsequently feature deformation and collapse occurrs. The patterns we designed allow us to qualitatively and quantitatively study pattern collapse and obtain consistent, reproducible results.
In the first part of the thesis work, a quick surface crosslink (called a reactive rinse) that involves the strengthening of the resist using crosslinking via carbodiimide chemistry while the resist structures are still in their wet state, has been developed and demonstrated. This technique provides efficient and significant improvement on the pattern collapse issue. In the second part of the thesis work, a triethoxysilane compound, vinyl ether silane (VE), has been successfully synthesized. It can be used to modify the silicon or silicon nitride substrates and form a covalent bond with the resist film instead of manipulating the surface energies using common HMDS. Compared to traditional Hexamethyldisilazane (HMDS) vapor primed surfaces, the implementation of the VE adhesion promoter resulted in a significant improvement in the adhesion and resistance to adhesion based pattern collapse failure in small sub-60 nm resist features. In the third part of the thesis work, the effect of drying rates and drying methods has been systematically studied. SEM analysis and critical stress results showed that fast drying appear to reduce the resist collapse. The line pair orientations in each pattern array with respect to the wafer radius reveal an apparent effect of fluid flow and centrifugal forces on collapse. Finally, a comprehensive pattern collapse model that incorporates adhesion based pattern failure and elastoplastic deformation-based failure, and dimensionally dependent resist modulus properties has been developed. This model provides such an excellent prediction of the experimental data and supports the idea that this level of combined adhesion-failure and elastoplastic-failure based pattern collapse modeling, where one explicitly considers the dimensionally dependent mechanical properties of the resist can be quantitatively predictive and useful for understanding the pattern collapse behavior of polymeric nanostructures.
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Musheghyan, Avetisyan Arevik. "Synthesis and characterization of multilayer graphene nanostructures." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667645.
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The goal of the present investigation is to examine the processing-structure-property relationships of multilayer graphene nanowall materials. Various plasma enhanced chemical vapor deposition (PECVD) processing parameters were altered to control the structure and morphology of the material. Growth parameters and substrate material were the major structural features studied, and these were characterized by spectroscopic techniques. The direct synthesis of graphene without catalysis on dielectric substrates, compatible with the complementary metal oxide semiconductor technology, is a stimulating but complex task.
The goal of the thesis has different tasks consisting of:
a) The design and construction of a new inductively coupled plasma remote chemical vapor deposition reactor in the PECVD-FEMAN laboratory of the Universitat de Barcelona.
b) Fabrication of vertical graphene nanostructures at low temperature on different conductive and nonconductive substrates.
c) Characterization of the vertical graphene obtained through different synthesis parameters in order to optimize their physical and surface properties; such as structural and morphological studies by Raman spectroscopy, SEM and TEM.
d) Functionalization of MLGNWs by MnO nanoparticles for hybrid supercapacitor systems.
The thesis consists of the following main parts:
In the first part of the thesis provides a brief introduction of carbon materials, graphene, graphene nanowalls and their history, discovery, outstanding properties and all the technologies that prompted their development during these years until the first application. Moreover, in this section the methods for the synthesis of carbon nanostructures and brief explanation of the fundamentals of each technique explains.
In the second part the concepts and technologies of plasma, plasma enhanced chemical vapor deposition (PECVD) and PECVD related techniques are exposed. In addition, in this section a deposition reactor designed by us are described, where all experiments carried out during this thesis took place. Also, the basics and work principles of different characterization techniques are briefly described. Furthermore, this part discusses the growth mechanism of MLGNWs synthesized by PECVD.
In the third part, which is the main results part, discusses the study of growing material along the entire length of the tube and the importance of sample location inside a tubular quartz reactor. The influence of the substrate material, growth time and growth temperature on the MLGNWs growth process have been examined by field emission scanning electron microscopy (FESEM),
transmission electron microscopy (TEM) and high resolution TEM (HRTEM) techniques. The chemical characteristics of as grown structures were studied by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrometer. The hydrogen and carbon contents in grown samples were determined by elemental analysis (EA). To study the photoluminescent properties of the carbon structure grown in the whole length of the tubular reactor, the room temperature PL spectra were conducted. In addition, the chemical reactions inside the tube under plasma deposition were controlled by optical emission spectroscopy (OES).
Also, in the part of results synthesis and characterization of MLGNWs/CNTs hybrid structure are discussed. The goal of MLGNWs/CNTs hybrid structure is increased chemical activity of CNTs. The morphological and structural characterization was carried out using SEM, High resolution TEM and Raman scattering analysis. Electrochemical properties of transferred MLGNWs/CNTs were studied by CV and charge/discharge measurements.
The last section of the part of the results are exposed information about application of MLGNWs in supercapacitors, in particular, supercapacitive performance of manganese dioxide/ graphene nanowalls electrodes deposited on stainless steel current collectors and annealing temperature effect are discussed. Composite electrodes MLGNWs/MnO2 were characterized by FESEM and Raman shift spectroscopy. The electrochemical properties of the MLGNWs/MnO2 for supercapacitor applications were investigated by cyclic voltammetry (CV), charge/discharge and electrochemical impedance spectroscopy (EIS). The influence of annealing temperature on the electrochemical performance has been studied as well.El grafeno, como material basado en el carbono, es un logro del desarrollo y los avances de la Nanotecnología. La síntesis directa de grafeno sin catálisis sobre sustratos dieléctricos, compatible con la tecnología de los semiconductores complementarios de óxido metálico, es una tarea estimulante pero compleja. La técnica PECVD, permite la síntesis directa de nanoestructuras de carbono a temperaturas más bajas y es el método principal utilizado en esta tesis. El objetivo de esta tesis es la síntesis y optimización de nanoparedes verticales de grafeno y su posible extensión a aplicaciones en sistemas que requieran superficies macroscópicas. Para ello, se han realizado diferentes tareas: a) Se ha diseñado y construido un reactor prototipo con plasma remoto en el laboratorio PECVD-FEMAN de la Facultad de Física (Universidad de Barcelona) con el fin último de crecer grafeno en forma de paredes/tabiques verticales nanométricos mediante la técnica PECVD. b) Se ha desarrollado un proceso PECVD modificado con el fin de mejorar los resultados actuales en términos de: 1) el tiempo de crecimiento, 2) la temperatura, 3) la naturaleza del substrato, 4) la presión, y 5) la cantidad de gas precursor para crecer grafeno vertical. Las muestras obtenidas fueron caracterizadas mediante microscopía TEM, SEM, XPS, XRD y mayormente mediante espectroscopia Raman, con el objetivo de optimizar el proceso y las propiedades físico-químicas y del grafeno vertical. c) Se ha desarrollado una estructura híbrida con nanoparedes y nanotubos de carbono. Para ello, se utilizaron tres equipos: el reactor “PEDRO” para la preparación del substrato, el reactor “CNTs” para el crecimiento de nanotubos de carbono y el reactor ICP-CVD para el crecimiento de nanoparedes de grafeno. En esta tesis se investigaron las caracterizaciones morfológicas y electroquímicas, pero aún se necesitan más estudios para confirmar posibles futuras aplicaciones. d) Para mejorar las propiedades de los supercapacitores basados en los electrodos desarrolladas con nanoparedes de grafeno y acero inoxidable, se ha realizado el crecimiento de capas delgadas de MnO2 mediante el método de electrodeposición. El efecto de la temperatura de recocido (annealing) en las propiedades electroquímicas de las muestras se ha estudiado en el rango de 70° C a 650° C.
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Abdelaaziz, Muftah Ali. "Synthesis of nanocomposites with nano-TiO2 particles and their applications as dental materials." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1534.
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Thesis submitted in fulfilment of the requirements for the degree
Magister of Technology: Dental Technology
In the Faculty of Health and Wellness Sciences
At the Cape Peninsula University of Technology, 2012A study of the modification of dental nanocomposites with nanosized fillers is presented. The incorporation of TiO2 (titania) nanoparticles, via a silane chemical bond, to a standard dental acrylic resin matrix was explored to determine whether there was an increase in the wear resistance, flexural strength and surface hardness properties of the dental nanocomposites. The principal aim of this study was to synthesize dental nanocomposites with different sizes, treated, nano-TiO2 fillers in urethane dimethacrylate (UDMA) for potential application in posterior restoration and to evaluate their mechanical properties. Treatment of the nano-TiO2 particles was carried out with a silane coupling agent, 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), to improve bonding between the nano-TiO2 particles and acrylic matrix (UDMA), and reduce agglomeration of the nano-TiO2. Characterisation of products was carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). TEM results were used to compare the particle size distributions of untreated TiO2 and treated TiO2 under various experimental conditions in an ethanol solvent, while SEM images showed the adhesion between the matrix (UDMA) and the nano-TiO2. FTIR was used to show the qualitative composition of untreated TiO2 and treated TiO2. Eighteen groups of experimental dental nanocomposites were evaluated. Each group contained different average particle sizes of nano-TiO2 (filler): 5 nm, 21 nm and 80 nm. Each particle size category was treated with three different concentrations of the silane, (MPTMS): 2.5, 10 and 30 wt %. Samples were prepared by mixing the monomer resin matrix of UDMA and nano-TiO2 particles. For comparison, a commercially available dental resin was reinforced with untreated and treated nano-TiO2 particle sizes 5, 21 and 80 nm. Wear resistance, flexural strength and surface hardness of TiO2 nanocomposites treated with 2.5 wt % MPTMS were significantly higher compared to those treated with 10 and 30 wt% MPTMS. The nanocomposites with 5 nm TiO2 had higher wear loss, lower flexural strength and lower surface hardness values compared to those with 21 nm and 80 nm TiO2. Statistical analysis showed that the effect of the concentrations of MPTMS on wear resistance and surface hardness of specimens was significant (p<0.001), which is less than 0.05, while the effect of the concentration of MPTMS on flexural strength was statistically not significant, (p=0.02). Control composites reinforced with treated 80 nm TiO2 particles had much better mechanical properties than any of the other specimens. It was concluded that the most available commercial product for dental restorations could be improved by the addition of nano-TiO2 with relatively large particle size.
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Wang, Debin. "Thermochemical nanolithography fabrication and atomic force microscopy characterization of functional nanostructures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34776.
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This thesis presents the development of a novel atomic force microscope (AFM) based nanofabrication technique termed as thermochemical nanolithography (TCNL). TCNL uses a resistively heated AFM cantilever to thermally activate chemical reactions on a surface with nanometer resolution. This technique can be used for fabrication of functional nanostructures that are appealing for various applications in nanofluidics, nanoelectronics, nanophotonics, and biosensing devices.
This thesis research is focused on three main objectives. The first objective is to study the fundamentals of TCNL writing aspects. We have conducted a systematic study of the heat transfer mechanism using finite element analysis modeling, Raman spectroscopy, and local glass transition measurement. In addition, based on thermal kinetics analysis, we have identified several key factors to achieve high resolution fabrication of nanostructures during the TCNL writing process.
The second objective is to demonstrate the use of TCNL on a variety of systems and thermochemical reactions. We show that TCNL can be employed to (1) modify the wettability of a polymer surface at the nanoscale, (2) fabricate nanoscale templates on polymer films for assembling nano-objects, such as proteins and DNA, (3) fabricate conjugated polymer semiconducting nanowires, and (4) reduce graphene oxide with nanometer resolution.
The last objective is to characterize the TCNL nanostructures using AFM based methods, such as friction force microscopy, phase imaging, electric force microscopy, and conductive AFM. We show that they are useful for in situ characterization of nanostructures, which is particularly challenging for conventional macroscopic analytical tools, such as Raman spectroscopy, IR spectroscopy, and fluorescence microscopy.
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Gabriel, Stefanie. "Assessment of Lead Chalcogenide Nanostructures as Possible Thermoelectric Materials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-128413.
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The assembly of nanostructures into “multi”-dimensional materials is one of the main topics occurring in nanoscience today. It is now possible to produce high quality nanostructures reproducibly but for their further application larger structures that are easier to handle are required. Nevertheless during their assembly their nanometer size and accompanying properties must be maintained. This challenge was addressed in this work. Lead chalcogenides have been chosen as an example system because they are expected to offer great opportunities as thermoelectric materials. Three different ways to achieve assemblies of lead chalcogenide nanostructures were used and the resulting structures characterized with respect to their potential application as thermoelectric material.
The first means by which a “multi”-dimensional assembly of lead chalcogenide quantum dots can be produced is the formation of porous structures such as aerogels and xerogels. A procedure, where the addition of an initiator such as oxidizers or incident radiation is unnecessary, is introduced and the formation process studied by absorption spectroscopy. The time-consuming aggregation step could be significantly reduced by employing a slightly elevated temperature during gelation that does not lead to any observable differences within the resulting gel structures. After either supercritical or subcritical drying, highly porous monolithic gel structures can be achieved. During the gel formation the size and the shape of the particles changed and they were directly linked together. Nevertheless the resulting porous structures remain crystalline and size dependent effects of the optical properties could be shown. Gels produced from a mixture of PbS and PbSe QDs show a homogenous distribution of both materials but it is not clear to what extent they form an alloy. Although the particles are directly linked together the resulting porous structures possess a very high resistivity and so it was not possible to characterize the semiconductor aerogels with regard to their thermoelectric properties. To achieve an enhanced conductivity porous structures containing PbS and Au nanoparticles have been produced. As has been seen for the pure semiconductor gels the size of the PbS quantum dots has increased and elongated particles were formed. In contrast to the PbS QDs the Au nanoparticles did not change their size and shape and are unevenly distributed within the PbS network. Through the use of the gold nanoparticles the conductivity could be increased and although the conductivity is still quite small, it was possible to determine Seebeck coefficients near room temperature for a mixed semiconductor-metal gel.
The second means by which QD solids could be formed was by the compaction of the QD building blocks into a material that is still nanostructured. Therefore the synthesis of PbS was optimized to achieve sufficient amounts of PbS quantum dots. The ligands used in the synthesis of the QDs unfortunately act as an insulating layer resulting in QD solids with resistivities as high as 2 Gigaohm. For this reason different surface modification strategies were introduced to minimize the interparticle distance and to increase the coupling between the QDs so as to increase the conductivity of the resulting quantum dot solids. One very promising method was the exchange of the initial ligands by shorter ones that can be destroyed at lower temperatures. By such heat treatments the resistivity could be decreased by up to six orders of magnitude. For the pressing of the quantum dots two different compaction methods (SPS and hydraulic pressing) were compared. While the grain growth within the SPS pressed samples is significantly higher the same densification can be achieved by a cold hydraulic pressing as well as by SPS. The densification could be further increased through the use of preheated PbS QDs due to the destruction of the ligands. Samples which had been surface modified with MPA and subsequently thermally treated show the best results with respect to their thermopower and resistivities. Nevertheless the conductivity of the QD solids is still too high for them to be used as efficient thermoelectric materials.
The final assembly method does not involve QDs but instead with one dimensional nanowires. Therefore a synthesis was developed that enables the formation of PbS nanowires of different diameters and one that is easy up-scalable. By the use of a less reactive sulfur precursor and an additional surfactant the formation of nuclei is significantly retarded and within an annealing time of two hours nanowires can be formed presumably by an oriented attachment mechanism. Single crystalline nanowires with a diameter of 65-105 nm could be achieved with the longest axes of the nanowires being parallel to [100]. The resulting nanowires were used as building blocks for film formation on glass substrates by an easily implemented method that requires no special equipment. To characterize the films with a view to their possible application as a thermoelectric material, surface modifications of the films were performed to improve the charge transfer in the films and the Seebeck coefficients of the resulting films measured. Therefore the previous approach of using MPA was applied and a subsequent thermal treatment demonstrated very promising results. In addition an crosslinking ligand was used for surface treatment that leads to similar results as was observed for the thermally treated MPA approach. Both approaches lead to an order of magnitude decrease in the resistivity and due to the fewer grain boundaries present in the films composed of nanowires as compared to the QD assemblies the conductivity is significantly higher. The Seebeck coefficient measurements show that the thermal treatment only slightly affects the Seebeck coefficients. Therefore a significantly higher power factor could be achieved for the nanowire films than for the QD solids.
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Milana, Silvia. "Light interaction with graphene, related materials and plasmonic nanostructures." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708643.
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Fletcher, Dean. "Synthesis of dispersible nanostructures using anti-sintering cast materials." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8591/.
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At the elevated temperatures required for metal carbide synthesis, atomic diffusion across particle boundaries can occur, resulting in the fusion of smaller particles into larger ones. This process is termed sintering. By providing a physical barrier for the inhibition of sintering, in the form of easily removable alkaline earth metal oxide “cast materials”, this thesis shows that Prussian Blue nanoparticles can undergo thermal decomposition to produce discrete Fe3C nanoparticles. The overarching aim of this work is to push the boundaries of metal carbide synthesis by forming the basis of a technique that can eventually be applied to the synthesis of a wide range of discrete metal carbide nanostructures. A combination of energy dispersive X-ray analysis and electron tomography provides evidence of efficient dispersal of Fe3C nanoparticles throughout various cast materials and ample evidence of < 100 nm Fe3C particle diameters. Scanning electron microscopy provides evidence of the ability to disperse these particles over a catalyst support, and superconducting quantum interference device measurements show superparamagnetic behaviour for the Fe3C particles. The technique is then extended to larger size regimes in the biotemplating of carbonised microcoils using the algae species spirulina.
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Memon, Muhammad Omar. "Carbon Nanostructures As Thermal Interface Materials: Processing And Properties." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1304020760.
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Liu, Mengmeng. "Self-assembled Photo-responsive Nanostructures for Smart Materials Applications." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1494160345663184.
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Li, Guangru. "Nanostructured materials for optoelectronic devices." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/263671.
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This thesis is about new ways to experimentally realise materials with desired nano-structures for solution-processable optoelectronic devices such as solar cells and light-emitting diodes (LEDs), and examine structure-performance relationships in these devices. Short exciton diffusion length limits the efficiency of most exciton-based solar cells. By introducing nano-structured architectures to solar cells, excitons can be separated more effectively, leading to an enhancement of the cell’s power conversion efficiency. We use diblock copolymer lithography combined with solvent-vapour-assisted imprinting to fabricate nano-structures with 20-80 nm feature sizes. We demonstrate nanostructured solar cell incorporating the high-performance polymer PBDTTT-CT. Furthermore, we demonstrated the patterning of singlet fission materials, including a TIPS-pentacene solar cell based on ZnO nanopillars. Recently perovskites have emerged as a promising semiconductor for optoelectronic applications. We demonstrate a perovskite light-emitting diode that employs perovskite nanoparticles embedded in a dielectric polymer matrix as the emissive layer. The emissive layer is spin-coated from perovskite precursor/polymer blend solution. The resultant polymer-perovskite composites effectively block shunt pathways within the LED, thus leading to an external quantum efficiency of 1.2%, one order of magnitude higher than previous reports. We demonstrate formations of stably emissive perovskite nanoparticles in an alumina nanoparticle matrix. These nanoparticles have much higher photoluminescence quantum efficiency (25%) than bulk perovskite and the emission is found to be stable over several months. Finally, we demonstrate a new vapour-phase crosslinking method to construct full-colour perovskite nanocrystal LEDs. With detailed structural and compositional analysis we are able to pinpoint the aluminium-based crosslinker that resides between the nanocrystals, which enables remarkably high EQE of 5.7% in CsPbI3 LEDs.
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Lee, Young-Su Ph D. Massachusetts Institute of Technology. "Electronic structure and quantum conductance of nanostructures." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37371.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 145-158).
This thesis is dedicated to development and application of a novel large-scale first-principles approach to study the electronic structure and quantum conductance of realistic nanoscale materials. Electron transport at the nanometer scale involves phenomena which are beyond the realm of classical transport theory: the wave character of the electrons becomes central, and the Schrddinger equation needs to be solved explicitly. First-principles calculations can nowadays deal with systems containing hundreds of electrons, but simulations for nanostructures that contain thousands of atoms or more need to rely on parametrized Hamiltonians. The core of our approach lies in the derivation of exact and chemically-specific Hamiltonians from first-principles calculations, in a basis of maximally-localized Wannier functions, that become explicit tight-binding orbitals. Once this optimal basis is determined, the Hamiltonian matrix becomes short-ranged, diagonally-dominant, and transferable - i.e. a large nanostructure can be constructed by assembling together the Hamiltonians of its constitutive building block. This approach is first demonstrated for pristine semiconducting and metallic nanotubes, demonstrating perfect agreement with full first-principles calculations in a complete planewave basis.
(cont.) Then, it is applied to study the electronic structure and quantum conductance of functionalized carbon nanotubes. The first class of functionalizing addends, represented by single-bond covalent ligands (e.g. hydrogens or aryls), turns out to affect very strongly the back-scattering and the conductance, since sp3 rehybridization at the sidewall carbon where a group is attached dramatically perturbs the conjugated [pi]-bonding network. Inspection on the shape and the on-site energy of MLWFs before and after functionalizations leads to the conclusion that the effect of sp3 rehybridization is essentially identical to removing a "half-filled" p-orbital from the [pi]-manifold. In this perspective, the chemical difference between functional groups (e.g. different electronegativity of the residues) is relatively minor, even if, of course, will lead to different doping of the tube. We also find that these single-bond ligands tend to cluster, and are more stable when two groups are located nearby (incidentally, the degree of perturbation at the Fermi level becomes weaker when such paired configuration is assumed). The second class of functionalizing addends, represented by cycloaddition functionalizations (e.g. carbenes and nitrenes), demonstrates a radically different behavior.
(cont.) These addends are bonded to two neighboring sidewall carbon atoms, creating a three-membered ring structure. On narrow-diameter tubes, cleaving of the sidewall bond takes place to release the high strain energy of a three-membered ring. In the process, the two sidewall carbons recover their original sp2 hybridization. This step is crucial, since the quantum conductance of a metallic nanotube then recovers almost perfectly the ideal limit of a pristine tube: the bond cleavage restores a transparent conduction manifold. Bond cleavage is controlled by the chemistry of the functional groups and the curvature of the nanotubes. High-curvature favors bond opening, whereas in graphene the bond is always closed; in between the two limits, chemistry determines the critical curvature at which the open-to-closed transition takes place. The preference for bond opening or closing has been screened extensively for different classes of functional groups, using initially some molecular homologues of the nanotubes. It is found that a subclass of addends, exemplified by dicyanocarbene, can assume both the open and closed form in the same tube around a narrow range of diameters.
(cont.) While these two forms are very similar in energy, and separated by a small barrier (hence they can be considered "fluxional" tautomers), the quantum conductance in the closed case is found to be significantly lower than that in the open case. Interconversion between the two minima could then be directed by optical or electrochemical means, in turn controlling the conductance of the functionalized tubes. We envision thus that this novel class of functionalization will offer a practical way toward non-destructive chemistry that can either preserve the metallic conductance of the tubes, or modulate it in real-time, with foreseeable applications in memories, sensors, imaging, and optoelectronic devices.
by Young-Su Lee.
Ph.D.
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Ilievski, Filip 1980. "Magnetic nanostructures patterned by block copolymer lithography." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44317.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008."June 2008."
Includes bibliographical references.
The aim of this research was twofold: understanding the methods of patterning magnetic films using self-assembled block copolymer masks and examining the magnetic reversal mechanisms of as deposited and patterned magnetic films. Ti / Co 66 at. % Cr 22 at. % Pt 12 at. % (CoCrPt) films with perpendicular magnetic anisotropy were deposited on silicon wafers by UHV sputtering. Ti was used as an adhesion layer and texture promoter so that the easy magnetic axis of Co is aligned perpendicular to the sample plane. Magnetic reversal of Ti/CoCrPt films and Ti/CoCrPt/Ti/CoCrPt pseudo spin valve films is a domain nucleation and growth process with a slow time-dependent magnetization reversal which was attributed to growth of reverse domains. The films were patterned into nanosized islands by block copolymer lithography using self assembled polystyrene-polyferrocenyldimethylsilane (PS-PFS) as a mask. The islands reverse their magnetization in a coherent and independent fashion (StonerWohlfarth reversal), in contrast to the continuous film. Micromagnetic simulation confirmed the coherent reversal of the thicker islands. Two graphoepitaxy methods were examined for inducing long range order (LRO) in block copolymers. Nanoimprint lithography with in-situ annealing was successful in guiding the self assembly of the block copolymers in the grooves, however, no LRO was achieved. Selectively removable polymeric templates fabricated out of BARL-i@ anti reflection coating guide the self-assembly of PFS domains with good LRO and very few defects over a large area. The ordered arrays were then transferred into silica and W, forming an ordered array of cp-packed W islands with period of 29 nm and island diameter of 17 nm. Transfer of the pattern into CoCrPt is difficult due to the nonselective ion beam etching process.
by Filip Ilievski.
Ph.D.
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Chen, Haitao, and 陈海涛. "On strain-mediated magnetoelectric effects in multiferroic composite nanostructures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50899934.
Full textAbstract:
Multiferroics which combine two or more order parameters of ferroelectricity, ferromagnetism and ferroelasticity, have drawn great interests in the past few years due to their promising potential of application in sensors, transducers, spintronics and multistate memories. Coupling between the ferroelectricity and ferromagnetism renders the induction of an electric polarization P upon applying a magnetic field, or the induction of a magnetization M upon applying an electric field which is called magnetoelectric coupling effect. There are single phase multiferroics which simultaneously possess ferroelectricity and magnetism in nature. However, these natural multiferroics only exhibit weak magnetoelectric coupling effect at very low temperature which hinders the practical applications. An alternative and more promising choice is to fabricate multiferroic composites. In the multiferroic composite systems, large magnetoelectric coupling effects can be produced indirectly from the strain-mediated interaction even at room temperature and great design flexibility can be obtained. In the present study, two types of multiferroic composite nanostructures are investigated: the vertical heteroepitaxial multiferroic thin films and film-on-substrate heterogeneous bilayers with incorporation of various influences, such as film thickness, misfit strains and flexoelectricity.
Since the first fabrication of vertical epitaxial multiferroic nanostructures, great scientific interests have been attracted for the potential large magnetoelectric effects arising from the relaxed substrate constraint and large interfacial area between the ferroelectric and ferromagnetic phases. A three dimensional phase field model is devised to precisely describe the complex strain state of this nanostructure. The simulation results demonstrate that both film thickness and misfit strains are important in determining the magnitude of magnetoelectric effect.
Due to the strong strain-mediated magnetoelectric coupling effect in film-on-substrate system with a ferromagnetic thin film directly growing on a thick ferroelectric substrate, precision electric control of local ferromagnetism, i.e. ferromagnetic domain pattern and domain wall properties, are achievable. The results show that the domain pattern of the ferroelectric substrate can be fully transferred onto the as-deposited ferromagnetic thin film. High stability of the magnetic domain is observed when the system is subjected to an external magnetic field. Under an applied electric field, the transferred domain pattern in magnetic film can be either maintained or erased depending on the direction of applied electric field. Moreover, when a pulse of in-plane electric field is applied, the magnetic domain wall motion can be observed in concurrence with the ferroelectric domain wall motion.
With the decrease of material size, some effects that can be neglected in bulk materials may play an important role on the overall properties of material, such as flexoelectric effects which describe the induction of polarization from strain gradient. A two dimensional phase field model is adopted to study the influence of flexoelectric effects on the epitaxial ferroelectric films. A thermodynamic phenomenological model is then utilized to analyze the influence of flexoelectric effects on magnetic field induced electric polarization in the multiferroic nanocomposite bilayers. By decreasing the film thickness, the induced polarization from flexoelectric effects becomes more and more dominant and finally overcomes the electrostrictive induced polarization which is dominant when film thickness is large.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
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Lok, Shu Kin. "MBE grown Fe-based nanostructures /." View abstract or full-text, 2010. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202010%20LOK.
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Wen, Xiaoming. "Ultrafast spectroscopy of semiconductor nanostructures." Australasian Digital Thesis Program, 2007. http://adt.lib.swin.edu.au/public/adt-VSWT20070426.110438/index.html.
Full textAbstract:
Thesis (PhD) - Swinburne University of Technology, Centre for Atom Optics and Ultrafast Spectroscopy, 2007.Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, 2007. Typescript. Bibliography: p. 122-144.
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Tong, Wing-yun, and 唐穎潤. "Organic optoelectronic materials: optical properties and 1D nanostructure fabrication." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38574597.
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Feng, Lin. "Photoluminescence studies of single zinc oxide nanostructures /." View abstract or full-text, 2010. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202010%20FENG.
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Duong, Binh. "PROCESSING AND ANALYSIS OF ONE-DIMENSIONAL CARBON NANOSTRUCTURES." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/205414.
Full textAbstract:
Fabrication and synthesis of nanostructured materials are essential aspects of nanoscience and nanotechnology. Although researchers are now able to create and tailor different nanostructured materials, the ability to precisely control the materials' sizes, shapes, and properties at the nanoscale level remains challenging. The aim of this dissertation was to develop new methods to aid researchers in overcoming these challenges. The study investigated two different methods used to create one-dimensional carbon nanostructures, i.e. carbon nanotubes and carbon nanopillars.In the first section, chemical vapor deposition method was used to grow carbon nanotubes (CNTs). Studies examining the effects of methane and hydrogen flow rates on the growth of CNTs were conducted. Results indicated that multi-walled CNTs with metallic properties could be obtained at a methane flow rates as low as 300 cc/min. At higher methane flow rates, i.e. 600-700 cc/min, semiconducting single-walled CNTs and double-walled CNTs were produced. Another phase of this section developed a new and simple CNT growth method using a solid carbon source and indicated polyacrylonitrile and nanosized SiO₂ were effective in producing MWCNTs. In the second part, a new nanoimprint technique was developed to enable printing of nanostructures at sub-100nm level using various polymers. This technique inherited its high-resolution feature from traditional nanoimprint lithography, but without the use of pressure. To demonstrate, PAN nanopillar structures were printed and converted to carbon. In another phase of the part, the use of our imprint technique resulted in the creation and conversion of polysilazane nanostructures to ceramic for the first time.The final section of this dissertation is devoted to study the impact of porosity in gas diffusion layers (GDLs) on the performance of fuel cells. In one study, a new technique using SEM images to determine GDL porosity was developed. The difference between SEM calculated porosities and mercury intrusion porosimetry measurements were less than 2%. The second study characterized fuel cell performances using GDLs constructed with additional micro porous layers (MPLs) and treated with different wet proofing treatments (WPT). Results showed that when MPL is added, cell performance decreases. However, the increase in WPT in the MPL improved cell performance.
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Cheng, Chun. "Fabrication and characterization of one dimensional ZnO nanostructures /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?NSNT%202009%20CHENG.
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Szeifert, Johann. "Mesoporous Titania Materials - Tuning and Optimizing Nanostructures and Porous Morphologies." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-132055.
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Zheng, Changlin. "Investigation of magnetic materials and semiconductor nanostructures by electron holography." Göttingen Cuvillier, 2009. http://d-nb.info/998762822/04.
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