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1
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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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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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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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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Liu, Yong. "Novel nanostructured electrodes." Department of Chemistry - Faculty of Science, 2007. http://ro.uow.edu.au/theses/14.
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Nanotechnology provides an effective and direct way to create novel properties and phenomena through the reduction in material sizes without changing the materials’ chemical composition. A number of routes to the preparation of novel nanostructured electrodes were investigated in this thesis. These involve the formation of nanoporous opaline electrodes, three dimensional nanofibrous networks and the synthesis of flexible nanoelectrodes based on highly dense ordered aligned carbon nanotubes and conducting polymers. Excellent improvements with the use of nanostructures in a wide range of application areas such as methanol oxidation, photoelectrochemical cells, enzyme biosensors, cell culturing and energy storage are presented in this research work.Nanoporous opaline structures including inverse opals and opals were prepared by either electrodepositing Pt or sputter coating ITO onto self-assembled polystyrene (PS) synthetic opals, followed by the removal of the PS opal templates. A highly ordered dense nanoporous structure with the porous structure on the top (so-called Pt inverse opal) or with the porous structure on the bottom (so-called ITO opal) was consequently obtained after the removal of PS templates. The improvement in electrochemical area with the use of nanostructures was observed during electrochemical characterisation. The resultant nanostructured Pt inverse opal electrodes were employed in electro-oxidation of methanol. Compared with the Pt film electrode, the nanostructured Pt inverse opal electrode showed a higher catalytic performance and good stability with a 100 mV negative shift of the potential of methanol oxidation. The mesoporous ITO opal electrode was used as the substrate for the electrodeposition of polyterthiophene and the resultant structure was subsequently utilized in photoelectrochemical cells. An excellent power-conversion efficiency of 0.109% and an outstanding short circuit current density of 1470 μA•cm-2 for polyterthiophene deposited at room temperature were obtained; dramatically improved from the previous published work.Nanofibrous electrodes were fabricated from biomaterials (such as DNA and poly(styrene-β-isobutylene-β-styrene) (SIBS)) and single-walled carbon nanotubes (SWNTs) using the electrospinning technique. Initial studies quantitatively determined the influence of solution properties (such as the solution ionic conductivity, surface tension and viscosity) and process parameters (e.g. tip-to-collector distance, applied potential and the feed rate) on the electrospinning results. Results showed that good electrospun fibrous networks could be obtained from the solution with comparatively high conductivity and viscosity with low surface tension. It was also found that the average diameter of the electrospun fibers decreased with decreased feed rates, increased tip-to-collector distance and increase in the potential employed. With the addition of SWNT, both biomaterial nanofiber electrodes exhibited enhanced electrochemical properties. The resulting DNA based electrospun fiber electrode showed a broad linearity range and high sensitivity in enzyme biosensors. The SIBS/SWNT nanofibrous electrode demonstrated excellent biocompatibility and suitability for the growth of L-929 cells.Flexible, light and highly conductive nanostructured electrodes were prepared from aligned carbon nanotubes (ACNTs) and conducting polymers by coating with Pt coated poly(vinylidene fluoride) (PVDF) or poly(3,4-ethylenedioxythiophene) (PEDOT)/PVDF. Pt nanoparticles were subsequently electrodeposited on the ACNT/Pt/PVDF structure. The utilization of the nanostructured ACNT/conducting polymer electrodes in anodic methanol oxidation and as anodic materials in Lithium-ion batteries was demonstrated. Pt nanoparticles coated ACNT/Pt/PVDF electrode exhibited an outstanding electrochemical capacity (133 Fg-1) and amazing electrochemical surface area (143 m2g-1 for Pt nanoparticles). The Pt nanoparticles-ACNT/Pt/PVDF electrode also showed a 2.5 times higher steady current density for methanol oxidation when compared with the ACNT/Pt/PVDF electrode. A stable current density over a long period (more than 12 hours) was obtained. A 50% improvement in capacity during Lithium-ion battery tests when compared with a SWNT paper was obtained with the ACNT/PEDOT/PVDF electrode.Nanostructured flexible and conductive electrodes were also obtained from ACNTs and biomaterials (such as SIBS and poly(lactide-co-glycolide)). SWNTs or Pt were introduced to improve the conductivity. A significant improvement in electrochemical properties with the addition of Pt or SWNT was obtained. The biocompatibility of ACNTs, SWNTs and Pt was confirmed during cell culturing experiments.
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Gilbank, Alexander. "Ceramic nanostructured catalysts." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648952.
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Catalysis has an effect on almost every aspect of our lives. They are used to help grow the food we eat, clean the water we drink and produce the fuels our civilisation is so dependent upon. Homogeneous catalysts, those in the same phase as the reaction medium, are highly selective as a result of their tuneable nature, for example through changes to ligands in a metal complex. However, their separation from the reaction medium can become a problematic, costly, non-green issue, overcome through the use of heterogeneous catalysts which can be removed and recycled by simple separation techniques such as filtering and sedimentation. A major limitation on understanding the behaviour of heterogeneous catalysts is the presence of different active sites due to different exposed crystal surface, concentration of defects and morphological variations. With such considerations, the first section of this thesis focuses on the synthesis of discrete and well-defined nanostructured materials (ceria and titanate) using a single-step hydrothermal method. Nanostructured ceria with different morphologies (particles, rods and cubes), present a high oxygen storage capacity and thermal stability. Their oxidation catalytic activity was assessed using CO oxidation as a model reaction as a function of their physical and chemical properties, tuned by morphological control at the nanoscale. An inverse relationship is observed between crystallite size and rates of reaction normalised per surface area. Smaller crystallites present a constrained geometry resulting in a higher concentration of defects, highly active catalytically due to their unsatisfied coordination and high surface energy. The surface to bulk oxygen ratio generally increased as the surface area increased, however, ceria nanorods present a higher surface oxygen content than that which would be predicted according to their surface area, likely due to the selective exposure of the (110) and (100) dominating crystal surfaces presenting more facile oxygen atoms in their surface. Additionally a relationship between surface to bulk oxygen ratios and activation energies was also ascribed to the more facile nature of oxygen atoms on these surfaces and their more readily formed oxygen vacancies as a result. This activity is as a result of the formation of oxygen vacancies being the rate-controlling step. The thermal stability of nanostructured ceria (particles, rods and cubes) was also studied to investigate their performance under cyclic high temperature applications. For this, the materials were pre-treated at 1000 °C under different atmospheres (inert, oxidative and reducing). In all cases, the materials sinter, consequently resulting in a dramatic decrease in surface area. Interestingly, their catalytic activity per surface area towards CO oxidation, seems to be maintained, although those materials pre-treated under inert and oxidising atmospheres became inactive in consecutive catalytic runs. However, nanostructured ceria pre-treated at 1000 °C under hydrogen appeared to maintain its activity per surface area. The presence of hydrogen during thermal treatment does not only facilitate the removal of surface oxygen, but also the bulk oxygen, resulting in a rearrangement of the structure that facilitates its catalytic stability. Titanate nanotubes were shown to be inactive for CO oxidation and thus were used in the second part of this thesis as a support for platinum nanoparticles to study the effect of the structure and metal-support interaction on the resulting catalytic activity. The study focuses on the effect of different loading methods (ion exchange and incipient wetness impregnation) of platinum nanoparticles on the resulting metal particle size, dispersion, metal-support interaction and consequently their resulting catalytic activity. Ion exchange consistently resulted in smaller nanoparticles with a lower dispersion of sizes and more active catalyst, both in terms of turnover frequency values and activation energy, compared with incipient wetness impregnation. The catalytic activity of the platinum supported on titanate nanotubes increases as the metal particle size decreases to a size value (between 1 and 2.5 nm) below which a dramatic decrease in activity is observed. Despite initial differences in catalytic activity between the different catalysts, it was observed that after initial reactions to 400 °C, the activation energy was independent of metal loading weight and was instead inherent of the loading method, suggesting the presence of similar active sites.
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Musselman, Kevin Philip Duncan. "Nanostructured solar cells." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609003.
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Deplace, Fanny. "Waterborne nanostructured adhesives." Paris 6, 2008. http://www.theses.fr/2008PA066035.
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Nous avons étudié les propriétés d’adhésifs préparés à partir de particules de latex nanostructurées. Une méthodologie basée sur deux critères rhéologiques a été proposée pour optimiser les performances adhésives. Elle nous a permis d’identifier des stratégies applicables dans le cas particulier de PSA préparés à partir de particules de latex ayant une morphologie cœur-écorce. Une stratégie intéressante est l’activation d’une réaction de réticulation interparticule pendant le séchage du latex. Nous avons montré l’effet remarquable de cette réaction de réticulation sur les propriétés en grandes déformations. Ces propriétés sont assez bien décrites par un modèle non-linéaire combinant le modèle de Maxwell sur convecté et le modèle de Gent. Les meilleurs résultats d’adhésion sont obtenus pour des PSA préparés à partir de particules de latex ayant une fine écorce réticulée et un cœur mou et caractérisés par un net ramollissement à déformations intermédiaires suivi d’un rhéodurcissement. Dans un registre plus industriel, des performances adhésives prometteuses ont été obtenues avec des PSA préparés à partir de latex tackifiés in situ synthétisés par polymérisation en miniémulsion.
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Vandamme, Nicolas. "Nanostructured ultrathin GaAs solar cells." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112111/document.
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L’amincissement des cellules solaires semi-conductrices est motivé par la réduction des coûts de production et l’augmentation des rendements de conversion. Mais en deçà de quelques centaines de nanomètres, il requiert de nouvelles stratégies de piégeage optique. Nous proposons d’utiliser des concepts de la nanophotonique et de la plasmonique pour absorber la lumière sur une large bande spectrale dans des couches ultrafines de GaAs. Nous concevons et fabriquons pour ce faire des structures multi-résonantes formées de réseaux de nanostructures métalliques. Dans un premier temps, nous montrons qu’il est possible de confiner la lumière dans une couche de 25 nm de GaAs à l’aide d’une nanogrille bidimensionnelle pouvant servir de contact électrique en face avant. Nous analysons numériquement les modes résonants qui conduisent à une absorption moyenne de 80% de la lumière incidente entre 450 nm et 850 nm. Ces résultats sont validés par la fabrication et la caractérisation de super-absorbeurs ultrafins multi-résonants. Dans un second temps, nous appliquons une approche similaire dans le but d’obtenir des cellules photovoltaïques dix fois plus fines que les cellules GaAs records, avec des absorbeurs de 120 nm et 220 nm seulement. Un miroir arrière nanostructuré en argent, associé à des contacts ohmiques localisés, permet d’améliorer l’absorption tout en garantissant une collecte optimale des porteurs photo-générés. Nos calculs montrent que les densités de courant de court-circuit (Jsc) dans ces structures optimisées peuvent atteindre 22.4 mA/cm2 et 26.0 mA/cm2 pour les absorbeurs d’épaisseurs respectives t=120 nm et t=220 nm. Ces performances sont obtenues grâce à l’excitation d’une grande variété de modes résonants (Fabry-Pérot, modes guidés,…). En parallèle, nous avons développé un procédé de fabrication complet de ces cellules utilisant la nano-impression et le transfert des couches actives. Les mesures montrent des Jsc records de 17.5 mA/cm2 (t=120 nm) et 22.8 mA/cm2 (t=220 nm). Ces résultats ouvrent la voie à l’obtention de rendements supérieurs à 20% avec des cellules solaires simple jonction d’épaisseur inférieure à 200 nmThe thickness reduction of solar cells is motivated by the reduction of production costs and the enhancement of conversion efficiencies. However, for thicknesses below a few hundreds of nanometers, new light trapping strategies are required. We propose to introduce nanophotonics and plasmonics concepts to absorb light on a wide spectral range in ultrathin GaAs layers. We conceive and fabricate multi-resonant structures made of arrays of metal nanostructures. First, we design a super-absorber made of a 25 nm-thick GaAs slab transferred on a back metallic mirror with a top metal nanogrid that can serve as an alternative front electrode. We analyze numerically the resonance mechanisms that result in an average light absorption of 80% over the 450nm-850nm spectral range. The results are validated by the fabrication and characterization of these multi-resonant super-absorbers made of ultrathin GaAs. Second, we use a similar strategy for GaAs solar cells with thicknesses 10 times thinner than record single-junction photovoltaic devices. A silver nanostructured back mirror is used to enhance the absorption efficiency by the excitation of various resonant modes (Fabry-Perot, guided modes,…). It is combined with localized ohmic contacts in order to enhance the absorption efficiency and to optimize the collection of photogenerated carriers. According to numerical calculations, the short-circuit current densities (Jsc) can reach 22.4 mA/cm2 and 26.0 mA/cm2 for absorber thicknesses of t=120 nm and t=220 nm, respectively. We have developed a fabrication process based on nano-imprint lithography and on the transfer of the active layers. Measurements exhibit record short-circuit currents up to 17.5 mA/cm2 (t=120 nm) and 22.8 mA/cm2 (t=220 nm). These results pave the way toward conversion efficiencies above 20% with single junction solar cells made of absorbers thinner than 200 nm
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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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Wang, Lingyan. "Design and fabrication of functional nanomaterials with tunable electrical, optical, and magnetic properties." Diss., Online access via UMI:, 2007.
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Chubilleau, Caroline. "Influence d'inclusions de PbTe ou de ZnO sur les propriétés thermoélectriques de matériaux skutterudites." Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL059N/document.
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Ce travail a été réalisé dans le cadre d’une étude sur les matériaux massifs thermoélectriques nanostructurés, composés dont les propriétés peuvent potentiellement être améliorées grâce aux nombreuses interfaces. Il concerne la réalisation et la caractérisation de composites à matrices skutterudites (CoSb3 ou In0,4Co4Sb12) contenant différents taux d’inclusions nanométriques de PbTe ou de ZnO. Des techniques de métallurgie des poudres et de fracturation laser en milieu liquide ont été conjuguées à divers moyens de caractérisation (RX, MEB, MET) pour mettre au point le protocole d’élaboration des matériaux. L’observation des microstructures des composites a révélé que l’étape de dispersion des particules dans le matériau est la plus délicate de la préparation. Celles-ci forment des amas localisés aux joints de grains. La porosité est également relativement importante lorsque le taux d’inclusions est élevé en particulier avec ZnO. Les propriétés électriques (pouvoir thermoélectrique, résistivité électrique, effet Hall) et thermiques (conductivité thermique) ont été mesurées sur une large gamme de température (2-800 K) puis corrélées aux microstructures. L’analyse des résultats a permis de montrer que le PbTe tend à dégrader les propriétés électriques des deux matrices du fait notamment d’une réaction des nanoparticules avec les skutterudites. Par contre, l’ajout de ZnO semble plus prometteur même s’il est difficile de conclure définitivement quant à son rôle réel compte tenu de la complexité des microstructures (défauts, pores, joints de grains). Un modèle théorique développé afin de mieux comprendre l’impact des tailles de particules sur les propriétés thermiques a mis en évidence qu’il est plus intéressant de travailler avec des skutterudites partiellement remplies plutôt qu’avec CoSb3 puisque les inclusions affectent majoritairement les phonons les moins énergétiques. Les tendances qui se dégagent de cette étude vont plutôt dans le sens d’une détérioration des propriétés avec ce type de nanostructuration lorsque les taux de nanoparticules excèdent quelques pourcents mais l’utilisation de quantités plus faibles et une porosité mieux maîtrisée pourrait avoir un effet positifThis work was carried out as part of a study on nanostructured bulk thermoelectric materials, compounds whose properties can potentially be improved with many interfaces. It is related to the synthesis and characterization of skutterudites (CoSb3 or In0.4Co4Sb12) containing nanoinclusions of PbTe or ZnO. Techniques of powder metallurgy and laser fragmentation in liquid medium were combined to X-rays diffraction analyses, SEM and TEM observations to develop the experimental procedure for the preparation of materials. The microstructures of the composites show that the dispersion step is the most difficult part of the preparation as it leads to agglomerates located at the grain boundaries. The porosity is also relatively large when the quantity of inclusions is high especially with ZnO. The electrical and thermal properties (thermoelectric power, electrical resistivity, Hall effect, thermal conductivity) have been measured over a wide temperature range (2-800 K) and correlated with the microstructures. The results analysis showed that PbTe tends to degrade the electrical properties of the two matrixes because of a reaction between the nanoparticles and the skutterudites. Contrarily, the addition of ZnO seems more promising although it is difficult to conclude definitively on its effectiveness given the complexity of the microstructures (defects, pores, grain boundaries). A theoretical model developed to better understand the impact of the particle sizes on the thermal properties showed that it is more interesting to work with partially filled skutterudites instead of pure CoSb3 since the inclusions mostly affect the scattering of long wavelength phonons. The trends that emerge from this study are rather in the sense of a deterioration of the thermoelectric properties with this type of nanostructure when the quantities of nanoparticles exceed a few percentage. The use of smaller quantities and a better controlled porosity should be considered
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Al-Ajili, Adwan Nayef Hameed. "Photoluminescence of nanostructured silicon." Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/26999.
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The photoluminescence (PL) emitted by porous silicon has been investigated under different conditions of excitation using a pulsed nitrogen laser source, and the continuous tunable DV synchrotron source at Daresbury Laboratory. The project involved sample preparation, and PL measurements using a custom-built optical laser-based system for lifetime measurements. This in itself necessitated software and hardware development to enable interfacing and data-logging using an IBM-compatible PC. The equipment development formed a major part of the project.
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Barlow, Iain J. "Nanostructured Molecular Electronic Devices." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486548.
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Candidate organic semiconductor materials based on a,ro-dihexylquaterthiophene (dH4T) and a,ro-dihexylbis(phenylene)bithiophene (dHPTTP) core systems were synthesised. The tenninal positions of the alkyl substituents were substituted with, thioacetate, phosphonic acid, glycolic ester and allyl ether groups to enable the fonnation of self-assembled monolayers (SAMs) of the adsorbates onto Au, Ah03 and H-Si surfaces. These were then probed with x-ray photoelectron spectroscopy (XPS) and friction force microscopy (FFM). Analysis of the XPS spectra confirmed that the oligomers fonned monolayer films onto the respective substrates although the allyl-terminated oligomers were subject to oxidation when attached onto H-Si by thermally-initiated radical attachment. Comparison of this method with photochemical initiation highlighted a potentially competing photolysis reaction. FFM showed that the frictional properties of both the thiolate and phosphonic acid SAMs on Au and Ah03 for the oligomers depended on both the tail group polarity and the density of packing for the adsorbates, whilst the allyl-capped materials formed disordered monolayers on H-Si. Chemical patterns of the thioacetate and phosphonic acid-terminated oligomers were produced by the irradiation of methyl-tenninated alkanethiols and alkylphosphonic acids with 244 nm UV light. The irradiation and subsequent displacement of the exposed adsorbates with the dH4T and dHPTTP-based thioactetates and phosphonic acids resulted in areas of relatively high and low friction, which was imaged by FFM. The SAM photomodification process on Ah03 was monitored by XPS, and suggested C-P bond photolysis as a potential mechanism. Scanning near-field photolithography (SNP) was then used to generate dH4T and dHPTTP features into alkanethiol and phosphonate SAMs. The smallest features, of 40 nm fwhm demonstrate that SNP is a viable method for the preparation of organic semiconductors with nanometre resolution, with potential application in the production of self-assembled monolayer field-effect transistors (SAMFETs).
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Marshall, Matthew Spiro James. "Nanostructured strontium titanate surfaces." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509992.
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Arias, Dylan H. "Coherence in nanostructured excitons." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82310.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 159-184).
Nanotechnology and optoelectronics have the potential to revolutionize the medicine, communications, and energy industries, with applications utilizing nanotechnology beginning to appear. However, there are still fundamental questions about optoelectronic devices incorporating nanotechnology. In particular, how do nanometer-scale materials affect potential functionality, and how can we take advantage of this scale to design nanomaterials for applications? Natural light harvesting systems in bacteria and plants provide exquisite examples of nanomaterial design, featuring remarkably efficient light harvesting antennas. Sunlight absorption first creates excitons. Complex antenna architectures control the excitons, directing them to reaction centers for conversion to chemical energy. Recently, studies found that excitonic interactions play a significant role in controlling antennas' light harvesting abilities, and that coherence may greatly affect energy transport efficiencies. While these studies have propelled our understanding of excitons in these systems, it is desirable to extend our expertise to artificial systems. In this thesis I describe experiments uncovering many fundamental properties of excitons in various nanostructured materials, relating physical structure to excitonic structure and perhaps to subsequent function in an excitonic device. Nonlinear spectroscopy offers distinct possibilities for detailed exploration of excitonic properties and processes in nanomaterials. Transient grating experiments are sensitive to population dynamics and energy transport, while multi-dimensional spectroscopy clearly reveals excitonic interactions, correlations, and coherence. In this thesis, these techniques are performed with a unique multi-dimensional spectrometer using femtosecond pulse shaping. I present results on two classes of artificial nanostructures: supramolecular J-aggregates and semiconductor quantum wells. In J-aggregate thin films I determined that coherence is controlled by thermal dephasing rather than film inhomogeneities, even at cryogenic temperatures. Tubular J-aggregates in solution undergo morphological rearrangement while maintaining a common sub-unit that remains relatively intact both structurally and excitonically. In semiconductor quantum wells, many-body correlations among excitons were shown to decay on the timescale picoseconds, depending on the exciton density and therefore revealing of high-order correlations. These insights into coherence and excitonic structure are important in determining the origin and strength of coherence in excitonic systems, potentially leading toward methods to alter or control exciton dynamics and toward possible novel application of coherence in optoelectronic devices.
by Dylan H. Arias.
Ph.D.
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Finnemore, Alexander. "On biomimetic nanostructured materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610543.
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Alenezi, Mohammad Rabia. "Nanostructured zinc oxide sensors." Thesis, University of Surrey, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616927.
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This thesis focuses on the hydrothermal synthesis of different ZnO nanostructures where rational control over their morphology allows for the optimization of the · different morphologies for a range of sensing applications. ZnO nanostructures with different dimensionalities have been synthesized through low temperature hydrothermal techniques. One dimensional ZnO NW s have been synthesized with and without the assistance of a seed layer, with a higher degree of control over their structure, morphology, density and dimensions. The large scale production of two dimensional ZnO nanodisks with a high fi.-action of exposed polar mcets have also been produced through using zinc counter ions with preferential capping capabilities on defined mcets. Furthermore, using a multistage hydrothermal synthesis, a range of three dimensional hierarchical ZnO nanostructures grown from initial mono-morphological ZnO nanostlUctmes/seeds has been reported. The growth parameters, such as the nutlient concentration, quantity of polyethylenirnine, growth time, and zinc counter ions have had a substantial impact on the morphological properties of the grown structures.
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Trofimovaite, Rima. "Nanostructured promoted titania photocatalysts." Thesis, Aston University, 2018. http://publications.aston.ac.uk/37498/.
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Concern over the economics of accessing fossil fuel and widespread acceptance of the anthropogenic origin of rising CO2 emissions and associated climate change is driving academic and commercial research into new routes to sustainable fuels, to meet the demands of a rapidly rising global population and reduce an impact on the environment. The titania oxide semiconductor has attracted a great interest as a photocatalyst for wide-ranging applications including wastewater depollution, solar fuels via both H2 production and CO2 reduction. Tailoring the physicochemical properties of titania photocatalysts, and their resulting reactivity, in a predictable fashion remains challenging. The thesis explores the impact of thermal processing, macroporosity and metal deposition on the surfactant-templated mesoporous TiO2 and dual soft-hard templated macro-mesoporous TiO2 series and resulting activity in aqueous phase photocatalytic dye degradation, H2 production and CO2 reduction reactions. Control over the structural and photophysical properties of mesoporous titania enables systematic tuning of Methyl Orange photocatalytic depollution and H2 evolution. Hierarchical macro-mesoporous titanias exhibit uniform mesopores with macropore diameters that can be systematically tuned between 140-310 nm, resulting in a close-packed, ordered macropore framework. Hierarchically-structured TiO2 display two fold increase in photoactivity relative to mesoporous counterparts in the H2 production. Ultra-low concentrations (0.02-0.1 wt%) of copper introduced into the mesoporous and macro-mesoporous titania surfaces by wet-impregnation enhance activity for dye degradation by six fold, and for H2 production four fold, through the genesis of isolated Cu (I) species which suppress charge recombination. Furthermore, promotion with Pt increases photocatalytic activity in Methyl Orange degradation by eleven fold, H2 production 16-26 times and are the only series which display activity in the CO2 reduction reaction. Moreover, the impact of the macropore diameter on the activity of the Methyl Orange degradation is observed for Cu and Pt promoted macro-mesoporous TiO2 series. Nanostructured promoted titanias offer an insight into the relative importance of physicochemical and electronic properties upon their associated activity together with significantly enhanced photocatalytic performance.
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Jara, Olivares Angelica Yuliana. "Biocompatible nanostructured multilayer systems." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT222/document.
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Le domaine des couches minces fait l’objet d’un grand nombre d’études en raison du vaste champ d’applications. La modification de surfaces par des revêtements sous forme de couches minces a ainsi été étudiée dans le domaine biomédical afin d’améliorer les propriétés de bioactivité et biocompatibilité des matériaux. Des couches minces monocouches, Ta et TaN, ainsi que bi-couches, TaN/Ta, ont été déposées sur des substrats de verre, d’acier, SS316LVM, et de titane par pulvérisation cathodique. La caractérisation des couches par diffraction des rayons X (XRD and GIXRD) a montré que la nature du substrat a une forte influence sur la nature de la phase, Ta, formée. La formation de la phase ordonnée, Ta-a, est obtenue sur le substrat acier alors que la phase désordonnée métastable, Ta-b, se forme sur le substrat titane. Quant à la phase TaN, elle cristallise sous la forme cubique de type NaCl (Fm3m) sur les différents substrats mais présente une orientation préférentielle selon le plan (200) dans le cas du substrat verre. L’étude de la composition chimique par XPS a montré que les couches sont également constituées de phases oxydes, telles que TaxOy et TaOxNy, en raison de la forte affinité du tantale avec l’oxygène. Les observations en microscopie électronique à balayage ont mis en évidence une croissance colonnaire des couches avec une microstructure de surface dite de type « chou-fleur ». Cette microstructure est caractéristique du procédé de pulvérisation cathodique et correspond à la microstructure dite de zone I prédite par le modèle de Thornton, dérivé du modèle de Movchan and Demchishin. Des méthodes biomimétiques ont été utilisées afin d’évaluer la bioactivité des couches minces étudiées. Dans ce but, les échantillons ont été immergés dans un fluide biologique (SBF, Simulated Body Fluid) afin de promouvoir le dépôt de phosphate de calcium. Après étude de fluides de compositions différentes, le fluide SBF 1.5, enrichi en ions Ca2 + and PO43-, a été choisi. Les analyses par XRD, FTIR et XPS ont mis en évidence la formation en surface d’une couche cristalline d’hydroxyapatite quelle que soit la nature des sous-couches, Ta, TaN ou TaN/Ta, après immersion de trois semaines. Le mécanisme de dépôt d’hydroxyapatite implique la formation de liaisons Ta-OH par hydratation de la couche passive d’oxyde de tantale présente en surface.Pour étudier les propriétés de biocompatibilité, les échantillons ont été placés en milieux de culture contenant des ostéoblastes. Tous les matériaux observés présentent une adhésion des cellules en surface avec la formation de filipodia. L’un des principaux problèmes des implants osseux est la formation en surface d’un biofilm du à la colonisation de bactéries. Des essais en milieu bactériologique ont donc été réalisés avec des bactéries de type Pseudomonas Aeruginosa, agents pathogènes très fréquemment observés lors d’opérations chirurgicales. Ces essais expérimentaux ont permis de déterminer la réaction des différents matériaux étudiés au contact de ces bactéries. Il s’est avéré que l’adjonction de couches de tantale permet de réduire fortement la formation de bio-films en comparaison avec des couches de titane, qui présentent une croissance importante de bio-films à base de P. aeruginosa.Des films minces de silice ont également été étudiés en tant qu’agents bactéricides. Ces études ont montré l’absence de colonies microbiennes et l’absence de la formation de bio-films en surfaceThin films have been the subject of intense study in materials because they offer multiple applications of great interest. Various surfaces have been modified with thin films or coatings to study how to improve their bioactivity and biocompatibility properties to form a biomaterial. Thin films of Ta, TaN and Ta/TaN were deposited on glass substrates, metallic substrates, SS316LVM and Ti, by RF Sputtering technique. By High angle XRD and GIXRD it was found that the nature of the substrate has a strong influence on the Ta phase formed. Formation of ordered α-Ta phase was obtained on SS316LVM, but the disordered metastable β-Ta phase was formed on Ti and on TaN substrates. While TaN crystallizes in the cubic phase (Fm3m) NaCl type on metallic substrates but shows a preferential orientation in the (200) plane on the glass substrate. The chemical analysis of the surfaces by XPS reveals that in the surfaces of the deposited layers are several oxidized chemical species such as Ta2O5, TaOxNy TaxOy due to Ta is a very reactive metal and is readily oxidized even at low partial pressures as for our synthesis conditions. Characterization by Scanning Electron Microscopy reveals that the microstructure of the films was homogeneous with small clusters size and a cauliflower type, also the films exhibit the typical columnar growth for films deposited by PVD techniques, following the growth of zone I described by the model developed by Movchan and Demchisin and Thornton. Biomimetic method was used to evaluate the bioactivity in all surfaces which involves immersing the thin films in simulated body fluid (SBF) to promote the deposition of calcium phosphates, two concentrations were used to assess qualitatively which could deposit the stoichiometric calcium phosphate hydroxyapatite and make it more efficiently. The SBF 1.5 enriched in Ca2 + and PO43- ions was chosen. A new layer was deposited upon the surfaces and it was determined by XRD, FTIR and XPS that crystalline Hydroxyapatite phase was formed, so that all our surfaces have the ability to form apatite spontaneously after an immersion period of three weeks. The mechanism of deposition of HAp involves the formation of small amounts of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. To study biocompatibility properties, films were placed in cell culture containing osteoblasts, all surfaces exhibit cell adhesion and formation of filipodia. Whereas one of the main problems of bone implants is biofilm formation caused by bacterial colonization, tests were made with the bacterium Pseudomonas Aeruginosa, which is a major human opportunistic pathogens in surgical procedures, causing infections in soft tissue, bones, among others. This assay allowed us to know how the different surfaces react when exposed to this bacteria, Titanium had greater growth of P. aeruginosa and biofilm formation in all periods of study, while Ta surfaces showed the lowest activity of biofilm formation. Mesoporous silica thin films where used as bactericidal agents, and it was found by MEB that no microbial colonization or biofilm formation occur on these surfaces
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Bradley, Kieren Adam. "Photoelectrochemistry of nanostructured semiconductors." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687604.
Full textAbstract:
Semiconductors are vital components in the challenge of harvesting solar power to provide sufficient carbon neutral energy for a growing global population. A trend in semiconductor devices is to nanostructure some of the layers in order to obtain improvements in optical and electrical properties. This work focusses on two materials that have been gaining academic and commercial interest over a number of years. Zinc oxide (ZnO) is a wide bandgap semiconductor that can be grown via a number of physical and chemical deposition methods; the work on ZnO builds upon research on a chemical growth route which can create well aligned hexagonal rods with diameters from ~20 nm to Illm, with lengths of hundreds of nanometres to tens of microns. Changes in the growth solution led to either aligned or disordered rods, but the irreproducibility of the technique is evident. The second material studied is indium gallium nitride (InxGa1-xN), a semiconductor which can have its optoelectronic properties tuned by changing the ratio of In to Ga. Tuneable bandgaps are desirable for absorbing the optimum fraction of solar energy. Photoelectrochemistry is used to probe the optoelectronic characteristics of the semiconductors and theoretical models are used to simulate the combination of the optics and electronics in nanostructured electrodes, with waveguiding effects being shown to alter the expected efficiency of photoelectrochemical reactions in nanorods. A model based on the semiconductor continuity equation and Shockley-Read-Hall recombination is developed to describe the time dependent photoelectrochemical current of semiconductors with mid-band defect states, as functions of applied potential and illumination intensity. From the model a novel technique is provided to calculate the position and density of the defect states; the technique is successfully demonstrated on ZnO nanorods for the first time and evaluated for its effectiveness .
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Smith, Steven P. "Lanthanide-containing Nanostructured Materials." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145459.
Full textAbstract:
The research described in this Dissertation is concerned generally with the exploration of the potential use of lanthanide elements in nanostructured materials for the purpose of modification of the magnetic and optical properties. This is explored through a focus on the development of lanthanide-containing iron oxide nanosystems. Our objectives of producing lanthanide containing nanostructured materials with potentially useful optical and magnetic applications has been achieved through the development of lanthanide-doped Fe3O4 and -Fe2O3 nanoparticles, as well as a unique core-shell magnetic-upconverting nanoparticle system.Necessary background information on nanomaterials, rationale for the study of lanthanide-containing iron oxide nanosystems and context for discussion of the results obtained in each project is provided in the Introduction Chapter. The syntheses of Fe3O4 nanoparticles doped with Eu(III) and Sm(III) are discussed, along with structural characterization and magnetic property investigation of products In Chapter 2. The following Chapter expands the study of lanthanide doping to -Fe2O3, a closely related yet distinct magnetic nanoparticle system. A completely different synthesis is attempted, and comparisons between the two systems are made.The development of novel synthetic methodologies used to create such products has yielded high-quality lanthanide-containing materials and are evidenced by TEM images displaying nearly monodisperse particles in each of our efforts. The modifications to the magnetic properties resulting from lanthanide doping include theobservation of ferromagnetism in the Fe3O4 system and increased magnetic saturation of -Fe2O3 nanoparticles, and are characterized by VSM and the visual observation of magnetic alignment of products. Our efforts towards developing a novel methodology capable of producing high quality Fe3O4 nanoparticles, and subsequent characterization of products, were published in the Journal of the American Chemical Society.Optically active, magnetic, core-shell nanoparticles are investigated in Chapter 4 for the potential uses in diagnosis and treatment of cancer. This multifunctional system uses Fe3O4 as a magnetic core, shelled by upconverting lanthanide-containing nanomaterials, and is rendered biocompatible through encapsulation of the core-shell structure by a silica shell. Added functionality is achieved through amine functionalization of the silica surface, with the goal of coupling the inorganic nanoparticle with drug targeting groups. TEM results indicate successful formation of the core-shell nanoparticles, and expected magnetic and optical properties are shown by visual observation and luminescence spectroscopy, respectively.
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Favaro, Matteo. "Nanostructured flexible radiation sensors." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/310045.
Full textAbstract:
Flexible scintillating radiation detectors have gained increasing attention in the scientific community in the last decade. They represent a fast and easy way for monitoring the impinging radiation in real time and acquire the dose released in medical treatments, like cancer radio- or proton-therapy sessions. Flexible linear-chain polysiloxane detectors offer the possibility to overcome geometrical limitations, they possess superior optical transparency and flexibility, and can be obtained with contained production costs and times, making them highly competitive with respect to traditional single-crystals and plastics. Unlike phenyl-containing siloxanes, linear polysiloxanes does not show direct interaction with the impinging radiation, therefore they can be used just as matrices for hosting luminescent materials, such as nanocrystals or nanopowders. Quantum dots (QDs) are nanocrystals showing quantum confinement effects, with an incredible light yield, a tunable emission wavelength and a fast decay lifetime. For these reasons, they are worth being incorporated in siloxane-based scintillators as primary dyes, without the need of complex ternary systems. Part of this thesis analyzes the effects of ionizing radiation on the luminescence and temporal response of QD-loaded polysiloxanes for radiation detection and monitoring, with special focus on real-time measurements under proton beam. Another possibility is to embed luminescent nanopowders, such as zinc oxide (ZnO) and reduced zinc oxide (ZnO:Zn). The Zn-rich form shows a remarked green luminescence, with increasing light yield as a function of the reduction degree, i.e. zinc content. In view of the above, this thesis reports the advances on polysiloxanes loaded with ZnO and ZnO:Zn phosphors. The core of the thesis is devoted to the progresses in ZnO production and treatment for the realization of multi-layered flexible scintillators. A special focus is putted on a novel production route based on atmospheric pressure plasma (APPJ), that allows for the co-deposition of ZnO-loaded plasma polymers and for the doping via liquid precursor solution.
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Favaro, Matteo. "Nanostructured flexible radiation sensors." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/310045.
Full textAbstract:
Flexible scintillating radiation detectors have gained increasing attention in the scientific community in the last decade. They represent a fast and easy way for monitoring the impinging radiation in real time and acquire the dose released in medical treatments, like cancer radio- or proton-therapy sessions. Flexible linear-chain polysiloxane detectors offer the possibility to overcome geometrical limitations, they possess superior optical transparency and flexibility, and can be obtained with contained production costs and times, making them highly competitive with respect to traditional single-crystals and plastics. Unlike phenyl-containing siloxanes, linear polysiloxanes does not show direct interaction with the impinging radiation, therefore they can be used just as matrices for hosting luminescent materials, such as nanocrystals or nanopowders.
Quantum dots (QDs) are nanocrystals showing quantum confinement effects, with an incredible light yield, a tunable emission wavelength and a fast decay lifetime. For these reasons, they are worth being incorporated in siloxane-based scintillators as primary dyes, without the need of complex ternary systems. Part of this thesis analyzes the effects of ionizing radiation on the luminescence and temporal response of QD-loaded polysiloxanes for radiation detection and monitoring, with special focus on real-time measurements under proton beam.
Another possibility is to embed luminescent nanopowders, such as zinc oxide (ZnO) and reduced zinc oxide (ZnO:Zn). The Zn-rich form shows a remarked green luminescence, with increasing light yield as a function of the reduction degree, i.e. zinc content. In view of the above, this thesis reports the advances on polysiloxanes loaded with ZnO and ZnO:Zn phosphors. The core of the thesis is devoted to the progresses in ZnO production and treatment for the realization of multi-layered flexible scintillators. A special focus is putted on a novel production route based on atmospheric pressure plasma (APPJ), that allows for the co-deposition of ZnO-loaded plasma polymers and for the doping via liquid precursor solution.
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Isotta, Eleonora. "Nanostructured thermoelectric kesterite Cu2ZnSnS4." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/315174.
Full textAbstract:
To support the growing global demand for energy, new sustainable solutions are needed both economically and environmentally. Thermoelectric waste heat recovery and energy harvesting could contribute by increasing industrial process efficiency, as well as powering stand-alone devices, microgenerators, and small body appliances.The structural complexity of quaternary chalcogenide materials provides an opportunity for engineering defects and disorder, to modify and possibly improve specific properties. Cu2ZnSnS4 (CZTS, often kesterite), valued for the abundance and non-toxicity of the raw materials, seems particularly suited to explore these possibilities, as it presents several structural defects and polymorphic phase transformations. The aim of this doctoral work is to systematically investigate the effects of structural polymorphism, disorder, and defects on the thermoelectric properties of CZTS, with particular emphasis to their physical origin. A remarkable case is the order-disorder transition of tetragonal CZTS, which is found responsible for a sharp enhancement in the Seebeck coefficient due to a flattening and degeneracy of the electronic energy bands. This effect, involving a randomization of Cu and Zn cations in certain crystallographic planes, is verified in bulk and thin film samples, and applications are proposed to exploit the reversible dependence of electronic properties on disorder. Low-temperature mechanical alloying is instead discovered stabilizing a novel polymorph of CZTS, which disordered cubic structure is studied in detail, and proposed deriving from sphalerite-ZnS. The total cation disorder in this compound provides an uncommon occurrence in thermoelectricity: a concurrent optimization of Seebeck coefficient, electrical and thermal conductivity. These findings, besides providing new and general understanding of CZTS, can cast light on profitable mechanisms to enhance the thermoelectric performance of semiconducting chalcogenides, as well as delineate alternative and fruitful applications.
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Isotta, Eleonora. "Nanostructured thermoelectric kesterite Cu2ZnSnS4." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/315174.
Full textAbstract:
To support the growing global demand for energy, new sustainable solutions are
needed both economically and environmentally. Thermoelectric waste heat recovery
and energy harvesting could contribute by increasing industrial process efficiency, as
well as powering stand-alone devices, microgenerators, and small body appliances.
The structural complexity of quaternary chalcogenide materials provides an
opportunity for engineering defects and disorder, to modify and possibly improve
specific properties. Cu2ZnSnS4 (CZTS, often kesterite), valued for the abundance and
non-toxicity of the raw materials, seems particularly suited to explore these
possibilities, as it presents several structural defects and polymorphic phase
transformations.
The aim of this doctoral work is to systematically investigate the effects of structural
polymorphism, disorder, and defects on the thermoelectric properties of CZTS, with
particular emphasis to their physical origin.
A remarkable case is the order-disorder transition of tetragonal CZTS, which is found
responsible for a sharp enhancement in the Seebeck coefficient due to a flattening and
degeneracy of the electronic energy bands. This effect, involving a randomization of
Cu and Zn cations in certain crystallographic planes, is verified in bulk and thin film
samples, and applications are proposed to exploit the reversible dependence of
electronic properties on disorder. Low-temperature mechanical alloying is instead
discovered stabilizing a novel polymorph of CZTS, which disordered cubic structure
is studied in detail, and proposed deriving from sphalerite-ZnS. The total cation
disorder in this compound provides an uncommon occurrence in thermoelectricity: a
concurrent optimization of Seebeck coefficient, electrical and thermal conductivity.
These findings, besides providing new and general understanding of CZTS, can cast
light on profitable mechanisms to enhance the thermoelectric performance of
semiconducting chalcogenides, as well as delineate alternative and fruitful applications.
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Saba, Johan. "Electrodéposition de polymère conducteur électronique sur des fibres de carbone greffées de nanotubes de carbone." Thesis, Cachan, Ecole normale supérieure, 2012. http://www.theses.fr/2012DENS0073.
Full textAbstract:
Cette thèse s'inscrit dans le cadre du projet ANR « PROCOM » du programme Matériaux et Procédés dont le coordinateur est EADS IW. Elle a eu pour objectif la mise en place et le développement d’un procédé industrialisable consistant en la fabrication de renforts fibreux pour les composites de haute performance. Elle intègre des nouveaux concepts à nano/micro-échelles et un traitement de surface par voie électrochimique. Les travaux de cette thèse présentent la synthèse d’un polymère conducteur électronique, le polypyrrole, par voie électrochimique, effectuée à la surface de renforts hybrides qui sont des fibres de carbone greffées de nanotubes de carbone (NTCs). Dans un premier temps il s’agit d’optimiser la synthèse du polymère et d’observer l’influence des différents paramètres liés à l’électrochimie sur le taux de dopage et l’épaisseur du film polymère. Les paramètres étudiés étant le potentiel appliqué, le temps de polymérisation, la nature de l’électrolyte et le dopant. Puis il s’agit d’évaluer l’influence du dépôt de polymère sur trois paramètres très importants. Ces paramètres sont la conductivité électrique, les propriétés mécaniques et l’accrochage des NTCs à la surface de la fibre de carbone. Les propriétés électriques sont importantes car ces composites seront utilisés pour le fuselage d’aéronefs qui doivent pouvoir dissiper le courant en cas de foudre. Les bonnes propriétés électriques intrinsèques des NTCs ainsi que l’utilisation d’un polymère conducteur ont permis d’améliorer les propriétés conductrices du renfort. Le polymère joue également le rôle d’interface entre le renfort qui est la fibre hybride et la matrice dans le but d’améliorer les propriétés mécaniques du matériau final. Cependant pour améliorer l’interface différents pré-traitements ont été effectués, tels qu’un traitement thermique, une fonctionnalisation de surface par plasma et le greffage d’une couche d’accroche. Enfin, le polymère joue un rôle protecteur au niveau de la dissémination des NTCs dans l’atmosphère afin d’éviter tout risque sanitaire. Dans un deuxième temps, un système permettant l’électropolymérisation des fibres hybrides en continu a été mis au point en vue de la réalisation d’un procédé pilote par les partenaires industriels du projetThis thesis is part of the ANR project “PROCOM” from the Mat&Pro program whose coordinator is EADS IW. The aim of the project is the development of a process likely to be scaled up industrially to produce fibrous reinforcements for high performance composites. The project incorporates new concepts in nano / micro-scale and an electrochemical surface treatment. This PhD work presents the synthesis of an electronically conductive polymer (polypyrrole) by an electrochemical route, on the surface of hybrid reinforcements which are carbon fibers grafted by carbon nanotubes (CNTs). At first, the polymer synthesis has been optimized and the influence of different electrochemical parameters on the doping level and the thickness of the polymer layer was investigated. The parameters studied were the applied potential, the polymerization time, the nature of the electrolyte and the dopant. Then, the influence of polymer deposition on three very important parameters was considered. These parameters are the electrical conductivity, the mechanical properties and the adhesion of CNTs on the surface of the carbon fibers. The electrical properties are important because these composites are intended to be used for the fuselage of aircraft that must be able to dissipate the current from lightning. Good intrinsic electrical properties of CNTs and the use of a conductive polymer have improved the conductive properties of reinforcements. The polymer, which is at the interface between the reinforcing hybrid fibers and the matrix, is expected to improve the mechanical properties of the final material. However, to improve this interface different pre-treatments were carried out, such as heat treatment, plasma surface functionalization and incorporation of a grafting layer. Finally, the polymer plays a protective role in the dissemination of CNTs in the atmosphere in order to avoid any health risk. In a second step, a system for the electropolymerization of hybrid fibers in continuous was implemented with the aim of developing an industrially scalable 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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Ye, Yueping. "Microstructure and properties of epoxy/halloysite nanocomposite /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20YE.
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Stolk, Jonathan Douglas. "Development of low thermal expansion, high conductivity nanocomposites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Kariuki, Nancy N. "Nanostructured materials for electroanalytical applications." Diss., Online access via UMI:, 2005.
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Assfour, Bassem. "Hydrogen Storage In Nanostructured Materials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-65858.
Full textAbstract:
Hydrogen is an appealing energy carrier for clean energy use. However, storage of hydrogen is still the main bottleneck for the realization of an energy economy based on hydrogen. Many materials with outstanding properties have been synthesized with the aim to store enough amount of hydrogen under ambient conditions.
Such efforts need guidance from material science, which includes predictive theoretical tools.
Carbon nanotubes were considered as promising candidates for hydrogen storage applications, but later on it was found to be unable to store enough amounts of hydrogen under ambient conditions. New arrangements of carbon nanotubes were constructed and hydrogen sorption properties were investigated using state-of-the-art simulation methods. The simulations indicate outstanding total hydrogen uptake (up to 19.0 wt.% at 77 K and 5.52wt.% at 300 K), which makes these materials excellent candidates for storage applications. This reopens the carbon route to superior materials for a hydrogen-based economy.
Zeolite imidazolate frameworks are subclass of MOFs with an exceptional chemical and thermal stability. The hydrogen adsorption in ZIFs was investigated as a function of network geometry and organic linker exchange. Ab initio calculations performed at the MP2 level to obtain correct interaction energies between hydrogen molecules and the ZIF framework. Subsequently, GCMC simulations are carried out to obtain the hydrogen uptake of ZIFs at different thermodynamic conditions. The best of these materials (ZIF-8) is found to be able to store up to 5 wt.% at 77 K and high pressure.
We expected possible improvement of hydrogen capacity of ZIFs by substituting the metal atom (Zn 2+) in the structure by lighter elements such as B or Li. Therefore, we investigated the energy landscape of LiB(IM)4 polymorphs in detail and analyzed their hydrogen storage capacities. The structure with the fau topology was shown to be one of the best materials for hydrogen storage. Its total hydrogen uptake at 77 K and 100 bar amounts to 7.8 wt.% comparable to the total uptake reported of MOF-177 (10 wt.%), which is a benchmark material for high pressure and low temperature H2 adsorption.
Covalent organic frameworks are new class of nanoporous materials constructed solely from light elements (C, H, B, and O). The number of adsorption sites as well as the strength of adsorption are essential prerequisites for hydrogen storage in porous materials because they determine the storage capacity and the operational conditions. Currently, to the best of our knowledge, no experimental data are available on the position of preferential H2 adsorption sites in COFs. Molecular dynamics simulations were applied to determine the position of preferential hydrogen sites in COFs. Our results demonstrate that H2 molecule adsorbed at low temperature in seven different adsorption sites in COFs. The calculated adsorption energies are about 3 kJ/mol, comparable to that found for MOF systems. The gravimetric uptake for COF-108 reached 4.17 wt.% at room temperature and 100 bar, which makes this class of materials promising for hydrogen storage applications.
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Kubo, Shiori. "Nanostructured carbohydrate-derived carbonaceous materials." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5315/.
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Nanoporous carbon materials are widely used in industry as adsorbents or catalyst supports, whilst becoming increasingly critical to the developing fields of energy storage / generation or separation technologies. In this thesis, the combined use of carbohydrate hydrothermal carbonisation (HTC) and templating strategies is demonstrated as an efficient route to nanostructured carbonaceous materials. HTC is an aqueous-phase, low-temperature (e.g. 130 – 200 °C) carbonisation, which proceeds via dehydration / poly-condensation of carbon precursors (e.g. carbohydrates and their derivatives), allowing facile access to highly functional carbonaceous materials. Whilst possessing utile, modifiable surface functional groups (e.g. -OH and -C=O-containing moieties), materials synthesised via HTC typically present limited accessible surface area or pore volume. Therefore, this thesis focuses on the development of fabrication routes to HTC materials which present enhanced textural properties and well-defined porosity.
In the first discussed synthesis, a combined hard templating / HTC route was investigated using a range of sacrificial inorganic templates (e.g. mesoporous silica beads and macroporous alumina membranes (AAO)). Via pore impregnation of mesoporous silica beads with a biomass-derived carbon source (e.g. 2-furaldehyde) and subsequent HTC at 180 oC, an inorganic / carbonaceous hybrid material was produced. Removal of the template component by acid etching revealed the replication of the silica into mesoporous carbonaceous spheres (particle size ~ 5 μm), representing the inverse morphological structure of the original inorganic body. Surface analysis (e.g. FTIR) indicated a material decorated with hydrophilic (oxygenated) functional groups. Further thermal treatment at increasingly elevated temperatures (e.g. at 350, 550, 750 oC) under inert atmosphere allowed manipulation of functionalities from polar hydrophilic to increasingly non-polar / hydrophobic structural motifs (e.g. extension of the aromatic / pseudo-graphitic nature), thus demonstrating a process capable of simultaneous control of nanostructure and surface / bulk chemistry.
As an extension of this approach, carbonaceous tubular nanostructures with controlled surface functionality were synthesised by the nanocasting of uniform, linear macropores of an AAO template (~ 200 nm). In this example, material porosity could be controlled, showing increasingly microporous tube wall features as post carbonisation temperature increased. Additionally, by taking advantage of modifiable surface groups, the introduction of useful polymeric moieties (i.e. grafting of thermoresponsive poly(N-isopropylacrylamide)) was also demonstrated, potentially enabling application of these interesting tubular structures in the fields of biotechnology (e.g. enzyme immobilization) and medicine (e.g. as drug micro-containers).
Complimentary to these hard templating routes, a combined HTC / soft templating route for the direct synthesis of ordered porous carbonaceous materials was also developed. After selection of structural directing agents and optimisation of synthesis composition, the F127 triblock copolymer (i.e. ethylene oxide (EO)106 propylene oxide (PO)70 ethylene oxide (EO)106) / D-Fructose system was extensively studied. D-Fructose was found to be a useful carbon precursor as the HTC process could be performed at 130 oC, thus allowing access to stable micellular phase. Thermolytic template removal from the synthesised ordered copolymer / carbon composite yielded functional cuboctahedron single crystalline-like particles (~ 5 μm) with well ordered pore structure of a near perfect cubic Im3m symmetry. N2 sorption analysis revealed a predominantly microporous carbonaceous material (i.e. Type I isotherm, SBET = 257 m2g-1, 79 % microporosity) possessing a pore size of ca. 0.9 nm. The addition of a simple pore swelling additive (e.g. trimethylbenzene (TMB)) to this system was found to direct pore size into the mesopore size domain (i.e. Type IV isotherm, SBET = 116 m2g-1, 60 % mesoporosity) generating pore size of ca. 4 nm. It is proposed that in both cases as HTC proceeds to generate a polyfuran-like network, the organised block copolymer micellular phase is essentially “templated”, either via hydrogen bonding between hydrophilic poly(EO) moiety and the carbohydrate or via hydrophobic interaction between hydrophobic poly(PO) moiety and forming polyfuran-like network, whilst the additive TMB presumably interact with poly(PO) moieties, thus swelling the hydrophobic region expanding the micelle template size further into the mesopore range.Nanoporöse kohlenstoffbasierte Materialien sind in der Industrie als Adsorbentien und Katalysatorträger weit verbreitet und gewinnen im aufstrebenden Bereich der Energiespeicherung/erzeugung und für Trennverfahren an wachsender Bedeutung. In der vorliegenden Arbeit wird gezeigt, dass die Kombination aus hydrothermaler Karbonisierung von Zuckern (HTC) mit Templatierungsstrategien einen effizienten Weg zu nanostrukturierten kohlenstoffbasierten Materialien darstellt. HTC ist ein in Wasser und bei niedrigen Temperaturen (130 - 200 °C) durchgeführter Karbonisierungsprozess, bei dem Zucker und deren Derivate einen einfachen Zugang zu hochfunktionalisierten Materialien erlauben. Obwohl diese sauerstoffhaltige Funktionalitäten auf der Oberfläche besitzen, an welche andere chemische Gruppen gebunden werden könnten, was die Verwendung für Trennverfahren und in der verzögerten Wirkstofffreisetzung ermöglichen sollte, ist die mittels HTC hergestellte Kohle für solche Anwendungen nicht porös genug. Das Ziel dieser Arbeit ist es daher, Methoden zu entwickeln, um wohldefinierte Poren in solchen Materialien zu erzeugen. Hierbei führte unter anderem der Einsatz von anorganischen formgebenden mesoporösen Silikapartikeln und makroporösen Aluminiumoxid-Membranen zum Erfolg. Durch Zugabe einer Kohlenstoffquelle (z. B. 2-Furfural), HTC und anschließender Entfernung des Templats konnten poröse kohlenstoffbasierte Partikel und röhrenförmige Nanostrukturen hergestellt werden. Gleichzeitig konnte durch eine zusätzliche Nachbehandlung bei hoher Temperatur (350-750 °C) auch noch die Oberflächenfunktionalität hin zu aromatischen Systemen verschoben werden. Analog zur Formgebung durch anorganische Template konnte mit sog. Soft-Templaten, z. B. PEO-PPO-PEO Blockcopolymeren, eine funktionelle poröse Struktur induziert werden. Hierbei machte man sich die Ausbildung geordneter Mizellen mit der Kohlenstoffquelle D-Fructose zu Nutze. Das erhaltene Material wies hochgeordnete Mikroporen mit einem Durchmesser von ca. 0,9 nm auf. Dieser konnte desweiteren durch Zugabe von Quell-Additiven (z. B. Trimethylbenzol) auf 4 nm in den mesoporösen Bereich vergrößert werden. Zusammenfassend lässt sich sagen, dass beide untersuchten Synthesewege nanostrukturierte kohlenstoffbasierte Materialien mit vielfältiger Oberflächenchemie liefern, und das mittels einer bei relativ niedriger Temperatur in Wasser ablaufenden Reaktion und einer billigen, nachhaltigen Kohlenstoffquelle. Die so hergestellten Produkte eröffnen vielseitige Anwendungsmöglichkeiten, z. B. zur Molekültrennung in der Flüssigchromatographie, in der Energiespeicherung als Anodenmaterial in Li-Ionen Akkus oder Superkondensatoren, oder als Trägermaterial für die gezielte Pharmakotherapie.
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Melberg, Brita. "Nanostructured surfaces with patterned wettability." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19410.
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This project aims at the fabrication of a rough polydimethylsiloxane(PDMS) surface with patterned smooth areas. The idea is that such a surface will allow for water capturing on the smooth areas of the surface. The applications for this kind of surface are many, but especially the prospects of a surface able to trap droplets of cells in suspension by simply dipping the surface into the suspension is intriguing.From a previous project[1], and another student’s master’s thesis[2], the use of an etched copper surface seemed promising for the fabrication of a rough mold. This was abandoned after sandpaper turned out to be an even better mold, giving superhydrophobic PDMS(162, 33 ± 1, 40degrees).The negative photoresist SU-8 5 was used to pattern the sandpaper with small, circular features on the P1000 sandpaper(400μm and 1mm in diameter). The PDMS replica from this mold was a rough surface with smooth wells. This was not able to capture water droplets effectively, partly because air bubbles were trapped in the wells during the immersion in water. To avoid this, another mold was procured by the silanization of the previously made PDMS surface. The PDMS replica of the silanized PDMS had smooth pillars instead of wells, and did not succeed in trapping water droplets either. In fact, the smooth wells seemed to better at capturing the water.This project has succeeded in producing high enough roughness on PDMS to alter the contact angle with water by ∼ 61 degrees to a contact angle exceeding the lower limit for superhydrophobic surfaces by ∼ 12 degrees. The use of a sandpaper mold has proven to is simple, inexpensive and effective at producing PDMS with high contact angles.
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Stannard, Andrew David. "Pattern Formation in Nanostructured Systems." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523471.
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Krishnan, Jagadamma Lethy. "Characterisation of nanostructured light emitters." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=17192.
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Group III-nitride semiconductors are the dominant inorganic solid state light emitting materials, spanning the UV to infra-red spectral range. InGaN/GaN based LEDs and lasers are commercially available and intense research is being pursued to improve their efficiency. One practical approach is the development of functionalised and/or improved materials patterned on a nanometre length scale. This thesis presents the optical, morphological and compositional characterisation of III-nitride based nanostructured light emitters. The III-nitride nanostructures studied are GaN coalesced above arrays of either nanopyramids or nanocolumns, semipolar and nonpolar InGaN QWs on the facets of GaN nanopyramids, and thin epilayers of AlInN and AlInGaN. Spatially resolved optical characterisation of nano-ELOG GaN layers revealed a shift in the exciton-related band edge emission across the coalesced layer. This is related to Si doping and to strain effects. Study of the semipolar {1011} InGaN QWs grown on the facets of GaN nanopyramids identified a blue shift in QW emission energy as the sampled region is moved up the pyramid facets. This shift is found to follow the release of the tensile strain towards the top of nanopyramid. Luminescence properties of nearly lattice matched AlInN epilayers investigated using CL, PL and PLE spectroscopic techniques revealed that the emission and bandgap energy of the AlInN layers are at higher energy than that of GaN. Results obtained from polarisation resolved PL measurements of AlInN epilayers point to two possible implications: the observed higher energy AlInN emission is either related to defects or this emission is due to carrier recombination occurring in InN clusters similar to those of InGaN epilayers. Optical properties of thin AlInGaN epilayers investigated using PL and PLE spectroscopy revealed a redshift in bandgap energy with increase in InN fraction. The observed spatial intensity fluctuations are discussed in terms of the InN compositional fluctuations and inhomogeneous strain effects.
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Reiman, Kenneth Helmut. "Nanostructured eletrodes for battery applications." Thesis, University of Southampton, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500855.
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Huang, C. "Atom diffractometry from nanostructured surfaces." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604697.
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Chapter 1 introduces the basic principles of atom diffractometry and scattering from surfaces. I discuss the experimental and theoretical methods employed to determine the atom-surface interaction potential. In addition, a brief description of the apparatus and typical measurements are given. In Chapter 2, a new method is developed for determining the atom-surface interaction potential by interference effects. Based on a 0.5 ML Ni-Cu(100) surface, the helium interaction potential on an unreconstructed Ni(100) overlayer is determined experimentally, which would not have been previously possible due to the absence of diffractive and resonant scattering intensity. A detailed investigation of growth mechanism and surface structure of Ni-Cu(100) is presented in Chapter 3. It is observed that the nickel growth occurs by forming ordered overlayer structures at and below room-temperature, whilst proceeds via alloying processes at high temperatures. The second growth system, Li-Cu(100), is studied in Chapter 4. A sequence of ordered overlayer structures with unusual electronic corrugations are observed in the growth at low temperatures. The surface corrugation for helium scattering from a complex structure, c(5V 2 x v 2)R45° Li-Cu (100), is derived through a diffraction analysis using the exact, close-coupled channels method. Finally, a comparison between neon and helium scattering from an ordered c(2x2) Li-Cu(100) structure is presented in Chapter 5. The surface corrugation for neon scattering is determined on a metallic overlayer for the first time. it is found that the neon corrugation amplitude is at least one order of magnitude larger than for helium. Such a difference exceeds those observed previously on low-index transition metal surfaces.
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Kuzume, Akiyoshi. "Electron transfer at nanostructured interfaces." Thesis, University of Liverpool, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402324.
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Al-Aaraji, Mohammed. "Nanostructured ferroelectric ceramics and coatings." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/nanostructured-ferroelectric-ceramics-and-coatings(fee6c466-fce3-40f1-806a-2f26ecacdf82).html.
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Lead-based and lead-free ferroelectric ceramic materials were prepared at low sintering temperatures with particular regard to their applications in thick film piezoelectric components. This project is focused on the development of processing methods and novel compositions to be used for thick film production by electrophoretic deposition (EPD) on heat-resistant alloys. Lead-based glasses and an oxide mixture (LiCO3, Bi2O3 and CuO), denoted LBCu, with low melting points were used as sintering aids for lanthanum-doped lead zirconate titanate (PLZT) ceramics. The required temperature to achieve dense ceramics was reduced from 1250 to 950 °C. It was found that the highest ferroelectric properties were obtained by the use of LBCu in comparison with those incorporating glass additives due to the shielding effect of the glass phase between the ferroelectric grains. However, the results of thick film preparation shown that the samples with glass additives were much smoother and relatively free of cracks up to 1000 ÂoC. In terms of lead-free ceramics, novel compositions were prepared, based on (Ba,Ca)(Zr,Ti)O3-(K0.5Bi0.5)TiO3 (BCZT-KBT) solid solutions having various Ca and Zr contents. The new solid solutions exhibited interesting features comprising core-shell type microstructures and relaxor ferroelectric behaviour in addition to reduced sintering temperatures and higher Curie point compared with BCZT ceramics. The required sintering temperature reduced to 1125 °C at 65% KBT, in comparison with 1500 °C for pure BCZT. The results showed that the compositional heterogeneity in the shell regions was reduced by air quenching, relative to that of the slow-cooled state, due to the retention of the more chemically-homogeneous high temperature state by the quenching process. The improvements were evident in increased polarisation, piezoelectric coefficient and depolarisation temperature values. However, the slow-cooled samples exhibited high reversible strain levels due to the presence of polar nanoregions (PNRs) in the ergodic state within the shell regions. Comparing the results obtained for two BCZT compositions, it was demonstrated that the stability of the ferroelectric tetragonal phase in slow-cooled BCZT-KBT samples was improved for the ceramic with lower Ca and Zr concentrations, denoted x=0.06, in comparison with that for higher levels, denoted x=0.15. Moreover, the electric field-induced ferroelectric state in the quenched ceramic with x=0.06 was found to be more stable during heating, giving rise to an enhanced depolarisation temperature.
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Heffernan, Shane. "Nanostructured CU₂O solar cells." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709220.
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Gordon, Jeremy B. "Thermorheological properties of nanostructured dispersions." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39866.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 143-149).
Nanostructured dispersions, which consist of nanometer-sized particles, tubes, sheets, or droplets that are dispersed in liquids, have exhibited substantially higher thermal conductivities over those of the liquids alone. While it is desirable to synthesize a fluid that has improved heat transfer characteristics, it is necessary that the viscosity remain low, so as not to appreciably increase the pumping power needed to employ these fluids in "real world" applications. To this end, the theological and thermal properties of twenty-six different nanostructured dispersions were examined. In terms of rheometry, both steady flow and creep tests were employed, while the transient hot wire technique was utilized to perform measurements of the thermal conductivity of each fluid. Characterization of the dispersed phase was completed using dynamic light scattering and transmission electron microscopy. In particular, the dispersion properties examined were nanostructure material, nanoparticle size, base fluid material, nanostructure concentration, and presence of a surfactant. It was observed that several of the fluids or nanopowders obtained from commercial manufacturers either contained no particles, had the presence of a relatively large proportion of water in ethylene glycol-based fluids, or were composed of particles with sizes far in excess of those claimed by the manufacturer.
(cont.) Ultimately, it was determined that while most of the fluids studied demonstrated Newtonian or slightly shear thinning behavior, several of the fluids exhibited undesirable yield stresses that could be attributed to the formation of a network structure of aggregated nanoparticles. However, it was observed that the addition of a surfactant helped to keep the nanoparticles from clustering to the same degree, thereby eliminating the presence of a yield stress, and reducing the viscosity of the fluid over the entire range of shear rates. The surfactant also contributed to an increase in thermal conductivity enhancement, thereby producing a highly desirable behavior.
by Jeremy B. Gordon.
S.M.
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Ahn, Edward Sun 1972. "Nanostructured apatites as orthopedic biomaterials." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8627.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2001.Includes bibliographical references.
Historically, using suitable mechanical replacements for bone has been a priority in designing permanent, load-bearing orthopedic implants. As a result, the biomaterials used in these implants have been largely limited to bioinert titanium-based alloys, as well as to polycrystalline alumina and zirconia ceramics. However, analysis of implants incorporating these traditional biomaterials indicated that most failures involved an unstable implant-tissue interface and/or a mismatch of the mechanical behavior of the implant with the surrounding tissues. As a result, up to 20% of patients receiving permanent, load-bearing implants may undergo a revision operation. The objective of this research was to develop an alternative biomaterial that combined both mechanical resilience and an osteoconductive surface to provide a stable interface with the surrounding connective tissue so that the need for revision operations may be significantly reduced. In the effort to address the issue of mechanical strength and bioactivity simultaneously, hydroxyapatite (HAP) has generated considerable interest. Though a commonly used bioceramic, HAP has been limited by its processability. This material is sensitive to non-stoichiometry and impurities during synthesis and processing due to its complex composition and crystal structure (Ca10(P04)6(OH)2, P63/m).
(cont.) Consequently, conventionally processed HAP materials lack phase purity and homogeneity. Densification of HAP requires high temperatures that result in grain growth and decomposition into undesired phases with poor mechanical and chemical stability. To circumvent densification at high temperatures, glassy additives have been introduced to promote liquid-phase sintering at a lower temperature. However, the presence of a secondary glassy phase gave rise to poor mechanical characteristics. Hence, clinical applications of HAP have been limited to powders, coatings, porous bodies, and non-load-bearing implants. To overcome the deficiencies of conventionally processed HAP, nanostructure processing was applied, which allowed for materials design from the molecular level. By using an aqueous chemical precipitation technique, a fully dense, transparent, nanostructured HAP-based bioceramic that exhibited superior mechanical properties and enhanced tissue bonding was obtained. Processing parameters affecting the molecular and structural development of HAP were used to tailor HAP stoichiometry, crystallite size, morphology and surface chemistry for optimal thermal stability and sinterability. Unlike conventionally processed HAP, the stoichiometric, equiaxed, nanocrystalline HAP powders demonstrated significantly enhanced sinterability by fully densifying at a remarkably low temperature of 900ʻC with pressure-assisted sintering.
(cont.) Furthermore, high-resolution electron micrographs illustrated that the sintered compact possessed a uniform and ultrafine microstructure with an average grain size of -100 nm, with no glassy or amorphous interfaces along the grain boundaries. The crystallinity of the HAP grains and grain boundaries and the minimal flaw sizes could be credited for the superior strength of nanostructured HAP compared to conventional HAP. Compared to polycrystalline HAP, nanocrystalline HAP also provided greater osteoblast function. In vitro experiments indicated that nanocrystalline HAP surfaces enhanced cell attachment, proliferation and mineralization. The larger grain boundary volume resulting from the ultrafine microstructure might have enhanced protein adsorption, ...
by Edward Sun Ahn.
Ph.D.
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Clavel, Guylhaine. "Magnetic impurities in nanostructured materials." Doctoral thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/3210.
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Doutoramento em QuímicaOs resultados apresentados aqui foram alcançados no âmbito do programa de doutoramento intitulado “Impurezas Magnéticas em Materiais Nanoestruturados”. O objectivo do estudo foi a síntese e caracterização de óxido contendo impurezas magnéticas. Durante este trabalho, sínteses de sol-gel não-aquoso têm sido desenvolvidos para a síntese de óxidos dopados com metais de transição (ZnO e ZrO2). A dopagem uniforme é particularmente importante no estudo de semicondutores magnéticos diluídos (DMSs) e o ponto principal deste estudo foi verificar o estado de oxidação e a estrutura local do dopante e para excluir a existência de uma fase secundária como a origem do ferromagnetismo. Para alargar o âmbito da investigação e explorar plenamente o conceito de "impurezas magnéticas em materiais nanoestruturados" estudamos as propriedades de nanopartículas magnéticas dispersas em uma matriz de óxido. As nanopartículas (ferrita de cobalto) foram depositadas como um filme e cobertas com um óxido metálico semicondutor ou dielétrico (ZnO, TiO2). Estes hetero-sistemas podem ser considerados como a dispersão de impurezas magnéticas em um óxido. As caracterizações exigidas por estes nanomateriais têm sido conduzidas na Universidade de Aveiro e Universidade de Montpellier, devido ao equipamento complementar.
The results presented here have been achieved under the PhD program entitled “Magnetic Impurities in Nanostructured Materials”. This study had as purpose the synthesis and characterization of oxidic semiconductor containing magnetic impurities. During this work we have developed non-aqueous sol-gel routes, leading to well controlled oxide nanomaterials, to the synthesis of transition-metal doped oxides (ZnO and ZrO2). Homogeneous doping is particularly important in the comprehensive study of diluted magnetic semiconductors (DMSs), and the main point of this study was to ascertain the oxidation state and local structure of the dopant, as well as to exclude the existence of secondary phase as the origin of ferromagnetism. To enlarge the field of research and fully explore the concept of “magnetic impurities in nanostructured materials” we have studied the magnetic properties of nanoparticles embedded in an oxide matrix. The nanoparticles (cobalt ferrite) were deposited as a film and coated by a semiconducting or dielectric metal oxide (ZnO, TiO2). These hetero-systems can be regarded as dispersion of magnetic impurities in oxides. The characterizations needed by these nanomaterials were performed at the University of Aveiro and University of Montpellier because of complementary available equipments.
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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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Gherbaz, Gabriele. "Nanostructured polymers : morphology and properties." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/66593/.
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This study is aimed to investigate the relationship between morphology and properties of non polar polymers in the presence of polar additives of different nature. The addi- tion of the physical gel dibenzylidene sorbitol (DBS) in a polyethylene (PE) blend has shown to act as a nucleation site on the polymer. Electron microscopy was used to reveal the fibrillar network formed by the DBS and its interaction with the PE. Moreover, the nucleation density in each material was obtained as a function of the crystallization temperature, which showed an increase in the number of nuclei in the clarified system compared to the unclarified one. However, this was found to be temperature dependent. The nucleation of PE on DBS was also studied through the induction time, which revealed a reduced surface energy of the polymer nucleus in the presence of the DBS. Space charge measurements were taken to investigate the charge transport in PE/DBS blends and the space charge at low concentration of the gelator was found to improve the space charge distribution. The same polyethylene blend has then been studied also upon addition of relatively polar ethylene/ vinyl acetate copolymers (EVA), with a VA content varying from 9 % to 40 %. Morphology studies showed that three main factors control the phase separation, namely the the time the blend is kept in the melt, the PE:EVA ratio and also the EVA molecular weight. However, breakdown testing demonstrated that the polarity of EVA decreased the breakdown strength of the blends, independently on the morphology. Finally, a preliminary study was conducted with EVA based nanocomposites to determine the effect of filler on the dielectric properties of the nanocomposite. Two relatively polar copolymers, EVA9 and EVA18, were processed by solution blending together with 5 % of o-MMT ( I30P and I44PA), and the time of solution blending was varied from 10 min to 100 min. X-ray scattering data showed intercalation in the case of EVA9 based anocomposites and potential exfoliation for EVA18 based nanocomposites. However, X-ray results suggest that the solution blending could extract a fraction of the organo-modified ions from in between the MMT galleries, leading to shrinkage of the clay spacing. The nanocomposite was also analysed from the point of view of its breakdown properties, which were shown to be unaffected by the presence of fillers.
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Zhu, Ronghua (Richard). "Atomistic Simulation of Nanostructured Materials." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164059775.
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