Dissertations / Theses on the topic 'Properties Tuning'
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1
Lloyd, Gareth Owen. "Anion-tuning of supramolecular gel properties." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/186/.
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Low molecular weight gelators (LMWGs) are a class of compounds that has garnered great interest from material, synthetic, supramolecular and biological chemists. Anion tuning of these supramolecular gels is a burgeoning field of study. Two classes of compounds, chiral bisureas and urea derivatised pyrazoles are studied. The synthesized chiral bisurea compounds act as gelators in a variety of solvents. Addition of anions in the form of tetrabutyl ammonium salts was found to afford break up of the gels. Studies reveal that the rheological characteristics of these materials can be tuned using the simple addition of sub-stoichiometric amounts of anion. Variation in the length of the alkyl chain of the spacer separating the chiral and bisurea moieties affects the gel formation of a series of related compounds. Compounds with even numbered spaced alkyl chains were found to gel, whereas the odd numbered spaced alkyl chain compounds did not. Crystal growth within the gel matrix influences the crystallization processes and the use of anion induced break down of the LMWGs allows for easy recovery of the grown crystals. Drug compounds, bound upon gelation of a solution containing the drugs, were found to be released in a controlled manner from the gel matrix. Urea functionalised pyrazoles were synthesized. Crystallographic determination of the hydrogen bonding of the compounds as well as the coordination chemistry of these compounds was obtained. Anion binding studies, in addition to the crystallographic results, reveal that the urea or thiourea groups form an intramolecular hydrogen bond with the pyrazole group resulting in an anti conformation. This prevents formation of gels except in one case. The gelation of 1-(3-methyl-1H-pyrazol-5-yl)-3-(3-nitrophenyl)urea in acidic water overcomes this problem by protonation of the pyrazole group resulting in a syn conformation of the urea group. Anion tuning of the gel properties is revealed where nitrate and chloride result in precipitation of gels and the rheological characteristics can be tuned by changing the anion’s identity.
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Makhort, Anatolii. "Tuning photovoltaic properties in ferroelectric materials." Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE031.
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Les cellules photovoltaïques conventionnelles approchent leur limite fondamentale. Bien que les matériaux électriquement polaires offrent une solution alternative, la compréhension de leurs propriétés photovoltaïques, ainsi que la rareté des composés efficaces constituent un défi important. Cette thèse été consacrée à la recherche d'un composé photovoltaïque dit modèle et optimisation de sa performance. En conséquence, les propriétés photovoltaïques ont été découvertes dans le complexe PMN–xPT. Il est démontré l'existence d'une non-linéarité dans le photo-courant dans l'état de polarisation saturée qui peut également entraîner un effet de mémoire optique. Les études de l'influence de la température et de la déformation sur l'effet photovoltaïque ont été également menées. Les résultats globaux obtenus suggèrent fortement la nature hautement sensible et réglable des effets photovoltaïques et ouvrent les perspectives pour augmenter l'efficacité des cellules photovoltaïques et au-delàConventional solar cells are ultimately approaching their fundamental limit. Although electrically polar materials provide an alternative solution, understanding their photovoltaic properties, as well as a scarcity of efficient compounds constitute an important challenge. Therefore, this thesis was devoted to finding a model photovoltaic compound and optimization of its performance. As a result, the photovoltaic properties were discovered in the PMN–xPT complex. It was shown a nonlinearity in the photocurrent in the saturated polarization state that also results in optical memory effect. The stress and temperature-dependent studies of the photovoltaicity were performed as well. The overall obtained results strongly suggest the highly tunable nature of photovoltaic effects and open the prospect for additional degrees of freedom to increase ferroelectric-based photovoltaic cells efficiency and beyond
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Ustahüseyin, Oya [Verfasser]. "Tuning mechanical properties of hydrogels / Oya Ustahüseyin." Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/115184974X/34.
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Frei, Katherine Rebecca. "Morphology Tuning and Mechanical Properties of Nanoporous Gold." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/91899.
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Nanoporous gold is an exciting topic that has been highly researched due to its potential in applications including sensing, catalysts, gas storage, and heat exchangers, made possible by its high surface area to volume ratio and high porosity. However, these applications tend to require a specific morphology, which is often difficult to control. In this work, significant strides have been made in tuning the morphology of nanoporous gold by studying the effect of different fabrication parameters on the ligament diameter, pore diameter, and ligament length, three characteristics which are most discussed in previous studies concerning nanoporous gold. This material also, generally shows a brittle behavior despite it consisting of a normally ductile constituent element, limiting many commercial applications. There have been multiple simulated studies on the tensile mechanical properties and the fracture mode of this material, but limited experimental tensile testing research exists due to technical difficulty of conducting such experiments with small fragile samples. We examine the tensile mechanical behavior of nanoporous gold with ligament sizes ranging from 10 to 30 nm using in situ tensile testing under an environmental scanning electron microscope (ESEM). A specially designed tensile stage and sample holders are used to deform the sample inside the ESEM, allowing us to observing both the macro and microscopic structure changes. Our experimental results advance our understandings of how porous structure influence the mechanical properties of nanoporous gold, and they also serve to increase the accuracy of future simulation studies that will take this material a step towards commercial use by providing a thorough understanding of its structural mechanical limitations.MS
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Khademi, Ali. "Tuning graphene’s electronic and transport properties via adatom deposition." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62588.
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This thesis investigates the effect of adatom deposition, especially alkali and heavy
adatoms, on graphene’s electronic and transport properties. While there are many
theoretical predictions for tuning graphene’s properties via adatom deposition, only
a few of them have been observed. Solving this enigma of inconsistency between
theory and experiment raises the need for deeper experimental investigation of this
matter. To achieve this goal, an experimental set up was built which enables us to
evaporate different metal adatoms on graphene samples while they are at cryogenic
temperatures and ultra-high vacuum (UHV) conditions.
The critical role of in situ high-temperature annealing in creating reliable interactions
between adatoms and graphene is observed. This contradicts the commonly
accepted assumption in the transport community that placing a graphene sample in
UHV and performing in situ 400-500 K annealing is enough to provide a reliable
adatom-graphene interaction. Even charge doping by alkali atoms (Li), which is
arguably the simplest of all adatom effects, cannot be achieved completely without
in situ 900 K annealing. This observation may explain the difficulty many
groups have faced in inducing superconductivity, spin-orbit interaction, or similar
electronic modifications to graphene by adatom deposition, and it points toward a
straightforward, if experimentally challenging, solution.
The first experimental evidence of short-range scattering due to alkali adatoms
in graphene is presented in this thesis, a result that contradicts the naive expectation
that alkali adatoms on graphene only cause long-range Coulomb scattering.
The induced short-range scattering by Li caused decline of intervalley time and
length (i.e., enhancement of intervalley scattering). No signatures of theoretically
predicted superconductivity of Li doped graphene were observed down to 3 K. Cryogenic deposition of copper increased the dephasing rate of graphene. This
increase in dephasing rate is either a sign of inducing spin-orbit interaction or magnetic
moments by copper. No similar effect was observed for indium.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Mickenberg, Seth F. (Seth Fox). "Tuning the photophysical properties of amidophosphine complexes of copper." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49753.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.Vita.
Includes bibliographical references (leaves 23-24).
A series of monomeric copper complexes that allow for the tuning of the emission properties is reported. Luminescence lifetimes up to 150 [mu]s are observed in benzene solution at ambient temperature, which are comparable to the lifetimes of the longest-lived previously reported copper luminophores. These complexes also exhibit quantum yields up to 0 = 0.70 at 298 K. The results of time-dependent density functional theory (TDDFT) calculations indicate emission from a triplet state in all cases. The calculations also successfully correlate the energy of the transition from this triplet state to the energy of the observed emission. Such luminescence from a first-row metal is highly unusual, especially when considering the phosphine-based ligand framework used.
by Seth F. Mickenberg.
S.M.
7
Nicolas, Chantel I. "Tuning the electronic properties of carbon-based nanohybrid materials." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2014. http://digitalcommons.auctr.edu/dissertations/1530.
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Single-walled carbon nanotubes and graphene are tunable for chemical sensors and field effect transistors (FETs). In order to tune the electronic, structural, and optical properties of these nanomaterials, covalent and noncovalent functionalization has been effective. Covalent functionalization of graphene and carbon nanotubes have many advantages but may greatly compromise the organized rc-electron network within their honey-comb lattice structures. On the other hand, noncovalent functionalization affords the opportunity to maintain the sp2-hybridized planar network of carbons with extended % conjugation, which makes it an ideal material for electronics applications, even though significant impact on the electronics of these systems may not be achieved. This work features theoretical investigations of both covalent and noncovalent interactions between chemicals and the surfaces of carbon nanotubes and graphene.
Both experimental and theoretical investigations have shown that metallic singlewalled carbon nanotubes (SWNTs) have strong interactions with large aromatic molecules, such as pyrene, via tt-ti; stacking. However, pyrene molecules are not effective as dopants of graphene and carbon nanotubes. Polar derivatives of pyrene, however, have been demonstrated to both bind and modulate the properties of graphene. This is a particularly useful tool in biomimetics research. Also, because as-prepared carbon nanotubes are found in 2:1 bundles of metallic to semiconducting tubes, it is crucial that they are separated into tubes of similar type in order to better serve their functions in electronics applications. Experimental studies have shown that pyrene-azo compounds can selectively differentiate between carbon nanotube by (n,m) chirality and type. This project uses first-principles density-functional calculations to investigate mechanisms of interactions between these pyrene compounds and carbon nanomaterials, which will help to further elucidate binding mechanisms.
The binding of radical groups such as hydrogen or fluorine to the surface of graphene, leads to covalent bond formation and the subsequent changing of orbital hybridization from trigonal (sp2) to tetragonal (sp3). Such a transformation drastically modifies graphene's electronic properties, which leads to the opening of a band gap through the removal of the bands near the Fermi level of pristine graphene. A similar phenomenon occurs as a result of covalent functionalization of carbon nanotubes, which has many electronics applications. Using first-principles density-functional calculations, we have investigated the structural and electronic properties of fluorinated graphene as well as carbon nanotubes treated with fluorinated olefins in order to better understand their reaction mechanisms and comparisons to previous experimental work are provided.
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Götz, Sebastian, Claas Wilke, Matthias Schmidt, Sebastian Cech, and Uwe Aßmann. "Towards Energy Auto Tuning." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-116966.
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Energy efficiency is gaining more and more importance, since well-known ecological reasons lead to rising energy costs. In consequence, energy consumption is now also an important economical criterion. Energy consumption of single hardware resources has been thoroughly optimized for years. Now software becomes the major target of energy optimization. In this paper we introduce an approach called energy auto tuning(EAT), which optimizes energy efficiency of software systems running on multiple resources. The optimization of more than one resource leads to higher energy savings, because communication costs can be taken into account. E.g., if two components run on the same resource, the communication costs are likely to be less, compared to be running on different resources. The best results can be achieved in heterogeneous environments as different resource characteristics enlarge the synergy effects gainable by our optimization technique. EAT software systems derive all possible distributions of themselves on a given set of hardware resources and reconfigure themselves to achieve the lowest energy consumption possible at any time. In this paper we describe our software architecture to implement EAT.
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Götz, Sebastian, Claas Wilke, Matthias Schmidt, Sebastian Cech, and Uwe Aßmann. "Towards Energy Auto Tuning." Technische Universität Dresden, 2010. https://tud.qucosa.de/id/qucosa%3A26982.
Full textAbstract:
Energy efficiency is gaining more and more importance, since well-known ecological reasons lead to rising energy costs. In consequence, energy consumption is now also an important economical criterion. Energy consumption of single hardware resources has been thoroughly optimized for years. Now software becomes the major target of energy optimization. In this paper we introduce an approach called energy auto tuning(EAT), which optimizes energy efficiency of software systems running on multiple resources. The optimization of more than one resource leads to higher energy savings, because communication costs can be taken into account. E.g., if two components run on the same resource, the communication costs are likely to be less, compared to be running on different resources. The best results can be achieved in heterogeneous environments as different resource characteristics enlarge the synergy effects gainable by our optimization technique. EAT software systems derive all possible distributions of themselves on a given set of hardware resources and reconfigure themselves to achieve the lowest energy consumption possible at any time. In this paper we describe our software architecture to implement EAT.
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He, Zhengyu. "Tuning the electrical and optical properties of two dimensional materials." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:d794f6ee-8ea8-4c28-b199-6dbe28992e52.
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The emergence of 2D materials inspires the pursuit of all-2D materials based devices which are predicted to outperform those with conventional architectures and materials. To achieve this goal, thorough understanding of the fundamental electrical and optical properties of 2D materials separately and the ability to manipulate these properties via external modulation methods are essential. Graphene can perform as transparent electrodes, yet suffering from its high sheet resistance. It was demonstrated that it can be greatly reduced via doping iron (III) chloride solution onto graphene film with high optical transmission at visible range if an optimal dopant solution concentration was employed. Doping with nanoscale spatial resolution was then achieved with the help of aberration-corrected transmission electron micro- scope, allowing in-situ observation of the atomic structures of doped regions, which possess unique properties predicted by DFT calculations. Transition metal dichalcogenides (TMDCs) can perform as active materials due to their sizeable bandgap. Therefore, the focus of this thesis then shifted to the investigation of WS2 . Three different methods were employed to alter the optical properties of WS2 . Firstly, the photoluminescence (PL) of WS2 presents layer dependent response towards lateral electric field, with PL quenching in monolayer and PL enhancement in bilayer. The results of temperature dependent PL measurement ruled out the joule heating effect. A possible mechanism based on the inter-valley electron transfer induced recombination pathways modification was then proposed.
11
Lu, Qiyang. "Controlling properties of functional oxides by tuning oxygen defect chemistry." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115715.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 164-192).
Oxygen defects are essential building blocks for properties and functionalities of oxides, including electrical conductivity, magnetism, ferroelectricity as well as catalytic and electrocatalytic activity. Therefore, fundamental understanding of how to tune the oxygen defect chemistry is essential for advancing applications based on these defect sensitive properties. This thesis investigated pathways to controlling the concentration and structure of oxygen defects on selected case studies with model oxide systems. Three novel effects were assessed and shown to be operative for obtaining a large impact on the oxygen defect chemistry equilibria. These are heterogeneous chemical doping of the surface for improving surface electrocatalytic activity and stability, electrochemical bias to control phase with drastic changes obtained in electronic and phonon transport properties, as well as strain engineering to alter the oxygen interstitial capacity and oxygen exchange kinetics. Surface chemical modifications were applied to the near-surface regions of Lao.8Sro.2CoO 3 (LSC) by replacing the Co cations locally with less reducible cations, such as Hf and Ti. This strategy was shown to effectively stabilize the LSC surfaces and suppress surface segregation of Sr at elevated temperatures. This introduced surface stability by local chemical doping greatly enhanced the long-term electrochemical performance of LSC electrode, which provides a new route for improving the efficiency of solid oxide fuel and electrolysis cells. Applying electrical bias was investigated as another effective method to tune the oxygen stoichiometry, exemplified by the case studies on SrCoOx (SCO). In situ X-ray diffraction was used to investigate the topotactic phase transition between brownmillerite phase SrCoO2.5 (BM-SCO) and perovskite phase SrCoO 3 6 (P-SCO) triggered electrochemically at elevated temperatures. An electrical bias of merely 30 mV was shown sufficient to trigger the BM-->P phase transition. This is much more feasible than chemically induced phase transition, which requires high pressure (> 1 bar) and specialized pressurized apparatus. Moreover, the evolution of electronic structure during the BM4P phase transition was probed in operando by using ambient-pressure X-ray photoelectron and absorption spectroscopy (AP-XPS/XAS). The similar experimental scheme, which combines in operando surface characterizations and electrochemical controlling of oxygen stoichiometry, was extended to oxide systems beyond perovskites. This allows us to investigate the defect chemistry of oxides in a much broader range of effective oxygen partial pressure than what conventional methods can achieve. Firstly, we showed that the surface defect chemistry equilibrium of fluoritestructured Pro.iCeo.902-6 (PCO) strongly deviated from the bulk counterpart, due to the possibly enhanced defect-defect interactions or lattice strain effect at surfaces. Secondly, we found a novel metal-insulator transition triggered electrochemically in VO, by changing the phase between the metallic dioxide VO2 and the insulating pentoxide V2O5 Lastly, we lowered the operation temperature of this electrochemical control of oxygen stoichiometry down to room temperature by using ionic liquid or ion gels as the electrolyte. We achieved tuning of thermal conductivity in SrCoOx with a range of more than one order of magnitude, by using electrochemically triggered phase transitions at room temperature. We also investigated the effect of lattice strain on oxygen defect formation energy in Ruddlesden-Popper (RP) phase oxide Nd2NiO4+6 (NNO). We found that tensile strain along the c-axis of NNO lattice effectively reduced the formation enthalpy of oxygen interstitials, which can provide a new route for designing the defect chemistry of RP phase oxide for electrocatalytic applications..
by Qiyang Lu.
Ph. D.
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Malik, Surama. "Tuning of optical properties of InAs/GaAs self assembled quantum dots." Thesis, Imperial College London, 2003. http://hdl.handle.net/10044/1/7557.
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Abrahamsson, Maria. "Tuning of the Excited State Properties of Ruthenium(II)-Polypyridyl Complexes." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7230.
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Souza, de Almeida Jailton. "Designing and Tuning the Properties of Materials by Quantum Mechanical Calculations." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6923.
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Karakoti, Ajay. "Tuning the properties of nanomaterials as function of surface and environment." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4688.
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It is demonstrated that in this PEGyltaed CNPs system, the PEG essentially forms a complex with CNPs in the presence of hydrogen peroxide to facilitate this electron transfer process. The superoxide dismutase (SOD) and catalase mimetic ability of CNPs is described and special emphasis is given to its biocompatibility. The second half of the thesis emphasizes the role of synthesis and surface modification in influencing the catalytic performance of cerium oxide modified titanium dioxide catalysts for decomposition of methanol. Noble metals supported on oxide nanoparticles have been an area of active research in catalysis. It is demonstrated that the modification of surface of the oxide nanoparticles by noble metals is a function of the synthesis process. By keeping the size of the nanoparticles constant, it was demonstrated that the differences in the oxidation state of noble metals can lead to change in the activity of noble metals. This contribution adds to the already existing controversy in the open literature about the role of the oxidation state of platinum in catalysis. The core level shifts in the binding energy of the 4f electrons of platinum was used as a guide to the gauge the oxidation state. Results from an in-house built catalytic reactor coupled to mass spectrometer and in-situ diffuse reflectance infra-red spectroscopy are used to quantify the catalytic performance and identify the mechanism of reaction as well as products of methanol decomposition.; Nanotechnology has shaped the research and development in various disciplines of science and technology by redefining the interdisciplinary research. It has put the materials science at the forefront of technology by allowing the researchers to engineer materials with properties ranging from electronics to biomedical by using materials as diverse as ceramics to just plain carbon. These exceptional properties are achieved by minimizing the dimension of particles in such smaller domains that the boundary between the individual atoms, ions or cluster of particles is very small. This results in a change in conventional properties of particles from continuum physics to quantum physics and hence the properties of nanoparticles can be tuned based upon their size, shape and dimensionality. One of the most apparent changes upon decreasing the particle size is the increase in surface area to volume ratio. Thus nanoparticles possess greater tendency to interact with the environment in which they are present and similarly the environment can affect the properties of nanomaterials. The environment here is described as the immediate solid, liquid or gaseous material in immediate contact with the external surface of the nanoparticles. In order to control the physico-chemical properties of nanoparticles it is important to control the surface characteristics of nanoparticles and its immediate environment. The current thesis emphasizes the role of tuning the surface of nanoparticles and/or the environment around the nanoparticles to control their properties. The current approach in literature uses nanoparticles as a platform that can be used for a myriad of applications by just changing the surface species which can tune the properties of nanoparticles. Such surface modification can provide nanomaterials with hydrophilic, hydrophobic, biocompatible, sensing, fluorescence and/or electron transfer properties.; The current thesis demonstrates the interaction between nanoparticles and the environment by changing the surface characteristics of nanomaterials through the use of oxide nanoparticles as examples. The first part of the thesis discusses the synthesis, modification and properties of cerium oxide nanoparticles (CNPs), a versatile material used in wide range of applications from catalysis to glass polishing, for their potential use in biomedical applications as a function of medium. The thesis starts by projecting the effect of environment on the properties of nanomaterials wherein it is shown that simple medium, such as, water can influence the optical properties of nanoparticles. It was shown that the strong polarizing effect of water on the non-bonding f electrons can cause a blue shift in the optical properties of CNPs as a function of increase in trivalent oxidation state of cerium in CNPs. This phenomenon, contradictory to existing literature in solid state where a red shift is observed upon increasing the trivalent oxidation state of cerium in CNPs, is purely attributed to the medium-inflicted change in properties of nanoparticles. This concept is built upon in the first half of thesis by increasing the colloidal stability of nanoparticles by surface and/or medium modification. It is shown that the narrow range of pH in which the colloidal CNPs are stable can be extended by changing the medium from water to polyhydroxy compounds such as glucose and dextran. The synthesis was designed specially to avoid the traditional precipitation and re-dispersion strategy of synthesis of nanoparticles to preserve the surface activity. The complex forming ability of cerium with polysaccharides was employed to synthesize the CNPs in a one step process and the pH stability of the NPs was extended between 2.0 to 9.5.; The difference in the complexing ability of the monomer - glucose and its anhydro glucose polymer - dextran is reflected in the ability of cerium to form super-agglomerates with the monomer while anhydro gluco polymer forms extremely disperse 3-5 nm nanoparticles through steric modification. It is shown that the antioxidant activity of nanoparticles remain unchanged by surface modification by demonstrating the cycling of the oxidation state of cerium in CNPs, with time, through hydrogen peroxide mediated transition of oxidation states of cerium. It is demonstrated that the polymeric coatings, generally considered as passive surface coatings, can also play an active role in tuning the properties of nanomaterials and increasing their biocompatibility as well as bio-catalytic activity. It is demonstrated that the antioxidant activity of CNPs can be increased as a function of polyethylene glycol (PEG) while the biocompatibility is unaltered due to the biocompatible nature of PEG. The antioxidant activity of CNPs involves an electron transfer (ET) from the CNPs to the reactive oxygen species or vice versa. This heterogeneous ET system is further complicated by the presence of surface adsorbed species. Interfacial charge/electron transfer (ET) between a particle and adsorbed (or covalently bonded) molecule presents significant complexity as it involves a solid state electron transfer over long distance. Unlike a free ion, in solid state, the conducting electrons can be temporarily trapped by the coupling lattice sites. Adsorption/attachment of surface species to nanoparticle can disturb the electronic levels by further polarizing the electron cloud thereby localizing the electron and facilitating the charge transfer. Such an interfacial electron transfer between NPs and adsorbed organic species can be compared to the single electron transfer carried by organometallic systems with a metal ion core modified with electron delocalizing porphyrin ligands.ID: 028732931; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references.
Ph.D.
Doctorate
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
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Motta, Cecilia Margarida Mendes. "Tuning surface properties to optimize cell behavior for tissue engineering applications." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1561654810655256.
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Tarkuc, Simge. "Tuning The Optoelectronic Properties Of Conjugated Polymers Via Donor-acceptor-donor Architectures." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612103/index.pdf.
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A new class of π
-conjugated monomers was synthesized with combination of electron donating and electron-withdrawing heterocyclics to understand the effects of structural differences on electrochemical and optoelectronic properties of the resulting polymers. The use of this alternating donor-acceptor-donor strategy allows the synthesis of low band gap polymers in which the redox, electronic, and optical properties are controlled through easily approachable synthetic modification of the polymer backbone. This control allows fine-tuning of the band gap to values between 1.0 and 1.8 eV by making structural changes. These structural manipulations yield varied electronic absorption energies for a range of colors in the neutral polymer films, multi-colored electrochromism, and accessible states for reduction leading to n-type doping. The polymers prepared were characterized using cyclic voltammetry, colorimetry, and UV-Vis-NIR spectroscopy demonstrating that the polymers can undergo both p- and n-type doping and color changes in both redox states.
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Östmark, Emma. "Tuning Properties of Surfaces and Nanoscopic Objects using Dendronization and Controlled Polymerizations." Doctoral thesis, KTH, Fiber- och polymerteknik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4550.
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In this study, dendronization and grafting via controlled polymerization techniques, atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP), have been explored. Modification of surfaces and cellulose using these techniques, which enable grafting of well-defined polymer architectures, has been investigated. The interest in using cellulose stems from its renewability, biocompatibility, high molecular weight, and versatile functionalization possibilities. Dendronization was performed using disulfide-cored didendrons of 2,2-bis(methylol)propionic acid (bis-MPA) on gold surfaces, for the formation of self-assembled monolayers. It was found that the height of the monolayer increased with increasing dendron generation and that the end-group functionality controlled the wettability of the modified surface. Superhydrophobic cellulose surfaces could be obtained when a ‘graft-on-graft’ architecture was obtained using ATRP from filter paper after subsequent post-functionalized using a perfluorinated compound. The low wettability could be explained by a combination of a high surface roughness and the chemical composition. Biobased dendronized polymers were synthesized through the ‘attach to’ route employing dendronization of soluble cellulose, in the form of hydroxypropyl cellulose (HPC). The dendronized polymers were studied as nanosized objects using atomic force microscopy (AFM) and it was found that the dendron end-group functionality had a large effect on the molecular conformation on surfaces of spun cast molecules. ATRP of vinyl monomers was conducted from an initiator-functionalized HPC and an initiator-functionalized first generation dendron, which was attached to HPC. The produced comb polymers showed high molecular weight and their sizes could be estimated via AFM of spun cast molecules on mica and from dynamic light scattering in solution, to around 100-200 nm. The comb polymers formed isoporous membranes, exhibiting pores of a few micrometers, when drop cast from a volatile solvent in a humid environment. HPC was also used to initiate ROP of ε-caprolactone, which was chain extended using ATRP to achieve amphiphilic comb block copolymers. These polymers could be suspended in water, cross-linked and were able to solubilize a hydrophobic compound.QC 20100826
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Huijben, Mark. "Interface engineering for oxide electronics: tuning electronic properties by atomically controlled growth." Enschede : University of Twente [Host], 2006. http://doc.utwente.nl/55832.
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Fernando, Juwanmandadige Roshan. "Tuning the Opto-Electronic Properties of Core-Substituted Naphthalenediimides through Imide Substitution." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1401984667.
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Götz, Sebastian, Claas Wilke, Sebastian Cech, and Uwe Aßmann. "Architecture and Mechanisms of Energy Auto-Tuning." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-116748.
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Energy efficiency of IT infrastructures has been a well-discussed research topic for several decades. The resulting approaches include hardware optimizations, resource management in operating systems, network protocols, and many more. The approach the authors present in this chapter is a self-optimization technique for IT infrastructures, which takes hard- and software components as well as users of software applications into account. It is able to ensure minimal energy consumption for a user request along with a set of non-functional requirements (e.g., the refresh rate of a data extraction tool). To optimize the ratio between utility of end users and the cost in terms of energy consumption, the system needs inherent variability leading to differentiated energy profiles and mechanisms to reconfigure the system at runtime. The authors present their approach called Energy Auto-Tuning (EAT) comprised of these mechanisms and an architecture which automatically tunes the energy efficiency of IT systems.
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Götz, Sebastian, Claas Wilke, Sebastian Cech, and Uwe Aßmann. "Architecture and Mechanisms of Energy Auto-Tuning." Technische Universität Dresden, 2012. https://tud.qucosa.de/id/qucosa%3A26969.
Full textAbstract:
Energy efficiency of IT infrastructures has been a well-discussed research topic for several decades. The resulting approaches include hardware optimizations, resource management in operating systems, network protocols, and many more. The approach the authors present in this chapter is a self-optimization technique for IT infrastructures, which takes hard- and software components as well as users of software applications into account. It is able to ensure minimal energy consumption for a user request along with a set of non-functional requirements (e.g., the refresh rate of a data extraction tool). To optimize the ratio between utility of end users and the cost in terms of energy consumption, the system needs inherent variability leading to differentiated energy profiles and mechanisms to reconfigure the system at runtime. The authors present their approach called Energy Auto-Tuning (EAT) comprised of these mechanisms and an architecture which automatically tunes the energy efficiency of IT systems.
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Henwood, Adam Francis. "Tuning the physical and optoelectronic properties of phosphorescent iridium(III) complexes : applications to organic semiconductor devices." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/12976.
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This thesis explores the design, synthesis and characterisation of iridium(III) complexes for optoelectronic applications; in particular, cationic [Ir(CˆN)₂(NˆN)]⁺-type emitters (where CˆN is an anionic bidentate cyclometalating ligand such as 2-phenylpyridinato, ppy, and NˆN is a neutral bidentate ligand such as 2,2'-bipyridine, bpy) for use in light-emitting electrochemical cells (LEECs). Design strategies aim to achieve high photoluminescence quantum yields (Φ[sub](PL)) for these complexes. Chapter 1 provides an overview of the fundamental photophysics of luminescent transition metal complexes, before reviewing state of the art iridium complexes employed in LEEC devices. Chapter 2 employs a combination of the electron-deficient 2,4-difluorophenylpyridine (dFppy) CˆN ligand and various functionalised biimidazole (biim) NˆN ligands. Within the family of different biim ligands the emission energy does not vary significantly, but the excited state kinetics di.er depending on the rigidity of the biim ligand. Combining the lead biim ligand with a sterically bulkier CˆN ligand gives an iridium complex that emits deep blue light with 90% Φ[sub](PL) in MeCN. Chapter 3 describes an approach to replacing the electrochemically unstable aryl carbon-fluorine bonds in dFppy, while maintaining the deep blue emission colour observed for the complexes in Chapter 2. Chapter 4 expands on the concept of rigid biim ligands to bibenzimidazoles (bibenz). Combining conjugated bibenz NˆN ligands with more conjugated CˆN ligands allows for the emission colour of these complexes to be tuned to the orange/red. The Φ[sub](PL) necessarily falls due to the energy gap law, but is nevertheless higher than values measured for reference complexes. Chapter 5 explores the use of an arylazoimidazole ligand with donor-acceptor intraligand charge transfer characteristics in order to red-shift the emission further. The resultant complex is poorly emissive, but shows a panchromic absorption profile and high molar absorptivity, which is unusual for iridium(III) complexes. The absorption profile can be tuned as a function of the protonation state of the imidazole.
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Ayers, William R. "Structural Properties and Compositional Processes in Microtonal Equal Temperaments." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin153570341690339.
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Jiraporn, Sirison. "Studies on functional properties of soy lipophilic protein and its potential for food applications." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263363.
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Bellacanzone, Christian. "Tuning of the poly(p-phenylenevinylene) derivativesemission properties by phase change materials andsonochemistry." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/664005.
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Los polímeros conjugado (CP) son un material muy interesante con propiedades optoelectrónicas peculiares que hacen de estos polímeros óptimos candidatos por distintas aplicaciones cuáles OLEDs y celdas organicas fotovoltaicas y también por bioimagen y liberación de fármacos. En los últimos años creciente atención se ha dirigido hacía la modulación de las prioridades ópticas de los CP para poderlos emplear en distintos ámbitos. El objetivo de este trabajo es de lograr un ajuste fino de la emisión de los derivados de polifenileno vinileno (PPV) . Dos estrategias principales se han adoptados. I) Nanoparticulas de oligomeros de PPV con distintas longitudes de conjugación se han producido mediante síntesis sonoquímica. La irradiación con ultrasonidos ha sido aplicada a una solución heterogénea de polímero PPV para inducir la activación de especies radicales que rompen los enlaces doble del polímero cortándolo y generando oligomeros de PPV. La copresencia de un tensioactivo dirige la simultánea nanostructuración de los oligomeros generando nanoparticulas soluble en agua que presentan un progresivo cambio hipsocrómico de las bandas espectrales en absorción y emisión comparado con el polímero inicial. Tal nanoparticulas pueden ser utilizadas en OLEDs y bioimagen. II) los oligomeros y el polímero de PPV fueron mezclados con materiales a cambio de fase de distinto punto de fusión. Cuando tal sistema mixto es calentado, se induce la transición de solido a liquido en el PCM provocando un cambio de fluorescencia hacía el azul. Una vez que el sistema se enfríe y solidifica la emisión inicial es recuperada. Semejante sistema se puede utilizar por la fabricación de sensores de temperatura florecientes y multicolores. También podrías destinar a la realización de diodos orgánico de luz blanca termoregulados aprovechando de la emisión roja, verde y blue de los oligomeros obtenidos en este trabajoConjugated polymers (CP) are interesting materials with peculiar optoelectronic properties which make this class of polymers good candidate for several applications such as OLEDs, organic photovoltaics, but also for bioimaging and drug delivery. In the last decades, increasing attention has been directed to the tuning of the emission properties of CP to fully exploited their application in several fields. The aim of this thesis work is to achieve a fine emission tuning of a polyphenylene vinylene (PPV) derivatives. Two main strategies have been adopted. I) Nanoparticles of PPV oligomers with different conjugation length was obtained through sonochemical synthesis. Ultrasound irradiation of PPV polymer heterogenous solution was employed to induce the activation of radical species which cut the polymer chain forming PPV oligomers. The copresence of surfactant leads to a simultaneous nanostructuration of such oligomers producing water-soluble nanoparticles which exhibited a progressive hypsochromic shift of absorption/emission compared to the parental polymer. These nanoparticles that emitted in a wide range of the visible electromagnetic spectrum are promising materials for application such as polymers LEDs and bioimaging. II) The PPV polymers and oligomers were mixed with phase change materials with different melting point. Upon heating, solid-to-liquid phase transition is induced in the PCM/PPV system and its fluorescence is blue shifted. Once the system is cooled down the initial emission is recovered. Such system could be applied as multicolour emitting temperature sensor, or for thermoregulated white organic light emitting diode, thanks to the red, green and blue emission of the PPV derivatives obtained in this work.
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Algarni, Zaina Sluman. "Exploring Growth Kinematics and Tuning Optical and Electronic Properties of Indium Antimonide Nanowires." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404545/.
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This dissertation work is a study of the growth kinematics, synthesis strategies and intrinsic properties of InSb nanowires (NWs). The highlights of this work include a study of the effect of the growth parameters on the composition and crystallinity of NWs. A change in the temperature ramp-up rate as the substrate was heated to reach the NW growth temperature resulted in NWs that were either crystalline or amorphous. The as-grown NWs were found to have very different optical and electrical properties. The growth mechanism for crystalline NWs is the standard vapor-liquid-solid growth mechanism. This work proposes two possible growth mechanisms for amorphous NWs. The amorphous InSb NWs were found to be very sensitive to laser radiation and to heat treatment. Raman spectroscopy measurements on these NWs showed that intense laser light induced localized crystallization, most likely due to radiation induced annealing of defects in the region hit by the laser beam. Electron transport measurements revealed non-linear current-voltage characteristics that could not be explained by a Schottky diode behavior. Analysis of the experimental data showed that electrical conduction in this material is governed by space charge limited current (SCLC) in the high bias-field region and by Ohm's law in the low bias region. Temperature dependent conductivity measurements on these NWs revealed that conduction follows Mott variable range hopping mechanism at low temperatures and near neighbor hopping mechanism at high temperature. Low-temperature annealing of the amorphous NWs in an inert environment was found to induce a phase transformation of the NWs, causing their crystallinity to be enhanced. This thesis also proposes a new and low-cost strategy to grow p-type InSb NWs on InSb films grown on glass substrate. The high quality polycrystalline InSb film was used as the host on which the NWs were grown. The NWs with an average diameter of 150 nm and length of 20 μm were shown to have hole concentration of about 1017 cm-3 and mobility of about 1000 cm2V-1s-1. This thesis also proposes a strategy for the fabrication of metal-semiconductor nanocomposites. InSb NWs grown by electrochemical deposition were decorated with nanometer sized Au and Ag nanoparticles to form the nanocomposite.
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Gohlke, David Christopher. "Tuning the Properties and Interactions of Manganese Acceptors in Gallium Arsenide with STM." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354669837.
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Leach, Jacob H. "Tuning of electrical properties in InAlN/GaN HFETs and Ba0.5Sr0.5TiO3/YIG Phase Shifters." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2035.
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Engineers know well from an early point in their training the trials and tribulations of having to make design tradeoffs in order to optimize one performance parameter for another. Discovering tradeoff conditions that result in the elimination of a loss associated with the enhancement of some other parameter (an improvement over a typical tradeoff), therefore, ushers in a new paradigm of design in which the constraints which are typical of the task at hand are alleviated. We call such a design paradigm “tuning” as opposed to “trading off”, and this is the central theme of this work. We investigate two types of microwave electronic devices, namely GaN-based heterostructure field effect transistors (HFETs) and tunable ferroelectric-ferrite-based microwave phase shifters. The “tuning” associated with these types of devices arises from the notion of an optimal 2DEG density, capable of achieving higher performance in terms of electron velocity and enhanced reliability in the case of the HFET, and the coupling of ferroelectric and ferrite materials in tunable microwave phase shifters, capable of achieving high differential phase shifts while at the same time mitigating the losses associated with impedance mismatching which typically arise when the phase is tuned. Promises and problems associated with HFET devices based on the intriguing InAlN/GaN material system will be described. We focus on the fundamental problem associated with the induction of the large density of carriers at the interface, namely the disintegration of an excess of longitudinal optical phonons (hot phonons) in the channel. We use microwave measurements in conjunction with stress tests to evidence the existence of an optimal 2DEG density wherein the hot phonon effect can be “tuned,” which allows for enhanced high frequency performance as well as device reliability. Next, we focus on the design, fabrication, and measurement of tunable phase shifters consisting of thin films of BaxSr1-xTiO3 (BST), which has the advantage of having high dielectric tunability as well as relatively low microwave loss. We discuss the design, fabrication, and measurement of a simple coplanar waveguide (CPW) type of phase shifter as well as a more complicated “hybrid” phase shifter consisting of a ferrite (YIG) in addition to BST. The use of such a bilayer allows one to “tune” the impedance of the phase shifters independently of the phase velocity through careful selection of the DC biasing magnetic fields, or alternatively through the use of an additional piezoelectric layer, bonded to YIG whose permeability can then be tuned through magnetostriction.
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Miller, Mark Thomas. "Tuning the properties of copper(I) and nickel(II) through heterocyclic ligand design /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9944217.
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Gao, Jie. "Tuning the chiroptical properties of Goldhelices through their nanostructure optimization and hierarchical organization." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0138/document.
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Les matériaux chiraux peuvent avoir une forte influence sur la propagation de la lumière et ont attiré l'attention de la communauté des nanosciences. Les nanoparticules d'or, matériaux plasmoniques stables ayant une activité dans le visible (400 à 800 nm), sont des objets attrayants en tant que blocs de construction pour la formation de matériaux optiques. Précédemment, nous avons conçu et obtenu des Goldhelices en greffant des nanoparticules d’or sur des nano structures hélicoïdales de silice. Le travail présenté dans cette thèse vise à développer et à organiser les Goldhelices de manière à améliorer, modifier, réduire, voire même éliminer les propriétés chiroptiques. Les détails des nanostructures ainsi que la cinétique de formation de l'auto-assemblage organique utilisé comme support pour la formation de Goldhelices sont étudiés. Des Goldhelices sont ensuit organisées hiérarchiquement à l’aide de trois techniques : la microfluidique, le « dip coating » et le « Grazing Incidence Spraying ». Enfin, l’effet de ces organisations sur les propriétés optiques sont caractérisées par spectroscopies chirales et ellipsométrie. Nous démontrons qu'un tel système peut être utilisé pour la création de polariseur linéaire ou circulaire où une telle polarisation est uniquement dépendant par l'organisation des GoldhelicesChiral materials can have strong influence on the propagation of light and have attracted attention in the nano-science community. Gold nanoparticles (GNPs), stable plasmonic materials in the visible range (400-800 nm), are attractive objects as building blocks for optical materials. We have designed and obtained Goldhelices by grafting GNPs on silica nano-helical structures. The work presented in this thesis aims at developing tunable Goldhelices and organizing them in order to enhance, modify, reduce or even eliminate the chiroptical properties. The details of the nanostructures as well as the kinetics of formation of organic self-assembly which is used as templates for the formation of Goldhelices are fully studied. The hierarchical organization of the Goldhelices is investigated by the use of three techniques, the microfluidics, the dip-coating and the grazing incident spraying. Finally, the effect of the organization on their optical properties are characterized by chiral spectroscopies and Mueller matrix polarization ellipsometry. We demonstrate that such a system can be used for the creation of linear or circular polarizer where such polarization is solely tunable by the organization of the Goldhelices
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Götz, Sebastian. "Multi-Quality Auto-Tuning by Contract Negotiation." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-119938.
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A characteristic challenge of software development is the management of omnipresent change. Classically, this constant change is driven by customers changing their requirements. The wish to optimally leverage available resources opens another source of change: the software systems environment. Software is tailored to specific platforms (e.g., hardware architectures) resulting in many variants of the same software optimized for different environments. If the environment changes, a different variant is to be used, i.e., the system has to reconfigure to the variant optimized for the arisen situation. The automation of such adjustments is subject to the research community of self-adaptive systems. The basic principle is a control loop, as known from control theory. The system (and environment) is continuously monitored, the collected data is analyzed and decisions for or against a reconfiguration are computed and realized. Central problems in this field, which are addressed in this thesis, are the management of interdependencies between non-functional properties of the system, the handling of multiple criteria subject to decision making and the scalability.
In this thesis, a novel approach to self-adaptive software--Multi-Quality Auto-Tuning (MQuAT)--is presented, which provides design and operation principles for software systems which automatically provide the best possible utility to the user while producing the least possible cost. For this purpose, a component model has been developed, enabling the software developer to design and implement self-optimizing software systems in a model-driven way. This component model allows for the specification of the structure as well as the behavior of the system and is capable of covering the runtime state of the system. The notion of quality contracts is utilized to cover the non-functional behavior and, especially, the dependencies between non-functional properties of the system. At runtime the component model covers the runtime state of the system. This runtime model is used in combination with the contracts to generate optimization problems in different formalisms (Integer Linear Programming (ILP), Pseudo-Boolean Optimization (PBO), Ant Colony Optimization (ACO) and Multi-Objective Integer Linear Programming (MOILP)). Standard solvers are applied to derive solutions to these problems, which represent reconfiguration decisions, if the identified configuration differs from the current. Each approach is empirically evaluated in terms of its scalability showing the feasibility of all approaches, except for ACO, the superiority of ILP over PBO and the limits of all approaches: 100 component types for ILP, 30 for PBO, 10 for ACO and 30 for 2-objective MOILP. In presence of more than two objective functions the MOILP approach is shown to be infeasible.
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Häring, Felix [Verfasser]. "Tuning the magnetic properties of thin films by interaction with periodic nanostructures / Felix Häring." Ulm : Universität Ulm. Fakultät für Naturwissenschaften, 2014. http://d-nb.info/1053705670/34.
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Barzegar, HamidReza. "Synthesis and Characterization of Carbon Based One-Dimensional Structures : Tuning Physical and Chemical Properties." Doctoral thesis, Umeå universitet, Institutionen för fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-97551.
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Carbon nanostructures have been extensively used in different applications; ranging from electronic and optoelectronic devices to energy conversion. The interest stems from the fact that covalently bonded carbon atoms can form a wide variety of structures with zero-, one- and two-dimensional configuration with different physical properties. For instance, while fullerene molecules (zero-dimensional carbon structures) realize semiconductor behavior, two-dimensional graphene shows metallic behavior with exceptional electron mobility. Moreover the possibility to even further tune these fascinating properties by means of doping, chemical modification and combining carbon based sub-classes into new hybrid structures make the carbon nanostructure even more interesting for practical application. This thesis focuses on synthesizing SWCNT and different C60 one-dimensional structures as well as tuning their properties by means of different chemical and structural modification. The purpose of the study is to have better understanding of the synthesis and modification techniques, which opens for better control over the properties of the product for desired applications. In this thesis carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD) on iron/cobalt catalyst particles. The effect of catalyst particle size on the diameter of the grown CNTs is systematically studied and in the case of SWCNTs it is shown that the chirality distribution of the grown SWCNTs can be tuned by altering the catalyst particle composition. In further experiments, incorporation of the nitrogen atoms in SWCNTs structures is examined. A correlation between experimental characterization techniques and theoretical calculation enable for precise analysis of different types of nitrogen configuration in SWCNTs structure and in particular their effect on growth termination and electronic properties of SWCNTs are studied. C60 one-dimensional structures are grown through a solution based method known as Liquid-liquid interfacial precipitation (LLIP). By controlling the crystal seed formation at the early stage of the growth the morphology and size of the grown C60 one-dimensional structures where tuned from nanorods to large diameter rods and tubes. We further introduce a facile solution-based method to photo-polymerize the as-grown C60 nanorods, and show that such a method crates a polymeric C60 shell around the nanorods. The polymeric C60 shell exhibits high stability against common hydrophobic C60 solvents, which makes the photo-polymerized nanorods ideal for further solution-based processing. This is practically shown by decoration of both as grown and photo-polymerized nanorods by palladium nanoparticles and comparison between their electrochemical activities. The electrical properties of the C60 nanorods are also examined by utilizing a field effect transistor geometry comprising different C60 nanorods. In the last part of the study a variant of CNT is synthesized in which large diameter, few-walled CNTs spontaneously transform to a collapsed ribbon shape structure, the so called collapsed carbon nanotube (CCNT). By inserting C60 molecules into the duct edges of CCNT a new hybrid structure comprising C60 molecules and CCNT is synthesized and characterized. A further C60 insertion lead to reinflation of CCNTs, which eventually form few-walled CNT completely filled with C60 molecules.
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Ashcraft, James Nathan. "Tuning the transport properties of layer-by-layer thin films for fuel cell applications." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54207.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 138-148).
The increasing global focus on alternative energy sources has led to a renewed interest in fuel cells. For low power, portable applications, direct methanol fuel cells (DMFCs) are the most promising type of fuel cell. DMFCs can operate at ambient conditions and only require dilute methanol solutions and air to be input to the devices. At the core of these devices is a proton exchange membrane (PEM) that allows rapid proton transport through the polymer matrix while preventing fuel from permeating across. Additionally, PEMs must have long-term stability in the fuel cell environment, the ability to operate over a wide range of conditions (temperature and humidity), and be cost effective. A promising, robust method for fabricating polymer films with tunable properties is layer-by-layer (LbL) assembly. This technique consists of building a polymer film by sequential dipping into polymer solutions with complementary interactions, such as opposite electrostatic charges. The LbL method allows the formation of thin films that have perm-selective properties and high ionic conductivity values. This work describes the optimization of multilayer systems for use as the PEM in DMFCs. First, LbL assembled films of poly[bis(methoxyethoxyethoxy)-phosphazene] (MEEP) and poly (acrylic acid) (PAA) are demonstrated by utilizing the hydrogen bonding between these two polymers. These films show controlled thickness growth, high ionic conductivity, and excellent hydrolytic stability. The ionic conductivity of these films is optimized by tuning the assembly pH of initial polymer solutions and thereby controlling the hydrogen bonding characteristics.
(cont.) Despite similar film composition, MEEP/PAA LbL films assembled at higher pH values have enhanced water uptake and transport properties, which play a key role in increasing ion transport within the films. At fully humidified conditions, the ionic conductivity of MEEP/PAA is over one order of magnitude higher than previously studied hydrogen bonded LbL systems. The next LbL systems studied consist of a highly sulfonated aromatic polyether (sPPO) paired with amine containing polycations. The best performing sPPO system has ionic conductivity values which are the same order of magnitude as commercially relevant PEMs and has the highest ionic conductivity ever obtained from a LbL assembled film. Additionally, these LbL systems have methanol permeability values over two orders of magnitude lower than traditional PEMs. Incorporating the sPPO systems into DMFCs results in a 53% improvement in power output as compared with DMFCs using traditional PEMs. In-depth structure property studies are performed to understand the nature of the high ionic conductivity of the sPPO LbL systems with respect to film growth, composition, water uptake, and ionic crosslink density. Lastly, the mechanical properties of highly conducting LbL films are improved by forming the LbL matrix on highly tunable electrospun fiber mat (EFM) supports. Free-standing LbL films have moderate mechanical properties when dry, but are mechanically deficient when hydrated. Coating an EFM with the LbL dipping process produces composite membranes with interesting "bridged" morphologies, while still maintaining high ionic conductivity values.
(cont.) The spray LbL assembly is studied as a means for the rapid formation of LbL films on EFMs. At optimized conditions, the LbL materials conformally coat the individual fibers throughout the bulk of the EFM and have uniform surface coatings. The mechanical properties of the spray coated EMFs are shown to be superior to the pristine LbL systems.
by James Nathan Ashcraft.
Ph.D.
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Mitton, Renata. "Tuning the Physical Properties of Poly(arylene ether)s Prepared from 3,5-Difluorobenzene Sulfonamides." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1436957462.
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Zhu, Tiancong. "Tuning the Spin Transport and Magnetic Properties of 2D Materials at the Atomic Scale." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563385375225464.
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Loibl, Antonia [Verfasser]. "Pyridyl-substituted Phosphinines and Pyridines: Tuning Ligand Properties for Applications in Catalysis / Antonia Loibl." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/115188135X/34.
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Saha, Arpita. "Tuning the properties of quantum nanocrystals and magnetic nanoparticles using spherical ligands: carboranes and metallacarboranes." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667956.
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El primer capítulo trata de los puntos cuánticos acuosos (QDs) recubiertos con meta-carboranil fosfinado, lo que nos da una nueva arquitectura de QDs denominada como QDs de dosel central. Esta es la primera vez que los ligandos esféricos se utilizan experimentalmente para tapar los QD. Debido a esta arquitectura, obtuvimos una nueva propiedad de luminiscencia en estos QDs, llamada conmutación por fluorescencia cinética (KFS), la cual nunca antes se había reportado. Es un nuevo fenómeno en el que la luminiscencia se desvanece con el tiempo, pero al aplicar energía cinética recupera toda la intensidad de la emisión. Estos QDs de dosel central pueden atrapar aniones y actuar como condensadores, son comparados con otros QDs y caracterizados.
Este capítulo trata de la síntesis de los QDs en el agua utilizando una nueva configuración desarrollada por nosotros. Produce QDs con un alto PL, QY y una vida útil más larga de emisión en el medio acuático. La configuración utilizada es diferente al método basado en el reflujo utilizado para sintetizar los QDs en agua a 100oC. Aquí utilizamos un baño de arena aislado con corcho, con tubos de presión de vidrio. Los QDs se generan en estos tubos de presión a 150oC bajo presión autogénica producida por los tubos. Han sido comparados con los tradicionales QDs a base de agua y caracterizados. Estos QDs combinan la ventaja de la alta calidad y los diferentes colores de luminiscencia de los QDs sintetizados organometálicos y la producción fácil y barata de una síntesis a base de agua.
El siguiente capítulo trata de los nanocristales cuánticos (QNCs) que se sintetizan en el agua por primera vez. Hemos demostrado una ruta sintética fácil y un diseño de configuración que utiliza varillas cuánticas (Qrods) y anillos cuánticos (QRs) que pueden sintetizarse fácilmente en un medio acuático. Esta es la primera vez que se sintetiza y estudia experimentalmente. Estas QNCs pueden ser fácilmente almacenadas en forma de polvo, permaneciendo suspendidas en varios solventes por más de 18 meses, sin degradación en sus propiedades de estabilidad coloidal o luminiscencia. Además, pueden utilizarse para formar nanocompuestos utilizando polímeros. Estas películas poliméricas que contienen los QNCs mostraron una luminiscencia que duró más de un año y que también podría mostrar electroluminiscencia, haciéndolas viables para aplicaciones de QLED en el futuro.
El cuarto capítulo trata de trata de las nanopartículas magnéticas (MNP) recubiertas con metacarboranil fosfinado. Estos dan lugar a nuevos nanohíbridos que pueden utilizarse para la aplicación biológica de la terapia de captura de neutrones de boro (BNCT). Estos nanohíbridos han sido sintetizados, caracterizados y utilizados en aplicaciones biológicas. Sus propiedades magnéticas y estabilidad han sido estudiadas después de la esterilización en autoclave, así como su estabilidad coloidal en diferentes medios de cultivo biológicos. Luego se ha estudiado y cuantificado su absorción celular. La captación de los MNPs por las células tumorales ha sido visualizada y también estudiada in vivo para aplicaciones de la BNCT.
Finalmente, el último capítulo trata de la síntesis de MNPs y el recubrimiento con cáscara de sílice inorgánica. Estos MNPs recubiertos son funcionalzied más lejos con los grupos amino y carboxílicos para que sean unidos con los anticuerpos para los usos del biosensing. Los MWCNT también se utilizan en conjugación con estos MNPs para generar nanocompuestos magnéticos (MNCs). Tanto los MNPs como los MNCs se utilizan para generar por primera vez un complejo no ligado con H[COSAN]. H[COSAN] siendo una especie redox puede ser utilizada para manipular los niveles de HOMO-LUMO, permitiendo así que estos MNPs y MNCs sean materiales de capa de detección efectivos.The research presented in this thesis has been summarized as a compendium of articles published and to be published in the future. There are five chapters dealing with the results and discussions. The results and discussions are preceded by a general introduction and objectives. The summary of each chaper of the results is given below. The 1st chapter deals with aqueous quantum dots (QDs) capped with meta-carboranyl phosphinate which gives us a brand new architecture of QDs named as core-canopy QDs. This is the first time spherical ligands have been experimentally used to cap QDs. Due to this architecture, we obtained a new luminescence property in these QDs, called the kinetic fluorescence switching (KFS) which has never been reported before. It is a new phenomenon in which the luminescence fades with time but upon application of kinetic energy regains the full intensity of emission. These core-canopy QDs can trap anions and act like capacitors, they are compared with other QDs and characterized. The next chapter deals with synthesis of QDs in water using a new set up developed by us. It produces QDs with high PL, QY and longer lifetime of emission in water medium. The set up used is different to the reflux based method used to synthesize QDs in water at 100oC. Here we used a cork insulated sand bath, with ace pressure tubes of glass. The QDs are generated in these pressure tubes at 150oC under autogeneous pressure produced by the tubes. They have been compared to the traditional water based QDs and charaterized. These QDs combine the advanatge of high QY and different luminescence colours of organometallic synthesized QDs and the easy and cheap production of a water based synthesis. The next chapter deals with quantum nanocrystals (QNCs) being synthesized in water for the first time. We have demonstrated an easy synthetic route and setup design using which quantum rods (Qrods) and quantum rings (QRs) can be easily synthesized in a water medium. This is the first time that this has been experimentally synthesized and studied. These QNCs could be easily stored in powdered form, remain suspended in various solvents for more than 18 months, without degradation in their colloidal stability or luminescence properties. Moreover, they can be used to form nancomposites using polymers. These polymeric films containing the QNCs showed luminescence which lasted over a year and could also show electroluminescence, hence making them viable for QLED applications in the future. The 4th chapter of the results and discussions deals with magnetic nanoparticles (MNPs) coated with meta-carboranyl phosphinate. These give rise to new nano-hybrids which can be used for biological application of boron neutron capture therapy (BNCT). These nanohybrids have been synthesized, characterized and used in biological applications. Their magnetic properties and stability has been studied after autoclave sterilization, further their colloidal stability in different biological culture mediums has also been studied. Then their cellular uptake has been studied and quantified. The uptake of the MNPs by the glioblastoma tumor cells has been visualized and also studied in vivo for BNCT applications. Finally, the last chapter deals with the synthesis of MNPs and coating with inorganic silica shell. These coated MNPs are further functionalzied with amino and carboxylic groups for them to be attached with antibodies for biosensing applications. MWCNTs are also used in conjugation with these MNPs to generate magnetic nanocomposites (MNCs). Both the MNPs and MNCs are used to generate for the first time a non-bonded complex with H[COSAN]. H[COSAN] being a redox specie can be used to manipulate the HOMO-LUMO levels, thus enabling these MNPs and MNCs as effective sensing layer materials.
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Ngo, Thien-An. "Tuning the electronic properties of conjugated polyelectrolytes via complexation with lipid vesicles or silica nanobeads." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97001.
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This thesis describes luminescent nanostructures involving the anionic poly(phenylene vinylene) MPS-PPV in complex with lipid vesicles or silica beads. The vesicular encapsulation of light-emitting polymer produced a "liposome beacon," whose fluorescence response to the electron-transfer quencher methyl viologen or an energy-accepting carbocyanine dye (DiD) reported on the extent of encapsulation via ensemble spectroscopy and single-particle imaging of immobilized vesicles. Divalent cation was furthermore used to modulate interactions between MPS-PPV and zwitterionic lipid vesicles. Binding to the lipid vesicles disrupted polymer aggregates, enhancing and shifting the polymer's fluorescence. Fluorescence resonance energy transfer (FRET) elucidated the effect of divalent cation in promoting lipid-polymer association. Finally, MPS-PPV was adsorbed onto silica nanoparticles via electrostatic interactions. The effects of silica bead adsorption on MPS-PPV photophysical properties were investigated via ensemble spectroscopy and single-particle total-internal-reflection fluorescence microscopy. The MPS-PPV-coated silica bead exhibited similar sensitivity to methyl viologen as the free polyelectrolyte, and was resistant to the fluorescence effects of nonspecific interactions. Our results provide insight towards tuning the sensitivity of fluorescent water-soluble conjugated polyelectrolytes and contributing to the development of new applications for conjugated poly(phenylene vinylene)s in fluorescent assays.Les polymères conjugués (PC) ont une fluorescence amplifiée mais facilement supprimée, ce qui les rend utile pour la détection d'une vaste gamme de molécules. Ici on a crée des nouvelles structures luminescents basées sur les interactions entre la PC (poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene (MPS-PPV) et des liposomes ou des particules de silice de diamètre environ 100 nm. L'interaction entre la PC et les lipides est vérifié avec la spectroscopie. Ajoutant une autre fluorophore aux lipides, on voit fluorescence resonance energy transfer (FRET) de la PC au fluorophore. L'encapsulation de la PC est vérifié par la réponse de la fluorescence des complexes PC / lipide au méthyle viologène, et la conjugaison spécifique des complexes contenant des lipides biotinylées aux surfaces couvert de streptavidin. Le cation divalent de calcium a été utilisé pour modifier les interactions lipide-PC, ce qui était indiquée par FRET. En outre, MPS-PPV a été adsorbée sur les particules de silice via des interactions électrostatiques. Les effets de l'adsorption sur les caractéristiques photophysiques des complexes MPS-PPV / silice ont été étudiés avec la spectroscopie et la microscopie de fluorescence par réflexion totale interne (TIRFM). Leur réponse au méthyle viologène est aussi amplifiée que celui du polymère libre, mais leur luminescence résiste les effets des interactions hydrophobiques. Cette recherche donne des nouveaux aperçus sur la modification de la fluorescence amplifiée des PC, vers continuer le développement des systèmes utilisant des polyvinyles de para-phénylène pour la détection luminescent biologique et chimique.
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Brulatti, Pierpaolo. "New luminescent iridium (III) complexes containing NCN cyclometallated ligands : synthesis, photophysical properties and emission tuning." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/447/.
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The luminescence properties of cyclometallated iridium(III) complexes render them of interest, for example, as phosphorescent dopants in organic light-emitting devices (OLEDs), as photoactive units in solar energy conversion, and as biosensors. The vast majority comprise three bidentate ligands, archetypal examples being Ir(ppy)3 and [Ir(ppy)2(bpy)]+ (ppy = 2-phenylpyridine; bpy = 2,2'- bipyridine). The work described here explores the chemistry of iridium(III) complexes that contain a terdentate cyclometallating ligand. Most of the complexes studied have the general formula Ir(N^C^N)(N^C)X, where N^C^N represents a terdentate ligand based on 1,3-di(2-pyridyl)benzene; N^C a bidentate ligand such as ppy; and X is a monodentate ligand such as chloride, cyanide, thiocyanate or an acetylide. The synthetic methodology developed involves reaction of the N^CH^N proligand with iridium(III) chloride to give a dimer of the form [Ir(N^C^N)Cl(-Cl)]2, which is cleaved upon treatment with a bidentate N^CH ligand. The one remaining chloride ligand can then be exchanged for other monodentate ligands through silvercatalysed metathesis. Most of these complexes are highly luminescent, with quantum yields in degassed dichloromethane at room temperature between 0.2 and 0.9. The effect of substituents in both the aryl and pyridyl rings of the terdentate and bidentate ligands has been investigated, together with the influence of X. The emission energy has been shown to vary over a very wide range, from the blue to red regions (max = 456 to 667 nm). The trends have been partially rationalised using time-dependent density functional theory and cyclic voltammetry. Some complexes have been incorporated into multi-layer OLEDs that display unusually high efficiency, particularly for the red-emitting devices. Selected rhodium(III) analogues have been prepared, together with related iridium(III) complexes incorporating bidentate N^N (bpy) ligands. A preliminary investigation into the utility of these complexes for the construction of multimetallic assemblies has been made, through the introduction of bridging ligands into position X.
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Boi, Filippo. "Ferromagnetically filled carbon nanotubes : radial structures and tuning of magnetic properties through new synthesis methods." Thesis, Queen Mary, University of London, 2013. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8734.
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Multiwall carbon nanotubes filled with continuous single-crystals of the ferromagnetic phase -Fe were produced with two new synthesis methods: the boundary layer chemical vapour synthesis and the perturbed vapour chemical vapour deposition. In the first method, the nanotubes nucleate and grow radially from a central agglomeration of homogeneously nucleated spherical particles in a randomly fluctuating vapour created in the viscous boundary layer between a rough surface and a laminar pyrolyzed-ferrocene/Ar vapour flow. In the second method, the nanotubes nucleate and form in a flower-like arrangement departing from homogeneously nucleated particles. These particles are produced by the creation of a local perturbation in a vapour with a high density of Fe and C species obtained from the pyrolysis of ferrocene in a laminar Ar flow. Electron microscopy investigations revealed that the continuous single crystals obtained with both methods exhibit diameters much lower than the critical diameter for a single magnetic domain of -Fe (~ 66 nm). In the radial structures, the single-crystal diameter is in the range of ~ 17-37 nm, while in the flower-like structures the single crystals show mainly a diameter of ~ 30 nm and ~ 55 nm. The average single crystals length is 7-8 m in the case of the radial structures and 19-21 m in the case of the flower-like structures. DC magnetization measurements at 5 K show different magnetic behaviours. The flower-like structures present a very high saturation magnetization of 189.5 emu/g and a high coercivity of 580 Oe. The radial structures exhibit an exchange-coupled ferromagnetic/antiferromagnetic system despite only 2% of -Fe is present inside the nanotubes. The radial structures obtained at flow-rates of 3.5 ccm and 20 ccm, show saturation-magnetizations of 31emu/g and 13 emu/g, and coercivities of 790 Oe and 843 Oe respectively.
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Guo, Wenting. "Tuning the properties of high-Tc superconductor & Sr2IrO4, and exploring transport through single nanocrystals." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289764.
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This thesis is composed of three projects including the AC magnetic susceptibility study of high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$, the ionic-liquid gating study of the Mott insulator Sr$_2$IrO$_4$, and the single-electron study of quantum dot device with self-assembled nanocrystal PbS. Chapter 1 covers a general introduction to all three projects. The basic background and the motivation for each project are presented. Project I is covered in Chapter 2, Chapter 3, and Chapter 4. The first part of Chapter 2 is a theoretical introduction to the Bardeen-Cooper-Schrieffer theory of superconductivity with its main conclusions presented. This chapter builds a basis for the use of high pressure technique to YBa$_2$Cu$_3$O$_{7-\delta}$ in the later chapters. The rest of Chapter 2 reviews the work in the study of high-temperature superconductors, especially on YBa$_2$Cu$_3$O$_{7-\delta}$, on both experiments and theories and the possible applications of high-temperature superconductors. Chapter 3 introduces the YBa$_2$Cu$_3$O$_{7-\delta}$ sample preparation process and the characterisation. A dry cryomagnetic equipment was employed for the measurement. The results and the discussion are presented in Chapter 4. Project II is described in Chapter 5, Chapter 6, and Chapter 7. Chapter 5 firstly introduces the background knowledge of the gated material SrTiO$_3$ and the technical details of the ionic-liquid gating technique. Then the sample growth and the characterisation are presented. The fabrication process of Sr$_2$IrO$_4$ and SrTiO$_3$ (material for a control experiment) are described in Chapter 6. Chapter 7 covers the measurement and the result of the fabricated devices and related discussion. Project III ranges from Chapter 8, and Chapter 9. A literature review of quantum-dot devices and self-assembled nanocrystals is presented in Chapter 8. The experimental design of this nanocrystal quantum dot device is also included. Following it, the fabrication process of quantum-dot devices and the techniques used for fabrication are introduced in the start of Chapter 9. Chapter 9 also gives a description of the probe-station for measurements. The results and discussion of the measurements are covered in the last section of Chapter 9. Chapter 10 summarises and concludes the three projects stated above and gives some suggestions about the directions for future work.
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Persi, Erez. "Contrast and tuning response properties of neurons in the visual cortex : modeling and data analysis." Paris 6, 2008. http://www.theses.fr/2008PA066216.
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We have combined a theoretical and experimental approach to study the biophysical substrates for the coding of orientation and contrast in the activity of V1 neurons. We first explore theoretically how the emerging activity in V1 depends on the input properties, single neuron input-output transfer-function properties and the connectivity pattern within V1. We explain the conditions on the different input sources in a hypercolumn model, that allow for both contrast-invariant orientation tuning width and sigmoid contrast response functions (CRF). We emphasize the role of the systems' components and structure features and their relative contribution to the activity in V1. More specifically, we show that the nonlinearity in the input-output transfer function manifested by a power-law regime leads to the sharpening of both orientation tuning width and the CRF in V1 compared with its inputs. Saturation in the CRF is a result of sufficient cortical inhibition at high contrasts, which is easily achieved with power-law transfer functions. Then, we analyze experimental data of both in-vitro and in-vivo measurements, and show that the models' key assumptions are consistent with neuronal behavior. A central focus of our study is to explain the diversity in the CRFs parameters. We show that the model can account for this diversity with heterogeneity either in single neuron properties or in LGN input properties. A comparison with experimental data indicates an equal contribution of the two heterogeneity types. The theory presented here can be further developed and extended to several visual areas in order to investigate other mechanisms of visual processingAfin d’étudier les bases du codage de l’orientation et du contraste par les neurones du cortex visuel primaire (V1), nous avons utilisé une approche à la fois théorique et expérimentale. Nous analysons dans un premier temps et de façon théorique, comment l’activité émergente dans V1 dépend des propriétés d’entrée des neurones corticaux, de leur fonction de transfert « entrée-sortie » et des différents patrons de connectivité à l’intérieur de cette même structure. Nous nous penchons ensuite sur les différentes sources d’entrées d’un modèle d’hyper-colonne, en caractérisant les conditions qui permettent à la fois une sélectivité à l’orientation indépendante du contraste et une fonction de réponse au contraste (CRF) sigmoïde. De plus, nous soulignons le rôle des relations entre les propriétés intrinsèques des neurones et les propriétés du réseau. Plus précisément, nous montrons que les non-linéarités dans la fonction de transfert « entrée-sortie », caractérisées par une loi de puissance, entraînent l’étrécissement à la fois de la courbe de sélectivité à l’orientation et de la CRF dans V1. La saturation de la CRF résulte, elle, d’une inhibition corticale à fort contraste, ce qui est aisément réalisé avec des fonctions de transfert basées sur des lois de puissance. Dans un deuxième temps, nous analysons des données expérimentales provenant à la fois d’enregistrements in vitro et in vivo et montrons que les hypothèses clés de notre modèle sont en accord avec les comportements neuronaux. Un point central de notre étude est d’expliquer la diversité des paramètres de la CRF. Nous montrons que le modèle justifie cette diversité par l’hétérogénéité des propriétés du neurone lui-même ou de ses afférences thalamiques. De plus, les données expérimentales indiquent qu’il y a une contribution à part égale des deux types d’hétérogénéités. Les principes présentés ici sont valables pour d’autres aires visuelles et peuvent être appliqué d’autres mécanismes du traitement de l’information visuelle
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Luo, Wen. "Tuning the redox properties of cobalt particles supported on oxides by an In-between graphene layer." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF007/document.
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L'interaction métal-support (MSI) joue un rôle important dans la catalyse hétérogène. La compréhension et la modification du MSI sont des étapes essentielles pour développer catalyseurs de haute performance. Dans cette thèse, un nouveau concept, qu’il s’agit de recouvrir le support l'oxyde avec un revêtement mono-couche de graphène, a été proposé pour modifier le MSI. L'influence de la couche de graphène sur les interactions de métal (Co et Co-Pt) - oxyde (ZnO et SiO2) et sur les propriétés d'oxydo-réduction des particules métalliques ont été évaluées via des systèmes catalytiques de modèle. Les résultats ont montré que la mono-couche de graphène peut influencer considérablement les états d'oxydation et les morphologies des Co monométallique et Co-Pt bimétallique par rapport aux ceux résultent d’un dépôt direct sur les oxydes nus. En particulier, par calcination sous vide, le graphène protége Co d'être oxydé par ZnO, ce qui conduit à la formation d’un mélange métallique Co-Pt. Co interagit avec les substrats d'oxydes pour former des particules plates qui sont facilement oxydés par O2 en pression faible, tandis que l'insertion d'une couche intermédiaire de graphène entre la couche supérieure métallique et le supporte d’oxyde entraîne la formation des nanoparticules de Co en état très dispersés, qui sont résistants à l'oxydation. Sous la condition de réduction par H2, le graphène favorise clairement la réduction de Co. La quantité de dépôt de Co, le substrat d'oxyde, la température de calcination et l'environnement ont été prouvés pour pouvoir influencer la stabilité de graphène. Ces résultats ouvrent des nouvelles voies possibles d'utiliser le graphène comme promoteur dans des réactions catalytiques à l'avenirThe metal-support interaction (MSI) plays an important role in heterogeneous catalysis. Understanding and tuning the MSI are essential steps for developing catalysts with high performance. In this thesis, a new concept, which is coating the oxide supports with a single layer graphene, was introduced to modify the MSI. The influence of graphene layer on the metal (Co and Co-Pt) – oxide (ZnO and SiO2) interactions and on the redox properties of metal particles were evaluated through model catalyst systems. The results showed that single layer graphene can significantly influence the oxidation states and morphologies of both mono Co and bimetallic Co-Pt as compared to the one after direct deposition on bare oxides. In particular, under vacuum annealing, graphene protects Co from being oxidized by ZnO and results in Co-Pt metallic mixture. Co interacts with oxide substrates forming flat particles which are easily oxidized by low pressure O2, while insertion of a graphene interlayer between the metal overlayer and the oxide supports leads to the formation of highly dispersed Co nanoparticles, which are resistant to oxidation. Under H2 reduction condition, graphene evidently facilitates the reduction of Co. The deposition amount of Co, the oxide substrate, the annealing temperature and the environment were proved to influence the stability of graphene. These results explore new directions for the possible future of using graphene as a promoter in catalytic reactions
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Kittikorn, Thorsak. "Tuning the long-term properties to control biodegradation by surface modifications of agricultural fibres in biocomposites." Doctoral thesis, KTH, Träkemi och massateknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119915.
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Sustainable polymeric materials put emphasis on mastering the whole life-cycle of polymeric materials. This includes the choice of raw materials, selection of synthesis and processing, environmental impact during long-term use followed by detailed knowledge about recycling and waste management. Within this large efforts are put in the design and development of new biocomposites using renewable fibres instead of inert ones. The thesis deals with surface modifications of agricultural fibres and the design of biocomposites with optimal long-term properties balancing the potential risk for biodegradation. The first part of this thesis involved surface modifications of oil palm fibres and production of biocomposites with PP as matrix. The chemical surface modifications of oil palm fibres explored propionylation, PPgMA grafting via solution modification and reactive blending and vinyltrimethoxy silanization as methods. All modified fibre/PP biocomposites showed improvements in the mechanical properties followed also by an improvement of water resistance. In comparison with unmodificed fibres/PP matrix the highest water resistance after the surface modifications of oil palm fibres were observed for silanization followed by PPgMA modified, PPgMA blending and propionylation. The second part aimed at producing fully biodegradable biocomposites and analysing the resulting properties with respect to potential risk for biodegradation. Sisal fibres were incorporated in PLA and PHBV and the resulting risk for biodegradation using a fungus, Aspergillus niger, monitored. Neat PLA and PHBV were compared with the corresponding biocomposites and already without fibres both polymers were notably biodegraded by Aspergillus niger. The degree of biodegradation of PLA and PHBV matrices was related to the extent of the growth on the material surfaces. Adding sisal fibres gave a substantial increase in the growth on the surfaces of the biocomposites. Correlating the type of surface modification of sisal fibres with degree of biodegradation, it was demonstrated that all chemically modified sisal/PLA biocomposites were less biodegraded than unmodified sisal biocomposites. Propionylated sisal/PLA demonstrated the best resistance to biodegradation of all biocomposites while sisal/CA/PLA demonstrated high level of biodegradation after severe invasion by Aspergillus niger. In general, the biodegradation correlated strongly with the degree of water absorption and surface modifications that increase the hydrophobicity is a route to improve the resistance to biodegradation. Designing new biocomposites using renewable fibres and non-renewable and renewable matrices involve the balancing of the increase in mechanical properties, after improved adhesion between fibres and the polymer matrix, with the potential risk for biodegradation.QC 20130325
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Egan, Lindsay. "Tuning the magnetic properties of Prussian Blue analogues : size control and the effects of external stimuli." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3850.
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The hetero-bimetallic mixed valence metal polycyanides (Prussian Blue analogues (PBAs)) with formula AxMII[M’III(CN)6]y (where A= alkali-metal cation and M, M’= transition-metal cations respectively) are archetypal examples of molecule-based magnets, exhibiting a wealth of exotic electronic and magnetic behaviours. Similar intriguing electronic and magnetic properties are anticipated in nanoscale structures employing the PBA molecular building block. Herein investigations of multifunctional molecular magnets based on the PBA building block, with varying dimensionalities, are reported. Synthesis and characterisation of a novel family of mixed ferri-ferromagnets, RbNizMn(1-z)[Fe(CN)6] (0
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Thill, Alisson Steffli. "Tuning the electronic and structural properties of cerium oxide nanoparticles for the H2 production photocatalytic reaction." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/185814.
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The photocatalytic water splitting reaction showed to be a promising process to obtain renewable and clean energy, but the efficiency reached in this process is still low and must be improved to be viable. Considering this, the research on improving the efficiency of photocatalysts has attracted a strong interest in the past last years. Cerium oxide (CeO2−, 0 < x < 0.5) is a material recently investigated as a possible photocatalyst to obtain H2 from H2O. In this work, cerium oxide nanoparticles with high surface area (104 < S < 201 m2/g), high pore volume (32 < V < 132 mm3/g) values, wide range of diameter (2 < d < 90 nm) and O vacancies population (0.05 < x < 0.46) were applied to the H2 production photocatalytic reaction. The nanoparticles presented activity of up to 10 times higher than the commercial cerium oxide standard. UV-Vis, X-ray Diffraction, X-ray Absorption Spectroscopy, X-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy and Fourier Transform Infrared measurements were performed aiming to elucidate these results and to determine the main structural and electronic properties that can improve the H2 production photocatalytic reaction. It was obtained that the band gap energy depends on the nanoparticle synthesized and can be as low as 2.73 eV. The Ce 4f orbital occupation and the structural disorder presented by the nanoparticles is directly related with the band gap energies obtained. Density Functional Theory (DFT) calculations were performed to obtain the relation between the band structure (DOS) and the O vacancy population in order to explain the dependence of the band gap energy with the Ce 4f orbital occupation. Moreover, the O vacancies population at the surface have a very different effect depending on the presence or absence of mesopores, where a lower O vacancy population at the surface is better (worse) to the photocatalytic activity in the presence (absence) of mesopores. Furthermore O vacancies population at the surface plays a more fundamental role on the photocatalytic activity than the band gap energies for the samples presenting mesopores. The results allowed shedding light on the improvement of the properties of cerium oxide nanoparticles applied to optimize the H2 production photocatalytic activity.
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Etheridge, Forrest Samuel. "Tuning the Opto-Electronic Properties of Organic Semiconductors: Derivatives ofAzadipyrromethene, Naphthalene Diimide and Poly(3-hexylthiophene)." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1459352863.
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Jung, Alexandra. "Tuning the structural and magnetic properties of Sr2FeReO6 by substituting Fe and Re with valence invariant metals /." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=98039189X.
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