A growing need for developing new multi-functional materials operating at microwave frequencies is demanding a better understanding of ferroelectric and ferrimagnetic materials and their combinations. Some of these materials exhibit tunable physical properties, giving an extra degree of freedom in the device design. New multifunctional ferroelectric and ferrimagnetic thin film structures are investigated in this dissertation research, in which dielectric and magnetic properties can separately be tuned over a certain frequency range. The materials of choice, Ba0.5Sr0.5TiO3 (BST) and BaFe12O19 (BaM), both well studied and used in many microwave applications, were prepared using rf magnetron sputtering and pulsed laser ablation. Thin-film bilayers, multilayers and composite thin films were grown on various substrates, and their underlying microstructure and crystallographic properties were analyzed and optimized. After identifying the most successful growth conditions,dielectric and magnetic properties were measured. Unusual features in magnetic hysteresis loops in both sputtered and laser ablated films grown under different conditions were observed. Microcircuits were fabricated using optical lithography and microwave properties and tunability were tested in the range 1-65 GHz.

Cellular energy transduction processes are often driven by transmembrane ion gradients, and a number of artificial membrane systems have been developed that allow for chemically or light-induced transport of ions across lipid bilayers. These liposomal architectures, however, are not readily interfaced to a solid-state transducer. A significant step toward this goal is described here by assessing the possibility of coupling a lipid bilayer directly to a transducer to form a stable uniform film using hybrid bilayer membranes (HBMs).Although the surface attachment of self-assembled monolayer increases the robustness of the lipid assembly, HBMs cannot maintain film uniformity under harsher conditions due to the absence of strong lipid-lipid interactions. Therefore, HBMs were prepared and characterized using a cross-linking polymerizable lipid, bis-SorbPC. Several parameters relating to lipid deposition and film stabilization through polymerization were examined. Film characterization strongly suggests that polymerization of bis-SorbPC stabilizes the HBM such that its structure is largely preserved even after the dehydration process. This work suggests that network formation in the upper monolayer is not enough to prevent oligomer desorption, intermonolayer covalent linking is also a prerequisite in making uniform, defect-free planar supported lipid assemblies.Some of the challenges associated with the application of lipids involve the creation of supported bilayers that are stable to chemical and physical disruptions, yet retain their ion barrier properties, and allow transmembrane ion transport by lipid-soluble shuttles. Polymerized lipid films provide the stability required for these structures, but permeability properties of cations across poly(lipid) membranes are not known. Therefore, convenient liposome-based proton and calcium permeability assays were developed. These assays were applied to various poly(lipid) compositions.In addition, three novel sorbyl-substituted head group polymerizable lipids, which have been synthesized based on a strategy that head group polymerization would minimally perturb the characteristic ion impermeability of the membrane, were evaluated for their lipid characteristics and ability to form polymers. None of these compounds forms vesicles by itself. Therefore, attempts were made to form mixed vesicles with other fluid lipids. The miscibility of the mixed monolayers was assessed using Langmuir isotherms.

Thesis (Ph. D.)--University of Virginia, 2007. / Title from title page. Includes bibliographical references. Also available online through Digital Dissertations.

xii, 138 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Controlling colloidal interactions continues to receive a great deal of attention due both to basic scientific interests as well as industrial applications. However, many aspects of interactions between microparticles remain poorly understood, including the attraction observed between particles with the same kind of charge (like-charge attraction). This situation hinders progress in the generation of colloidal self-assembled structures. This thesis focuses on measurements of pair interactions of functionalized silica microspheres and the resulting insights into colloidal interactions. Silica microparticles were functionalized in two ways. For one method, each particle was coated with a lipid inlayer membrane. The charge density of the particle surface can thereby be easily tuned by controlling the type or amount of charged lipids. For the other method, the cholera toxin subunit B protein (CTB) was bound to lipid-functionalized microparticles. To measure pair interactions, we invented a line optical trap that enables nearly free one-dimensional Brownian motion of particles. Pair interaction energies of functionalized particles above the bottom of the experimental chamber can be extracted via a Boltzmann relationship. Both lipid-only and lipid-plus-protein functionalized microparticles show tunable, attractive pair interactions. For lipid-only coatings, the attraction becomes stronger by increasing the fraction of positively charged lipids. There is a linear relationship between pair potential and molar percentage of positively charged lipids. For lipid-plus-protein coatings, attractive potentials were weakened monotonically by binding more CTB. Decompositions of potential curves allow identification of directly charge-dependent and charge-independent contributions to colloidal like-charge attraction. Analysis shows that the correlations between attraction strength and range are opposite in these two sets of particles. Moreover, the correlations between particle-wall separation and attraction strength in lipid-only and lipid-plus-protein functionalized particles are also opposite. These comparisons show that like-charge attraction may result from more than one mechanism. Finally, we measured pair potential energies of lipid functionalized silica particles above a lipid functionalized glass chamber bottom, which exhibit a quadratic relationship between the attraction strength and the fraction of positively charged lipids. Compared with the situation of particle functionalization only, this relation indicates that confinement-induced like-charge attraction can be modulated by altering electrostatic properties of the confining wall. / Committee in charge: Dr. Stephen D. Kevan, Chair; Dr. Raghuveer Parthasarathy, Advisor; Dr. Hailin Wang; Dr. Miriam Deutsch; Dr. Marina G. Guenza

Submitted by Maike Costa (maiksebas@gmail.com) on 2016-03-15T13:17:25Z No. of bitstreams: 1 arquivototal.pdf: 5498676 bytes, checksum: 4a307b30b2c4f45e565cf9923519ec7f (MD5) / Made available in DSpace on 2016-03-15T13:17:25Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 5498676 bytes, checksum: 4a307b30b2c4f45e565cf9923519ec7f (MD5) Previous issue date: 2015-02-20 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Investigating the stability and electronic structure of nanomaterials is essential for their application in electronic devices. In this thesis were analysed two types of nanostructures, a derivative of h-BN and the other of graphene. This analysis was performed using first-principles calculations by Density Functional Theory (DFT), implemented by the SIESTA code. First we investigated two kinds of stacks of h-BN bilayer with impurities and by means of the calculation of interaction and formation energies was identified the most stable bilayers, both due to the nature of the stack and to the type impurity introduced. We also note that the combination of these two effects cause considerable variations in the gaps of energy and impurity. We also use an electric field perpendicular to the plane of the bilayer and observe different changes in the electronic structure related to the permanent electric dipole moment of each nanostructure. The second nanomaterial investigated in this work, the Carbon bicones have been proposed based on the experimental observation of nanocones. The possibility of bicones are experimentally obtained was analyzed by comparing the stability of these nanostructures with existing cones. It was found that some of them are as stable as the cones, which, at least theoretically, enables the synthesis of these nanomaterials. The effect of the electric field and impurities on the electronic structure of bicones were also analyzed, resulting in significant changes in the state density, evidenced by the emergence of new states near the Fermi level / Investigar a estabilidade e a estrutura eletrônica dos nanomateriais é imprescindível para a aplicação dos mesmos em dispositivos eletrônicos. Nesta tese foram analisados dois tipos de nanoestruturas, uma derivada do h-BN e a outra do grafeno. Tal análise foi realizada utilizando cálculos de primeiros princípios, através da Teoria do Funcional da Densidade (DFT), implementados pelo código SIESTA. Primeiramente investigamos dois tipos de empilhamentos de bicamadas de h-BN com impurezas e por meio das energias de interação e formação calculadas, identificamos as bicamadas mais estáveis, tanto em função da natureza do empilhamento, quanto em relação ao tipo de impureza introduzida. Constatamos também que a combinação destes dois efeitos, causa consideráveis variações nos gaps de energia e de impureza. Aplicamos ainda um campo elétrico perpendicular ao plano das bicamadas e observamos diferentes modificações na estrutura eletrônica, relacionadas ao momento de dipolo elétrico permanente de cada nanoestrutura. O segundo nanomaterial investigado neste trabalho, os bicones de Carbono, foram propostos tomando por base a constatação experimental dos nanocones. A possibilidade dos bicones serem obtidos experimentalmente foi analisada comparando a estabilidade destas nanoestruturas com a dos cones já existentes. Foi possível constatar que alguns deles são tão estáveis quanto os cones, o que, ao menos teoricamente, viabiliza a sintetização destes nanomateriais. O efeito do campo elétrico e das impurezas sobre a estrutura eletrônica dos bicones também foram analisados, resultando em mudanças relevantes na densidade de estado, evidenciadas através do surgimento de novos estados próximos ao nível de Fermi.

A presente tese versa sobre resultados obtidos na aplicação da microscopia eletroquímica de varredura no estudo de sistemas micelares e no estudo de bicamadas lipídicas. Os estudos envolvendo sistemas micelares foram realizados utilizando a SECM no modo substrato-gerador/microeletrodo-coletor. Neste modo de operação, um microeletrodo de platina foi posicionado próximo a um substrato de platina e utilizado para monitorar espécies eletrogeradas nesse substrato. Conhecendo o tempo necessário para a espécie eletrogerada difundir do substrato até o microeletrodo, foi possível aplicar a equação de Einstein-Smoluchowski para determinar o coeficiente de difusão da espécie eletroativa e de micelas de surfactantes. Como as micelas não são eletroativas, o ferroceno eletrogerado no substrato e incorporado nas micelas foi utilizado como sonda para a estimativa do tempo de difusão. Os resultados obtidos para o surfactante brometo de tetradecil trimetil amônio (C14TABr) corroboram dados reportados na literatura, demonstrando a utilidade da metodologia proposta no estudo de sistema micelares. Também foram realizados experimentos envolvendo micelas do surfactante cloreto de 1-alquil-3-metilimidazólio, CxMelmCl (x = 10, 12, 14, 16) e com os resultados obtidos foi possível evidenciar o efeito da cadeia carbônica no coeficiente de difusão das espécies. Os experimentos envolvendo a permeação de substâncias através de bicamadas lipídicas foram realizados em duas etapas. Os primeiros ensaios foram realizados utilizando modelo de membrana semipermeável (papel celofane) com o intuito de verificar a aplicabilidade da SECM no monitoramento de espécies eletroativas que permeiam através da membrana. Na segunda etapa, apresentou-se metodologia para a obtenção de microfuros em folhas de poliestireno utilizados para a formação das bicamadas lipídicas, assim como detalhes sobre a construção da célula de medidas utilizadas nos experimentos de permeação. Foram realizados experimentos envolvendo o uso de bicamadas lipídicas planas obtidas pelo método de Miller preparadas com lecitina de soja. Esses experimentos foram realizados com o intuito de avaliar a estabilidade e para verificar a permeabilidade de algumas substâncias nas bicamadas formadas. Os experimentos de permeação foram realizados posicionando um microeletrodo próximo à membrana, com posterior detecção amperométrica da espécie eletroativa que atravessa a membrana. / This thesis shows results on the use of scanning electrochemical microscopy in the study of micellar systems and lipid bilayers. Studies involving micellar systems were performed by using SECM in the substrate-generator/tip-collector mode. In this operation mode a platinum microelectrode was positioned close to a platinum substrate and used to monitor electrogenerated species on this surface. Taking into account the time for the electrogenerated species to diffuse from the substrate to the microelectrode, the diffusion coefficient of the electroactive species and of the micelles can be calculated by applying the Einstein-Smoluchowski equation. As micelles are not electroactive, ferrocene electrogenerated on the substrate and incorporated into the micelles was used as a probe to estimate the diffusion time. The results obtained for tetradecyl trimethyl ammonium bromide (C14TABr) corroborate those reported in the literature, demonstrating the applicability of the proposed methodology in the study of micellar systems. Experiments with micelles obtained from 1-alkyl-3-methylimidazolium, CxMelmCl (x = 10, 12, 14, 16) chloride surfactants were also performed and results showed the effect of the carbon chain in the diffusion coefficient. Experiments involving the permeation of chemical species through lipid bilayers were carried out in two steps. A membrane model (cellophane) was preliminary used in order to investigate the possibility of using SECM as a tool for monitoring the permeation of electroactive species through the membrane. Then, a methodology for obtaining microholes in polystyrene sheets used to form lipid bilayers was presented, as well as details about the design of an electrochemical cell used in the permeation experiments. Experiments involving the use of planar lipid bilayers obtained by the method of Miller prepared using soybean lecithin were performed. These experiments were carried out in order to evaluate the stability and to check the permeation of some substances through the prepared bilayers. Permeation experiments were performed by placing the microelectrode close to the membrane with subsequent amperometric detection of any electroactive species that cross the membrane

In vivo, les phopholipides interagissent avec des structures moléculaires rugueuses, telles des clusters ou fibrilles de protéines. Ce thème n’est pourtant que trop peu abordé dans la littérature scientifique, alors qu’il semblerait que la topologie de la surface sur laquelle repose ces molécules ou mêmes protéines influencent leurs propriétés. Notre projet s’est donc concentré sur les effets qu’un support accidenté pouvait soulever sur les bicouches lipidiques supportées (BLS).Dans un premier temps, nous avons étudié la mobilité de phopholipides déposés sur des supports plus ou moins rugueux par la méthode de recouvrement après photobleaching patterné (FRAPP pour Fluorescence Recovery After Patterned Photobleaching en anglais). Ces derniers ont été créés afin d’obtenir une large gamme de rugosité et caractérisés par Microscopie à Force Atomique.Nous sommes ensuite intéressés à la conformation d’une membrane sur ces substrats à l’aide de la technique non invasive de réflectivité de neutrons.Enfin, nous avons commencé à nous pencher sur les propriétés tribologiques des lipides lubrifiants nos surfaces rugueuses / In vivo lipid membranes interact with rough supramolecular structures such as protein clusters and fibrils However, this issue is not very developped in the state of art, while surface topology which interact with these molecules affects their properties. In this project, effects of rough surface on supported lipid bilayer (BLS) are investigated.First, lipid mobility are studied with the FRAPP method (Fluorescence Recovery After Photobleaching). BLS are deposited on rough supports which are characterized by AFM (Atomic Force Microscopy).Then, BLS structure on our rough surfaces are investigated by Neutron Reflectivity.Finally, first results on tribological properties of our systems are introduced

In organic photovoltaics (OPVs) the key processes relevant to device operation such as exciton dissociation and free carriers recombination occur at the donor-acceptor (D-A) interface. OPV devices require the bulk heterojunction (BHJ) architecture to function efficiently. In these BHJs, D-A interfaces are arranged in three dimensions, which makes molecular arrangements at these interfaces ill defined and hard to characterize. In addition, molecular materials used in OPVs are inherently disordered and may exhibit variable degrees of structural order in the same BHJ. Yet, D-A molecular arrangements and structure are crucial because they shape the energy landscape and photovoltaic (PV) performance in OPVs. Studies that use well-defined model systems to look in details at the interfacial molecular structure in OPVs and link it to interfacial energy landscape and device operation are critically lacking. We have used in situ photoelectron spectroscopy and ex situ x-ray scattering to study D-A interfaces in tailored bilayers and BHJs based on small molecule donors. We show preferential miscibility at the D-A interface depending on molecular conformation in zinc phthalocyanine (ZnPc)/ C60 bilayers and we derive implications for exciton dissociation. Using sexithiophene (6T), a crystalline donor, we show that the energy landscape at the D-A interface varies markedly depending on the molecular composition of the BHJ. Both the ionization energies of sexithiophene and C60 shift by over ~0.4 eV while the energy of the charge transfer state shifts by ~0.5 eV depending on composition. Such shifts create a downward energy landscape that helps interfacial excitons to overcome their binding energies. Finally, we demonstrate that when both disordered and ordered phases of D coexist at the interface, low-lying energy states form in ordered phases and significantly limit the Voc in devices. Overall our work underlines the importance of the aggregation and conformation states of molecular materials at and near the D-A interface in determining the operation and performance of OPV devices. This work shows that the role of D-A interfaces in complex BHJ devices can be unraveled through careful experimental design and by in depth characterization of planar heterojunction bilayer devices recreating model interfaces.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19478号 / 理博第4138号 / 新制||理||1595(附属図書館) / 32514 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 市川 正敏, 教授 佐々 真一, 教授 山本 潤 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

All organisms have cell membranes which are composed of lipids. The length of lipids affects the elastic properties of the cell membrane which play an important role in cell's survival. For instance, membrane flexibility controls the amount of stress that a membrane can sustain before pore formation. In the bacterial cell membranes, the pore formation is also induced by naturally occurring peptides and synthetic amphiphilic copolymers. For this reason, they are one of the most anticipated novel antimicrobial materials. Understanding the mechanism of their action is essential for their use against microbes. Using coarse-grained simulations and a mean field model, we study lipid bilayer membranes under the variation of stress and tail length, as well as their interaction with flexible amphiphilic copolymers. We used a polymer brush model to describe the free energy of the membrane in terms of entropic contributions and hydrophobic interactions. As the stress is increased on the membranes, at high stresses, the membrane transits to a stable pore state in agreement with simulation results. The increased hydrophobic interaction energy at the interface at high stresses leads to the formation of a pore. The hydrophobic interactions induce a contraction stress and the entropy of lipid tails induces a repulsive stress on the membrane. The simulations show that the entropic contribution to the stress, at its positive values, decreases as the length of lipid tails is increased. This increases the tendency of the membrane with the longer lipids to withstand larger stresses before rupturing into pores, as the internal repulsive stress is reduced. We show that copolymers can enhance the pore stability by decreasing the line tension due to the weak adsorption along the rim of the pore. The bilayers studied in our simulations do not require high copolymer concentration at the pores nor any self-organization of the copolymers to open the pore. This is in contrast to the commonly known barrel stave model where the copolymers are assumed to be strongly localised at the rim of the pore. In the presence of the copolymers, we observe a meta-stable pore state of membrane. This happens at a specific concentration of copolymers depending upon the stress acting on the membrane. If the concentration is further increased from this value, then, the membrane shifts to a stable pore state. An increase in the probability of pore formation is observed as the length of copolymers or stress on the membrane are increased. Both the solvent and copolymer permeability increase as the pore becomes stable.