In this report, electrostatic force microscopy (EFM), zeta-potential analyzer, circular dichroism Spectrophotometer and Fourier transform infrared spectroscopy are used to study the electrostatic property of surface on insulin fibril. EFM provides a simultaneous probe of topography and electrostatic property with highly local resolution in nanometer-scale. To understand the correlation between charge distribution on fibril surface and structure transformation, we controlled the incubation time and salt concentration. The results show that the surface charge increases with incubation time, and with the salt concentration increased, the pitch is found to decrease, variation of charge distribution are increased. In addition, we also have evaluated influence of amino acid sequence on growth rate of fibril associated with bovine, porcine and human insulin by atomic force microscopy and circular dichroism Spectrophotometer. The experimental results show that the number of hydrophilic groups on the peptide sequence will affect the speed of fibril generated, and the location of hydrophilic groups on the peptide sequence will affect the stability of the fibril under the frozen environment.

Submitted by Evandro Martin Lanzoni (evandrolanzoni@yahoo.com.br) on 2018-05-28T18:03:48Z No. of bitstreams: 1 dissertação mestrado evandro lanzoni_versão final.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-05-28T19:02:57Z (GMT) No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) / Made available in DSpace on 2018-05-28T19:02:57Z (GMT). No. of bitstreams: 1 lanzoni_em_me_bauru.pdf: 4510657 bytes, checksum: dadfb13eef638b712a1e377fddcf85d2 (MD5) Previous issue date: 2018-03-29 / As técnicas de microscopia de sonda Kelvin (KPFM) e de microscopia de força eletrostática (EFM) são amplamente utilizadas para analisar a distribuição do potencial de superfície, porém com pouca aplicação em nanoestruturas semicondutoras auto-organizadas embutidas em um substrato. Neste trabalho, investigamos diretamente o acúmulo de carga dentro de estruturas mesoscópicas de GaAs (MGS) [1]. As estruturas são fabricadas através do crescimento sobreposto de um modelo de nano orifícios usando epitaxia de feixe molecular. Para tal, uma combinação de desoxidação assistida por Ga e ataque químico por gotículas localizadas foram utilizadas para criar orifícios iniciais com uma profundidade de ca. 10 a 15nm, que são posteriormente cobertos com 15nm de barreira AlxGax-1As e GaAs com 1nm, 2nm, 5nm, 10nm de espessura. Microscopia de força atômica e microscopia eletrônica de transmissão mostraram que a forma do orifício é preservada durante o crescimento de AlGaAs. Em seguida, esses orifícios são preenchidos com GaAs formando uma estrutura alongada sobre o buraco [1]. Investigamos o potencial de superfície local e a distribuição das cargas nestas estruturas com a técnica KPFM de passagem única. Portanto, uma voltagem AC de 5 V é aplicada a uma ponta metalizada e varremos a amostra no modo de contato intermitente. Observamos uma clara diferença de potencial na região central da estrutura, onde esperamos o furo preenchido. Então, um estudo sistemático com a técnica de KPFM mostrou a influência no acúmulo de carga quando a espessura de GaAs é alterada, bem como, quando modificamos a concentração de Al na barreira de AlGaAs. O cálculo simulando um poço de potencial com barreiras semi-finitas e finitas mostrou que não ocorre acúmulo de carga quando a espessura do GaAs é menor que 1,5 nm, corroborando com nossos resultados. Simulações do diagrama de banda e da densidade de elétron da estrutura permitem atribuir o acumulo de carga observado, aos diferentes níveis de energia da estrutura mesoscópica de GaAs em comparação com as camadas de GaAs circundantes. / Kelvin probe force microscopy and electric force microscopy techniques are widely used to analyze the distribution of the surface potential with little application to self-assembled semiconductor nanostructures embedded into a substrate. In this work, we directly investigate the charge accumulation inside mesoscopic GaAs structures [1]. The structures are fabricated by overgrowth of a nanohole template using molecular beam epitaxy. Therefore, a combination of Ga assisted deoxidation and local droplet etching is used to create initial holes with a depth of ca. 10 to 15nm, which are covered subsequently with 15nm of AlxGax-1As barrier and GaAs caps with 1nm, 2nm, 5nm, 10nm thicknesses. Atomic force microscopy and transmission electron microscopy results showed that the hole shape is preserved during the AlGaAs overgrowth. Then filled with GaAs forming an elongated mount over the hole [1]. We investigate the local potential and the charge distribution in these structures with a single pass Kelvin probe force microscopy technique. Therefore, an AC voltage of 5 V is applied to a metalized tip and scanned in tapping mode over the sample. We observed a clear potential difference in Kelvin probe force microscopy measurements in the middle of the structure, where we expect a filled hole. We systematically study by Kelvin probe force microscopy the influence on the charge accumulation when the GaAs thickness is changed, as well as the Al concentration in the AlGaAs barrier. Calculation of the particle in the box for semi-finite and finite barriers were done and show that no charge accumulation is observed for GaAs thickness lower than 1.5nm in the semi-finite barrier, corroborating with our results. Simulations of band gap and electron wavefunction of the structure allow us to ascribe the charge accumulation observed, to the different confinement of carriers inside of the unstrained mesoscopic GaAs structure compared to the surrounding GaAs layers.

SILVA, José Júnior Alves da. Microscopia de força elétrica em amostra de óxido de grafeno. 2013. 100 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2013. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-05-13T21:31:02Z No. of bitstreams: 1 2013_tese_jjasilva.pdf: 30925308 bytes, checksum: b2e1379686008553b3699b7736b7335b (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-05-13T21:38:16Z (GMT) No. of bitstreams: 1 2013_tese_jjasilva.pdf: 30925308 bytes, checksum: b2e1379686008553b3699b7736b7335b (MD5) / Made available in DSpace on 2014-05-13T21:38:17Z (GMT). No. of bitstreams: 1 2013_tese_jjasilva.pdf: 30925308 bytes, checksum: b2e1379686008553b3699b7736b7335b (MD5) Previous issue date: 2013 / Carbon-based structures have played a major role in scientific and technological fields. This is due to the versatility of the element carbon, the pillar of organic chemistry, which can form a variety of structures (about 10 million compounds), besides being a basic constituent of all known life forms. Depending on the conditions, this phenomenal element can occur in several allotropic forms: from an extremely brittle material, such as graphite, so incredibly resistant materials such as diamond, carbon nanotubes and graphene. These graphitic materials have been studied extensively, and present unique properties and great potential for technological applications. Among these materials, graphene currently occupies the most prominent position by having special electronic and mechanical properties. The graphene oxide is a class of graphitic structure consisting essentially of a graphene layer decorated with epoxide and hydroxyl groups on the surface and carboxyl and carbonyl groups on the edges. Its stoichiometry depends strongly on the method of production. In addition the graphene oxide is one of the main routes for obtaining large-scale graphene also it has several interesting properties, which allow, for example, biological applications, since their functional groups make it very reactive, besides being easily dispersed in water. Many issues related to graphene oxide are yet unclear, as also its structure, training procedure and mechanisms of interaction. Thus, the electric force microscopy (EFM) was used as the main tool to study electrostatic properties of a graphene oxide sample obtained by a modified Hummer method. By means of a simplified model, it was possible to develop a method for the analysis of the EFM measurements and so determine the presence and the sign of the net charge of the sample. Furthermore it is possible to clarify the origin of the edge phenomenon observed in EFM experiments. / As estruturas a base de carbono tem um papel de grande importância nos campos da ciência e da tecnologia. Isso graças à versatilidade do elemento carbono, pilar da química orgânica, que consegue formar uma diversidade de estruturas (cerca de 10 milhões de compostos), além de ser um constituinte básico de toda forma de vida conhecida. Dependendo das condições de formação, este fenomenal elemento, pode se apresentar em diversas formas alotrópicas: desde um material extremamente frágil, como o grafite, até materiais incrivelmente resistentes como o diamante, nanotubos de carbono e o grafeno. Esses materiais grafíticos têm sido extensivamente estudados, apresentando propriedades únicas e grande potencial em aplicações tecnológicas. Dentre eles, o grafeno ocupa, atualmente, a posição de maior destaque por possuir propriedades mecânicas e eletrônicas diferenciadas. O óxido de grafeno é uma classe de estruturas grafíticas constituída basicamente de uma camada de grafeno decorada com grupos epóxido e hidroxila na superfície e grupos carboxílicos e carbonila nas bordas. A sua estequiometria depende fortemente do método de obtenção. Esse material, além de ser uma das principais rotas para a obtenção em larga escala do grafeno, também apresenta diversas propriedades interessantes, que possibilitam, por exemplo, aplicações biológicas, uma vez que seus grupos funcionais o tornam bastante reativo além de ser facilmente dispersado em água. Muitas questões relacionadas ao óxido de grafeno ainda não estão bem esclarecidas, como sua própria estrutura, processo de formação e mecanismos de interação. Nesse sentido, foi utilizada, como principal ferramenta, a microscopia de força elétrica (EFM) para estudar propriedades eletrostáticas de uma amostra de óxido de grafeno obtida utilizando-se um método de Hummer modificado. Por meio de um modelo simplificado, foi possível desenvolver um método para análise das medições de EFM e assim determinar a presença e o sinal da carga líquida da amostra. Além de ser possível esclarecer a origem do fenómeno de borda observado nos experimentos de EFM.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / As estruturas a base de carbono tem um papel de grande importÃncia nos campos da ciÃncia e da tecnologia. Isso graÃas à versatilidade do elemento carbono, pilar da quÃmica orgÃnica, que consegue formar uma diversidade de estruturas (cerca de 10 milhÃes de compostos), alÃm de ser um constituinte bÃsico de toda forma de vida conhecida. Dependendo das condiÃÃes de formaÃÃo, este fenomenal elemento, pode se apresentar em diversas formas alotrÃpicas: desde um material extremamente frÃgil, como o grafite, atà materiais incrivelmente resistentes como o diamante, nanotubos de carbono e o grafeno. Esses materiais grafÃticos tÃm sido extensivamente estudados, apresentando propriedades Ãnicas e grande potencial em aplicaÃÃes tecnolÃgicas. Dentre eles, o grafeno ocupa, atualmente, a posiÃÃo de maior destaque por possuir propriedades mecÃnicas e eletrÃnicas diferenciadas. O Ãxido de grafeno à uma classe de estruturas grafÃticas constituÃda basicamente de uma camada de grafeno decorada com grupos epÃxido e hidroxila na superfÃcie e grupos carboxÃlicos e carbonila nas bordas. A sua estequiometria depende fortemente do mÃtodo de obtenÃÃo. Esse material, alÃm de ser uma das principais rotas para a obtenÃÃo em larga escala do grafeno, tambÃm apresenta diversas propriedades interessantes, que possibilitam, por exemplo, aplicaÃÃes biolÃgicas, uma vez que seus grupos funcionais o tornam bastante reativo alÃm de ser facilmente dispersado em Ãgua. Muitas questÃes relacionadas ao Ãxido de grafeno ainda nÃo estÃo bem esclarecidas, como sua prÃpria estrutura, processo de formaÃÃo e mecanismos de interaÃÃo. Nesse sentido, foi utilizada, como principal ferramenta, a microscopia de forÃa elÃtrica (EFM) para estudar propriedades eletrostÃticas de uma amostra de Ãxido de grafeno obtida utilizando-se um mÃtodo de Hummer modificado. Por meio de um modelo simplificado, foi possÃvel desenvolver um mÃtodo para anÃlise das mediÃÃes de EFM e assim determinar a presenÃa e o sinal da carga lÃquida da amostra. AlÃm de ser possÃvel esclarecer a origem do fenÃmeno de borda observado nos experimentos de EFM. / Carbon-based structures have played a major role in scientific and technological fields. This is due to the versatility of the element carbon, the pillar of organic chemistry, which can form a variety of structures (about 10 million compounds), besides being a basic constituent of all known life forms. Depending on the conditions, this phenomenal element can occur in several allotropic forms: from an extremely brittle material, such as graphite, so incredibly resistant materials such as diamond, carbon nanotubes and graphene. These graphitic materials have been studied extensively, and present unique properties and great potential for technological applications. Among these materials, graphene currently occupies the most prominent position by having special electronic and mechanical properties. The graphene oxide is a class of graphitic structure consisting essentially of a graphene layer decorated with epoxide and hydroxyl groups on the surface and carboxyl and carbonyl groups on the edges. Its stoichiometry depends strongly on the method of production. In addition the graphene oxide is one of the main routes for obtaining large-scale graphene also it has several interesting properties, which allow, for example, biological applications, since their functional groups make it very reactive, besides being easily dispersed in water. Many issues related to graphene oxide are yet unclear, as also its structure, training procedure and mechanisms of interaction. Thus, the electric force microscopy (EFM) was used as the main tool to study electrostatic properties of a graphene oxide sample obtained by a modified Hummer method. By means of a simplified model, it was possible to develop a method for the analysis of the EFM measurements and so determine the presence and the sign of the net charge of the sample. Furthermore it is possible to clarify the origin of the edge phenomenon observed in EFM experiments.

This thesis presents the development of a novel atomic force microscope (AFM) based nanofabrication technique termed as thermochemical nanolithography (TCNL). TCNL uses a resistively heated AFM cantilever to thermally activate chemical reactions on a surface with nanometer resolution. This technique can be used for fabrication of functional nanostructures that are appealing for various applications in nanofluidics, nanoelectronics, nanophotonics, and biosensing devices. This thesis research is focused on three main objectives. The first objective is to study the fundamentals of TCNL writing aspects. We have conducted a systematic study of the heat transfer mechanism using finite element analysis modeling, Raman spectroscopy, and local glass transition measurement. In addition, based on thermal kinetics analysis, we have identified several key factors to achieve high resolution fabrication of nanostructures during the TCNL writing process. The second objective is to demonstrate the use of TCNL on a variety of systems and thermochemical reactions. We show that TCNL can be employed to (1) modify the wettability of a polymer surface at the nanoscale, (2) fabricate nanoscale templates on polymer films for assembling nano-objects, such as proteins and DNA, (3) fabricate conjugated polymer semiconducting nanowires, and (4) reduce graphene oxide with nanometer resolution. The last objective is to characterize the TCNL nanostructures using AFM based methods, such as friction force microscopy, phase imaging, electric force microscopy, and conductive AFM. We show that they are useful for in situ characterization of nanostructures, which is particularly challenging for conventional macroscopic analytical tools, such as Raman spectroscopy, IR spectroscopy, and fluorescence microscopy.

No description available.

Ce manuscrit présente une étude expérimentale de phase isolante non-conventionnelle, l'isolant d'Anderson, induit par le désordre, l'isolant de Mott, induit par les interactions de Coulomb, et les isolants topologiques.Dans une première partie du manuscrit, je décrirais le développement d'une méthode pour étudier la réponse de charge de nanoparticules par Microscopie à Force Electrostatique (EFM). Cette méthode a été appliquée à des nanoparticules de magnétite (Fe3O4), un matériau qui présente une transition métal-isolant, i.e. la transition de Verwey, lors de son refroidissement en dessous d'une température TV~120 K.Dans une seconde partie, ce manuscrit présente une étude détaillée de l'évolution de la densité d'états au travers de la transition métal-isolant entre un isolant de type Anderson-Mott et une phase métallique dans le matériau SrTiO3, et ceci, en fonction de la concentration de dopants, les lacunes d'oxygènes. Nous avons trouvé que dans un dispositif memoresistif de type Au-SrTiO3-Au, la concentration de dopants pouvait être ajustée par migration des lacunes d'oxygènes à l'aide d'un champ. Dans cette jonction tunnel, l'évolution de la densités d'états au travers de la transition métal-isolant peut être étudiée de façon continue. Finalement, dans une troisième partie, le manuscrit présente le développement d'une méthode pour la microfabrication d'anneaux de Aharonov-Bohm avec l'isolant topologique, Bi2Se3, déposée par épitaxie à jet moléculaire. Des résultats préliminaires sur les propriétés de transport quantique de ces dispositifs seront présentés. / This manuscript presents an experimental study of unconventional insulating phases, which are the Anderson insulator, induced by disorder, the Mott insulator, induced by Coulomb interactions, and topological insulators.In a first part of the manuscript, I will describe the development of a method to study the charge response of nanoparticles through Electrostatic Force Microscopy (EFM). This method has been applied to magnetite Fe3O4 nanoparticles, a material that presents a metal-insulator transition, i.e. the Verwey transition, upon cooling the system below a temperature Tv=120K. In a second part, this manuscript presents a detailed study of the evolution of the Density Of States (DOS) across the metal-insulator transition between an Anderson-Mott insulator and a metallic phase in the material SrTiO3 and this, as function of dopant concentration, i.e. oxygen vacancies. We found that in this memristive type device Au-SrTiO3-Au, the dopant concentration could be fine-tuned through electric-field migration of oxygen vacancies. In this tunnel junction device, the evolution of the DOS can be followed continuously across the metal-insulator transition. Finally, in a third part, the manuscript presents the development of a method for the microfabrication of Aharonov-Bohm rings with the topological insulator material, Bi2Se3, grown by molecular beam epitaxy. Preliminary results on the quantum transport properties of these devices will be presented.

Solid oxide fuel cells (SOFCs) represent a next generation energy source with high energy conversion efficiency, low pollutant emission, good flexibility with a wide variety of fuels, and excellent modularity suitable for distributed power generation. As an electrochemical energy conversion device, SOFC’s performance and reliability depend sensitively on the catalytic activity and stability of the electrode materials. To date, however, the development of electrode materials and microstructures is still based largely on trial-and-error methods because of inadequate understanding of the mechanisms of the electrode processes. Identifying key descriptors/properties of electrode materials or functional heterogeneous interfaces, especially under in situ conditions, may provide guidance to the design of electrode materials and microstructures. This thesis aims to gain insight into the electrochemical and catalytic processes occurring on the electrode surfaces using unique characterization tools with superior sensitivity, high spatial resolution, and excellent surface specificity applicable under in situ/operando conditions. Carbon deposition on nickel-based anodes is investigated with in situ Raman spectroscopy and SERS. Analysis shows a rapid nucleation of carbon deposition upon exposure to small amount of propane. Such nucleation process is sensitive to the presence of surface coating (e.g., GDC) and the concentration of steam. In particular, operando analysis of the Ni-YSZ boundary indicates special function of the interface for coking initiation and reformation. The coking-resistant catalysts (BaO, BZY, and BZCYYb) are systematically studied using in situ Raman spectroscopy, SERS, and EFM. In particular, time-resolved Raman analysis of the surface functional groups (-OH, -CO3, and adsorbed carbon) upon exposure to different gas atmospheres provides insight into the mechanisms related to carbon removal. The morphology and distribution of early stage carbon deposition are investigated with EFM, and the impact of BaO surface modification is evaluated. The surface species formed as a result of sulfur poisoning on nickel-based anode are examined with SERS. To identify the key factors responsible for sulfur tolerance, model cells with welldefined electrode-electrolyte interfaces are systematically studied. The Ni-BZCYYb interface exhibits superior sulfur tolerance. The oxygen reduction kinetics on LSCF, a typical cathode material of SOFC, is studied using model cells with patterned electrodes. The polarization behaviors of these micro- electrodes, as probed using a micro-probe impedance spectroscopy system, were correlated with the systematically varied geometries of the electrodes to identify the dominant paths for oxygen reduction under different electrode configurations. Effects of different catalyst modifications are also evaluated to gain insight into the mechanisms that enhance oxygen reduction activity. The causes of performance degradation of LSCF cathodes over long term operation are investigated using SERS. Spectral features are correlated with the formation of surface contamination upon the exposure to air containing Cr vapor, H2O, and CO2. Degradation in cathode performance occurs under normal operating conditions due to the poisoning effect of Cr from the interconnect between cells and the high operating temperature. The surface-modified LSCF cathode resists surface reactions with Cr vapor that impairs electrode performance, suggesting promising ways to mitigate performance degradation.

Le but de cette thèse était tout d'abord d'étudier les théories physiques qui décrivent la dynamique des polymères à l'échelle macroscopique. Le modèle de Rouse et la théorie d'enchevêtrement de P-G. de Gennes décrivent la dynamique des polymères non enchevêtrés et enchevêtrés, respectivement. Nous avons étudié les différentes transitions entre ces deux régimes en utilisant deux techniques expérimentales : Spéctroscopie dielectrique large bande et rhéologie. Un test complet du modèle de Rouse à été effectué en comparant les prédictions de ce modèle pour la dépendance en fréquence de la permittivité diélectrique et du module de cisaillement aux données expérimentales. Les effets d'enchevêtrement sur les spectres diélectriques ont été discutés. Nous avons ensuite développé des méthodes basées sur la microscopie à force électrostatique afin d'étudier les propriétés diélectriques locales. En utilisant une simulation numérique basée sur la Méthode des Charges Equivalentes, nous avons quantifié la constante diélectrique à partir de la mesure du gradient de force crée par un potentiel statique entre une pointe et un diélectrique. Cette méthode permet d'imager la constante diélectrique avec une résolution spatial de 40 nm. Le retard de phase de la composante en 2 omega de la force ou du gradient de force crée par un voltage alternatif est relié aux pertes diélectriques. Nous avons développé un mode d'imagerie des pertes diélectriques. Cette méthode simple pourrait être appliqué en biologie ou matière molle en générale afin d'étudier des variations locales de constantes dielectriques.

Amostras de Semicondutores III-V foram crescidas usando a técnica de Epitaxia por feixes Moleculares. As propriedades elétricas das estruturas de GaAs com dopagem planar com Silício foram investigadas, e também a saturação e a difusão do Silício nestas amostras. As propriedades ópticas e elétricas das estruturas dopadas planarmente com Selênio foram analisadas, usando as técnicas de Capacitância-voltagem e a de Tunelamento resonante. As propriedades elétricas dos poços quânticos a base de InGaAs/GaAs foram investigadas, em função da posição da impureza planarmente dopada com Silício. / III-V semiconductor samples were grown using the Molecular beam epitaxy technique, the electrical properties of the GaAs structures planar doped with silicon were investigated as well as the Silicon saturation and diffusion in these samles. The optcal and electrical properties of structures planar doped with Selenium were analyzed using the Capacitance Voltage and resonant Tunneling techniques. The electrical properties of InGaAs/ GaAs based quantum wells were investigated as a function of the planar doped with Silicon impurity position.