Orientador: José Antônio Brum / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T23:45:16Z (GMT). No. of bitstreams: 1 Andriolo_HelderFaria_M.pdf: 2066347 bytes, checksum: c0835c5528aa09df816a2dfb45249e5f (MD5) Previous issue date: 2015 / Resumo: Nesse trabalho estudamos um sistema de GaAs/In_{0.27}Ga_{0.73} As/Al_{0.3}Ga_{0.7}As, intencionalmente dopado com material do tipo-n, em que ocorre a transferência de elétrons, provenientes da dopagem, para o poço quântico de In_{0.27}Ga_{0.73}As, formando um gás de elétrons bidimensional no poço. A seguir o efeito da introdução de pontos quânticos auto-organizados de InAs na estrutura foi analisado. Nossos resultados mostram uma pequena mudança no perfil de potencial da estrutura. O que ocorre após a introdução dos pontos quânticos é, basicamente, uma redistribuição dos elétrons, que agora passam a ocupar o poço quântico e o ponto quântico. Estudamos também as propriedades ópticas, espectros de absorção e emissão, de pontos quânticos acoplados com gás de portadores. Para isso foi necessário estabelecer um método na qual discretizamos o contínuo de níveis energéticos do gás de portadores (elétrons), o método através da cadeia de Wilson foi o utilizado nos cálculos, embora outros dois métodos também tenham sido mostrados. Introduzimos, por fim, um íon de manganês no centro do ponto quântico e calculamos espectros de emissão desse sistema com os níveis do gás elétrons discretizados através da cadeia de Wilson / Abstract: In this work, we study a GaAs/In_{0.27}Ga_{0.73}As/Al_{0.3} Ga_{0.7}As system intentionally doped n-type material, which occurs a transfer of electrons from the doping into In_{0.27}Ga_{0.73}As quantum well, forming a two-dimensional electron gas in the well. Next, the effect of introducing self-assembled InAs quantum dots in the structure was analyzed. Our results show little change in potential profile of the structure. What happens after the introduction of quantum dots is basically a redistribution of electrons, that now occupy the quantum well and quantum dot. We also studied the optical properties, absorption and emission, of quantum dots coupled with carrier gas. This required establishing a method in which discretize the continuous energy levels of the carrier gas (electrons), the method by Wilson chain was used in the calculations, although other two methods also have been shown. Introduced, finally, a manganese ion in the center of the quantum dot, and we calculated emission spectra of this system, with the electron gas levels discretized by Wilson chain / Mestrado / Física / Mestre em Física / 131432/2013 / 2013/25371-1 / CNPQ / FAPESP

Carbon nanotubes have unique electronic, optical, mechanical, and transport properties which make them an important element of nanoscience and nanotechnology. However, successful application and integration of carbon nanotubes into new nanodevices requires fundamental understanding of their property changes under the influence of many external factors. This dissertation presents qualitative and quantitative theoretical understanding of property changes, while carbon nanotubes are exposed to the deformations, defects, external electric fields, and adsorption. Adsorption mechanisms due to Van der Waals dispersion forces are analyzed first for the interactions of graphitic materials and biological molecules with carbon nanotubes. In particular, the calculations are performed for the carbon nanotubes and graphene nanoribbons, DNA bases, and their radicals on the surface of carbon nanotubes in terms of binding energies, structural changes, and electronic properties alterations. The results have shown the importance of many-body effects and discrete nature of system, which are commonly neglected in many calculations for Van der Waals forces in the nanotube interactions with other materials at nanoscale. Then, the effect of the simultaneous application of two external factors, such as radial deformation and different defects (a Stone Wales, nitrogen impurity, and mono-vacancy) on properties of carbon nanotubes is studied. The results reveal significant changes in mechanical, electrical, and magnetic characteristics of nanotubes. The complicated interplay between radial deformation and different kinds of defects leads to the appearance of magnetism in carbon nanotubes which does not exist in perfect ones. Moreover, the combined effect of radial deformation and external electric fields on their electronic properties is shown for the first time. As a result, metal-semiconductor or semiconductor-metal transitions occur and are strongly correlated with the strength and direction of external electric field and the degree of radial deformations.

Molecular self-assembly or ligand-metal assembly is a process in which several individual molecules and metal ions organize themselves into an ordered arrangement without external stimuli, the defined structures can lead to distinctive electronic and photonic performances. In the meantime, as the scale of materials decreases, various unique properties arise from their minute scaled dimensions, such as surface effect, volume effect, quantum effect and dielectric confinement effect, etc. Therefore, the design and fabrication of the micro- and nanomaterial via the technique of molecular self-assembly or ligand-metal assembly is becoming an emerging research field, for the purpose of meeting the increased demands of multi-functional materials. Chapter 1 gives an overview of the advanced materials prepared by either molecular self-assembly or ligand-metal assembly. We described the interaction nature in detail, and enumerated the applications as well as developments of this scientific field. Furthermore, the detailed classifications as well as previous work of these advanced materials we researched on, such as two dimensional nanosheets, hetero-structured materials and cyclometalated iridium(Ⅲ) complexes were also amply summarized. Two-dimensional nanosheets have always been a research hotspot since graphene was discovered and isolated. In contrast, molecule-based organometallic nanosheets through bottom-up method exhibit more inner structures. In Chapter 2, we constructed two classes of organometallic nanosheets with different intermolecular forces, one is metal-ligand coordination, while the other one is the aromatic (π-π) interaction. Two-dimensional nanosheets with Hg-acetylide linkages, bis(dipyrrinato)metal linkages as well as bis(terpyridine)metal linkages were synthesized and characterized by UV-Vis absorption spectroscopy, FT-IR spectroscopy, optical and electron microscopy, photoluminescence spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy and so on. In addition, the potential applications were explored as well, including the tests of charge mobility and current capacitance. Meanwhile we also investigated the two-dimensional nanosheets self-assembled by aromatic (π-π) interaction. The morphology characterizations, crystal form measurements, besides elemental analyses were conducted. By means of surface control, the hybrid nanosheets could achieve many superior performances, like super hydrophobicity, high conductivity and soft magnetism. In Chapter 3, we firstly mentioned that organic hetero-structured micro- or nanomaterials are widely attractive on account of its extensive applications in lasers, bipolar transistors, field effect transistors and solar cells. In our work, we focus on the diverse microrods assembled from π-conjugated small molecules, especially in the construction of heterogeneous organic heterojunction materials with specific components distribution. Two novel kinds of heterostructure, multilayer core-shell structured heterojunction and heterogeneous rod-tail helix were fabricated and developed both via a stepwise seeded-growth route, in which the different constituents possess different colors of luminescence. Through the media of fluorescence microscopy and confocal microscopy, the core-shell hetero- structures can be observed, testified and recorded quite distinctly. Furthermore, the prepared method by employing seeded-precursor could give us a revelation about constructing more sophisticated and functional organic luminescent heterogeneous materials. Chapter 4 focuses on the syntheses and characterization of eight cyclometalated iridium(Ⅲ) complexes, Ir(TPY)2(Dipyrrinato), Ir(PIQ)2(Dipyrrinato), Ir(Ligand 1)2(Dipyrrinato), Ir(Ligand 2)2(Dipyrrinato), Ir(Ligand 3)2(Dipyrrinato), Ir(PPY)2 (Dipyrrinato), Ir(m-PPY)2(Dipyrrinato) and Ir(PPY-m)2(Dipyrrinato). As is known, iridium(Ⅲ) complexes can exploit the energy of both 25% singlet and 75% triplet excited states. Due to their highly efficient applications in phosphorescent OLEDs, these materials are considered as one of the potential candidates for flexible display screen as well as clearing luminary. Among those full-color light-emitting iridium(Ⅲ) phosphors, near-infrared (NIR) phosphors are broadly utilized in phototherapy as well as biosensors. Herein, our eight synthetic cyclometalated iridium(Ⅲ) complexes all gave photoluminescence at 680 - 700 nm in solution, which could be attributed to the NIR region. We continuously tune the extensive conjugation on the C^N ligands in order to make longer wavelength emitting phosphors. The HOMO and LUMO of eight synthetic iridium(Ⅲ) phosphors were also calculated according to their cyclic voltamograms (CV). The design and preparation strategy in this thesis can inspire us to develop near-infrared as well as higher-performance organometallic phosphors.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22459号 / 工博第4720号 / 新制||工||1737(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 作花 哲夫, 教授 安部 武志, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In this thesis, the single-level correlated quantum dot attached to two BCS superconducting leads is analyzed. A difference in the superconducting phases of the leads induces the DC Josephson supercurrent in the junction. In this setup, the influence of asymmetrical dot-lead couplings on transport properties is clarified analytically. The coupling asymmetry and the phase difference can be combined into one function, which allows us to calculate physical properties of a system with coupling asymmetry from the properties of its effective symmetric counterpart. The coupling asymmetry turns out to be an important parameter which influences the position of the 0 − �෰ quantum phase transition even in the strongly correlated Kondo regime. Further, this thesis contributes to the interpretation of an AC Josephson current measurement, in which a surprising drop in the amplitude was observed in the Kondo regime. The experimental setup is characterized using numerical renormalization group calculations of the equilibrium many-body spectra. Possible quantum-point-contact- based interpretations are discussed. Although a drop in the AC Josephson current at the experimental bias voltage is also expected in a quantum point contact, we conclude that the physical mechanisms causing it in the quantum dot system are likely not...

This master thesis is focused on characterization of electrical transport properties of one-dimensional nanostructures. First section of this work deals with theoretical description of the experimental approaches to realization of such measurements. This section involves also a detail discussion of preparation of contacts using e-beam lithography. Next, theoretical description of characterization of nanostructures using photoluminescence measurements is given. Second section describes practical application of the aforementioned electrical transport measurements. Presented results include transport and photoluminescence measurements of WS2 nanotubes, InAs and WO2.72 nanowires. The last section of this thesis deals with nanowire quantum well heterostructures. The section provides both a deeper theoretical view of the problem and results of the photoluminescence measurements are shown.

Color filters enable photosensors to obtain spectral composition of incoming radiation, be it to mimic human vision or to separate analytical signals. Efforts to increase the resolution of these photosensors lead to decrease in size of individual picture elements – pixels, which places increasing demands on the color filter technology. Conventional color filters operating on the principle of absorption of light in organic pigments are frequently used, but they are no longer meeting growing requirements of increasing sensor resolution. Here, metasurfaces comes to an aid, utilizing nanostructures to separate colors and thus creating structural coloration. There are many approaches to separate colors using metasurfaces, but each carries certain disadvantages with their principle of operation. In this thesis, we present a novel approach to separate colors which utilizes manipulation of radiation polarization. The presented color filter is first modeled and optimizes through numerical simulations and then manufactured using nanofabrication methods. Finally, the optical response of nanostructures is verified by several optical spectroscopy methods.

This master thesis deals with supercapacitors based on electrical double layer and proper carbon electrodes for this type of supercapacitors. In theoretical part of work is described theory of supercapacitors, energy storage principles and their properties. In the next part are described carbon materials, their properties and electrochemical methods of measurements that we used. In the experimental part is described preparation of electrodes, results and conclusion.

This diploma thesis discusses the gas sensor preparation via anodic oxidation. It names sensor types, deals with the sensing principle of electrochemical sensors in detail and submits sensor parameters. It describes preparation technology and characterization technology methods. In the experimental part, it focuses on both the measurement methodology and the electrochemical oxygen sensor covered with titanium dioxide nanocolumns fabrication. Not the least it discusses acquired research results.

This work deals with the preparation of gold nanostructures for future usage in electrochemical sensors and biosensors, methods for their characterization and production. The emphasis is focused on the template-based electrodeposition method of gold and on study of the effect of manufacturing conditions on physical properties, mainly electrical and topological of nanostructures. Thesis is focused also on overall function and sensitivity of the gold nanostructured electrode.