Submitted by Caio Santos (c.dehly@gmail.com) on 2017-10-26T20:56:53Z No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-11-10T12:12:33Z (GMT) No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Approved for entry into archive by Milena Rubi ( ri.bso@ufscar.br) on 2017-11-10T12:12:54Z (GMT) No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) / Made available in DSpace on 2017-11-10T12:13:12Z (GMT). No. of bitstreams: 2 Dissertação_Caio.pdf: 6450967 bytes, checksum: 9c0ad5f1b63e4ef97562046030ba0696 (MD5) Carta_Comprovante.pdf: 679811 bytes, checksum: b230eed541e4ff4ea1205d79507474d1 (MD5) Previous issue date: 2017-04-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Porous anodic alumina can be obtained, in addition to conventional methods such as potentiostatic and galvanostatic, or by pulsed method. Among these are the methods of discontinuous pulse, hybrid pulse and polarized pulse methods. The structures formed by these methods can be applied to sensors and photonic materials. In this work the influences of the pulse parameters for the porous anodic alumina were investigated by polarized pulse potentiostatic anodization. Data analysis was presented from the duty cycle seen in the literature, which provides important information about the structure formed for the applied conditions and, in addition, new ways of analyzing the data related to the pulse, such as the analysis of the potential difference and the pulse frequency, this latter complementing the analysis of the duty cycle. As a result it was possible to observe that the porous anodic alumina thickness obtained is proportional to the duty cycle applied, where the higher duty cycle, the greater the thickness obtained. From the potential difference, the differences in the morphological and optical parameters could be analyzed by the influence of the negative minimum voltage applied during the pulsed anodization. The pulse frequency, also discussed in this work, was used to analyze different pulse periods for the same duty cycle, demonstrating that can be obtained structures with different values by varying the value of the pulse frequency. For the porosity calculation, an application was developed that helped to obtain the pore distance, which is one of the variables used to calculate the porosity. With the porosity values, the effective refractive index of each sample was calculated to find the effective optical thickness (EOT) and, finally, the thickness of the obtained anodic alumina film. / A alumina anódica porosa pode ser obtida, além dos métodos convencionais como potenciostático e galvanostático, ou por métodos pulsados. Dentre estes destacam-se os métodos de pulso descontínuo, pulso híbrido e pulso polarizado. As estruturas formadas por estes métodos podem ser aplicadas em sensores e materiais fotônicos. Neste trabalho foram investigadas as influências dos parâmetros de pulso para a obtenção da alumina anódica porosa pelo método de anodização potenciostática com pulso polarizado. Foram apresentadas análises de dados a partir do ciclo de trabalho visto na literatura, onde traz importantes informações sobre a estrutura formada para as condições aplicadas e, além disto, novas formas de analisar os dados referentes aos pulsos, como a análise a partir da diferença de potencial e a frequência de pulso, este último complementando a análise do ciclo de trabalho. Como resultado foi possível observar que a espessura de alumina anódica porosa obtida é proporcional ao ciclo de trabalho aplicado, onde quanto maior o ciclo de trabalho, maior será a espessura obtida. A partir da diferença de potencial pôde-se analisar as diferenças nos parâmetros morfológicos e ópticos pela influência da tensão mínima negativa aplicada durante a anodização pulsada. A frequência de pulso, também abordada neste trabalho, foi utilizada para analisar diferentes períodos de pulsos para o mesmo ciclo de trabalho, demonstrando que variando o valor da frequência de pulso pode-se obter estruturas com valores distintos. Para o cálculo da porosidade foi desenvolvido um aplicativo que auxiliou na obtenção da distância entre poros, que é uma das variáveis utilizadas para o cálculo da porosidade. E com os valores de porosidade foi calculado o índice de refração efetivo de cada amostra para encontrar a sua espessura óptico efetivo (EOT, do inglês Effective Optical Thickness) e, por fim, a espessura do filme de alumina anódica obtido.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2016-11-17T17:43:21Z No. of bitstreams: 1 RODRIGUES_Karina_2015.pdf: 7918406 bytes, checksum: 5c7eded70cc8a9dd00ce5c1b2d70d846 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2016-11-17T17:43:31Z (GMT) No. of bitstreams: 1 RODRIGUES_Karina_2015.pdf: 7918406 bytes, checksum: 5c7eded70cc8a9dd00ce5c1b2d70d846 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2016-11-17T17:43:39Z (GMT) No. of bitstreams: 1 RODRIGUES_Karina_2015.pdf: 7918406 bytes, checksum: 5c7eded70cc8a9dd00ce5c1b2d70d846 (MD5) / Made available in DSpace on 2016-11-17T17:43:54Z (GMT). No. of bitstreams: 1 RODRIGUES_Karina_2015.pdf: 7918406 bytes, checksum: 5c7eded70cc8a9dd00ce5c1b2d70d846 (MD5) Previous issue date: 2015-06-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / In this study, the wettability of porous anodic alumina (PAA) surfaces modified by plasma was investigated. The porous anodic alumina films were grown on aluminum substrate using a two step anodization procedure in oxalic acid solution under potentiostatic regime. The surfaces of PAA films were modified by plasma treatment or plasma deposition techniques. Prior to surface modification, the impurities were removed by a plasma cleaning procedure. Oxygen was used in plasma treatment in order to produce hydrophilic surfaces. On the other hand, the plasma deposition (in HMDSO or HMDSO + argon mixture) was performed to produce hydrophobic surfaces or less hydrophilic surface. Electropolished aluminum without PAA film were used as reference. The influence of substrate morphology on wettability was analyzed. The morphological characterization was performed by scanning electron microscopy (SEM). The microstructural analysis was carried out using Fourier Transformed Infrared Spectroscopy (FTIR). A goniometer was used to measure the contact angle and evaluate the wettability of electroplished aluminum and PAA films. The results showed that the wettability of the samples was affect by chemical interactions of functional groups on the surface deposited after plasma treatment. The effect of the porous surface morphology on wettability was not significant compared to the plasma treated films with new chemical interactions effects. / Neste trabalho foram investigadas as propriedades de molhabilidade das superfícies nanoestruturadas da alumina anódica porosa (AAP) modificadas por plasma. Os filmes de AAP foram produzidos sobre substrato de alumínio pelo método de anodização potenciostática em duas etapas em solução de ácido oxálico. Após a fabricação, as amostras foram submetidas a um tratamento a plasma (com oxigênio) ou a deposição a plasma (em HMDSO ou em uma mistura de HMDSO e argônio). Antes das modificações das superfícies, removeram-se as impurezas das amostras através de técnicas de limpeza a plasma. No tratamento a plasma, o gás oxigênio foi utilizado para a obtenção de superfícies hidrofílicas. Por outro lado, para tornar a superfície hidrofóbica ou menos hidrofílica, foram feitas duas séries de deposição a plasma, uma contendo uma mistura de argônio e HMDSO e outra série somente com HMDSO. O tratamento ou deposição a plasma também foram feitas em amostras de alumínio eletropolido, sem a camada de AAP, a fim de verificar a influência morfológica do substrato na molhabilidade. A caracterização morfológica dos filmes de AAP foi feita por microscopia eletrônica de varredura (MEV), onde foi verificada a formação dos poros na superfície. A caracterização microestrutural foi feita por espectroscopia de absorção no infravermelho por transformada de Fourier (FTIR) com o objetivo de verificar as alterações químicas na superfície. A molhabilidade foi analisada utilizando um goniômetro, equipamento que realiza medição direta do ângulo de contato. Os resultados mostram que a molhabilidade da superfície é afetada por interações químicas dos grupos funcionais na superfície dos filmes. Por outro lado, o efeito da morfologia sobre a molhabilidade da superfície não é significativo nas condições estudadas.

<div>Self-assembled templates allow the creation of many complex arrays of nanostructures, which would be extremely difficult and expensive, if not impossible, to realize using any of the other available fabrication techniques. The complexity of these advanced nanostructures, synthesized using the various template assisted electrodeposition techniques, can be controlled to nanometer scale range by tuning the structural properties of the template, which is achieved by adjusting its various growth parameters during the self-assembly process.</div><div>Electrodeposition allows the creation of arrays of various metallic and semiconducting nanostructures. Monitoring the electrodeposition conditions permit the creation of single crystalline nanostructures of a particular material, or the formation of heterostructures using multiple electrodeposition steps. This work demonstrates the template assisted electrodeposition of vertically aligned nanowire arrays, both straight and branched, of metals, and a direct bandgap, III-V semiconductor, indium antimonide (InSb), which has one of the smallest known bandgap of any material. The template assisted electrodeposition of metallic, and InSb inverse opal (IO) structures is also shown, and the fabrication of a novel zipper shaped nanostructure by laser photomodification of a Ni IO structure is reported.</div><div>The optical characterization of the various nanostructures realized in this work have been examined. The results from this work confirm the ability to tune the optical spectra of nanostructures of the same material with similar volume fill fractions by structural modulation, where the different optical responses can be attributed to the structural differences of the actual structure as opposed to the material properties of the solid.</div>

This dissertation concerns the development, fabrication and integration in a gas sensing microdevice of a novel 3-dimensional (3D) nanostructured metal-oxide semiconducting film that effectively merges the benefits of inorganic nanomaterials with the simplicity offered by non-lithographic electrochemistry-based preparation techniques. The film is synthesized via the porous-anodic-alumina-assisted anodizing of an Al/Nb metal bilayer sputter-deposited on a SiO2/Si substrate and is basically composed of a 200 nm thick NbO2 layer holding an array of upright-standing spatially separated Nb2O5 nanocolumns, being 50 nm wide, up to 900 nm long and of 8109 cm2 population density. The nanocolumns work as semiconducting nano-channels, whose resistivity is greatly impacted by the surface and interface reactions. Either Pt or Au patterned electrodes are prepared on the top of the nanocolumn array using an innovative sensor design realized by means of microfabrication technology or via a direct original point electrodeposition technique, followed by selective dissolution of the alumina overlayer. For gas-sensing tests the film is mounted on a standard TO-8 package using the wire-bonding technique. Electrical characterization of the 3D niobium-oxide nanofilm reveals asymmetric electron transport properties due to a Schottky barrier that forms at the Au/Nb2O5 or Pt/Nb2O5 interface. Effects of the active film morphology, structure and composition on the electrical and gas-sensing performance focusing on sensitivity, selectivity, detection limits and response/recovery rates are explored in experimental detection of hydrogen gas and ammonia. The fast and intensive response to H2 confirms the potential of the 3D niobium-oxide nanofilm as highly appropriate active layer for sensing application. A computer-aided microfluidics simulation of gas diffusion in the 3D nanofilm predicts a possibility to substantially improve the gas-sensing performance through the formation of a perforated top electrode, optimizing the film morphology, altering the crystal structure and by introducing certain innovations in the electrode design. Preliminary experiments show that a 3D nanofilm synthesized from an alternative Al/W metal bilayer is another promising candidate for advanced sensor applications. The techniques and materials employed in this work are advantageous for developing technically simple, cost-effective and environmentally friendly solutions for practical micro- and nanodevices, where the well-defined nano-channels for charge carriers and surface reactions may bring unprecedented benefits.