Metal oxides have recently come under study thanks to their physical and electrical properties for different applications such as MOS devices, i.e. substituting the silicon oxide with a high-k material, or as MIM (Metal Insulator Metal) capacitors, to increase capacitance per unit area and circuit integration. One oxide of interest in this field is aluminum oxide since it features good electrical insulation and high dielectric constant. In-depth studies are presented here on the use of non-porous anodic Al2O3. Major physical and electrical parameters have been obtained, i.e. dielectric constant, stress, deformation, resistance, surface quality. Constant, low anodizing current density results in a denser oxide, with a thickness of around 100 nm. Performances such as capacitance, breakdown voltage, etc. can be improved when compared to other Al2O3 obtained by other methods. Results are also comparable to other high-k oxides. Fair performance is maintained for temperature raised up to 200°C, which opens new possible applications. Its mechanical and physical properties make it candidate in biological and MEMS devices. DNA re-association or hybridization is the underlining principle of DNA sensors. Different electrical Al structures protected by a thin anodic Al2O3 are tested. Interdigitated capacitors, the most promising electrical structure, were selected and process characterization performed. Three electrical extraction procedures are performed on the same device lying on a passivated silicon substrate: inter-electrodes capacitance, the self-resonance frequency, and the equivalent MOS capacitance between the short-circuited electrodes and the substrate. This study is the first of its kind to open the way for correlation studies and noise reduction techniques based on multiple electrical measurements of the same DNA hybridization event. The hybridization of concentrations as low as 50 pM target DNA has been successfully electrically detected using silver enhancement over gold nano-particles labeled DNA.

No description available.

The growth of barrier-type anodic alumina films formed by anodizing relatively rough substrates has been shown to proceed by high field ionic conduction. As a result of the ionic transport and the induced plasticity, smoothing of the oxide surfaces and the metal/oxide interfaces arises. However, such a smoothing model was deduced from topographical observations and, therefore little insight was gained about the transport mechanism leading to the flattening of the anodized specimens. Recently, the development of porous anodic alumina has been demonstrated to proceed by coupled ionic migration and material flow resulting from the field-induced mechanical stress. For rough metal surfaces, the electric field distribution is non-uniform across the specimen surface. Considering the square-dependence of the electrostrictive stress on the electric field and the distribution of the electric field across surface, a significant gradient of mechanical stress may arise across the anodic oxide layer during anodizing. As a result, stress-driven transport may participate, in addition to high field ionic conduction, to the smoothing of the specimen surface. Transport mechanisms were investigated during anodizing of patterned superpure aluminium specimens, by examination of the distributions of incorporated species, used as markers and tracers. The nature of the migration processes have been determined in correlation with the changes in the concentration of the tracer profiles as well as the variations in the anodic oxide film compositions.

Fundamental research on the growth of porous anodic alumina (PAA) films has been undertaken for many years because of the complexity of the processes involved and the wide range of commercial applications. In this study, a tungsten tracer approach has been used to determine the influences of current density and electrolyte temperature on the incorporation of the tracer and its distribution and consequently, the growth mechanisms of PAA films. The efficiencies of growth of PAA films, formed during anodizing at 5 mA cm-2 in the three major forming acids at 25°C, are ~60%, due to loss of outwardly migrating Al3+ ions at the film/electrolyte interface. Thus, only the inwardly migrating O2- ions contribute to formation of the anodic oxide at the film/metal interface. The pores are developed due to flow of alumina from beneath the pore base regions toward the cell walls, which is indicated by distortion of the incorporated Al-W alloy layers and retention of the tungsten species within the anodic films. PAA films formed at a low range of current densities (<2 mA cm-2) develop by a field-assisted dissolution mode, with significant losses of aluminium and tungsten species to the electrolyte, and low expansion factors of less than 1.2. Conversely, films formed at current densities ≥2 mA cm-2 grow by a flow mechanism: flow of film material transports the alumina oxide, including the incorporated tungsten tracers, from the barrier layer regions to the cell walls, resulting in relatively thicker films at higher current densities and retention of the tungsten within the films. The tungsten remains mainly within the inner cell region of the films, with a tungsten-free region present next to the pore wall. The efficiency of film growth increases from ~0.29 to ~0.73 with increase of current density from 0.5 to 30 mA cm-2, and from ~0.26 to ~0.88 with increasing current density between 0.5 and 50 mA cm-2 for anodizing in sulphuric and oxalic acids respectively.Comparatively, for PAA films formed at 15 mA cm-2 in oxalic acid, reduction of electrolyte temperature from 20 to 1°C gives rise to a slight increase of the anodizing efficiency from ~0.67 to ~0.74; the film expansion factor also increases from ~1.32 to ~1.43. The previous arises from reduced field-assisted ejection of Al3+ ions at the decreased electrolyte temperature.Anodizing of the aluminium substrates in phosphoric acid or neutral phosphate solution generates barrier anodic alumina films and the barrier layers of porous films respectively, which comprise phosphorus-containing outer regions and a phosphorus-free inner regions. The phosphorus-containing outer region accounts for ~0.67 of the barrier films and the ~0.80 of the barrier layer of the porous films. Further, the distributions of phosphorus species are not significantly affected by the incorporation of the tungsten tracer nanolayer into the films; the influence of the phosphorus species on the outward migration of the tungsten species is also negligible.This tungsten tracer study suggests a significant influence of the flow of alumina oxide, under the high electric field, on the formation of PAA films at current densities ≥2 mA cm-2.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23900号 / 工博第4987号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 邑瀬 邦明, 教授 宇田 哲也, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This work aims to investigate the effects of current density, electrolyte temperature and substrate composition on the morphology of porous anodic films formed on AA 2024-T3 alloy in sulphuric acid electrolytes and the factors that determine the transition between linear and sponge-like film porosities. Comparisons were made with pure aluminium. Particular attention is given to understanding the rising voltage that occurs during galvanostatic hard anodizing of the alloy and the role of oxygen in the anodizing process. Conditions were selected to be representative of typical hard and conventional anodizing processes. SEM was employed to observe the film morphology, which was then correlated with the voltage-time responses. The anodic film composition was investigated by TEM/EDX and SEM/EDX to determine the effect of alloy element enrichment and cell diameter on the distribution of copper species in the film. A real-time gravimetric method was developed to measure the rate of oxygen evolution during anodizing and its influence on the anodizing voltage and film morphology. Results showed that hard anodic films on AA 2024-T3 alloy formed at relatively high voltages have linear pores and cells, contrasting with sponge-like porosity under conventional anodizing. The linear porosity is shown to depend on the voltage, with a morphological transition occurring in the range 25 to 30 V, with linear cells promoted by a high current density and/or low electrolyte temperature. As the film thickens with time, pore blockage by oxygen bubbles, impedes oxidation of the alloy leading to current re-distribution and hence localized increases in the current density producing a rise of the anodizing voltage as anodizing proceeds. The rise of the anodizing voltage, which leads to an increasing call diameter and barrier layer thickness, has a minor influence on the rate of oxygen evolution, which typically consumes about 20 % of the applied current density. In contrast, the voltage rise in the presence of sponge-like films is comparatively negligible, which is suggested to be due to easier escape of oxygen from the film. The films comprising linear cells contain more copper than the sponge-like films, with copper being enriched at the cell boundaries. Moreover, a model is proposed to explain the enrichment of copper, suggesting that above a critical cell diameter, an alloy enrichment sufficient for oxidation of the alloying element can be maintained across the alloy/film interface. Below this diameter, the enrichment is less than that necessary for oxidation, and the alloying element is then incorporated into the film at the cell boundaries.

Nos últimos anos, a utilização de nanotubos (Nts) de dióxido de titânio (TiO2) têm atraído interesse tecnológico e científico de forma significativa devido às suas propriedades únicas, tais como grande área de superfície específica, alta capacidade de absorção e apresentam excelentes atividades fotoeletroquímicas e um meio para melhorar essas propriedades está relacionada ao controle da morfologia dos Nts durante a sua sintetização no processo de anodização. O objetivo desse estudo é avaliar a influência do potencial aplicado durante o processo de anodização para obtenção de Nts de TiO2, tendo em vista a utilização desses nanotubos como catalisador fotoeletroquímico. Para que houvesse a cristalização do óxido, realizou-se tratamento térmico a 400 °C ao ar, durante 3 h com taxa de aquecimento de 10 °C / min. Analisou-se a relação do potencial aplicado durante o processo de anodização com a morfologia dos nanotubos e a sua resposta fotoeletroquímica. As caracterizações foram realizadas através das técnicas de microscopia eletrônica de varredura com emissão de campo (MEV-FEG), difração de raios X (DRX), espectrofotometria no ultravioleta visível (UV-VÍS), voltametria linear e espectroscopia de impedância eletroquímica (EIE).Observou-se que o potencial de anodização exerce influência na geometria do nanotubo, isto é, no comprimento, na espessura da parede e no diâmetro, alterando a absorção de luz e, consequentemente, o desempenho fotoeletroquímico das amostras. Os resultados obtidos por espectroscopia de impedância eletroquímica mostraram pouca diferença na resistividade das amostras estudas. Contudo, as correntes desenvolvidas no ensaio de voltametria linear, indicaram que a amostra Nt30 é um fotoeletrodo promissor para formar heteroestruturas baseado em nanotubos de dióxido de titânio. / In recent years, the use of TiO2 nanotubes (Nts) has attracted technological and scientific interests in a significant way due to its unique properties, such as large specific surface area, high absorption capacity and excellent photoelectrochemical activities. One way to improve these properties is to control the nanotubular morphology during its synthesis through the anodizing process. The objective of this study is to evaluate the influence of the applied potential during the anodization process to obtain titanium dioxide (TiO2) nanotubes and applying these nanotubes as a photoelectrochemical catalyst. In order to crystallize the Nts, heat treatment was carried out at 400 ° C in air for 3 h at a heating rate of 10 ° C / min. The effect of the applied potential during the anodizing process on the morphology of the nanotubes and their photoelectrochemical response were analyzed. The characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), visible ultraviolet spectrophotometry (UV-VIS) and electrochemical impedance spectroscopy (EIS). It was observed that the anodization potential influences the geometry of the nanotubes, that is, their length, wall thickness and diameter, altering their light absorption properties; consequently, influencing the photoelectrochemical performance of the samples. The results obtained from the electrochemical impedance spectroscopy showed a slightly small difference in the charge transportation resistance of the studied samples. However, the currents developed in the linear voltammetry tests indicated that the Nt30 sample is a promising photoelectrode to apply for other applications such as heterostructures and cationic/anionic doped structures based on titanium dioxide nanotubes.

Nos últimos anos, a utilização de nanotubos (Nts) de dióxido de titânio (TiO2) têm atraído interesse tecnológico e científico de forma significativa devido às suas propriedades únicas, tais como grande área de superfície específica, alta capacidade de absorção e apresentam excelentes atividades fotoeletroquímicas e um meio para melhorar essas propriedades está relacionada ao controle da morfologia dos Nts durante a sua sintetização no processo de anodização. O objetivo desse estudo é avaliar a influência do potencial aplicado durante o processo de anodização para obtenção de Nts de TiO2, tendo em vista a utilização desses nanotubos como catalisador fotoeletroquímico. Para que houvesse a cristalização do óxido, realizou-se tratamento térmico a 400 °C ao ar, durante 3 h com taxa de aquecimento de 10 °C / min. Analisou-se a relação do potencial aplicado durante o processo de anodização com a morfologia dos nanotubos e a sua resposta fotoeletroquímica. As caracterizações foram realizadas através das técnicas de microscopia eletrônica de varredura com emissão de campo (MEV-FEG), difração de raios X (DRX), espectrofotometria no ultravioleta visível (UV-VÍS), voltametria linear e espectroscopia de impedância eletroquímica (EIE).Observou-se que o potencial de anodização exerce influência na geometria do nanotubo, isto é, no comprimento, na espessura da parede e no diâmetro, alterando a absorção de luz e, consequentemente, o desempenho fotoeletroquímico das amostras. Os resultados obtidos por espectroscopia de impedância eletroquímica mostraram pouca diferença na resistividade das amostras estudas. Contudo, as correntes desenvolvidas no ensaio de voltametria linear, indicaram que a amostra Nt30 é um fotoeletrodo promissor para formar heteroestruturas baseado em nanotubos de dióxido de titânio. / In recent years, the use of TiO2 nanotubes (Nts) has attracted technological and scientific interests in a significant way due to its unique properties, such as large specific surface area, high absorption capacity and excellent photoelectrochemical activities. One way to improve these properties is to control the nanotubular morphology during its synthesis through the anodizing process. The objective of this study is to evaluate the influence of the applied potential during the anodization process to obtain titanium dioxide (TiO2) nanotubes and applying these nanotubes as a photoelectrochemical catalyst. In order to crystallize the Nts, heat treatment was carried out at 400 ° C in air for 3 h at a heating rate of 10 ° C / min. The effect of the applied potential during the anodizing process on the morphology of the nanotubes and their photoelectrochemical response were analyzed. The characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), visible ultraviolet spectrophotometry (UV-VIS) and electrochemical impedance spectroscopy (EIS). It was observed that the anodization potential influences the geometry of the nanotubes, that is, their length, wall thickness and diameter, altering their light absorption properties; consequently, influencing the photoelectrochemical performance of the samples. The results obtained from the electrochemical impedance spectroscopy showed a slightly small difference in the charge transportation resistance of the studied samples. However, the currents developed in the linear voltammetry tests indicated that the Nt30 sample is a promising photoelectrode to apply for other applications such as heterostructures and cationic/anionic doped structures based on titanium dioxide nanotubes.

Submitted by MARIA FERNANDA LIMA Villaça-Carvalho (mfervillaca@hotmail.com) on 2016-03-29T02:07:44Z No. of bitstreams: 1 TESE MARIA FERNANDA merged.pdf: 3220002 bytes, checksum: cc48d2a3494318d6c9c1f4af8c06c37f (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-03-29T17:32:30Z (GMT) No. of bitstreams: 1 villacacarvalho_mfl_dr_sjc.pdf: 3220002 bytes, checksum: cc48d2a3494318d6c9c1f4af8c06c37f (MD5) / Made available in DSpace on 2016-03-29T17:32:30Z (GMT). No. of bitstreams: 1 villacacarvalho_mfl_dr_sjc.pdf: 3220002 bytes, checksum: cc48d2a3494318d6c9c1f4af8c06c37f (MD5) Previous issue date: 2016-01-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A Implantodontia é uma das áreas da Odontologia que mais tem evoluído nas últimas décadas. Diversos estudos são desenvolvidos na intenção de otimizar o processo de osseointegração utilizando a nanotopografia na superfície dos implantes. Atualmente o processo de anodização da superfície vem se destacando entre estas técnicas. Desta forma, o objetivo nesta pesquisa foi obter nano rugosidades e fase de anatase em implantes odontológicos de Titânio, buscando a otimização da osseointegração. Sessenta implantes foram caracterizados quanto à morfologia, por meio de microscopia de força atômica (AFM) e Microscopia Eletrônica de Varredura (MEV); quanto à composição química, por análise por detector de espectrometria por espalhamento de energia (EDS) e Espectroscopia Raman; e por fim, quanto ao potencial de corrosão, pela análise de impedância eletroquímica (EIE). A osteogênese, in vivo, foi comparada por Radiografia periapical (RP), Microtomografia Computadorizada (μTC) e teste de remoção por torque reverso; e, a análise in vitro, foi realizada por teste de citotoxicidade por MTT [(brometo de 3-4,5-dimetiltiazol-2-il)-2,5-difeniltetrazoliol]. Os implantes foram divididos em: G1 (controle); Grupo 2 (jateado); Grupo 3 (anodizado-experimental). Cada coelho recebeu um implante de cada grupo nas tíbias direita e esquerda, e cinco coelhos, foram eutanasiados 2 e 6 semanas após a cirurgia. Os implantes da tíbia direita foram submetidos à RP e à μTC; e os da tíbia esquerda, ao teste de torque reverso e análise de citotoxicidade por MTT. AFM e MEV comprovaram a presença de nano rugosidades na superfície em G3; análises de EDS e Espectroscopia Raman, demonstraram aumento da camada do filme de TiO2 e a obtenção de anatase em G3. Na RP, nenhum implante apresentou halo radiolúcido. Na μTC, G3 foi sempre superior aos demais grupos nos parâmetros observados: BV, BV/TV, Tb.Th. No teste de torque reverso, houve necessidade de maior força de remoção dos implantes anodizados. No teste por MTT, os implantes experimentais foram atóxicos células. Conclui-se que a anodização utilizada neste estudo afetou positivamente a composição química e estrutural do filme de TiO2, melhorando suas características biológicas na osseointegração. / The Implantology is one of the areas of dentistry that has most evolved in recent decades. Many studies have been developed with the intention of optimizing the osseointegration process using nanotopography on the surface of the implants. Currently the surface of the anodizing process has stood out among these techniques. Thus, the aim of this research was to obtain nano roughness and anatase phase in dental Titanium implants, seeking for the optimization of the osseointegration. Sixty implants were characterized for morphology by atomic force microscopy (AFM) and Scanning Electron Microscopy (SEM); in chemical composition, by mass spectrometry detector energy scattering (EDS) and Raman spectroscopy; and finally, as the potential for corrosion, the electrochemical impedance analysis (EIS). Osteogenesis in vivo was compared by Periapical Radiography (PR), Computed Microtomography (μTC), removal reverse torque test; and in vitro analysis, it was performed by MTT cytotoxicity assay [(bromide 3-4,5-dimethylthiazol-2-yl) -2,5-difeniltetrazoliol]. The implants were divided into G1 (control); Group 2 (sandblasted); Group 3 (anodized-experimental). Each rabbit received an implant of each group in the right and left tibias and five rabbits were euthanized 2 and 6 weeks after surgery. The implants of the right tibia underwent PR and μTC; and the left tibia, the reverse torque test and MTT cytotoxicity assay. AFM and SEM confirmed the presence of nano roughness on the surface in G3; EDS analysis and Raman spectroscopy showed increased TiO2 film layer and obtainment of anatase G3. In PR, no implant presented radiolucent halo. In μTC, G3 has always been higher than the other groups in the observed parameters: BV, BV / TV, Tb.Th. In the reverse torque test, It was required greater removal force of anodized implants. In the MTT test, the experimental implants were nontoxic to cells. It was conclude that the anodizing process used in this study positively affected the chemical and structural composition of TiO2 film, improving their biological characteristics at osseointegration.

Submitted by Liliane Lelis de Oliveira null (lilianelelis@yahoo.com.br) on 2016-09-08T12:25:39Z No. of bitstreams: 1 Oliveira_LL_me_guara.pdf: 2977189 bytes, checksum: 77ba3eeb3ac9b790efdbf9473d1bf8c6 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-09-08T14:25:50Z (GMT) No. of bitstreams: 1 oliveira_ll_me_guara.pdf: 2977189 bytes, checksum: 77ba3eeb3ac9b790efdbf9473d1bf8c6 (MD5) / Made available in DSpace on 2016-09-08T14:25:50Z (GMT). No. of bitstreams: 1 oliveira_ll_me_guara.pdf: 2977189 bytes, checksum: 77ba3eeb3ac9b790efdbf9473d1bf8c6 (MD5) Previous issue date: 2016-07-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O maior desafio no desenvolvimento de materiais para aplicações biomédicas é fazer com que estes tenham uma boa resposta e interação com o meio quando inseridos no corpo. Estudos sobre a topografia de superfície mostram que nanotubos de TiO2 podem contribuir para uma melhor adesão celular pois auxiliam a osseointegração e ancoragem óssea, entretanto essa mesma estrutura de superfície pode induzir o acúmulo e proliferação de bactérias na superfície do implante causando infecções e até mesmo a perda do implante. Nesse trabalho foi estudada a incorporação, ação antibactericida e fungicida da clorexidina na superfície da liga Ti-7,5Mo após o crescimento de nanotubos de TiO2 por oxidação anódica. As amostras foram divididas em dois grupos de acordo com o potencial de anodização de 10V e 20V com tempo de permanência de 24 horas, seguido de calcinação a 450ºC por 1 hora e resfriamento no forno. A partir destes procedimentos foram utilizadas técnicas de caracterização da superfície: Microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS) para analisar a morfologia da superfície tal como a composição química do filme formado. O ângulo de contato foi medido para analisar a molhabilidade da superfície do material e o ensaio eletroquímico mostrou o comportamento do material em meio SBS. A clorexidina foi incorporada na superfície por imersão por 30 minutos e se mostrou um bom agente bactericida e antifúngico em ação contra S. Aureus e Candida em estudos in vitro. / The challenge when developing materials for biomedical applications is to ensure that they have a good response and interaction when in the body. Studies about the surface topography show that TiO2 nanotubes can bring a better cell adhesion because they help osseointegration and bone anchorage, however, this same surface structure can induce the accumulation and bacteria proliferation in the implant surface causing infections and even loss of the implant. This study brings the incorporation and bactericidal action of chlorhexidine on the surface of Ti-alloy 7,5Mo after growth of TiO2 nanotubes by anodic oxidation. The samples weregrouped according to the anodizing potential of 10V and 20V with time to 24 hours stay, followed by calcination at 450 ° C for 1 hour and cooling into the oven. From these procedures were used as surface characterization techniques: scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to examine the surface morphology such as the chemical composition of the film. The contact angle was measured to analyze the surface wettability of the material and the electrochemical assay showed the behavior of the material in the middle of SBS. Chlorhexidine was incorporated into the surface by immersing for 30 minutes and showed a good bactericide and antifungal action against S. Aureus and Candida in vitro.