The production of magnetic materials is of great interest for use in the micro-fabrication industry. In particular, Permalloy (Ni80Fe20) is used in the production of micro-electromechanical systems (MEMS) due to its favourable magnetic properties (high relative permeability, low coercivity and high magnetic saturation). This leads to applications in devices such as inductors, transformers and micro-actuators. The electrodeposition of NiFe is also of fundamental electrochemical interest, as there is anomalous thermodynamic behaviour, with the less noble (iron) metal depositing preferentially to the more noble (nickel) metal. To enable consistent alloy deposition nickel and nickel-iron baths are currently almost exclusively based on boric acid. Boric acid has an important role in the deposition of NiFe films but its role(s) in the electro-deposition mechanism is (are) not wholly understood. Recently (2011) boric acid has been identified as a “substance of very high concern” based on the criteria established by EU chemical regulation, REACH. In anticipation of increased regulation an alternative was sought to provide a benign alternative to boric acid in the NiFe plating bath suitable for use in micro-fabrication. Initial work was performed to benchmark the performance of existing boric acid based electro-deposition baths. Cyclic voltammetry was performed, which demonstrated the deposition of nickel and nickel-iron from boric acid baths. Coulombic efficiencies up to 93 % were measured for the deposition of nickel using the electrochemical quartz crystal microbalance (EQCM) on platinum electrodes. For nickel-iron deposition control of the film composition was demonstrated on copper electrodes through varying the iron (II) concentration, current density and temperature. A citrate bath for the deposition of nickel-iron was then developed and characterised. Cyclic voltammetry was performed in these citrate baths demonstrating the deposition of nickel and nickel-iron. Optimal conditions for depositing Ni80Fe20 were demonstrated to be an elevated temperature (60 °C) with a current density of 20 mA cm-2 and a pH of 3. Using the EQCM the efficiency for nickel deposition was measured to be > 80 %. The effects of sodium saccharin and sodium dodecyl sulfate as additives were investigated; these were shown to influence morphology but not the coulombic efficiency. Decreasing the pH was shown to lower the efficiency of nickel deposition from the citrate bath. Comparisons of key properties were made between NiFe films deposited from a boric acid bath and the citrate bath developed in this work. Test structures were used to compare the strain in the films; no significant difference was found. For 2.2 μm thick Ni80Fe20 films the sheet resistance was measured using Greek cross structures as 0.078 ± 0.004 Ω/square for films deposited from the boric acid bath and 0.090 ± 0.006 Ω/square from the citrate bath. The magnetic saturation, Ms, was measured as 895 ± 66 emu cm-3 for deposits from the boric acid bath and 923 ± 111 emu cm-3 from the citrate bath. These again show no significant difference in these values within experimental error. Coercivities for these films were measured to be between 20 and 120 A m-1. In combination, this work demonstrates the development and characterisation of a new citrate based electrodeposition bath for nickel and nickel-iron. Similar chemical, electrical, mechanical and magnetic properties were found from films deposited from both baths, thus demonstrating the suitability of the citrate bath for the deposition of nickel-iron films in microfabrication.

A deposição eletroquímica, ou eletrodeposição, é uma técnica amplamente utilizada na obtenção de recobrimentos metálicos. A presença de certos compostos químicos (aditivos) nos banhos eletrolíticos pode influenciar o processo de eletrodeposição de maneira significativa. A glicina é um aminoácido presente em muitos banhos para a eletrodeposição de filmes finos de ligas de cobalto, que são interessantes devido às suas propriedades magnéticas. As propriedades de algumas ligas à base de cobalto obtidas a partir de banhos contendo glicina já foram bem descritas, mas há falta de estudos mais específicos sobre o papel do aminoácido no processo de eletrodeposição do cobalto. Esta Tese apresenta estudos realizados na tentativa de compreender a influência da glicina no mecanismo de eletrodeposição do cobalto. Técnicas de análise in situ, envolvendo espectroscopia no infravermelho por reflexão externa e medidas de pH na região próxima a interface via microeletrodo indicador foram acopladas aos estudos eletroquímicos. Depósitos de cobalto de boa qualidade foram obtidos a partir de banhos contendo glicina, e sob condições de sobrepotencial mais elevadas do que as possíveis para sistemas sem aditivos, onde ocorre precipitação de hidróxidos. Análises dos experimentos de voltametria cíclica indicaram a eletroatividade de complexos cobalto-glicina, e cinética de redução mais lenta foi observada, em relação a sistema sem glicina em valores de pH suficientemente elevados. Os estudos cinéticos foram dificultados pela reação de desprendimento de hidrogênio e a existência de diversos equilíbrios químicos em solução. Durante a eletrodeposição de cobalto em soluções contendo glicina, um aumento bastante significativo no pH próximo da interface foi observado. Os experimentos espectroeletroquímicos também demonstraram deslocamento dos equilíbrios químicos de complexação do cobalto em solução, devido ao aumento do pH interfacial. Todos os estudos mostraram que a presença de glicina favorece a reação de desprendimento de hidrogênio, diminuindo a eficiência de corrente do processo de eletrodeposição. Ainda assim, a glicina se mostrou eficaz na estabilização da solução eletrolítica. / The electrochemical deposition, or electrodeposition, is a widely used technique to obtain metallic coatings. The presence of certain chemical species (additives) in plating baths can significantly influence the metal electrodeposition process. Glycine is an aminoacid present in many electrolytic solutions for electrodeposition of cobalt thin films and alloys, which are interesting due to their magnetic properties. The properties of some Co-based alloys obtained from glycine-containing baths are well documented, but studies of the exact role of the aminoacid are lacking. This Thesis presents studies attempting to understand the influence of glycine on the mechanisms of cobalt electrodeposition. In situ analysis techniques - external reflection FTIR spectroscopy and pH measurement near the electrochemical interface using indicator microelectrodes - were coupled to the electrochemical studies. Good-quality cobalt deposits were obtained from glycine-containing baths, and under higher overpotentials than possible over systems with no additive (in which precipitation of hydroxides occurs). Analysis of the cyclic voltammetry experiments indicated the electroactivity of cobalt-glycine complexes, and the slower reduction kinetics in comparison with glycine-free solutions at sufficiently high pH values. The kinetic studies were hindered by the parallel hydrogen evolution reaction and the existence of several chemical equilibria in solution. During cobalt electrodeposition from glycine-containing solutions, an expressive elevation of the near interface pH was observed. The spectroelectrochemical experiments also showed the displacement of cobalt complexation equilibria in solution, caused by the increase in the interfacial pH. All the conducted studies showed that the presence of glycine favors the hydrogen evolution reaction, decreasing the current efficiency for the electrodeposition process. Nevertheless, glycine was able to stabilize the electrolyte solution.

"In the past decade nanomaterials have attracted the interest of scientists and engineers all over the world due to their unique properties. Through their devoted experimental efforts, limited advances have been made on the synthesis of nanomaterials, the integration of nanomaterials into the structures of larger scales, and the property study of nanomaterials to explore possible applications. Despite the huge amount of money, resources, and effort invested in nanomaterials, several challenges still remain as obstacles on the way towards the successful large scale use of nanomaterials to benefit human life and society. For example, the need for low-cost, robust, and highly productive manufacturing methods and the demand for efficient integration of nanomaterials with materials and devices of larger length scales are still left unmet. The objective of this work was to utilize cost-efficient nanofabrication methods such as template-assisted fabrication, electrodeposition, and chemical vapor deposition to fabricate nanomaterials, integrate nanomaterials with larger structures to form a hierarchical composite, and explore the application of unique nanostructured electrode in lithium-ion batteries. Thus the thesis consists of three main parts: (1) fabrication of one-dimensional inorganic nanomaterials such as metal nanowires, metal nanorods, and carbon nanotubes with good control over shape and dimension; (2) synthesis of hierarchical carbon nanofibers on carbon microfibers and/or glass microfibers; and (3) development of nanostructured anodes to improve high-rate capability of lithium-ion batteries by adapting nanorod arrays as miniature current collectors. "

Fiber-reinforced concrete (FRC) is nowadays extensively used in civil engineering throughout the world due to the composites of FRC can improve the toughness, flexural strength, tensile strength, and impact strength as well as the failure mode of the concrete. It is an easy crazed material compared to others materials in civil engineering. Concrete, like glass, is brittle, and hence has a low tensile strength and shear capacity. At present, there are different materials that have been employed to reinforce concrete. In our experiment, nanostructures iron oxide was prepared by electrodepostion in an electrolyte containing 0.2 mol/L sodium acetate (CH3COONa), 0.01 mol/L sodium sulfate (Na2SO4) and 0.01 mol/L ammonium ferrous sulfate (NH4)2Fe(SO4)2.6H2O under magnetic stirring. The resulted showed that pristine Fe2O3 particles, Fe2O3 nanorods and nanosheets were synthesized under current intensity of 1, 3, 5 mA, respectively. And the pull-out tests were performed by Autograph AGS-X Series. It is discovering that the load force potential of nanostructure fibers is almost 2 times as strong as the control sample.

Neste trabalho, é apresentado um estudo sobre a influência de aditivos em banhos de eletrodeposição de Au, análise da morfologia dos depósitos de Au e o crescimento de multicamadas da liga AuxSny por deposição eletroquímica. Os banhos de eletrodeposição estudados são baseados em uma composição, comum na literatura, formada por tetraclorourato(III) de potássio (KAuCl4), cloreto de estanho(II) (SnCl2), sulfito de sódio (Na2SO3), e citrato de amônio [(NH4)HC6H5O7]. Os contatos de solda da liga AuxSny, aplicáveis em diversos dispositivos microeletrônicos, podem ser formadas de maneira mais econômica a partir de banhos eletroquímicos. Banhos ácidos e reagentes de baixa toxicidade são exigências comuns dos novos banhos de eletrodeposição. A formação de multicamadas permite, ainda, ampliar o uso do metal de solda em dispositivos sensíveis a altas temperaturas, devido ao baixo ponto de fusão da liga. A obtenção das ligas AuxSny utilizando deposição eletroquímica, foi feita com base no estudo sobre banho de eletrodeposição e seus depósitos, a partir de um banho para deposição da liga AuxSny já conhecido. O aprimoramento do banho de eletrodeposição foi focado no banho de eletrodeposição de Au, com três opções de aditivos, buscando avaliar as características dos depósitos e o tempo de estabilidade do banho. Os aditivos utilizados foram hipofosfito de sódio (NaH2PO2), metanal (HCHO) e tiossulfato de sódio (Na2S2O3), separadamente. Esses banhos foram analisados por voltametria cíclica, e os depósitos obtidos a partir de eletrodeposições foram caracterizados por Espectrometria por Retroespalhamento de Rutherford (RBS), Microscopia Eletrônica de Varredura (SEM) e, em alguns casos, por Espectrometria de Energia Dispersiva de Raios X (EDS). Análises de dimensão fractal e de escalamento dinâmico da rugosidade forneceram detalhes importantes sobre a morfologia superficial dos depósitos. .A adição de Na2S2O3 ao banho permitiu o desenvolvimento de um novo banho de eletrodeposição para a co-deposição de Au AuxSny. O Na2S2O3 atua como um complexante dos íons de Au(I) juntamente com o sulfito de sódio. O emprego de 3 g L-1 de Na2S2O3 evita a degradação do banho durante as eletrodeposições. Finalmente, o estudo da eletrodeposição de multicamadas foi feito por controle do potencial aplicado e por controle da corrente aplicada. As multicamadas obtidas apresentaram camadas da liga AuxSny com a concentração de Sn incorporado, variando entre 6 % e 49 % (em porcentagem atômica). / It is shown in this work a study about the influence of additives in baths for electrodeposition of Au, analysis of morphology of gold deposits and the growth of multilayered AuxSny alloys from improved electrodeposition baths based on a common composition of the literature containing potassium gold(III) chloride (KAuCl4), tin(II) chloride (SnCl2), sodium sulfite (Na2SO3) and ammonium citrate dibasic [(NH4)HC6H5O7]. The AuxSny solders are commonly used in microelectronic devices. These solders can be applied in a number of ways, and electrochemical deposition is an attractive alternative due to the low cost process. Acidic baths and low toxicity reagents are common requirements of new electrochemical baths. The multilayered AuxSny alloys are applicable to temperature sensitive materials due to its reduced melting point temperature. Therefore, the study of electrodeposition of AuxSny alloys began with an already known bath and aiming its improvement. The focus of interest was the gold bath, which received additives to improve control of the deposits and their stability. The additives used were sodium hypophosphite (NaH2PO2), methanal (HCHO) and sodium thiosulfate (Na2S2O3), one of each time. These baths were analyzed by cyclic voltammetry and the deposits obtained from these baths were analyzed by Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscopy (SEM) and, in some cases, Energy Dispersive Spectrometry (EDS). Fractal dimension and dynamic scaling of the surface width analysis allowed one to quantify the surface morphology details. The addition of Na2S2O3 to the bath allowed the development of a new electrodeposition bath for co-deposition of AuxSny. The Na2S2O3 acts as complexing agent of Au(I) ions together with sodium sulfite. The use of 3 g L-1 of Na2S2O3 avoids bath degradation during the electrodepositions. Potential-controlled and current-controlled electrodepositions were employed to obtain multilayers of AuxSny alloys. The multilayer deposits obtained presented between 6 atomic % and 49 atomic % of tin.

Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização. / Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.

The effect of a magnetic field on copper electrodeposition was investigated. Copper was electrodeposited onto square copper cathodes 1 sq cm in area from an aqueous solution (0.5 M CuSO4, 0.5 M H2SO. A glass cell was placed between the pole pieces of an electromagnet, and the magnetic fields applied were in the range from 0 to 12.5 kG. The current density was in the range from 80 mA/sq cm to 880 mA/sq cm. In each of the experiments, cell current, cell voltage, and cell temperature were monitored with a microcomputer. The weight change, deposit surface and cross section morphology, and the hardness were also found. Anodes used in the experiments were studied to see the effect of various conditions on the surface finish. Copper was also electrodeposited onto copper grids in order to study how the uniformity of the deposit is affected by an applied magnetic field.

Synthesis and characterization of anisotropic micro- and nanoparticles, either in suspension or localized on a surface, are current areas of intense scientific interest because of their shape-tunable material properties with potential applications in catalysis, microelectronics, data storage and pharmaceutics. Electrochemical deposition represents a facile and versatile route to fabricate anisotropic particles since it offers a high degree of freedom in monitoring and manipulating particle growth processes. The first part of my dissertation presents an additive-mediated electrochemical approach to fabricate anisotropic copper micro- and nanoparticles. This work explores the possibility of using anisotropic copper particles as novel non-noble metal alternatives to expensive anode electrocatalysts (platinum and palladium) used in direct methanol fuel cells (DMFCs). Characterization using SEM, EDS, XRD and TEM confirms the anisotropic morphology and crystal structure of synthesized copper particles. A possible mechanism for anisotropic crystal growth is proposed based on preferential adsorption of additive ions onto selective crystal faces. Methanol oxidation is chosen as model experiment to test the electrocatalytic property of copper particles towards DMFC applications. Characterization using cyclic voltammetry demonstrates shape dependent enhancement in electrocatalytic activity of anisotropic copper particles for methanol oxidation. Chronoamperometry and thermal stability measurements indicate good catalyst stability and durability under steady-state conditions. The second part of my dissertation presents a novel electrochemical fabrication route to generate randomly rough surfaces over large areas. Surface roughness directly affects a material's performance at its functional interface. This work shows that by simple tuning of electrochemical deposition potential for a metal onto an electrode, island nucleation density can be systematically varied. Changes in nucleation density results in generation of thin films with different nanoscale surface roughness. Characterization using AFM illustrates the change in surface topography with applied potential. The fabricated roughness is successfully replicated onto other moldable soft materials (polystyrene and polyurethane) through an embossing and curing step. Roughness gradients were also generated by introducing a controlled mechanical retraction step to the process. Gradient surfaces serve as an effective probing tool for investigating a range of surface parameters in quick time using single experiment, enabling a cost-effective and high-throughput screening method. / acase@tulane.edu

Dans le but de réduire la morbidité et la durée d’hospitalisation, la médecine régénérative progresse de nos jours vers le développement de techniques chirurgicales moins invasives. Cette recherche en chirurgie mini-invasive a motivé le développement de matrices injectables pour l’ingénierie tissulaire osseuse. Ces matrices doivent aussi être capables de durcir une fois injectées in situ, acquérir la forme souhaitée ainsi que des propriétés mécaniques compatibles avec le tissu hôte qu’elles doivent réparer. De nombreux hydrogels sont déjà employés pour cette application mais aucun ne remplit complètement les propriétés requises. L’objectif de cette thèse est de développer de nouveaux substituts de greffe osseuse : des hydrogels à base de biopolymères associés à des cellules osseuses pour obtenir des greffons mi-synthétiques, mi-biologiques. Des nanoparticules de phosphates de calcium sont ajoutées pour améliorer les propriétés biologiques et mécaniques des hydrogels. L’hydroxyapatite, le phosphate de calcium choisi, est attrayante à cause de ses similitudes chimiques et structurales au constituent minéral de l’os humain. Le but de ce travail est de synthétiser des nanofils d’hydroxyapatite par la méthode template et des nanopoudres d’hydroxyapatite de taille contrôlée par sonoélectrochimie pulsée déphasée. Ensuite pour améliorer les propriétés intrinsèques des structures 3D, ces nanoparticules de phosphates de calcium seront insérées dans des matrices d’hydrogel synthétisées par le laboratoire d’ingénierie ostéo-articulaire et dentaire (LIOAD) de Nantes. Des mesures de coefficient de diffusion seront suivies par des tests de cytotoxicité et de biocompatibilité de ces matériaux. Des études en sous-cutané et après implantation en milieu osseux suivront. / In order to reduce morbidity and hospital stay, regenerative medicine is nowadays moving towards the development of less invasive surgical techniques. This search for a minimally invasive surgery has motivated the development of injectable matrices for bone tissue engineering. These matrices must also be able to harden in situ once injected, acquire the desired shape and mechanical properties compatible with the host tissue it intends to repair. Many hydrogels are already used for this application but none fully meets the required properties. The objective of this thesis is to develop new bone graft substitutes: hydrogels based on biopolymers associated with bone cells to achieve half synthetic and half biological grafts. Nanoparticles of calcium phosphates are added to improve the biological and mechanical properties of hydrogels. Hydroxyapatite, calcium phosphate chosen, has attracted much attention because of its chemical and structural similarity to the mineral constituent of human bone. The aim of this work is to synthesize firstly hydroxyapatite nanowires by the template method and secondly size controlled hydroxyapatite nanopowders by out-of-phase pulsed sonoelectrochemistry. Thirdly to improve the intrinsic properties of these three-dimensional structures, those nanoparticles of calcium phosphates will be added in the matrices of hydrogel synthesized by the LIOAD. Measurements of diffusion coefficient will be followed by testing cytotoxicity and biocompatibility of those materials. A subcutaneous study and bone model study will follow.

Copper corrosion and its inhibition are often associated with the presence of oxide films. Several studies have demonstrated that copper oxide films, which are normal corrosion products, protect copper substrate from further corrosion. However, little work has been carried out on the chemical formation of copper oxide films. On the other hand, the development of new polymer coatings is needed for corrosion prevention in aggressive environment. Although interest in the use of polypyrrole films for corrosion prevention has arisen recently, no successful utilisation of the polymer for control of copper corrosion has been reported, due to the difficulty in the deposition of the polymer. In this study, two new surface modification techniques, namely chemical formation of copper oxide films and the electrodeposition of polypyrrole on copper, have been developed to address the above issues. The influence of bicarbonate ions on the stability of copper oxide films and pitting corrosion were studied. Various approaches for the electrodeposition of polypyrrole (PPy) film onto copper substrate were investigated. The characteristics and properties of PPy films, particularly for the film formed in sodium tetraborate solution, were investigated. The redox reactions of copper substrate were inhibited completely by the presence of the polypyrrole film, formed in sodium tetraborate solution, in several weak alkaline solutions. The electrochemical behaviour of the Cu-PPy electrode is quite similar to Cu electrode in the presence of an effective corrosion inhibitor, such as benzotriazole, in several solutions. These properties of the PPy film clearly indicate that there is potential for the application of the polymer in the control of copper corrosion. / Doctor of Philosophy (PhD)